Continuum mechanical representation of the process-dependent caloric and thermomechanical behaviour of semicrystalline polymers

由于它们的多功能性，对半结晶聚合物的力学、物理化学和热力学的理解和表示多年来一直是研究项目的中心。半结晶聚合物表现出空间分离的区域，在这些区域中分子形成无定形和结晶相。在这两者之间，通常会有一个中间阶段。它的玻璃化转变温度通常高于可移动的非晶相，因此被称为刚性非晶相。目前的研究项目涉及半结晶聚合物在热和体积载荷下依赖于过程的行为的唯象和微观模拟，主要目标如下：1)在一致的实验数据库的基础上，模拟半结晶模型聚合物的结晶和熔融作为温度和压力的函数。为此，应用了具有内变量的唯象连续体热力学方法。建立了三维空间本构模型，并专门用来表示体积特性。为了了解相界的局域机制，并检验或改进唯象模型框架中的假设，如三相的存在或结晶程度演化方程的数学结构，将发展一种能够根据各相的微观行为来描述材料的介观性质的均匀化方法。2)熔融结晶的细观力学模拟。结晶动力学应该是一个简化的微结构模型的基础(基于RANK-1和RANK-2层板，具有本构模型的界面)，该模型允许从具有移动相边界的空间分辨模型开始对结晶过程进行定量的理解。将开发的两个本构模型提供了第一个模块，这是一个复杂的建模策略，超出了本项目的范围。模型聚合物的实验数据构成了量热和热力学本构表示的基本基础。为了建立模型和确定力学和热加载历史对结晶和熔融行为的影响，一个合适的模型聚合物是进行实验研究的。在唯象和细观力学模型中使用了尽可能多的材料参数(例如，非晶相和晶相的力学和热学材料参数)。这是可能的，因为这两种模型都表现出相似的物理性质。

Due to their versatility, the mechanical, physicochemical and thermodynamic understanding and the representation of semi-crystalline polymers are for many years in the centre of research projects. Semi-crystalline polymers exhibit spatially separated regions in which the molecules form amorphous and crystalline phases. In between, there is often an interphase. It usually possesses a higher glass transition temperature than the mobile amorphous phase and is therefore referred to as a rigid amorphous phase. The current research project deals with the phenomenological and micromechanical modelling of the process-dependent behaviour of semi-crystalline polymers under thermal and volumetric loads and has the following main objectives: 1) Modelling of crystallization and melting of a semi-crystalline model polymer as function of temperature and pressure on the basis of a consistent experimental database. To this end, the methods of phenomenological continuum thermomechanics with internal variables are applied. The constitutive model is formulated for three spatial dimensions and specialized to represent the volumetric behaviour. In order to understand the local mechanisms at the phase boundaries and to check or improve the assumptions made in the framework of the phenomenological model, such as the existence of three phases or the mathematical structure of the evolution equation for the degree of crystallization, a method of homogenisation will be developed that can describe the mesoscopic properties of the material on the basis of the microscopic behaviour of the individual phases. 2) Micro-mechanical modeling of melting and crystallization. The kinetics of the crystallization should be the basis of a simplified micro-structure model (based on rank-1 and rank-2-laminates with constitutively modelled interface) which allows a quantitative understanding of the crystallization, starting from a spatially resolved model with mobile phase boundaries. The two constitutive models to be developed provide first blocks are within a complex modeling strategy which goes beyond this project. Experimental data of a model polymer form an essential basis for the constitutive representation with respect to calorimetry and thermomechanics. For the model development and the identification of the influence of the mechanical and thermal loading histories on the crystallization and melting behavior, an appropriate model polymer is to investigate experimentally. As many material parameters as possible (for example, the mechanical and caloric material parameters of the amorphous and crystalline phases) are used for the phenomenological and micromechanical model. This is possible because both models exhibit similar physical properties.