Fatigue Design and Experimentations with Variable Amplitude Loadings in the Automotive Industry

Abstract

The paper presented gives an overview of the various problems that should be addressed to take into account the variable amplitude loadings undergone by the car components. One of the most important point is that all the steps of the design procedure (including experiments and computations) should be consistent with each other in terms of damage. For some reasons (efficiency, robustness, capitalization,…), variable amplitude loading may be converted into damage equivalent loadings. Tools such as cycle counting ,damage summation including the mean value effect and rainflow extrapolation are therefore necessary. The paper shows how single component and full scale tests are related with both customer and test track measurements, and how these experimental data are correlated with predictive fatigue computations, including the statistical aspects for reliability purpose. The paper will illustrate that if the consistency mentioned above is guaranteed, then the variable amplitude fatigue computation (such as the ones proposed in commercial codes) is no longer useful. It requires therefore an analysis of the material behavior under variable amplitude loadings in the automotive context. One of the most important advantage of this approach is that under simple assumptions, the computations can be realized before any prototype could be driven on a track. It allows to shorten the developments delays. These assessments will be illustrated by various examples showing how the loadings are analyzed in the measurements stages, and how they are applied in the experimental and computation stages.

Fatigue design of railway wheels: a probabilistic approach

“…The constructed severity distribution can be viewed as a probability density function. In order to evaluate the probability of fatigue failure, the 'stress-strength' method 11,38 is used.…”

Teaching durability in automotive applications using a reliability approach

“…This equivalent loading is chosen to produce the same fatigue damage than the vehicle will support in its whole life. The methodology is developed in ref [1,2]. Meanwhile, the component strength distribution is estimated through production surveys on similar components with the same fabrication process.…”

“…In the Education and Research Campus at Angers, the choice was made to present a comprehensive fatigue assessment approach using a probabilistic method, initially developed in the automotive industry and since extended to the aeronautical and mechanical industries. This method is known as the "stress-strength interference analysis" [1]. The "stress" represents the distribution of the driver severity; the "strength" the distribution of the fatigue strength of all the components.…”

Computational fatigue assessment of mooring chains under tension loading

“…The discussion presented next is dedicated to Tensile loading of the mooring chains. However, the generality of the proposed method permits a similar analysis of other loading conditions, such as Out-of-Plane Bending, as well as the extension to variable loading using a stress-resistance approach [35][36][37].…”