Static and dynamic behavior of unbalanced bonded joints with adhesion defects in automotive structures

Adhesive bonding is a universal connection method between dissimilar materials such as metal and plastics, which has the advantages of no holes required, uniform stress distribution, good damping and good sealing performance. However, some joining process-induced defects such as air bubbles are easily formed, which seriously affect the bond strength of adhesive joints. In this paper, the effects of bubble size, position and shape, as well as strain rate, on the shear strength of unbalanced composite/metal single lap joints (SLJ) were studied by experiment and simulation. Compared with balanced joints, adhesive joints between carbon fiber reinforced polymer (CFRP) and high strength steel (HSS) DP590 are more likely to cause cohesive failure when the defect is closer to the end of the CFRP, because the peak stress has moved from both ends to the end of CFRP with higher stiffness. When the defect locates at the middle position and has a constant area, the shape of the defect has no obvious influence on the strength of the joint. Under dynamic loading, when the defect position moves from the center towards the end of the HSS side, the enhancement effect of strain rate on shear strength is more obvious.