Waveform and Frequency Spectra of Acoustic Emissions

Abstract

Stress waves generated internally by deforming materials provide information about the operative deformation mechanisms. These stress waves are known as acoustic emissions. Acoustic emission stands alongside conventional ultrasonic methods as a useful technique of nondestructive testing. The frequency spectrum of the emissions varies according to the nature and location of the deformation, and it may also provide information about the integrity of the structure under test. On fundamental grounds we conclude that the emission waveform at source is a stress pulse (displacement step) whose frequency spectrum extends from zero up to a frequency which depends on the duration of the source event. Between generation and detection, the spectrum is modulated by structural resonances which tend to obscure the information contained in the source waveform. These effects should be borne in mind during the design of practical emission detection systems. Experimental results from adhesive bonds confirm the validity of our theoretical approach and show how information about the source event may be gained from the spectrum by looking beyond the structural resonances.

Application of a mobile system in diagnostics of power capacitors using the acoustic emission method

“…Studies regarding the possibility of applying the AE method in the diagnostics of insulating systems were initiated in the 1940s. Considerable interest in the AE method was observed in the 1960s, when the method was applied in studies of the PD phenomenon [31][32] . Studies involving perfecting the AE method applied to diagnose high-voltage insulating systems in power transformers have been carried out by many scientific and research centres [15][16][17][18][19][20][21][22][23][24][25][33][34] .…”

Design and Performance Analysis of 3-D MEMS Acoustic Emission Sensor

“…Within the frequency response range of the sensor, when the material is fractured and the frequency of sound wave generated by the crack is the same or close to the natural frequency of the sensor, the gap between the two electrodes vibrating in the Z direction will cause the change of capacitance, and thus generate a changing electrical signal. The acoustic emission signal frequency of the composite material is generally between 100kHz~1MHz [6] and can generate transient complex signals. Due to the rapid attenuation characteristics of higher frequency [7], the resonant frequency of the designed sensor in this paper is controlled within 100 kHz ~500kHz.…”

Study on Descriptors of Acoustic Emission Signals Generated by Partial Discharges under Laboratory Conditions and in On-Site Electrical Power Transformer

“…An acoustic emission phenomenon is wide spread and relatively well described in a contemporary scientific literature Bolin, 1979;Pierzga et al, 2013;Pollock, Stephens, 1971). Many different sources of AE are known and the most common of them are e.g.…”