To achieve the goal a new approach was developed in order to allow a reliable design even in the design phase and to shorten the development time. On two examples - a suspension arm and a wheel - the procedure was demonstrated and validated. This simultaneous approach combines the following main subjects:
- Determination of data concerning operational loading
- Derivation of operational stress spectra on components (measured and calculated)
- Fatigue life validation data under operational conditions
- Influence of material, manufacturing quality and joining technique on fatigue life
- Calculation procedure to determine the fatigue life of components for optimal design
- Evaluation of quality assurance measures.
On the example of a light-weight sports car, the Ferrari Testarossa F110, all decisive data were analyzed including extensive road measurements. The programmes of existing multiaxial test rigs were adjusted accordingly and design optimisations on a suspension arm and a wheel were executed by means of validation tests. Design variations were investigated by Fine-Element Calculations, which were validated by experimental stress analysis according to the different boundary conditions. Fatigue life data were determined by load spectrum tests on light alloy sheet-components manufactured by different joining technique. Based on achieved data and results the procedure for fatigue life estimation is worked out and the quality assurance requirements derived.
Modern calculation methods like FE-Method are often used to calculate global and local stresses on components. For an optimal design of highly stressed, safety components of vehicle suspensions decisive data are lacking : the accuracy of mathematical calculation methods, the knowledge about the fatigue life prediction under random service loading and the corresponding allowable stresses, which depend on load spectra, material and manufacturing process, are very limited. Especially for welded light alloy components, which are often used due to their economical and ecological advantages (low weight, energy saving, high recycling potential) no appropriate data for light weight design are available. In a combined approach the required data for a mathematical stess calculation shall be evaluated by means of experimental analysis. Fatigue tests under operational loading are used to derive the allowable stresses in order to adjust the calculation method. The procedure and data will provide a reliable and cost-effective design already in the development stage and an assessment of optimum welding parameters. Due to the detailed knowledge of allowable stress and failure criteria for complex stressed components a specific quality assurance can be carried out, which significantly will improve the reliability in service.
Funding SchemeCSC - Cost-sharing contracts
30030 Caltana Venezia