A stochastic approach to damage evolution in die-cast zinc alloys

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The goal of the proposed research project is to develop a method for predicting the influence of material damage and mechanical load on the life expectation of a typical industrial component. Exemplarily we consider window hardware made of ZAMAK, a zinc alloy which is typically die-cast and widely used for load-bearing parts. New designs, like large glass facades and hidden pivot architecture, require these parts to be small but safe over a long period of time.In the first funding period we focused on the microstructure of the ZAMAK alloy and studied the evolution of defects as a result of fluctuations and deterministic mechanical stresses.In the advised second funding period we scrutinize the structural response of the die-cast component under effects of distributed defects in the material and of uncertain loading conditions. Despite of the widespread use there are only few reliable data available regarding the long term behavior of ZAMAK components. The very high mechanical properties diminish in the course of the component's life. This motivates us to study the loss of mechanical strength in ZAMAK as a result of distributed defects in the material and of uncertain loading conditions. Especially the misuse of the window components in certain situations and the resulting high stresses under uncertain inputs will be considered in this project. To achieve this we will employ a multi-fidelity sampling-based approach.The general idea of incorporating models with different levels of fidelity is based on the definition of surrogate low-fidelity models. Most of the sampling is then done with these cheap, approximate models. To account for the discrepancy between the low-fidelity and the real, high-fidelity solution, a Bayesian regression is employed on a training sample. Then it is possible to use the correlation to gain a probability of the failure within the high-fidelity model.Summarizing we state that uncertain material properties, environmental effects, perturbations in the production process combined with uncertain loading conditions results in a large variations of limit loads and life-expectation of die-cast ZAMAK components.As the result of this research the decay of ZAMAK's mechanical strength andload carrying capacity will be predicted. Prediction is meant here in the sense that incomplete and uncertain information about the problem is accounted for and that probability distributions or error bars on mean values are provided as simulation results.