Failure and penetration response of borosilicate glass during multiple short-rod impact

In Anderson Jr CE, Orphal DL, Behner T, Templeton, DW [Failure and penetration response of borosilicate glass during short-rod impact. Int J Impact Eng 2009, doi:10.1016/ j.ijimpeng.2008.12.002.] it was demonstrated that the failure front (FF) produced by the penetration of a borosilicate glass target by a gold rod ceased to propagate a short time after the rod was fully eroded. This strongly suggests that progression of the FF is not described by a wave equation. Here it is shown that propagation of the FF is reinitiated if a second co-axial rod, spaced a distance from the first, impacts the glass at the bottom of the penetration channel. The experiments were performed in reverse ballistic mode with two short rods spaced apart. In some experiments both rods were gold; in other experiments, one rod was copper and the other gold. FF propagation was measured using high-speed photography; rod penetration was measured using multiple, independent flash X-rays. Much of the observed phenomenology can be modeled assuming that the rod, either first or second, “communicates” with the FF at a speed corresponding to the bulk sound speed of the undamaged glass.