Fatigue life prediction for LPBF-fabricated Ti-6Al-4V up to very-high-cycle regime based on continuum damage mechanics incorporating effect of defects

Defects and microstructural inhomogeneity have been recognized to have a significant impact on the fatigue performance of titanium alloys fabricated by laser powder bed fusion (LPBF). In this work, a modified Chaboche fatigue damage model incorporating the effect of defects was proposed to predict the fatigue life of LPBF-fabricated Ti-6Al-4V under different stress ratios up to very-high-cycle fatigue regime. A nonlinear effect of mean stress observed in LPBF-fabricated Ti-6Al-4V was also considered in the model. The S-N data, critical defect sizes and locations obtained from our previous experimental work were utilized to calibrate and validate the proposed model. The scatter in fatigue life up to 109 cycles is predicted by the model for samples with subsurface and internal defects of size ranging from 30 μm to 150 μm under different stress ratios, and the prediction results agree with the experimental results very well. Based on the statistics of defect sizes, the S-N curves for failure probabilities of 5%, 50% and 95% were obtained for these stress ratios, and shown to be in reasonable agreement with the experimental data.