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1 MBB3023 Course Outcomes
Apply knowledge of materials properties for engineering design and applications.
Select suitable materials for a given engineering application.
Interpret and analyze materials testing data.
Identify the appropriate material testing standards.1
2
3
4
At the end of the course, the students should beable to:
2
Metals and
Alloys
Ceramics
and GlassesPolymers
Composites
Wire-
reinforced
cement
(Cermet)
Filled polymers
CFRP GFRP
Steel-cord
tyres
3 Role of Materials in Product Success
Failure of products:
1. Insufficient design
2. Insufficient properties
“Design flaws occurs because the designers and tool fabricators never use the product - common in large corporations.”
Insufficient properties is a materials
engineering issue.
Properties: characteristic that
distinguish and identify a material.
Originate in the nature of material
at the atomic or molecular level.
Material properties
Chemical Mechanical Physical
4 Material properties
Chemical Mechanical Physical Thermal •Material
characteristics that
relates to the
structure of
materials, its
formation from the
elements, and its
reactivity with
chemicals, other
materials, and
environment.
•The
characteristics of
a material that
are displayed
when a force is
applied to the
material.
•Characteristics
of materials that
relate to the
interaction of
these materials
with various
forms of energy
and with human
senses.
Procurement/Manufacturing considerations are not listed in property handbooks
and not even legitimate category by most standards. However the available shapes,
sizes, surface Texture, tolerances on materials are often the most important selection
factors.
•The properties
of a material
change with
temperature,
usually for worst.
Start to creep or
oxide/degrade.
5 Materials Property Spectrum
Composition
Microstructure
Phases
Grain Size
Corrosion Resistance
Inclusions
Tensile/compressive
Toughness
Ductility
Fatigue
Hardness
Creep resistance
Shear strength
Available Shapes,
Sizes, Surface
Texture
Manufacturing
Tolerances
Composition
Fillers, Crystallinity
Molecular weight
Flammability
Spatial configuration
Chemical resistance
Tensile/compressive
Heat distortion
Pressure-velocity limit
Toughness, Stress
Rupture, Creep
Manufacturing tolerances,
Stability, Available Sizes,
moldability, surface
texture
Composition
Porosity
Grain size
Crystal Structure
Corrosion Resistance
Tensile/compressive
Fracture toughness
Transverse rupture
Hardness
Available Shapes,
Sizes, Surface Texture
Manufacturing
Tolerances, Stability
Composition
Matrix/reinforcement bond;
Volume fraction of
reinforcement;
Reinforcement nature
Tensile/compression
Fracture toughness
Creep resistance
Reinforcement orientation
Available shape and Sizes
Manufacturing tolerances
Stability
• Specific heat
• Coefficient of
Thermal
Expansion
• Thermal
conductivity
• Heat
distortion
temp
• Glass
transition
temp
• Magnetic
• Electrical
• Optical
• Acoustic
• Gravimetric
• Color
CHEMICAL PHYSICAL MECHANICALProcurement/ Manufacturing considerations
ME
TA
LS
PO
LY
ME
RS
CE
RA
MIC
SC
OM
PO
SIT
ES
6 “Properties-Product Design Relationship”
How the
properties of
engineering
materials
affect the way
in which
products are
designed.
Properties
Bulk mechanical properties
INTRINSIC ATTRIBUTIVE
Bulk non-mechanical properties
Surface properties
Price and Availability
Production properties: ease
of mfg, fabrication,
joining, finishing
Aesthetic properties:
appearance, texture, feel
7 “Properties-Product Design Relationship” How the Mechanical Properties of engineering materials affect the
way in which products are designed.
•“Elastic” means it springs back when released;
•Elastic stiffness – resistance to bending is set partly by its shape – thin strips are easy to bend – partly by a property of the material itself - its Elastic Modulus, E.
•Materials with high E, like steel, are intrinsically stiff; those with low E, like PE, are not.
8 “Properties-Product Design Relationship” How the Mechanical Properties of engineering materials affect the
way in which products are designed.
•Permanent deformation is related
to strength not stiffness.
•Permanent bent depends on its
shape and its Yield Strength , y.
•Large y (Ti) is hard to deform
permanently, even E is not high
•Low y like lead is deformed easily
•When metals deformed they
getting stronger („work
hardening‟) but there is limit called
Tensile strength, ts after this limit
the materials fails (the amount of
stretches before it breaks is called
“ductility”.
9 “Properties-Product Design Relationship” How the Mechanical Properties of engineering materials affect the
way in which products are designed.
•Fracture suddenly before it
acquires a permanent bend.
•No permanent deformation -
y is not the right property.
•Resistance of materials to
cracking and fracture is
measured instead by Fracture
Toughness, K1c.
•Steels are tough – have high
K1c; glass is brittle – low K1c
10 “Properties-Product Design Relationship” How the Mechanical Properties of engineering materials affect the
way in which products are designed.
Inadequate Stiffness
(E too low)Inadequate
Strength (y low)
Inadequate
Fracture &
Toughness
(K1c too low)
Inadequate
Density
( too high)
11 “Properties-Product Design Relationship”
How the Thermal Properties of engineering materials affect the way in
which products are designed.
