Acoustic emission: some applications of Lamb’s problem

Abstract

A method for obtaining the signatures (waveforms) of certain acoustic emission events has been developed. The waveform is that at the source, free of contamination by ringing of the specimen, apparatus, and transducer. The technique is based on the comparison of two signals at the transducer, one from the event in question and one from an artificial event of known waveform. The apparatus is also adapted to the calibration of transducers in a certain sense. The configurations of source (real or simulated acoustic−emission event) and receiving transducer correspond to those of some special cases of Lamb’s problem. As a byproduct, the results may be of some interest to seismologists. Subject Classification: 40.42; 35.54, 35.80, 35.68; 40.50; 85.44.

Acoustic Emission Sensor Calibration for Absolute Source Measurements

“…Example sources can be found in [16]. Mechanical sources such as pencil lead break [17], capillary fracture [18], and impact [3,9,19], are ideal because they are intuitively simple, and the forces they introduce to a specimen are directly linked to physically meaningful, directly measurable quantities. These sources are impulsive or step-like, so they are very broadband in frequency, and their short temporal duration results in ideal waveforms for straightforward identification of the various wave phases (P waves, S waves, etc.).…”

“…Capillary diameter is typically 100 to 400 μm, and under these conditions it typically breaks at a force of 5-25 N. When the capillary fractures, the surface unloads very rapidly. The force time history, f (t), that the capillary fracture imposes on the test specimen is very nearly equal to a step function with a rise time (unload time), t rise < 200 ns [16,18], though t rise has some dependence on the size of the capillary [3]. This source has been used by many researchers because the force at which the fracture occurs, f amp , is equal to the amplitude of the step, and can be independently measured for absolute calibration.…”

Absolute Measurement of Elastic Waves Excited by Hertzian Contacts in Boundary Restricted Systems

“…The source for the wave was a glass capillary tube (D ¼ £1:4 mm and d ¼ £1 mm) which was compressed until it burst on the surface of the plate. A glass capillary burst was chosen as a source because of its good excitation of high frequencies due to the rapid release of force [1] and that the following equation may be used:…”

Acoustic Emission: Establishing the Fundamentals

“…The development of the basic principles that make the calibration possible owes to Breckenridge, Tschiegg, and Greenspan [38].…”