Variability Of Fatigue Simulation Predictions For Automotive Components

SUMMARY & CONCLUSIONSModern automotive industry has an extremely challenging business development plan. The advent of the electric autonomous car have to cope with the historical constraints (high volume, low margin, shorter product development time).The standard to validate the design of automotive component was obtained through an iterative process that strongly relies on Finite Element Analysis (FEA) results. The mechanical endurance was typically evaluated according to rather conservative criteria based on the material's ultimate tensile strength (UTS), and basically targeting an infinite fatigue life endurance. For many years, this degree of conservatism permitted a quicker design validation without incurring in unexpected design related field failure (warranty failures).However, since a decade, this approach has revealed to be outdated in relation to a highly competitive market, where automotive components have to be designed with the goal of downsizing and design to cost. Their durability needs to be verified by tailored accelerated life tests based on a fatigue design criterion.Particularly for vibration, the validation concerns relatively complex systems (multi-materials components, prototype parts, representative system integration) in the high cyclic fatigue domain: rig tests are long, expensive and the results subject to high variability.From a component supplier perspective, the goal is to rely on FEA as early as possible even before the official nomination (e.g. "request for quotation" phase) .For this reason, we have developed methods & tools for a more tailored approach, where the design is validated by FEA simulations based on vibration fatigue criteria.In this framework, the risk related to the variability of the fatigue life results, associated to the range of the values of the chose model parameters) needs to be evaluated, so that it is possible to quantify the uncertainty of the estimated reliability.In this study we have investigated the influence of the simulation parameters (damping, rubber mount stiffness, and material parameters of plastic materials, Basquin coefficient, temperature, and amplitude) on the calculated fatigue life of engine cooling modules (ECM) undergoing vibration validation tests. The goal is to evaluate the effect of the simulation parameters on the component fatigue life predictions, as well as quantifying the "damage life margins" resulting from boundary limits of those parameters.