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Fundamentals of Materials Science and Engineering 5th ed Solutions
FMMM (Univerzitet u Sarajevu)
Studocu is not sponsored or endorsed by any college or university
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CH A PTE R 2
ATOMIC STRU CTU RE A ND INTERATOMIC BOND ING
2.3 (a) In order to determine the number of grams in one amu of material, appropriate manipulation of
the amu/atom, g/mol, and atom/mol relationships is all that is necessary, as
#g/amu =
1 mol
6.023 × 1023 atoms
1 g/mol
1 amu/atom
= 1.66 × 10−24 g/amu
2.14 (c) This portion of the problem asks that we determine for a K + -Cl− ion pair the interatomic spacing
(ro ) and the bonding energy (E o ). From E quation (2.11) for E N
A = 1.436
B = 5.86 × 10−6
n=9
Thus, using the solutions from Problem 2.13
ro =
A
nB
1/(1−n)
1.436
=
(9)(5.86 × 10−6 )
1/(1−9)
= 0.279 nm
and
Eo = −
1.436
1.436
(9)(5.86 × 10−6 )
1/(1−9) + 5.86 × 10−6
9/(1−9)
1.436
(9)(5.86 × 10−6 )
= −4.57 eV
2.19 The percent ionic character is a function of the electronegativities of the ions X A and X B according
to E quation (2.10). The electronegativities of the elements are found in Figure 2.7.
For TiO 2 , X Ti = 1.5 and X O = 3.5, and therefore,
2
% IC = 1 − e (−0.25)(3.5−1.5) × 100 = 63.2%
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CH A PTE R 3
STRU CTU RES OF META LS A ND CERA MICS
3.3
For this problem, we are asked to calculate the volume of a unit cell of aluminum. A luminum has an
FCC crystal structure (Table 3.1). The FCC unit cell volume may be computed from E quation (3.4)
as
√
√
V C = 16R 3 2 = (16)(0.143 × 10−9 m) 3 2 = 6.62 × 10−29 m 3
3.7
This problem calls for a demonstration that the A PF for H CP is 0.74. A gain, the A PF is just the
total sphere-unit cell volume ratio. For H CP, there are the equivalent of six spheres per unit cell,
and thus
4␲R 3
VS = 6
= 8␲R 3
3
Now, the unit cell volume is just the product of the base area times the cell height, c. This base area
is just three times the area of the parallelepiped ACD E shown below.
D
C
a = 2R
30
60
A
E
B
a = 2R
a = 2R
The area of ACD E is just the length of CD times the height BC. But CD is just a or 2R,
and
√
2R 3
◦
BC = 2R cos(30 ) =
2
Thus, the base area is just
√ √
2R 3
A R E A = (3)(CD )(BC) = (3)(2R )
= 6R 2 3
2
and since c = 1.633a = 2R(1.633)
√
√
√
V C = (A R E A )(c) = 6R 2 c 3 = (6R 2 3)(2)(1.633)R = 12 3(1.633)R 3
2
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Thus,
A PF =
8␲R 3
VS
= √
= 0.74
VC
12 3(1.633)R 3
3.12. (a) This portion of the problem asks that we compute the volume of the unit cell for Z r. This volume
may be computed using E quation (3.5) as
VC =
nA Z r
␳ NA
Now, for H CP, n = 6 atoms/unit cell, and for Z r, A Zr = 91.2 g/mol. Thus,
VC =
(6 atoms/unit cell)(91.2 g/mol)
(6.51 g/cm 3 )(6.023 × 1023 atoms/mol)
= 1.396 × 10−22 cm 3 /unit cell = 1.396 × 10−28 m 3 /unit cell
(b) We are now to compute the values of a and c, given that c/a = 1.593. From the solution to
Problem 3.7, since a = 2R, then, for H CP
√
3 3a 2 c
VC =
2
but, since c = 1.593a
√
3 3(1.593)a 3
= 1.396 × 10−22 cm 3 /unit cell
VC =
2
Now, solving for a
a=
(2)(1.396 × 10−22 cm 3 )
√
(3)( 3)(1.593)
1/3
= 3.23 × 10−8 cm = 0.323 nm
A nd finally
c = 1.593a = (1.593)(0.323 nm) = 0.515 nm
3.17 In this problem we are given that iodine has an orthorhombic unit cell for which the a, b, and c
lattice parameters are 0.479, 0.725, and 0.978 nm, respectively.
(a) G iven that the atomic packing factor and atomic radius are 0.547 and 0.177 nm, respectively we are to determine the number of atoms in each unit cell. From the definition of the
A PF
A PF =
VS
=
VC
n
4
␲R 3
3
abc
3
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we may solve for the number of atoms per unit cell, n, as
n=
=
(A PF)abc
4
␲R 3
3
(0.547)(4.79)(7.25)(9.78)(10−24 cm 3 )
4
␲(1.77 × 10−8 cm) 3
3
= 8.0 atoms/unit cell
(b) In order to compute the density, we just employ E quation (3.5) as
␳ =
=
nA I
abcN A
(8 atoms/unit cell)(126.91 g/mol)
[(4.79)(7.25)(9.78) × 10−24 cm 3 /unit cell](6.023 × 1023 atoms/mol)
= 4.96 g/cm 3
3.22 This question asks that we generate a three-dimensional unit cell for AuCu 3 using the Molecule
D efinition File on the CD -RO M. O ne set of directions that may be used to construct this unit cell
and that are entered on the Notepad are as follows:
[D isplayProps]
R otatez=−30
R otatey=−15
[A tomProps]
G old=LtR ed,0.14
Copper=LtYellow,0.13
[BondProps]
SingleSolid=LtG ray
[A toms]
Au1=1,0,0,G old
Au2=0,0,0,G old
Au3=0,1,0,G old
Au4=1,1,0,G old
Au5=1,0,1,G old
Au6=0,0,1,G old
Au7=0,1,1,G old
Au8=1,1,1,G old
Cu1=0.5,0,0.5,Copper
Cu2=0,0.5,0.5,Copper
Cu3=0.5,1,0.5,Copper
Cu4=1,0.5,0.5,Copper
Cu5=0.5,0.5,1,Copper
Cu6=0.5,0.5,0,Copper
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[Bonds]
B1=Au1,Au5,SingleSolid
B2=Au5,Au6,SingleSolid
B3=Au6,Au2,SingleSolid
B4=Au2,Au1,SingleSolid
B5=Au4,Au8,SingleSolid
B6=Au8,Au7,SingleSolid
B7=Au7,Au3,SingleSolid
B8=Au3,Au4,SingleSolid
B9=Au1,Au4,SingleSolid
B10=Au8,Au5,SingleSolid
B11=Au2,Au3,SingleSolid
B12=Au6,Au7,SingleSolid
When saving these instructions, the file name that is chosen should end with a period followed by
mdf and the entire file name needs to be enclosed within quotation marks. For example, if one
wants to name the file AuCu3, the name by which it should be saved is “AuCu3.mdf”. In addition,
the file should be saved as a “Text D ocument.”
3.27 In this problem we are asked to show that the minimum cation-to-anion radius ratio for a coordination number of six is 0.414. Below is shown one of the faces of the rock salt crystal structure in
which anions and cations just touch along the edges, and also the face diagonals.
r
A
r
C
H
G
F
From triangle FGH,
G F = 2r A
and
FH = G H = r A + r C
Since FGH is a right triangle
(G H ) 2 + (FH ) 2 = (FG ) 2
or
(r A + r C ) 2 + (r A + r C ) 2 = (2r A ) 2
which leads to
2r A
rA + rC = √
2
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O r, solving for rC /rA
rC
=
rA
2
√ − 1 = 0.414
2
3.29 This problem calls for us to predict crystal structures for several ceramic materials on the basis of
ionic charge and ionic radii.
(a) For CsI, from Table 3.4
r Cs+
0.170 nm
=
= 0.773
r I−
0.220 nm
Now, from Table 3.3, the coordination number for each cation (Cs+ ) is eight, and, using Table 3.5,
the predicted crystal structure is cesium chloride.
(c) For KI, from Table 3.4
r K+
0.138 nm
=
= 0.627
r I−
0.220 nm
The coordination number is six (Table 3.3), and the predicted crystal structure is sodium chloride
(Table 3.5).
3.36 This problem asks that we compute the theoretical density of diamond given that the C ––C distance and bond angle are 0.154 nm and 109.5◦ , respectively. The first thing we need do is to
determine the unit cell edge length from the given C ––C distance. The drawing below shows
the cubic unit cell with those carbon atoms that bond to one another in one-quarter of the unit
cell.
a
y
θ
φ x
From this figure, ␾ is one-half of the bond angle or ␾ = 109.5◦ /2 = 54.75◦ , which means that
␪ = 90◦ − 54.75◦ = 35.25◦
since the triangle shown is a right triangle. A lso, y = 0.154 nm, the carbon-carbon bond distance.
Furthermore, x = a/4, and therefore,
x=
a
= y sin ␪
4
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Or
a = 4y sin ␪ = (4)(0.154 nm)(sin 35.25◦ ) = 0.356 nm
= 3.56 × 10−8 cm
The unit cell volume, V C , is just a3 , that is
V C = a 3 = (3.56 × 10−8 cm) 3 = 4.51 × 10−23 cm 3
We must now utilize a modified E quation (3.6) since there is only one atom type. There are eight
equivalent atoms per unit cell (i.e., one equivalent corner, three equivalent faces, and four interior
atoms), and therefore
␳ =
=
n′A C
VC NA
(4.51 ×
(8 atoms/unit cell)(12.01 g/g-atom)
cm 3 /unit cell)(6.023 × 1023 atoms/g-atom)
10−23
= 3.54 g/cm 3
The measured density is 3.51 g/cm 3 .
3.39 (a) We are asked to compute the density of CsCl. Modifying the result of Problem 3.4, we get
a=
2(0.170 nm) + 2(0.181 nm)
2r Cs+ + 2r Cl−
=
√
√
3
3
= 0.405 nm = 4.05 × 10−8 cm
From E quation (3.6)
␳=
n ′ (A Cs + A Cl )
n ′ (A Cs + A Cl )
=
VC NA
a3NA
For the CsCl crystal structure, n′ = 1 formula unit/unit cell, and thus
␳ =
(1 formula unit/unit cell)(132.91 g/mol + 35.45 g/mol)
(4.05 × 10−8 cm) 3 /unit cell(6.023 × 1023 formula units/mol)
= 4.20 g/cm 3
(b) This value of the density is greater than the measured density. The reason for this discrepancy
is that the ionic radii in Table 3.4, used for this computation, were for a coordination number of six,
when, in fact, the coordination number of both Cs+ and Cl− is eight. U nder these circumstances,
the actual ionic radii and unit cell volume (V C ) will be slightly greater than calculated values;
consequently, the measured density is smaller than the calculated density.
3.45 We are asked in this problem to compute the atomic packing factor for the CsCl crystal structure.
This requires that we take the ratio of the sphere volume within the unit cell and the total unit cell
volume. From Figure 3.6 there is the equivalent of one Cs and one Cl ion per unit cell; the ionic radii
of these two ions are 0.170 nm and 0.181 nm, respectively (Table 3.4). Thus, the sphere volume, V S ,
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is just
VS =
4
(␲)[(0.170 nm) 3 + (0.181 nm) 3 ] = 0.0454 nm 3
3
For CsCl the unit cell edge length, a, in terms of the atomic radii is just
a=
2(0.170 nm) + 2(0.181 nm)
2r Cs+ + 2r Cl−
=
√
√
3
3
= 0.405 nm
Since V C = a3
V C = (0.405 nm) 3 = 0.0664 nm 3
A nd, finally the atomic packing factor is just
A PF =
0.0454 nm 3
VS
=
= 0.684
VC
0.0664 nm 3
3.50 (a) We are asked for the indices of the two directions sketched in the figure. For direction 1, the
projection on the x-axis is zero (since it lies in the y-z plane), while projections on the y- and z-axes
are b/2 and c, respectively. This is an [012] direction as indicated in the summary below.
Projections
Projections in terms of a, b, and c
R eduction to integers
E nclosure
x
y
z
0a
0
0
b/2
1/2
1
[012]
c
1
2
3.51 This problem asks for us to sketch several directions within a cubic unit cell. The [110], [121], and
[012] directions are indicated below.
_
[012]
z
__
[121]
_
[110]
y
x
3.53 This problem asks that we determine indices for several directions that have been drawn within a
cubic unit cell. D irection B is a [232] direction, the determination of which is summarized as follows.
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We first of all position the origin of the coordinate system at the tail of the direction vector; then
in terms of this new coordinate system
x
Projections
Projections in terms of a, b, and c
R eduction to integers
2a
3
2
3
2
E nclosure
y
−b
−1
−3
z
2c
3
2
3
2
[232]
D irection D is a [136] direction, the determination of which is summarized as follows. We
first of all position the origin of the coordinate system at the tail of the direction vector; then in
terms of this new coordinate system
Projections
Projections in terms of a, b, and c
R eduction to integers
x
y
a
6
1
6
1
b
2
1
2
3
E nclosure
[136]
z
−c
−1
−6
3.56 This problem asks that we determine the Miller indices for planes that have been drawn within a unit
cell. For plane B we will move the origin of the unit cell one unit cell distance to the right along the y
axis, and one unit cell distance parallel to the x axis; thus, this is a (112) plane, as summarized below.
x
y
Intercepts
−a
−b
Intercepts in terms of a, b, and c
−1
−1
R eciprocals of intercepts
−1
−1
E nclosure
z
c
2
1
2
2
(112)
3.58 For plane B we will leave the origin at the unit cell as shown; this is a (221) plane, as summarized
below.
Intercepts
Intercepts in terms of a, b, and c
R eciprocals of intercepts
E nclosure
x
y
a
2
1
2
2
b
2
1
2
2
(221)
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z
c
1
1
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3.59 The (1101) plane in a hexagonal unit cell is shown below.
z
a
2
a
3
a
1
_
(1101)
3.60 This problem asks that we specify the Miller indices for planes that have been drawn within hexagonal unit cells.
(a) For this plane we will leave the origin of the coordinate system as shown; thus, this is a (1100)
plane, as summarized below.
Intercepts
Intercepts in terms of a’s and c
R eciprocals of intercepts
E nclosure
a1
a2
a
1
1
−a
∞a
−1
∞
−1
0
(1100)
a3
z
∞c
∞
0
3.61 This problem asks for us to sketch several planes within a cubic unit cell. The (011) and (102) planes
are indicated below.
z
__
(011)
y
x
_
(102)
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3.63 This problem asks that we represent specific crystallographic planes for various ceramic crystal
structures.
(a) A (100) plane for the rock salt crystal structure would appear as
+
Na
Cl
3.64 For the unit cell shown in Problem 3.21 we are asked to determine, from three given sets of crystallographic planes, which are equivalent.
(a) The unit cell in Problem 3.21 is body-centered tetragonal. O nly the (100) (front face) and (010)
(left side face) planes are equivalent since the dimensions of these planes within the unit cell (and
therefore the distances between adjacent atoms) are the same (namely 0.40 nm × 0.30 nm), which
are different than the (001) (top face) plane (namely 0.30 nm × 0.30 nm).
3.66 This question is concerned with the zinc blende crystal structure in terms of close-packed planes of
anions.
(a) The stacking sequence of close-packed planes of anions for the zinc blende crystal structure
will be the same as FCC (and not H CP) because the anion packing is FCC (Table 3.5).
