Material fatigue properties for assessing mechanical components weakened by notches and defects

This paper addresses the problem of estimating the material fatigue properties for assessing real mechanical components. Initially, some practical rules are proposed to estimate the fully reversed plain fatigue limit, Deltasigma(0), using the material tensile stress. These rules are obtained by subdividing materials into five different groups: carbon steels, low-alloy steels, high-alloy steels, aluminium alloys and cast irons. Subsequently, using a large database of fatigue data found in the literature, it is demonstrated that the fully reversed torsional plain fatigue limit can be directly estimated from the fully reversed uniaxial plain fatigue limit by simply using Von Mises' formula. Finally, some empirical equations are proposed to estimate El Haddad's short crack constant, a(0). These equations are based on the assumption that this material property can be derived from the plain fatigue limit determined at a given load ratio, R. Since the a(0) values depend on the load ratio, so a(0) versus Deltasigma(0) relationships can directly account for the R influence. The aim of this paper is to provide engineers engaged in assessing real structural components with empirical rules to estimate the material fatigue properties. All these pieces of information are needed to apply the most modern methods suitable for assessing components weakened by any kind of geometrical feature and subjected to any kind of fatigue loading.