Location

La Jolla, CA

Start Date

1979 12:00 AM

Description

The ability to excite new wave types, such as the horizontally polarized shear (SH) waves, enables EMAT's to perform functions not easily realized with conventional piezoelectric transducers. This paper describes two examples. An ultrasonic ellipsometer is presented which can excite, and detect, shear waves of arbitrary elliptical polarization. It therefore becomes possible to make precision measurements of elastic properties by making direct comparison of the propagation properties of the SH and SV (vertically polarized) components of the wave. The principles of operation are demonstrated by measuring fluid level, a surface property which .produces differential attenuation of the two components of the wave and thus a change in its elliptical polarization, and texture, a bulk property which produces differential velocity shifts. Preliminary data directed towards the measurement of adhesive bond strength is also included. A second technique presented is a new approach to the problem of detecting cracks under fasteners in wing lap joints. It has be.en found that SH waves, excited on the outer surface of the wing, can be injected into the lower surface of the joint by a wave guiding effect. The reflections of these waves from fastener holes contains information indicating the presence, and size, of flaws. Preliminary experimental results demonstrating this new technique are included.

Book Title

Proceedings of the ARPA/AFML Review of Progress in Quantitative NDE

Chapter

4. Reduction to Practice New Technology

Pages

40-45

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

New EMAT Applications: Ultrasonic Ellipsometer and Detection of Cracks under Fasteners

La Jolla, CA

The ability to excite new wave types, such as the horizontally polarized shear (SH) waves, enables EMAT's to perform functions not easily realized with conventional piezoelectric transducers. This paper describes two examples. An ultrasonic ellipsometer is presented which can excite, and detect, shear waves of arbitrary elliptical polarization. It therefore becomes possible to make precision measurements of elastic properties by making direct comparison of the propagation properties of the SH and SV (vertically polarized) components of the wave. The principles of operation are demonstrated by measuring fluid level, a surface property which .produces differential attenuation of the two components of the wave and thus a change in its elliptical polarization, and texture, a bulk property which produces differential velocity shifts. Preliminary data directed towards the measurement of adhesive bond strength is also included. A second technique presented is a new approach to the problem of detecting cracks under fasteners in wing lap joints. It has be.en found that SH waves, excited on the outer surface of the wing, can be injected into the lower surface of the joint by a wave guiding effect. The reflections of these waves from fastener holes contains information indicating the presence, and size, of flaws. Preliminary experimental results demonstrating this new technique are included.