Rheologic fracture of PMMA material at different strain rates

Abstract

Polymethyl methacrylate(PMMA) is a kind of typical viscoelastic polymer materials, whose deformation and rheologic fracture are related not only with time and temperature, but also with strain rate on loading. By the quasi-static uniaxial tension test at defferent loading rates, the strain-rate-dependent stress-time equation of PMMA material was gotten with H-K mode. In the range of given strain rates, tes, E ₂($\dot \varepsilon$) is almost not varied with strain rate, but E ₁($\dot \varepsilon$) and η₁($\dot \varepsilon$) augment with strain rate reducing, which shows that viscosity of PMMA material responds more strongly; whereas, they reduce with strain rate increasing, which shows that the viscosity of PMMA material responds more feebly; when the strain rate is added up to infinite, E ₁($\dot \varepsilon$) goes to constant and η₁($\dot \varepsilon$) to naught, which shows that PMMA material responds elasticity by constitutive mode. Based on the theory of continuum mechanics, median stress is defined as the ratio of fracture strain energy density to fracture strain, according to the energy conservation law and Cauchy median law. The median stress of PMMA is not related with strain rate in the range of the given strain rates, so it is represented as a parameter to scale the fracture of PMMA.