Recent developments in velocity and stress measurements applied to the dynamic characterization of brittle materials

The synthesis of novel brittle materials with tailored microstructures requires the understanding of new physical phenomena related to the failure of these materials. Observation capabilities with spatial resolution of atomic dimensions, e.g., scanning tunneling microscopy (STM) and high resolution electron microscopy (HREM), have opened new frontiers in the mechanical characterization of these advanced materials. The challenge is to design experiments capable of loading the material in a controlled fashion such that defects, resulting in well defined macroscopic stress and velocity features, are produced. In this article, techniques for the measurement of surface and in-material particle velocities and in-material axial and transverse stress measurements are reviewed. Examples on the usefulness of these techniques in the study of brittle failure are provided. A variable sensitivity displacement interferometer is used in the measurement of normal and in-plane motion in pressure-shear recovery experiments conducted on fiber composite materials. In-material stress measurements with piezoresistance gauges are used in the identification of so-called failure waves in glasses.