Advantages of Nonlinear Wave Modulation Spectroscopy (NWMS) compared to some linear acoustic techniques

Document type: Conference Papers
Peer reviewed: Yes
Author(s): Kristian Haller, Claes Hedberg
Title: Advantages of Nonlinear Wave Modulation Spectroscopy (NWMS) compared to some linear acoustic techniques
Conference name: Ultrasonic International
Year: 2003
Publisher: Elsevier
City: Granada
Organization: Blekinge Institute of Technology
Department: Dept. of Mechanical Engineering (Institutionen för maskinteknik)
Dept. of Mechanical Engineering S-371 79 Karlskrona
+46 455 38 50 00
http://www.ima.bth.se/
Authors e-mail: kristian.haller@bth.se
Language: English
Abstract: This paper describes test results of a nonlinear wave modulation spectroscopy (NWMS) technique. These techniques are based on the strong connection between nonlinearity and presence of micro or macro-cracks. NWMS includes existence of higher harmonics, the presence of sidebands and ratio between excitation frequency and sideband components.
Tests of different nonlinear techniques have been performed and compared to linear techniques. Tensile beams have been used as specimens. Piezoceramics were applied and a high frequency signal transmitted into the specimen simultaneously as a low frequency. Sideband around the high frequency and higher harmonics were then studied to detect nonlinearities. If there are cracks present, the NWMS show nonlinearities by combining the different frequencies shown as sidebands from the high frequency component, and the higher harmonics' amplitudes will increase.
NWMS techniques are more sensitive than linear as they can detect smaller cracks. NWMS is faster to evaluate than a linear scanning method, as it can interrogate a complete object in just one measurement, and NWMS is not as limited by complicated geometry of the specimen.
Subject: Mechanical Engineering\Structural Dynamics
Keywords: Nonlinear Wave Modulation Spectroscopy, Nonlinear non-destructive testing, Crack detection, Damage detection
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