Crack propagation in PCBA-PMMA sandwich plates

The crack propagation in PCBA (Lexan)-PMMA (Plexiglas) sandwich plates has been studied by means of the high-speed photography together with a dynamic caustics method. Various phenomena were observed in these experiments: the time lag between the two cracks propagating into the two phases of the sandwich, the time coincidence of the two propagating cracks and phenomena of acceleration, deceleration and bifurcation of the propagating cracks. More precisely, the initial crack begins to propagate first into the brittle (PMMA) phase while a second crack begins to propagate later into the ductile (PCBA) phase of the sandwich plate. The time lag and the time coincidence depend on the nature and the degree of compatibility of the two phases of the sandwich plate.