Predicting failure of bonded patches using a fracture mechanics approach

Adhesively bonded joints have found important application areas in the marine and offshore industry during the last years. One particular application is the use of bonded patches to repair steel structures such as floating production storage and offloading units (FPSOs). Experience has shown that FPSOs develop corrosion and cracks during service. Welding, which is frequently applied when repairing such kinds of defects, is hot work that is not allowed for FPSOs during production. Closing down the production can be very expensive. Thus, composite patch repair using adhesives is an attractive alternative, which means that there is a need to investigate the strength of bonded steel-composite joints.In the present paper, the strength of adhesively bonded lap-shear joints has been studied. Failure loads obtained experimentally have been presented and compared with theoretical predictions. Capacity estimates provided by traditional strength of materials approaches do not agree with experiments. On the other hand, results obtained by a recent inelastic fracture-based analysis represent measured strength values well. Furthermore, finite element analysis using cohesive elements for the adhesive bondline is shown to be a powerful tool in strength predictions of adhesively bonded joints. In addition to provide accurate estimates of the ultimate failure loads, the fracture process can be modelled, and the analysis method is applicable to a wide range of joint geometries.