Stress analysis of adhesive-bonded tubular-coupler joints with optimum-stiffness-composite adherend under axial tension, pressure, and thermal loading

With descriptions of fiber orientation variation, variable-stiffness composites (VSCs) have opened many new opportunities for structural designs because they offer tailorable material properties to increase the performance of composite structures. Using the concept of VSCs, this study aimed to determine the optimum adhesive-bonded tubular coupler joints subjected to tension, pressure, thermal load, and/or combinations thereof. The joint consists of three axisymmetric cylindrical adherends. The two inner adherends are made of a linear elastic isotropic material, whereas the outer adherend is composed of a symmetric balanced laminate. As the most complicated cases among others, owing to various stress components induced in the adherends and adhesive, the joints under these dominant in-plane normal force loadings are modeled to efficiently minimize stress concentrations in the thin adhesive layer. The unified theory of adhesive-bonded tubular joints was modified one step further to compute the optimum fiber angle variation using the constraint of linear distribution of the axial resultant forces in the adherends. From the methodological viewpoint, the results unveiled that the interfacial shear stress concentration in the adhesive layer was considerably diminished or even vanishes under all loading scenarios. The possibility of multiple optimum composite joints can be achieved, which otherwise are not straightforward to determine when using other analytical tubular joint models and optimization methods. Parametric studies of geometrical variables were also performed to provide a design guideline for optimum coupler joints with efficient mitigation of peak adhesive interfacial stresses.