Fatigue life predictions of automotive bonded structures using fracture mechanics: a practical approach

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Fatigue life predictions of automotive bonded structures using fracture mechanics: a practical approach

Mirza, Salim / Hackmair, Christina

A fracture mechanics based approach which can be applied to predict the fatigue life of automotive bonded structures is described. The approach has been applied to obtain the predicted S-N curve of a representative automotive joint and validated by comparison with experimental data to show the predictive capability of the approach. The Finite Element Analysis technique has been employed to model the crack growth in the bonded structure and to develop the relationship between the strain energy release rate and crack growth. Detailed crack growth modelling was carried out to obtain the strain energy release rate as a function of crack size. Using this data along with the Model I fatigue crack growth models, calculations were carried out to obtain the fracture mechanics predicted S-N curve of a representative automotive joint. The calculated S-N curve is in close agreement with the experimental data. The close agreement between the predicted and experimental results validates the fracture mechanics approach under Mode-I loading conditions as a practical tool for predicting the fatigue life of structurally bonded automotive joints. Sensitivity of the predictions to the modelling parameters has also been carried out to show the effectiveness and limitations of the approach. The influence of fatigue crack growth model, mesh type and mesh size, and global-local modelling approach has been assessed. An assessment has also been made on how the approach can be implemented into the current finite element models of the body in white structures used during the design process.