A METHOD FOR DETERMINING A COMPLETE S-N CURVE USING MAXIMUM LIKELIHOOD

Abstract eng:
The study presents two methods to estimate the S-N curve. The first method is commonly known as the traditional approach and well documented in the normative sources. It consists in determining the curve using the least squares method in a limited fatigue life regime. A staircase method is used to determine the fatigue limit. The second approach assumes normal distribution of fatigue life and fatigue limit. A probability of failure is determined as a product of fatigue life probability distribution function and fatigue limit probability distribution function. The curve parameters are determined using the maximum likelihood estimation method. This is an alternative approach. The advantage of the latter approach is the ability to determine a complete S-N curve using less specimens than required in the traditional approach. The alternative method allows to use non-failed specimens for statistical calculations, which is not possible in the traditional approach. Comparison of those methods was presented using fatigue data for S355J2+C steel. The tests were carried out using the testing machine for rotating bending tests. The study also compares the accuracy of the alternative approach with the traditional approach, which is generally considered accurate.

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