混凝土断裂及亚临界扩展的细观机制

通过模型和三点弯曲断裂SEM试验,详细研究了混凝土断裂全过程及亚临界扩展的细观机理。结果表明:混凝土断裂是一个复杂的不规则过程,存在明显的亚临界扩展现象。混凝土亚临界扩展路径是曲折的,并非经典断裂力学假定的平直路径,混凝土亚临界扩展和临界失稳扩展呈现分形特征。用起裂断裂韧性K_ICⁱ和分形等效断裂韧性K_IC^e,f来描述混凝土抵抗初裂和临界失稳扩展的能力。给出了考虑亚临界扩展弯折效应的混凝土亚临界扩展长度、混凝土起裂断裂韧性K_ICⁱ和分形等效断裂韧性K_IC^e,f的计算表达式。计算表明:混凝土失稳断裂时的分形等效断裂韧性K_IC^e,f与混凝土亚临界扩展的分维数D成正比。

THE MESOMECHANISM OF FRACTURE PROCESS AND SUBCRITICAL CRACK GROWTH IN CONCRETE

The mechanisms of concrete fracture process and subcritical crack growth in mesoscale level have been systematically investigated through the model tests and the three-point bending fracture tests with Scanning Electron Microscope (SEM). It is shown that the fracture of concrete behaved complicatedly and irregularly, which underwent explicitly a subcritical crack growth prior to the unstable crack propagation. The subcritical crack growth appeared a kink path rather than a straight path assumed in the conventional fracture mechanics. The subcritical crack growth and the critical unstable growth behaved the fractal features. The initial fracture toughness iICK and the fractal equivalent fracture toughness feICK, were proposed to quantify the resistance capacity against the initial crack propagation and the critical unstable crack propagation in concrete. The formulas of the subcritical crack growth length, the initial fracture toughness iICK and the fractal equivalent fracture toughness feICK, were deduced in this paper. It indicates that the fractal equivalent fracture toughness feICK, at the critical unstable crack propagation is positively proportional to the fractal dimension of subcritical crack propagation.