Abstract: Based on real vehicle test on the proving ground, combining with the finite element dynamic simulation and fatigue durability simulation of components, the difference of fatigue life prediction of automobile components with the consideration of small load strengthening effect and Miner criterion is explored in the paper. Fatigue damage risk point of the front knuckle (the road test strain monitoring point) is determined by joint analysis of indoor vehicle vibration test and finite element simulation; the strain time history of strain monitoring points of strengthened road on the proving ground is acquired, after pretreatment, time domain acceleration, extrapolation of rain flow matrix and load spectrum classification, ten-grade equivalent stress spectrum is obtained. Combining with the low load strengthening theory and the linear cumulative damage theory, the fatigue effect and damage effect of the ten-grade equivalent stress spectrum are analyzed, in contrast to the traditional Miner criteria, considering the strengthening effect of small load on the increase of the fatigue limit of the component in the process of loading, the component S-N (simplified) curve needs to be modified, offset upward from the initial S-N curve. The predicted fatigue life of the knuckle based on the modified S-N curve and linear fatigue damage accumulation theory is 40.6% higher than that of the Miner criterion. Taking into account of the effect of material strengthening behavior, this method makes up for the defect of the Miner theory which does not take into account of the interaction between different loads and the effect of material hardening transient behavior to a certain extent, and provides a new reference for fatigue life estimation and lightweight design of real components

Key words: fatigue damage, small load strengthening, Miner rule, steering knuckle, load spectrum