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

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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.