Fatigue life prediction under variable amplitude loading using a non-linear damage accumulation model

Most of engineering components in service are usually subjected to variable cyclic loading. It is important to predict fatigue life and deal with the issue about fatigue damage accumulation for these components. One of the largest difficulties in fatigue failure analysis is to find a representative ‘damage criterion’ which can be easily connected with the Wöhler curve taken as the known material data. The most commonly used model is the Miner’s rule which ignores the loading history effect, under the same loading conditions the experimental results are higher than the Miner expectations for low-to-high load sequence and are lower than the Miner expectations for high-to-low load sequence. The fatigue driving stress that causes fatigue damage is presented to predict residual fatigue life under variable amplitude loading. It increases with loading cycles until equals the fatigue strength when fracture occurs. By determining the equivalent number of cycles that yields the same fatigue driving stress as the previous loads, the remaining life can be predicted. The proposed damage criterion is connected cycle by cycle to the Wöhler curve and the experimental results are in a good agreement with the model predictions.