Strength improvement of composite-steel lap joint by grading the joint area with carbon and glass fiber and also mechanical interference by reverse step

Effectively joining metals and composites in an efficient manner is challenging due to their dissimilar physical compositions and mechanical properties. Failure of bonded joints is generally strongly influenced by the non-uniform distribution of stresses and strains that usually with the maximum value, commonly located near the ends of the overlaps. In this study, carbon is used as a reinforcing element in the adhesive layer and to improve the distribution of stress, properties are graded by fibers along the overlap. Also, using a new method, the effect of the reverse step on joint strength has been investigated. In addition, finite element modeling is used to express the distribution of shear and peel stresses in the adhesive layer and also to analyze the reasons for increasing joint strength in stepped specimens. Use of carbon at the joint surface, grading of the joint area and mechanical interference through reverse steps, have positive effects on strength. By grading the overlap by carbon and glass, the distribution of shear and peel stress have become more uniform and load and displacement of failure compared to the base specimen, which has a shear strength of 1.92 kN, increased by 34%. Creating the reverse step changes the failure mode. The presence of one step 40%, and the placement of carbon at the joint interface of that, has increased 112% of strength. But the greatest increase in strength and displacement failure is achieved using two reverse steps and carbon in the joint surface, by a significant amount of 172%.