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.