On the mechanical properties and damage mechanisms of short fibers reinforced composite submitted to hydrothermal aging: Application to sheet molding compound composite

Abstract

Sheet Molding compound (SMC) composites were subjected to water immersion tests in order to study their durability since such composites are of interest in automotive applications. Water sorption tests were conducted by immersing specimens in distilled water at 25-90°C for different time durations. In order to investigate the combined action of water and temperature over time on composite mechanical behavior, tensile tests and quasi-static loading were conducted. The mechanical properties of water immersed specimens were evaluated and compared alongside to dry composite behaviour. The tensile tests and quasi-static properties of the studied composite were found to decrease with the increase in moisture uptake. This decrease was attributed toinner structure dégradations by means of osmosis phenomenon. It was shown that hydrothermal aging affects mainly the fiber/matrix interfacial zone while a good adhesion between the reinforcement and the matrix was observed for the virgin samples. In order to well understand the damage mechanisms, scanning electron microspy (in-situ three point bending) tests were performed on aged and non aged specimens. Damage mechanisms were identified for different material states. Results display clearly that damage evolution always begins at the interface regions. Furthermore, a quantitave analysis was performed at a local scale in a representative zone of the tensile area.