The mean stress influence on lifetime under high-cycle fatigue combined loading

Abstract

This paper summarizes the results from the field of combined loading. This study builds on experiments that have been performed during the last ten years and provides information on sinusoidal in-phase stress components and tenseness distribution. Unfortunately, there is no exact method for estimating the damage caused by already known stress history. The main aim of experimental works was to determine the analytical form of Haigh diagrams and analytical expression of terminal lines equations. This article deals with different combinations of tension and torsion pre-stresses and contains results of experiments carried out in the laboratory of Institute of Thermomechanics in Pilsen. The lifetime curves (S-N curves) for combined pre-stress for different damage effect of normal and shear stress components have been obtained. The final results have been compiled and displayed at the threedimensional Haigh diagram with normalized coordinates. The terminal lines equations are solved by non-linear regression by Fletcher’s version of the Levenberg-Maquardt algorithm for the minimization of a sum of squares of equation residuals.