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

Abstract 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.