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The problem of detection, identification and sizing of planar defects, particularly cracks in various parts and items is one of the most relevant to non-destructive testing. This problem becomes even more complicated in case when testing is possible only with one surface of the part (e.g., during in-service inspection of various pipelines, vessels, equipment corps with limited access to the inner surface) to detect cracks, located in the opposite (inner) surface, both in the parent metal and in welds.

Hypocenter locations of shallow earthquakes in Horonobe area, northern Hokkaido, Japan, which is near the convergent boundary between Okhotsk and Amuria plates, were determined to reveal the subsurface structure and the mechanisms of earthquake occurrence. The absolute source locations of 211 earthquakes, which occurred in the period from December 2002 to September 2005, were determined; then, those earthquakes with similar waveforms were identified, and the source locations of 26 multiplet groups were relocated by using cross-spectrum and clustering analyses. The relocated hypocenters allowed two seismically active areas to be identified, at 1020 km and 2530 km depth. The earthquake locations indicate structures trending nearly N-S direction, and the structures causing repeated stick-slips at asperities, thus generating similar earthquakes. The relationships between magnitude and the distance to the next event, and between magnitude and the time interval of event occurrences were investigated. The relationships between them suggest that earthquake swarms would be induced by continuous strain accumulation at asperities along faults and its subsequent release as a result of plate tectonic movements. A cutoff line could be also seen in the relationship between magnitude and the distance to the next event, suggesting that the distance between the source locations depends on the event magnitude. These results have given us the knowledge that the asperities on the delineated faults intermittently release strain energy as similar earthquakes with magnitudes of less than about 3.0.

Several regulatory rules, such as the Best Practices Guideline (GBP) [1], exist for acoustic emission (AE) testing of pressure vessels in France and the rest of the world and allow AE testing based on two techniques (zonal location and planar source location methods). However, the analysis criteria of data recorded during the testing lack adequate basis. This work highlights inconsistencies in analysis methods defined in these guides or codes based on modelling calculations in Part 1 of this study [2], while this paper shows, from a real case (AE testing of a 2000 m3 spherical storage tank), that the results of an AE test cannot be reproducible due to a lack of strictness in the application rules of AE. Thus, depending on the testing configuration used, some emissive defects can be detected or missed. This study may also be used as a basis for defining a new AE testing standard specifically and quantitatively defining a methodology of analysis based on a different approach from those used currently. Today, the CETIM may apply this new testing methodology based on significant feedback enabling a greater reproducibility and sensitivity of AE testing.

Bending, concrete, fracture mode, steel fibers. Introduction The application of fiber reinforcement in cementitious materials continues to expand. Fibers restrain the breakage of the brittle matrix and enhance its weak tensile properties (Stahli and van Mier, 2007). As the content of the fibers increases, the possibility that the crack growth will be hindered through an arrest mechanism also increases. As a result, the material toughness is also increased (Mobasher et al., 1990, Sivakuram and Sathanam, 2007). An unreinforced concrete member fails catastrophically at the maximum load. Fibers mainly improve its post-peak behavior, while in many cases the maximum load is also significantly increased (Fischer and Li, 2007, Washer et al. 2004). To clarify the mechanisms for this behavior, acoustic emission (AE) monitoring has been carried out during fracture tests. There are numerous applications of the AE technique for damage characterization of concrete structures (Shiotani and Aggelis, 2007, Shiotani et al. 2007, 2001, Aggelis et al. 2007, Triantafyllou and Papanikolaou, 2006, Golaski et al., 2006, Shah and Weiss 2006). Study of the AE behavior can lead to the characterization and quantification of the damage level via the use of AE descriptors and thus provides an early warning prior to the macroscopically observed fracture. Further study of the transient waveforms provides information about the fracture process. The source of the AE activity is closely connected to the mode of fracture (Shigeishi and Ohtsu, 1999). Nucleation of shear cracks follows tensile crack nucleation. Therefore, the determination of the dominant mode provides an early warning prior catastrophic failure. However, the application of AE to such materials entails certain difficulties. These mainly concern the accurate interpretation of the results due to the different individual processes that contribute to the fracture of concrete. Fracture occurs between different interfaces; cement paste and sand, mortar and aggregates, concrete and fibers. Additionally, failure includes aggregate crushing a