Development and Application-oriented Validation of a Reliable Smoothed Particle Hydrodynamics Discretization for Solids to describe Friction Stir Welding

本研究是该项目的第二阶段，致力于利用光滑粒子流体动力学（SPH）方法对搅拌摩擦焊接（FSW）过程进行精确模拟。FSW是一种固态焊接过程，它是由多种相互依存的物理现象描述的，包括高应变和应变率的塑性、非弹性热产生、摩擦和固态结合。SPH离散化方法具有无网格特性，为处理大变形和各种物理效应提供了一个框架。在项目的第一阶段，开发并实施了一种新的基于物理的材料模型，以便为FSW提供改进的材料行为描述。粒子取向的问题也进行了调查、解决和测试，随后以出版物的形式提供了文档。作为第二部分的一部分，对SPH中基于离散误差的自适应进行了研究，提供了一种处理粒子细化和粗化的新颖策略。项目第二阶段的总体目标是在第一阶段的基础上发展起来的。为了实现固体SPH配方的重大改进，并通过这些手段不仅提供了FSW的精确模拟，而且还开发了一种可靠的，创新的模拟技术，能够处理广泛的工业应用的模拟。由于FSW结合了可变特性，这在许多其他工业过程中也很常见，因此它为后来的研究成果转移提供了充分的背景。由于前一个项目的时间框架缩短，无法全面处理所有方面，因此将其转化为这个项目。材料模型的一些最终改进，包括沉淀硬化和离散化的适应性验证，以及材料粘合准则的制定，都将完成。此外，在项目的第一部分，确定了进一步的研究领域。其中包括改进的SPH稳定配方，基于材料行为的摩擦模型的扩展，以及热行为模型的增强和验证。作为最后一步，改进的SPH固体配方将应用于FSW工艺，以预测最终连接的几何形状、焊缝质量和微观组织行为。预报的精度将通过与世界气象组织进行的实验进行比较来检验。

This research is a second phase of the project, devoted to the accurate simulation of the friction stir welding (FSW) process by means of the Smoothed Particle Hydrodynamics (SPH) method. FSW is a solid state welding process, which is described by multiple interdependent physical phenomena, including plasticity with high strains and strain rates, inelastic heat generation, friction, and solid state bonding. The SPH discretization method, with its meshless nature, provides a framework, which is capable of dealing with large deformations and various physical effects.In the first phase of the project, a novel physically based material model was developed and implemented in order to provide an improved material behavior description specific for FSW. The issue of the particle orientation was also investigated, resolved and tested, followed by the documentation in form of a publication. As a part of the second package, a research on discretization-error based adaptivity in SPH was conducted, providing an original strategy dealing with particle refinement and coarsening.The overall objective of the second phase of the project developed from the first phase. To achieve a major improvement of the SPH formulation for solids, and by these means not only to provide a precise simulation of FSW, but also to develop a reliable, innovative simulation technique, which is able to deal with the simulation of a wide range of industrial applications. Due to the fact that FSW combines variable characteristics, which are also common for many other industrial processes, it offers a sufficient background for a later transfer of he research results.As the time frame of the preceding project was shortened and did not allow to deal with all the aspects in full, they are translated into this project. Some final improvements of the material model by including precipitation hardening and validation of adaption of the discretization are to be accomplished, as well as the development of a material bonding criterion are to be performed in full. Additionally, during the first part of the project, further areas of research were determined. These include an improved SPH stabilization formulation, extension of the friction model based on material behavior, and enhancement and validation of the thermal behavior model. As a final step, the improved SPH solid formulation will be applied to the FSW process in order to predict the final joined geometry, quality of the weld, and microstructural behavior. The precision of the prediction will be examined through comparison with experiments conducted by the IMWF.