基于界面能密度的界面效应表征理论及其对纳米复合材料力学性能的研究

Due to the relative large ratio of interface area to volume, the mechanical properties of nanocomposites exhibit a size-dependent behavior, i.e., the interface effects of nanocomposites. An interface elastic constant was introduced in the existing meso-mechanics models considering the interface effects, which is very difficult to be determined and brings inconvenience to practical applications. Considering the interface energy density as a critical physical quantity characterizing interface properties, the present project aims to develop an interface energy density-based theoretical model, in order to characterize the mechanical behavior of materials with nano-scale interfaces, then the interface elastic constants is no longer involved. Firstly, considering the influences of the interface deformation on the interface energy, we will study analytical formulations of interface energy density based on the lattice model, which will be combined with the stress discontinuity condition in terms of the interface energy density to develop a new theory characterizing interface effect within the framework of continuum mechanics. Secondly, elastic and elasto-plastic meso-mechanics models will be established based on the new theoretical model, in order to predict mechanical behaviors of nanocomposites and analyze the interface effect on the mechanical properties of nanocomposites. Finally, mechanical tests of nanoparticle-reinforced composite will be carried out. Combining the experimental research and theoretical analysis, microstructure design methods will be proposed to improve the service performance of nanocomposites. The achievements of this project should be helpful for predicting the mechanical properties of nanocomposites and providing theoretical guidance for the design and application of nanocomposites.

纳米复合材料由于具有较大比界面积，其力学性能显现出尺寸相关特征，即界面效应。已有考虑界面效应的理论模型普遍使用界面弹性常数，该参量的确定给理论应用带来一定困难。由于界面能密度是公认的表征界面性能的物理参量，本项目旨在发展一种基于界面能密度的理论模型，刻画含纳尺度界面微结构材料的力学行为，同时避免引入界面弹性常数。首先，基于原子晶格模型，考虑界面变形对界面能量的影响，研究界面能密度的解析表述，结合包含界面能密度的应力不连续条件，建立在连续介质力学框架下的新界面效应表征理论。其次，基于新表征理论建立弹性和弹塑性细观力学模型，预测纳米复合材料的力学行为，分析界面性质对材料宏观力学性能的影响机理。最后，开展纳米颗粒增强复合材料的力学实验，结合理论研究，提出微结构设计方法，以改善纳米复合材料的服役性能。本项目成果可以更方便地预测纳米复合材料力学性能，同时为纳米复合材料设计和应用提供更合理的理论指导。

纳米复合材料由于具有较大比界面积，其力学性能显现出尺寸相关特征，即界面效应。已有考虑界面效应的理论模型普遍使用界面弹性常数，该参量的确定给理论应用带来一定困难。由于界面能密度是公认的表征界面性能的物理参量，本项目基于界面能密度概念发展了一种纳米复合材料界面效应的弹性表征理论，该理论模型中不包含界面弹性常数，仅包含形成界面的两种材料在块体状态下的表面能密度、两种材料的表面弛豫参数及其形成共格界面时的表面晶格失配参数，三类参数均可通过实验或简单计算获得。运用该理论预测了纳米复合材料弹性性能的尺寸效应，揭示了界面共格/非共格结构及界面变形对纳米复合材料界面结合及等效弹性模量的影响机制；运用第一性原理方法揭示了纳米复合材料共格/非共格界面能密度尺寸效应的原子尺度物理机制；建立了考虑界面损伤的弹塑性细观力学模型，揭示了界面脱粘对颗粒增强金属基复合材料力学性能的影响；系统研究了纳米颗粒增强硅橡胶基复合材料的微观强韧机制，并建立了能够准确预测颗粒填充软基复合材料大变形力学行为的本构模型；理论结合实验，设计并制备了高强高韧及高强高粘的柔性纳米复合材料。本项目研究成果能够为精准预测纳米复合材料力学行为提供有效的理论工具，为先进复合材料体系的优化设计提供理论指导，并发展了微纳米力学和复合材料力学。