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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

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