Sensitivity and optimisation of the Chaboche plasticity model parameters in strain-life fatigue predictions

The aerospace industry is widely employing strain-life methodologies for structural fatigue predictions. Under spectrum loading, overloads significantly affect the fatigue, therefore it is very important to accurately account for the cyclic transient deformation phenomena. Describing these phenomena requires advanced plasticity models that involve a set of material parameters. Even for the well-known Chaboche model, there is lack of understanding of each parameter's sensitivity in strain-life fatigue calculation among engineering practitioners. A parameter optimisation technique using a multi-objective genetic algorithm is applied for the Chaboche model parameters by employing varying strain and stress controlled uniaxial data from tests on Aluminium Alloy 7075-T6. The parameters obtained from each of the optimisations and for various workflows, are then used in strain-life fatigue calculations with a Defence Science and Technology Group in-house software. Fatigue life predictions for P-3C aircraft load spectra are compared against experimental lives obtained from the Masing model to ascertain the parameters offering the most accurate results. The optimum uniaxial material dataset for strain-life predictions employing the Chaboche model is determined. The results of this study offer new insights of the model parameters' function and their sensitivity in fatigue predictions.