Effect of hygrothermal conditioning on the energy release rate and failure mechanism of metal only adherend-glass fibre prepreg co-cured single lap joints

Abstract

Fibre-reinforced composite materials are extensively used in repair and rehabilitation of oil and gas metal infrastructures which are largely exposed to water and hydrocarbon. An important aspect to this is applying adequate surface preparation to the metal to ensure a durable bond between the composite and metal substrate. In this paper, mild steel surface was prepared using grit blasting and single lap joint (SLJ) test specimens were manufactured and tested to investigate the adhesion in terms of total energy release rate (G_T) of the interface between mild steel adherend and glass fibre prepreg. An out-of-water usable epoxy resin primer was incorporated to join mild steel adherend with glass fibre prepreg by curing at a temperature of 55 °C for 48 h. Upon durability testing of the SLJ specimens using hygrothermal conditioning at a temperature of 55 °C for 1000 h, the experimental G_T values were seen to reduce significantly. Comparatively lower amount of cohesive failure and increased amount of swelling or delamination of the adhesive was observed for conditioned SLJ specimens when compared to controlled SLJ specimens. Furthermore, the experimental G_T values were found to correlate well with an analytical adhesive interface model.