| The dissipative processes that occur during opening and shear dominated dynamic fracture of amorphous polymers were examined in a combined experimental, computational, and analytical investigation. Experiments were performed using two materials, nominally brittle polymethyl methacrylate, and nominally ductile polycarbonate, to quantify crack tip heating and identify dominant dissipative mechanisms. Shear dominated dynamic fracture of polymethyl methacrylate was found to exhibit some heating from the formation of polymer crazes, but the bulk of the heating was due to frictional sliding of the fracture surfaces aft of the propagating crack tip. Heating in polycarbonate during shear dominated dynamic fracture was from two dissipative processes, the formation of an adiabatic shear band and plastic deformation surrounding the propagating shear crack. Plastic deformation heating was noted for opening mode fracture of polycarbonate. Detailed finite element simulations of dynamic crack growth in polycarbonate were performed to isolate the heating contribution from thermoplasticity. The simulations indicated that although thermoplastic heating does occur, thermofracture heating may be significant. Heating from polymer craze formation was observed during opening mode fracture of polymethyl methacrylate, with a single craze evolving into multiple, layered crazes as crack tip speed increased. A dissipative cohesive zone model was developed to predict heating from thermofracture mechanisms associated with polymer crazing. The model predictions were consistent with measurements of single craze heating during opening mode fracture of polymethyl methacrylate. |
