Effect of laser patterned microscale interlocking features on aluminum adhesive-bonded single lap joints

Many attempts have been made to enhance the strength or toughness of adhesive-bonded joints by fabricating macroscopic interlocking features on adherends or resorting to 3D-printing to produce microscale surface structures. Laser ablation has recently been proposed as a method to manufacture serrated surface profiles on aluminum single lap joints with the aim of improving strength; however, increases have so far been limited due to joint failure resulting from peeling phenomena at the end of the overlap, making enhancements in mechanical interlocking ineffective in the loading direction. The present work seeks to overcome these limitations, increasing the role of interlocking in strengthening laser patterned joints by employing deeper tooth-like features to increase geometric interlocking and thicker substrates to minimize the effect of bending-induced peeling on the initiation and development of failure. Several different patterns have been produced and tested, including both symmetrical (identical adherends) and asymmetrical (complementary adherends) with different feature orientations with respect to the loading direction. The results have revealed that, on single lap joints with thicker adherends, by using deeper asymmetrical features, the strength can be increased by 40% compared to that obtained with flat adherends.