DETERMINATION OF TRUE STRESS-STRAIN CURVE FOR INCOMPRESSIBLE MATERIALS.

A simple method is presented to obtain a true stress-strain curve for incompressible materials with measurement of only the initial cross-sectional area. The degree of validity of incompressibility conditions applied to very large deformations was cross-checked with comparison with direct measurement. In the case of engineering materials, such as metals, the engineering stress is used. Since such materials exhibit very small strains, the changes in the width and the thickness of the specimen are very small and using eq (2a) or (2b) practically gives the same value. Therefore, use of engineering stress or true stress results in practically indentical stress-strain curves, at least in the elastic region. In all engineering literature the engineering stress is used as the definition of stress.