Shock-induced brittle failure of boron carbide

The mechanism for the failure of brittle materials during uniaxial compressive shock-loading has been the subject of much discussion. In particular, the physical interpretation of the yield point, the Hugoniot elastic limit, remains poorly understood. It is additionally hypothesized that different materials display differing modes of deformation at the limit of elastic behaviour. Other work has shown that boron carbide (B(4)C) exhibits a type of behaviour in a different class to that of other brittle materials. In particular, other ceramics show smooth stress and particle velocity profiles at Lagrangian positions within the flow, while boron carbide shows jagged histories at such points, perhaps indicating that fragmentation at the sensor position is more extreme. To try and explain the origin of this behaviour, another part of the stress field has been probed. By using the longitudinal and now the lateral stress profiles, it is possible to elucidate how the strength of the material varies across the shock front. In other ceramics, failure has been seen to occur behind a travelling boundary that follows a shock front that has been called a failure wave, across which the strength of the material is dramatically reduced. In order to elucidate whether this failure process occurs, gauges were embedded to measure the lateral stress behind the shock front in B(4)C. As in other materials, the stress in B(4)C was seen to rise across a failure front. However, this phenomenon only occurred over certain stress ranges. More significantly, the failure penetrated further into the ceramic than has been seen in other materials. A mechanical interpretation is suggested to explain the observed behaviour. This paper shows that boron carbide exhibits a unique shock response. Although a polycrystalline ceramic, it shows a behaviour similar to an amorphous glass. It gives indications of the form of a comprehensive material description for brittle materials that will form the basis for future work.