The Paper describes a vehicle steering knuckle under time-varying load during its service life.Fatigue behavior is, therefore, a key consideration in its design and performance evaluation. This paper is aimed at assessing fatigue life and compare fatigue performance of steering knuckles made from three materials of different manufacturing processes. These include forged steel, cast aluminum, and cast iron knuckles. In light of the high volume of forged steel vehicle components, the forging process was considered as base for investigation. Monotonic and strain-controlled fatigue tests of specimens machined from the three knuckles were conducted. Static as well as baseline cyclic deformation and fatigue properties were obtained and compared. The paper envisages that in addition, a number of load-controlled fatigue component tests were conducted for the forged steel and cast aluminum knuckles. Finite element models of the steering knuckles were also analyzed to obtain stress distributions in each component.
[...] It was found that except for the case of precise geometries of the three steering knuckles, fixing the bolt holes, for which the value of a Coordinate Measuring Machine (CMM) was stress was lower and the critical location was used, with the resulting digitized models as different, all the other three cases provided presented in Figure 1. approximately similar results. Therefore, the choice of fixing the hub bolt hole-centerlines was selected. For the cast iron knuckle, where the geometry and service conditions are close to the cast aluminum knuckle, similar loading and boundary conditions were applied. [...]
[...] In the high-cycle regime, forged steel resulted in about an order of magnitude longer life than the cast iron, and about a factor of 3 longer life, compared to the cast aluminum The differences between measured and FEA predicted strains obtained for the forged steel and cast aluminum knuckles were found to be reasonable for the complex knuckle geometries considered Component testing results showed the forged steel knuckle to have about two orders of magnitude longer life than the cast aluminum knuckle, for the same stress amplitude level. [...]
[...] A., “Durability Design Process of a Vehicle Suspension Component,” Journal of Testing and Evaluation, Vol pp. 354- Beranger, A. S., Berard, J. Y., and Vittori, J. F., Fatigue Life Assessment Methodology for Automotive Components,” Fatigue Design of Components, ESIS Publication 22, Proceedings of the Second International Symposium on Fatigue Design, FD'95, 5-8 September Helsinki, Finland, Marquis, G., Solin, J., Eds pp. 17- Conle, F. A. and Chu, C. C., “Fatigue Analysis and the Local Stress-Strain Approach in Complex Vehicular Structures,” International Journal of Fatigue, Vol No pp. S317-S Savaidis, G., “Analysis of Fatigue [...]
[...] The Basquin equation was then COMPARISONS OF FATIGUE BEHAVIORS PREDICTIONS COMPONENT AND LIFE Manufacturing process, such as forging or casting, generally determines the strength level and scatter of mechanical properties, but the geometry can suppress the influence of the material, as indicated by Berger et al. According to Sonsino et al. for a complex component geometry where no notch factors could be used to obtain the fatigue life using the material properties listed in Table σNf = σ'f(2Nf)b Normally, a surface finish reduction factor is applied to the fatigue strength of a component. [...]
[...] A problem that arises at the fatigue design stage of components is the transferability of data from smooth specimens to the component. The component geometry and surface specifications often deviate from that of the specimen investigated and neither a nominal stress nor a notch factor can be defined in most cases. Gunnarson at al investigated replacing conventional forged quenched and tempered steel with precipitation hardened pearlitic ferritic cast steels. They also compared toughness and machinability characteristics of forging versus casting components. [...]
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