A strain rate dependent yield criterion for isotropic polymers: Low to high rates of loading

In this study, strain rate sensitivity of yield behavior in a semicrystalline polymer, Nylon 101, was experimentally investigated. A precise definition of yield was established for the polymer by deforming several specimens to certain levels of strain and measuring the residual strains after unloading and strain recovery. The material was then subjected to different loading conditions (uniaxial to multiaxial) at four different quasi-static and intermediate strain rates to determine several points on the materialʹs yield loci. Due to positive strain rate sensitivity of this polymer, the materialʹs yield loci expanded uniformly as the strain rates were increased to higher values. Further, an empirical hydrostatic pressure dependent yield equation (with four material constants) was developed to simulate these behaviors as a function of strain rate. The capability of the developed criterion was examined by simulating high strain rate yield behavior of the material in tension and in compression. The simulation results revealed very good correlations/predictions between the experimental data and the responses determined from the proposed yield criterion.