Speaker
Description
Current research is shifting from minimizing or eliminating residual stresses in components to intentionally introducing them during the manufacturing process. Hot bulk forming processing enables the controlled modification of residual stresses by leveraging thermal, mechanical, and metallurgical interactions in order to evoke e.g. improved durabilty. Typically, hot bulk forming involves heating the material, here 100Cr6, above 1000°C, leading to full austenitization and an assumed stress-free initial state, followed by forming and cooling down to room temperature. Rapid cooling, i.e. evoked by quenching in water, initiates a diffusionless phase transformation from austenite to martensite in the considered material [1]. Hot bulk forming with adapted cooling strategies helps to avoid the need for costly and time-consuming subsequent steps such as heat treatments.
This contribution focuses on modeling the cooling process and the associated phase transformation generating residual stresses at both the micro- and macroscale of the component. To differentiate between the various types of residual stresses, which are classified based on the scale at which they occur, two-scale finite element (FE²) simulations may be conducted [2,3]. These simulations require a representative volume element that accurately reflects the phase transformation and other microscopic features. Single-scale finite element simulations are first performed to determine the macroscopic thermal and mechanical conditions, which then serve as the driving force for a subsequent thermo-mechanically coupled multi-phase-field model at the microscale [4]. This approach allows for the evaluation and analysis of martensitic evolution and microscopic residual stresses.
References
[1] B.-A. Behrens, J. Schröder, D. Brands, K. Brunotte, H. Wester, L. Scheunemann, S. Uebing and C. Kock. Numerische Prozessauslegung zur gezielten Eigenspannungseinstellung in warmmassivumgeformten Bauteilen unter Berücksichtigung von Makro- und Mikroskala, Forschung im Ingenieurwesen (Engineering Research), 85, 757-771, 10.1007/s10010-021-00482-x, (2021).
[2] S. Uebing, D. Brands, L. Scheunemann and J. Schröder. Residual stresses in hot bulk formed parts: microscopic stress analysis for austenite-to-martensite phase transformation, Archive of Applied Mechanics, 91, 3603–3625, (2021).
[3] J Schröder. A numerical two-scale homogenization scheme: the FE2-method. In J. Schröder and K. Hackl (Eds.), Plasticity and Beyond - Microstructures, Crystal-Plasticity and Phase Transitions, Volume 550 of CISM Courses and Lectures, 1–64. Springer, (2014).
