Modelling of Deformation Behavior of Micro-Mezo-Macroscopic Scale of Glassy Polymers

在玻璃聚合物变形行为的本构模型的发展中，分子链网络理论已经发展到考虑由于分子链的排列和纠缠点数量的变化而引起的应变诱导的各向异性。然而，能够再现高分子材料一般变形行为的合适的本构方程，以及具有从分子到宏观连续层次结构的高分子材料的微观和宏观行为之间的关系，目前还没有得到明确的认识。本文提出了一种新的分子链网络模型——非仿射模型，该模型允许由于温度变化引起的热激活和分子链因局部变形而从纠缠点中拉出而导致纠缠点数量的变化。本文提出了一种实验与计算模拟相结合的识别方法，通过对实验结果的计算预测，建立了更有效的方程。此外，在不同的变形条件下，拉伸变形和剪切变形均表现出特殊的失稳传播行为。其次，为了建立覆盖单体分子结构对中观和宏观变形行为响应的分层本构模型，我们应用原子力显微镜，明确了微观和宏观行为之间的关系。对于高取向超高分子量聚乙烯（UHMW-PE），可以观察到从微米到埃的层次结构，如沿拉伸方向排列的微纤维结构和数十纳米的纳米纤维结构。在分子水平上，纳米纤维结构表面形成规则的链状结构。通过观察玻璃状聚合物PC在单轴拉伸颈传播作用下的微观表面轮廓，发现微纤维结构在表面沿拉伸方向排列，且由于剪切应变作用，排列微纤维结构的旋转相对于塑性拉伸主方向的旋转有明显的延迟，说明了建立非结合框架的必要性。少

In the development of a constitutive model of deformation behavior for a glassy polymer, molecular chain network theories have been developed to take account of the strain-induced anisotropy due to the alignment of the molecular chains and the changes in the number of entangled points. However, the suitable constitutive equation which can duplicate the general deformation behavior of polymeric materials and relationship betweenn the micro-and macroscopic behaviors of polymeric materials, that have hierarchical structures at successive molecular to macrolevels, have not been clarified vet.In this work, a new molecular chain network model, nonaffine model, which allows the change in the number of entangled points due to the thermal activation caused by the temperature change and the pullout of the molecular chain from the entangled points by local deformation. An identification method employing both experiments and computational simulation has been developed and thus established constitu … More tive equation has been approved through the computational prediction of experimental results. Furthermore, the peculiar instability propagation behavior observed in the tensile deformation as well as in the shear deformation under different deformation conditions.Next, in order to estabish the hierarchical constitutive model covering the response of molecular structure of mononer leading to deformation on a mezzo-and macroscopic deformation behavior, we applied AFM and clarified the relationship between the micro-and macroscopic behaviors. For highly oriented ultrahigh molecular weight polyethylene, (UHMW-PE), hierarchical structures with scales from microns to angstroms were observed such as microfibril structure aligned along the drawing direction, and nanofibril structure with dozens of nanometers. On the molecular level, regular chain pattern is formed on the surface of the nanofibril structure. The observation of microscopic surface profiles of PC,a glassy polymer, under uniaxial tension with neck propagation has clarified that the formation of microfibril structures aligned along the tensile direction on the surface and the clear delay in the rotation of aligned microfibril structures with rsepect to that of principal direction of plastic stretch due to shear strain, which suggests the necessity of the establishment of the nonassociative frame work for the constitutive equation. Less