Characterization of metallic bushings in RTM-made composites by in-situ leak detection under mechanical loading

Abstract

Fiber reinforced plastics/polymers (FRP) provide excellent mechanical properties and corrosion resistance. Therefore, they are increasingly integrated into multi-material designs. This again requires intelligent solutions for the connection of different materials, e.g. FRP with metals. Metal bushings inserted in the FRP laminate can provide for removable connections for load transfer or fluid handling. Most research to this date was focused on mechanical aspects but not on leak formation. A pipe going through a FRP laminate is an application independent bushing used in this study to investigate the performance of different metals in terms of permanent tightness of the metal-FRP interface. For this, a customized leak detection method was established to detect leaks under in-plane cyclic loading. Three different metal alloys were tested and the bushing integration was varied (cutting a hole in the fabric vs. displacing the fibers). A special RTM-tooling was developed to manufacture the hybrid specimens. The maximum permissible strain for leak onset is used as characteristic parameter. The results show that the insertion method of the bushing has the greatest effect compared to the different alloys. Pressure sensitive films showed that compaction and residual stresses could be the reason for this.