Subhendu K. Datta

Bio: Subhendu K. Datta is an academic researcher from University of Colorado Boulder. The author has contributed to research in topics: Scattering & Wave propagation. The author has an hindex of 25, co-authored 101 publications receiving 1484 citations. Previous affiliations of Subhendu K. Datta include Cooperative Institute for Research in Environmental Sciences.

Mode-coupling of waves in laminated tubes

Abstract: The dispersive and modal behavior of specially orthotropic fiber-rein forced laminated tubes is investigated over a range of frequencies. A wave propagation based method with finite element discretization in the radial direction is used to allow modeling which includes the radial variation of the constitutive properties of such lami nated tubes. Tubes with different numbers of total plies are compared in order to determine at what frequencies the ply lay-up affects the character of the propagating modes and cou pling between these modes. In particular, coupling between predominantly longitudinal (axial-radial and radial-axial) and predominantly torsional modes is examined.

Transient Ultrasonic Waves in Multilayered Superconducting Plates

Abstract: Transient response of multilayered superconducting tapes has been studied in this paper. These tapes are usually composed of layers of a superconducting material (like YBa2Cu3O7?, or YBCO, for simplicity) alternating between layers of a metallic material (like nickel or silver). The tapes are thin, in the range of 100?200 µm. The superconducting layer is orthotropic with a thickness of 5?10 µm. In applications, tapes are long and have a finite width. In this paper, attention has been focused on the transient response of homogeneous and three-layered tapes assuming that the width is infinite and that the thickness of the superconducting layer is much smaller than the metal layer. The problem considered here is of general interest for understanding the effect of anisotropy of thin coating or interface layers in composite plate structures on ultrasonic guided waves. Three plate geometries are considered as prototype examples: a homogeneous nickel (Ni) layer, a three-layered YBCO/Ni/YBCO, and a three-layered Ni/YBCO/Ni. Transient response due to a line force applied normal to the surface of the tape has been studied by means of Fourier transforms and direct numerical integration. Numerical results are presented using an exact model and a first-order approximation to the thin YBCO layer. The first-order approximation simplifies the problem to that of a homogeneous isotropic plate subject to effective boundary conditions representing the thin anisotropic layers. Both are seen to agree well (except when the center frequency of the force is high) and capture the coupling of the longitudinal, S, (or flexural, A) motion and the shear-horizontal (SH) motion. Detailed analysis of the influence of the thin layers, especially their anisotropy, on this coupling and the transient response shows significant differences among the three cases. The model results provide insight into the coupling phenomenon and indicate the feasibility of careful experiments to exploit the significant changes in the transient response caused by coupling for the determination of the in-plane elastic constants of thin coating or interface layers. ©2002 ASME

Diffraction of SH‐Waves in a Spherically Isotropic Medium by a Rigid or Fluid Spherical Core

Abstract: Suininary In this paper we have considered the diffraction of SH-waves from a point source by a rigid or fluid spherical core. The medium outside the core is assumed to be spherically isotropic about the centre of the core. It is found that the propagation of SH-waves in such a medium is characterized by two elastic parameters associated with the phase velocities C1 and C, along and perpendicular to a radius, respectively. Depending on the ratio l/a of these two velocities and the distance of the source from the centre, the region of space outside the core can be separated into three different regions: (i) an illuminated zone which is reached either by the rays going left or right from the source and their reflections from the sphere; (ii) a shadow zone, which may be bounded; and (iii) if the shadow is bounded, then there is a third zone which may be reached by both rays going left and right and their reflections. This classification is true provided c1 is greater than one, which is true in most geophysical applications. Furthermore, if c1 is 2 2, then there is no shadow when the distance b of the source from the centre is large enough. We have discussed the solutions for 1 < c1 < 2 and have given simple geometrical interpretations to these solutions.