(b) The cations will fill tetrahedral positions since the coordination number for cations is four
(Table 3.5).
(c) O nly one-half of the tetrahedral positions will be occupied because there are two tetrahedral
sites per anion, and yet only one cation per anion.
3.70* In this problem we are to compute the linear densities of several crystallographic planes for the
face-centered cubic crystal structure. For FCC the linear density of the [100] direction is computed
as follows:
The linear density, LD , is defined by the ratio
LD =
Lc
Ll
where Ll is the line length within the unit cell along the [100] direction, and Lc is line length passing
through intersection circles. Now, Ll is just
√ the unit cell edge length, a which, for FCC is related to
the atomic radius R according to a = 2R 2 [E quation (3.1)]. A lso for this situation, Lc = 2R and
therefore
LD =
2R
√ = 0.71
2R 2
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3.73* In this problem we are to compute the planar densities of several crystallographic planes for the
body-centered cubic crystal structure. Planar density, PD , is defined as
PD =
Ac
Ap
where A p is the total plane area within the unit cell and A c is the circle plane area within this same
plane. For (110), that portion of a plane that passes through a BCC unit cell forms a rectangle as
shown below.
4R
3
R
4R 2
3
In terms of the atomic radius R, the length of the rectangle base is
4R
. Therefore, the area of this rectangle, which is just A p is
a= √
3
Ap =
√
4R
√ 2,
3
whereas the height is
√ √
4R
16R 2 2
4R 2
=
√
√
3
3
3
Now for the number equivalent atoms within this plane. O ne-fourth of each corner atom and the
entirety of the center atom belong to the unit cell. Therefore, there is an equivalent of 2 atoms
within the unit cell. H ence
A c = 2(␲R 2 )
and
PD =
2␲R 2
√ = 0.83
16R 2 2
3
3.80* U sing the data for aluminum in Table 3.1, we are asked to compute the interplanar spacings for
the (110) and (221) sets of planes. From the table, aluminum has an FCC crystal structure and an
atomic radius of 0.1431 nm. U sing E quation (3.1) the lattice parameter, a, may be computed as
√
√
a = 2R 2 = (2)(0.1431 nm)( 2) = 0.4047 nm
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Now, the d110 interplanar spacing may be determined using E quation (3.11) as
a
0.4047 nm
= 0.2862 nm
d 110 = =
√
2
2
2
2
(1) + (1) + (0)
3.84* From the diffraction pattern for ␣-iron shown in Figure 3.37, we are asked to compute the interplanar spacing for each set of planes that has been indexed; we are also to determine the lattice
parameter of Fe for each peak. In order to compute the interplanar spacing and the lattice parameter we must employ E quations (3.11) and (3.10), respectively. For the first peak which occurs
at 45.0◦
d 110 =
n␭
(1)(0.1542 nm)
= 0.2015 nm
=
45.0◦
2 sin ␪
(2) sin
2
A nd
a = d hkl (h) 2 + (k) 2 + (l) 2 = d 110 (1) 2 + (1) 2 + (0) 2
√
= (0.2015 nm) 2 = 0.2850 nm
Similar computations are made for the other peaks which results are tabulated below:
Peak Index
2␪
d hkl (nm)
a (nm)
200
211
65.1
82.8
0.1433
0.1166
0.2866
0.2856
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CH A PTE R 4
POLYMER STRU CTU RES
4.4 We are asked to compute the number-average degree of polymerization for polypropylene, given that
the number-average molecular weight is 1,000,000 g/mol. The mer molecular weight of polypropylene
is just
m = 3(A C ) + 6(A H )
= (3)(12.01 g/mol) + (6)(1.008 g/mol) = 42.08 g/mol
If we let nn represent the number-average degree of polymerization, then from E quation (4.4a)
nn =
106 g/mol
Mn
=
= 23,700
m
42.08 g/mol
4.6 (a) From the tabulated data, we are asked to compute Mn , the number-average molecular weight.
This is carried out below.
Molecular wt
R ange
Mean M i
xi
xi M i
8,000–16,000
16,000–24,000
24,000–32,000
32,000–40,000
40,000–48,000
48,000–56,000
12,000
20,000
28,000
36,000
44,000
52,000
0.05
0.16
0.24
0.28
0.20
0.07
600
3200
6720
10,080
8800
3640
Mn =
xi M i = 33,040 g/mol
(c) Now we are asked to compute nn (the number-average degree of polymerization), using the
E quation (4.4a). For polypropylene,
m = 3(A C ) + 6(A H )
= (3)(12.01 g/mol) + (6)(1.008 g/mol) = 42.08 g/mol
A nd
nn =
Mn
33040 g/mol
=
= 785
m
42.08 g/mol
4.11 This problem first of all asks for us to calculate, using E quation (4.11), the average total chain
length, L, for a linear polytetrafluoroethylene polymer having a number-average molecular weight
of 500,000 g/mol. It is necessary to calculate the number-average degree of polymerization, nn , using
E quation (4.4a). For PTFE , from Table 4.3, each mer unit has two carbons and four fluorines. Thus,
m = 2(A C ) + 4(A F )
= (2)(12.01 g/mol) + (4)(19.00 g/mol) = 100.02 g/mol
and
nn =
Mn
500000 g/mol
=
= 5000
m
100.02 g/mol
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which is the number of mer units along an average chain. Since there are two carbon atoms per mer
unit, there are two C ––C chain bonds per mer, which means that the total number of chain bonds in
the molecule, N, is just (2)(5000) = 10,000 bonds. Furthermore, assume that for single carbon-carbon
bonds, d = 0.154 nm and ␪ = 109◦ (Section 4.4); therefore, from E quation (4.11)
L = Nd sin
␪
2
109◦
= 1254 nm
= (10,000)(0.154 nm) sin
2
It is now possible to calculate the average chain end-to-end distance, r, using E quation (4.12) as
√
√
r = d N = (0.154 nm) 10000 = 15.4 nm
4.19 For a poly(styrene-butadiene) alternating copolymer with a number-average molecular weight of
1,350,000 g/mol, we are asked to determine the average number of styrene and butadiene mer units
per molecule.
Since it is an alternating copolymer, the number of both types of mer units will be the
same. Therefore, consider them as a single mer unit, and determine the number-average degree of
polymerization. For the styrene mer, there are eight carbon atoms and eight hydrogen atoms, while
the butadiene mer consists of four carbon atoms and six hydrogen atoms. Therefore, the styrenebutadiene combined mer weight is just
m = 12(A C ) + 14(A H )
= (12)(12.01 g/mol) + (14)(1.008 g/mol) = 158.23 g/mol
From E quation (4.4a), the number-average degree of polymerization is just
nn =
Mn
1350000 g/mol
=
= 8530
m
158.23 g/mol
Thus, there is an average of 8530 of both mer types per molecule.
4.28 G iven that polyethylene has an orthorhombic unit cell with two equivalent mer units, we are asked to
compute the density of totally crystalline polyethylene. In order to solve this problem it is necessary
to employ E quation (3.5), in which n represents the number of mer units within the unit cell (n = 2),
and A is the mer molecular weight, which for polyethylene is just
A = 2(A C ) + 4(A H )
= (2)(12.01 g/mol) + (4)(1.008 g/mol) = 28.05 g/mol
A lso, V C is the unit cell volume, which is just the product of the three unit cell edge lengths in
Figure 4.10. Thus,
␳ =
=
nA
VC NA
(7.41 ×
10−8
= 0.998 g/cm 3
(2 mers/uc)(28.05 g/mol)
cm)(4.94 × 10−8 cm)(2.55 × 10−8 cm)/uc(6.023 × 1023 mers/mol)
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CH A PTE R 5
IMPERFECTIONS IN SOLID S
5.1 In order to compute the fraction of atom sites that are vacant in lead at 600 K, we must employ
E quation (5.1). A s stated in the problem, Q V = 0.55 eV/atom. Thus,
QV
NV
0.55 eV/atom
= exp −
= exp −
N
kT
(8.62 × 10−5 eV/atom-K)(600 K)
= 2.41 × 10−5
5.4 This problem calls for a determination of the number of atoms per cubic meter of aluminum. In
order to solve this problem, one must employ E quation (5.2),
N=
NA ␳A l
A Al
The density of A l (from the table inside of the front cover) is 2.71 g/cm 3 , while its atomic weight is
26.98 g/mol. Thus,
N=
(6.023 × 1023 atoms/mol)(2.71 g/cm 3 )
26.98 g/mol
= 6.05 × 1022 atoms/cm 3 = 6.05 × 1028 atoms/m 3
5.9 In the drawing below is shown the atoms on the (100) face of an FCC unit cell; the interstitial site is
at the center of the edge.
R
R
2r
a
The diameter of an atom that will just fit into this site (2r) is just the difference between that unit
cell edge length (a) and the radii of the two host atoms that are located on either side of the site (R);
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that is
2r = a − 2R
√
H owever, for FCC a is related to R according to E quation (3.1) as a = 2R 2; therefore, solving for
r gives
√
a − 2R
2R 2 − 2R
r=
=
= 0.41R
2
2
5.10 (a) For Li+ substituting for Ca 2+ in CaO, oxygen vacancies would be created. For each Li+ substituting
for Ca 2+ , one positive charge is removed; in order to maintain charge neutrality, a single negative
charge may be removed. Negative charges are eliminated by creating oxygen vacancies, and for every
two Li+ ions added, a single oxygen vacancy is formed.
5.15 This problem asks that we determine the composition, in atom percent, of an alloy that contains 98 g
tin and 65 g of lead. The concentration of an element in an alloy, in atom percent, may be computed
using E quation (5.5). With this problem, it first becomes necessary to compute the number of moles
of both Sn and Pb, for which E quation (5.4) is employed. Thus, the number of moles of Sn is just
n m Sn =
m ′Sn
98 g
=
= 0.826 mol
A Sn
118.69 g/mol
Likewise, for Pb
n m Pb =
65 g
= 0.314 mol
207.2 g/mol
Now, use of E quation (5.5) yields
C ′Sn =
n m Sn
× 100
n m Sn + n m Pb
=
0.826 mol
× 100 = 72.5 at%
0.826 mol + 0.314 mol
C ′Pb =
0.314 mol
× 100 = 27.5 at%
0.826 mol + 0.314 mol
A lso,
5.27 This problem asks us to determine the weight percent of Nb that must be added to V such that
the resultant alloy will contain 1.55 × 1022 Nb atoms per cubic centimeter. To solve this problem,
employment of E quation (5.18) is necessary, using the following values:
N 1 = N Nb = 1.55 × 1022 atoms/cm 3
␳ 1 = ␳ Nb = 8.57 g/cm 3
␳ 2 = ␳ V = 6.10 g/cm 3
A 1 = A Nb = 92.91 g/mol
A 2 = A V = 50.94 g/mol
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Thus
C Nb =
=
100
␳V
NA ␳V
−
1+
N Nb A Nb
␳ Nb
100
6.10 g/cm 3
(6.023 × 20 atoms/mole)(6.10 g/cm 3 )
1+
−
(1.55 × 1022 atoms/cm 3 )(92.91 g/mol)
8.57 g/cm 3
23
= 35.2 wt%
5.30 In this problem we are given a general equation which may be used to determine the Burgers vector
and are asked to give Burgers vector representations for specific crystal structures, and then to
compute Burgers vector magnitudes.
(a) The Burgers vector will point in that direction having the highest linear density. From Problem
3.70 the linear density for the [110] direction in FCC is 1.0, the maximum possible; therefore for FCC
b=
a
[110]
2
√
(b) For A l which has an FCC crystal structure, R = 0.1431 nm (Table 3.1) and a = 2R 2 = 0.4047 nm
[E quation (3.1)]; therefore
a 2
h + k 2 + l2
2
0.4047 nm
=
(1) 2 + (1) 2 + (0) 2 = 0.2862 nm
2
b=
5.37 (a) We are asked for the number of grains per square inch (N) at a magnification of 100X, and for
an A STM grain size of 4. From E quation (5.16), n = 4, and
N = 2(n−1) = 2(4−1) = 23 = 8
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CH A PTE R 6
D IFFU SION
6.8 This problem calls for computation of the diffusion coefficient for a steady-state diffusion situation.
Let us first convert the carbon concentrations from wt% to kg C/m 3 using E quation (5.9a); the
densities of carbon and iron (from inside the front cover of the book) are 2.25 and 7.87 g/cm 3 . For
0.012 wt% C




CC
 × 103
C ′′C = 
 CC
C Fe 
+
␳C
␳ Fe


=



0.012
 × 103
99.988 
0.012
+
2.25 g/cm 3
7.87 g/cm 3
= 0.944 kg C/m 3
Similarly, for 0.0075 wt% C


C ′′C = 



0.0075
 × 103
99.9925 
0.0075
+
2.25 g/cm 3
7.87 g/cm 3
= 0.590 kg C/m 3
Now, using a form of E quation (6.3)
D = −J
xA − xB
CA − CB
−8
= −(1.40 × 10
2
kg/m -s)
−10−3 m
0.944 kg/m 3 − 0.590 kg/m 3
= 3.95 × 10−11 m 2 /s
6.13 This problem asks us to compute the nitrogen concentration (Cx ) at the 1 mm position after a 10 h
diffusion time, when diffusion is nonsteady-state. From E quation (6.5)
Cx − Co
Cx − 0
x
=
= 1 − erf √
Cs − Co
0.1 − 0
2 Dt
= 1 − erf
10−3 m
(2) (2.5 × 10−11 m 2 /s)(10 h)(3600 s/h)
= 1 − erf(0.527)
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U sing data in Table 6.1 and linear interpolation
z
erf(z)
0.500
0.527
0.550
0.5205
y
0.5633
0.527 − 0.500
y − 0.5205
=
0.550 − 0.500
0.5633 − 0.5205
from which
y = erf(0.527) = 0.5436
Thus,
Cx − 0
= 1.0 − 0.5436
0.1 − 0
This expression gives
C x = 0.046 wt% N
6.15 This problem calls for an estimate of the time necessary to achieve a carbon concentration of
0.45 wt% at a point 5 mm from the surface. From E quation (6.6b),
x2
= constant
Dt
But since the temperature is constant, so also is D constant, and
x2
= constant
t
or
x21
x2
= 2
t1
t2
Thus,
(2.5 mm) 2
(5.0 mm) 2
=
10 h
t2
from which
t 2 = 40 h
6.21 (a) U sing E quation (6.9a), we set up two simultaneous equations with Q d and D o as unknowns.
Solving for Q d in terms of temperatures T1 and T2 (1273 K and 1473 K) and D 1 and D 2 (9.4 × 10−16
and 2.4 × 10−14 m 2 /s), we get
Q d = −R
=−
ln D 1 − ln D 2
1/T 1 − 1/T 2
(8.31 J/mol-K)[ln(9.4 × 10−16 ) − ln(2.4 × 10−14 )]
1/(1273 K) − 1/(1473 K)
= 252,400 J/mol
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Now, solving for D o from E quation (6.8)
D o = D 1 exp
Qd
RT 1
= (9.4 × 10−16 m 2 /s) exp
252400 J/mol
(8.31 J/mol-K)(1273 K)
= 2.2 × 10−5 m 2 /s
(b) U sing these values of D o and Q d , D at 1373 K is just
D = (2.2 × 10−5 m 2 /s) exp −
252400 J/mol
(8.31 J/mol-K)(1373 K)
= 5.4 × 10−15 m 2 /s
6.29 For this problem, a diffusion couple is prepared using two hypothetical A and B metals. A fter a 30-h
heat treatment at 1000 K, the concentration of A in B is 3.2 wt% at the 15.5-mm position. A fter
another heat treatment at 800 K for 30 h, we are to determine at what position the composition will
be 3.2 wt% A . In order to make this determination, we must employ E quation (6.6b) with t constant.
