Effect of curing time on the performances of hybrid/mixed joints

In this research work a mixed method for joining aluminium alloy with glass reinforced polymer's substrates (in the next GFRP) is studied: the self-piercing riveting (in the next SPR) is applied on a co-cured joint; our aim is evaluating the influence of time of inserting the rivets on the mechanical behaviour of the mixed joints. So, three different joints were realised: adhesive by co-curing technique, mechanical by self piercing riveting (in the next SPR) and the mixed one in which the joining techniques (i.e. adhesive and mechanical) were combined. In particular, to determine the optimum time of inserting the rivets, the self-piercing rivets were added to the co-cured adhesive joints at varying of the curing time of the resin (i.e. after 2 h, 5h and 24 h from the moment of mixing resin with its hardener, respectively). Moreover, for each condition, the oil pressure of the riveting system needed to optimize the performances of the joints was investigated. To determinate the times of riveting to be investigated, the curing process of the epoxy resin was previously analyzed by means of a differential scanning calorimetry (DSC) and a stress controlled rheometer. All the realised samples (i.e. five for each configuration) were characterized by single lap joint tests