Erstellung einer geschlossenen Simulationskette zur Optimierung der Schwingfestigkeit von geschmiedeten Bauteilen aus Nickelbasislegierungen

Translated title of the contribution: Generating a closed simulation chain for optimizing the fatigue strength of forged components made of nickel-based alloys

Hermann Maderbacher

Research output: ThesisDoctoral Thesis


To ensure an ever-decreasing cost and time spent concerning development cycle together with increasing reliability and energy efficiency, not only different loading scenarios but also whole manufacturing processes are simulated virtually today. Thereby, the long term aim is the ability to describe the whole manufacturing and design process in an integrated simulation chain, starting from the raw material, followed by the component design and all the relevant manufacturing steps up to the fatigue endurance calculation under real loads. Once this simulation chain is available, manufacturing parameters can be adjusted in a way using reverse engineering and optimization tools so that they have the most positive effect on the desired thermal and mechanical behavior. Heavy duty aircraft components are often produced in hot forging process to meet the demanding requirements of the aerospace industry. Here the titanium alloy Ti6Al4V and the nickel based superalloy Inconel®718 can often be found, depending on whether high strength at low density, or high temperature strength are required. By a forging and subsequent heat treatment process not only a component with complex geometry near the final shape can be produced; additionally the mechanical properties, in this case with the focus on the fatigue endurance, can be influenced systematically through the strong process dependence of the resulting microstructure. In the present work tools for an integrated simulation chain of hot forged aerospace components have been developed and already existing ones have been expanded. Thereby it is possible to generate a component in a topology and shape optimization which possesses maximum rigidity with minimum weight. In a subsequent step a special microstructure can be provided for the optimized geometry which promises the best local fatigue endurance by optimizing the forging and heat treatment process. Therefore an interface between the software for forging simulation and an optimizer has been created, whereby a plurality of forging and heat treatment parameters can be optimized in terms of fatigue. To provide a link between fatigue-, forging- and heat-treatment-parameters, ensuring optimization possibilities, an understanding of the relationship of two key elements is of great importance. The first element is the dependency of the microstructure from the forging- and heat treatment process, for which a microstructure model is required that is valid over a wide temperature, strain range and strain rate. The second element has to enable the description of the influence of the microstructure on the local fatigue strength to allow for the prediction of local SN-curves. While microstructure models for both alloys and a microstructure dependant SN-curve model for Ti6Al4V are already available at Böhler Schmiedetechnik GmbH & Co KG, the development of a microstructure dependent SN-curve model for Inconel®718 is a major part of this work. Numerous micrographs and fracture surfaces of forged components were analyzed and compared with the results of fatigue tests to get a temperature and microstructure dependent SN-curve model. Using statistical evaluation methods, these microstructure parameters were isolated from numerous investigated ones, for which a significant correlation with fatigue lifetime was found. The SN-curve model has been described in terms of formulas as a function of operating temperature and relevant microstructure parameters. To close the optimization loop, a postprocessor is used developed by Böhler Schmiedetechnik GmbH & Co KG. Besides others, it takes the results from topology- and shape-optimization as well as these from forging- and heat-treatment-optimization as an input. This postprocessor enables the lifetime calculation of components optimized concerning fatigue under consideration of influences like the local microstructure dependent fatigue endurance and
Translated title of the contributionGenerating a closed simulation chain for optimizing the fatigue strength of forged components made of nickel-based alloys
Original languageGerman
  • Grün, Florian, Assessor A (internal)
  • Buchmayr, Bruno, Assessor B (internal)
Publication statusPublished - 2013

Bibliographical note

no embargo


  • Fatigue strength
  • S/N-curve model
  • titanium alloy
  • nickel-based alloy
  • forging process
  • aircraft engineering
  • optimization

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