Abstract
Most fatigue theories neglect the loads below fatigue limit in damage accumulation, which leads to inconsistency between the predicted and the actual fatigue lives. In this study, a novel damage model is proposed to take into account the loads below fatigue limit from two aspects: the strengthening effect and the cumulative damage. The strengthening effect is introduced by an exponential function and the cumulative damage is calculated by fuzzy method with membership functions (MFs). The proposed model is verified against the experimental data under variable amplitude loading conditions. It is found the modified model with Cauchy MF significantly reduces the relative error of predicted life from 35.18% (linear model) and 16.09% (original Chaboche model) to 8.38% (proposed model). As a case study, the proposed damage model is implemented to evaluate the service life of a compressor blade under variable amplitude loading spectrum containing small loads below the fatigue limit.
Highlights
Over the past few decades of fatigue damage research, it is found that damage accumulation depends on loading parameters, such as the stress ratio, the mean stress and the loading sequence [1].So the Miner’s linear damage rule [2] is inevitable to miscalculate fatigue life due to the assumption that the cumulative damage per cycle is independent of load
It can be seen that the Wöhler model provides the longest life prediction with the lowest accuracy, the Wöhler model and the Leipholz’s model show better results but the predictions are still over-optimistic
The Chaboche model accounts the interaction between the loading parameters and the damage accumulation, and considers the influences of the loading sequence and the load below the fatigue limit
Summary
Over the past few decades of fatigue damage research, it is found that damage accumulation depends on loading parameters, such as the stress ratio, the mean stress and the loading sequence [1]. Sosnovskiy [12] analysed the concept of entropy in continuum mechanics and thermodynamics to study the tribo-fatigue and a nonlinear damage model is developed regarding the damage accumulation as an irreversible process [13,14,15] These sorts of damage model consider the correlation between loading parameters and cumulative damage [16,17]. In order to study the influence of the strengthening effect on damage behaviour, Zhu [27] proposed a modified linear rule on the basis of the S–N curve so the loads below the fatigue limit cannot be calculated. A modified damage model is proposed to consider the effect caused by the low-amplitude loading cycles below the fatigue limit on the damage accumulation. The fatigue life of an aero-engine compressor blade is evaluated using the actual loading spectrum
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