(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
