Split Hopkinson bar testing to study failure waves in brittle materials

Abstract
Evaluation of the mechanical properties of brittle materials submitted to high strain rates is fundamental for a deep understanding of events that take place during ballistic impacts or high-speed mechanical processes. In special, brittle materials are an important component of ballistic protection systems. A number of tests were carried out on a short split Hopkinson pressure bar facility to obtain more information about the dynamic crack propagation on an experimental alumina-niobia composition. Strain rates as high as 1825 s ^{- 1} were measured during dynamic testing of ceramic resistance. Stress and deformation history were obtained from the stress-strain curve. The fractured samples were analyzed by scanning electron microscopy (SEM). The images showed wave marks on the alumina surface. The electronic instrumentation acquired the spalling time leading to crack velocity values that are consistent with Broek's theory.