Resonant Airborne Acoustic Emission for Nondestructive Testing and Defect Imaging in Composites

Abstract

A new version of an acoustic emission mode which is different from its traditional counterpart is discussed in view of applications for nondestructive testing. It is based on the effect of acoustic waves generation from the defect area in ambient air by local standing wave vibration developed in this area at the defect resonant frequency. Another approach which does not require preliminary knowledge of local defect-resonance frequency is one that uses wideband acoustic activation by a noise-like input signal. The acoustic emission field from the defect area is a “fingerprint” of the radiation source, and thus is applicable to defect detection and imaging. This enables the use of commercial microphone scanning for detecting and imaging various defects in composites. An improvement in the acoustic-emission scanning mode based on a multiple-axis robot is studied to applications to complex shape components. A rapid, full-field imaging of the acoustic-emission field is implemented by means of an array of microphones (acoustic camera). Numerous case studies validate the potential of the resonant acoustic-emission modes for integration in the defect imaging system based on inexpensive, fully acoustic instrumental components.

Analysis of Eigenfrequencies of a Circular Interface Delamination in Elastic Media Based on the Boundary Integral Equation Method

“…The authors believe that the proposed advanced BIEM will be useful for damage identification because each delamination has a unique set of the spectral points or resonance frequencies, which can be estimated from experimental data [4,5]. Besides, the introduction of the SBCs allows to distinguish and identify more kinds of delaminations.…”

“…Therefore, the eigenfrequencies of circular interface delaminations can be separated into different classes in accordance with the order m of the trigonometric functions in series (5). Accordingly, the eigenfrequencies ωm n are enumerated using two indices.…”

“…Recently, local defect resonances were employed in the matters of non-destructive testing. For instance, inverse problems of the crack identification based on natural frequencies were studied theoretically and experimentally for rods [2,3] and plates [4,5].…”

Detection and Identification of Hidden Defects in Layered Polymer Composites Using Combination of Acoustic Resonance and Interferometric Monitoring of Surface Displacements

“…According to the literature data [6,10,12], the displacement of the surface of the LC along its normal over the SD when it is detected during AW irradiation is approximately 10...50 nm. Gyroscopes, speckle interferometers, and laser vibrometers are usually used for the testing and analysis of such magnitude of displacements [4,5,[13][14][15].…”

“…The percentage of using composite structural elements is increasing rapidly in the modern aircraft building [1,2]. Although the problem of detection and identification of SD in the structural elements of modern products made of LCM has been dealt with for decades, it remains extremely relevant [3][4][5][6]. The most dangerous difficult to detect SDs include unbounded areas between layers during construction, delamination, internal damages such as cracks and areas of crumpling during its operation.…”