THE EFFECT OF LONG-TERM ULTRAVIOLET-LIGHT IRRADIATION ON POLYMER MATRIX COMPOSITES

This study reports the individual and combined effects of ultraviolet light and thermal shock on the physical properties of polymer matrix c omposites in air and in a ''near-vacuum system.'' The longest exposure time was 180 days. It was found that the weight loss of composites in creased with irradiation time. In the graphite/epoxy system, the weigh t loss in air was 2-3 times that in a ''near-vacuum system.'' Similarl y, the weight loss of the glass/epoxy system in air was 3-6 times that in a ''near-vacuum system.'' The weight loss of the glass/epoxy syste m was always larger than that of the graphite/epoxy system. In all cas es, the UV irradiation and 1000 times thermal shock did not change the fracture mechanism-it was always brittle fracture in addition to fibe r pullout. Surface erosion was observed in the irradiated surfaces by scanning electron microscopy. For both graphite/epoxy and glass/epoxy composites, the tensile strength decreased with increasing irradiation time irrespective of the irradiation environment. However, the decrea se was not significant. By SEM, cracks could be observed in the up-sur face and side-surface of the glass/epoxy system that was irradiated mo re than 1 month in air and through 1000 times thermal shock. Obviously , UV light cannot deeply penetrate the sample, and only the surface of the sample will be influenced. The UV radiation initiated microcracks , which propagated through the thermal shock.