That is
x2
= constant
D
Or
x2
x2800
= 1000
D 800
D 1000
It is necessary to compute both D 800 and D 1000 using E quation (6.8), as follows:
152000 J/mol
D 800 = (1.8 × 10−5 m 2 /s) exp −
(8.31 J/mol-K)(800 K)
= 2.12 × 10−15 m 2 /s
D 1000 = (1.8 × 10−5 m 2 /s) exp −
152000 J/mol
(8.31 J/mol-K)(1000 K)
= 2.05 × 10−13 m 2 /s
Now, solving for x800 yields
x800 = x1000
D 800
D 1000
= (15.5 mm)
2.12 × 10−15 m 2 /s
2.05 × 10−13 m 2 /s
= 1.6 mm
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CH A PTE R 7
MECHA NICA L PROPERTIES
7.4
We are asked to compute the maximum length of a cylindrical titanium alloy specimen that is
deformed elastically in tension. For a cylindrical specimen
Ao = ␲
do
2
2
where do is the original diameter. Combining E quations (7.1), (7.2), and (7.5) and solving for lo
leads to
lo =
=
E ␲d 2o l
4F
(107 × 109 N/m 2 )(␲)(3.8 × 10−3 m) 2 (0.42 × 10−3 m)
(4)(2000 N)
= 0.25 m = 250 mm (10 in.)
7.9
This problem asks that we calculate the elongation l of a specimen of steel the stress-strain
behavior of which is shown in Figure 7.33. First it becomes necessary to compute the stress when a
load of 23,500 N is applied as
␴=
F
=
Ao
F
do
␲
2
2 =
23500 N
10 × 10−3 m
␲
2
2 = 300 MPa (44,400 psi)
R eferring to Figure 7.33, at this stress level we are in the elastic region on the stress-strain curve,
which corresponds to a strain of 0.0013. Now, utilization of E quation (7.2) yields
l = εlo = (0.0013)(75 mm) = 0.10 mm (0.004 in.)
7.14 (a) We are asked, in this portion of the problem, to determine the elongation of a cylindrical
specimen of aluminum. U sing E quations (7.1), (7.2), and (7.5)
l
F
2 =E
lo
do
␲
4
Or
l =
=
4Flo
␲d 2o E
(4)(48,800 N)(200 × 10−3 m)
= 0.50 mm (0.02 in.)
(␲)(19 × 10−3 m) 2 (69 × 109 N/m 2 )
(b) We are now called upon to determine the change in diameter, d. U sing E quation (7.8)
␯=−
d/d o
εx
=−
εz
l/lo
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From Table 7.1, for A l, ␯ = 0.33. Now, solving for d yields
d = −
(0.33)(0.50 mm)(19 mm)
␯ld o
=−
lo
200 mm
= −1.6 × 10−2 mm (−6.2 × 10−4 in.)
The diameter will decrease.
7.16 This problem asks that we compute Poisson’s ratio for the metal alloy. From E quations (7.5) and (7.1)
εz =
␴
F/A o
=
=
E
E
F
do
␲
2
2
=
E
4F
␲d 2o E
Since the transverse strain εx is just
εx =
d
do
and Poisson’s ratio is defined by E quation (7.8) then
␯=−
=−
d/d o
d o d␲E
εx
=−
= −
4F
εz
4F
␲d 2o E
(8 × 10−3 m)(−5 × 10−6 m)(␲)(140 × 109 N/m 2 )
= 0.280
(4)(15,700 N)
7.21 (a) This portion of the problem asks that we compute the elongation of the brass specimen. The
first calculation necessary is that of the applied stress using E quation (7.1), as
␴=
F
=
Ao
F
do
␲
2
2 =
5000 N
6 × 10−3 m
␲
2
2 = 177 MPa (25,000 psi)
From the stress-strain plot in Figure 7.12, this stress corresponds to a strain of about 2.0 × 10−3 .
From the definition of strain, E quation (7.2),
l = εlo = (2.0 × 10−3 )(50 mm) = 0.10 mm (4 × 10−3 in.)
(b) In order to determine the reduction in diameter d, it is necessary to use E quation (7.8) and
the definition of lateral strain (i.e., εx = d/do ) as follows:
d = d o εx = −d o ␯εz = −(6 mm)(0.30)(2.0 × 10−3 )
= −3.6 × 10−3 mm (−1.4 × 10−4 in.)
7.27 This problem asks us to determine the deformation characteristics of a steel specimen, the stressstrain behavior of which is shown in Figure 7.33.
(a) In order to ascertain whether the deformation is elastic or plastic, we must first compute the
stress, then locate it on the stress-strain curve, and, finally, note whether this point is on the elastic
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or plastic region. Thus,
␴=
F
=
Ao
44500 N
10 × 10−3 m
␲
2
2 = 565 MPa (80,000 psi)
The 565 MPa point is past the linear portion of the curve, and, therefore, the deformation will be
both elastic and plastic.
(b) This portion of the problem asks us to compute the increase in specimen length. From the
stress-strain curve, the strain at 565 MPa is approximately 0.008. Thus, from E quation (7.2)
l = εlo = (0.008)(500 mm) = 4 mm (0.16 in.)
7.29 This problem calls for us to make a stress-strain plot for aluminum, given its tensile load-length
data, and then to determine some of its mechanical characteristics.
(a) The data are plotted below on two plots: the first corresponds to the entire stress-strain curve,
while for the second, the curve extends just beyond the elastic region of deformation.
300
Stress (MPa)
200
100
0
0.000
0.002
0.004
0.006
0.008
0.010
Strain
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(b) The elastic modulus is the slope in the linear elastic region as
E=
200 MPa − 0 MPa
␴
=
= 62.5 × 103 MPa = 62.5 G Pa (9.1 × 106 psi)
ε
0.0032 − 0
(c) For the yield strength, the 0.002 strain offset line is drawn dashed. It intersects the stress-strain
curve at approximately 285 MPa (41,000 psi).
(d) The tensile strength is approximately 370 MPa (54,000 psi), corresponding to the maximum
stress on the complete stress-strain plot.
(e) The ductility, in percent elongation, is just the plastic strain at fracture, multiplied by onehundred. The total fracture strain at fracture is 0.165; subtracting out the elastic strain (which is
about 0.005) leaves a plastic strain of 0.160. Thus, the ductility is about 16% E L.
(f) From E quation (7.14), the modulus of resilience is just
Ur =
␴y2
2E
which, using data computed in the problem yields a value of
Ur =
(285 MPa) 2
= 6.5 × 105 J/m 3 (93.8 in.-lb f /in.3 )
(2)(62.5 × 103 MPa)
7.32 This problem asks us to calculate the moduli of resilience for the materials having the stress-strain
behaviors shown in Figures 7.12 and 7.33. A ccording to E quation (7.14), the modulus of resilience
U r is a function of the yield strength and the modulus of elasticity as
Ur =
␴y2
2E
The values for ␴y and E for the brass in Figure 7.12 are 250 MPa (36,000 psi) and 93.9 G Pa
(13.6 × 106 psi), respectively. Thus
Ur =
(250 MPa) 2
= 3.32 × 105 J/m 3 (47.6 in.-lb f /in.3 )
(2)(93.9 × 103 MPa)
7.41 For this problem, we are given two values of εT and ␴T , from which we are asked to calculate the
true stress which produces a true plastic strain of 0.25. E mploying E quation (7.19), we may set up
two simultaneous equations with two unknowns (the unknowns being K and n), as
log(50,000 psi) = log K + n log(0.10)
log(60,000 psi) = log K + n log(0.20)
From these two expressions,
n=
log(50,000) − log(60,000)
= 0.263
log(0.1) − log(0.2)
log K = 4.96 or K = 91,623 psi
Thus, for εT = 0.25
␴T = K(εT ) 2 = (91,623 psi)(0.25) 0.263 = 63,700 psi (440 MPa)
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7.45 This problem calls for us to utilize the appropriate data from Problem 7.29 in order to determine
the values of n and K for this material. From E quation (7.32) the slope and intercept of a log ␴T
versus log εT plot will yield n and log K, respectively. H owever, E quation (7.19) is only valid in
the region of plastic deformation to the point of necking; thus, only the 7th, 8th, 9th, and 10th data
points may be utilized. The log-log plot with these data points is given below.
2.60
2.58
log true stress (MPa)
2.56
2.54
2.52
2.50
2.48
2.46
-2.2
-2.0
-1.8
-1.6
-1.4
-1.2
log true strain
The slope yields a value of 0.136 for n, whereas the intercept gives a value of 2.7497 for log K, and
thus K = 562 MPa.
7.50 For this problem, the load is given at which a circular specimen of aluminum oxide fractures when
subjected to a three-point bending test; we are then are asked to determine the load at which a
specimen of the same material having a square cross-section fractures. It is first necessary to compute the flexural strength of the alumina using E quation (7.20b), and then, using this value, we may
calculate the value of Ff in E quation (7.20a). From E quation (7.20b)
␴fs =
=
FfL
␲R 3
(950 N)(50 × 10−3 m)
= 352 × 106 N/m 2 = 352 MPa (50,000 psi)
(␲)(3.5 × 10−3 m) 3
Now, solving for Ff from E quation (7.20a), realizing that b = d = 12 mm, yields
Ff =
=
2␴fs d 3
3L
(2)(352 × 106 N/m 2 )(12 × 10−3 m) 3
= 10,100 N (2165 lb f )
(3)(40 × 10−3 m)
7.54* (a) This part of the problem asks us to determine the flexural strength of nonporous MgO assuming that the value of n in E quation (7.22) is 3.75. Taking natural logarithms of both sides of
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E quation (7.22) yields
ln ␴fs = ln ␴o − nP
In Table 7.2 it is noted that for P = 0.05, ␴fs = 105 MPa. For the nonporous material P = 0 and,
ln ␴o = ln ␴fs . Solving for ln ␴o from the above equation gives and using these data gives
ln ␴o = ln ␴fs + nP
= ln(105 MPa) + (3.75)(0.05) = 4.841
or
␴o = e 4.841 = 127 MPa (18,100 psi)
(b) Now we are asked to compute the volume percent porosity to yield a ␴fs of 62 MPa (9000 psi).
Taking the natural logarithm of E quation (7.22) and solving for P leads to
ln ␴o − ln ␴fs
n
ln(127 MPa) − ln(62 MPa)
=
3.75
= 0.19 or 19 vol%
P=
7.65 This problem calls for estimations of Brinell and R ockwell hardnesses.
(a) For the brass specimen, the stress-strain behavior for which is shown in Figure 7.12, the tensile
strength is 450 MPa (65,000 psi). From Figure 7.31, the hardness for brass corresponding to this
tensile strength is about 125 H B or 70 H R B.
7.70 The working stresses for the two alloys, the stress-strain behaviors of which are shown in Figures
7.12 and 7.33, are calculated by dividing the yield strength by a factor of safety, which we will take
to be 2. For the brass alloy (Figure 7.12), since ␴y = 250 MPa (36,000 psi), the working stress is
125 MPa (18,000 psi), whereas for the steel alloy (Figure 7.33), ␴y = 570 MPa (82,000 psi), and,
therefore, ␴w = 285 MPa (41,000 psi).
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CH A PTE R 8
D EFORMATION A ND STRENGTHENING MECHA NISMS
8.7
In the manner of Figure 8.6b, we are to sketch the atomic packing for a BCC {110} type plane, and
with arrows indicate two different 111 type directions. Such is shown below.
8.10* We are asked to compute the Schmid factor for an FCC crystal oriented with its [100] direction
parallel to the loading axis. With this scheme, slip may occur on the (111) plane and in the [110]
direction as noted in the figure below.
z
[111]
φ
λ
y
_
[110]
[100]
x
The angle between the [100] and [110] directions, ␭, is 45◦ . For the (111) plane,
the angle
√
−1 a 2
between its normal (which is the [111] direction) and the [100] direction, ␾, is tan ( a ) = 54.74◦ ;
therefore
cos ␭ cos ␾ = cos(45◦ ) cos(54.74◦ ) = 0.408
8.20 We are asked to determine the grain diameter for an iron which will give a yield strength of 205 MPa
(30,000 psi). The best way to solve this problem is to first establish two simultaneous expressions of
E quation (8.5), solve for ␴o and ky , and finally determine the value of d when ␴y = 205 MPa. The
data pertaining to this problem may be tabulated as follows:
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d (mm)
d −1/2 (mm) −1/2
5 × 10−2
8 × 10−3
4.47
11.18
␴y
135 MPa
260 MPa
The two equations thus become
135 MPa = ␴o + (4.47)k y
260 MPa = ␴o + (11.18)k y
which yield the values, ␴o = 51.7 MPa and ky = 18.63 MPa(mm) 1/2 . A t a yield strength of 205 MPa
205 MPa = 51.7 MPa + [18.63 MPa(mm) 1/2 ]d −1/2
or d−1/2 = 8.23 (mm) −1/2 , which gives d = 1.48 × 10−2 mm.
8.25 This problem stipulates that two previously undeformed cylindrical specimens of an alloy are to be
strain hardened by reducing their cross-sectional areas. For one specimen, the initial and deformed
radii are 16 mm and 11 mm, respectively. The second specimen with an initial radius of 12 mm is to
have the same deformed hardness as the first specimen. We are asked to compute the radius of the
second specimen after deformation. In order for these two cylindrical specimens to have the same
deformed hardness, they must be deformed to the same percent cold work. For the first specimen
% CW =
=
␲r 2 − ␲r 2
Ao − Ad
× 100 = o 2 d × 100
Ao
␲r o
␲(16 mm) 2 − ␲(11 mm) 2
× 100 = 52.7% CW
␲(16 mm) 2
For the second specimen, the deformed radius is computed using the above equation and solving
for rd as
rd = ro 1 −
% CW
100
= (12 mm) 1 −
52.7% CW
= 8.25 mm
100
8.27 This problem calls for us to calculate the precold-worked radius of a cylindrical specimen of copper
that has a cold-worked ductility of 25% E L. From Figure 8.19(c), copper that has a ductility of
25% E L will have experienced a deformation of about 11% CW. For a cylindrical specimen, E quation
(8.6) becomes
% CW =
␲r 2o − ␲r 2d
␲r 2o
× 100
Since rd = 10 mm (0.40 in.), solving for ro yields
ro = rd
% CW
1−
100
= 10 mm
11.0
1−
100
= 10.6 mm (0.424 in.)
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8.35 In this problem, we are asked for the length of time required for the average grain size of a brass
material to increase a specified amount using Figure 8.25.
(a) A t 500◦ C, the time necessary for the average grain diameter to increase from 0.01 to 0.1 mm is
approximately 3500 min.
(b) A t 600◦ C the time required for this same grain size increase is approximately 150 min.
