MECHANICS OF FAILURE OF PLASTICS BY THERMAL IMAGING EXAMINATION OF A THERMOPLASTIC POLYPROPYLENE PLUS EPDM BLEND

Thermal wave imaging combined with stress pattern analysis by measurem ent of thermal emission (SPATE) is used to study the failure behavior of a polypropylene (PP) + ethylene propylene diene (EPDM) polymer blen d. Images corresponding to a propagating crack in a single edge-notche d specimen were measured at three rates of testing: 4 mm/min, 8 mm/min , and 20 mm/min. Conversion to stress values is made through use of a thermoelastic function. It is found that in a 4 mm/min test the crack tip radii blunt rather than propagate with little initiation. Large-sc ale necking precedes fracture. At 8 mm/min, some blunting occurs, foll owed by fast crack propagation. At 20 mm/min, fast crack propagation o ccurs. The images are digitized to obtain the values of the temperatur es at every point in the sample. Data corresponding to the plane of th e propagating crack over the span of the test are presented.