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A model for the ultrasonic detection of surface-breaking cracks by the Scanning Laser-Source technique

Summary: A model for the ultrasonic detection of surface-breaking
cracks by the Scanning Laser-Source technique
Irene Ariasa and Jan D. Achenbachb
aGraduate Aeronautical Laboratories, California Institute of Technology, 1200 E. California
Blvd. MC: 205-45, Pasadena, CA 91125, USA;
bCenter for Quality Engineering and Failure Prevention, Northwestern University, 2137
Sheridan Road, Evanston, IL 60208, USA
A model for the Scanning Laser Source (SLS) technique is presented. The SLS is a novel laser based inspection
method for the ultrasonic detection of small surface-breaking cracks. The generated ultrasonic signal is monitored
as a line-focused laser is scanned over the defect. Characteristic changes in the amplitude and the frequency
content are observed. The modelling approach is based on the decomposition of the field generated by the laser
in a cracked two-dimensional half-space, by virtue of linear superposition, into the incident and the scattered
fields. The incident field is that generated by laser illumination of a defect-free half-space. A thermoelastic model
has been used which takes account of the effect of thermal diffusion, as well as the finite width and duration of
the laser source. The scattered field incorporates the interactions of the incident field with the surface-breaking
crack. It has been analyzed numerically by a direct frequency domain boundary element method. A comparison
with an experiment for a large defect shows that the model captures the observed phenomena.
Keywords: Laser ultrasonics, thermoelastic regime, line-source, surface-breaking crack, modelling, Scanning
Laser Source technique


Source: Arias, Irene - Departament de Matemàtica Aplicada III, Universitat Politècnica de Catalunya


Collections: Engineering; Materials Science