13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- 3.2. Sensor distribution and source localization tests Ad hoc tests are performed to reproduce AE source using pencil-lead break on the right-side surface of the masonry abutment. Six sensors are attached to the surfaces, shown in Fig. 4. In particular, 19 different pencil-lead break points (artificial source) are drawn on this surface, and for each point the tip of a pencil is broken 8 times, so a total of 152 measurements are recorded. For this test 912 AE events from the six sensors are obtained and then sensor distribution and the source localizations of all the 19 points are analyzed in the following sections. Figure 4. Results of the source localization calculated from the classical and the modified methods. In [a, b, c], a is the average error of all the available breaks from the classical method, and b is the average error of all the available breaks from the modified method, and c is the available breaks which can be used for each point. 4. Accuracy analysis of AE locations based on the test 4.1. Degree of inhomogeneity The classical localization method can be used in the concrete structures according to the experiences [6-8]. But the localization of AE source in masonry structures is highly complicated, as attenuation and wave velocity are dependent on the heterogeneity of the material (not only the interface between bricks and mortar, but also cracks and cavities in existing structures). The theoretical analysis in Section 2 and the test result in Section 3.1 both illustrate that the classical localization method based on Eq. (2) cannot be used directly in masonry. A modified method based
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