Analyzes of Fracture Process Zone by AE and Constitution of its Numerical Model

一般认为，断裂过程区由含有大量微裂纹的微裂纹区和具有内聚力的桥接区组成。然而，混凝土和砂浆中这些区域的长度、宽度和形状尚不清楚。为了识别混凝土和砂浆试件中的微裂缝区域，我们在接近最大载荷和应变软化区的三维声发射源位置使用了由声发射事件计数率控制的加载方法。混凝土和砂浆试件的尺寸为高150 mm，厚94 mm，宽550 mm。这些试件的骨料最大粒径分别为15 mm和5 mm。经鉴定，混凝土和砂浆中微裂纹区的平均长度分别为51 mm和61 mm，平均宽度分别为71 mm和57 mm。此外，通过染料的渗透，我们确定了混凝土和砂浆试件中的桥接区分别为54毫米和31毫米。根据上述结果，混凝土和砂浆试件的断裂过程区总长度分别为105 mm和92 mm。基于声发射波形分析得到的微裂纹表面方向的统计分布，我们建立了各向异性的连续损伤理论。然后，利用该理论和有限元方法，建立了断裂过程区的数值模型，分析了三点弯曲试验中裂纹的扩展情况。与试验结果相比，断裂过程区的各种损伤程度都比较好，但最大载荷-位移曲线并不理想。

It is generally recognized that the fracture process zone is composed of a microcracking zone including very many microcracks and bridging zone with cohesive stress. However, lengths, widths and shapes of these zones in concrete and mortar have not been clarified.To identify the microcracking zones in concrete and mortar specimens, we used the loading method controlled by the AE event count rate in near the maximum load and strain softening-region and three-dimensional AE source location. The dimensions of concrete and mortar specimens are 150 mm high, 94 mm thick and 550 wide. The maximum grain sizes of aggregate in these specimens are 15 and 5 mm respectively. As a result of identification, the average lengths of microcracking zones in concrete and mortar were 51 and 61 mm respectively, and their average widths were 71 and 57 mm respectively. In addition, by penetration of dye, we identified that the bridging zones in concrete and mortar specimens were 54 and 31 mm. From the above results, the total lengths of fracture process zones in concrete and mortar specimens were 105 and 92 mm.Based on the statistical distributions of directions of microcrack surfaces obtained by the AE waveform analysis, we formulated an anisotropic continuum damage theory. Then, by this theory and the finite element method, we constituted a numerical model of the fracture process zone, and analyzed crack growth in the three-point bending test. Compared with experimental results, the extent of various damage levels of the fracture process zone was fairly good, but the maximum load-displacement curve was not satisfactory.