A General Method for Estimating Reliability of Machine Elements Subjected to Fluctuating Load

Abstract

In this paper, with the aid of approximate Taylor’s expansions for mean and standard deviation, a general method for estimating fatigue reliability of a machine element under a combined state of stresses is derived based on the theory proposed by Prof. Kececioglu [1] and a normal-distribution assumption. A method of reduction of experimental strength probability distribution of a standard specimen to actual strength probability distribution is proposed; general formulae for determining stress probability distribution are derived; and the calculation of fatigue reliability for limited life is discussed as well. Three typical cases—uniform rods under simple tensile load, shafts subjected to combined bending and torsional stresses, and rectangular bars subjected to torsional alternating load—are discussed and calculation examples are given. Finally, the author suggests that reliability be used to replace the traditional criterion, factor of safety, in the case of designing machine elements with high reliability requirements.