Nouvelle méthodologie d’essais en fatigue des matériaux en vue de vérifier des lois de cumul d’endommagement

A new methodology of tests to verify the cumulative damage laws in fatigue of metals

Laboratoire d'Application de Méthodes et d'Essais à la Fatigue LAMEF-ENSAM, Esplanade des Arts et Métiers, Talence.

Abstract

The great scatter in fatigue lives and the complexity of their distribution make the verification of damage theories and cumulative damage laws, in the crack initiation field, difficult.

In order to solve this problem, we made partitions, from sets of specimens chosen at random, with regard to specimens performances in several loading conditions. We suppose that the best specimens resist at a loading level, the best they will resist at another one.

After tests, we formed “usable classes” : for each class, the lives distribution is identified, and a mean specimen is considered representative of the class number i for several loadings.

The method was tested with success to define the Wöhler’s curves (S-N) related to the classes of a sample and to determine the remaining life ratio at a second level, after a first one.