Estimation of fatigue strength under multiaxial cyclic loading by varying the critical plane orientation

Marta Kurek,Sabrina Vantadori,Tadeusz Agoda,Andrea Carpinteri

doi:10.3221/igf-esis.37.29

Abstract

The main purpose of this paper is to examine the influence of the critical plane orientation on the estimated fatigue strength of metals under multiaxial loading. The algorithm employed to evaluate fatigue strength implements the criterion of maximum normal and shear stress on a suitable damage plane (critical plane). The angle beta defining the critical plane orientation is measured with respect to the direction that maximises the applied normal stress. Eleven (11) structural materials under combined bending and torsion cyclic loading are examined. For each analysed material, the value of beta angle is selected so that the value of the scatter, defined by a root-mean-square value, is minimum. On the basis of such a calculation, an empirical expression for beta is proposed, that takes into account the values of bending and torsion fatigue strengths at a reference number of loading cycles. According to such an expression, beta is constant for a given material.

Highlights

S tructural components of machines and devices are subjected to service loads which often include multiaxial load conditions
The main purpose of this paper is to examine the influence of the critical plane orientation on the estimated fatigue strength of metals under multiaxial loading
The algorithm employed to evaluate fatigue strength implements the criterion of maximum normal and shear stress on a suitable damage plane

Summary

INTRODUCTION

S tructural components of machines and devices are subjected to service loads which often include multiaxial load conditions. The complex nature of the fatigue processes has produced several fatigue criteria which, implemented in algorithms, constitute a basic tool for estimating fatigue strength/life. These criteria generally reduce the spatial stress state to an equivalent uniaxial one. In 1935, Stanfield suggested the use of the critical plane to describe multiaxial fatigue [1]. Such a concept gains an increasing interest. The paper presents both a model for estimating fatigue life and the analysis of the influence of the critical plane orientation on such an estimation.

FATIGUE STRENGTH EVALUATION

MATERIALS EXAMINED

FATIGUE STRENGTH SCATTER CALCULATION

CONCLUSIONS