The stress-strain curve provides information about a material's response to stress. It relates the stress placed on a material to the strain or deformation produced. The linear portion of the curve is used to determine Young's modulus, which represents a material's stiffness. Beyond the material's yield point, plastic deformation occurs, which may be partially reversible through strain hardening. Further stress leads to necking and ultimately fracture of the material. Engineers apply a safety factor to account for these responses when selecting materials and designing structures.

1. An Overview of The
Stress Strain Curve
Omar Bin Mahfodh, B.Eng.
1

2. What Is Stress Strain Curve
• Stress Strain Curve will provide the engineer with information about
the response of the material under stress. The response is
represented in terms of strain (increase in length).
• Why is important?
• It helps the engineer to pick the right material for the application
2

3. Young's Modulus
E=Stress/Strain
• Young’s Modulus is a property of the material
• Stress = Force / Area - Strain = Change of length
• Young’s Modulus can be calculated
Using the elastic (linear) part of
the curve
3

4. Elasticity
• Reversable deformation in the material
• The linear section of the curve is the elastic part
• When applying a small load is applied the material will go under a
very small deformation and this change is reversable as long as it is in
the linear section
4

5. Strength
• The maximum stress a material can withstand in elastic region
What happens when we go over the maximum strength?
• Material will go to plastic deformation, plastic is partially or fully
irreversible
5

6. Strain Hardening
Straining the material above Yield point and below Ultimate strength
6

7. Strain Hardening
• Removing the stress after passing the Yield point, the material will
reverse some part of the deformation
• The irrevocable portion is Epsilon p
and it is about .002
7

8. Strain Hardening
• The dashed line from point 3 in the figure shows us that the elastic
region got longer, this means that the
same material can withstand more
more stress in the elastic region.
8

9. Necking
Nicking occurs after the Ultimate Strength point and before fracture. It
can be seen in the figure on the left that the material is getting thinner
from the center
9

10. Failure of Material Under Load
Fracture occurs after necking,
different fracture pattern point to
failure under different types of
loadings.
10

11. Safety Factor
• Engineers always consider a safety factor when designing
• Basic formula is Safety Factor = Material Strength / Working Stress
• A safety factor is different depends on the application
11