13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- Figure 6. Differences Δt between automatically and manually picked arrival times for the STA/LTA (top) and the AIC-picker (bottom). The pie charts show the performance of both automatic pickers. The signals have different reading precisions of their onsets, depending on the signal to noise ratio and how impulsive onsets are. The results from the two methods are both acceptable, although the STA/LTA-picker obviously shows a trade-off. With the AIC-picker almost twice as many signals than the STA/LTA-picker are picked in a very good correlation, Δt ≤ 1.25μs. Also, the number of mispicks with Δt ≥ 5μs in the noise and picks too late in the signal could be reduced from 26.5% of that in STA/LTA-picker to 18.5%. Accordingly, the AIC-picker can be suggested as a reliable and accurate algorithm to determine the onset times of AE signals in masonry structures. 5. Discussion and conclusion With wide existence of masonry structures, the monitoring techniques have received considerable attention due to the increasing demand of the structural retrofit and strengthening. As one of the non-destructive monitoring techniques, acoustic emission technique is employed for the masonry cracking analysis. For AE applications in monitoring, localization of AE sources is important to offer the information of the active damage region. The investigation of the localization accuracy has shown that monitoring results are greatly influenced by the material of structures. Classical localization method is mostly adopted to realize the localization operation in metal and concrete structures. However, for the masonry structures, the complicated material properties make the classical localization method cannot be applied directly. The modified localization method proposed in this paper allows giving a reasonable location results. In the modified method, a modified factor ki related to inhomogeneous or propagation delay is introduced. The degree of the heterogeneity in ki plays a key role to eliminate the effect of the inhomogeneous of the material. Accordingly, the pencil-lead break velocity tests on the masonry
RkJQdWJsaXNoZXIy MjM0NDE=