Study of the Fatigue Life and Weight Optimization of an Automobile Aluminium Alloy Part under Random Road Excitation

A Saoudi,D Marceau,M Bouazara

doi:10.1155/2010/845609

Abstract

Weight optimization of aluminium alloy automobile parts reduces their weight while maintaining their natural frequency away from the frequency range of the power spectral density (PSD) that describes the roadway profile. We present our algorithm developed to optimize the weight of an aluminium alloy sample relative to its fatigue life. This new method reduces calculation time; It takes into account the multipoint excitation signal shifted in time, giving a tangle of the constraint signals of the material mesh elements; It also reduces programming costs. We model an aluminium alloy lower vehicle suspension arm under real conditions. The natural frequencies of the part are inversely proportional to the mass and proportional to flexural stiffness, and assumed to be invariable during the process of optimization. The objective function developed in this study is linked directly to the notion of fatigue. The method identifies elements that have less than 10% of the fatigue life of the part's critical element. We achieved a weight loss of 5 to 11% by removing the identified elements following the first iteration.

Highlights

We examine the fatigue life and weight optimization of a real, complex aluminium alloy part: the lower suspension arm of a vehicle, an essential component of the suspension system
Haiba et al [1] have developed an objective function to optimize the weight of a mechanical component without affecting natural frequencies and fatigue life distribution
Elmarakbi et al [2] used an energy model taking into consideration two parameters: stress and strain. They studied the validity of the multiaxial fatigue criterion based on strain energy density, but did not propose a rejection ratio for weight optimization

Summary

Introduction

We examine the fatigue life and weight optimization of a real, complex aluminium alloy part: the lower suspension arm of a vehicle, an essential component of the suspension system. Haiba et al [1] have developed an objective function to optimize the weight of a mechanical component without affecting natural frequencies and fatigue life distribution. Elmarakbi et al [2] used an energy model taking into consideration two parameters: stress and strain They studied the validity of the multiaxial fatigue criterion based on strain energy density, but did not propose a rejection ratio for weight optimization. Instead, they provided a model to assess the predictive capabilities of several theories of multiaxial fatigue, such as bending, twisting or testing combinations of flexion-torsion made by SAE (Society of Automotive Engineers). The model developed in this study is based on vertical motion and road excitation

Road profile model development

Elasto-plastic numerical model development

Development of optimization algorithm based on strain energy density

Findings

Conclusion