动态荷载下随机分布纤维增强混凝土的破坏机制研究

Mechanical characteristics of fiber reinforced concrete (FRC) under kinetic loading, such like explosive shock wave or hyper speed impact, are quite different to the one under quasi-static loading. The involvement of fibers makes loading features of FRC even more complicated. Study on failure mechanism of FRC under various kinetic shock waves, interface control pattern, content and ratio of fiber, is therefore proposed to be conducted on a multiple-phases heterogenic composite, which is made of a concrete matrix and mixed of fibers and stick interfaces. The study is based on meso-damage mechanics, elastic-brittle theory and kinetic FEM. Heterogeneity of material and viscoelastic boundary conditions are also involved in to generate a meso-mechanical numerical model for FRC under kinetic impact. In addition, techniques of parallel FEM based on MPI have been developed for carrying out such intensive computations. The purpose of this study is to reveal the macro mechanical properties of FRC, dynamic toughness strengthening mechanism of fiber and dynamic failure mechanism of FRC by investigating the procedure of crack initialization, development and run-through, analyzing dynamic loading features of fibers, identifying influence of fiber ratio and understanding failure characteristics of interface etc. In this study, adopting meso-kinetic mechanics and parallel computational techniques will be helpful to overcome difficulties in simulating micro failures when stress wave is propagated. It will break through difficulties in finding solutions of wave propagation in a multiple-phases heterogenic media with infinite domain. The whole dynamic failure processes of FRC can, therefore, be simulated. This study is valuable to dynamic failure theory of FRC and application in engineering.

纤维增强混凝土材料在爆炸冲击波和高速侵彻等动力作用下力学特性，与准静态时有明显不同，而纤维的掺入使得混凝土受力特点更具复杂性。针对以混凝土材料为基质、纤维材料及其粘结带组成的多相非均匀复合材料，基于细观损伤力学、弹脆性理论与动力有限元，引入材料的非均匀性与粘弹性边界方法，建立纤维混凝土在动力冲击作用下的细观力学模型，并发展基于MPI的并行有限元模拟方法，研究在不同动力荷载波形、界面控制、纤维含量和混杂比例下的破坏机理。通过研究动力下的裂纹萌生、扩展与贯通过程，分析纤维材料动态受力特点、纤维混杂比例的影响、界面动态破坏特性等，揭示其宏观力学性能、纤维动态增强增韧机理、动态断裂破坏机制。本研究采用细观动力学与并行计算，克服应力波传播过程中的细观层次上微破裂模拟的困难，突破无限域非均匀多相介质中波动问题求解，实现纤维混凝土的宏观动态破坏过程模拟，对于提升其动态破坏理论及工程应用，都具有重要价值。

本项目建立应变率依赖性的混凝土动态强度准则，在并行计算平台上建立纤维混凝土材料动力破坏的并行模拟方法，研究混凝土动态本构模型、并行模拟算法及细观参数选取、应变率本质特征、动态冲击破坏、纤维混凝土单丝与双丝拉拔变形破坏等问题。.（1）理论模型与并行计算研究：基于等效连续损伤理论方法，通过引入动态强度增强因子，基于OpenMP类库和超松弛预处理共轭梯度法的并行算法，实现动态荷载作用下混凝土材料变形破坏全过程的模拟。.（2）霍普金森压杆的冲击试验与数值模拟研究：建立了混凝土霍普金森压杆冲击试验数值模型，揭示影响混凝土真实动态强度、惯性承载力和混凝土应力状态的相关因素及其相互作用规律。通过物理实验和数值模拟相结合的方法，分别探讨了动载下的应变率效应和预制裂缝的巴西圆盘试件劈裂试验，研究裂缝条数、裂纹夹角对混凝土冲击破坏的影响规律。.（3）混凝土试件的动态单丝和双丝拉拔模拟研究：模拟研究动载作用下混凝土试样单丝和双丝拉拔条件下的混凝土-纤维界面性能演化规律，分析界面弹性模量、双丝拉拔试件基体性能，以及纤维埋深等对试件的破裂模式和相关力学性能，采用并行模拟方法对基体水泥中不同掺量钢纤维、聚丙烯纤维和玻璃纤维对双丝拉拔混凝土试件力学性能的影响进行研究。.（4）混凝土颗粒和孔洞缺陷对动态裂纹扩展路径的影响：通过建立落锤冲击数值模型，研究混凝土动态裂纹扩展路径中颗粒和孔洞等宏观非均匀特征对动态承载力的影响，揭示了动载作用下骨料颗粒提升混凝土试样强度的力学机理。.本研究数值模拟方法克服了应力波传播过程中的细观层次上微破裂模拟的困难，揭示了动态荷载作用下的混凝土应变率效应，总结了混凝土单丝与双丝拉拔试验中的界面力学性能的影响，对于理解纤维增强混凝土的动态破坏理论与工程应用，具有重要的参考意义。.通过4年研究基本完成研究任务，发表标注基金资助号论文17篇，培养博士研究生3名、硕士生8名，参加学术会议7人次。