Consistent implementation of sustainable designs and resource and energy efficiency means that components of machines and systems are becoming more complex and their thermal and mechanical loads are increasing. Trial-and-error in the design of the manufacturing process and the testing of prototypes in bench tests are time-consuming and expensive. Through intelligent use of digital tools and simulation methods such as the finite element method, manufacturing processes can be optimized and service loads can be tested on virtual prototypes in the computer. This leads not only to a better understanding of the loading of components and materials, but also to a reduction in development time and costs. In addition, a digital twin of the real component is created, which carries all the information from production and operation and thus enables a forward-looking strategy for efficient use.

In the research and development projects of Professor Dr.-Ing. Thomas Seifert, advanced simulation methods and tools for virtual component development and the digital twin are being developed for practical use now and in the future. The focus is on the material with its thermal and mechanical properties, as it is usually in the spotlight in case of component failure. By improving the description of the material behavior in the simulations, the relevant damage mechanisms can be identified on the virtual prototype. Via "computer experiments", the component design and material selection can be iteratively adapted to the load at hand. The result: resource- and energy-efficient, safe and reliable as well as competitive components for machines and systems.

Professor Seifert supervises the following ongoing projects:

→ Professor Seifert's research group on ResearchGate

Digital tools for improving electroplated coating using the example of chromium(III)-based processes (DigiChrom) - Simulation-based characterization of coatings (BMBF project)

Project duration: 1.12.2023 to 30.11.2026

In technical applications, experimental trial and error approaches are usually used to optimize an electroplated coating system. However, electroplated coatings have complex process-structure-property relationships, the experimental investigation of which is very time-consuming and provides only limited information. Simulations can be used to obtain information on material behaviour that is not accessible experimentally or only with great effort, such as local stress and strain distributions in inhomogeneous microstructures and interfacial stresses that are relevant for the optimization of coating systems. Therefore, the combination of experiments and simulations and the application of digital methods such as machine learning and ontologies offers the possibility to systematically investigate and explicitly demonstrate process-structure-property relationships and to develop new ones from existing relationships. In this project on simulation-based characterization of coatings, which is part of a joint project within the framework of → MaterialDigital, the aim is therefore to supplement the material data space generated for the optimization of galvanic coating systems in the joint project with relevant simulation data. For this purpose, the experimental data on hard chrome and dispersion coatings obtained in other sub-projects are used to determine data on the macroscopic and microscopic mechanical properties of the coatings, which are not accessible in experiments, from finite element simulations. The project thus makes it possible to link experimental and simulated data with digital methods. Through this link, the added value of an extended material data space for the optimization of the coating system can be demonstrated.

Scale-Bridging Microstructure-Sensitive Assessment of Intergranular Cracking during High-Temperature Dwell-Time Fatigue of Polycrystalline Superalloys (→ DFG project)

project duration: 1.7.2023 to 30.6.2025

Reliable operation of today's aircraft engines and stationary gas turbines under widely varying operating conditions requires superalloys that combine high fatigue and creep resistance with excellent corrosion resistance. However, at increasing loads, "dynamic embrittlement (DE)" can occur in superalloys, where the interfacial cohesion is reduced by stress-assisted diffusion of an embrittling element into the grain boundary. DE of polycrystalline superalloys strongly depends on the microstructure of the material, in particular the grain boundary type, which determines the diffusion rates and thus the local concentration of the embrittling element in the grain boundary. However, the interrelationships of microstructure and DE are not well understood to date. Therefore, the objective of this project is to develop a microstructure-dependent modeling approach for diffusion-controlled intergranular fatigue crack growth at elevated temperature due to DE. This modeling approach combines microstructure-based finite element models with a finite difference method to solve for stress-assisted interfacial diffusion and ab-initio calculations related to grain boundary properties. In this context, the microstructure-based finite element simulation is performed at the Offenburg University of Applied Sciences and the ab-initio calculations are carried out at the Fraunhofer Institute for Mechanics of Materials IWM. RWTH Aachen University is contributing cross-scale experimental investigations for the development and validation of the modeling approach to the project. In the future, the modeling approach will allow computer-aided optimization of the microstructure of polycrystalline superalloys.

