Fatigue performance and life estimation of automotive adhesive joints using a fracture mechanics approach

Practical fatigue life prediction methods using computer aided engineering (CAE) for adhesively bonded joints are needed to reduce the risk of potential fatigue failures and unnecessary over-designs for automotive body structures. This paper presents an investigation on the tensile and fatigue behaviors of adhesively bonded lap shear and coach peel joints for A5754-O. From suspended tensile tests, macroscopic cracks were found in the adhesive layer of the lap shear joints before the joints reached the peak quasi-static strengths. A fatigue life estimation approach for automotive adhesive joints was developed based on coarsely meshed finite element models and the analytical J-integral solution. This approach also includes the influence of the macroscopic cracks in the adhesive layer on the fatigue life of lap shear joints. Finally, the fatigue life estimation approach was validated with fatigue test results of U-shape specimens, and it was found that the J-integral based parameter can effectively predict the fatigue life of adhesive joints with different substrate thicknesses and various joint types.