Thermomechanical Behavior of Amorphous Polymers During High-Speed Crack Propagation

Report No. ARL-TR-2793
Authors: Todd W. Bjerke
Date/Pages: August 2002; 192 pages
Abstract: 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 heating from craze formation and 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 crack. Plastic deformation heating was noted for opening mode fracture of polycarbonate. Finite-element simulations of dynamic crack growth in polycarbonate were performed to isolate the heating from thermoplasticity. The simulations indicated that although thermoplastic heating does occur, thermofracture heating may be significant. Heating from craze formation was observed during opening mode fracture of polymethyl methacrylate. 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.
Distribution: Approved for public release
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Last Update / Reviewed: August 1, 2002