EML 3004C
CHAPTER 11
Materials and Mechanical Engineeirng
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-1
EML 3004C
Relative Mechanical Properties of Materials at
Room Temperature
TABLE 2.1
Strength
Glass fibers
Graphite fibers
Kevlar fibers
Carbides
Molybdenum
Steels
Tantalum
Titanium
Copper
Reinforced
Reinforced
Thermoplastics
Lead
Hardness
Diamond
Cubic boron nitride
Carbides
Hardened steels
Titanium
Cast irons
Copper
Thermosets
Magnesium
thermosets
thermoplastics
Lead
Rubbers
Namas Chandra
Introduction to Mechanical engineering
Toughness
Ductile metals
Reinforced plastics
Thermoplastics
Wood
Thermosets
Ceramics
Glass
Ceramics
Reinforced
Thermoplastics
Tin
Thermoplastics
Stiffness
Diamond
Carbides
Tungsten
Steel
Copper
Titanium
Aluminum
Tantalum
plastics
Wood
Thermosets
Strength/Density
Reinforced plastics
Titanium
Steel
Aluminum
Magnesium
Beryllium
Copper
Chapter 11-2
EML 3004C
Tensile-Test Specimen and Machine
(b)
Figure 2.1 (a) A standard tensile-test specimen before and after pulling, showing original and final
gage lengths. (b) A typical tensile-testing machine.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-3
EML 3004C
Stress-Strain Curve
Figure 2.2 A typical stressstrain curve obtained from a
tension test, showing various
features.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-4
EML 3004C
Mechanical Properties of Various Materials at
Room Temperature
TABLE 2.2 Mechanical Properties of Various Materials at Room Temperature
Metals (Wrought)
E (GPa)
Y (MPa)
UTS (MPa)
Elongation
in 50 mm
(%)
Aluminum and its alloys
Copper and its alloys
Lead and its alloys
Magnesium and its alloys
Molybdenum and its alloys
Nickel and its alloys
Steels
Titanium and its alloys
Tungsten and its alloys
69–79
105–150
14
41–45
330–360
180–214
190–200
80–130
350–400
35–550
76–1100
14
130–305
80–2070
105–1200
205–1725
344–1380
550–690
90–600
140–1310
20–55
240–380
90–2340
345–1450
415–1750
415–1450
620–760
45–4
65–3
50–9
21–5
40–30
60–5
65–2
25–7
0
Nonmetallic materials
Ceramics
70–1000
—
140–2600
0
Diamond
820–1050
—
—
—
Glass and porcelain
70-80
—
140
—
Rubbers
0.01–0.1
—
—
—
Thermoplastics
1.4–3.4
—
7–80
1000–5
Thermoplastics, reinforced
2–50
—
20–120
10–1
Thermosets
3.5–17
—
35–170
0
Boron fibers
380
—
3500
0
Carbon fibers
275–415
—
2000–3000
0
Glass fibers
73–85
—
3500–4600
0
Kevlar fibers
62–117
—
2800
0
Note: In the upper table the lowest values for E, Y, and UTS and the highest values for elongation are for pure metals.
Multiply gigapascals (GPa) by 145,000 to obtain pounds per square in. (psi), megapascals (MPa) by 145 to obtain psi.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-5
EML 3004C
Loading and Unloading of Tensile-Test
Specimen
Figure 2.3 Schematic illustration of the
loading and the unloading of a tensile- test
specimen. Note that, during unloading,
the curve follows a path parallel to the
original elastic slope.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-6
EML 3004C
Elongation versus % Area Reduction
Approximate
relationship
between elongation
and tensile
reduction of area
for various groups
of metals.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-7
EML 3004C
Construction of True Stress-True Strain Curve
(a) Load-elongation curve in
tension testing of a stainless steel
specimen.
(b) Engineering stressengineering strain curve, drawn
from the data in (a.)
(c) True stress-true strain curve,
drawn from the data in (b). Note
that this curve has a positive slope,
indicating that the material is
becoming stronger as it is strained.