8.45* This problem gives us the tensile strengths and associated number-average molecular weights for
two polymethyl methacrylate materials and then asks that we estimate the tensile strength for
Mn = 30,000 g/mol. E quation (8.9) provides the dependence of the tensile strength on Mn . Thus,
using the data provided in the problem, we may set up two simultaneous equations from which it
is possible to solve for the two constants TS∞ and A . These equations are as follows:
107 MPa = TS∞ −
A
40000 g/mol
170 MPa = TS∞ −
A
60000 g/mol
Thus, the values of the two constants are TS∞ = 296 MPa and A = 7.56 × 106 MPa-g/mol. Substituting these values into an equation for which Mn = 30,000 g/mol leads to
TS = TS∞ −
A
30000 g/mol
= 296 MPa −
7.56 × 106 MPa-g/mol
30000 g/mol
= 44 MPa
8.54 This problem asks that we compute the fraction of possible crosslink sites in 10 kg of polybutadiene
when 4.8 kg of S is added, assuming that, on the average, 4.5 sulfur atoms participate in each
crosslink bond. G iven the butadiene mer unit in Table 4.5, we may calculate its molecular weight
as follows:
A (butadiene) = 4(A C ) + 6(A H )
= (4)(12.01 g/mol) + 6(1.008 g/mol) = 54.09 g/mol
10000 g
which means that in 10 kg of butadiene there are 54.09
g/mol = 184.9 mol.
For the vulcanization of polybutadiene, there are two possible crosslink sites per mer—one
for each of the two carbon atoms that are doubly bonded. Furthermore, each of these crosslinks
forms a bridge between two mers. Therefore, we can say that there is the equivalent of one crosslink
per mer. Therefore, let us now calculate the number of moles of sulfur (nsulfur) that react with the
butadiene, by taking the mole ratio of sulfur to butadiene, and then dividing this ratio by 4.5 atoms
per crosslink; this yields the fraction of possible sites that are crosslinked. Thus
n sulfur =
4800 g
= 149.7 mol
32.06 g/mol
A nd
149.7 mol
184.9 mol
fraction sites crosslinked =
= 0.180
4.5
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8.D 1 This problem calls for us to determine whether or not it is possible to cold work steel so as to give
a minimum Brinell hardness of 225 and a ductility of at least 12% E L. A ccording to Figure 7.31, a
Brinell hardness of 225 corresponds to a tensile strength of 800 MPa (116,000 psi). Furthermore,
from Figure 8.19(b), in order to achieve a tensile strength of 800 MPa, deformation of at least
13% CW is necessary. Finally, if we cold work the steel to 13% CW, then the ductility is reduced to
only 14% E L from Figure 8.19(c). Therefore, it is possible to meet both of these criteria by plastically
deforming the steel.
8.D 6 This problem stipulates that a cylindrical rod of copper originally 16.0 mm in diameter is to be cold
worked by drawing; a cold-worked yield strength in excess of 250 MPa and a ductility of at least
12% E L are required, whereas the final diameter must be 11.3 mm. We are to explain how this is
to be accomplished. Let us first calculate the percent cold work and attendant yield strength and
ductility if the drawing is carried out without interruption. From E quation (8.6)
␲
% CW =
do
2
2
−␲
dd
2
2
× 100
2
do
␲
2
2
2
11.3 mm
16 mm
−␲
␲
2
2
× 100 = 50% CW
=
2
16 mm
␲
2
A t 50% CW, the copper will have a yield strength on the order of 330 MPa (48,000 psi),
Figure 8.19(a), which is adequate; however, the ductility will be about 4% E L, Figure 8.19(c), which
is insufficient.
Instead of performing the drawing in a single operation, let us initially draw some fraction
of the total deformation, then anneal to recrystallize, and, finally, cold work the material a second
time in order to achieve the final diameter, yield strength, and ductility.
R eference to Figure 8.19(a) indicates that 21% CW is necessary to give a yield strength of
250 MPa. Similarly, a maximum of 23% CW is possible for 12% E L [Figure 8.19(c)]. The average
of these two values is 22% CW, which we will use in the calculations. If the final diameter after the
first drawing is d′o , then
22% CW =
d′
␲ o
2
2
11.3
−␲
2
′ 2
d
␲ o
2
2
× 100
A nd, solving for d′o yields d′o = 12.8 mm (0.50 in.).
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CH A PTE R 9
FA ILU RE
9.7
We are asked for the critical crack tip radius for an A l2 O 3 material. From E quation (9.1b)
m = 2o
a
t
1/2
Fracture will occur when m reaches the fracture strength of the material, which is given as E/10;
thus
1/2
a
E
= 2o
10
t
O r, solving for t
t =
400ao2
E2
From Table 7.1, E = 393 G Pa, and thus,
t =
(400)(2 × 10−3 mm)(275 MPa) 2
(393 × 103 MPa) 2
= 3.9 × 10−7 mm = 0.39 nm
9.8
9.12*
We may determine the critical stress required for the propagation of a surface crack in soda-lime
glass using E quation (9.3); taking the value of 69 G Pa (Table 7.1) as the modulus of elasticity, we get
c =
2E s
a
=
(2)(69 × 109 N/m 2 )(0.30 N/m)
= 16.2 × 106 N/m 2 = 16.2 MPa
()(5 × 10−5 m)
This problem deals with a tensile specimen, a drawing of which is provided.
(a) In this portion of the problem it is necessary to compute the stress at point P when the applied
stress is 100 MPa (14,500 psi). In order to determine the stress concentration it is necessary to
consult Figure 9.8c. From the geometry of the specimen, w/h = (25 mm)/(20 mm) = 1.25; furthermore, the r/h ratio is (3 mm)/(20 mm) = 0.15. U sing the w/h = 1.25 curve in Figure 9.8c, the
Kt value at r/h = 0.15 is 1.7. A nd since Kt = ␴␴mo , then
m = K t o = (1.7)(100 MPa) = 170 MPa (24,650 psi)
9.15*
This problem calls for us to determine the value of B, the minimum component thickness for which
the condition of plane strain is valid using E quation (9.12) for the metal alloys listed in Table 9.1.
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For the 2024-T3 aluminum alloy
√ 2
2
K lc
44 MPa m
B = 2.5
= 0.041 m = 41 mm (1.60 in.)
= (2.5)
y
345 MPa
For the 4340 alloy steel tempered at 260◦ C
B = (2.5)
9.19
√ 2
50 MPa m
= 0.0023 m = 2.3 mm (0.09 in.)
1640 MPa
For this problem, we are given values of Klc , ␴, and Y for a large plate and are asked to determine
the minimum length of a surface crack that will lead to fracture. A ll we need do is to solve for ac
using E quation (9.14); therefore
√ 2
2
1 K lc
1 55 MPa m
ac =
=
= 0.024 m = 24 mm (0.95 in.)
Y
(1)(200 MPa)
This problem first provides a tabulation of Charpy impact data for a ductile cast iron.
(a) The plot of impact energy versus temperature is shown below.
140
120
100
Impact Energy, J
9.26
80
60
40
20
0
-200
-150
-100
-50
0
Temperature, °C
(b) This portion of the problem asks us to determine the ductile-to-brittle transition temperature
as that temperature corresponding to the average of the maximum and minimum impact energies.
From these data, this average is
Average =
124 J + 6 J
= 65 J
2
A s indicated on the plot by the one set of dashed lines, the ductile-to-brittle transition temperature
according to this criterion is about −105◦ C.
(c) A lso as noted on the plot by the other set of dashed lines, the ductile-to-brittle transition
temperature for an impact energy of 80 J is about −95◦ C.
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9.31
We are asked to determine the fatigue life for a cylindrical red brass rod given its diameter
(8.0 mm) and the maximum tensile and compressive loads (+7500 N and −7500 N, respectively).
The first thing that is necessary is to calculate values of max and min using E quation (7.1). Thus
max =
F max
=
Ao
F max
2
do
2
7500 N
=
8.0 × 10−3 m
()
2
min =
6
2
2 = 150 × 10 N/m = 150 MPa (22,500 psi)
F min
2
do
2
−7500 N
=
8.0 × 10−3 m
()
2
6
2
2 = −150 × 10 N/m = −150 MPa (−22,500 psi)
Now it becomes necessary to compute the stress amplitude using E quation (9.23) as
a =
max − min
150 MPa − (−150 MPa)
=
= 150 MPa (22,500 psi)
2
2
From Figure 9.46 for the red brass, the number of cycles to failure at this stress amplitude is about
1 × 105 cycles.
This problem first provides a tabulation of fatigue data (i.e., stress amplitude and cycles to failure)
for a brass alloy.
(a) These fatigue data are plotted below.
300
Stress amplitude, MPa
9.33
200
100
5
6
7
8
Log cycles to failure
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10
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(b) A s indicated by one set of dashed lines on the plot, the fatigue strength at 5 × 105 cycles
[log (5 × 105 ) = 5.7] is about 250 MPa.
(c) A s noted by the other set of dashed lines, the fatigue life for 200 MPa is about 2 × 106 cycles
(i.e., the log of the lifetime is about 6.3).
9.34
We are asked to compute the maximum torsional stress amplitude possible at each of several fatigue lifetimes for the brass alloy, the fatigue behavior of which is given in Problem 9.33. For each
lifetime, first compute the number of cycles, and then read the corresponding fatigue strength
from the above plot.
(a) Fatigue lifetime = (1 yr)(365 days/yr)(24 h/day)(60 min/h)(1500 cycles/min) = 7.9 × 108 cycles. The stress amplitude corresponding to this lifetime is about 130 MPa.
(c) Fatigue lifetime = (24 h)(60 min/h)(1200 cycles/min) = 2.2 × 106 cycles. The stress amplitude
corresponding to this lifetime is about 195 MPa.
9.48
This problem asks that we determine the total elongation of a low carbon-nickel alloy that is exposed to a tensile stress of 40 MPa (5800 psi) at 538◦ C for 5000 h; the instantaneous and primary
creep elongations are 1.5 mm (0.06 in.).
From the 538◦ C line in Figure 9.43, the steady-state creep rate, ε̇s , is about 0.15% /1000 h
(or 1.5 × 10−4 % /h) at 40 MPa. The steady-state creep strain, εs , therefore, is just the product of
ε̇s and time as
εs = ε̇s × (time)
= (1.5 × 10−4 % /h)(5000 h) = 0.75% = 7.5 × 10−3
Strain and elongation are related as in E quation (7.2); solving for the steady-state elongation,
ls , leads to
ls = lo εs = (750 mm)(7.5 × 10−3 ) = 5.6 mm (0.23 in.)
Finally, the total elongation is just the sum of this ls and the total of both instantaneous and primary creep elongations [i.e., 1.5 mm (0.06 in.)]. Therefore, the total elongation is 7.1 mm (0.29 in.).
9.52*
The slope of the line from a log ε̇s versus log plot yields the value of n in E quation (9.33);
that is
n=
log ε̇s
log We are asked to determine the values of n for the creep data at the three temperatures in Figure 9.43. This is accomplished by taking ratios of the differences between two log ε̇s and log values. Thus for 427◦ C
n=
log ε̇s
log (10−1 ) − log (10−2 )
=
= 5.3
log log (85 MPa) − log (55 MPa)
n=
log ε̇s
log (1.0) − log (10−2 )
=
= 4.9
log log (59 MPa) − log (23 MPa)
and for 538◦ C
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9.55*
This problem gives ε̇s values at two different temperatures and 70 MPa (10,000 psi), and the stress
exponent n = 7.0, and asks that we determine the steady-state creep rate at a stress of 50 MPa
(7250 psi) and 1250 K.
Taking the natural logarithm of E quation (9.34) yields
ln ε̇s = ln K 2 + n ln −
Qc
RT
With the given data there are two unknowns in this equation—namely K2 and Q c . U sing the data
provided in the problem we can set up two independent equations as follows:
ln[1.0 × 10−5 (h) −1 ] = ln K 2 + (7.0) ln(70 MPa) −
Qc
(8.31 J/mol-K)(977 K)
ln[2.5 × 10−3 (h) −1 ] = ln K 2 + (7.0) ln(70 MPa) −
Qc
(8.31 J/mol-K)(1089 K)
Now, solving simultaneously for K2 and Q c leads to K2 = 2.55 × 105 (h) −1 and Q c = 436,000 J/mol.
Thus it is now possible to solve for ε̇s at 50 MPa and 1250 K using E quation (9.34) as
Qc
ε̇s = K 2 n exp −
RT
ε̇s = [2.55 × 10 (h)
5
−1
](50 MPa)
7.0
exp −
436000 J/mol
(8.31 J/mol-K)(1250 K)
= 0.118 (h) −1
9.D 1* This problem asks us to calculate the minimum Klc necessary to ensure that failure will not occur
for a flat plate given an expression from which Y(a/W) may be determined, the internal crack
length, 2a (20 mm), the plate width, W (90 mm), and the value of (375 MPa). First we must
compute the value of Y(a/W) using E quation (9.10), as follows:
Y(a/W) =
a
W
tan
a
W
1/2
()(10 mm)
90 mm
tan
=
()(10 mm)
90 mm
1/2
= 1.021
Now, using E quation (9.11) it is possible to determine Klc ; thus
√
K lc = Y(a/W) a
√
√
= (1.021)(375 MPa) ()(10 × 10−3 m) = 67.9 MPa m (62.3 ksi in.)
9.D 7* We are asked in this problem to estimate the maximum tensile stress that will yield a fatigue life
of 2.5 × 107 cycles, given values of ao , ac , m, A , and Y. Since Y is independent of crack length we
may utilize E quation (9.31) which, upon integration, takes the form
Nf =
1
m/2
A () m Y m
ac
a −m/2 da
ao
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A nd for m = 3.5
Nf =
1
1.75
A () 3.5 Y 3.5
ac
a −1.75 da
ao
1
1
1.33
− 0.75
=−
A 1.75 () 3.5 Y 3.5 a 0.75
ao
c
Now, solving for from this expression yields
=
=
1
1
1.33
−
N f A 1.75 Y 3.5 a 0.75
a 0.75
o
c
1/3.5
1
1.33
1
−
(2.5 × 107 )(2 × 10−14 )() 1.75 (1.4) 3.5 (1.5 × 10−4 ) 0.75
(4.5 × 10−3 ) 0.75
1/3.5
= 178 MPa
This 178 MPa will be the maximum tensile stress since we can show that the minimum stress
is a compressive one—when min is negative, is taken to be max . If we take max = 178
MPa, and since m is stipulated in the problem to have a value of 25 MPa, then from E quation (9.21)
min = 2m − max = 2(25 MPa) − 178 MPa = −128 MPa
Therefore min is negative and we are justified in taking max to be 178 MPa.
9.D 16* We are asked in this problem to calculate the stress levels at which the rupture lifetime will be
5 years and 20 years when an 18-8 Mo stainless steel component is subjected to a temperature of
500◦ C (773 K). It first becomes necessary, using the specified temperature and times, to calculate
the values of the Larson-Miller parameter at each temperature. The values of tr corresponding
to 5 and 20 years are 4.38 × 104 h and 1.75 × 105 h, respectively. H ence, for a lifetime of 5
years
T(20 + log t r ) = 773[20 + log (4.38 × 104 )] = 19.05 × 103
A nd for tr = 20 years
T(20 + log t r ) = 773[20 + log (1.75 × 105 )] = 19.51 × 103
U sing the curve shown in Figure 9.47, the stress values corresponding to the five- and twenty-year
lifetimes are approximately 260 MPa (37,500 psi) and 225 MPa (32,600 psi), respectively.
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CH A PTE R 10
PHA SE D IAGRA MS
10.5
This problem asks that we cite the phase or phases present for several alloys at specified temperatures.
