基于非局部连续介质理论的水泥基材料多尺度力学研究

This project aims to build up the elementary theory framework of multiscale mechanics of cementitious materials based on the nonlocal continuum field theory, which is concerned with the physics of material bodies whose behavior at a material point is influenced by the state of all points of the body. The nonlocal theory links the materials'mechanics information of atom-scale and/or micro-scale to the mechanics properties of macro-scale by the parameter of material's internal characteristic length and the kernel function, which are all included in the nonlocal constitutive equation. To determine the exact nonlocal constitutive equation, the atom-scale constitutive is first examined by molecular dynamic method based on the atom model of cementitious materials.For micro-scale mechanics properties,the microstructure of cementitious materials is considered as composites material containing three phases,the C-S-H system phase,the unhydrated cement grain phase and the pore phase. The distribution law of strain and stress in the micro-scale composites is investigated when the size of each phase changes. Then the mechanics information of atom scale and/or micro-scale can be transferred to the nonlocal theory to help determine the exact internal characteristic length and the kernel function. Thus, the theory framework of multiscale mechanics of cementitious materials is completed，which offers the theory basis to improve the design level of cementitious materials and overcome the difficulty of concrete materials and structures' durability problem in civil engineering.This research can also be contributed to promote the mordern concrete theory to the rational mechanics.

本课题旨在初步建立水泥基材料原子尺度-微观尺度-宏观尺度的多尺度力学理论框架。通过寻找水泥基材料内部特征尺度的确定方法和弹性核函数的确定表达，建立基于非局部连续介质理论的多尺度力学模型。为此，首先建立水泥基材料典型水化产物的原子模型，采用分子动力学方法研究原子尺度C-S-H凝胶簇的本构关系。其次在微观尺度上，将水泥基材料看做C-S-H凝胶簇、未水化水泥颗粒和孔洞组成的三相复合材料，研究各组成相的尺寸变化与变形场和应力场分布规律的关系。通过把原子尺度的力学信息传递到微观尺度，把原子尺度和微观尺度的力学信息传递到宏观尺度，建立基于非局部连续介质理论的水泥基材料多尺度力学计算体系。这一研究将为进一步提高混凝土材料的设计水平、突破现有混凝土材料和结构耐久性问题的技术瓶颈奠定理论基础，同时也为现代混凝土材料理论向理性力学的方向发展做出基础性贡献。

水泥基材料原子尺度-微观尺度-宏观尺度的多尺度力学计算是混凝土高性能设计和耐久性问题的理论基础。本项目在这一问题上做了初步探索。首先通过一系列微观测试与表征方法，解析了水泥基材料的基本矿物成分及其化学结构，基于此采用两种方法建立了C-S-H凝胶分子模型，并对C-S-H凝胶进行了基本力学性能的分子动力学模拟；通过微观测试技术，表征了水泥基材料的微观形貌和孔隙结构特征，建立了材料的微观结构模型，探讨了多相孔隙材料在力场作用下的应力分布规律；最后建立了基于非局部连续介质理论的材料多尺度本构模型和裂尖应力计算方法。这一研究将为水泥基材料多尺度研究的进一步深化和系统建立水泥基材料的“材料基因”计算体系奠定初步基础。