IMPACT FRAGMENTATION OF BRITTLE MATERIALS

Impacts of high speed soft projectiles on finite and "semi-infinite" brittle blocks are described. Penetration is accompanied by projectile erosion and by the comminution and ejection of fine debris from a crater, the kinetic energy of this debris accounting for over 50% of the projectile impact kinetic energy. The conservation of momentum requires a small forward velocity of the centre of mass, and reflection of stress waves from distal surfaces and interaction of these reflected waves results in spalling and fragmentation of the block. The volume of finely fragmented material ejected is proportional to the size of the impact crater, and thus related to the intensity of the impact, i.e. the mass and velocity of the projectile. Fracture into larger fragments away from the impact crater is also related to the impact intensity, which determines the stress level and the sizes of flaws which are activated, and hence both the fragment velocity and size. The elastic strain energy is converted into the kinetic energy of expansion of this debris cloud.