Analysis of Methods for Determining High Cycle Fatigue Strength of a Material With Investigation of Ti-6Al-4V Gigacycle Fatigue Behavior

摘要

This research utilized the benefits of numerical simulation to investigate the staircase method for use in fatigue strength testing. The staircase method is a commonly used fatigue strength test, but its ability to characterize fatigue strength variability is extremely suspect. A modified staircase approach was developed and shown to significantly reduce bias and scatter in estimates for fatigue strength variance. Experimental validation of this proposed test strategy was accomplished using a dual-phase Ti-6Al-4V alloy. The HCF behavior of a second material with a very different microstructure (beta annealed Ti-6Al-4V) was also investigated. The random fatigue limit (RFL) model was investigated to characterize stress-life behavior. Two alternative models (bilinear and hyperbolic) were developed based on maximum likelihood methods to characterize the Ti-6Al-4V fatigue life behavior. Based on this research, designers should be better able to make reliable estimates of fatigue strength parameters using small-sample testing.