Sequential law in multiaxial fatigue, a new damage indicator

One of the largest difficulties in fatigue damage is to find a representative 'Damage indicator' which can be easily connected with the Wohler curve taken as known data of the material. The most used model is the Miner's rule but this does not take into account the loading history, so for the same loading level the experimental results are higher than the Miner expectations for increasing loading and are lower than the Miner expectations for decreasing loading. The proposed damage indicator is connected cycle by cycle to the Wohler curve and the experimental results are in agreement with model expectations. We define a damage stress as the stress corresponding to, on the S-N curve, the instantaneous residual life. The active stress can be taken as the equivalent von Mises stress and the instantaneous fatigue can be taken from different multiaxial models. The damage is reported from one level of stress to the other and the damage stress goes to the ultimate stress at the last cycle before failure. (C) 2004 Elsevier Ltd. All rights reserved.