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断裂参数研究是UHPFRC(超高性能纤维改性混凝土)断裂性能研究的关键课题之一。该文假设钢纤维对应力强度因子和裂纹尖端张开位移的闭合作用服从线性分布,短钢纤维三维乱向随机均匀分布于UHPFRC基质内,推导了基于钢纤维几何性能参量和物理性能参量的UHPFRC断裂参数,即临界应力强度因子和临界裂纹尖端张开位移的理论表达。据此推导了抗力阻值曲线的计算参数,构造了UHPFRC的抗力阻值曲线。利用柔度理论和所构造的R曲线方程,预报了具有不同初始刻槽的UHPFRC三点弯曲梁的载荷变形关系。同时开展了具有不同初始刻槽的三点弯曲梁加载试验。模型预报结果与实验数据对比表明:该文给出的短钢纤维的桥联作用引起的应力强度因子衰减和裂纹尖端张开位移的闭合作用模型假设相对合理。由于给出的断裂参数是钢纤维的几何性能参量和物理性能参量的函数,这样为开展基于断裂力学的纤维混凝土材料的微观组分配比设计提供了新思路。该文给出的UHPFRC双参数断裂模型,还可作为UHPFRC结构安全评定有限元软件开发的模型参考。
Fracture parameter research is one of the key issues in the study of the fracture properties of UHPFRC (ultra-high performance fiber-modified concrete). This paper assumes that the close interaction between steel fiber stress intensity factor and crack tip open displacement obeys a linear distribution, and the three-dimensional random distribution of short steel fiber is uniformly and uniformly distributed in the UHPFRC matrix. The UHPFRC based on geometrical and physical properties of steel fiber is derived Fracture parameters, namely the critical stress intensity factor and the theoretical expression of the critical crack tip opening displacement. Based on this, the calculation parameters of resistance resistance curve are deduced, and the resistance resistance curve of UHPFRC is constructed. Using the flexibility theory and the constructed R curve equation, the load deformation relationship of UHPFRC three-point bending beams with different initial grooves is predicted. Three-point bending beam loading tests with different initial grooves were also carried out. The comparison between the model prediction results and the experimental data shows that the model of the closure effect of the stress intensity factor attenuation caused by the bridging action of short steel fibers and the crack tip opening displacement is relatively reasonable. Since the fracture parameters given are a function of the geometrical and physical properties of the steel fiber, this provides a new idea for the design of the microstructure ratio of the fiber-reinforced concrete based on fracture mechanics. The UHPFRC dual-parameter fracture model presented in this paper can also be used as a reference for the development of UHFFRC structural safety assessment finite element software.