The Normal Stress Response in Nonlinear Viscoelastic Materials: Some Experimental Findings

In a previous paper we presented the interesting theoretical result that in a two-step torsional or simple shearing deformation where the magnitude of the second step is one-half the magnitude of the first step, the normal stress response is predicted to be independent of the duration of the first step and equal to the single step response to a deformation of the same magnitude as the second step. Experimental support for this prediction is presented here based on tests run on two greatly different polymeric systems—a 19.3% solution of polyisobutylene in cetane and glassy poly(methyl methacrylate).