Experimental investigation of the effects of adhesive defects on the single lap joint strength

For robust design of the joints in the engineering structures, it is necessary to determine the stress and strain under a certain load and predict the failure potential. Adhesive joints are susceptible to defect and separation, especially the joints with high overlap area. The aim of this study is the experimental investigation on the influences of the size and shape of 2D and 3D defects on the ultimate shear strength of the adhesive single lap joints. So, square, triangular and circular defects with different sizes are artificially embedded into the Araldite 2015 adhesive layer of the Aluminum 2024-T3 joints. The artificially defective samples are examined under the axial tensile tests according to ASTM D1002-01 standard. In the case of the single lap joints with 3D defects, there is an approximately linear decrease in the joint strength as the defect area increases. However, when 2D defects are applied in adhesive joint, a non-linear decrease in the joint strength is observed. Actually, the joint strength decreases gradually when the defect area/overlap area is smaller than 30%. The decline rate in the joint strength for bigger defect is more sever, indicating that the edges of the overlap area become more important as the local strains exceeding the limiting values in this zone. The survey about the defect shape show that the least decline in the strength of single lap joints occurs with circular defects. The greatest disparity in reducing the strength compared to the other 2D and 3D defects is approximately 11% and 8%, respectively. Based on the experimental results, functions are proposed to estimate the ultimate strength in defected samples with respect to defect-free samples.