The quantificational exploration of the propagation law of fracture process zone (FPZ) is of great importance to the research on concrete fracture. This paper performed fracture experiments on pre-cracked concrete beams under various loading rates. Digital image correlation (DIC) method was applied to obtain the whole field displacement of concrete in the fracture test. The crack opening displacement (COD) and the evolution of FPZ were determined based on the whole field displacement. The results show that the length of FPZ first increases and then decreases with the development of the effective crack length and the maximum length of FPZ is about 60 mm. It can be found that the length of FPZ corresponding to the peak load decreases with the increase of loading rates. Based on the fictitious crack model, a bilinear softening model was established. According to the proposed model, the mechanical behavior and the propagation law of FPZ were analyzed. The bilinear softening model can reflect the microcrack development and the aggregate interlocking in the FPZ.

中文翻译：

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不同荷载速率下混凝土裂缝扩展的数字图像相关试验研究

断裂过程带(FPZ)扩展规律的量化探索对于混凝土断裂研究具有重要意义。本文对预裂混凝土梁进行了不同加载速率下的断裂试验。应用数字图像相关（DIC）方法获得混凝土在断裂试验中的全场位移。基于整个场位移确定裂纹张开位移（COD）和FPZ的演变。结果表明，随着有效裂纹长度的发展，FPZ的长度先增加后减小，FPZ的最大长度约为60 mm。可以发现，峰值载荷对应的FPZ长度随着加载速率的增加而减小。在虚构裂纹模型的基础上，建立了双线性软化模型。根据所提出的模型，分析了FPZ的力学行为和传播规律。双线性软化模型可以反映FPZ中微裂纹的发展和骨料的互锁。