EFFECT OF HYBRIDIZATION ON THE CREEP AND STRESS-RELAXATION CHARACTERISTICS OF PULTRUDED COMPOSITES

Pultrusion manufacturing process is a well established technique for t he cost-effective production of high-modulus and lightweight composite materials having constant cross-sectional profiles. The pultruded com posites are widely used as structural members viz., beams, trusses and stiffeners, owing to the presence of high proportion of axial fibers necessary to sustain large tractive forces. These structural members a re subjected to a combination of static and dynamic loading conditions at wide temperature ranges and over longer periods. Since polymeric c omposites exhibit viscoelastic behavior, the effectiveness of these ma terials as structural members must be thoroughly evaluated to ensure l ong-term stability. In previous research, the dynamic performance char acteristics of pultruded glass-graphite/epoxy hybrids were evaluated a t room temperature. The effects of temperature, frequency, post-curing , along with the type and placement of fibers on the dynamic flexural properties of glass/epoxy and hybrid glass-graphite/epoxy were also in vestigated. This paper focuses on the evaluation of creep and stress r elaxation performance characteristics of pultruded glass-graphite/epox y hybrid composites. Dynamic mechanical analysis technique was adopted for the accelerated creep and stress relaxation testing. Time-tempera ture superposition principle, which greatly reduced the experimental t ime, was effectively utilized for predicting the creep and stress rela xation properties of the hybrid composites. Results indicate that the type and amount of fibers as well as their lay-up sequence plays a sig nificant role in determining the flow and load bearing characteristics .