A modified SWT model for very high cycle fatigue life prediction of L-PBF Ti-6Al-4V alloy based on Single Defect: Effect of building orientation

Abstract

The ultrasonic fatigue tests on laser-powder bed fused (L-PBF) Ti-6Al-4V specimens manufactured at 0°, 45°, and 90° building orientations were conducted. It is found that the very high cycle fatigue (VHCF) lives decrease with the building orientation from 0°, 45°, to 90°. All the fatigue cracks initiate from internal pores or Lack of Fusion defects. Mode Ι cracks grow perpendicular to the direction of the maximum opening stress, regardless of the building orientation. The maximum prospective defect evaluated by the extreme value statistics (EVS) method is used as the typical defect for VHCF life prediction. A modified Smith-Waston-Topper (SWT) model was proposed and combined with the Critical Distance Method to predict ultra-high cycle fatigue life. The life prediction accuracy was validated by using both experimental data obtained from the experiments conducted in this paper and experimental data taken from the literature. The results show that 84% of the predicted fatigue lives are within a scatter band of 2 standard deviation, and 16% of the predicted lives are outside a scatter band of 2 standard deviation and within a scatter band of 3 standard deviation.