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The increased use of fiber-reinforced polyester composites in an outdoor environment has led to questions concerning the environmental durability of these materials, particularly as related to ultraviolet (UV) exposure. In this research the effects of UV radiation on mechanical properties of glass/polyester composites were studied. Since the photo degradation is a surface mechanism and is restricted to degradation of mechanical properties of resin (fiber is not degraded), this research is focused on resin properties. For this reason, test samples made of polyester resin were prepared and treated in a UV chamber through accelerated tests. Three types of specimen were manufactured. The tensile testing samples were prepared based on ASTM D638 standard with a nominal thickness of 1 mm. Also, Arcan specimens for shear tests and ASTM D3410 for compression tests were manufactured. To obtain time dependent mechanical properties of polyester resin under UV radiation, samples were radiated in three different time intervals, equivalent to 3, 6 and 12 months, using an artificial UV exposure chamber. Test specimens were tested under tension load and showed a decrease of up to 15% in average failure strain, a decrease of up to 30% in ultimate strength, and 18% decrease in tensile modulus after 100 h exposure. Also, significant changes were considered in shear modulus and strength of polyester. The effect of ultraviolet absorbers (UVA) on preventing polyester mechanical properties degradation is also studied. The results showed that the samples which have UVA additives were not degraded after UV exposure. After obtaining matrix properties due to exposure, mechanical properties of unidirectional laminate of glass/polyester composites under UV radiation were simulated using micromechanics theories. The results of simulation were validated with tensile testing of ASTM D3039 specimens of 0/90s glass/polyester laminated composites. The results show that shear modulus of this laminate decreased about 20% due to UV exposure.
Shokrieh et al. (Thu,) studied this question.