A theory of the densification-induced fragmentation in glasses and ceramics under dynamic compression

A boundary of failure which follows a shock front is observed in glasses and ceramics above a critical compressive shock load. This boundary, called the failure wave leaves behind a damaged material with newly evolved properties. These include the Tresca yield behavior and the reduction in sound speed. The evolution of the Mescall zone during long-rod penetration of these materials is associated with this wave. But, the failure wave and this accompanying process of fragmentation under dynamic compression are still not understood. It is known that some brittle solids undergo an irreversible density increase when subjected to high compression. This phenomenon, called densification is linked to the formations of slip lines and cracks in intensely compressed regions of silica glass. It also corresponds directly to the losses in shock wave speeds. Once densified, a region tends to shrink, straining the interface between it and the original solid. Stressed interfaces are unstable and may roughen, causing local cracking. On this basis, the failure wave is idealized as a propagating fracture boundary layer where the solid is comminuted by a process of densification interface roughness. The kinetics for this process are established using the fluctuation dissipation theorem. Shear and tensile modes of fragmentation are studied in plane stress. The theory predicts the powder size in the Mescall zone of silica glass. Nevertheless, this theory still needs experimental verification