In situ characterisation of dynamic fracture in \(Al_2O_3\) using ultra-fast X-ray phase contrast radioscopy: effects of porosity and crack speed

The dynamic fracture properties of porous ceramics were studied using single bunch synchrotron X-ray phase contrast imaging. The modified brazilian geometry was used to initiate and propagate a pure mode I crack. The specimen was compressed using the Split Hopkinson bars at strain rates of the order of \(10^2\) s\(^{-1}\). Main cracks were isolated for four different grades of \(Al_2O_3\), one dense alumina, and three porous grades with \(20~\%\) to \(60~\%\) porosity. The maximum measured crack velocities for three grades is of the order of \(0.6c_R\) and \(0.4c_R\) for the most porous. The fracture energy was estimated using a FE numerical simulation to quantify the influence of inertial effects induced by crack propagation. The results show that these inertial effects are far from negligible (up to \(80~\%\) of the stored energy) and that the dynamic correction factors known from the literature tend to overestimate the fracture energy. The values obtained vary from 22 J/m\(^2\) for the densest to 5 J/m\(^2\) for the most porous.