Effects of time and stress state on fracture of closed-cell polyvinyl chloride foam

The effects of time and stress state on fracture behaviors and mechanisms of polyvinyl chloride foam have been evaluated by varying displacement rates (0.1 to 1000 mm/min) and specimen thicknesses (5 to 37.5 mm). For thin specimens, the crack tips were under plane-stress condition at all displacement rates. The excessive deformation under plane-stress condition induced severe damages of cell walls around the crack tip, which resulted in low fracture toughness. For thick specimens at low displacement rate, the crack tips were under plane-stress condition. The marginal inelastic deformation under plane-stress condition was high enough to cause crack-tip blunting. Thus, relatively high fracture toughnesses were observed. For thick specimens at high displacement rate, the crack tips were under plane-strain condition. Brittle fracture of cell walls around crack tip was observed. The fracture toughnesses were lower than those of thick specimens at low displacement rate.