Cohesive zone modeling of structural joint failure

Riveting and spot-welding are widely used joining technologies in the automotive and aerospace industries. General failure models to predict the fracture behavior of joints made by riveting and spot-welding are needed by designers but have not yet been developed. The current work uses cohesive zone modeling within finite element calculations to capture the deformation and fracture of blind-riveted and spot-welded joints. This technique uses two material parameters, cohesive strength and toughness, to characterize material behavior under each mode of loading. A mixed-mode failure criterion is used to combine the effects of multiple loading modes. Results from numerical calculations are compared with experimental data to determine the values of the cohesive parameters. A methodology is presented for determining parameters values when more than one type of failure (i.e. nugget fracture or weld pullout in spot-welded joints) is possible. These parameters are then used to predict the behavior of new joint geometries, illustrating the generality of this analysis technique.; Joints incorporating a rivet plus a layer of adhesive (rivbond) or a spot-weld plus a layer of adhesive (weldbond) are also modeled. Differences between weldbonded, spot-welded and adhesive-bonded joint behavior are detailed. Results show improvement in both strength and fracture energy for weldbonded joints over adhesive-bonded and spot-welded joints, but the magnitude of the improvement is not always dramatic and depends on the joint geometry/loading. Possible implications for designs incorporating spot-welded and/or weldbonded joints are discussed.; The main body of the thesis concludes with a dimensional analysis of a spot-welded joint. A specific example of a spot-welded coach peel joint is used to show the application of the method to spot-welded joints. Dimensionless groups are compared to specific design variables and the relative importance of each is briefly discussed. Observations regarding the influences of each dimensionless group on normalized joint strength and energy absorption during fracture are made.