Narrow-Band Hybrid Pulsed Laser/EMAT System for Noncontact Ultrasonic Inspection Using Angled Shear Waves

摘要

Angled, shear wave ultrasonic testing using piezoelectric transducers has been used in industry for years to inspect the plate welds of steel vessels. This method's reliance on viscous surface couplants limits its repro-ducibility as well as its applicability for testing surfaces at elevated temperatures. In this work, a pulsed laser/meander line EMAT (electromagnetic acoustic transducer) system was demonstrated to perform testing using vertically polarized, angled, shear waves. This capability was augmented with a narrow-bandwidth laser excitation technique to increase signal-to-noise ratio. The system was tested on both aluminum and steel plates containing saw cuts to mimic cracks. Finally, a steel weld specimen with known defects was tested with good results.