Strain Energy Function for Rubberlike Materials Based on a Generalized Measure of Strain

A strain energy density function is proposed which is based on a generalized measure of strain. The function has the form W=(2G/n)IE+BIEm where G, B, n, and m are material constants, and IE is the first invariant of the (generalized) Lagrangean strain (λan−1)/n. The function fits data on natural rubber and on a synthetic rubber in various homogeneous stress fields up to the point of break. The powers n and m are sensibly independent of temperature, while the two moduli G and B depend linearly on temperature, over the range investigated.