Polyamide exhibits hygroscopic nature and can absorb up to 10% of moisture relative to its dry weight. The absorbed moisture increases the mobility of the molecular chains and causes a reduction in the glass transition temperature. Thus, depending on the moisture distribution, a polyamide component can show different stiffness and relaxation times. Moreover, the moisture distribution also depends on the mechanical loading of the material as the volumetric deformation results in a change of the available free volume for the moisture. Thus, a strongly coupled model is required to describe the material behaviour. In this work, a thermodynamically consistent coupled model within the framework of mixture theory is developed. The mechanical deformation of polyamide 6 (PA6) is based on a linear viscoelastic material model, and the moisture transport is based on a nonlinear diffusion model. The stiffness and the relaxation time of the viscoelastic model change with the moisture concentration. Furthermore, the moisture transport is affected by the pressure gradient generated by the mechanical loading of the material. This strongly coupled model has been implemented using the finite element method, and simulation results are presented for a three-point bending experiment.

聚酰胺具有吸湿性，相对于其干重可吸收高达10％的水分。吸收的水分增加了分子链的迁移率，并导致玻璃化转变温度降低。因此，取决于水分分布，聚酰胺组分可显示出不同的刚度和松弛时间。此外，水分的分布还取决于材料的机械负荷，因为体积变形会导致水分的可用自由体积发生变化。因此，需要一个强耦合模型来描述材料的行为。在这项工作中，建立了混合理论框架内的热力学一致耦合模型。聚酰胺6（PA6）的机械变形基于线性粘弹性材料模型，水分传输基于非线性扩散模型。粘弹性模型的刚度和松弛时间随水分浓度而变化。此外，水分输送受材料的机械负载产生的压力梯度的影响。使用有限元方法实现了这种强耦合模型，并针对三点弯曲实验给出了仿真结果。