Acoustic-emission diagnostics of the initiation of fatigue fracture of 1201-T aluminum alloy
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ACOUSTIC-EMISSION DIAGNOSTICS OF THE INITIATION OF FATIGUE FRACTURE OF 1201-T ALUMINUM ALLOY V. R. Skal’s’kyi,1,2 I. M. Lyasota,1 and O. M. Stankevych1
UDC 621.791.05:620.179.17
We consider the specific features of generation of acoustic emission caused by the fatigue fracture of thermally strengthened 1201-T aluminum alloy. Based on the metallographic and fractographic investigations and analysis of typical signals, we establish that this alloy is destroyed by the brittle-ductile mechanism. The character of acoustic-emission radiation depends on the alloy microstructure and mechanical properties, and the area of the formed defect is proportional to the sum of amplitudes of the recorded signals. The passage from the initiation of a fatigue crack to its stable propagation is accompanied by a sharp jump of the acoustic-emission activity. Keywords: aluminum alloy, acoustic emission, microstructure, microfractogram, wavelet transform.
The present-day development of industry in Ukraine stimulates an increase in the volume of production of aluminum and its high-strength alloys because, owing to a complex of physicomechanical, corrosive, and technological properties, they are successfully used in practically all branches of science and engineering. In the course of operation, under the influence of different factors, including a variable load, microfracture and macrofracture are often initiated in structural elements made of aluminum alloys (AA). The propagation of cracks can be detected fairly efficiently by the acoustic-emission (AE) method [1]. However, it has been used too little for the determination of the fatigue strength of AA [2]. Therefore, for high-quality AE diagnostics of the state of structural elements made of AA, it is important to know the AE activity and features of signals in the course of initiation and development of the processes of fatigue fracture in these alloys. State of the Art As is known [3], the length of a fatigue crack in the early stage of its initiation is proportional to the sum of amplitudes of the recorded AE signals (AES). However, its subsequent growth is accompanied by a jump-like change in the AE activity [4–6]. As established in [6], in the case of high-cycle fatigue fracture of a cobalt- and chrome-base alloy, the dependence of the sum of AES amplitudes on the number of loading cycles changes “stepwise.” In the work indicated, it was asserted that the periodic sharp increase in the AE activity is an evidence of the jump-like macrocrack growth, and between these jumps, during the so-called incubation period (the formation of a plastic zone at the crack spike), AES of small amplitudes are generated. With the help of the AE method, the propagation of fatigue cracks in 7075-T6 aluminum alloy and alloyed steel was investigated in [7, 8]. The correlation was established between the macrocrack growth, stress intensity factor, and the parameters of AES as well as between the total count of AES and energy released in the course of crack propagation for a single loading cycle. As shown in
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