31 Acoustic Emission Monitoring of Rock Specimens During Fatigue Tests 245 100 1.0 2.0 3.0 1.0 2.0 3.0 200 300 400 500 600 700 800 100 200 300 400 t (minutes) b-value b-value t (minutes) 500 600 700 800 a b Fig. 31.6 b-Values for Granite (a) and Magnetite (b) specimens: Third phase. The b-value changes from higher to lower values close to 1 in correspondence of the final failure of the specimens 31.5 Conclusions In this paper, laboratory tests were performed on different kind of rocks with the aid a new AE equipment. The cumulated AE number is used to detect the damage evolution during cyclic tests. The fatigue damage evolution obtained by AE data lead to recognize three different phases during the tests. In particular the first and the last phase are characterized by a sudden increment into the AE number. By adopting statistical analysis on AE data was possible to describe the damage accumulation due to fatigue by a fractal description of the damage domain through the b-value. The trend observed for this parameter may be useful to recognize in advance the final failure condition in order to prevent the collapse due to fatigue in rock materials. Aknowledgements The Authors gratefully acknowledge Dr. M. Spampani and Dr. Michele Pedroni, and Alessandro Mitillo (Leane net. srl) for their valuable cooperation throughout the development of the new AE monitoring system. References 1. Lacidogna G, Manuello A, Niccolini G, Carpinteri A (2012) Acoustic emission monitoring of Italian historical buildings and the case study of the Athena temple in Syracuse. Architect Sci Rev 11(3):359–366 2. Carpinteri A, Lacidogna G, Pugno N (2004) A fractal approach for damage detection in concrete and masonry structures by the acoustic emission technique. Acoustique et Techniques 38:31–37 3. Carpinteri A, Lacidogna G (2006) Structural monitoring and integrity assessment of medieval towers. J Struct Eng (ASCE) 132:1681–1690 4. Carpinteri A, Lacidogna G (2006) Damage monitoring of an historical masonry building by the acoustic emission technique. Mater Struct 39:161–167 5. Carpinteri A, Lacidogna G, Paggi M (2007) Acoustic emission monitoring and numerical modeling of FRP delamination in RC beams with non-rectangular cross-section. Mater Struct (RILEM) 40:553–566 6. Carpinteri A, Lacidogna G (2007) Damage evaluation of three masonry towers by acoustic emission. Eng Struct 29:1569–1579 7. Carpinteri A, Lacidogna G, Manuello A (2011) Stability of the ancient Athena temple in Syracuse investigated by the b-value analysis. Strain 47:243–253 8. Carpinteri A, Lacidogna G, Niccolini G (2006) 2006 Critical behaviour in concrete structures and damage localization by acoustic emission. Key Eng Mater 312:305–310 9. Bieniawski ZT (1967) Mechanism of brittle rock fracture. Part II. Experimental studies. Int J Rock Mech Mining Sci Geomech Abstr 4:407–423 10. Brace WF, Paulding BW Jr, Scholz C (1966) Dilatancy in the fracture of crystalline rocks. J Geophys Res 71:3939–3953 11. Scholz CH (1968) Microfracturing and the inelastic deformation of rock in compression. J Geophys Res 73:1417–1432 12. Ohnaka M, Mogi K (1982) Frequency characteristics of acoustic emissions in rocks under uniaxial compression and its relation to the fracturing process to failure. J Geophys Res 87:3873–3884 13. Khair AW (1984) Acoustic emission pattern: an indicator of mode of failure in geologic materials as affected by their natural imperfections. In: Hardy HR Jr, Leighton FW (eds) Proceedings of the 3rd conference on acoustic emission/microseismic activity in geologic structures and materials, 1981, University Park, PA. Trans Tech Publications, Clausthal, pp 45–66 14. Eberhardt E, Stead D, Stimpson B, Read RS (1998) Identifying crack initiation and propagation thresholds in brittle rock. J Can Geotech 35:222–233 15. Carpinteri A, Lacidogna G, Niccolini G, Puzzi S (2008) Critical defect size distributions in concrete structures detected by the acoustic emission technique. Meccanica 43:349–363 16. Carpinteri A, Lacidogna G, Niccolini G, Puzzi S (2009) Morphological fractal dimension versus power-law exponent in the scaling of damaged media. Int J Damage Mech 18(3):259–282
RkJQdWJsaXNoZXIy MTMzNzEzMQ==