Adhesively bonded lap joints with extreme interface geometry

The role of adhesive–adherend interface morphology (through intentional deviation from a flat joint plane) on the mechanical behavior of adhesively bonded lap joints is studied. Two mirror-image types of joints with a zigzag interface containing ‘positive and negative’ interlocking teeth were fabricated and their tensile behavior was measured and compared to the response of a standard flat joint. Numerical simulations were used to explore the role of tooth height and width on the stress distribution in the adhesive, and on crack propagation and arrest after initial fracture. The data suggest that stress distribution along the bond line – and thus, the initial fracture load of the joint – is altered considerably by the positive and negative interlocking teeth. The tendency of a crack to either propagate along the bond or to arrest also depends strongly on morphological details. When crack arrests, the bonded joint can sustain a higher load and thus benefits from some of the intrinsic properties of the adherends (e.g. the plasticity of metal adherends) to enhance energy absorption and toughness. Our findings provide insight for the development of robust multi-material and multi-component structural systems with tailorable properties, and for understanding the role of interface morphology in some biological systems.