Fatigue maps and multistage life prediction methods

Various methods have been recently developed for life prediction under creep-fatigue conditions. This study is concerned with continuous damage models. In particular, a model developed at ONERA, which evaluates the creep and fatigue contributions separately and which sums the corresponding differential damage, has been used for fitting the high-temperature experimental data for IN 738 test bars. The data were taken both from the literature and from our own tests. In addition, it was found that the model can also be used to derive schematic fatigue maps. Following the introduction of Ashby maps for creep, several other maps have been proposed for fatigue. However, the task for fatigue maps is more difficult to define. This work presents a discussion of the whole problem, a review of existing proposals, and some indicative maps that have been obtained for IN 100. Even though the approach appears to be promising for outlining approximate fatigue maps, metallographic observations are still a necessary complement for mapping single domains where given microstructural mechanisms are predominant.