Abstract: Accurately estimating the fatigue life is critical to reliability and lightweight design of automobile parts. But the lives predicted based on existing methods under service loading histories are usually conservative, for which considers load will only cause damage. However, researches show that specific loads under fatigue limit are of strengthening effect on fatigue strength. Therefore, a fatigue life prediction method which takes into account the strengthening effect of loads below fatigue limit is proposed based on Miner’s rule. In this method, the process of fatigue life prediction is divided into two parts, and the damaging and strengthening effect of loads below fatigue limit are considered separately. And the relationship between strengthening effect and strengthening load and their reversals are simplified by linearization. Taking rear axle of automobile as an example, fatigue life is predicted by this new method and traditional Miner’s rule. Comparing with the lives of fatigue tests on road load simulator, results show that this new method is of higher accuracy.

Key words: Fatigue life, Fatigue strength, Load spectrum, Low-amplitude-load strengthening, Rear axle