High strain rate compressive behavior of PMMA

Polymethylmethacrylate (PMMA) materials are extensively used for diverse applications e.g., protective vehicular windows to eye protection devices. However, the high strain rate deformation and fracture mechanisms of PMMA are far from well understood. Therefore, controlled split Hopkinson pressure bar (SHPB) experiments that could lead to deformation with and without fracture were conducted on PMMA samples at strain rates of ~4 × 10⁰ to 1.3 × 10³ s⁻¹. With increase in strain rate, the maximum compressive yield strength of PMMA is enhanced by about 25 %. Absence of global failure characterized the deformation at relatively lower strain rates (e.g., ~4.75 × 10² to 6.75 × 10² s⁻¹), while its marked presence characterized the same at comparatively higher strain rates (e.g., ~7.69 × 10² to 9.31 × 10² s⁻¹). Attempts were made to explain these observations by the subtle changes in failure mechanisms as revealed from the fractographic examinations of the PMMA samples deformed with and without failures. The implications of the test-condition induced restrictions on the degrees of freedom locally available to the polymeric chains were discussed in the perspective of the relative strain rate dependencies of the yield behaviors of the present PMMA samples.