ISE 240
Introduction and Materials
What is Manufacturing?
• Manu factus – “made by hand”
• Converting raw materials into products
• Making discrete or continuous products,
equipment, machines, tools, assemblies…
• Production engineering
• Adding value to raw materials
Manufacturing Activities
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Product Design
Machines/Tooling
Process Planning
Materials
Manufacturing
Production Control
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Purchasing
Shipping
Support Services
Marketing
Sales
Customer Service
Material Classifications
• Ferrous metals –
carbon/alloy/stainless/tool & die steels
• Nonferrous metals – Aluminum, copper,
nickel, titanium, precious metals
• Plastics (polymers) – thermoplastics,
thermosets, elastomers
• Ceramics, glasses, diamond, graphite, etc.
• Composites and new materials with unique
properties
Material Properties
• Mechanical – strength, toughness, ductility,
hardness, elasticity, fatigue, creep, ratios
• Physical – density, specific heat, thermal
expansion, thermal conductivity, melting
point, magnetic and electrical qualities
• Chemical – oxidation, corrosion, degradation,
toxicity, flammability
• Manufacturing – manufacturability, effects on
product properties, service life, cost
Material Properties
• The properties of materials determine the
possible manufacturing processes that can
be used to make products
• The properties of materials are influenced
by the manufacturing processes that are
used to make products
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.
These are engineering properties of materials
Physical Properties of Materials
TABLE 3.2 Physical Properties of Materials, in Descending Order
Density
Melting point
Specific heat
Thermal
conductivity
Thermal
expansion
Electrical
conductivity
Platinum
Gold
Tungsten
Tantalum
Lead
Silver
Molybdenum
Copper
Steel
Titanium
Aluminum
Beryllium
Glass
Magnesium
Plastics
Tungsten
Tantalum
Molybdenum
Columbium
Titanium
Iron
Beryllium
Copper
Gold
Silver
Aluminum
Magnesium
Lead
Tin
Plastics
Wood
Beryllium
Porcelain
Aluminum
Graphite
Glass
Titanium
Iron
Copper
Molybdenum
Tungsten
Lead
Silver
Copper
Gold
Aluminum
Magnesium
Graphite
Tungsten
Beryllium
Zinc
Steel
Tantalum
Ceramics
Titanium
Glass
Plastics
Plastics
Lead
Tin
Magnesium
Aluminum
Copper
Steel
Gold
Ceramics
Glass
Tungsten
Silver
Copper
Gold
Aluminum
Magnesium
Tungsten
Beryllium
Steel
Tin
Graphite
Ceramics
Glass
Plastics
Quartz
Crystal Structure of Metals
• Unit cell – the smallest group of atoms showing the
characteristic lattice structure of a particular metal
• Allotropism or Polymorphism – having more than one type
of crystal structure
• Anisotropy – when a single crystal has different properties
when tested in different directions (like plywood)
Body Centered Cubic (bcc)
Alpha iron, chromium, molybdenum, tantalum, tungsten,
vanadium
Face Centered Cubic (fcc)
Gamma iron, aluminum, copper, nickel, lead, silvver,
gold, platinum
Hexagonal Close Packed (hcp)
Beryllium, cadmium, cobalt, magnesium, alpha titanium,
zinc, zirconium
Grain Boundaries and Size
• High nucleation rate – large number of smaller grains per unit volume
• High growth rate relative to nucleation – fewer grains, larger grain sizes
• Rapid cooling produces smaller grains, whereas slow cooling produces
larger grains
Plastic Deformation of
Polycrystalline Metals
When sheet metal
is subjected to
further forming
operations,
cracks form in
the direction of
rolling
Imperfections - Dislocations
Work/Strain Hardening
• Entangled
dislocations
interfere with each
other
• Grain boundaries
or impurities
impede slip
Deformation
• Elastic – returns to original shape when force is removed
• Plastic – permanent deformation
• Slip Plane – planes of atoms slip over each other due to shear stress
• Twinning – a portion of the crystal abruptly forms a mirror image of
itself across a plane
Shear stress = Applied Shearing Force / Cross Sectional Area
• Slip Systems – slip planes in different directions –
countable for different crystal structures
• bcc – 48 – high probability that externally applied shear stress will act
on a slip plane, but high stresses needed – materials have good
strength and moderate ductility
• fcc – 12 – moderate probability but low stresses needed – materials
have moderate strength and good ductility
• hcp – 3 – low probability but more slip systems become active at
higher temperatures – materials are brittle at room temperature
Material Behavior - Tension
• Tension test – used to find mechanical properties such as strength,
ductility, toughness, elastic modulus, and strain hardening
• Typical gage length lo=50 cm, cross-sectional area Ao, and diameter
12.5 mm
• The load applied and the extension of the specimen are measured
during the test
(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.
