Development and analysis of a material model based on the reptation theory for the description of the strain behaviour of PET at high strain rates

两阶段拉伸吹塑成型工艺被确立为生产具有优异机械和光学性能的高质量塑料中空体的方法。在该过程中材料的拉伸导致分子链的强取向并形成层状结构。这些结构导致材料强度的急剧增加。材料行为的预测有助于解释工艺过程，并有助于提高中空体或薄膜生产中的材料效率。为了预测材料行为，使用不同的材料模型。材料模型目前通过弹簧-阻尼器方法描述，并通过应力-应变曲线进行校准。这些模型可以很好地预测校准范围内的变形，但在此范围外不太准确。本研究的目的是建立和分析一个基于蠕动理论的材料模型，该模型描述了聚乙烯醇（PET）的应力-应变行为。为此目的，用于描述聚合物熔体中产生的应力的蠕动理论的方程组被实施并利用所确定的无定形（A）和半结晶（C）PET的材料数据进行校准。该项目的第一步是开发材料模型。为此，描述塑料熔体的蠕动理论方程组适合于描述PET的行为。该模型的性能进行了检查，在不同的条件下为指定的PET类型。通过对不同温度下的应力应变曲线的计算与实验结果的比较，对模型进行了验证。并将该模型应用于薄膜膨胀流变仪（MIR）和拉伸吹塑过程的模拟，通过与实验的对比分析了模型的准确性。MIR的实际和模拟测量之间的比较允许在变形过程中的小时间步长的应变行为的分析。因此，可以识别模型的准确性，但也可以识别模型的弱点。最后，将材料模型嵌入到两阶段拉伸吹塑成型过程的模拟中。验证是通过实验实现的，并与现有的PET超弹性材料模型进行比较。预制件的复杂几何形状和材料中的不均匀温度分布对模型的精度提出了很高的要求。通过对PET材料性能的了解和模型的分析质量，解决了材料和能源效率问题。

The two-stage stretch blow moulding process is established as a method for producing high-quality plastic hollow bodies with excellent mechanical and optical properties. The stretching of the material during the process leads to a strong orientation of the molecular chains and to a formation of lamella like structures. These structures lead to a sharp increase in the strength of the material. The prediction of the material behaviour helps in the interpretation of the process and in the increase of the material efficiency in the production of hollow bodies or films. For the prediction of the material behaviour, different material models are used. Material models are currently described through spring-damper approaches and are calibrated through stress-strain curves. These models can predict the deformation within the calibrated range well, but are less accurate outside this range. The aim of this research project is the development and analysis of a material model, which depicts the stress strain behaviour of Polyethylenterephthalat (PET) based on the reptation theory. For this purpose, the equation set of the reptation theory for the description of the resulting stress in polymer melts is implemented and calibrated with the material data for amorphous (A) and semi-crystalline (C) PET determined. The first step of the project is the development of the material model. For this purpose, the equation system of the reptation theory for the description of plastic melts is fit to describe the behaviour of PET. The performance of the model is examined under different conditions for the specified PET types. The validation of the model is carried out by comparing the calculated stress strain curves for different temperatures with experiments. Furthermore, the model is applied in simulations of membrane-inflation rheometer (MIR) and the stretch blow moulding process to analyse the models accuracy by the comparison with experiments. A comparison between practical and simulated measurement of the MIR allows the analysis of the strain behaviour in small time steps during the deformation process. Therewith, the accuracy, but also weaknesses, of the model can be identified. Finally, the material model is embedded in a simulation of the two-stage stretch blow moulding process. The validation is realised through experiments and compared to an existing hyper elastic material model for PET. The complex geometry of the preforms and the inhomogeneous temperature distribution in the material make high demands on the accuracy of the model. With the acquired knowledge of the material behaviour of PET and the analysed quality of the model, the material and energy efficiency is addressed.