Date of Publication :22nd February 2018

Abstract: The demand of modern industries to use lightweight assemblies has promoted the use of composite materials. Using traditional joining methods to assemble these materials leads to the introduction of stress concentrations which reduce the strength of the assembly. Adhesive bonding technique is used to overcome this limitation. Stress analysis carried out on double lap joint by previous researchers using mono adhesive layer indicates stress concentrations at the ends of the overlap. The present research is done in the view of reducing the stress concentration at the ends and thus increasing the joint strength. The greater adhesive shear strains at the overlap edges necessitate the use of more ductile adhesive at the edges and less ductile adhesive in the middle. This has been achieved by grading the adhesive layer from stiff in the middle to ductile at the ends using smooth and continuous gradation profiles. Three-dimensional finite element analyses are carried out on the double lap joint and the stresses at the various interfacial surfaces have been determined. The onset of failure has been predicted using Tsai-Wu coupled stress failure criterion. The critical location has been found to be present between the main adherent and adhesive layer. The successive numerical simulations carried out using various modulus ratios indicate a considerable reduction in failure index at the critical locations. The results indicate an increase in joint strength using functionally graded adhesive than using mono adhesive layer.

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