Static and Fatigue Strength of Resin Transfer Molded Composites

Abstract

Fiber reinforced polymer composites are preferred in many structural applications for their ease of production and high specific strengths. Although fatigue loading is commonly encountered in structural applications, behavior of composites under cyclic loading is less understood compared to fatigue behavior of more conventional metals and their alloys. In this work, the response of resin transfer molded (RTM) glass/epoxy composites to static tensile and fatigue loading is investigated. Center-gated, disk shaped composites are fabricated using EPON 815C epoxy resin and EPICURE 3282 curing agent. A randomly oriented, planar glass fiber preform with 0.459kg/m2 surface density is used as the reinforcement material. Two and six layers of preforms are used to achieve 7.9 and 28.9% fiber volume fractions respectively. In addition, neat polymer parts are molded without performs to study the effect of fiber content on the tensile and fatigue behavior. Initially, ultimate tensile strength (UTS) and stiffness for three different fiber volume fractions (i.e., 0, 7.9, and 28.9%) are reported. Then, fatigue tests are conducted for stress level (σmax/UTS) of 0.5 and stress ratio (σmax/σmin) of 0.1 at a test frequency of 10 Hz. Loss of stiffness and cycles to failure are the two fatigue properties investigated. As the fiber volume fraction increased from 7.9 to 28.9%, the ultimate tensile strength and stiffness increased by 140 and 100%, respectively. During fatigue loading, the stiffness gradually dropped by approximately 13% for 7.9% and 28.9% fiber volume fractions. However, neat polymer samples did not show considerable decrease in stiffness during cycling. It is also shown that the number of cycles before failure significantly increased with the fiber content.