A Comparison of the Prediction of Fatigue Damage and Crack Growth in Adhesively Bonded Joints Using Fracture Mechanics and Damage Mechanics Progressive Damage Methods

Lifetime prediction of adhesively bonded joints under constant amplitude fatigue has been carried out using two finite element-based, progressive damage modelling methods. The first method used a fracture mechanics (FM)-based crack growth law in which the relationship between strain energy release rate and crack growth rate under fatigue was determined from experiments using compound double cantilever beam specimens. It was found that the FM approach predicted the fatigue life well at higher fatigue loads but under-predicted the fatigue life at lower fatigue loads. This was attributed to the increasing importance of crack initiation at lower fatigue loads. This problem was solved in the second predictive method, which was based on a continuum damage mechanics approach. A power law relationship to plastic strain was used to define the damage rate. The damage law was able to simulate damage evolution prior to crack growth and excellent predictions of fatigue life were found at all fatigue loads.