ELASTIC BEHAVIOUR OF A
MATERIAL – STRESS-STRAIN
DIAGRAM
GENERAL OBJECTIVE:
• To assess the elastic behaviour of materials through stressstrain diagram
SPECIFIC OBJECTIVES:
1.
2.
3.
4.
5.
sketch stress-strain curve (S)
identify proportional limit, elastic limit and yield point (S)
predict ultimate tensile strength and breaking stress(S)
list four uses of stress-strain diagram (T)
identify ductile and brittle regions from stress-strain curve (E)
STRESS – STRAIN DIAGRAM
• Consider a body subjected to uniform increasing stress,
which results in a change in its dimension.
• The relation between stress and strain is studied using a
graph.
• This graph is called stress – strain graph
STRESS – STRAIN DIAGRAM
• OA – proportionality limit
• OB - elastic limit (perfectly
elastic region)
• B - Yield point (large
increase of strain with less
increase of stress)
• D - Breaking stress
(maximum stress before
rupture)
• E – Rupture or breaking
point (material breaks)
PROPORTIONAL LIMIT
• Proportional limit is point on the curve up to which the value
of stress and strain remains proportional.
ELASTIC LIMIT
• Elastic limit is the limiting value of stress up to which the
material is perfectly elastic.
YIELD STRESS POINT
• Yield stress is defined as the stress after which material
extension takes place more quickly with no or little increase
in load.
Ultimate strength
• The greatest stress that the body can experience without
breaking or rupturing.
breaking stress
• Stress at which the material breaks.
Modulus of Resilience
• The resilience of the material is its ability to absorb
energy without creating a permanent distortion.
Modulus of Toughness
• The toughness of a material is its ability to absorb energy
without causing it to break.
Working Stress
• Working
stress is defined as the actual stress of a
material under a given loading.
Allowable Stress
• The
maximum safe stress that a material can carry is
termed as the allowable stress.
Factor of Safety
• It
is the ratio of the breaking stress of a material or
structure to the calculated maximum stress when in use. It
is also called as safety factor.
USES OF STRESS – STRAIN DIAGRAM
• Strength
• Hardness
• Ductility
• Brittleness
• Toughness
Example 1. The elastic limit for steel is
2.48 x 108 Pa. What is the maximum
weight that can be supported without
exceeding the elastic limit?
Recall: A = 3.14 x10-6 m2
L
L
A
A
F
F
Stress   2.48 x 108 Pa
A
F = (2.48 x 108 Pa) A
F = (2.48 x 108 Pa)(3.14 x 10-6 m2)
FF == 779
779N
N
Example 2 The ultimate strength
for steel is 4089 x 108 Pa. What is the
maximum weight that can be
supported without breaking the wire?
Recall: A = 3.14 x 10-6 m2
L
L
A
A
F
F
Stress   4.89 x 108 Pa
A
F = (4.89 x 108 Pa) A
F = (4.89 x 108 Pa)(3.14 x 10-6 m2)
FF == 1536
1536N
N
DUCTILE AND BRITTLE MATERIALS
STRESS-STRAIN CURVE
Brittle
Ductile
Strain
MIND MAP
SUMMARY
• Elastic behaviour of a material – stress-strain diagram
• Proportional limit, elastic limit, yield point
• Ultimate tensile strength, breaking stress
• Four uses of stress-strain diagram
STIMULATING QUESTIONS
1. Why does the slope of typical Stress-Strain curve
decrease after yielding?
2. Do soft solids like gels possess elasticity or plasticity?
Comment.
THANK YOU……