(d) True stress-true strain curve
plotted on log-log paper and based
on the corrected curve in ©. The
correction is due to the triaxial
state of stress that exists in the
necked region of a specimen.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-8
EML 3004C
Typical Values for K and n at Room
Temperature
TABLE
Aluminum
1100–O
2024–T4
6061–O
6061–T6
7075–O
Brass
70–30, annealed
85–15, cold-rolled
Cobalt-base alloy, heat-treated
Copper, annealed
Steel
Low-C annealed
4135 annealed
4135 cold-rolled
4340 annealed
304 stainless, annealed
410 stainless, annealed
Namas Chandra
Introduction to Mechanical engineering
K (MPa)
n
180
690
205
410
400
0.20
0.16
0.20
0.05
0.17
900
580
2070
315
0.49
0.34
0.50
0.54
530
1015
1100
640
1275
960
0.26
0.17
0.14
0.15
0.45
0.10
Chapter 11-9
EML 3004C
True Stress-True Strain Curves
Figure 2.6 True stress-true
strain curves in tension at
room temperature for
various metals. The curves
start at a finite level of
stress: The elastic regions
have too steep a slope to be
shown in this figure, and so
each curve starts at the
yield stress, Y, of the
material.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-10
EML 3004C
Temperature Effects on Stress-Strain Curves
Figure Typical effects of temperature on
stress-strain curves. Note that temperature
affects the modulus of elasticity, the yield
stress, the ultimate tensile strength, and the
toughness (area under the curve) of
materials.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-11
EML 3004C
Typical Ranges of Strain and Deformation Rate in
Manufacturing Processes
TABLE
Process
Cold working
Forging, rolling
Wire and tube drawing
Explosive forming
Hot working and warm working
Forging, rolling
Extrusion
Machining
Sheet-metal forming
Superplastic forming
Namas Chandra
Introduction to Mechanical engineering
True strain
Deformation rate
(m/s)
0.1–0.5
0.05–0.5
0.05–0.2
0.1–100
0.1–100
10–100
0.1–0.5
2–5
1–10
0.1–0.5
0.2–3
0.1–30
0.1–1
0.1–100
0.05–2
-4
-2
10 -10
Chapter 11-12
EML 3004C
Effect of Strain Rate on Ultimate Tensile
Strength
The effect of strain rate on the
ultimate tensile strength for
aluminum. Note that, as the
temperature increases, the
slopes of the curves increase;
thus, strength becomes more
and more sensitive to strain rate
as temperature increases.
Source: J. H. Hollomon.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-13
EML 3004C
Disk and Torsion-Test Specimens
Disk test on a brittle material,
showing the direction of loading
and the fracture path.
Typical torsion-test specimen; it is
mounted between the two heads of a
testing machine and twisted. Note the
shear deformation of an element in the
reduced section of the specimen.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-14
EML 3004C
Bending
Two bend-test methods for
brittle materials: (a) three-point
bending; (b) four-point bending.
The areas on the beams
represent the bending-moment
diagrams, described in texts on
mechanics of solids. Note the
region of constant maximum
bending moment in (b); by
contrast, the maximum bending
moment occurs only at the
center of the specimen in (a).
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-15
EML 3004C
Hardness Tests
General characteristics
of hardness-testing
methods and formulas
for calculating
hardness. The quantity
P is the load applied.
Source: H. W. Hayden,
et al., The Structure and
Properties of Materials,
Vol. III (John Wiley &
Sons, 1965).
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-16
EML 3004C
Brinell Testing
(c)
Namas Chandra
Introduction to Mechanical engineering
Indentation geometry in Brinell testing;
(a) annealed metal; (b) work-hardened
metal; (c) deformation of mild steel
under a spherical indenter. Note that the
depth of the permanently deformed zone
is about one order of magnitude larger
than the depth of indentation. For a
hardness test to be valid, this zone
should be fully developed in the
material. Source: M. C. Shaw and C. T.
Yang.
Chapter 11-17
EML 3004C
Hardness
Conversion
Chart
Chart for
converting various
hardness scales.
