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Nondestructive Testing
Published in Dale Ensminger, Leonard J. Bond, Ultrasonics, 2011
Dale Ensminger, Leonard J. Bond
In direct, contact, gap, or immersion methods, nearly all modes of ultrasonic waves used in NDT, except longitudinal, are produced by mode conversion at the boundaries between the couplant and the test piece. The incident wave is generated by a transducer operating in a longitudinal mode. If testing is to be done using a longitudinal wave, the transducer is oriented so that the wave impinges at normal incidence on the surface of the test piece. If a shear-wave technique is to be used, the incidence angle is made larger than the critical angle for longitudinal waves. When direct contact coupling is used with shear-wave testing, the transducer is mounted on a solid wedge (plastic) in which the velocity of sound is lower than that in the test piece. The angle of incidence is designed to produce the desired refraction angle for the shear wave in the test piece. When immersion coupling is used, the inspector can exercise greater freedom in choosing the incidence angle and, therefore, the refraction angle within the test piece.
Introduction to Wave Propagation
Published in Srinivasan Gopalakrishnan, Elastic Wave Propagation in Structures and Materials, 2023
As mentioned earlier, wave propagation is an exciting field having applications cutting across many disciplines. In the area of structures and materials, wave propagation-based tools have found increasing applications, especially in the area of structural health monitoring and active control of vibrations and noise. In addition, there has been tremendous progress in the area of material science, wherein a new class of structural materials is designed based on wave propagation analysis to meet the particular design standards. In most cases, these materials are not isotropic as in metallic structures. These are either anisotropic (as in the case of laminated composite structures) or inhomogeneous (as in the case of functionally graded materials). These structures introduce some special behavior that are not present in conventional structures. For example, laminated composites can exhibit stiffness and inertial coupling depending upon the way the composite plies are stacked. Due to these couplings, motions in all the three dimensions get coupled. That is, in a laminated composite beam, if the plies are stacked unsymmetrically, the axial motion and bending motion get coupled. In wave propagation terminology, stiffness and inertial coupling induces mode conversion. That is, an axial impact causes bending motion and vice versa. References [69] and [117] give a good overview of the behavior of laminated composites and the effect of stiffness and inertial coupling on their response. Similarly, when the medium in which the wave is propagating is inhomogeneous as in the case of functionally graded material structures, the traditional definition of plane wave gets destroyed and the waves in such a medium propagate with attenuation. In these material systems, a systematic wave propagation analysis will help us in understanding the behavioral physics of these systems better.
Laser Light Propagation and Interaction with Plasma
Published in M.B. Hooper, Laser-Plasma Interactions 4, 2020
For the Nd laser wavelength estimates show that a linear theory of resonance absorption is satisfactory as long as the intensity does not exceed approximately 1014W/cm2. At higher intensities a nonlinear theory of mode conversion must be developed. In general, a complete description of this phenomenon can only be obtained by including Maxwell’s equations and employing numerical methods. However, in order to make analytical predictions, models of resonant electron plasma wave excitation can be used. The simplest one is again the capacitor model. The corresponding wave equation is best expressed in terms of the electron oscillatory motion υe and the Lagrangian coordinates a and t (see Ref.[1], p. 69): () ∂2∂t2υe+sϵ2γenoγe∂2∂t∂a(no1+∂/∂a∫υedt)γe+ωp2(a,t)υe=−12ω2υde−iωt+cc.
High power millimeter-wave TE03 to TM11 mode converters
Published in International Journal of Electronics, 2019
Amit Patel, Riddhi Goswami, Keyur Mahant, Pujita Bhatt, Hiren Mewada, Alpesh Vala, Sathyanarayana K, Sanjay Kulkarni
The simulated transmission efficiency of the proposed TE03 to TE02 mode converter using corresponding design parameters is shown in Figure 7. It generates TE02 mode from TE03 mode with efficiency over 89.60% at 42 GHz for the waveguide diameter mm. For improving the mode conversion efficiency, it is required to optimise the physical parameters using mode matching techniques. The calculated and optimised values of design parameters are tabulated in Table 3. Thus, these optimised values mentioned in Table 3 gives 99.15% mode conversion efficiency at 42 GHz frequency as shown in Figure 8.
The contribution of numerical models to Lamb-wave-driven NDT processes – part II: experimental design and numerical studies
Published in Advanced Composite Materials, 2023
Morten Voß, Artur Szewieczek, Wolfgang Hillger, till Vallée, Friedrich von Dungern
In ultrasonic NDT processes, a widely exploited phenomenon for defect identification/localisation represents the effect of mode conversion. In short, mode conversions occur at the interface of two materials having different acoustic impedances, whereby the incident wave gets converted when its incidence angle is not perpendicular to the respective interface [29]. Depending on the type of signal as well as further component-specific conditions (materials, geometry, type of defect etc.), developing conversion effects may vary, cf. [30]. In 2019, Pudipeddi et al. [31] investigated the influence of delamination size on converted LW signals in a quasi-isotropic composite laminate and found that A0-S0 converted signals tend to increase with anomaly size. Further investigations with regard to conversion effects at material imperfections have been presented by Wandowski et al. [32], who showed that LW displacements recorded at the surface of a plate made of glass fibre-reinforced polymer (G-FRP) can be used to locate a delamination as well as to draw conclusions about its size and shape. This short literature survey shows that developing conversion effects may differ, but also that these can principally be used to draw conclusions about the anomalies to be detected. However, for an efficient NDT process, numerical computations have to be linked to the inspection system in order to predict occurring LW interactions within the component and conversion effects. The present study is thus intended to illustrate the numerical modelling process step-by-step for an exemplary component, as well as to show how simulation results can be used to assist the design of an experimental setup.
Measurement of metal–roll interface during metal rolling using normal and oblique ultrasonic reflection
Published in Tribology - Materials, Surfaces & Interfaces, 2020
G. J. Adeyemi, R. S. Dwyer-Joyce, J. T. Stephen, A. Adebayo
The oblique transmission and reflection of longitudinal and shear incidence waves at a solid–solid interface is shown schematically in Figure 1(b). is the longitudinal incidence wave and is the angle of incidence. , , , and are the reflected longitudinal, reflected shear, transmitted longitudinal and shear transmitted waves respectively, while and, and are angles of reflection and transmission of each wave. When a longitudinal or shear ultrasonic wave hits the contact interface of the two media at any angle , mode conversion occurs at the boundary (reflection of incidence wave and refraction of the transmitted wave). Some portion of the wave is reflected at angle the same as angle of incidence for the longitudinal wave, whilst the remainder of the wave that is transmitted into the second material refracted at the boundary and divided into two parts; longitudinal with an angle of and shear with an angle of . The angles of reflection and refraction of the transmitted waves depend on the acoustic properties of the materials, the angle of incidence and the nature of the interface.