(a) For an alloy composed of 90 wt% Z n-10 wt% Cu and at 400◦ C, from Figure 10.17, ε and ␩
phases are present, and
C ε = 87 wt% Z n-13 wt% Cu
C ␩ = 97 wt% Z n-3 wt% Cu
(c) For an alloy composed of 55 wt% A g-45 wt% Cu and at 900◦ C, from Figure 10.6, only the
liquid phase is present; its composition is 55 wt% A g-45 wt% Cu.
10.7
This problem asks that we determine the phase mass fractions for the alloys and temperatures in
Problem 10.5.
(a) For an alloy composed of 90 wt% Z n-10 wt% Cu and at 400◦ C, ε and ␩ phases are present,
and
C o = 90 wt% Z n
C ε = 87 wt% Z n
C ␩ = 97 wt% Z n
Therefore, using modified forms of E quation (10.2b) we get
Wε =
C␩ − Co
97 − 90
=
= 0.70
C␩ − Cε
97 − 87
W␩ =
Co − Cε
90 − 87
= 0.30
=
C␩ − Cε
97 − 87
(c) For an alloy composed of 55 wt% A g-45 wt% Cu and at 900◦ C, since only the liquid phase is
present, then WL = 1.0.
10.9
This problem asks that we determine the phase volume fractions for the alloys and temperatures
in Problem 10.5a, b, and c. This is accomplished by using the technique illustrated in E xample
Problem 10.3, and the results of Problem 10.7.
(a) This is a Cu-Z n alloy at 400◦ C, wherein
C ε = 87 wt% Z n-13 wt% Cu
C ␩ = 97 wt% Z n-3 wt% Cu
W ε = 0.70
W ␩ = 0.30
␳ Cu = 8.77 g/cm 3
␳ Z n = 6.83 g/cm 3
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U sing these data it is first necessary to compute the densities of the ε and ␩ phases using
E quation (5.10a). Thus
␳ε =
=
␳␩ =
=
100
C Z n(ε)
C Cu(ε)
+
␳Z n
␳ Cu
100
= 7.03 g/cm 3
87
13
+
6.83 g/cm 3
8.77 g/cm 3
100
C Cu(␩)
C Z n(␩)
+
␳Z n
␳ Cu
100
= 6.88 g/cm 3
97
3
+
6.83 g/cm 3
8.77 g/cm 3
Now we may determine the V ε and V ␩ values using E quation 10.6. Thus,
Vε =
Wε
␳ε
W␩
Wε
+
␳ε
␳␩
0.70
7.03 g/cm 3
=
= 0.70
0.70
0.30
+
7.03 g/cm 3
6.88 g/cm 3
W␩
␳␩
V␩ =
W␩
Wε
+
␳ε
␳␩
0.30
6.88 g/cm 3
= 0.30
=
0.70
0.30
+
7.03 g/cm 3
6.88 g/cm 3
10.12 (a) We are asked to determine how much sugar will dissolve in 1500 g of water at 90◦ C. From the
solubility limit curve in Figure 10.1, at 90◦ C the maximum concentration of sugar in the syrup is
about 77 wt% . It is now possible to calculate the mass of sugar using E quation (5.3) as
C sugar (wt% ) =
m sugar
× 100
m sugar + m water
77 wt% =
m sugar
× 100
m sugar + 1500 g
Solving for msugar yields msugar = 5022 g.
(b) A gain using this same plot, at 20◦ C the solubility limit (or the concentration of the saturated
solution) is about 64 wt% sugar.
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(c) The mass of sugar in this saturated solution at 20◦ C (m′sugar) may also be calculated using
E quation (5.3) as follows:
64 wt% =
m ′sugar
m ′sugar + 1500 g
× 100
which yields a value for m′sugar of 2667 g. Subtracting the latter from the former of these sugar
concentrations yields the amount of sugar that precipitated out of the solution upon cooling m′′sugar;
that is
m ′′sugar = m sugar − m ′sugar = 5022 g − 2667 g = 2355 g
10.21 U pon cooling a 50 wt% Pb-50 wt% Mg alloy from 700◦ C and utilizing Figure 10.18:
(a) The first solid phase forms at the temperature at which a vertical line at this composition
intersects the L-(␣ + L) phase boundary—i.e., about 550◦ C;
(b) The composition of this solid phase corresponds to the intersection with the ␣-(␣ + L)
phase boundary, of a tie line constructed across the ␣ + L phase region at 550◦ C—i.e., 22 wt%
Pb-78 wt% Mg;
(c) Complete solidification of the alloy occurs at the intersection of this same vertical line at
50 wt% Pb with the eutectic isotherm—i.e., about 465◦ C;
(d) The composition of the last liquid phase remaining prior to complete solidification corresponds
to the eutectic composition—i.e., about 66 wt% Pb-34 wt% Mg.
10.24 (a) We are given that the mass fractions of ␣ and liquid phases are both 0.5 for a 30 wt% Sn-70
wt% Pb alloy and asked to estimate the temperature of the alloy. U sing the appropriate phase
diagram, Figure 10.7, by trial and error with a ruler, a tie line within the ␣ + L phase region that
is divided in half for an alloy of this composition exists at about 230◦ C.
(b) We are now asked to determine the compositions of the two phases. This is accomplished
by noting the intersections of this tie line with both the solidus and liquidus lines. From these
intersections, C␣ = 15 wt% Sn, and CL = 42 wt% Sn.
10.28 This problem asks if it is possible to have a Cu-A g alloy of composition 50 wt% A g-50 wt% Cu that
consists of mass fractions W␣ = 0.60 and W␤ = 0.40. Such an alloy is not possible, based on the
following argument. U sing the appropriate phase diagram, Figure 10.6, and, using E quations (10.1)
and (10.2) let us determine W␣ and W␤ at just below the eutectic temperature and also at room
temperature. A t just below the eutectic, C␣ = 8.0 wt% A g and C␤ = 91.2 wt% A g; thus,
W␣ =
C␤ − Co
91.2 − 50
=
= 0.50
C␤ − C␣
91.2 − 8
W ␤ = 1.0 − W ␣ = 1.0 − 0.5 = 0.50
Furthermore, at room temperature, C␣ = 0 wt% A g and C␤ = 100 wt% A g; employment of E quations (10.1) and (10.2) yields
W␣ =
C␤ − Co
100 − 50
=
= 0.50
C␤ − C␣
100 − 0
A nd, W␤ = 0.50. Thus, the mass fractions of the ␣ and ␤ phases, upon cooling through the ␣ + ␤
phase region will remain approximately constant at about 0.5, and will never have values of
W␣ = 0.60 and W␤ = 0.40 as called for in the problem.
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10.35* This problem asks that we determine the composition of a Pb-Sn alloy at 180◦ C given that W␤′ =
0.57 and We = 0.43. Since there is a primary ␤ microconstituent present, then we know that the
alloy composition, Co , is between 61.9 and 97.8 wt% Sn (Figure 10.7). Furthermore, this figure
also indicates that C␤ = 97.8 wt% Sn and Ceutectic = 61.9 wt% Sn. A pplying the appropriate lever
rule expression for W␤′
W ␤′ =
C o − C eutectic
C o − 61.9
=
= 0.57
C ␤ − C eutectic
97.8 − 61.9
and solving for Co yields Co = 82.4 wt% Sn.
10.47* We are asked to specify the value of F for G ibbs phase rule at point B on the pressure-temperature
diagram for H 2 O. G ibbs phase rule in general form is
P+F =C+N
For this system, the number of components, C, is 1, whereas N, the number of noncompositional
variables, is 2—viz. temperature and pressure. Thus, the phase rule now becomes
P+F =1+2=3
Or
F =3−P
where P is the number of phases present at equilibrium.
A t point B on the figure, only a single (vapor) phase is present (i.e., P = 1), or
F =3−P =3−1=2
which means that both temperature and pressure are necessary to define the system.
10.54 This problem asks that we compute the carbon concentration of an iron-carbon alloy for which
the fraction of total ferrite is 0.94. A pplication of the lever rule [of the form of E quation (10.12)]
yields
W ␣ = 0.94 =
6.70 − C ′o
C Fe 3 C − C ′o
=
C Fe 3 C − C ␣
6.70 − 0.022
and solving for C′o
C ′o = 0.42 wt% C
10.59 This problem asks that we determine the carbon concentration in an iron-carbon alloy, given the
mass fractions of proeutectoid ferrite and pearlite. From E quation (10.20)
W p = 0.714 =
C ′o − 0.022
0.74
which yields C′o = 0.55 wt% C.
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10.64 This problem asks if it is possible to have an iron-carbon alloy for which W␣ = 0.846 and WFe 3 C′ =
0.049. In order to make this determination, it is necessary to set up lever rule expressions for these
two mass fractions in terms of the alloy composition, then to solve for the alloy composition of
each; if both alloy composition values are equal, then such an alloy is possible. The expression for
the mass fraction of total ferrite is
W␣ =
6.70 − C o
C Fe 3 C − C o
=
= 0.846
C Fe 3 C − C ␣
6.70 − 0.022
Solving for this Co yields Co = 1.05 wt% C. Now for WFe 3 C′ we utilize E quation (10.23) as
W Fe 3 C ′ =
C ′1 − 0.76
= 0.049
5.94
This expression leads to C′1 = 1.05 wt% C. A nd, since Co = C′1 , this alloy is possible.
10.70 This problem asks that we determine the approximate Brinell hardness of a 99.8 wt% Fe-0.2 wt%
C alloy. First, we compute the mass fractions of pearlite and proeutectoid ferrite using E quations
(10.20) and (10.21), as
C ′o − 0.022
0.20 − 0.022
=
= 0.24
0.74
0.74
0.76 − C ′o
0.76 − 0.20
=
=
= 0.76
0.74
0.74
Wp =
W ␣′
Now, we compute the Brinell hardness of the alloy as
H B alloy = H B ␣′ W ␣′ + H B p W p
= (80)(0.76) + (280)(0.24) = 128
10.73* We are asked to consider a steel alloy of composition 93.8 wt% Fe, 6.0 wt% Ni, and 0.2 wt% C.
(a) From Figure 10.36, the eutectoid temperature for 6 wt% Ni is approximately 650◦ C (1200◦ F).
(b) From Figure 10.37, the eutectoid composition is approximately 0.62 wt% C. Since the carbon
concentration in the alloy (0.2 wt% ) is less than the eutectoid, the proeutectoid phase is ferrite.
(c) A ssume that the ␣-(␣ + Fe 3 C) phase boundary is at a negligible carbon concentration. Modifying E quation (10.21) leads to
W ␣′ =
0.62 − C ′o
0.62 − 0.20
=
= 0.68
0.62 − 0
0.62
Likewise, using a modified E quation (10.20)
Wp =
C ′o − 0
0.20
=
= 0.32
0.62 − 0
0.62
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CH A PTE R 11
PHA SE TRA NSFORMATIONS
11.4
This problem gives us the value of y (0.40) at some time t (200 min), and also the value of n (2.5)
for the recrystallization of an alloy at some temperature, and then asks that we determine the
rate of recrystallization at this same temperature. It is first necessary to calculate the value of k in
E quation (11.1) as
ln(1 − y)
tn
ln(1 − 0.4)
=−
= 9.0 × 10−7
(200 min) 2.5
k=−
A t this point we want to compute t0.5 , the value of t for y = 0.5, also using E quation (11.1).
Thus
1/n
ln(1 − 0.5)
t 0.5 = −
k
1/2.5
ln(1 − 0.5)
= 226.3 min
= −
9.0 × 10−7
A nd, therefore, from E quation (11.2), the rate is just
rate =
11.7
1
1
= 4.42 × 10−3 (min) −1
=
t 0.5
226.3 min
This problem asks us to consider the percent recrystallized versus logarithm of time curves for
copper shown in Figure 11.2.
(a) The rates at the different temperatures are determined using E quation (11.2), which rates are
tabulated below:
Temperature ( ◦ C)
R ate (min) −1
135
119
113
102
88
43
0.105
4.4 × 10−2
2.9 × 10−2
1.25 × 10−2
4.2 × 10−3
3.8 × 10−5
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(b) These data are plotted below as ln rate versus the reciprocal of absolute temperature.
-4
Rate
-6
-8
ln
(1/min)
-2
-10
-12
0.0024
0.0026
0.0028
1/T
0.0030
0.0032
(1/K)
The activation energy, Q, is related to the slope of the line drawn through the data points
as
Q = −Slope(R )
where R is the gas constant. The slope of this line is −1.126 × 104 K, and thus
Q = −(−1.126 × 104 K)(8.31 J/mol-K)
= 93,600 J/mol
(c) A t room temperature (20◦ C), 1/T = 3.41 × 10−3 K −1 . E xtrapolation of the data in the plot to
this 1/T value gives
ln(rate) ∼
= −12.8
or
rate ∼
= e −12.8 = 2.76 × 10−6 (min) −1
But since
rate =
1
t 0.5
then
t 0.5 =
1 ∼
1
=
rate
2.76 × 10−6 (min) −1
∼
= 250 days
= 3.62 × 105 min ∼
11.15 Below is shown an isothermal transformation diagram for a eutectoid iron-carbon alloy, with a
time-temperature path that will produce (a) 100% coarse pearlite.
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11.18 Below is shown an isothermal transformation diagram for a 0.45 wt% C iron-carbon alloy, with a
time-temperature path that will produce (b) 50% fine pearlite and 50% bainite.
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11.20* Below is shown a continuous cooling transformation diagram for a 1.13 wt% C iron-carbon alloy,
with a continuous cooling path that will produce (a) fine pearlite and proeutectoid cementite.
11.34 This problem asks for estimates of R ockwell hardness values for specimens of an iron-carbon alloy
of eutectoid composition that have been subjected to some of the heat treatments described in
Problem 11.14.
(b) The microstructural product of this heat treatment is 100% spheroidite. A ccording to
Figure 11.22(a) the hardness of a 0.76 wt% C alloy with spheroidite is about 87 H R B.
(g) The microstructural product of this heat treatment is 100% fine pearlite. A ccording to
Figure 11.22(a), the hardness of a 0.76 wt% C alloy consisting of fine pearlite is about 27 H R C.
11.37 For this problem we are asked to describe isothermal heat treatments required to yield specimens
having several Brinell hardnesses.
(a) From Figure 11.22(a), in order for a 0.76 wt% C alloy to have a R ockwell hardness of 93 H R B,
the microstructure must be coarse pearlite. Thus, utilizing the isothermal transformation diagram
for this alloy, Figure 11.14, we must rapidly cool to a temperature at which coarse pearlite forms
(i.e., to about 675◦ C), allowing the specimen to isothermally and completely transform to coarse
pearlite. A t this temperature an isothermal heat treatment for at least 200 s is required.
11.D 1 This problem inquires as to the possibility of producing an iron-carbon alloy of eutectoid composition that has a minimum hardness of 90 H R B and a minimum ductility of 35% R A . If the alloy
is possible, then the continuous cooling heat treatment is to be stipulated.
A ccording to Figures 11.22(a) and (b), the following is a tabulation of R ockwell B hardnesses and percents reduction of area for fine and coarse pearlites and spheroidite for a 0.76 wt%
C alloy.
Microstructure
HRB
% RA
Fine pearlite
Coarse pearlite
Spheroidite
>100
93
88
22
29
68
Therefore, none of the microstructures meets both of these criteria. Both fine and coarse pearlites
are hard enough, but lack the required ductility. Spheroidite is sufficiently ductile, but does not
meet the hardness criterion.
