Quasi-static and dynamic compressive behaviour of poly(methyl methacrylate) and polystyrene at temperatures from 293 K to 363 K

Flow stress, Young’s Modulus, energy and strain of fracture of poly(methyl methacrylate) (PMMA) and polystyrene (PS) were studied under compressive loading at strain rates of 10−4–10 s−1 and temperatures from 293 K to temperatures ∼20 K below T g. It was found that the energy of fracture shows an increase in the quasi-static strain rate (10−4–10−3 s−1) region and becomes constant in the low strain rate (10−2–10 s−1) region, while the strain of fracture shows a slow decrease with rate over the strain rate range tested. The activation energies and volumes of PMMA and PS at yield stress, 20% and 30% strain were evaluated using Eyring’s theory of viscous flow. ΔG was found to be constant for all strain rates and strains for both PMMA and PS. The activation volume for both materials increased as a function of strain.