超高韧性水泥基复合材料延性断裂模型的研究

Ultra-high toughness cementitious composites (UHTCC), which is a kind of fiber reinforced cementitious composites, strongly improves the tensile brittleness and fracture toughness of concrete. This material exhibits ductile fracture, which is more safe and durable for structures in contract with quasi-brittle fracture of concrete and fiber reinforced concrete. Theoretical and mechanical investigation on the ductile fracture model of UHTCC is carried out in this project. Firstly, based on the ductile fracture mechanism and the constitutive relation model, a double-parameter fracture model of UHTCC is developed, with initial-cracking fracture toughness and failure fracture toughness as its parameters. Energy field superposition theory is employed to explain the calculation relationship of the two parameters. Secondly, in order to calculate these two parameters, the fracture energy is achieved through J-integral method, while the equivalent critical quantity of crack propagation is obtained by the specimen's deformation. Then, a calculation formula of these two parameters of fracture toughness is derived. Meanwhile, the size effect of the model parameters is studied, as well as the influence of fiber volume fraction. Thirdly, the crack propagation resistance curve (R curve) and the simplified R model of this material are constructed according to the experimental results of type I fracture. The relation between the simplified R model and the ductile fracture model is illustrated. In addition, a comparative study on the performance of the two models on evaluating the ductile fracture toughness is taken. In a word, The research objective of this project is to develop the fracture model of UHTCC, and to calculate the model parameters, for the purpose of developing a theoretical basis for engineering application and safety assessment of this material.

超高韧性水泥基复合材料对改善混凝土的拉伸脆性与断裂韧性均有显著成效。该种材料具有延性断裂性能，与准脆性断裂相比，延性断裂在失效前存在充分缓冲空间，可有效提高工程结构的安全性与耐久性。本项目对超高韧性水泥基复合材料的I型断裂模型进行了理论与试验研究：基于该材料的本构关系模型与延性断裂机理，建立延性断裂双参数模型，即起裂断裂韧度与失效断裂韧度，根据能量叠加方法，建立双参数的运算关系；应用J积分求解断裂能，通过试件变形量计算临界裂缝等效扩展量，再用能量法建立临界断裂韧度的计算理论，并研究其是否具有尺寸效应以及纤维体积掺量的影响效果；构建裂缝发展R阻力曲线与简化R模型，建立该模型与延性断裂模型的联系，对比二者对评价超高韧性水泥基复合材料断裂韧性的优缺点。本研究旨在建立超高韧性水泥基复合材料的延性断裂模型并确定模型参量的确定方法，为工程应用与安全评估提供依据。

超高韧性水泥基复合材料（UHTCC）具有延性断裂性能，可有效提高工程结构的安全性与耐久性。本项目基于非线性断裂力学分析了UHTCC的I型断裂性能，建立了该材料的延性断裂模型。.对UHTCC预制切口梁进行了I型断裂与疲劳断裂试验。得出试件的荷载-裂缝口张开位移曲线，分阶段分析断裂过程及疲劳裂缝扩展过程，说明UHTCC的断裂破坏方式及裂缝发展模式。.提出评价UHTCC断裂性能的断裂准则。用非线性断裂力学J积分方法表征UHTCC的延性断裂性能，建立双参数断裂准则：起裂断裂能与失效断裂能，分别表示为开裂临界与失效临界。推导断裂参数的计算理论，根据试验数据计算得出起裂断裂能与失效断裂能。.建立UHTCC的JR阻力曲线公式。用宏观裂缝覆盖面积发展量代替裂缝扩展长度，作为描述裂缝发展的参量，说明JR阻力曲线的三阶段线性关系，分界点为宏观裂缝出现点与主裂缝局部化点。引入等效屈服应力，给出裂缝稳态发展阶段的J积分阻力曲线公式。.构建UHTCC的裂缝扩展规律公式。基于描述裂纹扩展规律的Paris公式，本项目提出了UHTCC的裂纹扩展规律公式，以J积分与裂缝覆盖面积表征。分析纤维掺量对裂缝扩展速率的影响，结果表明，随纤维掺量的增加，UHTCC试件的疲劳裂纹扩展速率成递减趋势，纤维掺量的影响愈加明显。.给出UHTCC延性断裂的损伤扩展模型。假定该材料为各向同性的均质材料，应用连续损伤力学分析断裂情况下该材料的损伤发展过程，建立损伤发展模型。同时。由于J积分作为自变量受试件尺寸影响很大，本项目应用疲劳应力水平作为损伤扩展的自变量，研究表明，损伤量与应力水平之间存在单对数线性关系。.本项目提出了用断裂能表征UHTCC断裂性能的断裂准则，发展了JR阻力曲线公式，构建了表征多裂缝发展过程的裂缝扩展规律公式，建立了延性断裂过程的损伤扩展模型，并应用试验数据计算相应模型参数。项目研究成果为该材料的工程应用与安全评估提供理论依据，并完善了UHTCC的延性断裂理论。

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