Mechanical Performance of Fiber-reinforced Polymer Composites Under Concurrent Hygro-thermo-mechanical Loading

Fiber-reinforced polymer composites are used in a variety of engineering structures, where they may be subject to service conditions with concurrent static and fatigue mechanical loading, thermal fluctuations, moisture in water or service fluids. Predicting the durability of such materials in service conditions is critical to ensure that the appropriate condition-based maintenance routines are carried out, with consequences on structural safety. In this work, sandwich composite samples are manufactured with unidirectional T700/vinylester skins and polyvinyl chloride (PVC) foam core, using a conventional out-of-autoclave Vacuum Assisted Resin Transfer Molding. The skin orientation selected for this study is 90 deg., to trigger a polymerdriven response. Polymeric foam samples and sandwich composite samples were tested under concurrent hygrothermo-mechanical loading in a custom-made testing apparatus, where displacements are obtained from resistance changes, which can be monitored continuously by digital multimeters. Specimens are immersed in deionized water at room temperature while being concurrently loaded in three-point bending, at set percentages of their dry ultimate static load. After immersion, the specimens are tested to failure. A multi-scale model incorporating the time-dependent responses of the polymers in the sandwich skins and core is used to investigate the experimental results of this study. The multi-scale model consists of a micromechanics model for the fiber-reinforced polymeric skins and layered beam elements, in order to predict the deformations of sandwich composites under coupled mechanical and non-mechanical effects.