METHOD FOR DETERMINING THE S-N CURVE FOR A LOW PROBABILITY OF FAILURE

This paper presents a new method for determining the S-N curve for a low probability of failure, e.g., 5%. To apply this method, only eight fatigue tests are needed, which is fewer than standard methods require. This could be achieved because the standard deviation, which is necessary for estimating the normal distribution of fatigue life, was derived from the distribution of logarithm of the yield strength. The tensile tests necessary to get the yield strength are relatively simple and cost-effective. Verification of the method was performed for fatigue tests on S355J2+C structural steel, 1.4301 and 1.4404 stainless steels, medium carbon steel C45 and AW 6063 & AW 2017A aluminium alloys. The results showed that the proposed method gave fatigue strength for 5% failure probability with a more reliable fatigue life than the S-N curve estimated according to ASTM E-739-10, 2015. Considering that the proposed method is conservative and low-cost, it can be used in engineering practice.