Influence of confining prestress on the transition from interface defeat topenetration in ceramic targets

Replica scaled impact experiments with unconfined ceramic targets have shown that the transition velocity, i.e., the impact velocity at whichinterface defeat ceases and ceramic penetration occurs, decreased as the length scale increased. A possible explanation of how this scale effect isrelated to the formation of a cone crack in the ceramic has been presented by the authors in an earlier paper. Here, the influence of confinementand prestress on cone cracking and transition velocity is investigated. The hypothesis is that prestress will suppress the formation and growth ofthe cone crack by lowering the driving stress. A set of impact experiments has been performed in which the transition velocity for four differentlevels of prestress has been determined. The transition velocities as a function of the level of confining prestress is compared to an analytical modelfor the influence of prestress on the formation and extension of the cone crack in the ceramic material. Both experiments and model indicate thatprestress has a strong influence on the transition from interface defeat to penetration, although the model underestimates the influence of prestress.