Experimental and numerical assesment of the influence of hydrogen and microstructure on the fatigue behavior of duplex steels (→ DFG project)

project duration: 1.1.2023 to 31.12.2025

In the context of the energy transition, duplex steels are increasingly used in offshore technology, where they are exposed to the influence of hydrogen through cathodic polarization. This can lead to cracking in duplex steels as a result of hydrogen embrittlement. Due to the different elastic-plastic properties of the two phases, internal stresses occur at the phase boundaries, which influence hydrogen diffusion. It can be assumed that the transient inhomogeneous stress distribution under cyclic loading affects the hydrogen diffusion in the two-phase duplex microstructure and leads to a fatigue damage evolution depending on the cycle time and the global and local hydrogen concentration. Therefore, the objective of this project is to gain an understanding of the interaction of material and loading history on hydrogen embrittlement of duplex steels. The necessary experimental investigations are carried out at RWTH Aachen University, while microstructure-sensitive simulation models are developed at Offenburg University of Applied Sciences to understand the interactions between mechanics and diffusion. With an understanding of the interaction, material properties can be specifically adapted to the operating conditions by optimizing the two-phase microstructure, and increases in component service life can be achieved.

Lifetime assessment of ferritic-martensitic steels for power plants, heat storage and solar thermal power plants considering creep-fatigue deformation interaction and scatter band (AiF project)

project duration: 1.9.2021 to 28.2.2024

Ferritic-martensitic steels are used, among other things, for highly stressed components in heat storage facilities and power plants, which have to be operated in residual load mode to compensate for the fluctuations caused by the priority use of renewable energies for power generation. With increasing operating time, the risk of failure of the components originally designed for creep stress thus increases. Established rules and standards exist for service life assessment in load-flexible plant operation. However, the frequent start-stop cycles contribute significantly to material softening and lead to accelerated creep in the subsequent steady-state operating phases, which is not taken into account by the standards. In addition, the individual creep properties of the steel used are not taken into account when evaluating creep damage. In this project, therefore, a concept is being developed in collaboration with the Fraunhofer Institute for Mechanics of Materials IWM which, by determining the current material condition and the scatter band position of the installed material, allows a significantly improved service life assessment of components made of ferritic-martensitic steels subjected to creep-fatigue loading. The particular focus is on the development and validation of a multiaxial material model, which can describe the creep-fatigue deformation interaction and cyclic material softening observed in near-service tests with quasi-elastic deformation during load cycles, allows a practicable adaptation to the scatter band position of the actually installed steel on the basis of strain measurements on components and can be used for service life evaluation on the basis of operating data.

The following projects have already been completed:

Development of a methodology for the assessment of the fatigue life of hot forging dies based on advanced material models (DFG project), project duration: 1.1.2015 to 28.2.2017 and 1.6.2019 to 30.6.2023

Influence of the cyclic thermal and mechanical loading history on crack closure, crack growth and fatigue life of nickel-base alloys (DFG project), project duration: 1.10.2018 to 30.6.2022

Simulation of thermomechanical fatigue crack growth in highly loaded components of efficient internal combustion engines (TMF-CraX) (BMBF-Projekt), project duration: 1.9.2018 to 30.4.2022

Component tests for validation of computational methods for the life prediction of aluminium cast components under combined thermomechanical and high-frequency loading (FVV project), project duration: 1.10.2020 bis 31.3.2022 

Experimental and numerical analysis of strain hardening in single and polycrystalline alloys during cyclic loading (Bauschinger effect) (DFG project), project duration: 1.9.2018 to 31.12.2021

Model-based diagnostic tool for the state of health of lithium-ion batteries (LIBlife) (Land Baden-Württemberg), project duration: 1.11.2018 to 30.6.2021

HERCULES-2, Fuel flexible, near-zero emissions, adaptive performance marine engine (EU project), project duration: 1.1.2017 to 28.2.2018

Determination of the material properties and material model development for computational lifetime assessment of rocket combustion chambers (industrial project), project duration: 1.10.2016 to 31.3.2019

Computational assessement of the lifetime of cast aluminium components under combined thermomechanical fatigue and high cycle fatigue loading conditions (AiF project), project duration: 1.1.2016 to 31.12.2018

Impact of the thermo-mechanical loading history on mechanical material properties (industrial project), project duration: 1.11.2014 to 31.12.2016

Development of probabilistic material models for service life prediction of turbine components (industrial project), project duration: 1.9.2012 to 31.8.2015

Microstructure-based modelling of cast iron with lamellar graphite under cyclic plastic loading (DFG project), project duration: 1.9.2011 to 31.8.2015

Optimization of the numerical calculation of deformation and failure for service life prediction under creep-fatigue loading conditions (DFG project), project duration: 1.1.2010 to 31.3.2013

T. Seifert, Computational methods for fatigue life prediction of high temperature components in combustion engines and exhaust systems, Shaker Verlag, ISBN 978-3-8322-7061-2, 2008