Application of a laser/EMAT system for using shear and LS mode converted waves

Area of Science:

• Materials Science
• Non-Destructive Testing
• Ultrasonics

Background:

• Accurate monitoring of metal plate thickness is crucial for industrial applications.
• Traditional methods can be contact-based, time-consuming, or limited in scope.
• Developing non-contact, efficient thickness measurement techniques is an ongoing challenge.

Purpose of the Study:

• To develop and demonstrate an effective non-contact method for monitoring metal plate thickness.
• To utilize quantitative time-of-flight analysis of laser-generated waves for thickness measurement.
• To assess the capability of the method for visualizing thickness variations.

Main Methods:

• Q-switched Nd:YAG laser pulses (18 mJ) delivered via optical fiber and focused to a line source.
• Excitation of surface waves, longitudinal waves, and shear waves.
• Detection of reflected bulk waves using an electro-magnetic acoustic transducer (EMAT).
• Generation of B-scans and 2-D intensity profiles for thickness visualization.
• Utilizing longitudinal-shear (L-S) and shear-longitudinal (S-L) mode-converted waves for simultaneous monitoring.

Main Results:

• The method successfully enabled non-contact monitoring of metal plate thickness.
• B-scan compilation provided easy visualization of thickness changes.
• Mode-converted waves allowed simultaneous monitoring of two points on the far surface.
• Accurate thickness determination for aluminum samples ranging from 5 to 70 mm was achieved.

Conclusions:

• Quantitative time-of-flight analysis of laser-generated waves is an effective non-contact method for metal plate thickness monitoring.
• The technique offers precise visualization and simultaneous monitoring capabilities.
• This method shows significant potential for quality control and inspection in various industries.