Material Characterization and Continuum Modeling of Poly (Methyl Methacrylate) (PMMA) above the Glass Transition
Uniaxial compression tests were conducted on poly (methyl methacrylate) (PMMA) over a wide range of strain rates and temperatures in and above the glass transition (from 102°C to 130°C). PMMA exhibits different behavior close to the glass transition (below 115°C) as compared to temperatures farther above the glass transition. In the temperature range just above the glass transition, a clear yield point and strain hardening at higher strains is observed. At temperatures farther above the glass transition, PMMA shows more fluid-like behavior, with no clear yield point or strain hardening at high strains. This change in behavior with temperature poses difficulties in using some of the existing constitutive models, as illustrated by the use of two different models, namely, the Dupaix-Boyce model and the Doi-Edwards model. The data obtained is used to calibrate the two models in order to predict the behavior of PMMA across this industrially significant range of processing temperatures for hot embossing applications.