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CH A PTE R 12
ELECTRICA L PROPERTIES
12.5
(a) In order to compute the resistance of this copper wire it is necessary to employ E quations (12.2)
and (12.4). Solving for the resistance in terms of the conductivity,
R=
l
␳l
=
A
␴A
From Table 12.1, the conductivity of copper is 6.0 × 107 (-m) −1 , and
R =
l
=
␴A
2m
[6.0 ×
107
(-m) −1 ](␲)
3 × 10−3 m
2
2
= 4.7 × 10−3 (b) If V = 0.05 V then, from E quation (12.1)
I=
V
0.05 V
=
= 10.6 A
R
4.7 × 10−3 (c) The current density is just
J=
I
=
A
10.6 A
I
6
2
2 = 1.5 × 10 A /m
2 = d
3 × 10−3 m
␲
␲
2
2
(d) The electric field is just
E=
V
0.05 V
=
= 2.5 × 10−2 V/m
l
2m
12.13 (a) The number of free electrons per cubic meter for copper at room temperature may be computed
using E quation (12.8) as
n=
=
␴
|e|␮e
6.0 × 107 (-m) −1
(1.602 × 10−19 C)(0.0030 m 2 /V-s)
= 1.25 × 1029 m −3
(b) In order to calculate the number of free electrons per copper atom, we must first determine
the number of copper atoms per cubic meter, N Cu . From E quation (5.2)
N Cu =
NA ␳ ′
A Cu
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Note: in the above expression, density is represented by ␳ ′ in order to avoid confusion with
resistivity which is designated by ␳ . Thus
N Cu =
(6.023 × 1023 atoms/mol)(8.94 g/cm 3 )(106 cm 3 /m 3 )
63.55 g/mol
= 8.47 × 1028 m −3
The number of free electrons per copper atom is just
1.25 × 1029 m −3
n
=
= 1.48
N
8.47 × 1028 m −3
12.18 This problem asks for us to compute the room-temperature conductivity of a two-phase Cu-Sn
alloy. It is first necessary for us to determine the volume fractions of the ␣ and ε phases, after which
the resistivity (and subsequently, the conductivity) may be calculated using E quation (12.12).
Weight fractions of the two phases are first calculated using the phase diagram information provided in the problem.
We might represent the phase diagram near room temperature as shown below.
A pplying the lever rule to this situation
W␣ =
Cε − Co
37 − 8
= 0.784
=
Cε − C␣
37 − 0
Wε =
8−0
Co − C␣
=
= 0.216
Cε − C␣
37 − 0
We must now convert these mass fractions into volume fractions using the phase densities given
in the problem. (Note: in the following expressions, density is represented by ␳ ′ in order to avoid
confusion with resistivity which is designated by ␳ .) U tilization of E quations (10.6a) and (10.6b)
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leads to
V␣ =
W␣
␳ ␣′
W␣
Wε
+ ′
′
␳␣
␳ε
0.784
8.94 g/cm 3
=
0.216
0.784
+
3
8.94 g/cm
8.25 g/cm 3
= 0.770
Vε =
Wε
␳ ε′
W␣
Wε
+ ′
′
␳␣
␳ε
0.216
8.25 g/cm 3
=
0.784
0.216
+
3
8.94 g/cm
8.25 g/cm 3
= 0.230
Now, using E quation (12.12)
␳ = ␳␣V␣ + ␳ε Vε
= (1.88 × 10−8 -m)(0.770) + (5.32 × 10−7 -m)(0.230)
= 1.368 × 10−7 -m
Finally, for the conductivity
␴=
1
1
=
= 7.31 × 106 (-m) −1
␳
1.368 × 10−7 -m
12.30 (a) In this problem, for a Si specimen, we are given p and ␴, while ␮h and ␮e are included in
Table 12.2. In order to solve for n we must use E quation (12.13), which, after rearrangement, leads
to
n=
=
␴ − p|e|␮h
|e|␮e
103 (-m) −1 − (1.0 × 1023 m −3 )(1.602 × 10−19 C)(0.05 m 2 /V-s)
(1.602 × 10−19 C)(0.14 m 2 /V-s)
= 8.9 × 1021 m −3
(b) This material is p-type extrinsic since p (1.0 × 1023 m −3 ) is greater than n (8.9 × 1021 m −3 ).
12.38 For this problem, we are given conductivity values at two different temperatures for an intrinsic semiconductor, and are then asked to determine its band gap energy. It is possible, using
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E quation (12.18), to set up two independent equations with C and E g as unknowns. A t 20◦ C
ln ␴ = C −
ln[1.0 (-m) −1 ] = C −
Eg
2kT
Eg
(2)(8.62 × 10−5 eV/atom-K)(293 K)
or
C = 19.80E g
A t 373 K
ln[500 (-m) −1 ] = C −
(2)(8.62 ×
10−5
Eg
eV/atom-K)(373 K)
6.21 = C − 15.55E g
From these two expressions
E g = 1.46 eV
12.45* In this problem we are asked to determine the magnetic field required to produce a H all voltage of
−1.0 × 10−7 V, given that ␴ = 1.5 × 107 (-m) −1 , ␮e = 0.0020 m 2 /V-s, Ix = 45 A , and d = 35 mm.
Combining E quations (12.21) and (12.23b), and after solving for B z , we get
Bz =
=
|V H |␴d
I x ␮e
(|−1.0 × 10−7 V|)[1.5 × 107 (-m) −1 ](35 × 10−3 m)
(45 A )(0.0020 m 2 /V-s)
= 0.58 tesla
12.52* We want to compute the plate spacing of a parallel-plate capacitor as the dielectric constant is
increased from 2.5 to 4.0, while maintaining the capacitance constant. Combining E quations (12.29)
and (12.30) yields
C=
εr εo A
l
Now, let us use the subscripts 1 and 2 to denote the initial and final states, respectively. Since
C1 = C2 , then
εr1 εo A
εr2 εo A
=
l1
l2
A nd, solving for l2
l2 =
(4.0)(1 mm)
εr2 l1
= 1.6 mm
=
εr1
2.5
12.58* (a) We want to solve for the voltage when Q = 3.5 × 10−11 C, A = 160 mm 2 , l = 3.5 mm, and
εr = 5.0. Combining E quations (12.27), (12.29), and (12.30) yields
Q
A
= εr εo
V
l
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A nd, solving for V
V=
=
Ql
εr εo A
(3.5 × 10−11 C)(3.5 × 10−3 m)
(5.0)(8.85 × 10−12 F/m)(160 mm 2 )(1 m 2 /106 mm 2 )
= 17.3 V
(b) For this same capacitor, if a vacuum is used
V=
=
Ql
εo A
(3.5 × 10−11 C)(3.5 × 10−3 m)
(8.85 × 10−12 F/m)(160 × 10−6 m 2 )
= 86.5 V
(e) The polarization is determined using E quations (12.35) and (12.6) as
P = εo (εr − 1)
=
V
l
(8.85 × 10−12 F/m)(5.0 − 1)(17.3 V)
3.5 × 10−3 m
= 1.75 × 10−7 C/m 2
12.D 2 This problem asks that we determine the electrical conductivity of an 80 wt% Cu-20 wt% Z n alloy
at −150◦ C using information contained in Figures 12.8 and 12.35. In order to solve this problem it
is necessary to employ E quation (12.9) which is of the form
␳ total = ␳ t + ␳ i
since it is assumed that the alloy is undeformed. Let us first determine the value of ␳ i at room
temperature (25◦ C), a value which will be independent of temperature. From Figure (12.8), at 25◦ C
and for pure Cu, ␳ t (25) = 1.75 × 10−8 -m. Now, since it is assumed that the curve in Figure 12.35
was generated also at room temperature, we may take ␳ as ␳ total (25) at 80 wt% Cu-20 wt% Z n
which has a value of 5.3 × 10−8 -m. Thus
␳ i = ␳ total (25) − ␳ t (25)
= 5.3 × 10−8 -m − 1.75 × 10−8 -m = 3.55 × 10−8 -m
Finally, we may determine the resistivity at −150◦ C, ␳ total (−150), by taking the resistivity of pure
Cu at −150◦ C from Figure 12.8, which gives us ␳ t (−150) = 0.55 × 10−8 -m. Therefore
␳ total (−150) = ␳ i + ␳ t (−150)
= 3.55 × 10−8 -m + 0.55 × 10−8 -m = 4.10 × 10−8 -m
A nd, using E quation (12.4) the conductivity is calculated as
␴=
1
1
=
= 2.44 × 107 (-m) −1
␳
4.10 × 10−8 -m
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CH A PTE R 13
TYPES A ND A PPLICATIONS OF MATERIA LS
13.5
We are asked to compute the volume percent graphite in a 3.5 wt% C cast iron. It first becomes
necessary to compute mass fractions using the lever rule. From the iron-carbon phase diagram
(Figure 13.2), the tie-line in the ␣ and graphite phase field extends from essentially 0 wt% C to
100 wt% C. Thus, for a 3.5 wt% C cast iron
W␣ =
WG r =
100 − 3.5
CG r − Co
=
= 0.965
CG r − C␣
100 − 0
3.5 − 0
Co − C␣
=
= 0.035
CG r − C␣
100 − 0
Conversion from weight fraction to volume fraction of graphite is possible using
E quation (10.6a) as
VG r
WG r
␳G r
=
WG r
W␣
+
␳␣
␳G r
0.035
2.3 g/cm 3
=
0.965
0.035
+
7.9 g/cm 3
2.3 g/cm 3
= 0.111 or 11.1 vol%
13.21* In this problem we are asked to find the maximum temperatures to which magnesia-alumina
refractories may be heated before a liquid phase will appear.
(a) For a spinel-bonded alumina material of composition 95 wt% A l2 O 3 -5 wt% MgO we must
use Figure 10.22. A ccording to this phase diagram, the maximum temperature without a liquid
phase corresponds to the temperature of the eutectic isotherm on the A l2 O 3 -rich side of the phase
diagram, which is approximately 2000◦ C (3630◦ F).
13.23* This problem calls for us to compute the mass fractions of liquid for four refractory materials at
1600◦ C. In order to solve this problem it is necessary that we use the SiO 2 -A l2 O 3 phase diagram
(Figure 10.24), in conjunction with tie-lines and the lever rule at 1600◦ C.
(a) For Co = 6 wt% A l2 O 3 the mass fraction of liquid WL is just
WL =
=
C o − C SiO 2
C L − C SiO 2
6−0
= 0.86
7−0
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CH A PTE R 14
SYNTHESIS, FA BRICATION, A ND PROCESSING OF MATERIA LS
14.19 (a) This part of the problem calls for us to construct a radial hardness profile for a 50 mm (2 in.)
diameter cylindrical specimen of an 8640 steel that has been quenched in moderately agitated oil.
In the manner of E xample Problem 14.1, the equivalent distances and hardnesses tabulated below
were determined from Figures 14.8 and 14.11.
R adial
Position
E quivalent
D istance, mm (in.)
HRC
H ardness
Surface
3/4 R
Midradius
Center
7 (5/16)
11 (7/16)
14 (9/16)
16 (10/16)
54
50
45
44
The resulting profile is plotted below.
14.26 (a) Below is shown the logarithm viscosity versus reciprocal of temperature plot for the borosilicate
glass, using the data in Figure 14.16.
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(b) Solving for the activation energy, Q vis , from the equation given in the problem, we get
Q vis = RT ln ␩ + RT ln A
The activation energy, Q vis , may be computed from this plot according to


 ln ␩ 

Q vis = R 
 1 
T
where R is the gas constant, and ln ␩/(1/T) is the slope of the line that has been constructed.
The value of this slope is 4.36 × 104 . Therefore,
Q vis = (8.31 J/mol-K)(4.36 × 104 )
= 362,000 J/mol
14.43 (a) This problem asks that we determine how much adipic acid must be added to 50.0 kg of
ethylene glycol to produce a linear chain structure of polyester according to E quation 14.5. Since
the chemical formulas are provided in this equation we may calculate the molecular weights of
each of these materials as follows:
A (adipic) = 6(A C ) + 10(A H ) + 4(A O )
= 6(12.01 g/mol) + 10(1.008 g/mol) + 4(16.00 g/mol) = 146.14 g/mol
A (glycol) = 2(A C ) + 6(A H ) + 2(A O )
= 2(12.01 g/mol) + 6(1.008 g/mol) + 2(16.00 g/mol) = 62.07 g/mol
50000 g
The 50.0 kg mass of ethylene glycol equals 50,000 g or 62.07
g/mol = 805.5 mol. A ccording to E quation
(14.5), each mole of adipic acid used requires one mole of ethylene glycol, which is equivalent to
(805.5 mol)(146.14 g/mol) = 1.177 × 105 g = 117.7 kg.
(b) Now we are asked for the mass of the resulting polyester. Inasmuch as one mole of water is
given off for every mer unit produced, this corresponds to 805.5 moles or (805.5 mol)(18.02 g/mol) =
14,500 g or 14.5 kg since the molecular weight of water is 18.02 g/mol. The mass of polyester is just
the sum of the masses of the two reactant materials (as computed in part a) minus the mass of
water released, or
mass(polyester) = 50.0 kg + 117.7 kg − 14.5 kg = 153.2 kg
14.D 1 A one-inch diameter steel specimen is to be quenched in moderately agitated oil. We are to decide
which of five different steels will have surface and center hardnesses of at least 55 and 50 H R C,
respectively.
In moderately agitated oil, the equivalent distances from the quenched end for a one-inch
diameter bar for surface and center positions are 3 mm (1/8 in.) and 8 mm (11/32 in.), respectively
[Figure 14.11(b)]. The hardnesses at these two positions for the alloys cited (as determined using
Figure 14.8) are given below.
A lloy
Surface
H ardness (H R C)
1040
5140
4340
4140
8640
50
55
57
56
56
Center
H ardness (H R C)
30
47
57
54
52.5
Thus, alloys 4340, 4140, and 8640 will satisfy the criteria for both surface and center hardnesses.
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14.D 5 We are asked to determine the maximum diameter possible for a cylindrical piece of 4140 steel
that is to be quenched in moderately agitated oil such that the microstructure will consist of
at least 50% martensite throughout the entire piece. From Figure 14.8, the equivalent distance
from the quenched end of a 4140 steel to give 50% martensite (or a 42.5 H R C hardness) is
26 mm (1–1/16 in.). Thus, the quenching rate at the center of the specimen should correspond
to this equivalent distance. U sing Figure 14.11(b), the center specimen curve takes on a value of
26 mm (1–1/16 in.) equivalent distance at a diameter of about 75 mm (3 in.).
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CH A PTE R 15
COMPOSITES
15.4
This problem asks for the maximum and minimum thermal conductivity values for a TiC-Co cermet.
U sing a modified form of E quation (15.1) the maximum thermal conductivity kc (u) is calculated as
k c (u) = k m V m + k p V p = k Co V Co + k TiC V TiC
= (69 W/m-K)(0.15) + (27 W/m-K)(0.85) = 33.3 W/m-K
The minimum thermal conductivity kc (l) will be
k c (l) =
=
k Co k TiC
V Co k TiC + V TiC k Co
(69 W/m-K)(27 W/m-K)
(0.15)(27 W/m-K) + (0.85)(69 W/m-K)
= 29.7 W/m-K
15.12 This problem asks for us to determine if it is possible to produce a continuous and oriented aramid
fiber-epoxy matrix composite having longitudinal and transverse moduli of elasticity of 57.1 G Pa
and 4.12 G Pa, respectively, given that the modulus of elasticity for the epoxy is 2.4 G Pa. A lso, from
Table 15.4 the value of E for aramid fibers is 131 G Pa. The approach to solving this problem is to
calculate two values of V f using the data and E quations (15.10b) and (15.16); if they are the same
then this composite is possible.
