Acoustic emission (AE) is the phenomenon of radiation of acoustic (elastic) waves in solids that occurs when a material undergoes irreversible changes in its internal structure, for example as a result of crack formation or plastic deformation due to aging, temperature gradients, or external mechanical forces.[1]
In particular, AE occurs during the processes of mechanical loading of materials and structures accompanied by structural changes that generate local sources of elastic waves.[2] This results in small surface displacements of a material produced by elastic or stress waves[3] generated when the accumulated elastic energy in a material or on its surface is released rapidly.[4][5][6]
The mechanism of emission of the primary elastic pulse AE (act or event AE) may have a different physical nature. The figure shows the mechanism of the AE act (event) during the nucleation of a microcrack due to the breakthrough of the dislocations pile-up (dislocation is a linear defect in the crystal lattice of a material) across the boundary in metals with a body-centered cubic (bcc) lattice under mechanical loading, as well as time diagrams of the stream of AE acts (events) (1) and the stream of recorded AE signals (2).[5][6]
The AE method makes it possible to study the kinetics of processes at the earliest stages of microdeformation, dislocation nucleation and accumulation of microcracks. Roughly speaking, each crack seems to "scream" about its growth. This makes it possible to diagnose the moment of crack origin itself by the accompanying AE. In addition, for each crack that has already arisen, there is a certain critical size, depending on the properties of the material.[5][6] Up to this size, the crack grows very slowly (sometimes for decades) through a huge number of small discrete jumps accompanied by AE radiation. After the crack reaches a critical size, catastrophic destruction occurs, because its further growth is already at a speed close to half the speed of sound in the material of the structure. Taking with the help of special highly sensitive equipment and measuring in the simplest case the intensity of dNa/dt (quantity per unit of time), as well as the total number of acts (events) of AE, Na, it is possible to experimentally estimate the growth rate, crack length and predict the proximity of destruction according to AE data.[5][6]
The waves generated by sources of AE are of practical interest in structural health monitoring (SHM), quality control, system feedback, process monitoring, and other fields. In SHM applications, AE is typically used to detect, locate,[7] and characterise[8] damage.
- ^ Acoustic Emission. Baltimore: ASTM, STP-505. 1972. pp. 1–337.
- ^ Dunegan H.L., Harris D.O., Tatro C. A. (1968). "Fracture Analysis by Use of Acoustic Emission". Eng. Frac. Mech. 1 (1): 105–122. doi:10.1016/0013-7944(68)90018-0.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ pacuk.co.uk website Archived December 27, 2011, at the Wayback Machine. Retrieved 2011-12-05.
- ^ Sotirios J. Vahaviolos (1999). Acoustic Emission: Standards and Technology Update. Vol. STP-1353. Philadelphia, PA: ASTM International (publishing). p. 81. ISBN 978-0-8031-2498-1.
- ^ a b c d Cite error: The named reference
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:1was invoked but never defined (see the help page). - ^ Eaton, M.J.; Pullin, R.; Holford, K.M. (June 2012). "Acoustic emission source location in composite materials using Delta T Mapping". Composites Part A: Applied Science and Manufacturing. 43 (6): 856–863. doi:10.1016/j.compositesa.2012.01.023.
- ^ McCrory, John P.; Al-Jumaili, Safaa Kh.; Crivelli, Davide; Pearson, Matthew R.; Eaton, Mark J.; Featherston, Carol A.; Guagliano, Mario; Holford, Karen M.; Pullin, Rhys (January 2015). "Damage classification in carbon fibre composites using acoustic emission: A comparison of three techniques". Composites Part B: Engineering. 68: 424–430. doi:10.1016/j.compositesb.2014.08.046. hdl:11311/890355.