Dynamic fracture tests of polymethylmethacrylate using a semicircular bend technique

Abstract

We adopt a recently developed technique, dynamic semicircular bend testing, to measure the fracture initiation toughness, fracture propagation toughness, and fracture velocity of polymethylmethacrylate (PMMA). A modified split Hopkinson pressure bar system is used to apply the dynamic load. In this method, both the fracture initiation toughness and fracture energy, and thus the average fracture propagation toughness, are determined. The initiation toughness is found to be similar to the propagation toughness, and both toughnesses are loading rate-dependent. Our initiation toughness values for PMMA are in accord with those reported in the independent literature. The fracture velocity increases and then becomes saturated as the propagation toughness increases. We also measure the fracture surface roughness of the recovered fragments. While the surface roughness increases with the fracture energy, the increase of surface area alone is not sufficient to accommodate the increase in fracture energy, suggesting other energy dissipation mechanisms in the dynamic fracture process besides free surface creation.