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A second study of the interaction of Lamb waves with a circular defect is presented. The Lamb wave mode chosen was the So mode in the low frequency-thickness regime. A three dimensional Finite Element mesh was generated, representing an area of the plate with a circular part-depth hole (33% or 50% of the plate thickness deep). The specular reflection of an incident So wave was predicted and showed the importance of several factors, such as the decay in amplitude of the reflected wave and the generation of "creeping waves" which travel around the hole. [ABSTRACT FROM AUTHOR]

A finite element (FE) technique for computing the properties of guided waves that can exist in an isotropic beam of arbitrary cross section is presented. The FE model uses a two-dimensional mesh to represent a cross section through the beam and cyclic axial symmetry conditions to prescribe the displacement field perpendicular to the mesh. FE results are presented for plate and angle sections. Excitability functions are calculated and implications for transducer placement are considered. [ABSTRACT FROM AUTHOR]

An initial study of the interaction of Lamb waves with circular defects in plates is presented. The Lamb wave mode chosen for this paper was the S[sub 0] mode in the low frequency-thickness regime. The geometrical properties of this mode allow it to be analyzed using a 2D membrane finite element model which is computationally simpler than the alternative 3D case. A mesh was generated representing an area of the plate with a circular through-thickness hole. The reflection and scattering of an incident S[sub 0] wave at different monitoring angles are predicted showing that the scattered field contains the SH[sub 0] mode as well as S[sub 0]. The amplitude of the reflected field is verified experimentally. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reflection of the fundamental modes a[sub 0] and s[sub 0] from the end of a plate is studied, in order to identify the extent to which the generation of non-propagating modes influences the field and could therefore affect Lamb wave NDE of the plate. Analytical predictions, Finite Element simulations and experimental measurements are presented for frequencies below the a[sub 1] cut-off. It is shown that reflection of the a[sub 0] mode is delayed by 90 degrees in phase and that there is significant additional motion due to non-propagating modes within about 5 plate thicknesses of the end. Reflection of the s[sub 0] mode occurs without significant evidence of non-propagating modes or phase delay. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The interaction of the fundamental antisymmetric Lamb wave (a[sub o]) with cracks and with notches of different depth and width has been investigated both experimentally and by finite element analysis. Excellent agreement between the predictions and the measurements has been obtained. It has been shown that the reflection coefficient is a function of both the notch width to wavelength and notch depth to wavelength ratios. Both the relationship between the reflection coefficient and notch, depth, and the frequency dependence of the reflection coefficient, are very different for the a[sub o] mode compared to the s[sub o] mode which was studied earlier. Physical insight into the reasons for the different behavior is given by examination of the stress fields and opening displacements at the crack or notch. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]