Chapter 1
Introduction
“MECHANICAL PROPERTIES OF MATERIALS”
TESERA ADDIS WUBET
DEBRE MARKOS UNIVERSITY INSTITUTE OF TECHNOLOGY
INTRODUCTION:
⚫The practical application of engineering materials
In Civil engineering depends upon a thorough
knowledge of their particular properties under a wide
range of conditions.
⚫The term”property” is a qualitative or quantitative
measure of response of materials to externally imposed
conditions like forces and temperatures.
⚫However,the range of properties found in different
classes of materials is very large.
Classification of material property:
MECHANICAL PROPERTIES:
⚫The properties of material that determine its behaviour
under applied forces are known as mechanical properties.
⚫They are usually related to the elastic and plastic
behaviour of the material.
⚫These properties are expressed as functions of stress-
strain,etc.
⚫A sound knowledge of mechanical properties of materials
provides the basis for predicting behaviour of materials
under different load conditions and designing the
components out of them.
STRESS AND STRAIN
⚫Experience shows that any material subjected to a load
may either deform, yield or break, depending upon the
⚫The Magnitude of load
⚫Nature of the material
⚫Cross sectional dimension
CONTI..
⚫The sum total of all the elementary interatomic forces or
internal resistances which the material is called upon to
exert to counteract the applied load is called stress.
⚫Mathematically, the stress is expressed as force divided
by cross-sectional area.
CONTI…
⚫ Strain is the dimensional response given by material against
mechanical loading/Deformation produced per unit length.
⚫ Mathematically Strain is change in length divided by original
length.
STRENGTH
⚫ The strength of a material is its capacity to withstand
destruction under the action of external loads.
⚫ It determines the ability of a material to withstand
stress without failure.
⚫ The maximum stress that any material will withstand
before destruction is called ultimate strength.
ELASTICITY:
⚫ The property of material by virtue of which deformation caused
by applied load disappears upon removal of load.
⚫ Elasticity of a material is the power of coming back to its original
position after deformation when the stress or load is removed.
bonds
stretch
return to
initial
F Elastic means reversible.
CONTI..
PLASTICITY:
⚫ The plasticity of a material is its ability to undergo some degree
of permanent deformation without rupture or failure.
⚫ Plastic deformation will take only after the elastic limit is
exceeded.
⚫ It increases with increase in temperature.
linear linear
elastic elastic
plastic
Plastic means permanent.
STRESS STRAIN CURVE SHOWS ELASTICITY AND
PLASTICITY FOR MATERIALS:
STIFFNESS:
⚫ The resistance of a material to elastic deformation or
deflection is called stiffness or rigidity.
⚫ A material which suffers slight deformation under load
has a high degree of stiffness or rigidity.
⚫ E.g. Steel beam is more stiffer or more rigid than
aluminium beam.
DUCTILITY:
⚫ It is the property of a material which enables it to draw out into
thin wires.
⚫ E.g., Mild steel is a ductile material.
⚫ The percent elongation and the reduction in area in tension is
often used as emperical measures of ductility.
Malleability:
⚫ Malleability of a material is its ability to be flattened
into thin sheets without cracking by hot or cold
working.
⚫ E.g Lead can be readily rolled and hammered into thin
sheets but can be drawn into wire.
Comparision of ductility and malleability
⚫ Ductility and Malleability are frequently used
interchangeably many times.
⚫ Ductility is tensile quality, while malleability is
compressive quality.
RESILIENCE:
⚫ It is the capacity of a material to absorb energy elastically.
⚫ The maximum energy which can be stored in a body upto
elastic limit is called the proof resilience, and the proof
resilience per unit volume is called modulus of resilience.
⚫ The quantity gives capacity of the material to bear shocks
and vibrations.
HARDNESS:
⚫ Hardness is a fundamental property which is closely related
to strength.
⚫ Hardness is usually defined in terms of the ability of a
material to resist to scratching, abrasion, cutting,
identation,or penetration.
⚫ Methods used for determining hardness: Brinell, Rockwell
,Vickers.
BRITTLENESS:
⚫ It is the property of breaking without much
permanent distortion.
⚫ Non-Ductile material is considered to be brittle
material.
⚫ E.g, Glass, Cast iron,etc.
CREEP:
⚫ The slow and progressive deformation of a material with
time at constant stress is called creep.
⚫ Depending on temperature, stresses even below the elastic
limit can cause some permanent deformation.
⚫ It is most generally defined as time-depndent strain
occuring under stress.
FATIGUE:
⚫ This phenomenon leads to fracture under repeated or
fluctuating stress.
⚫ Fatigue fractures are progressive beginning as minute
cracks and grow under the action of fluctuating stress.
⚫ Many components of high speed aero and turbine engines
are of this type.
