Characterisation and Modeling of the Moisture Dependent Thermomechanical Behaviour of Poylamide

该项目的目的是提供关于聚酰胺-66（PA）的耦合热机械行为的广泛基础知识。到目前为止，许多工作组已经报道了湿度和温度对PA力学行为的影响。最近发表的论文的重点在于水分输送过程中，这是受散装材料内的自由体积。此外，力学行为与自由体积之间存在着很强的相关性。因此，水分传输机制和施加载荷的相互关系将通过适当的测试方法与无损检测的应用进行阐述，并包括在随后的材料建模中。LKT将提供样本，并制定测试方法和程序，以确定水分含量对机械性能的影响，反之亦然。在第一步中，将进行条件试样的实验，以获得与水分相关的宏观材料行为的一般信息，然后在试验装置上调整原位水分测量方法，以考虑水分传输等微观效应。此外，将通过开发适当的样品和测试方法来确定尺寸以及叠加载荷状态对这种行为的影响。LLB将开发基于太赫兹波的测量和重建方法，以检索PA中水分的分布和动态参数（局部和全局水分含量，深度梯度）。太赫兹的发展是由几个工作包，开始与整体水分测定，然后其横向分布，并最终确定的深度梯度。分包商将进行正电子湮没寿命谱（帕尔斯）测量，以获得单个自由体积量作为参考。LLB结果将补充LKT的应力-应变数据，并将作为LTM连续介质力学材料模型的输入数据，从而有助于改进和验证它。LTM工作的目的是连续介质力学模型的水分传输和PA的水分依赖性热机械性能。因此，扩散模型将完全耦合到PA的粘弹性材料模型。一方面，扩散模型耦合到自由体积，另一方面，粘弹性模型的刚度和松弛时间将取决于水分浓度。在这种情况下，必须考虑水分传输和机械性能之间的强耦合以及对负载的依赖性。从大量的实验测试，LLB和LKT，使材料参数的识别，通过使用逆方法通过一个强大的数值实现的多场问题。

The aim of this project is to provide a broad basic knowledge on the coupled thermo-mechanical behaviour of polyamide-66 (PA). The influence of moisture and temperature on the mechanical behaviour of PA has been reported by many workgroups so far. Focus of more recently published papers lies on processes of moisture transport, which are influenced by the free volume inside the bulk material. Besides, there is a strong interrelation of mechanical behaviour and free volume. Therefore, the interrelation of moisture transport mechanisms and applied loadings is to be elaborated by appropriate test methodologies with the application of non-destructive testing and included in a subsequent material modelling.The LKT will provide the specimens and develop test methodologies and procedures to determine the influence of moisture content on the mechanical behaviour and vice versa. In a first step, experiments on conditioned specimens will be conducted to gain general information on the moisture dependent macroscopic material behaviour, followed by the adaption of in-situ moisture measurement methods on the test device for considering microscopic effects such as moisture transport. Furthermore, the influence of dimensions as well as superposed loading states on this behaviour will be determined by developing appropriate specimens and test methods.The LLB will develop a measurement and reconstruction method based on terahertz waves in order to retrieve the parameters of the distribution and dynamics of the moisture in PA (local and global moisture content, depth gradient). The THz development is comprised of several work packages, starting with integral moisture determination, then its lateral distribution and finally determination of the depth gradient. A sub-contractor will perform Positron Annihilation Lifetime Spectroscopy (PALS) measurements in order to obtain the individual amount of free volume as a reference. The LLB results will complement the stress-strain-data from LKT and will serve as input data for the continuum mechanical material model from LTM, thus helping to improve and verify it.Aim of work of the LTM is the continuum mechanical modelling of moisture transport and the moisture dependent thermo-mechanical properties of PA. Therefore, a diffusion model will be fully coupled to a viscoelastic material model for the PA. On the one hand, the diffusion model is coupled to the free volume, one the other hand, the stiffness and relaxation times of the viscoelastic model will depend on the moisture concentration. In this context strong coupling between moisture transport and mechanical properties as well as dependency on the load has to be considered. Data obtained from a multitude of experimental tests, made by LLB and LKT, enables the identification of material parameters by using inverse methods by means of a robust numerical implementation of the multifield problem.