Influence of strain rate, temperature and adiabatic heating on the mechanical behaviour of poly-methyl-methacrylate: Experimental and modelling analyses

The goal of this paper is to investigate the strain-rate and temperature sensitivity of PMMA (polymethylmethacrylate) polymer through uniaxial compression tests under quasi-static and dynamic loading at room temperature. The experiments were conducted with an universal testing machine coupled to a climatic chamber for a range of strain rates and temperatures varying respectively from of 0.001 s−1 to 0.1 s−1 and 213–378 K. Moreover, dynamic behaviour of the material at high strain rate from 700 to 4000 s−1 was investigated using a Split Hopkinson Pressure Bar (SHPB) technique. At strain rate equal or higher than 0.1 s−1 the thermal softening effect due to adiabatic heating cannot be neglected and a correction procedure was used to take it into account. According to quasi-static and dynamic experimental results, the compressive behaviour of PMMA is greatly influenced by the applied strain rate and initial temperature; indeed, an elastic brittle or quasi-brittle response is observed at high strain rates or low temperatures whereas a ductile behaviour is obtained otherwise. The secondary relaxation temperature corresponding to the rotation of the lateral ester group was used to explain this brittle–ductile transition. Finally, the obtained experimental results were compared to the analytical predictions provided by the cooperative model proposed in the literature. Based on experimental results a new constitutive model was also proposed to describe the strain rate and temperature sensitivity and the strain hardening or softening behaviour observed during experiments.