Numerical analysis of adhesive thickness effect on fracture toughness in adhesive-bonded joints

In this study, effect of adhesive thickness on the fracture behavior of adhesive joints, finite element analysis and experimental investigation are carried out for compact tension specimens with different bond thickness. Numerical results indicate that the crack tip stress field is affected by bond thickness due to the restriction of plastic deformation. At the same fracture toughness (K-I) level, a higher opening stress is observed in the joint with a smaller bond thickness. Beyond the crack tip region, a self-similar stress field can be described by the normalized loading parameter. The relationship between K-I and crack tip opening displacement depend on the bond thickness. For small bond thickness, toughness is linearly proportional to bond thickness due to the high constraint. After reaching a critical bond thickness, the toughness decreases with further increase of adhesive thickness due to the rapid opening of crack tip with loading. A simple model is proposed to predict the variation of toughness with bond thickness.