Characterisation and Modeling of the Moisture Dependent Thermomechanical Behaviour of Poylamide

本项目的目的是提供关于聚酰胺-66(PA)的热-机械耦合行为的广泛的基本知识。到目前为止，许多工作组都报道了水分和温度对PA力学行为的影响。最近发表的论文的焦点集中在水分传输过程上，这一过程受到散体材料内部自由体积的影响。此外，力学行为和自由体积之间存在很强的相互关系。因此，水分传输机制和施加载荷之间的相互关系将通过应用无损检测的适当测试方法进行详细阐述，并包括在后续的材料模型中。LKT将提供样品并开发测试方法和程序，以确定水分含量对机械性能的影响，反之亦然。在第一步中，将对有条件的试件进行实验，以获得与水分相关的宏观材料行为的一般信息，然后在测试设备上采用现场水分测量方法，以考虑水分传输等微观影响。此外，尺寸和叠加加载状态对这种行为的影响将通过开发适当的样品和测试方法来确定。LLB将开发一种基于太赫兹波的测量和重建方法，以恢复PA中水分的分布和动态参数(局部和全球水分含量，深度梯度)。太赫兹的开发由几个工作包组成，首先是积分水分测定，然后是横向分布，最后是深度梯度的确定。分包商将进行正电子湮没寿命谱(PALS)测量，以获得作为参考的个人自由体积数量。LLB结果将补充LKT的应力-应变数据，并将作为来自LTM的连续介质力学材料模型的输入数据，从而帮助改进和验证该模型。LTM的工作目标是水分传输的连续介质力学模型和PA的与水分相关的热机械性能。因此，扩散模型将完全耦合到PA的粘弹性材料模型。一方面，扩散模型与自由体积相耦合，另一方面，粘弹性模型的刚度和松弛时间取决于水分浓度。在这种情况下，必须考虑水分传输和机械性能之间的强烈耦合以及对载荷的依赖性。从LLB和LKT的大量实验测试中获得的数据，通过对多场问题的稳健的数值实现，能够使用逆方法来识别材料参数。

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.