MAYURBHANJ SCHOOL OF ENGINEERING,BARIPADA
Branch : Automobile Engineering�Semester : 5th Sem, WINTER :2021
Subject : TH5- Automobile Component Design
Chapter : 01 Introduction
Topic : Machine Design Basic Concept and properties of material
Faculty : Er. Sidhartha Kumar Mohanta
supporting material.
- Tension Load: As the ends of material are pulled apart
to make the material longer, the load is called a tension
load.
- Compression Load: As the ends of material are pushed in
to make the material smaller, the load is called
a compression load.
Tension
Compression
Classifying Loads on Materials
pulling apart
Pressure
Cargo
Classifying Loads on Materials
Stress and Strain
In order to compare materials, we must have measures.
F : load applied in pounds
A : cross sectional area in in²
: stress in psi
A
F
F
- Ratio of elongation of a material to the original length
- unit deformation
e : elongation (ft)
Lo : unloaded(original) length of a material (ft)
: strain (ft/ft) or (in/in)
Elongation:
L : loaded length of a material (ft)
Lo
e
L
Stress and Strain
Baldwin Hydraulic Machine for Tension & Compression test
Stress-Strain Diagram
material properties.
diagram.
Strain ( ) (e/Lo)
4
1
2
3
5
Stress (F/A)
Elastic
Region
Plastic
Region
Strain
Hardening
Fracture
ultimate
tensile strength
Slope=E
Elastic region
slope=Young’s(elastic) modulus
yield strength
Plastic region
ultimate tensile strength
strain hardening
fracture
necking
yield
strength
Stress-Strain Diagram
- The material will return to its original shape
after the material is unloaded( like a rubber band).
- The stress is linearly proportional to the strain in
this region.
: Stress (psi)
E : Elastic modulus (Young’s Modulus) (psi)
: Strain (in/in)
deformation occurs. ( If it is passed, the material will
no longer return to its original length.)
or
Stress-Strain Diagram
Plastic Region (Point 2 –3)
- If the material is loaded beyond the yield strength,
the material will not return to its original shape
after unloading.
- It will have some permanent deformation.
- If the material is unloaded at Point 3, the curve will
proceed from Point 3 to Point 4. The slope will be
the as the slope between Point 1 and 2.
- The distance between Point 1 and 4 indicates the
amount of permanent deformation.
Stress-Strain Diagram
Strain Hardening
- If the material is loaded again from Point 4, the
curve will follow back to Point 3 with the same
Elastic Modulus(slope).
- The material now has a higher yield strength of
Point 4.
- Raising the yield strength by permanently straining
the material is called Strain Hardening.
Stress-Strain Diagram
Tensile Strength (Point 3)
- The largest value of stress on the diagram is called
Tensile Strength(TS) or Ultimate Tensile Strength
(UTS)
- It is the maximum stress which the material can
support without breaking.
Fracture (Point 5)
- If the material is stretched beyond Point 3, the stress
decreases as necking and non-uniform deformation
occur.
- Fracture will finally occur at Point 5.
Stress-Strain Diagram
A36 Steel
Stress-Strain Diagram
5.4 Material Properties
Characteristics of Material are described as
Strength:
- Measure of the material property to resist deformation
and to maintain its shape
- It is quantified in terms of yield stress or ultimate
tensile strength .
- High carbon steels and metal alloys have higher strength
than pure metals.
- Ceramic also exhibit high strength characteristics.
Material Properties
σult
σy
Hardness:
- Measure of the material property to resist indentation,
abrasion and wear.
- It is quantified by hardness scale such as Rockwell and
Brinell hardness scale that measure indentation /
penetration under a load.
- Hardness and Strength correlate well because both
properties are related to inter-molecular bonding. A
high-strength material is typically resistant to wear
and abrasion.
Material Properties
Ductility:
- Measure of the material property to deform before failure.
- It is quantified by reading the value of strain at the
fracture point on the stress strain curve.
- Ductile materials can be pulled or drawn into pipes, wire,
and other structural shapes
- Examples of ductile material :
low carbon steel
aluminum
copper
brass
Material Properties
Brittleness:
- Measure of the material’s inability to deform before failure.
- The opposite of ductility.
- Example of ductile material : glass, high carbon steel,
ceramics
Ductile
Brittle
Stress
Strain
Material Properties
Toughness:
- Measure of the material ability to absorb energy.
- It is measured by two methods.
a) Integration of stress strain curve
- Slow absorption of energy
- Absorbed energy per unit volume
unit : (lb/in²) *(in/in) =lb·in/in³
b) Charpy test
- Ability to absorb energy of an impact without
fracturing.
- Impact toughness can be measured.
Material Properties
Charpy V-Notch Test:
Material Properties
Fatigue:
an oscillating load such as vibration.
Cycles N at Fatigue Failure
Stress (psi)
Steel
Aluminum
Endurance Limit : A certain threshold
stress which will not cause the fatigue
failure for the number of cycles.
Aluminum has no endurance limit
Material Properties
MAXIMUM stress decreases as the number of loading cycles increases.
Example:
Mooring line length =100 ft
diameter=1.0 in
Axial loading applied=25,000 lb
Elongation due to loading=1.0 in
mooring line
loading
1) Find the normal stress.
2) Find the strain.
Example:
- Salvage crane is lifting an object of 20,000 lb.
- Characteristics of the cable
diameter=1.0 in, length prior to lifting =50 ft
1) Find the normal stress in the cable.
2) Find the strain.
3) Determine the cable stretch in inches.
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