Application of multi-axial fatigue life estimation methods to aircraft structural components

The fatigue life of a typical aircraft structural component, which is subjected to a representative proportional multi-axial stress state, was evaluated using three different multi-axial fatigue life estimation models. Comparisons between the evaluation results obtained by multi-and uni-axial fatigue models and those with the test results were performed. Finite element analysis indicates that plasticity strain is significant on the fatigue critical details when the structure endurance reaches 88% of the peak load, therefore, low-cycle fatigue (LCF) life prediction models are reasonable. Three LCF models based on critical plane theory are selected to estimate the fatigue life of the structure, i.e., Wang-Shang's model, Smith-Watson-Topper(SWT)'s model and Morrow-Brown-Miller's model. Multi-axial fatigue test was also conducted to investigate the validity of the models for engineering application. The comparison results are as follows. The estimatied results of the three multiaxial models are all conservative, in which Wang-Shang's model gives a relatively smaller error and is acceptable for such structures. The errors of SWT's model and Morrow-Brown-Miller's model are much greater. For the fatigue assessment of such structural components subjected to multi-axial loading, multi-axial fatigue life estimation methods must be used since the uni-axial fatigue life method will give too dangerous estimation.