基于近场动力学理论的混凝土非局部本构建模与渐进破坏研究

Even though concrete materials and structures have been studied for many years, their failure process has not been fully understood yet. Especially, the progressive failure process in concrete materials and structures cannot be predicted accurately due to the incapability of current available simulation tools. To potentially solve this problem, the objective of the proposed research is to study the effect of microstructures on mechanical behavior of concrete， and shed new light on predictability of damage accumulation and progressive cracking in concrete materials and structures using a novel and promising numerical tool of non-local peridynamics. .The proposed study is divided into the following three major tasks:(a) characterizing the microstructures of concrete with experiments and statistical analysis, and developing an integral-type non-local peridynamic constitutive model for concrete correspondingly.(b)establishing the theoretical aspects for homogenization, mesh adaptivity and error estimation under the framework of peridynamics, and then conducting numerical simulations on damage accumulation, crack initiation and propagation in concrete materials and structures. Without using the gradient of displacement in its equation of motions, the non-local peridynamic model in the proposed study can evidently enhance its capacity of solving discontinuity problems, as compared to commonly used classical differential models based on continuum mechanics.(c) validating and calibrating the peridynamic model and numerical methods with experiments, and summarizing guidelines for peridynamics-based constitutive model and numerical simulation methods for progressive cracking of concrete materials and structures..A thorough investigation will be conducted into the effect of microstructures of material on mechanical behavior and the progressive failure mechanism of concrete under the framework of peridynamics in the proposed research. The final product of the proposed study is a fundamental design framework for high performance damage-tolerant concrete, and a concise summary of practical guidelines for failure prediction and safety evaluation of concrete structures with the aid of adaptive non-local peridynamics modelling and simulation. A reliable numerical framework as proposed in this study will reduce dependence on experimental methods for evaluation of concrete structural performance. Furthermore, the non-local model and integral-type numerical method proposed in this study provides a new promising alternative for analyzing complicated discontinuity problems, such as three dimensional damage accumulation and progressive cracking in concrete and other heterogeneous and isotropic materials.

混凝土材料和结构的破坏一直是研究者关注的焦点，但其损伤累积和渐进破坏机制尚无法精确描述。本项目引入新兴的适于求解不连续问题的近场动力学（Peridynamics，PD）思想，对混凝土细微观结构进行参数表征和统计分析，基于物质点间的相互作用建立考虑材料细微观结构特征的混凝土积分型非局部PD本构模型；构建相应的混凝土PD模型均质化方法、自适应算法以及误差估计方法，通过求解空间积分方程模拟混凝土结构中损伤累积以及裂纹萌生、扩展、贯通的渐进破坏全过程，突破基于连续介质力学理论的传统方法在模拟破坏问题时的瓶颈；通过不同静、动荷载实验验证混凝土PD本构模型和算法模拟结构渐进破坏的精度与效率；根据数值模拟结果找出混凝土细微观结构参数与宏观力学特性之间的内在联系，分析混凝土破坏的物理机制，为新型高性能混凝土的研发和混凝土结构的安全评估提供科学依据，并为混凝土类复杂非均质材料的损伤破坏模拟提供新的思路。

混凝土材料和结构的破坏一直是研究者关注的焦点，但其损伤累积和渐进破坏机制尚未能得到准确描述。本项目引入新兴的适于求解不连续问题的近场动力学（Peridynamics，PD）思想，考虑混凝土材料的细微观结构特征，建立了能描述混凝土损伤累积和渐进破坏全过程的近场动力学模型和完整的数值计算体系，并成功应用于典型混凝土结构的变形破坏连续仿真中。通过项目研究，取得如下成果：.1、.构建了适合于描述混凝土力学特性和破坏规律的非局部PD本构模型。.在传统“键型”PD本构模型的基础上，引入能考虑长程力作用效应的修正项并结合连续介质力学微极理论，提出了能突破常规PD本构函数限制且定量计算精度更高的双参数PD本构力模型；充分考虑混凝土宏观力学行为的拉压异性及其细观结构特征引起的断裂特性，引入细微观的统计结果在物质点的尺度上定义物质点对的断裂以及局部损伤；在细观尺度，考虑混凝土的细观组分，构建考虑骨料、砂浆和界面性质以及考虑含微孔隙的混凝土PD模型；在微观尺度，针对水泥水化主要产物——水化硅酸钙（C-S-H）的特征，结合纳米压痕试验结果，将分子动力学方法和近场动力学方法结合起来，构建了水泥净浆和水泥砂浆的微尺度PD分析模型。.2、开发了完整的能连续模拟混凝土变形破坏全过程的PD算法体系.借鉴经典有限元法、分子动力学方法和传统无网格及粒子类方法中的离散、加载、迭代、求解模式等，引入局部阻尼比、失衡力收敛准则、物质点尺度比、时间步长自适应调整、外力边界等效转换与分级加载等概念，构建了完整的能够连续模拟混凝土变形破坏全过程，能以统一的格式求解不同静/动力、连续/不连续力学问题的PD数值计算体系。.3、实现典型混凝土构件渐进破坏过程的PD模拟，分析混凝土破坏的内在机制。.通过经典算例分析验证了所提出的模型和方法的计算精度与效率。在此基础上，分别开展了宏观、细观和微观尺度的典型混凝土变形破坏过程的PD模拟，分析了混凝土破坏的内在机制。.项目的研究成果为分析混凝土的力学行为以及混凝土结构安全可靠性和寿命预测提供了新的思路，也能为改善混凝土性能、研发新型高性能混凝土以及根据工程特点充分利用混凝土的长处、避开混凝土的短处提供科学依据，对构建非均质各向异性材料及其它复杂材料的本构模型和不连续介质力学问题的新型数值计算方法也具有重要的意义。