Elastic˗Plastic Stress˗Strain Model for Material Response

Key Concept: One model to represent nonlinear material response is to assume a linear relationship between stress and strain up to the yield stress followed by a constant stress. Again, the slope in the

linear range is E, the Modulus of Elasticity also called Young's Modulus. See the figure below.

In a Nut Shell: The equation relating stress and strain in the linear range remains as:

σ = E ε

where σ is the normal stress (lb/in², mPa, N/mm²)

ε is the normal strain (in/in, mm/mm, microstrain)

E is the Modulus of Elasticity (a material property ˗ psi, MPa)

Also σ_y is the yield stress for the material (lb/in², mPa, N/mm²)

Material	Value of Modulus of Elasticity, E
Mild Steel	29 x 10^6 psi	400 MPa
Aluminum	10.5 x 10^6 psi	100 MPa

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