1. The strength of materials fails, it starts to „creep‟
(to sag slowly over time), it may oxidize, degrade or
decompose (figures).
This means that there is a limiting temperature called
the Maximum Service Temperature, Tmax, above which
its use is impractical.
12 “Properties-Product Design Relationship”
How the Thermal Properties of engineering materials affect the way in
which products are designed.
2. Most materials expand when they are heated, but by different amount depending on their Thermal Expansion Coefficient,. The expansion is small but its consequences can be large. E.g. buckling of the rod. (the rod is constrained and then heated – the expansion forces the rod against the constraint, causing it to buckle). E.g: railway tracks.
13 “Properties-Product Design Relationship”
How the Thermal Properties of engineering materials affect the way in
which products are designed.
High Conductivity,
3. Some materials-metals-feel cold; others-wood-feel warm. This feel has to do with
two thermal properties of materials: Thermal Conductivity, and Heat Capacity. -
measures the rate at which heat flows through the material when one side is hot and
the other cold: High is needed in conducting heat from one place to another
(cooking pans, radiators, heat exchangers). Low is useful in insulate homes,
reduce energy consumptions of refrigerators and freezers and enable space vehicles
to re-enter the earth’s atmosphere.
When time is limited, Heat Capacity, Cp is matter. It measures the amount of heat
that it takes to make the temp. of material rise by a given amount.
14 The Price & Availability of Materials
Consider how the materials used for building bridges in Cambridge
have changed over the centuries. Fig. 1.2 (Queens’ Bridge) suggests,
until 150 years or so ago wood was commonly used for bridge
building. It was cheap, and high-quality timber was still available in
large sections from natural forests. Stone, too, as the picture of Clare
Bridge (Fig. 1.3) shows, was widely used. In the 18th century the
ready availability of cast-iron, with its relatively low assembly costs,
led to many cast-iron bridges of the type exemplified by Magdalene
Bridge (Fig. 1.4). Metallurgical developments of the later 19th century
allowed large mild-steel structures to be built (the Fort St. George
Footbridge, Fig. 1.5). Finally, the advent of cheap reinforced concrete
led to graceful and durable structures like that of the Garret Hostel
Lane bridge (Fig. 1.6).
“This evolution clearly illustrates how availability influences the
choice of materials. Nowadays, wood, steel and reinforced concrete
are often used interchangeably in structures, reflecting the relatively
small price differences between them. The choice of which of the
three materials to use is mainly dictated by the kind of structure the
architect wishes to build: chunky and solid (stone), structurally
efficient (steel), slender and graceful (pre-stressed concrete.”
Fig. 1.2
Fig. 1.3
Fig. 1.4
Fig. 1.5
15 Mechanical Properties of Materials
Learning Objectives: students should be able to:
1. Achieve an understanding of the difference between
strength and toughness.
2. Gain a secure knowledge of tensile testing and its
product.
3. Learn how to use mechanical properties in materials
selection and failure analysis.
16 Spectrum of Mechanical Properties
Mechanical properties
Strength
Tensile
Yield
Compression
Flexural
Shear
Creep
Stress rupture
Formability
% elongation;
% reduction area;
Bend radius
Stiffness
Modulus of elasticity
Flexural modulus
Toughness
Impact strength; Notch sensitivity; Critical stress intensity factor
Durability
Hardness; Wear resistance; Fatigue strength
17
What is tensile testing?
What is it used for?
How does it work?
Important parts on a tensile tester:
– Specimen‟s pulling/pushing mechanism
– Grips
– Extensometer
– Fixtures
Type of loading
Definition of elastic modulus
Yield strength
Tensile strength
Determining percent elongation
True stress and strain
Poisson‟s ratio
Tensile Testing
18 Tensile Test
The key mechanical properties obtained from a Tensile Test:1-Modulus of Elasticity (E); 2-Yield Strength (Y.S).3-Tensile Strength (TS); 4-Ductility, 100xєfailure (elastic recovery occurs after fracture); 5-Toughness (measured under load; hence the dashed line is vertical)
19 The tensile test is the most common test for determining such mechanical properties of materials as strength, ductility, toughness, elastic modulus, and strain-hardening capability.
20 Significance of Stress-Strain Data
Parameter Description
Modulus of
elasticity
Used to measure the relative stiffness of materials.
Yield strength(YS) Design stresses must be lower than the YS to ensure
that a part does not fail by plastic deformation. Shear
strength may be estimated from this YS.
Ultimate tensile
strength (UTS)
The ultimate tensile stress is the maximum stress
observed in a tensile test. Necking begins when the
value is reached.
UTS/YS ratio The ratio provides an indication of the degree of work
hardening that has occurred.
% elongation Indication of material ductility and toughness
% reduction in area Indication of material ductility and toughness
General shape of
curve
Area under the curve provides a relative indication of
material toughness. Interstitial activity in the material
can be observed. Relative level of work hardening are
assessed.