Effects of hygrothermal and ambient humidity conditioning on shear strength of metal-GFRP single lap joints co-cured in and out of water

Installing and repairing of oil and gas infrastructure is required to be conducted out of water (OW) and in water (IW). In service, this infrastructure is subjected to various environmental ageing which may affect its mechanical performance. In this study the shear strength of metal-glass epoxy prepreg composites was investigated using single lap joint (SLJ) testing. For this, three different surface preparation methods (grit blasting, wire brushing and needle gunning) and two different manufacturing methods (OW and IW) were employed. Results showed that the specimens prepared by grit blasting had superior shear strength followed by these by needle gunning and wire brushed for both OW and IW methods. Manufactured specimens were also subjected to hygrothermal conditioning (WC) and ambient humidity conditioning (HC) to assess the durability of the produced SLJ specimens. The WC specimens absorbed more moisture than the HC specimens and the shear strength of the WC specimens were found to have deteriorated more than the HC specimens. For the conditioned SLJ specimens, the lower loss of shear strength was found with specimens manufactured IW when compared to specimens manufactured OW for grit blasted and needle gunned specimens and an opposite trend was seen for wire brushed specimens. However, the loss of shear strength was found to be varied with the moisture uptake for individual surface preparation technique and the variation was considered to be due to a combination of many factors other than the type of adhesive used such as metal surface profile, failure mode, rust formation and presence of black coloured metallic remnants.