Fluctuations of the dynamic fracture energy values related to the amount of created fracture surface

Several strip band fracture tests have been performed with rubber toughened polymethylmethacrylate (RT-PMMA) samples. Using different types of profilometer, the precise amounts of created surfaces for different locations along the fracture were measured both before and after branching at different scales. It was observed that the fluctuations of the dynamic fracture energy that could be of the order of 300%, are well explained by the fluctuations of the actual amount of created surface when the fracture roughness is sampled at a scale of the order of 0.1 μm. This study shows that the classic approach, which approximates the amount of created surface during propagation as a flat rectangle defined as the sample thickness multiplied by the crack length, is not appropriate for a convenient estimate of fracture energy. Indeed, it is shown that the real 3D topography of the created surface has to be included in the energy balance to quantify an intrinsic material fracture energy. If not, fracture energy can be significantly underestimated.