EXPERIMENTAL INVESTIGATION OF TENSILE FRACTURE IN POLYURETHANE FOAMS

Polyurethane foams have been used for their shock-absorption propertie s in various packaging applications. In many lightweight structural ap plications, polyurethane foams are used as the core material in sandwi ch beams or in panel construction. The mechanical properties of these foams have come under increased scrutiny because of their application to nuclear-waste shipment packages, and their use as ''bone simulants' ' in testing orthopedic implants. This paper describes a number of tes ts performed on polyurethane foams of various densities to understand their tensile fracture characteristics. Uniaxial tension, torsion, and Flexure tests were conducted to study size effect and other fracture- related phenomena. Nonlinear fracture phenomena were studied using opt ical microscopy and holographic interferometry at the microscopic and macroscopic level. Uniaxial tensile tests show linear elastic response leading to brittle failure. However, other experiments demonstrate no nlinear phenomena such as the existence of a fracture process zone and the demonstration of a size effect less than that predicted by linear elastic fracture mechanics. Factors affecting various mechanical prop erties were examined with the existing theories of solid mechanics.