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Lamb wave near field enhancements for surface breaking defects in plates
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Image of FIG. 1.
FIG. 1.

Group velocity dispersion curve for Lamb waves in aluminium. Frequency range of interest is shown by dashed boxes for the A0 mode (α) and S0 mode (β).

Image of FIG. 2.
FIG. 2.

Experimental sample showing scanning schematic and defect geometry.

Image of FIG. 3.
FIG. 3.

(a) Multimodal Lamb wave A-scan (0.5 mm sheet), (b) B-scan for 0.5 mm sheet with 0.375 mm deep defect. Incident (i), reflected (r), and transmitted (t) fundamental modes are labelled.

Image of FIG. 4.
FIG. 4.

Time frequency representations for 1.5 mm thickness sheet with 100% through thickness defect for (a) no defect region and (b) enhanced scan position.

Image of FIG. 5.
FIG. 5.

Variation in peak magnitude within chosen region across scan. Enhancements can be observed in many different frequency regions; shown here are the enhancements in the (a) A0 region and the (b) S0 region.

Image of FIG. 6.
FIG. 6.

Enhancement factors in a 1.5 mm sheet for both experimental and FEM simulations as a function of percentage defect depth for both (a) A0 and (b) S0 waves.

Image of FIG. 7.
FIG. 7.

Defect schematic for test models, showing (a) square based notch and (b) open mouthed crack.

Image of FIG. 8.
FIG. 8.

Square based notch scattering interactions at (a) interface 1, (b) interface 2, and (c) interface 3. Arrows show direction of incident (I), reflected (R) and transmitted (T) waves.

Image of FIG. 9.
FIG. 9.

Out-of-plane and in-plane material displacements for (a) A0 wave modes and (b) S0 wave modes in 0.5 mm thick sheets for frequency-thickness of 1.3 MHz mm.

Image of FIG. 10.
FIG. 10.

Enhancement factors for experimental, simulation, and test model data as a function of defect depth for varying sheet thicknesses; (a) 0.5 mm, (b) 1.0 mm, and (c) 1.5 mm.


Generic image for table
Table I.

Examples of reflection and transmission coefficients for a 50% depth defect at fd = 1.12 MHz mm. Values are shown for the open mouthed crack and interfaces 1 and 2 of the square based notch.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Lamb wave near field enhancements for surface breaking defects in plates