Effects of surface microstructure on the strength of adhesively bonded structures

Adhesively bonded joints have found widespread use in industry because of their structural and functional advantages. This dissertation is focused on establishing a relationship between adherend surface morphology and interfacial fracture resistance of adhesive joints. The results from this dissertation provide not only fundamental understanding of interface adhesion and fracture mechanisms of adhesive bonds, but also guidance in tailoring surface morphologies to enhance interfacial fracture resistance.; For a ductile interfacial fracture process taking place in a sandwich joint, cavity growth and coalescence in front of a growing crack are believed to constitute the dominant interfacial fracture mechanism. This fracture process is extensively studied in the present research. Self-similar crack-tip conditions confine the study of the fracture process to the analysis of a single cavity-containing unit cell. Three cell models—spherically symmetric, plane-strain and axisymmetric—are analytically studied in detail. The stress-separation relation of the unit cells is estimated using the principle of virtual work rate. Our results show that the fracture resistance depends strongly on the strain-hardening exponent of the adhesive, moderately on the initial cavity size and the aspect ratio of the cell models, and weakly on the mechanical properties of the adhesive.; The experimental investigation in the present research is focused on the influence of surface roughness on the fracture resistance of an aluminum-epoxy interface. A layered double cantilever beam (LDCB) specimen was chosen for this experiment. The LDCB specimen was debonded by peeling off the epoxy layer from the aluminum substrate using a steel wedge. Interfacial fracture energy was extracted from the debond length by developing a closed-form solution for the specimen geometry based on a “beam on an elastic foundation” model. The experimental observations established a direct relationship between the surface roughness of aluminum substrates and the fracture resistance of the aluminum-epoxy interface. This relationship provides guidance to tailor optimal surface pretreatments of aluminum substrate to improve interfacial adhesion performance.