Finite Element Based Design and Adhesion Failure Analysis of Bonded Tubular Socket Joints Made with Laminated FRP Composites

This paper deals with Finite Element Analysis of bonded Tubular Socket Joints (TSJs) made with laminated Fibre Reinforced Plastic (FRP) composite structures. The effective coupling length for suitable performance of the joint is determined based on the Tsai–Wu failure criterion. The analysis revealed the three-dimensional nature of the stresses and are found to be concentrated in the close vicinity of the free edges and junction of the adherends in the coupling region of the bonded TSJ. Shear stress ( τ_r ), though comparatively small in magnitude, is found to be extremely sensitive to three-dimensional effects as compared to stresses τ_zr and σ_r . Failure indices at different critical interfaces are determined using Quadratic Failure Criterion (QFC) within the adhesive and Tsai–Wu coupled stress criterion for the adherend–adhesive and socket–adhesive interfaces. Based on the latter criterion, locations prone to adhesion failure initiation are identified to be existing near the free edges of the adherend–adhesive interfaces in the coupling region of the bonded TSJ. Strain Energy Release Rate (SERR) calculated using Modified Crack Closure Integral (MCCI) vis-à-vis Virtual Crack Closure Technique (VCCT) has been used as the characterizing parameter for assessing the growth of adhesion failures. The adhesion failure damages have been observed to propagate at the same rate in a self-similar manner mainly in the in-plane shearing mode. Quasi-isotropic and angle-ply orientations of the FRP composite laminates are more resistant to opening mode growth of failure, whereas cross-ply and unidirectional oriented socket/adherends offer better resistance to in-plane shearing mode of adhesion failure damage growth. Plies oriented in the direction of the applied load, especially Graphite/Epoxy (Gr/E) 90]₁₆, are found to offer the best resistance to all types of adhesion failure growth modes and hence are the most preferred fibre orientations for the bonded TSJ under tension. Increasing the degree of anisotropy of the composite socket/adherends improves the adhesion failure damage growth resistance of the bonded TSJ. Boron/Epoxy (B/E) FRP composites are found to be the best in slowing down the growth rate of the adhesion failures among the various FRP composite socket/adherends considered in the present study.