Hybrid joints consisting of pre-tensioned bolts and a bonded connection, Part II: Large-scale experiments

This review paper is focused on the load transfer mechanisms and mechanical behaviour of hybrid joints that combine adhesive bonding and pre-tensioned bolts. The first part of the review presented discussions related to small-scale tests that highlighted the significant effect of compressive stresses on the corresponding shear strength. Based thereupon, two models were presented for the hybrid joint: either a classical pre-tensioned bolted connection with the adhesive layer merely increasing friction or as an adhesively bonded joint with pre-tension reducing the peeling stresses. In the first case, we would expect no significant influence of either the overlap length or the disposition of the bolts, but a significant influence of the level of pre-tension. However, as shown in this second part the importance of bolt disposition about joint strength is not clear, and the role pre-tension plays is yet not fully elucidated. While the significance of the overlap length for joint capacity tends to support the idea that hybrid joints are a form of bonded joints, the relatively little influence of the adhesive itself behaviour mitigates this. Similarly, assuming hybrid joints are adhesively bonded with pre-tensioned bolts only reducing tensile stresses at the end of the overlap, the effect of bolt positioning remains inconclusive. The inconclusiveness is largely because the studies presented in this review paper never covered all aspects of the full complexity of hybrid joints. Many studies that investigated the influence of adhesives failed to fully characterize them, and some experimental campaigns varied more than one parameter but not independently. The complexity of hybrid joints, which require knowledge from different fields of engineering, is further compounded by the difficulty in manufacturing and testing large-scale samples. Many publications report a low number of replicates, and cross-comparison between different experimental campaigns is challenging due to the involvement of many variables. Further research is necessary to fully understand the load transfer mechanisms and behaviour of hybrid joints and improve their design and practical applications.