On the estimation of finite lifetime under fretting fatigue loading
2018
The aim of this paper is to formulate and validate an alternative design approach suitable for
predicting finite lifetime of mechanical assemblies subjected to constant amplitude (CA) fretting
fatigue loading. The design methodology being proposed is based on the use of the Modified Wӧhler
Curve Method (MWCM) applied in conjunction with both the Theory of Critical Distance (TCD) and
the Shear Stress-Maximum Variance Method (τ-MVM). In more detail, the TCD, applied in the form
of the Point Method (PM), is used to take into account the damaging effect of the multiaxial stress
gradients acting on the material in the vicinity of the contact region. The time-variable linear-elastic
stress state at the critical locations is then post-processed according to the MWCM which is a biparametrical
criterion that estimates fatigue lifetime via the stress components relative to those
planes experiencing the maximum shear stress amplitude. Thanks to its specific features, the MWCM
is capable of modelling not only the presence of non-zero mean stresses, but also the degree of
multiaxiality and non-proportionality of the local load history being investigated. In this setting, the
τ-MVM is used to calculate the stress quantities relative to the critical plane whose orientation is
determined numerically by locating that plane containing the direction experiencing the maximum
variance of the resolved shear stress. The accuracy and reliability of the proposed design
methodology was checked against a number of experimental data taken from the literature and
generated by testing four different metallic materials. The agreement between experiments and
estimates being obtained strongly supports the idea that the proposed approach can be used to
perform a rapid assessment of mechanical assemblies damaged by in-service fretting fatigue loading.
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