Engineering Stress-Strain Curve
• Tensile specimens initially show elongation proportional to the load
in the linear elastic behavior region
• As load is increased above the yield stress, the specimen starts to
plastically and permanently deform
• 0.2% elongation point, or
an offset of 0.002 strain
helps identify Y for ductile
materials
• Necking occurs beyond
the UTS or maximum
engineering stress of the
material
• Eventually, fracture stress
is reached
Figure 2.2 A typical stress- strain curve obtained from
a tension test, showing various features.
Definitions
Engineering or nominal stress
Engineering strain
e
l  l0
l0
 eng  P / A0
Volume constancy
V  A0l0  Al
Elastic modulus (Young’s) = stress/strain in the elastic region
Yield point or yield stress – elastic limit – permanent or plastic
deformation begins. Quite difficult to determine so value quoted is most
often a proof or offset stress, typically the 0.2% proof stress represents
the yield stress.
 0.002  P0.002 / A0
Ultimate tensile strength or tensile strength
UTS  Pmax / A0
Ductile Material
Uniform deformation
Deformation concentrated in neck
Neck begins to form – max. load
Fracture
Ductile Failure
Copper
Duralumin
Ductile materials exhibit significant permanent deformation
after yielding before fracture.
Brittle Materials
Exhibit very little deformation after yielding and fracture immediately
Measures of Ductility
Percent elongation
l f  l0
l0
Percent reduction in area
A0  A f
A0
Toughness = area under the stress/strain curve
For ductile materials these measures are quite high.
For brittle materials these measures are close to zero
To produce a new shape by a mechanical deformation process the
material must be ductile otherwise fracture occurs
Chalk has zero ductility because it does not stretch or reduce in cross
sectional area, where as clay does
Loading and Unloading of Tensile-Test Specimen
For the second loading the yield
point is greater than before. i.e.
higher stresses are need to cause
further permanent deformation.
This phenomenon is known as work
hardening and means that materials
that have been previously cold
worked are more difficult to deform
and behave in a more brittle way.
Heat treatment called annealing is
required to restore the previous
material properties
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.
True Stress and Strain
• Engineering stress is based on the original cross sectional area Ao
rather than the instantaneous area
• For small values of strain, engineering and true strains are
approximately equal
P
Engineerin gStress   
Ao
P
TrueStress   
A
Since the cross sectional area is always reducing then True stress is
always greater than true strain.
l  lo
Engineerin gStrain  e 
lo
  ln
l  l  l0   ln  l0  l  l0   ln 1  e
l
 ln 0
l
l0
l0
l0 
 0
e 2 e3 e 4
ln 1  e   e     ..............
2 3 4
l
dl
A 
 ln    ln  0 
l0 l
 A
 lo 
TrueStrain   
l
True strain is always less
than engineering strain
and the difference
increases with increased
strain.
Comparison of Stress/Strain Graphs
True Stress and Strain vs
Engineering/Nominal/Apparent Stress and Strain
Figure 2.5 (a) Load-elongation curve in
tension testing of a stainless steel
specimen. (b) Engineering stressengineering strain curve, drawn from the
data in Fig. 2.5a. (c) True stress-true
strain curve, drawn from the data in Fig.
2.5b. 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 Fig. 2.5c. The correction is due
to the triaxial state of stress that exists in
the necked region of a specimen.