Note the limited
range of most
scales. Because of
the many factors
involved, these
conversions are
approximate.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-18
EML 3004C
S-N Curves
Typical S-N curves for two
metals. Note that, unlike
steel, aluminum does not
have an endurance limit.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-19
EML 3004C
Creep Curve
Figure 2.17 Schematic
illustration of a typical creep
curve. The linear segment of
the curve (secondary) is used
in designing components for a
specific creep life.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-20
EML 3004C
Impact Test Specimens
Impact test specimens:
(a) Charpy; (b) Izod.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-21
EML 3004C
Failures of Materials and Fractures in
Tension
Schematic illustration of types of
failures in materials: (a) necking
and fracture of ductile materials; (b)
Buckling of ductile materials under
a compressive load; (c) fracture of
brittle materials in compression; (d)
cracking on the barreled surface of
ductile materials in compression.
Schematic illustration of the types of fracture in
tension: (a) brittle fracture in polycrystalline metals;
(b) shear fracture in ductile single crystals--see also
Fig. 1.6a; (c) ductile cup-and-cone fracture in
polycrystalline metals; (d) complete ductile fracture in
polycrystalline metals, with 100% reduction of area.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-22
EML 3004C
Ductile Fracture
Surface of ductile fracture in lowcarbon steel, showing dimples.
Fracture is usually initiated at
impurities, inclusions, or
preexisting voids (microporosity) in
the metal. Source: K.-H. Habig and
D. Klaffke. Photo by BAM
Berlin/Germany.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-23
EML 3004C
Fracture of a Tensile-Test Specimen
Figure 2.22 Sequence of events in necking and fracture of a tensile-test specimen: (a) early stage of
necking; (b) small voids begin to form within the necked region; (c) voids coalesce, producing an
internal crack; (d) the rest of the cross-section begins to fail at the periphery, by shearing; (e) the final
fracture surfaces, known as cup- (top fracture surface) and cone- (bottom surface) fracture.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-24
EML 3004C
Deformation of Soft and Hard Inclusions
Figure 2.23 Schematic illustration of the deformation of soft and hard inclusions and of their effect on void
formation in plastic deformation. Note that, because they do not comply with the overall deformation of the
ductile matrix, hard inclusions can cause internal voids.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-25
EML 3004C
Transition Temperature
Figure 2.24 Schematic
illustration of transition
temperature in metals.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-26
EML 3004C
Brittle Fracture Surface
Figure 2.25 Fracture
surface of steel that has
failed in a brittle manner.
The fracture path is
transgranular (through the
grains). Magnification:
200X. Source: Courtesy
of B. J. Schulze and S. L.
Meiley and Packer
Engineering Associates,
Inc.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-27
EML 3004C
Intergranular Fracture
Figure 2.26 Intergranular
fracture, at two different
magnifications. Grains
and grain boundaries are
clearly visible in this
micrograph. Te fracture
path is along the grain
boundaries.
Magnification: left, 100X;
right, 500X. Source:
Courtesy of B. J. Schulze
and S. L. Meiley and
Packer Engineering
Associates, Inc.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-28
EML 3004C
Fatigue-Fracture Surface
Figure 2.27 Typical
fatigue-fracture surface on
metals, showing beach
marks. Magnification:
left, 500X; right, 1000X.
Source: Courtesy of B. J.
Schulze and S. L. Meiley
and Packer Engineering
Associates, Inc.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-29
EML 3004C
Residual Stresses
Residual stresses developed in bending a beam having a rectangular cross-section. Note that the horizontal
forces and moments caused by residual stresses in the beam must be balanced internally. Because of
nonuniform deformation during metalworking operations, most parts develop residual stresses.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-30
EML 3004C
Distortion of Parts with Residual Stresses
Distortion of parts, with residual stresses, after cutting or slitting: (a) flat sheet or plate;
(b) solid round rod; (c) think-walled tubing or pipe.
Namas Chandra
Introduction to Mechanical engineering
Chapter 11-31