Most suitable evaluation method for adhesive strength to minimize bend effect in lap joints in terms of the intensity of singular stress field

The lap joint testing is designed to investigate the adhesive strength under pure shear loading. However, actually pure shear testing is very difficult to be realized in the experiment because of the bend deformation during testing causing the peeling force appearing at the adhesive region. To reduce the bend effect, this paper focuses on the intensity of singular stress field (ISSF) at the interface end in order to minimize the ISSF for lap joints. The results show that the ISSF decreases with increasing the adherend thickness. The minimum ISSF is obtained when the adherend thickness is large enough with the small deformation angle defined at the interface end. Since the strength of double lap joint (DLJ) is sometimes about two times larger than the strength of single lap joint (SLJ), the equivalent strength condition is discussed by changing adherend thicknesses of DLJ and SLJ. It is found that the strength of SLJ with adherend thickness t1=7 mm is nearly equal to that of double lap joint with t1=1.5 mm prescribed in Japanese Industrial Standard.