For the longitudinal modulus E cl ,
E cl = E m [1 − V fl ] + E f V fl
57.1 G Pa = (2.4 G Pa)[1 − V fl ] + (131 G Pa)V fl
Solving this expression for V fl yields V fl = 0.425.
Now, repeating this procedure for the transverse modulus E ct
E ct =
4.12 G Pa =
EmEf
[1 − V ft ]E f + V ft E m
(2.4 G Pa)(131 G Pa)
[1 − V ft ](131 G Pa) + V ft (2.4 G Pa)
Solving this expression for V ft leads to V ft = 0.425. Thus, since V fl and V ft are equal, the proposed
composite is possible.
15.17 The problem stipulates that the cross-sectional area of a composite, A c , is 320 mm 2 (0.50 in.2 ), and
the longitudinal load, Fc , is 44,500 N (10,000 lb f ) for the composite described in Problem 15.11.
(a) First, we are asked to calculate the Ff /Fm ratio. A ccording to E quation (15.11)
Ff
E fVf
(131 G Pa)(0.30)
=
=
= 23.4
Fm
E m Vm
(2.4 G Pa)(0.70)
O r, Ff = 23.4Fm
(b) Now, the actual loads carried by both phases are called for. Since
F f + F m = F c = 44,500 N
23.4F m + F m = 44,500 N
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which leads to
F m = 1824 N (410 lb f )
F f = 44,500 N − 1824 N = 42,676 N (9590 lb f )
(c) To compute the stress on each of the phases, it is first necessary to know the cross-sectional
areas of both fiber and matrix. These are determined as
A f = V f A c = (0.30)(320 mm 2 ) = 96 mm 2 (0.15 in.2 )
A m = V m A c = (0.70)(320 mm 2 ) = 224 mm 2 (0.35 in.2 )
Now, for the stresses,
f =
Ff
42676 N
= 445 MPa (63,930 psi)
=
Af
(96 mm 2 )
m =
1824 N
Fm
= 8.14 MPa (1170 psi)
=
Am
(224 mm 2 )
(d) The strain on the composite is the same as the strain on each of the matrix and fiber phases, as
εm =
εf =
m
8.14 MPa
=
= 3.39 × 10−3
Em
2.4 × 103 MPa
445 MPa
f
= 3.39 × 10−3
=
Ef
131 × 103 MPa
15.21 In this problem, for an aligned glass fiber-epoxy matrix composite, we are asked to compute the longitudinal tensile strength given the following: the average fiber diameter (0.010 mm), the average
fiber length (2.5 mm), the volume fraction of fibers (0.40), the fiber fracture strength (3500 MPa),
the fiber-matrix bond strength (75 MPa), and the matrix stress at composite failure (8.0 MPa). It
is first necessary to compute the value of the critical fiber length using E quation (15.3). If the fiber
length is much greater than lc , then we may determine cl∗ using E quation (15.17), otherwise, use
of either E quation (15.18) or (15.19) is necessary. Thus,
lc =
f∗ d
(3500 MPa)(0.010 mm)
= 0.233 mm (0.0093 in.)
=
2␶c
2(75 MPa)
Inasmuch as l > lc (2.5 mm > 0.233 mm), but l is not much greater than lc , then use of E quation (15.18) is necessary. Therefore,
∗
␴cd
lc
+ ␴m′ (1 − V f )
=
1−
2l
0.233 mm
+ (8.0 MPa)(1 − 0.40)
= (3500 MPa)(0.40) 1 −
(2)(2.5 mm)
␴f∗ V f
= 1340 MPa (194,400 psi)
15.D 1 In order to solve this problem, we want to make longitudinal elastic modulus and tensile strength
computations assuming 50 vol% fibers for all three fiber materials, in order to see which meet
the stipulated criteria [i.e., a minimum elastic modulus of 50 G Pa (7.3 ×106 psi), and a minimum
tensile strength of 1300 MPa (189,000 psi)]. Thus, it becomes necessary to use E quations (15.10b)
and (15.17) with V m = 0.5 and V f = 0.5, E m = 3.1 G Pa, and ␴m∗ = 75 MPa.
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For glass, E f = 72.5 G Pa and f∗ = 3450 MPa. Therefore,
E cl = E m (1 − V f ) + E f V f
= (3.1 G Pa)(1 − 0.5) + (72.5 G Pa)(0.5) = 37.8 G Pa (5.48 × 106 psi)
Since this is less than the specified minimum, glass is not an acceptable candidate.
For carbon (PA N standard-modulus), E f = 230 G Pa and f∗ = 4000 MPa (the average of
the range of values in Table B.4), thus
E cl = (3.1 G Pa)(0.5) + (230 G Pa)(0.5) = 116.6 G Pa (16.9 × 106 psi)
which is greater than the specified minimum. In addition, from E quation (15.17)
cl∗ = m′ (1 − V f ) + f∗ V f
= (30 MPa)(0.5) + (4000 MPa)(0.5) = 2015 MPa (292,200 psi)
which is also greater than the minimum. Thus, carbon (PA N standard-modulus) is a candidate.
For aramid, E f = 131 G Pa and f∗ = 3850 MPa (the average of the range of values in
Table B.4), thus
E cl = (3.1 G Pa)(0.5) + (131 G Pa)(0.5) = 67.1 G Pa (9.73 × 106 psi)
which value is greater than the minimum. A lso, from E quation (15.17)
cl∗ = m′ (1 − V f ) + f∗ V f
= (50 MPa)(0.5) + (3850 MPa)(0.5) = 1950 MPa (283,600 psi)
which is also greater than the minimum strength value. Therefore, of the three fiber materials, both
the carbon (PA N standard-modulus) and the aramid meet both minimum criteria.
15.D 3 This problem asks us to determine whether or not it is possible to produce a continuous and
oriented glass fiber-reinforced polyester having a tensile strength of at least 1400 MPa in the longitudinal direction, and a maximum specific gravity of 1.65. We will first calculate the minimum
volume fraction of fibers to give the stipulated tensile strength, and then the maximum volume
fraction of fibers possible to yield the maximum permissible specific gravity; if there is an overlap
of these two fiber volume fractions then such a composite is possible.
With regard to tensile strength, from E quation (15.17)
cl∗ = m′ (1 − V f ) + f∗ V f
1400 MPa = (15 MPa)(1 − V f ) + (3500 MPa)(V f )
Solving for V f yields V f = 0.397. Therefore, V f > 0.397 to give the minimum desired tensile
strength.
Now, upon consideration of the specific gravity, ␳ , we employ the following relationship:
␳ c = ␳ m (1 − V f ) + ␳ f V f
1.65 = 1.35(1 − V f ) + 2.50(V f )
A nd, solving for V f from this expression gives V f = 0.261. Therefore, it is necessary for V f < 0.261
in order to have a composite specific gravity less than 1.65.
H ence, such a composite is not possible since there is no overlap of the fiber volume
fractions as computed using the two stipulated criteria.
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CH A PTE R 16
CORROSION A ND D EGRA DATION OF MATERIA LS
16.5 (a) We are asked to compute the voltage of a nonstandard Cd-Fe electrochemical cell. Since iron is
lower in the emf series (Table 16.1), we will begin by assuming that iron is oxidized and cadmium
is reduced, as
Fe + Cd 2+ −→ Fe 2+ + Cd
and
V = (V ◦Cd − V ◦Fe ) −
[Fe 2+ ]
0.0592
log
2
[Cd 2+ ]
= [−0.403 V − (−0.440 V)] −
0.40
0.0592
log
2
2 × 10−3
= −0.031 V
(b) Since the V is negative, the spontaneous cell direction is just the reverse of that above, or
Fe 2+ + Cd −→ Fe + Cd 2+
16.13 This problem calls for us to compute the time of submersion of a steel piece. In order to solve this
problem, we must first rearrange E quation (16.23), as
t=
KW
␳ A (CPR )
Thus,
t=
(534)(2.6 × 106 mg)
(7.9 g/cm 3 )(10 in.2 )(200 mpy)
= 8.8 × 104 h = 10 yr
16.20 (a) This portion of the problem asks that we compute the rate of oxidation for Pb given that both
the oxidation and reduction reactions are controlled by activation polarization, and also given the
polarization data for both lead oxidation and hydrogen reduction. The first thing necessary is to
establish relationships of the form of E quation (16.25) for the potentials of both oxidation and
reduction reactions. Next we will set these expressions equal to one another, and then solve for
the value of i which is really the corrosion current density, ic . Finally, the corrosion rate may be
calculated using E quation (16.24). The two potential expressions are as follows:
For hydrogen reduction
V H = V (H + /H 2 ) + ␤H log
i
io H
A nd for Pb oxidation
V Pb = V
(Pb/Pb 2+ )
i
+ ␤Pb log
io Pb
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Setting V H = V Pb and solving for log i (log ic ) leads to
1
log ic =
[V (H + /H 2 ) − V (Pb/Pb 2+ ) − ␤H log io H + ␤Pb log io Pb ]
␤Pb − ␤H
1
[0 − (−0.126) − (−0.10){log(1.0 × 10−8 )} + (0.12){log(2 × 10−9 )}]
=
0.12 − (−0.10)
= −7.809
Or
ic = 10−7.809 = 1.55 × 10−8 A /cm 2
A nd from E quation (16.24)
r=
=
ic
nF
1.55 × 10−8 C/s-cm 2
= 8.03 × 10−14 mol/cm 2 -s
(2)(96500 C/mol)
16.34 For this problem we are given, for three metals, their densities, chemical formulas, and oxide
densities, and are asked to compute the Pilling-Bedworth ratios, and then specify whether or not
the oxide scales that form will be protective. The general form of the equation used to calculate
this ratio is E quation (16.33) [or E quation (16.32)]. For tin, oxidation occurs by the reaction
Sn + O 2 −→ SnO 2
and therefore
P-B ratio =
=
A SnO 2 ␳ Sn
A Sn ␳ SnO 2
(150.69 g/mol)(7.30 g/cm 3 )
= 1.33
(118.69 g/mol)(6.95 g/cm 3 )
H ence, the film would most likely be protective since the ratio lies between one and two.
16.36 For this problem we are given weight gain-time data for the oxidation of Cu at an elevated temperature.
(a) We are first asked to determine whether the oxidation kinetics obey a parabolic, linear, or
logarithmic rate expression, expressions which are described by E quations (16.34), (16.35), and
(16.36), respectively. O ne way to make this determination is by trial and error. Let us assume that
the parabolic relationship is valid; that is, from E quation (16.34)
W2 = K1t + K2
which means that we may establish three simultaneous equations using the three sets of given W
and t values, then using two combinations of two pairs of equations, solve for K1 and K2 ; if K1 and
K2 have the same values for both solutions, then the kinetics are parabolic. If the values are not
identical then the other kinetic relationships need to be explored. Thus, the three equations are
(0.316) 2 = 0.100 = 15K 1 + K 2
(0.524) 2 = 0.275 = 50K 1 + K 2
(0.725) 2 = 0.526 = 100K 1 + K 2
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From the first two equations K1 = 5 × 10−3 and K2 = 0.025; these same two values are obtained
using the last two equations. H ence, the oxidation rate law is parabolic.
(b) Since a parabolic relationship is valid, this portion of the problem calls for us to determine W
after a total time of 450 min. A gain, using E quation (16.34) and the values of K1 and K2
W2 = K1t + K2
Or W =
√
= (0.005)(450 min) + 0.025 = 2.28
2.28 = 1.51 mg/cm 2 .
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CH A PTE R 17
THERMA L PROPERTIES
17.4
(a) For aluminum, Cv at 50 K may be approximated by E quation (17.2), since this temperature
is significantly below the D ebye temperature. The value of Cv at 30 K is given, and thus, we may
compute the constant A as
A=
Cv
0.81 J/mol-K
=
= 3 × 10−5 J/mol-K 4
3
T
(30 K) 3
Therefore, at 50 K
C v = AT 3 = (3 × 10−5 J/mol-K 4 )(50 K) 3 = 3.75 J/mol-K
and
cv = (3.75 J/mol-K)(1 mol/26.98 g)(1000 g/kg) = 139 J/kg-K
(b) Since 425 K is above the D ebye temperature, a good approximation for Cv is
C v = 3R
= (3)(8.31 J/mol-K) = 24.9 J/mol-K
A nd, converting this to specific heat
cv = (24.9 J/mol-K)(1 mol/26.98 g)(1000 g/kg) = 925 J/kg-K
17.14 This problem asks for us to determine the temperature to which a cylindrical rod of tungsten
10.000 mm in diameter must be heated in order for it to just fit into a 9.988 mm diameter circular
hole in a plate of 316 stainless steel, assuming that the initial temperature is 25◦ C. This requires
the use of E quation (17.3a), which is applied to the diameters of the rod and hole. That is
df − do
= ␣l (T f − T o )
do
Solving this expression for df yields
d f = d o [1 + ␣l (T f − T o )]
Now all we need do is to establish expressions for df (316 stainless) and df (W), set them equal to
one another, and solve for Tf . A ccording to Table 17.1, ␣l (316 stainless) = 16.0 × 10−6 ( ◦ C) −1 and
␣l (W) = 4.5 × 10−6 ( ◦ C) −1 . Thus
d f (316 stainless) = d f (W)
(9.988 mm)[1 + {16.0 × 10−6 ( ◦ C) −1 }(T f − 25◦ C)]
= (10.000 mm)[1 + {4.5 × 10−6 ( ◦ C) −1 }(T f − 25◦ C)]
Now solving for Tf gives Tf = 129.5◦ C.
