Simulation of laser-generated ultrasonic waves in layered plates

Abstract

A model is presented for the pulsed laser generation of ultrasound in isotropic layered plates. The stresses and displacements of the plate have been formulated in the Hankel and Laplace transform domains using the Thompson transfer matrix approach. The time domain response has been obtained by numerically inverting the transforms. Several numerical results are presented showing the normal surface displacement in the following configurations: single-layer film on a semi-infinite substrate, two layers on a semi-infinite substrate, and three-layer plates. The model provides a useful tool for the determination of which modes are generated by a laser source in a layered system. It can also be used to determine how sensitive the modes are to small changes in density, thickness, or elastic properties of the layers and to help in the selection of experimental parameters ͑laser spot size, pulse length, and source to receiver distance͒ for optimal sensitivity.

Surface wave testing of pavements.

“…Dispersion curves of a bilayered plate were investigated by Jones and Thrower ͑1965͒, Laperre and Thys ͑1993͒, Lee and Cheng ͑2001͒, and Simonetti ͑2004͒. Similar studies on multilayered plates have been presented by Cheng et al ͑2001͒ andShull et al ͑1994͒. To the author's knowledge, there are no studies on a threelayered half-space with large velocity contrasts and decreasing velocity with depth, where multiple modes of guided waves have been studied in the complex wave number domain.…”

“…Related studies have dealt with the case of one stiff ͑fast͒ layer on a lower velocity half-space ͑Press and Dobrin, 1956;Lefeuvre et al, 1998;Cheng et al, 2001;. Yapura and Kinra ͑1995͒ investigated dispersion curves and mode shapes for a fluid-solid bilayer.…”

Modeling laser-generated guided waves in bonded plates by the finite element method

“…Seifried et al [3] have used analytical and computational models to develop a quantitative understanding of the propagation of guided Lamb waves in multi-layered adhesive bonded components. Cheng et al [4] have simulated laser-generated ultrasonic guided waves in layered plates using the numerical inversion of the Hankel-Laplace transform solution by applying the continuity conditions at layer interfaces. Cheng and Du [5] have developed the twolayer normal mode expansion (NME) method for modeling the transient laser-generated ultrasonic guided wave in bonded plates.…”

Surface acoustic wave depth profiling of a functionally graded material

“…This method, described in detail by Glorieux et al 6 is straightforward and equivalent with transfer matrix methods. [8][9][10] These methods are usually simpler to implement than methods based on a Green's function approach. [11][12][13][14] The accuracy can be set to any desired level, by choosing a sufficiently large number of layers.…”