Experimental and numerical modeling and analysis of microstructural residual stresses in hot bulk forming parts under specific cooling

在成形金属部件中，避免或最小化残余应力一直是迄今为止的主要目标，目的是提高使用寿命和可制造性。以残馀应力为目标来改善性能，例如在成形技术领域的操作强度，到目前为止还很少受到关注。本项目的目的是通过有针对性的工艺控制，采用实验和数值模拟相结合的方法，分析热机械加工零件中残余应力分布和稳定性的影响。为此，在不同的工艺条件下，对带有偏心孔的圆柱形试件进行热机械处理，以研究由此产生的不均匀残余应力状态。为了对所用材料中残余应力的演变和分布进行实验和数值分析，在第一个供资期间对材料的热、冶金和机械性能进行了全面的表征。由于第一类、第二类和第三类残余应力的分类，考虑了多尺度数值模式。实验和数值模拟之间的密切互动使模型和材料描述的校准和验证成为可能。利用这些模型对参考过程中残余应力的发展进行了较好的预测。此外，在第二个供资期间使用了所开发的数值模型，并针对新的工作方案进行了改进和优化。因此，基于热机械和冶金性质的有限元框架内的宏观唯象描述被用来表示第一类残余应力。在模拟第二类和第三类组织残余应力和组织演化时，采用了相场模型和多尺度有限元模拟。在材料数据验证后，目前的目标是研究残余应力的可控性，以改善热成形零件的性能。除了对成形参数的具体控制外，还将主动温度管理的喷雾场冷却融入成形过程，这也使得数值模型的进一步修改是必要的。随后的数值和实验研究被用来分析工艺参数和残余应力之间的相互作用。从长远来看，应该开发一种方法，使人们能够更深入地了解与热成形过程中产生的残余应力演变相关的热机械材料现象。基于这些知识，它的目标是模拟辅助工艺设计，面向目标地调整定义的、稳定的残余应力，这些残余应力对部件的性能产生积极影响。

In formed metallic components, the avoidance or minimization of residual stresses has so far been the main objective, with the aim of improving service life and manufacturability. A goal-oriented use of residual stresses for improvement of properties e.g. the operational strength in the field of forming technology has received rare attention until now. The aim of this project is to analyse the influences on distribution and stability of the residual stress development in thermo-mechanically processed components by means of a targeted process control using both experiments as well as numerical simulations. For this purpose, cylindrical specimen with eccentric holes are thermo-mechanically treated in various process cases in order to investigate the resulting inhomogeneous residual stress states. For the experimental as well as numerical analysis of the evolution and distribution of residual stresses in the used material a comprehensive characterisation of the thermal, metallurgical and mechanical properties was carried out in the first funding period. Due to the classification of residual stresses in 1st, 2nd and 3rd type multiscale numerical models were taken into account. The close interaction between experiment and numerical simulation allowed a calibration and validation of models and material descriptions. With these models a good prediction on the development of residual stresses in the reference process was gained. Furthermore, the developed numerical models are used during the second funding period and enhanced as well as optimized with respect to the new work program. Thereby, a macroscopic, phenomenological description in the framework of the Finite Element Method (FEM) based on thermo-mechanical and metallurgical properties is used for the representation of the residual stresses of the 1st type. For modelling microstructural residual stresses (2nd and 3rd type) and microstructure evolution phasefield models and multiscale FEM simulations are applied. After the validation of material data, the current aim is to investigate the controllability of residual stresses with regard to improve the properties of the hot-formed components. Besides specific control of the forming parameters, spray field cooling for active temperature management will be integrated into the forming process, which makes also further modification of the numerical models necessary. Subsequent numerical and experimental studies are used to analyse the interactions between process parameters and residual stresses. In the long term, a methodology should be developed which allows a deeper understanding of the thermo-mechanical material phenomena in connection with the resulting residual stress evolution occuring during the hot forming. Based on this knowledge, it is aimed for a simulation-aided process design with regard to the goal-oriented adjustment of defined, stable residual stresses, which positively influence the component properties.