RELIABILITY OF METAL COMPONENTS IN FATIGUE - A SIMPLE ALGORITHM FOR THE EXACT SOLUTION

An efficient and accurate method for computing the fatigue-life distribution of metal structures is presented. The problem is governed by the basic equations of the Coffin-Manson-Neuber local-strain fatigue theory for notched components. The coefficients of fatigue strength and fatigue ductility, the fatigue notch factor as well as the nominal-stress amplitude may be random variables with an arbitrary joint distribution. In order to arrive at a direct solution for the fatigue-life distribution, hence an assessment of the reliability of a component, a collocation method has been developed which gives the total-strain amplitude as an explicit function of the stress amplitude and the fatigue notch factor. This explicit equation has very close conformity to the corresponding, true, implicit equation. The fatigue-life distribution is finally expressed in a multiple-integral closed form. A simple algorithm termed the ''complete-probability fast integration'' (CPFI) is developed which gives the exact solution, to any desired accuracy, for the entire ranges of fatigue-life and reliability CPFI is superior when compared to the results and procedures of the approximate methods currently employed.