The dynamic mechanical behavior of polymethyl methacrylate

Abstract

In order to investigate the short time response of solid polymers, a high resolution laser interferometer has been employed to observe the detailed structure of stress waves produced by the impact of polymeric plates. From the observed stress waves the loading and unloading stress-strain paths followed by the material can be determined. For the polymer, polymethyl methacrylate, over the stress range from 0–60 kbar such observations have disclosed a stress-strain behavior which exhibits large strain nonlinearities and significant rate-dependence. For stress levels below ≈7 kbar and above ≈40 kbar, rate-effects are of secondary importance and the observed wave profiles may be modeled using a nonlinear elastic description of the material behavior. However, at about 7 kbar, a transition is observed in the dynamic stress-strain behavior which is characterized by greater stress relaxation and significant hysteresis upon unloading. This transition, which we attribute to a yield phenomenon, requires a rate-dependent description of the material behavior to be used in the stress range of approximately 7–40 kbar.