Tribikram Kundu

Ultrasonic Nondestructive Evaluation : Engineering and Biological Material Characterization

Mechanics of Elastic Waves and Ultrasonic NDE T. Kundu, University of Arizona, USA Modeling of Ultrasonic Field by Distributed Point Source Method D. Placko, Ecole Normale Superieure, Cachan, France T. Kundu, University of Arizona, USA Ultrasonic Systems for Industrial NDE D. Bray, Don E. Bray, Inc, USA Guided Waves for Plate Inspection T. Kundu, University of Arizona, USA Cylindrical Waveguides and Their Applications in Ultrasonic Evaluation J. Qu and L. Jacobs, Georgia Institute of Technology, USA Fundamentals and Applications of Nonlinear Ultrasonic NDE J. Cantrell, NASA Langely Research Center, USA Theory and Applications of Laser-Ultrasonic Techniques S. Krishnaswami, Northwestern University, USA Electro-Magnetic Acoustic Transducers: EMATS B. Maxfield, Industrial Sensors and Actuators, USA Ultrasonic NDE for Structural Health Monitoring: Built-In Diagnostics for Hot Spot Monitoring in Metallic and Composite Structures J.-B. Ihn and F. K. Chang, Stanford University, USA, Brillouin Scattering Measurement of SAW Velocities for Determining Near-surface Elastic Properties M. Beghi, Milano Polytechnic, Italy A. G. Every, University of the Witwatersrand, South Africa P. Zinin, University of Hawaii, USA Theory and Applications of Acoustic Microscopy P. Zinin, University of Hawaii, USA Wieland Weise, Physikalisch-Technische Bundesanstalt, Braunschweig, Germany Ultrasonic Characterization of Biological Cells J. Bereiter-Hahn and C. Blase, J. W. Goethe University, Germany Ultrasonic Characterization of Hard Tissues Kay Raum, Martin Luther University of Halle-Wittenberg, Germany Clinical Applications of Ultrasonic NDE Y. Saijo, Tohoku University, Japan

Efficient use of Lamb modes for detecting defects in large plates

In this paper, Lamb wave propagation in large plates and its use in internal defect detection have been studied. The Lamb modes which are most efficient for detecting different types of internal defects are identified. Stress fields inside the plate for different Lamb modes are computed. From these stress plots one can conclude which Lamb mode should be efficient for detecting which type of material defect. Theoretical predictions are experimentally verified.

Locating point of impact in anisotropic fiber reinforced composite plates

The conventional triangulation technique cannot predict the point of impact in an anisotropic composite plate because the triangulation technique assumes that the wave speed is independent of the direction of propagation which is not the case for anisotropic plates. An alternative method based on the optimization scheme was proposed by Kundu et al. [T. Kundu, S. Das, K.V. Jata, Point of impact prediction in isotropic and anistropic plates from the acoustic emission data, J. Acoust. Soc. Am. 122, 2007, 2057-2066] to locate the point of impact in plates by analyzing the time of arrival of the ultrasonic signals received by the passive sensors attached to the plate. In this paper, that objective function is modified further to overcome the inherent difficulties associated with multiple singularities and to maximize the efficiency of the acoustic emission data for multiple receiving sensors. With this modified objective function the impact point on an anisotropic composite plate is predicted from the acoustic emission data. Experiments are carried out by dropping steel and ping pong balls on a graphite-epoxy composite plate and recording acoustic signals by passive transducers adhesively bonded to the plate at three different locations. The impact point is predicted by the proposed method and compared with the actual location of impact.

Elastic waves in a multilayered solid due to a dislocation source

Abstract A modified version of the wave number integral approach is applied to the calculation of the motion produced in a multilayered solid by dynamic sources. A new method of pole removal is introduced to facilitate separation of the continuous and the discrete spectral responses of the medium. The well-known numerical difficulties associated with the calculation of the integrands of the continuous spectra and the mode shapes of the discrete spectra are avoided through the use of delta matrices. Special numerical integration schemes are used to calculate the body wave integrals accurately at smaller distances and higher frequencies.

Acoustic source localization

In this article different techniques for localizing acoustic sources are described and the advantages/disadvantages of these techniques are discussed. Some source localization techniques are restricted to isotropic structures while other methods can be applied to anisotropic structures as well. Some techniques require precise knowledge of the direction dependent velocity profiles in the anisotropic body while other techniques do not require that knowledge. Some methods require accurate values of the time of arrival of the acoustic waves at the receivers while other techniques can function without that information. Published papers introducing various techniques emphasize the advantages of the introduced techniques while ignoring and often not mentioning the limitations and weaknesses of the new techniques. What is lacking in the literature is a comprehensive review and comparison of the available techniques; this article attempts to do that. After reviewing various techniques the paper concludes which source localization technique should be most effective for what type of structure and what the current research needs are.

Acoustic source localization in anisotropic plates.

The conventional triangulation technique cannot locate the acoustic source in an anisotropic plate because this technique requires the wave speed to be independent of the propagation direction which is not the case for an anisotropic plate. All methods proposed so far for source localization in anisotropic plates require either the knowledge of the direction dependent velocity profile or a dense array of sensors. In this paper for the first time a technique is proposed to locate the acoustic source in large anisotropic plates with the help of only six sensors without knowing the direction dependent velocity profile in the plate. Experimental results show that the proposed technique works for both isotropic and anisotropic structures. For isotropic plates the required number of sensors can be reduced from 6 to 4.

