Study of microstructure of dielectric polymer nanocomposites subjected to electromagnetic fields for development of self-toughening, self-awareness li

在复合材料中提出一种可控的预加应力/增韧技术是极其复杂的，在超过聚合物屈服点的压缩下很容易发生基质开裂。为了克服这一问题，EPSRC资助的自调优纤维增强聚合物自适应纳米复合材料(STRAINcomp；EP/R016828/1)旨在开发一种新的微压缩方法，通过电磁暴露将被动压缩应力场局部均匀地引入到介电增强复合材料的基体结构中。通过引入介电纳米材料来增强聚合物在分子尺度上形成的网络的性质，严重地降低了粒子的分子迁移率/振动。在其玻璃化的固体基质中，一旦纳米增强聚合物暴露在介电场(例如微波)中，就会在与基质的界面处引入应力，因为分子振动突然增加，从而将应力引入到其周围的基质中。这种压应力增强了微尺度的裂纹闭合能力，防止了基质开裂，可以通过调整介质场来调整应力水平。因此，基质的力学性能将得到改善，从而产生自校正的自适应材料。然而，除了一些孤立的稀有研究外(例如，奥德加德等人)。2015，J.Polmer)，对纳米材料-聚合物界面如何以及在多大程度上对电磁场进行微观机械响应的理解，在现有文献中仍然是一个很大的知识缺口。这样的理解和量化是拟议的博士项目的基础。这一发现将导致一种响应迅速、体积吸收辐射的自校正技术，并可应用于跨不同部门的刚性复合材料结构。在力学加载和电磁场的边界条件下，建立了三种粘结不同材料体系(纳米材料、聚合物和界面)的多物理问题的新的理论本构材料方程，以便将材料的介电性质、界面结构和电磁驱动的偶极矩与系统的力学性质和性能联系起来，例如用应力张量和应变张量分别表示的连续介质力学定律和材料常数矩阵。利用两个多尺度模型数值研究了存在电磁场的三种材料体系的微观力学性能。MD模拟模型将使用LAMMPS开发，连续介质模型将由ABAQUS/Intel-Fortran驱动(在介观尺度上用于模拟纳米材料-聚合物局部应变和变形)。(从MD模型获得的关于界面性能的数据将被馈入用于模拟三种材料相互作用的介观模型中)，并在STFC钻石光源和曼彻斯特罗伊斯研究所的X射线成像设施上使用原位X射线层析、光栅干涉和平版层析技术实验研究纳米材料-聚合物界面。这些测量(通过机械测试和EM曝光的现场)不仅帮助博士生和团队了解在界面水平曝光期间的变形机制、结合质量、形态效应和任何可能的分子结构演变，而且还将为MD和介观模型参数的校准和开发提供数据。

Proposing a controllable pre-stressing/toughening technique in composites is extremely complex being susceptible to matrix cracking in compression beyond the polymers yield point. To overcome this, the EPSRC funded project Self-Tuning Fibre-Reinforced Polymer Adaptive Nanocomposite (STRAINcomp; EP/R016828/1) aims to develop a novel micro-compression method to locally and uniformly introduce a passive compressive stress field to the matrix microstructure of dielectric enhanced composites via EM exposure. Incorporating dielectric nanomaterials to enhance the properties of the polymer forming networks at a molecular scale severely reduces particles molecular mobility/vibration. In its vitrified solid matrix, stress is introduced at the interface with the matrix once the nano-enhanced polymer is exposed to a dielectric field (e.g. microwave), since the molecular vibration abruptly increases which introduces stress to their surrounding matrix. This compressive stress enhances the crack closure capability at microscale preventing matrix cracking, enabling adjusting the levels of the stress via adjusting the dielectric field. As a result, the mechanical properties of the matrix will be improved resulting in a self-tuning adaptive material. However, except some isolated scarce research (e.g. Odegard et al. 2015, J. Polymer), an understanding of how, and to what quantifiable extent, the nanomaterial-polymer interface responds to an EM field micromechanically has remained a big knowledge gap in the extant literature. Such an understanding and quantification is the foundation of the proposed PhD project. This discovery will lead to a self-tuning technology which is swift in response, volumetric in radiation absorption, and can be applied to rigid composite structures across various sectors. Develop novel theoretical constitutive material equations for the Multiphysics problem of three bonded dissimilar materials system (nanomaterial, polymer and interface) with boundary conditions of mechanical loading and EM field, in order to correlate the materials dielectric properties, interface structure and the EM driven dipole moment with the system's mechanical properties and thus performance e.g. expressed by the continuum mechanics law of where the stress and strain tensors respectively and is material constants matrix.Numerically study the micromechanical performance of the three-material system in the presence of an EM field using two multiscale modelling. The MD simulation model will be developed using LAMMPS and continuum model will be driven by Abaqus/Intel-Fortran (at meso-scale for modelling the nanomaterial-polymer localised straining and deformation) based on the constitutive law developed in Objective 1. (Data obtained from the MD model for the interface performance will be fed into the meso-scale model for modelling the three-material interaction), and Experimentally study the nanomaterial-polymer interface using in-situ X-ray tomography, grating interferometry and ptycho-tomography at the STFC Diamond Light source and The X-ray Imaging facility at the Royce Institute, Manchester. Such measurements (in-situ with mechanical testing and EM exposure) not only assist the PhD student and the team to understand the deformation mechanisms, bonding quality, morphological effects and any possibility of molecular structural evolution during exposure at the interface level, they will also provide data for calibration and development of the MD and meso-scale models' parameters.