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17.24 This problem asks that we treat a porous material as a composite wherein one of the phases is
a pore phase, and that we estimate upper and lower limits for the room-temperature thermal
conductivity of a magnesium oxide material having a 0.30 volume fraction of pores. The upper
limit of k (kupper) may be determined using E quation (15.1) with thermal conductivity substituted
for the elastic modulus, E. From Table 17.1, the value of k for MgO is 37.7 W/m-K, while for still
air in the pore phase, k = 0.02 W/m-K. Thus
k upper = V p k air + V MgO k MgO
= (0.30)(0.02 W/m-K) + (0.70)(37.7 W/m-K) = 26.4 W/m-K
For the lower limit we employ a modification of E quation (15.2) as
k lower =
=
k air k MgO
V p k MgO + V MgO k air
(0.02 W/m-K)(37.7 W/m-K)
= 0.067 W/m-K
(0.30)(37.7 W/m-K) + (0.70)(0.02 W/m-K)
17.29 We want to heat the copper wire in order to reduce the stress level from 70 MPa to 35 MPa; in doing
so, we reduce the stress in the wire by 70 MPa − 35 MPa = 35 MPa, which will be a compressive
stress (i.e., ␴ = −35 MPa). Taking a value for E of 110 G Pa (Table 7.1) and solving for Tf from
E quation (17.8)
Tf = To −
␴
E ␣1
= 20◦ C −
−35 MPa
(110 × 103 MPa)[17 × 10−6 ( ◦ C) −1 ]
= 20◦ C + 19◦ C = 39◦ C (101◦ F)
17.D 1 This problem stipulates that 1025 steel railroad tracks are laid at a temperature of 10°C. We are
asked to determine the hottest possible temperature that can be tolerated without the introduction
of thermal stresses if the rails are 11.9 m long, and for a joint space of 4.6 mm. For these railroad
tracks, each end is allowed to expand one-half of the joint space distance, or the track may expand
a total of this distance (4.6 mm). E quation (17.3a) is used to solve for Tf , where ␣l for the 1025
steel is found in Table 17.1. Thus,
Tf =
=
l
+ To
␣l lo
4.6 × 10−3 m
+ 10◦ C
[12.0 × 10−6 ( ◦ C) −1 ] (11.9 m)
= 32.2◦ C + 10◦ C = 42.2◦ C (108◦ F)
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CH A PTE R 18
MAGNETIC PROPERTIES
18.1 This problem concerns a coil of wire 0.20 m long that has 200 turns and carries 10 A .
(a) We may calculate the magnetic field strength generated by this coil using E quation (18.1) as
NI
l
(200 turns)(10 A )
= 10,000 A -turns/m
=
0.2 m
H =
(b) In a vacuum, the flux density is determined from E quation (18.3). Thus,
B o = ␮o H
= (1.257 × 10−6 H /m)(10,000 A -turns/m) = 1.257 × 10−2 tesla
(c) When a bar of titanium is positioned within the coil, we must use an expression that is a
combination of E quations (18.5) and (18.6) in order to compute the flux density given the magnetic
susceptibility. Inasmuch as ␹ m = 1.81 × 10−4 (Table 18.2), then
B = ␮o H + ␮o M = ␮o H + ␮o ␹ m H = ␮o H (1 + ␹ m )
= (1.257 × 10−6 H /m)(10,000 A -turns/m)(1 + 1.81 × 10−4 )
∼
= 1.257 × 10−2 tesla
which is essentially the same result as part (b). This is to say that the influence of the titanium bar
within the coil makes an imperceptible difference in the magnitude of the B field.
(d) The magnetization is computed from E quation (18.6):
M = ␹ m H = (1.81 × 10−4 )(10,000 A -turns/m) = 1.81 A /m
18.4 For this problem, we want to convert the volume susceptibility of silver (i.e., 2.38 × 10−5 ) into other
systems of units.
For the mass susceptibility
␹ m (kg) =
=
␹m
␳ (kg/m 3 )
−2.38 × 10−5
= −2.27 × 10−9
10.49 × 103 kg/m 3
For the atomic susceptibility
␹ m (a) = ␹ m (kg) × [atomic weight (in kg)]
= (−2.27 × 10−9 )(0.10787 kg/mol) = −2.45 × 10−10
18.6 This problem stipulates that the magnetic flux density within a bar of some material is 0.435 tesla
at an H field of 3.44 × 105 A /m.
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(a) We are first of all asked to compute the magnetic permeability of this material. This is possible
using E quation (18.2) as
␮=
B
0.435 tesla
=
= 1.2645 × 10−6 H /m
H
3.44 × 105 A /m
(b) The magnetic susceptibility is calculated as
␹m =
1.2645 × 10−6 H /m
␮
−1=
−1
␮o
1.257 × 10−6 H /m
= 6 × 10−3
18.27 (a) The B-H data provided in the problem are plotted below.
1.6
B (tesla)
1.2
0.8
0.4
0.0
0
200
400
600
800
1000
1200
H (A/m)
(b) This portion of the problem asks for us to determine values of the initial permeability and initial
relative permeability. The first four data points are plotted below.
0.3
B (tesla)
0.2
µi
0.1
0.0
0
10
20
30
40
H (A/m)
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The slope of the initial portion of the curve is ␮i (as shown), is
␮i =
B
(0.15 − 0) tesla
=
= 3.0 × 10−3 H /m
H
(50 − 0) A /m
A lso, the initial relative permeability [E quation (18.4)] is just
␮ri =
3.0 × 10−3 H /m
␮i
=
= 2400
␮o
1.257 × 10−6 H /m
(c) The maximum permeability is the tangent to the B-H curve having the greatest slope; it is drawn
on the plot below, and designated as ␮(max).
1.6
µ(max)
B (tesla)
1.2
0.8
0.4
0.0
0
200
400
600
800
1000
1200
H (A/m)
The value of ␮(max) is
␮(max) =
B
(1.3 − 0.3) tesla
=
= 8.70 × 10−3 H /m
H
(160 − 45) A -m
18.32 (a) G iven E quation (18.12) and the data in Table 18.7, we are asked to calculate the critical magnetic
fields for tin at 1.5 and 2.5 K. From the table, for Sn, TC = 3.72 K and B C (0) = 0.0305 tesla. Thus,
from E quation (18.3)
H C (0) =
=
B C (0)
␮o
0.0305 tesla
= 2.43 × 104 A /m
1.257 × 10−6 H /m
Now, solving for H C (2.5) using E quation (18.12) yields
T2
H C (T) = H C (0) 1 − 2
TC
(2.5 K) 2
H C (2.5) = (2.43 × 10 A /m) 1 −
= 1.33 × 104 A /m
(3.72 K) 2
4
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(b) Now we are to determine the temperature to which lead must be cooled in a magnetic field of
20,000 A /m in order for it to be superconductive. The value of H C (0) must first be determined using
B C (0) given in the table (i.e., 0.0803 tesla); thus
H C (0) =
0.0803 tesla
B C (0)
= 6.39 × 104 A /m
=
␮o
1.257 × 10−6 H /m
Since TC = 7.19 K we may solve for T using E quation (18.12) as
H C (T)
H C (0)
20000 A /m
= (7.19 K) 1 −
= 5.96 K
63900 A /m
T = TC 1 −
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CH A PTE R 19
OPTICA L PROPERTIES
19.9 We want to compute the velocity of light in calcium fluoride given that εr = 2.056 and ␹ m =
−1.43 × 10−5 . The velocity is determined using E quation (19.8); but first, we must calculate the
values of ε and ␮ for calcium fluoride. A ccording to E quation (12.30)
ε = εr εo = (2.056)(8.85 × 10−12 F/m) = 1.82 × 10−11 F/m
Now, utilizing E quations (18.4) and (18.7)
␮ = ␮o (␹ m + 1)
= (1.257 × 10−6 H /m)(1 − 1.43 × 10−5 ) = 1.257 × 10−6 H /m
A nd, finally
1
v= √
ε␮
1
= −11
(1.82 × 10
F/m)(1.257 × 10−6 H /m)
= 2.09 × 108 m/s
19.11 This problem asks for us, using data in Table 19.1, to estimate the dielectric constants for silica glass,
soda-lime glass, PTFE , polyethylene, and polystyrene, and then to compare these values with those
cited in Table 12.4 and briefly explain any discrepancies. From E quation (19.10)
εr = n 2
Thus, for fused silica, since n = 1.458
εr = (1.458) 2 = 2.13
When we compare this value with that given in Table 12.4 at a frequency of 1 MH z (i.e., εr = 3.8)
there is a significant discrepancy. The reason for this is that, for this material, an ionic component
to the dielectric constant is present at 1 MH z, which is absent at frequencies within the visible
electromagnetic spectrum, frequencies which are on the order 109 MH z. This effect may be noted
in Figure 12.32.
19.19 In this problem we are asked to calculate the fraction of nonreflected light transmitted through a
20 mm thickness of transparent material, given that the fraction transmitted through a 10 mm width
is 0.90. From E quation (19.18), the fraction of nonreflected light transmitted is just I′T /I′o . U sing this
expression we must first determine the value of ␤ as
′ I
1
␤ = − ln T′
x
Io
1
ln(0.90) = 1.05 × 10−2 mm −1
=−
10 mm
Now, solving for
I′T
I′o
when x = 20 mm
I ′T
= exp(−␤x)
I ′o
exp[−(1.05 × 10−2 mm −1 )(20 mm)] = 0.81
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19.30 This problem asks for the difference in energy between metastable and ground electron states for
a ruby laser. The wavelength of the radiation emitted by an electron transition from the metastable
to ground state is cited as 0.6943 ␮m. The difference in energy between these states, E, may be
determined from E quation (19.6), as
E = h␯ =
=
hc
␭
(4.13 × 10−15 eV-s)(3 × 108 m/s)
6.943 × 10−7 m
= 1.78 eV
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CH A PTE R 20
MATERIA LS SELECTION A ND D ESIGN CONSID ERATIONS
20.D 3 (a) This portion of the problem asks that we derive a performance index expression for strength
analogous to E quation (20.9) for a cylindrical cantilever beam that is stressed in the manner shown
in the accompanying figure. The stress on the unfixed end, , for an imposed force, F, is given by
the expression [E quation (20.24) in the textbook]
=
FLr
I
(20.D 1)
where L and r are the rod length and radius, respectively, and I is the moment of inertia; for a
cylinder the expression for I is provided in Figure 7.18:
I=
r 4
4
(20.D 2)
Substitution for I into E quation (20.D 1) leads to
=
4FL
r 3
(20.D 3)
Now, the mass m of some given quantity of material is the product of its density ( ) and volume.
Inasmuch as the volume of a cylinder is just r2 L, then
m = r 2 L
(20.D 4)
(20.D 5)
From this expression, the radius is just
r=
m
L
Inclusion of E quation (20.D 5) into E quation (20.D 3) yields
=
4F 1/2 L 5/2 3/2
m 3/2
(20.D 6)
A nd solving for the mass gives
m = (16F 2 L 5 ) 1/3
2/3
(20.D 7)
To ensure that the beam will not fail, we replace stress in E quation (20.D 7) with the yield strength
(y ) divided by a factor of safety (N) as
m = (16F 2 L 5 N 2 ) 1/3
2/3
y
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(20.D 8)
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Thus, the best materials to be used for this cylindrical cantilever beam when strength is a consideration are those having low ␳2/3 ratios. Furthermore, the strength performance index, P, is just the
reciprocal of this ratio, or y
2/3
P=
y
␳
(20.D 9)
The second portion of the problem asks for an expression for the stiffness performance
index. Let us begin by consideration of E quation (20.25) which relates ␦, the elastic deflection at
the unfixed end, to the force (F), beam length (L), the modulus of elasticity (E), and moment of
inertia (I) as
␦=
FL 3
3E I
(20.25)
A gain, E quation (20.D 2) gives an expression for I for a cylinder, which when substituted into
E quation (20.25) yields
␦=
4FL 3
3E r 4
(20.D 10)
A nd, substitution of the expression for r [E quation (20.D 5)] into E quation (20.D 10), leads to
=
=
4FL 3
4
m
3E
L
4FL 5 2
3E m 2
(20.D 11)
Now solving this expression for the mass m yields
m=
4FL 5 3
1/2
√
E
(20.D 12)
O r, for this cantilever situation, the mass of material experiencing a given deflection produced by a
specific force is proportional to the √ ratio for that material. A nd, finally, the stiffness performance
E
index, P, is just the reciprocal of this ratio, or
P=
√
E
(20.D 13)
(b) H ere we are asked to select those metal alloys in the database that have stiffness performance
indices greater than 3.0 (in SI units). (Note: for this performance index of 3.0, density has been
taken in terms of g/cm 3 √
rather than in the SI units of kg/m 3 .) Seventeen metal alloys satisfy this
criterion; they and their E/ values are listed below, and ranked from highest to lowest value.
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A lloy
A Z 31B Mg
A Z 31B Mg
A Z 91D Mg
356.0 A l
356.0 A l
356.0 A l
6061 A l
6061 A l
6061 A l
2024 A l
2024 A l
2024 A l
1100 A l
1100 A l
7075 A l
7075 A l
7075 A l
Condition
√
E
␳
R olled
E xtruded
A s cast
A s cast, high production
A s cast, custom
T6
O
T6
T651
O
T3
T351
O
H 14
O
T6
T651
3.790
3.790
3.706
3.163
3.163
3.163
3.077
3.077
3.077
3.072
3.072
3.072
3.065
3.065
3.009
3.009
3.009
√
(c) We are now asked to do a cost analysis on the above alloys. Below are tabulated the ␳ / E
ratio, the relative material cost ( c̄), and the product of these two parameters; also those alloys for
which cost data are provided are ranked, from least to most expensive.
A lloy
A Z 91D Mg
6061 A l
356.0 A l
6061 A l
A Z 31B Mg
1100 A l
A Z 31B Mg
7075 A l
2024 A l
356.0 A l
356.0 A l
2024 A l
1100 A l
2024 A l
6061 A l
7075 A l
7075 A l
Condition
A s cast
T6
A s cast, high production
T651
E xtruded
O
R olled
T6
T3
A s cast, custom
T6
T351
H 14
O
O
O
T651
␳
√
E
c̄
␳
c̄ √
E
0.2640
0.3250
0.3162
0.3250
0.2640
0.3263
0.2640
0.3323
0.3255
0.3162
0.3162
0.3255
0.3263
0.3255
0.3250
0.3323
0.3323
5.4
7.6
7.9
8.7
12.6
12.3
15.7
13.4
14.1
15.7
16.6
16.2
–
–
–
–
–
1.43
2.47
2.50
2.83
3.33
4.01
4.14
4.45
4.59
4.96
5.25
5.27
–
–
–
–
–
It is up to the student to select the best metal alloy to be used for this cantilever beam on a
stiffness-per-mass basis, including the element of cost, and other relevant considerations.
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20.D 6 (a) This portion of the problem asks that we compute the maximum tensile load that may be
applied to a spring constructed of a 14 hard 304 stainless steel such that the total deflection is
less than 5 mm; there are 10 coils in the spring, whereas, its center-to-center diameter is 15 mm,
and the wire diameter is 2.0 mm. The total spring deflection ␦s may be determined by combining
E quations (20.14) and (20.15); solving for the load F from the combined equation leads to
F=
␦sd4G
8N c D 3
H owever, it becomes necessary to determine the value of the shear modulus G. This is possible
using E quation (7.9) and values of the modulus of elasticity (193 G Pa) and Poisson’s ratio (0.30)
as taken from Tables B.2 and B.3 in A ppendix B. Thus
G =
=
E
2(1 + ␯)
193 G Pa
= 74.2 G Pa
2(1 + 0.30)
Substitution of this value and values of the other parameters into the above equation for F leads
to
F=
(5 × 10−3 m)(2 × 10−3 m) 4 (74.2 × 109 N/m 2 )
(8)(10 coils)(15 × 10−3 m) 3
= 22.0 N (5.1 lb f )
(b) We are now asked to compute the maximum tensile load that may be applied without any
permanent deformation of the spring wire. This requires that we combine E quations (20.12) and
(20.13), and then solve for F. H owever, it is first necessary to calculate the shear yield strength
and substitute it for ␶ in E quation (20.12). The problem statement stipulates that ␶y = 0.6 y . From
Table B.4 in A ppendix B, we note that the tensile yield strength for this alloy in the 1/4 hardened
state is 515 MPa; thus y = 309 MPa. Thus, solving for F as outlined above
F=
=
y d 3
−0.140
D
(1.6)(8)(D )
d
(309 × 106 N/m 2 )(2 × 10−3 m) 3
−0.140
15 × 10−3 m
(1.6)(8)(15 × 10−3 m)
2 × 10−3 m
= 53.6 N (12.5 lb f )
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