Properties of Engineering Materials
Syllabus
Mechanical Properties, Tensile,
Fatigue, Creep, Impact, Hardness, Chemical
Properties, Physical properties, Corrosion and
Cathodic Protection,
Carbon Steel, Low alloy Steel, High temperature
and Heat Resistant Steel, Tools and High Speed
Steel,
Copper and Its Alloys,
Aluminum Alloys, Nickel Alloys, Thermal and
Insulating Materials, Engineering Inspections,
Composite Materials, Plastics, Ceramics.
References:
1-DONALD R. ASKELAND
"THE SCIENCE AND ENGINEERING OF
MATERIALS"
2-William D. Callister,
Jr."MATERIALSSCIENCEAND ENGINEERING AN
INTRODUCTION"
3-WILLIAM F. HOSFORD
MECHANICAL BEHAVIOR OF MATERIALS
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Mechanical Properties of Eng.
Materials
How do metals respond to external
loads?
� Stress and Strain
� Tension
� Compression
� Shear
� Torsion
� Elastic deformation
� Plastic Deformation
� Yield Strength
� Tensile Strength
� Ductility
� Toughness
� Hardness
Introduction
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To understand and describe how materials
deform(elongate, compress, twist) or break as
a function of applied load, time, temperature,
and other conditions we need first to discuss
standard test methods and standard language
for mechanical properties of materials.
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The motion of dislocations
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The yield strength and tensile strength
vary with prior thermal and mechanical
treatment, impurity levels, etc. This
variability is related to the behavior of
dislocations in the material. But elastic
moduli are relatively insensitive to these
effects.
The yield and tensile strengths and
modulus of elasticity decrease with
increasing temperature, ductility increases
with temperature.
Tensile Test & the properties obtained from the
1-Tensile Test
Effect of Temperature
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2-The Bend Test for Brittle Material
Due to the presence of flaw at the
surface, in many brittle materials, the
normal tensile test cannot easily be
performed.
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True Stress-True Strain
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True Strain and True Stress
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Strain Hardening
σ= flow (true) stress
K= Strength coefficient
n =strain hardening exponent
Effect of Strain Rate
𝜎 = 𝐶 𝜀∙
𝑚
σ= flow (true) stress
𝜀=Strain rate
m=strain rate sensitivity
C=constant
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Hardness
Hardness is a measure of the material’s
resistance to localized plastic
deformation (e.g. dent or scratch)
A qualitative Moh’s scale, determined by
the ability of a material to scratch another
material: from 1 (softest= talc) to 10
(hardest = diamond).
Different types of quantitative hardness
test has been designed (Rockwell, Brinell,
Vickers, etc.).
Usually a small indenter (sphere, cone, or
pyramid) is forced into the surface of a
material under conditions of controlled
magnitude and rate of loading. The depth
or size of indentation is measured. The
tests somewhat approximate, but popular
because they are easy and non-destructive
(except for the small dent).
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Both tensile strength and hardness may be
regarded as degree of resistance to plastic
deformation.
Hardness is proportional to the tensile
strength – but note that the proportionality
constant is different for different materials.
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1. Perfect elastic Fig 1.17 a:
The behavior of this material is defined completely by its
stiffness, indicated by the modulus of elasticity (E), example
ceramic, cast iron, and thermosetting. This material is not
good for forming operation.
2. Elastic and perfect plastic Fig 1.17 b:
This material has stiffness defined by (E). Once the yield
strength (Y) is reached, the material deforms plastically at
the same stress level, flow curve K=Y and n=0. Example,
lead at room temperature, material when heated to a high
temperature under melting point temperatures.
3. Elastic and strain hardening Fig 1.17 c:
This material obeys Hook's low in the elastic region and
reach yield strength Y and then deformed by a flow curve
which K<Y and n#0, example, ductile material.
Figure
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