Showing papers by "Prabhu Rajagopal published in 2007"

Short range scattering of the fundamental shear horizontal guided wave mode normally incident at a through-thickness crack in an isotropic plate

Abstract: Interaction of the fundamental shear horizontal mode with through-thickness cracks in an isotropic plate is studied in the context of low frequency array imaging for ultrasonic guided wave nondestructive evaluation with improved resolution. Circular wave fronts are used and the symmetric case where a line from the wave source bisects the crack face normally is considered. Finite element simulations are employed to obtain trends subject to analytical and experimental validation. The influence of the crack length and of the location of source and measurement positions on the specular reflection from the crack face is first examined. These studies show that low frequency short range scattering is strongly affected by diffraction phenomena, leading to focusing of energy by the crack in the backscatter direction. Study of the diffraction from the crack edges reveals contributions due to a direct diffraction at the edges and multiple reverberations across the crack length. A simple diffraction model is shown to adequately represent cracks up to moderate lengths, providing an easy means of estimating the far field of the waves. The presence of multiple diffraction components is quantitatively established and surface waves on the crack face are identified as equivalent to low frequency symmetric modes of rectangular ridge waveguides.

Scattering of the Fundamental Shear Horizontal Guided Wave Mode Incident at an Arbitrary Angle on Finite Slits in an Isotropic Plate

Abstract: This paper considers the interaction of the fundamental shear horizontal (SH0) mode with through‐slits in an isotropic plate, in the context of higher resolution ultrasonic guided wave NDE. The background to this research and the case of normal incidence of the SH0 mode on through‐cracks were presented at QNDE, 2005. Here the results of the previous study are first validated with some preliminary experiments and further comparison with literature. Insights from these are then used to understand the more complex multi‐parameter case of scattering at an arbitrary angle of incidence. Finally the findings are used to draw implications for some key questions involving the development of array imaging procedures.