Inversion of ultrasonic, plane-wave transmission data in composite plates to infer viscoelastic material properties

Abstract Stiffness and damping properties of viscoelastic materials are given by the real and imaginary components, respectively, of the material constants. A new technique is proposed to experimentally measure the real and imaginary components of anisotropic (and isotropic) viscoelastic plates. Main advantage of this technique is that material properties of thin plates can be measured where many other techniques fail. Material properties are obtained by numerically inverting the transmitted ultrasonic fields, obtained for different incident angles. Simplex inversion algorithm is applied to initial estimates of plate thickness and plate properties. By this iterative technique the values of the unknown parameters (material properties and plate thickness) are continuously modified to give better agreement between the experimental and theoretical transmitted fields. After a certain number of iterations the speed of convergence of the Simplex scheme is significantly reduced. To improve the accuracy of convergence the Newton–Raphson inversion technique is adopted at that point. By this technique material properties of different types of plates are measured. These is a glass plate (isotropic plate with no damping), a polymer plate (isotropic plate with damping), and glass fiber reinforced epoxy plates with different fiber orientations (anisotropic plates with damping). Both real and imaginary components are successfully measured for all these plates. In a relative scale the measurement error for the imaginary components is higher. Reliability of the measured material constants of fiber reinforced epoxy plates is verified by the method of invariance. All experiments are carried out in the frequency range that is appropriate for satisfying two conditions—the specimen homogeneity and the plane wave conditions.

Detection of kissing bonds by Lamb waves

Abstract Closed cracks under compressive normal stresses are difficult to detect by the conventional ultrasonic techniques. When the crack surfaces stay in very close contact with each other then the bond between the two surfaces of the crack is called a ‘kissing bond’. This is a very dangerous bond. Catastrophic failures can result if the system is subjected to crack opening normal stresses or shear stresses. When the crack surfaces are smooth then kissing bonds cannot transmit shear stress very well but can carry compressive normal stress, these bonds are called ‘slip bonds’. Conventional P-wave scans (C-scan or A-scan) are based on the assumptions that P-waves are reflected by the defective interface. However, an interface subjected to a large compressive stress cannot reflect P-waves effectively, hence these bonds remain invisible to the conventional P-wave based C-scan or A-scan techniques. In this paper it is shown that the kissing bonds can be effectively detected by some leaky Lamb mode. Theoretical and experimental results are presented to show that using the Lamb waves is an effective way of detecting kissing bonds.

Elastic Wave Propagation in Sinusoidally Corrugated Waveguides

The ultrasonic wave propagation in sinusoidally corrugated waveguides is studied in this paper. Periodically corrugated waveguides are gaining popularity in the field of vibration control and for designing structures with desired acoustic band gaps. Currently only numerical method (Boundary Element Method or Finite Element Method) based packages (e.g., PZFlex) are in principle capable of modeling ultrasonic fields in complex structures with rapid change of curvatures at the interfaces and boundaries but no analyses have been reported. However, the packages are very CPU intensive; it requires a huge amount of computation memory and time for its execution. In this paper a new semi-analytical technique called Distributed Point Source Method (DPSM) is used to model the ultrasonic field in sinusoidally corrugated waveguides immersed in water where the interface curvature changes rapidly. DPSM results are compared with analytical solutions. It is found that when a narrow ultrasonic beam hits the corrugation peaks at an angle, the wave propagates in the backward direction in waveguides with high corrugation depth. However, in waveguides with small corrugation the wave propagates in the forward direction. The forward and backward propagation phenomenon is found to be independent of the signal frequency and depends on the degree of corrugation.

Cell property determination from the acoustic microscope generated voltage versus frequency curves

Among the methods for the determination of mechanical properties of living cells acoustic microscopy provides some extraordinary advantages. It is relatively fast, of excellent spatial resolution and of minimal invasiveness. Sound velocity is a measure of the stiffness or Youngs modulus of the cell. Attenuation of cytoplasm is a measure of supramolecular interactions. These parameters are of crucial interest for studies of cell motility, volume regulations and to establish the functional role of the various elements of the cytoskeleton. Using a phase and amplitude sensitive modulation of a scanning acoustic microscope (Hillman et al., 1994, J. Alloys Compounds. 211/212:625-627) longitudinal wave speed, attenuation and thickness profile of a biological cell are obtained from the voltage versus frequency or V(f) curves. A series of pictures, for instance in the frequency range 980-1100 MHz with an increment of 20 MHz, allows the experimental generation of V(f) curves for each pixel while keeping the lens-specimen distance unchanged. Both amplitude and phase values of the V(f) curves are used for obtaining the cell properties and the cell thickness profile. The theoretical analysis shows that the thin liquid layer, between the cell and the substrate, has a strong influence on the reflection coefficient and should not be ignored during the analysis. Cell properties, cell profile and the thickness of the thin liquid layer are obtained from the V(f) curves by the simplex inversion algorithm. The main advantages of this new method are that imaging can be done near the focal plane, therefore an optimal signal to noise ratio is achieved, no interference with Rayleigh waves occurs, and the method requires only an approximate estimate of the material properties of the solid substratum where the cells are growing on.