Seleção de material para manga de eixo de um veículo fora de estrada

Abstract

The steering knuckle is a highly critical automotive suspension component, given that multiple forces load it and, as a part of the unsprung mass of the vehicle, it is desirable to have the lowest weight as possible. In this context, knuckle's material choice will directly influence the accomplishment of the project's requirements and objectives. Due to the great variety of materials available, multi-criteria decision methods (MCDMs) have been used in determining the most appropriate option. Therefore, this work aims to select a material for an off-road vehicle's steering knuckle, based on technical and economic criteria. The study was based on a Baja prototype by the "Pato BAJA" team from UTFPR - Pato Branco campus. The selection started in the definition of the design requirements, which consisted of yield strength, stiffness, fatigue strength, specific mass, and cost. Computational simulations via the finite element method were performed to estimate the minimum yield stress, which resulted in 238 MPa. From an initial set of 3600 materials, it was excluded all options whose specific mass and cost were higher than 3.0 g/cm³ and 50% those of the original material (Al 7075-T651), respectively, resulting in 126 pre-selected materials. One candidate from each alloy family was chosen based on the following criteria: 1°) higher fatigue strength/ρ; 2°) higher toughness/ρ and 3°) lower cost (R$/kg). Then, the finalists were classified by Analytic Hierarchy Process (AHP) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) methods. The three best-evaluated alloys were Al 206.0-T7, Mg ZC71, and Al 6111-T62. Aluminum alloy 206.0-T7, the best-ranked candidate, has a similar density to 7075-T651, with the advantage of having a higher resistance to fatigue, toughness and ductility, besides being cheaper.