Evaluation of the staircase and the accelerated test methods for fatigue limit distributions

There are many existing test methods and data reduction techniques for statistical properties of fatigue strength at a specific fatigue life, but none of them have been validated by experiment and simulation. Validation by simulation is preferable because high cycle fatigue tests are usually very subjective, not repeatable, and time consuming. This paper compares two qualitatively different approaches for evaluation of fatigue limit distributions. The analysis is based on computer simulations. The first approach contains two methods of data reduction (by Dixon and Mood as well as that by Zhang and Kececioglu) based on simulated staircase test data. Another approach includes two methods of extrapolation from shorter fatigue lives (the ray-projected and the parallel-projected methods). The analysis in the first approach is based on the assumed target distribution of the fatigue limit, while the analysis in the second approach is dependent on the method of initial extrapolation of the target distribution to the shorter lives. Several simulation-based algorithms for the generation of fatigue limit data and low cycle fatigue data were developed based on a given statistical distribution of the fatigue limit. The simulated test results were statistically evaluated against the given distributions with a target mean and two different coefficients of variation of fatigue Limits (COV (S-FL)). It was concluded that for a regular COV (S-FL) (say 3.3%), the parallel-projected method is the best, followed by the Dixon and Mood approach. In an extremely large COV (S-FL) (say 30%), the Dixon and Mood method is recommended. (C) 2001 Elsevier Science Ltd. All rights reserved.