The Paton Welding Journal, 2013, №01



2013 №01 (04)

2013 №01 (06)

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The Paton Welding Journal, 2013, #1, 21-27 pages  

PECULIARITIES OF ACOUSTIC EMISSION SIGNALS IN EVALUATION OF FRACTURE MECHANISM IN WELDED JOINTS ON ALUMINIUM ALLOYS

V.R. SKALSKY, I.N. LYASOTA and E.M. STANKEVICH

H.V. Karpenko Physico-Mechanical Institute, NASU, Lvov, Ukraine
 
 
Abstract
High-strength aluminium alloys are widely applied in modern science and technology owing to a combination of their physical-mechanical and corrosion properties. Electron beam welding is used to join structural members, in particular in aircraft engineering. Micro- and macrofractures often occur in operation of such members under the effect of various factors. Crack propagation can be very effectively determined by the acoustic emission method. The purpose of this study was to investigate peculiarities of generation of the acoustic emission signals under static loading of specimens, and identify the character of fracture in different regions of the welded joints on aluminium alloy 1201-T. Crack resistance of the specimens measuring 10 x 20 x 160 mm made from the through electron beam welded joints on 20 mm thick 1201-T alloy plates was investigated by the three-point bending tests. The acoustic emission signals were fixed by using system SKOP-8M. The parallel measuring channel method was employed to select useful signals from noise. As established on the basis of analysis of wave reflections and continuous wavelet-transforms of the fixed acoustic emission signals, the method allows identifying sources of their generation in static fracture of aluminium alloys and their welded joints. Tough (weld and HAZ metals) and brittle-tough (base metal) fractures of a solid solution of copper in aluminium generate signals of low and medium amplitudes (A = 0.2-0.5 mV), for which the criterial index varies from 0.15 to 0.30. Detachment of melted grains is accompanied by generation of the acoustic emission signals with an amplitude range of A = 0.4-0.5 mV and index k = 0.3-0.4, whereas cracking of brittle intermetallics is accompanied by generation of high-power signals (A = 0.5-4.0 mV) with index k = 0.5-0.9. 15 Ref., 5 Figures.
 
 
Keywords: aluminium alloy, welded joints, acoustic emission, microstructure, microfractography pattern, wavelet-transform, fracture mechanism
 
 
Received:                09.07.12
Published:               28.01.12
 
 
References
1. Nazarchuk, Z.T., Skalsky, V.R. (2009) Acoustic emission diagnostics of structural members. Kyiv: Naukova Dumka.
2. Skalsky, V.R., Lyasota, I.M. (2009) Application of acoustic emission phenomenon for diagnostics of fracture of welded aluminium alloy joints (Review). Mashynoznavstvo, 9, 42-47.
3. Mezintsev, E.D., Tikhy, V.G., Karasyov, L.P. (1982) Application of simulated defects in testing of the technical diagnostics acoustic emission system. Avtomatich. Svarka, 9, 28-30.
4. Tikhonov, L.V., Prokopenko, G.I. (1991) Detonation mechanisms of deformation, fracture and acoustic emission in aluminium and its alloys. Tekhn. Diagnostika i Nerazrush. Kontrol, 1, 73-76.
5. Tikhy, V.G., Sanin, F.P., Borshchevskaya, D.G. (1982) Study of dependence of the acoustic emission signals on the character of welding defects in alloy AMg6. Avtomatich. Svarka, 9, 36-38.
6. Skalsky, V.R., Sergienko, O.M., Golaski, L. (1999) Generation of acoustic emission from cracks propagating in welded joints. Tekhn. Diagnostika i Nerazrush. Kontrol, 4, 23-31.
7. Skalsky, V.R., Koval, P.M. (2005) Acoustic emission in fracture of materials, products and structures. Lviv: SPOLOM.
8. Venkitakrishnan, P.V., Sinha, P.P., Krishnamurthy, R. (2006) Study and analysis of effect of various thermal processes in AA2219 annealed sheet using acoustic emissions. Mater. and Design, 27, 770-775.
9. GOST 25506-85: Methods of mechanical tests of metals. Determination of crack resistance (fracture toughness) characteristic in static loading. Moscow: Standart.
10. Skalsky, V.R., Lyasota, I.M. (2012) Application of the acoustic emission method for determination of moment of initiation of macrofracture in aluminium alloy welded joint. Tekhn. Diagnostika i Nerazrush. Kontrol, 3, 7-12.
11. Lozovskaya, A.V., Chaika, A.A., Bondarev, A.A. et al. (2001) Softening of high-strength aluminium alloys in different fusion welding processes. The Paton Welding J., 3, 13-17.
12. Astafieva, N.M. (1996) Wavelet-analysis: theoretical principles and application examples. Uspekhi Fizich. Nauk, 166(11), 1145-1170.
13. Skalsky, V.R., Bujlo, S.I., Stankevich, E.M. (2012) Criterion for evaluation of brittle fracture of glass from acoustic emission signals. Defektoskopiya, 5, 26-34.
14. Skalsky, V.P., Botvina, L.R., Stankevich, O.M. (2011) Diagnostics of fracture mechanisms in steel 38KhN3MFA by using wavelet-transforms of acoustic emission signals. Tekhn. Diagnostika i Nerazrush. Kontrol, 3, 12-17.
15. Vallen system: The Acoustic Emission Company. www.vallen.de

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