Manufacturing process effects on fatigue design and optimization of automotive components: An analytical and experimental study

Numerous fatigue-critical parts could be found in ground vehicles, and time-varying loads have always challenged automotive designers. Fatigue design and life assessment of these components are essentially influenced by the material used and manufacturing processes chosen. Exploring the design criteria and optimization potentials with respect to manufacturing processes is vital to the industry.; This study was aimed at developing general procedures for fatigue analysis and optimization of safety-critical automotive components with manufacturing considerations. A literature survey was conducted, specimen and component tests were performed, and finite element stress analysis and durability and optimization evaluations of similar components produced by different manufacturing technologies were made to achieve the objectives. The typical example component chosen was a vehicle steering knuckle made of three competing materials and manufacturing processes including forged steel, cast aluminum and cast iron.; In the literature survey, manufacturing processes were studied and compared with focus on mechanical behavior. The methods used in the literature for fatigue life evaluation and prediction of automotive components, as well as for optimization studies with respect to geometry, material and manufacturing aspects were also reviewed. Specimen strain-controlled tests were conducted to obtain material monotonic and cyclic deformation and fatigue properties. Components' fatigue behaviors were investigated via constant-amplitude load-controlled fatigue tests. Comparisons of materials monotonic and fatigue properties, and components' fatigue behaviors were made for competing material and manufacturing processes. In terms of structural performance and durability, based on both material testing and component evaluation, forged steel was found superior to cast iron which in turn was found superior to cast aluminum.; Finite element models of the components were analyzed, using linear and nonlinear stress analyses. The nominal stress and local stress and strain approaches were employed to assess durability of the components. Experimental and analytical stress and fatigue life results were compared to evaluate the validity of the analytical approaches. The strength and shortages of the applied models and alternative analyses were also investigated. It was concluded that the local life prediction approaches in combination with either nonlinear finite element analysis results, or linear finite element analysis results corrected for local plasticity, yielded satisfactory predictions.; A procedure was developed to optimize forged automotive components for weight reduction and cost savings with fatigue strength as the key performance indicator. (Abstract shortened by UMI.)...