Damage assessment of a swirl glass mat reinforced polyurethane composite using nondestructive test methods

Continuous swirl glass mat (CSM) reinforced polyurethane composite samples were fatigue and creep tested either in a standard environment of air with 50% relative humidity or while immersed in distilled water or windshield washer fluid. Pre- and post-test samples were examined nondestructively, using C-scan ultrasonics and light-transmission microscopy (LTM). Additionally, selected samples that failed during the tests were further examined by scanning electron microscopy (SEM) to evaluate the extent of damage in the vicinity of the fracture surface. The pre- and post-test C-scan ultrasonic and LTM images were compared and analyzed to determine changes in the CSM composite, attributed to damage. Combining these analyses with SEM results, correlations were made between environmental exposure and changes in the creep and fatigue properties of the material. Changes in the mechanical properties corresponded to changes observed from the analyses and comparison of the nondestructive evaluation results. It was found that exposure to distilled water and windshield washer fluid caused a decrease in the stiffness and in the fatigue life of the material. In the case of the windshield washer fluid, this decrease was discerned to be the result of plasticization of the matrix. The distilled water was found to have a more detrimental effect on the glass fiber reinforcement, attacking at the fiber/matrix interface. The plasticization of the CSM composite as a result of environmental exposure was considered a probability as the solubility parameters of the environments and the polyurethane matrix are of similar values.