Study on the accumulative fatigue damage rules under multiaxial two‐stage step spectra constructed by loadings with similar lives

Abstract

In this paper, the influence on the multiaxial fatigue damage accumulation caused by loading path variation was studied. For 2024‐T4 aluminium alloy, the damage evolution during the entire life was first observed. On the basis of the observation, the stage I of fatigue damage evolution was further divided into two sub‐stages, and the dominant stress parameters of these two sub‐stages were proposed. Taking the dominant stress parameters into account, a phased accumulative fatigue damage model was proposed. Then, 12 multiaxial two‐stage step spectra constructed by loadings with approximately identical fatigue lives were carried out on 2024‐T4 aluminium alloy. The accumulative fatigue damage was calculated by the proposed model, and another five commonly used models and the calculated results were compared. According to the comparison, the newly proposed model had the most accurate results with the smallest scatter.

A novel accumulative fatigue damage model for multiaxial step spectrum considering the variations of loading amplitude and loading path

“…In Ref. , the average accumulative damage is 0.973, and the standard deviation is 0.107. Now, after introducing the non‐piecewise dominant stress and two additional samples, the calculated result gets a little worse.…”

“…In Ref. [21], the average accumulative damage is 0.973, and the standard deviation is 0.107. Now, after introducing the non-piecewise dominant stress and two Although the deviation to 1 becomes slightly larger, the new model is much easier to be applied than the old version, after taking into account that there is no need to make a choice before the application.…”

“…In Ref. , for the fully reversed multiaxial fatigue loadings, a dominant normal stress, in which the normal stress and shear stress on the critical plane are combined with a weighted square root, is proposed: where τ CP,a is shear stress amplitude on the critical plane, σ CP,a is the normal stress amplitude on the critical plane, σ −1 and τ −1 are the uniaxial fatigue limit and torsional fatigue limit, with R = −1, respectively. Using Taylor's expansion, Eq.…”

“…In Ref. [21], for the fully reversed multiaxial fatigue loadings, a dominant normal stress, in which the normal stress and shear stress on the critical plane are combined with a weighted square root, is proposed:…”

The design of durability tests by fatigue damage spectrum approach

“…The fatigue damage evaluation related to mechanical systems or components subjected to variable amplitude loadings and, in particular, to dynamic ones is an argument of actual interest for the scientific community that works on fatigue design. [1][2][3] For these loading conditions, both random loads (ie, inputs) and multiaxial stress state conditions (ie, outputs) are subjects of great interest. Avoiding to analyze the outputs in terms of stress state and focusing on the inputs, two are the principal aims of the present activity.…”