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A compact in-situ tensile stress fixture was designed for the study of the combined effects of stress and automotive environments on structural glass fiber-reinforced composite materials. With this fixture, a standardized 300 hour laboratory screening test was developed to compare the residual property loss of composite materials due to concurrent exposure to stress and environment. It is of great importance that the data gathered in the laboratory have correlation to on-vehicle (in-service) performance, and that both lab and real world data be taken with a test system (in-situ test fixtures) capable of providing accurate and consistent results under either test condition.

Two investigations into the effects of environmental exposure on the mechanical properties of glass reinforced polymer composites are described. In the first, a glass/vinyl ester composite showed a 15% decrease in the tensile strength and a 6% increase in the tensile modulus after an 840 hour exposure to sulfuric acid. In the second investigation, prestressed tensile specimens were exposed to distilled water for 307 hours. The results showed that both strength and modulus were decreased by increasing prestress. A prestress of 50% of tensile strength resulted in a 12% decrease in strength and 14% decrease in modulus.