Bai-Xiang Xu
Mechanics of Functional Materials
Institute of Materials Science
Technische Universität Darmstadt

Material properties are related to the underlying microstructure which depends further on processing mostly in multiphysics scenarios. Particularly for the most advanced processing technique like additive manufacturing the process-microstructure relation goes beyond the current understanding, due to the extreme thermal conditions. Also, for the technology enabler like Lithium-ion batteries their fast capacity loss has been shown to be more than just an electrochemical issue but essentially related to chemo-mechanics degradation. To reveal such multiphysics mechanisms and to accelerate interdisciplinary design of new materials, it is essential to develop coupled theoretical models and effective simulation tools.   

The phase-field approach, consistent with the energy variational method, manifests itself as a successful and general tool to serve this purpose. It applies order parameters to represent microstructure in a general sense and can simultaneously include thermodynamic quantities like temperature (or internal energy) and mechanical fields. The evolution equations of the order parameters and the conjugated quantities of the state variables can be obtained from the variational derivative of a thermodynamic potential functional. Thanks to the merits including generality of the theoretical framework, straightforward numerical implementation and flexible coupling of multi-physics, phase-field models have been extensively developed for the study of microstructure evolution during processing and performance stage.

In the talk I present two case studies, if time allows. One is non-isothermal phase-field modeling and finite element simulations of microstructure evolution (grain structure and pore) during powder bed fusion additive manufacturing. I will outline shortly the model development and the numerical strategies to reduce the computation cost, followed by selective sintering and melting simulation results on stainless steel 316L to reveal the influences of beam power and scan speed on the microstructure features, such as porosity, surface morphology and residual stress. The other case study is electro-chemo-mechanical phase-field modeling and finite element simulations of phase separation and mechanical deformation and fracture in Li-ion electrode materials during (de)-lithiation. 

Brief CV: In 2008 Xu received her PhD degree from Peking University, China in the research field of Micromechanics of Solids. From 2008 to 2010 she received the Alexander von Humboldt fellowship and worked as a postdoctoral research at TU Darmstadt and TU Kaiserslautern, Germany subsequently. In 2011 she became a Junior professor and chaired the research group Mechanics of Functional Materials in the Institute of Materials Science, TU Darmstadt. After successful tenure track she was appointed in 2016 as a university professor and continues leading the research group. The group is devoted to description and optimization of microstructure and the related mechanical and functional properties in functional and energy materials by multiphysics models and numerical simulations. Her current research topics include multiphysics phase-field modeling and finite element simulations on battery materials, ferromagnetic and ferroelectric materials, as well as the additive manufacturing of crystalline materials.