Multi-parameter fatigue equivalence loadings for specification applications

This paper deals with a method to define Equivalent Fatigue Loads (EFL) from in-service load measurement in the case of a structure subjected to multiple variable fatigue loadings. EFL can be used in order to define tests on full scale structures for an experimental validation approach. It can be also used for the evaluation of the severity of the in-service loads, useful step in a reliability approach, in order to optimize the geometry with respect to the fatigue damage. The aim of the paper is to define the mathematical and mechanical concept of the Equivalence Fatigue Method in the case of multi-parameters loading for specification application. This method uses fatigue damage evaluation from statistical in-service measurement data. The specificity of the method presented here is to use a fully multi-parameters equivalence method. Damages is evaluated using life prediction method based on multiaxial criteria. The method is used for rotating structures, applied to a specific family of structure: train wheels. Train wheels are critical safety railway components mainly subjected to random multiaxial fatigue induced by multi-parameters loading. In this paper an approach to evaluate damage from this measurement in order to find the EFL with a damage equivalence optimization is developed.