Fatigue initiation in heterogeneous brittle materials
Résumé
The fatigue process can be schematically divided into an initiation stage and the propagation period. In this paper, we consider brittle materials where only the initiation phase needs to be studied, since the propagation is always unstable. We suppose that the initiation is due to some initial randomly distributed defects that grow according to a generalized Paris' law and become critical for a given number of cycles and for a given load level (characterized by a maximum equivalent stress over a cycle). The purpose of this paper is to present a statistical approach of the initiation stage in fatigue derived from a unified framework of the failure probability in the case of monotonic and cyclic loadings. We will show in particular that the iso-probability curves in a Woehler diagram, have a shape which is independent of the initial statistical distribution of defects. Applications of this study are to be found in the case of engineering ceramics.
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