13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- structure to measure the relation between the wave velocity and travelling distance should be fulfilled before the monitoring. Based on this test result, the value can be obtained and employed in the monitoring process. The sensor arrangement is another task which should be carefully considered. The investigation of the localization accuracy has shown that the sensor distribution is essential for monitoring AE activity in the specimen. The ideal condition is to ensure that all relevant regions are covered by enough sensors before the monitoring starts. Detected events are only a fractional amount of all recorded AE signals and, again, only a limited number of all detected events can be localized with a sufficient accuracy. For a good imaging of crack progression it is necessary that enough events could be localized. Therefore the proper arrangement of the sensors can give us more available points, which is well testified by the c value in Fig. 4. In conclusion, with the assistance of the reliable onset time picker (AIC-picker) and proper sensor distribution, the source localization in masonry can be realized properly by the modified model. References [1] A. Carpinteri, G. Lacidogna, G. Niccolini, Acoustic emission monitoring of medieval towers considered as sensitive earthquake receptors. Natural Hazards and Earth System Sciences, 7 (2007) 251-261. [2] C. Melbourne, AK. Tomor, Application of Acoustic Emission for Masonry Arch Bridges. Strain, 42 (2006) 165-172. [3] A. Carpinteri, G. Lacidogna, Damage monitoring of an historical masonry building by the acoustic emission technique. Materials and Structures, 39 (2006) 161-167. [4] J. Xu, G. Lacidogna, Modified Acoustic Emission source localization method to determine crack locations for masonry arch bridge. Applied Mechanics and Materials, 71-78 (2011) 4823–4826. [5] E. Verstrynge, L. Schueremans, DV. Gemert, M. Wevers, Application of the acoustic emission technique to assess damage in masonry under increasing and sustained axial loading, in: NDTCE’09, Non-Destructive Testing in Civil Engineering. Nantes, France, 2009. [6] A. Carpinteri, J. Xu, G. Lacidogna, A. Manuello, Reliable onset time determination and source location of acoustic emissions in concrete structures. Cement & Concrete Composites, 34 (2012) 529-537. [7] CU. Grosse, M. Ohtsu, Acoustic Emission Testing: Basics for Research - Applications in Civil Engineering, Springer, 2009. [8] B. Schechinger, T. Vogel, Acoustic emission for monitoring a reinforced concrete beam subject to four-point-bending. Construction and Building Materials, 21 (2007) 483-490. [9] E. Verstrynge, L. Schueremans, D. Gemert, M. Wevers, Monitoring and predicting masonry's creep failure with the acoustic emission technique. NDT & E International, 42 (2009) 518-523. [10] D. Dutta, H. Sohn, KA. Harries, P. Rizzo, A Nonlinear Acoustic Technique for Crack Detection in Metallic Structures. Structural Health Monitoring, 8 (2009) 251-262. [11] G. Niccolini, J. Xu, A. Manuello, G. Lacidogna, A. Carpinteri, Onset time determination of acoustic and electromagnetic emission during rock fracture. Progress In Electromagnetics
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