Associated People

J. Schröder, B.-A. Behrens (Hannover), D. Brands, L. Scheunemann, R. Niekamp, A. Chugreev (Hannover), C. Kock (Hannover), S. Uebing, M. Sarhil

Abstract

The consideration of residual stresses in metallic components produced by forming has primarily been undertaken with a view only to avoid or minimize them so far in order to improve the durability and manufacturability. A targeted use for improvement of properties e.g. the operational strength in the field of forming technology has so far received little attention.The aim of this project is to investigate the various influences on distribution and stability of the residual stress development in thermo-mechanically processed components by means of controlled cooling in both the experiment as well as the numerical simulations. In the long term, the goal is to optimize the forming process in such a way that a targeted use for improvement of the properties of the component becomes possible. A precise representation of the residual stresses, their development in numerical simulation as well as their interpretation in experimental results requires a profound knowledge of the thermal, mechanical as well as metallurgical properties of the used material. For this reason, in addition to the characterization of the microstructure transformation behavior, extensive investigations of the thermomechanical deformation behavior will be carried out.As an experimental demonstrator component, a cylindrical sample with an eccentric drilled hole will be considered, which will be isothermally compressed in a forming simulator and subsequently cooled in a targeted manner. The eccentric upsetting specimen evokes an inhomogeneous residual stress state, thus enabling the targeted investigation of different cooling scenarios. The numerical modeling of the residual stresses requires a multiscale view because of their classification into of 1st, 2nd and 3rd type. A macroscopic, phenomenological description in the framework of the Finite Element Methods (FEM) taking into account the thermo-mechanical and metallurgical properties will be used for the representation of the residual stresses of the 1st kind whereas, the phasefield theory and the FEM will be used to model the microstructural residual stresses (2nd and 3rd type). The microstructural transformation will be simulated by means of a phase-field model and representative volume elements will be created, which are to be used for the subsequent FEM simulations on the microscale.The close interaction between experiment and numerical simulation allows the calibration and validation of models and material descriptions during the first step. In the long term, a methodology is to be developed which will allow a deeper understanding of the phenomena occurring in the material and their relationship to the resulting residual stresses. From these findings, the process and simulation parameters can be modified in such a way that after cooling a stable residual stress distribution, which positively influences the properties of the component, can be produced in the workpiece.

References

Behrens, B.-A. und Olle, P. 2008. Consideration of transformation-induced stresses in the
simulation of press hardening. Proceeding of International Plasticity. 2008.

Brands, D., et al. 2016. Computational modeling of dual-phase steels based on representative
three-dimensional microstructures obtained from EBSD data. Archive of Applied Mechanics.
2016, Bd. 86, 3, S. 575-598.

Steinbach, I. 2009. Phase-field models in materials science. Modelling and Simulation in
Materials Science and Engineering. 2009, Bd. 17, 7, S. 073001.