Gc versus crack velocity in single groove double cantilever beam specimens of polycarbonate

The dependence of G _c on crack velocity in single-groove double cantilever beams (SG DCB) is negligible over the range of crack velocities from 0.2 to 1100 in. min^–1. The constancy of G _c appears to reflect a counterbalancing of the rise in yield stress by a decrease in crack opening displacement. The latter occurs through a decrease in the gauge length of material engulfed by yielding rather than by a decrease in the ultimate plastic strain in the crack tip plastic zone. The energy of shear lip formation at any crack velocity appears to be accurately estimated from G _c's for SG DCB specimens fractured at low velocity.