Statistical Analysis of Temperature Effect on Fatigue Lifetime of Thin Welded Stainless Steel Sheets

Abstract

Martensitic stainless steel sheets with 12% Cr are used as protective envelopes for hot and vibrating structures such as aircraft engines and gas turbines. Since the envelope shape may be complex, butt welding is chosen to assemble the parts which can undergo fatigue failure especially in the heat-affected zone (HAZ). The aim of this study is to present experimental fatigue life results showing the effect of temperature and to present a reliable statistical approach in order to correctly describe a given loading level, in relation to its fatigue life, which has not yet been tested using the only available experimental data. This situation is dictated by optimizing the costly and lengthy fatigue experiments for modeling. Normal and Weibull statistical models are used to predict fatigue lifetime based on S-N curves in welded and seamless plates. Both models provide comparable results with experimental data at 293 K and 690 K for failure probability limits of 5% and 95%. Based on Weibull model, untested levels are assessed using a cumulative fatigue life function. Two new dimensionless parameters (X: square stress ratio and H: thermal life ratio) are used to calculate, for a given stress level, the corresponding fatigue life in accordance to the sought lower and upper confidence limits. The proposed modified Weibull approach delivers results within less than 5% error.
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