Abstract
A new approach based on the direct spectral method for fatigue analysis of elements subjected to bimodal stress histories, including high compression effects, is proposed. A correction factor, taking into account the influence of the mean compressive stresses, is used in the proposed method. Equivalent amplitude is estimated, based on criteria proposed by Smith, Watson, and Tooper, and by Bergmann and Seeger. The method is presented with example of a thrust roller bearing. Two cases in which the rollers were subjected to constant force 206 N (where constant amplitude stresses occurred in the rollers) and cyclic force (where bimodal stresses with variable amplitudes occurred in the rollers) are studied. It is observed that multiaxial fatigue criteria (Crossland, Papadopoulos) do not include the influence of bimodal stresses and should not be used for such loading conditions. The proposed method includes both kinds of stress waveforms in the fatigue analysis and can be applied for the accurate identification of stress components and the determination of fatigue life. The damage rate calculated by the proposed approach for rollers subjected to a cyclic force (equivalent load equal to 151 N) was 0.86, which is in good agreement with the recommendations provided in the literature. The obtained accuracy of the proposed method is above 95%.
Highlights
Fatigue loading was determined based on the assumption that the fatigue life of the bearing should be equal to 1 million rotations of the bearing at a 90% rating life
The modified spectral method was proposed in this paper and successfully applied to the analysis of a roller bearing subjected to constant and cyclic force
Multiaxial high-cycle fatigue criteria cannot be applied for an analysis in which stresses do not have constant amplitude waveforms
Summary
Analyses of fatigue strength or remaining service life of mechanical components that are subjected to cyclic loading are essential for safety and economic reasons [1,2]. Fatigue failures are caused by random, repetitive, or cyclic loads that are generally significantly lower than loadings that would lead to the plastic deformation of the material. The applied fatigue loads may be uniaxial (with one stress component), biaxial (with two stress components), or multiaxial (with more than two stress components) [9,10,11]. In the case of uniaxial random loadings, classical methods such as rainflow counting, cumulative damage models, and S-N curves can be used [10]
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