Question

What is the difference between 

(a) Nominal stress and true stress 

(b) Nominal strain and true strain?

Answer 1

(a) Nominal Stress and True Stress Nominal stress or engineering stress is the ratio of force per initial cross sectional area (original area of cross-section).

Nominal stress = Force/initial area of cross-section = p/A₀

True stress is the ratio of force per actual (instantaneous) cross-sectional area taking lateral strain into consideration. 

True stress = Force/Actual area of cross-section = p/A

 (b) Nominal Strain and True Strain 

Nominal Strain is the ratio of change in length per initial length.

Nominal strain = Change in length/Initial length = ∆L/L

True strain is the ratio of change in length per actual length (instantaneous length) taking longitudinal strain into consideration