Acoustic emission

About: Acoustic emission is a research topic. Over the lifetime, 16293 publications have been published within this topic receiving 211456 citations.

A new method for waveform analysis for estimating AE wave arrival times using wavelet decomposition

Abstract: Here we describe a new method for determination of Acoustic Emission (AE) wave arrival times for source location purposes. In complex structures or structures of small dimension, an AE source can rapidly become distorted by the presence of several modes travelling at different speeds, and through contamination by reflections and mode conversions. Using a simple geometry of carbon-fibre reinforced plastic, the responses acquired from two-sensor and four-sensor arrays have been analysed using a variety of techniques, which are variants on identification of first arrival time and/or the arrival of the maximum intensity of the wave. The methods are compared in terms of the consistency of the velocity which is indicated at different points in the arrays, and a method based on wavelet decomposition, filtering and threshold-crossing is recommended as the most consistent and accurate method of determining arrival time.

A dual passive cavitation detector for localized detection of lithotripsy-induced cavitation in vitro.

Abstract: A passive cavitation detector (PCD) identifies cavitation events by sensing acoustic emissions generated by the collapse of bubbles. In this work, a dual passive cavitation detector (dual PCD), consisting of a pair of orthogonal confocal receivers, is described for use in shock wave lithotripsy. Cavitation events are detected by both receivers and can be localized to within 5 mm by the nature of the small intersecting volume of the focal areas of the two receivers in association with a coincidence detection algorithm. A calibration technique, based on the impulse response of the transducer, was employed to estimate radiated pressures at collapse near the bubble. Results are presented for the in vitro cavitation fields of both a clinical and a research electrohydraulic lithotripter. The measured lifetime of the primary growth-and-collapse of the cavitation bubbles increased from 180 to 420 microseconds as the power setting was increased from 12 to 24 kV. The measured lifetime compared well with calculations based on the Gilmore-Akulichev formulation for bubble dynamics. The radiated acoustic pressure 10 mm from the collapsing cavitation bubble was measured to vary from 4 to 16 MPa with increasing power setting; although the trends agreed with calculations, the predicted values were four times larger than measured values. The axial length of the cavitation field correlated well with the 6-dB region of the acoustic field. However, the width of the cavitation field (10 mm) was significantly narrower than the acoustic field (25 mm) as bubbles appeared to be drawn to the acoustic axis during the collapse. The dual PCD also detected signals from "rebounds," secondary and tertiary growth-and-collapse cycles. The measured rebound time did not agree with calculations from the single-bubble model. The rebounds could be fitted to a Rayleigh collapse model by considering the entire bubble cloud as an effective single bubble. The results from the dual PCD agreed well with images from high-speed photography. The results indicate that single-bubble theory is sufficient to model lithotripsy cavitation dynamics up to time of the main collapse, but that upon collapse bubble cloud dynamics becomes important.

An initial investigation on the potential applicability of Acoustic Emission to rail track fault detection

Abstract: In light of recent accidents in the rail industry, the assessment of the mechanical integrity of rail-track is of vital importance. This encompasses the integrity of the track due to rolling contact fatigue and surface wear. Whilst numerous techniques are employed for crack detection, several defects have clearly been missed. In Europe, more than 100 rails are broken each year and rail maintenance costs within the European Union is estimated at 300-million Euros annually [Inst Mech Engrs 216 (2001) 249]. The derailment of a train at Hatfield in October 2000 is a tragic example of a fractured rail going undetected. This paper presents an experimental study on the applicability of Acoustic Emissions (AE) for rail-track defect diagnosis. An experimental test-rig was employed for this programme. This allowed for a surface defect to be seeded onto the test-rig. The investigation presented is part of an on-going attempt to develop the non-destructive technique of AE for assessing the surface integrity of rail-track. The AE technique is not new but the application in this particular instance is unique. It is concluded that the AE technique offers a complementary tool for rail track defect detection.