Adhesion failure analyses of bonded tubular single lap joints in laminated fibre reinforced plastic composites

This research presents a finite element based simulation technique for the analysis of adhesively bonded joints in tubular Fibre Reinforced Plastic (FRP) composite structures using Finite Element Method (FEM). Results of the bonded Tubular Single Lap Joint (TSLJ) have been compared with those available in literature and are found to be in good agreement. Effective overlap length for suitable performance of the joint is determined based on the Tsai-Wu failure criterion. Three-dimensional stress analyses have been carried out which revealed the importance of not neglecting the three-dimensional effects in the joint. Shear stress (τθr) is found to be extremely sensitive to three-dimensional effects as compared to other out-of-plane stresses (τzr, σr). Failure indices at different critical interfaces are evaluated using Quadratic Failure Criterion (QFC) within the adhesive and Tsai-Wu coupled stress criterion for the adherend–adhesive interfaces. Based on the later criteria, locations prone to adhesion failure initiation are identified to be existing at the interface of the loaded tube and the adhesive at the edge of the overlap length nearer to the clamped end of the TSLJ. Strain Energy Release Rate (SERR) calculated using Virtual Crack Closure Technique (VCCT) is used as the characterizing parameter for assessing the growth of adhesion failure. Adhesion failure damage propagation has been observed to be self-similar and it is found to propagate mainly in inplane shearing mode. Angle-ply fibre oriented adherends are found to be more susceptible to the opening mode of adhesion failure, whereas GR/E [45/−45]4s and GR/E [30/60]4s fibre oriented adherends are least resistive to mode-II growth of adhesion failure. Plies oriented in the direction of applied load, especially GR/E [90]16, are found to offer better resistance to both the opening and inplane shearing mode growths of adhesion failure and hence are the most preferred fibre orientations for the bonded TSLJ under tension. Increasing the degree of anisotropy of the composite adherends improves the adhesion failure damage growth resistance. Boron/Epoxy (B/E) FRP composites are found to be the best among the various FRP composite adherends considered in the present study.