Model for Fatigue Life Prediction on Auto Parts Based on Stress Equivalence Relation
For predicting the fatigue life of auto parts under multi-stage stress loading,the existing nonlinear models usually need to rely on a large number of test data,or it is difficult to select a suitable reference value,which makes the application of fatigue reliability theory in automotive field has certain limitation.Due to this issue,a fatigue damage transformation process between two stage stresses is analyzed based on the fatigue life characteristic curve of material.Then a relationship considering equivalent transformation of adjacent loads is established.The equivalent formula of fatigue cumulative damage and the expression of residual fatigue life between adjacent stresses under two-,three-,and higher-stage stress are derived.Then a fatigue life prediction model based on stress equivalence relation is proposed.The calculation process of proposed model requires only the fatigue life test result of the material with no less than two sage stresses.Existing two-,three-,four-,and five-stage stress loading test data are used for verification.The average and maximum relative errors of Miner model,Manson model,Subramanyan model,Hashin model,and the proposed model are calculated and compared respectively.Furthermore,the predicted result of fatigue cumulative damage and fatigue cumulative life,and the distribution of difference between fatigue cumulative damage and test cumulative damage predicted by each model are summarized under two-to five-stage stress.The result indicates that the proposed model based on equivalent transformation of adjacent loads has better overall fatigue life prediction result than Miner model,Manson model,Subramanyan model,and Hashin model.That can be more accurately applied to the fatigue life/damage prediction under multi-stage stress.
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