  K n
K = strength coefficient
n = work-hardening
exponent
Toughness = area under the
true stress-true strain
curve
Strain Hardening Index
True strain at
which neck
forms
Tension and Compression
Figure 2.19 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.
Figure 2.20 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-andcone fracture in polycrystalline metals; (d) complete
ductile fracture in polycrystalline metals, with 100%
reduction of area.
Compression and Torsion Tests
Figure 2.9 Disk test on a brittle material, showing the direction of loading and the
fracture path.
2P
TensileStr ess   
dt
Figure 2.10 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.
ShearStress   
T
2r 2t
ShearStrain   
r
l
Effects on Temperature on Material Properties
•
Increasing temperature:
• Raises ductility and toughness
• Lowers yield stress and modulus
of elasticity
• Can cause problems with
oxidation
• May reduce accuracy of finished
products
• Increases costs due to energy
input required to raise
temperatures
Figure 2.7 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.
Recrystallization and Annealing
Annealing is a heat treatment process in which the temperature of
previously cold worked material is raised above the recrystallization
temperature and allowed to cool slowly. A new grain structure is formed with
lower strength and increased ductility
Recrystallization Temperatures
Metals are in the recrystallization range if temperatures are raised above
half of the melting point on the absolute temperature scale
Hot Working Conditions
• If metal working is carried out above the
recrystallization temperature these are called hot
working conditions
• Strain hardening and recrystallization take place
at the same time so deformation is easier and
ductility is improved
• Hot working conditions are defined as
temperatures above half the melting point on the
absolute scale (text book uses 0.6 of melting
point
• Cold working is below 0.3 of melting point and
warm working is the intermediate range between
0.3 and 0.5 of melting point.
Homologous Temperature Scale
Temperature scale between
0 and 1, where 1
corresponds to the melting
point of the metal in degrees
absolute. This enables hot,
warm and cold working
conditions to be defined for
all metals.
Hardness Tests
Figure 2.12 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).
Hardness
Conversion
Chart
Figure 2.14 Chart for
converting various hardness
scales. Note the limited range
of most scales. Because of the
many factors involved, these
conversions are approximate.
Brittle materials generally
have increased hardness.
UTS for steels is
approximately proportional
to hardness for steels.
Impact Test
Charpy test
Izod test
Energy absorbed in breaking the specimen is a measure of the impact
strength. Brittle materials break more easily than ductile materials
Fatigue and S-N Curves
Figure 2.15 Typical S-N curves for two metals. Note
that, unlike steel, aluminum does not have an
endurance limit.
Fatigue Strength can be improved by inducing compressive residual stresses on surfaces
(i.e., shot peening); surface or case hardening, providing a fine surface finish to reduce the
effects of imperfections, or selecting appropriate materials with specified quality standards.
Fatigue Strength can be decreased by tensile residual stresses, decarburization, surface
pits (corrosion), hydrogen embrittlement, galvanization, and electroplating.
Fatigue Testing
Fatigue Failure
Fatigue is failure that results from the repeated application of what may be
relatively light stresses repeatedly over many cycles. Fatigue resistance is
important for applications in which stresses are applied repeatedly, e.g.
rotating shafts, pressure vessels, aircraft structures, etc.
Creep and Creep Testing
Creep is permanent deformation results
from constant loads (stresses) applied
over long periods. These loads are
usually less than those that would
normally cause yielding of the material.
Creep increases with elevated
temperatures
Typical creep curve
Creep and Creep Testing
Creep is important in applications where constant stresses are applied over
long periods, particularly at elevated temperatures. Examples are gas
turbine blades, plastic water pipes, pressure vessels, etc.
Creep resistant materials can be developed. Grain boundaries contribute to
creep, particularly those perpendicular to the direction of loading. This has
led to special casting techniques to produce single crystal turbine blades.
Residual Stresses
• Stresses that are locked up in the product after processing due
localized deformation or heating.
– Machining and surface processing
– Bending stresses
– Welded fabrications, etc.
• Can result in unwanted distortion, stress-corrosion failure in service,
reduced fatigue life, etc.
Material Costs