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。在这种情况下，基于连续预测模型的非等温加载条件下的聚合物器件的响应的建设是非常重要的技术设计，以及新材料的生产。该研究项目的目标是为非晶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与速率和温度相关的微观结构演变。要开发的模型必须考虑微观现象，如竞争的微剪切屈服和银纹。这些微观现象的演化与分子机制有关，包括解缠结、断裂、组成大分子的塑性取向。宏观上的副生长决定了材料的脆韧性转变。细观力学效应的目的是描述两个新的热机械模型的概念，（i）细观尺度的方法，小尺度的现象的分辨率，其中银纹是由一个cohesive类型的内聚区理论和（ii）混合微观宏观方法的大规模分析，其中银纹是由宏观结构张量建模。该项目的总体成果将是新的理论和算法公式，用于预测大规模分析无定形聚合物的热机械变形过程。本项目附有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.