Stress and Failure Analyses of Adhesive-Bonded Composite Joints Using ASTM D3165 Specimens

An analytical model was developed to determine the stress and strain distributions of single-lap adhesive-bonded composite joints under tension. Both the adherend and the adhesive were assumed linear elastic in the derivations. The Laminated Plate Theory was used in defining the mechanical behavior of the composite adherends, whereas the linear elasticity theory was applied to describe the material response of the adhesive. By doing so, the stresses in the adhesive can vary through the bondline thickness. After the overall system of governing equations was determined by energy method, it was solved by using a symbolic solver—Maple with appropriate boundary conditions. Results from the analytical model were verified with finite element analysis using commercial software ABAQUS. Single-lap composite joint experiments were conducted following ASTM D3165, Strength Properties of Adhesives in Shear by Tension Loading of Single-Lap-Joint Laminated Assemblies. Although all three failure modes of bonded joints, substrate, cohesive, and adhesive failure, were present as the experimental results, the substrate failure mode was the major failure mode observed. Therefore, only substrate failure mode was analyzed using the developed model in the present paper. Four failure criteria, Tsai-Hill failure criterion, von Mises failure criterion, maximum interlaminar tensile stress criterion, and maximum normal stress criterion, were used to correlate the stresses and failure load. Nonlinear regression was conducted to determine the necessary parameters in the failure criteria. Based on the experimental results, thicker bondlines result in weaker joints. The variation of failure load for joints with various bondline thicknesses was consistent with the predicted results.