Experimental study on the performance of hybrid metal-composite joints at quasi-static and intermediate strain rates

Carbon Fibre Reinforced Plastics (CFRP) offer excellent specific mechanical properties, making them ideal for lightweight structural applications. However, in practice it is difficult to produce a viable design concept from just one material system, so a variety of different materials are required to produce an optimum design. Joining of dissimilar materials efficiently poses a significant challenge to the implementation of multi-material design concepts. Hybrid joining processes possess the advantages of both the mechanical fastening and adhesive bonding methods. This research considers a novel, interlocked/bonded technique for joining metals to CFRPs. The technique presented herein employs interlocking bond-surface morphology formed on the faying surfaces of male (metal) and female (composite) adherends that mechanically interlock in shear when coupled with a layer of adhesive. In this study, a single-lap joint (SLJ) configuration is employed to examine the effect of the interlocking features on lap shear strength and work-to-failure. The results are compared to data obtained from standard bonded SLJs. Two adhesives were studied for bonding of the standard SLJ adherends: (i) a two-part acrylic-based adhesive and (ii) a one-part crash-toughened epoxy adhesive. The toughened epoxy exhibited preferable performance characteristics, so was chosen to bond the interlocking adhesive joints (IAJs). The baseline SLJ and IAJ were tested at two test velocities - 1 mm/min (quasi-static) and 0.5 m/s (intermediate). The quasi-static and intermediate loading rate tests were performed on an electromechanical universal test machine (UTM) and high-speed servo-hydraulic UTM, respectively. The IAJs displayed an increased performance at intermediate loading rate compared to the standard SLJs but showed a reduced performance at quasi-static loading rates.