Determination of critical distance for steel grade sensitivity to fretting fatigue in multiaxially loaded mechanical contacts

• The results of the fatigue test are characterised by a unique composition of uniaxial and multiaxial loadings of component contact. • The determination of critical distances for a number of multiaxial strength criteria has been shown to demonstrate the differing sensitivities. • The critical distance was accurately predicted using the Richards proportional multiaxial crack threshold model and the QCP method for pure rotating bending and rotating bending with cyclic torsion of steel C45 + N. • The critical distances of pure torsional loaded specimen are multiple higher than expected. • Simplified formula for strength estimation in design or analysis process with multiaxiality exponent was introduced. In drivetrain design, the strength and susceptibility to fretting fatigue of shaft-hub connections is a key concern. Recent studies have revealed that the sensitivity of these connections to different steel grades plays a critical role in determining their resistance to multiaxial mechanical loading. In the context of competitionrelated optimisation and subsequent overestimation of strength, an increase in damage to component contacts has been observed. Designing these components is challenging due to the numerous influencing factors that must be considered, including the critical distance concept. In this study, the authors present a methodology for calculating multiaxially stressed shrink-fit connections based on fatigue tests and considering uniaxial and multiaxial loads. The presented method delineates the boundary conditions for determining critical distances, employing the point method, for a reference geometry of two typical steel materials in the normalised and quenched and tempered condition. The employment of the multiaxial strength criteria, founded upon the stress-based cutting plane approach, has yielded the following outcomes: firstly, a method to determine the critical distances for pure rotating bending, cyclic torsional loading and a combination of both bending types has been developed. Secondly, the present study aims to compare the critical distances derived from experimental numerical analysis with those obtained through multiaxial modification of the El-Haddad equation for equivalent stress and equivalent threshold of crack stress intensity. In consideration of the material behaviour of the elastic–plastic material, the tribological steady state and the mixed mode approach according to Richard, it was determined that the QCP criterion provides the smallest calculation error at half the intrinsic length a 0 / 2 for specimens subjected to bending and combined loads. In the context of torsion, it is imperative to employ the full-length a 0 in the process of strength verification, notwithstanding the development of an adjustment. Moreover, a streamlined empirical equation that takes into account material sensitivity is proposed as a rapid design instrument for multiaxially loaded contacts, utilising the multiaxiality exponent.