Analysis of Guided Waves in a Bilayered Plate

Abstract: Inspection of coated material is vital in order to ensure the integrity of the protective barrier. In some cases, the inspection process is complicated by the fact that the surface of the protective coating may not be accessible, thus the inspection must proceed with only access to the surface of the opposite side (this will be referred to as the inner surface). One method which can be applied in such a situation is the excitation of guided waves or Lamb waves in the coated material. Lamb waves excited from the inner surface will sense the variation in the coating conditions as well as flaws in the steel plate. Therefore for a correct and unambiguous interpretation of Lamb wave data for corrosion-related flaws, the effects of the coating and how they differ from the effects of corrosion-related flaws must be understood. To this end this paper will concentrate on the effects of the coating and its influence on dispersive characteristics of a soft layer bonded to a steel plate. By calculating the dispersion relations for a bare and coated steel plate and comparing the calculated results, unique new modes are seen to emerge in the coated plate. In addition, the coated plate is also modeled as a thin layer on a halfspace allowing a comparison between the problem of a coated halfspace and a coated plate. The comparison demonstrates that only limited information can be obtained by treating the problem as a layered halfspace. More detailed information can be obtained by treating the problem as a coated plate of finite thickness.

Variational and Related Methods for the Overall Properties of Composites

Abstract: Publisher Summary This chapter focuses on variational and related methods for the overall properties of composites. A wide range of phenomena that are observable macroscopically are governed by partial differential equations that are linear and self-adjoint. This chapter is concerned with such phenomena for materials, such as fiber-reinforced composites or polycrystals, whose properties vary in a complicated fashion from point to point over a small, “microscopic” length scale, while they appear “on average” (that is, relative to the larger, macroscopic scale) to be uniform. This chapter treats the elastic behavior of composites, and emphasizes that a number of other properties (conductivity, viscosity of a suspension, etc.) are described by the same equations. Extensions to viscoelastic and thermoelastic behavior are presented, for both of which the variational characterization given is believed to be new. Problems, such as the resistance to flow of viscous fluid through a fixed bed of particles are mentioned, and a model problem that involves diffusion is presented in some detail. This displays the same difficulty in relation to divergence of an integral and is one problem of this type that has so far been approached variationally. Methods related to the Hashin–Shtrikman variational principle are also described in the chapter.

Ultrasonic Guided Waves in Solid Media

Abstract: Preface Acknowledgments 1. Introduction 2. Dispersion principles 3. Unbounded isotropic and anisotropic media 4. Reflection and refraction 5. Oblique incidence 6. Waves in plates 7. Surface and subsurface waves 8. Finite element method for guided wave mechanics 9. The semi-analytical finite element method (SAFE) 10. Guided waves in hollow cylinders 11. Circumferential guided waves 12. Guided waves in layered structures 13. Source influence on guided wave excitation 14. Horizontal shear 15. Guided waves in anisotropic media 16. Guided wave phased arrays in piping 17. Guided waves in viscoelastic media 18. Ultrasonic vibrations 19. Guided wave array transducers 20. Introduction to guided wave nonlinear methods 21. Guided wave imaging methods Appendix A: ultrasonic nondestructive testing principles, analysis and display technology Appendix B: basic formulas and concepts in the theory of elasticity Appendix C: physically based signal processing concepts for guided waves Appendix D: guided wave mode and frequency selection tips.

Guided wave based structural health monitoring: A review

Abstract: The paper provides a state of the art review of guided wave based structural health monitoring (SHM). First, the fundamental concepts of guided wave propagation and its implementation for SHM is explained. Following sections present the different modeling schemes adopted, developments in the area of transducers for generation, and sensing of wave, signal processing and imaging technique, statistical and machine learning schemes for feature extraction. Next, a section is presented on the recent advancements in nonlinear guided wave for SHM. This is followed by section on Rayleigh and SH waves. Next is a section on real-life implementation of guided wave for industrial problems. The paper, though briefly talks about the early development for completeness,. is primarily focussed on the recent progress made in the last decade. The paper ends by discussing and highlighting the future directions and open areas of research in guided wave based SHM.

A Baseline and Vision of Ultrasonic Guided Wave Inspection Potential

Abstract: Ultrasonic guided wave inspection is expanding rapidly to many different areas of manufacturing and in-service inspection. The purpose of this paper is to provide a vision of ultrasonic guided wave inspection potential aswe move forward into the new millennium. An increased understanding of the basic physics and wave mechanics associated with guided wave inspection has led to an increase in practical nondestructive evaluation and inspection problems. Some fundamental concepts and a number of different applications that are currently being considered will be presented in the paper along with a brief description of the sensor and software technology that will make ultrasonic guided wave inspection commonplace in the next century.