Thermomechanical Models for Amorphous Polymers Accounting for Shear Yielding and Crazing

聚碳酸酯或聚苯乙烯等无定形聚合物的工业应用涵盖汽车工业、医疗技术和高科技电子设备的生产。在这种背景下，建立基于连续介质的聚合物器件在非等温载荷条件下的响应预测模型，对于工艺设计和新材料的生产具有重要意义。该研究项目的目标是为非晶态聚合物开发一种完全耦合的热粘塑性材料描述，该描述本质上体现了微结构随速度和温度的变化。要开发的模型必须考虑到微观现象，如微观剪切屈服和银纹的竞争。这些微观现象的演化与分子机制有关，涉及组成大分子的解缠、断裂、塑性取向。整体宏观水平上的结果决定了材料从脆性到延性的转变。细观力学效应可用两个新的热力学模型概念来描述，一种是细观方法，用于解决小尺度现象，其中银纹化由断裂型内聚区理论模拟；(Ii)微观-宏观混合方法，用于大规模分析，其中银纹化由宏观结构张量模拟。该项目的总体成果将是用于预测大规模非晶态聚合物热机械变形过程的新的理论和算法公式。该项目伴随着一个实验方案和模型参数辨识程序。

Industrial applications of amorphous polymers such as polycarbonates or polystyrenes cover the automotive industry, the medical technology and the production of high-tech electronic devices. In this context, the construction of predictive continuum-based models for the response of polymeric devices under non-isothermal loading conditions is of high importance for the technological design as well as the production of new materials. Goal of the research project is the development of a fully coupled thermo-viscoplastic material description for amorphous polymers that inherently embodies the rate- and temperaturedependent micro structure evolution. The models to be developed must account for microphenomena such as the competition of micro-shear yielding and crazing. The evolution of these micro-phenomena is associated with molecular mechanisms involving disentanglement, scission, plastic orientation of the constituent macromolecules. The outgrowth on the overall macro-level determines the brittle to ductile transition of the material. The micromechanical effects are intended to be described by two new thermomechanical model concepts, a (i) meso-scale approach for the resolution of small-scale phenomena, where the crazing is modeled by a fracture-type cohesive zone theory and a (ii) hybrid micro-macro approach for large-scale analyses, where the crazing is modeled by macroscopic structural tensors. The overall result of the project will be new theoretical and algorithmic formulations for predictive large-scale analyses of thermomechanical deformation processes of amorphous polymers. The project is accompanied by an experimental program and model parameter identification procedures.