Interrelation of creep and relaxation for nonlinearly viscoelastic materials: application to ligament and metal

where J(t) is the creep compliance as it depends on time t, and E(t) is the relaxation modulus. Many constitutive models have been developed to describe the nonlinear viscoelastic behavior of materials; see Schapery (1969) and Findley et al. (1976). Models described by Johnson et al. (1996) are for large deformations and Pioletti et al. (1998) take into account the strain rate. In the present study we consider a singleintegral form called nonlinear superposition. This allows the relaxation function to depend on strain level and creep to depend on stress: