Damage evolution of hot-pressed boron carbide under confined dynamic compression

The dynamic response of hot-pressed boron carbide was studied under uniaxial and confined loading conditions using a modified compression Kolsky bar setup at strain rates of 102 - 103 s-1. The progression of damage in the prismatic specimens was captured using a high-speed camera. This experimental approach was reproduced in a quasi-static regime (10-4 - 10-3 s-1) to study the rate dependance of the strengths and damage modes. The results showed that the compressive strength of boron carbide was both stress state and strain rate dependent. A real-time visualization showed a change in the crack path under confined compression loading. Our observations revealed the formation of column-like fragments and slabs in the uniaxial and confined compression, respectively. Collected fragments of the specimens were used to investigate failure mechanisms by SEM and TEM. Both observations showed transgranular fracture. It was found that microcracks originate at large carbon inclusions and have tensile character. TEM examinations also point to the absence of stress-induced damage at grain boundaries and inside boron carbide grains. The formation of microcracks was responsible for experimentally observed inelastic response under dynamic loading conditions.