Scattering of Lamb Waves Near Lamé Point at an Opening Crack

2020 ◽  
Vol 143 (4) ◽  
Author(s):  
Xuwei Cao ◽  
Liang Zeng ◽  
Jing Lin
Keyword(s):  
Structural Information ◽  
Lamb Waves ◽  
Mode Conversion ◽  
Mode Shapes ◽  
Internal Crack ◽  
Strain Condition ◽  
Scattering Coefficients ◽  
Conversion Point ◽  
Calculation Results ◽  
Scattered Fields

Abstract The scattered fields of Lamb waves resulting from damage have been extensively studied because they carry rich structural information that allow us to identify and evaluate damage. This paper investigates the interaction of the fundamental symmetric Lamb mode (S0) near the first Lamé point with opening cracks of various heights under the plane strain condition. The scattering coefficients obtained by the semi-analytical method indicate a significant non-mode-conversion point, where the mode conversion is very weak. The frequency of this non-mode-conversion point originates in the first Lamé point and increases linearly with the crack height when the normalized height is less than 25%. The finite element simulations validate the calculation results. In addition, similar phenomena are also observed for the scattering at a symmetric internal crack. These interesting scattering characteristics are related to the special mode shapes near the Lamé point, which may provide a candidate to evaluate the height of an opening crack.

scholarly journals Propagation and Scattering of Lamb Waves at Conical Points in Plates

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
David M. Stobbe ◽  
Clemens M. Grünsteidl ◽  
Todd W. Murray
Keyword(s):  
Group Velocity ◽  
Lamb Waves ◽  
Mode Conversion ◽  
Wave Interaction ◽  
Conical Point ◽  
Wave Number ◽  
Mode Shapes ◽  
Accidental Degeneracy ◽  
Near Degeneracy ◽  
Thickness Mode

Abstract Lamb waves exhibit conical dispersion at zero wave number when an accidental degeneracy occurs between thickness mode longitudinal and shear resonances of the same symmetry. Here we investigate the propagation of Lamb waves generated at the conical point frequency and the interaction of these waves with defects and interfaces. The group velocity and mode shapes of Lamb waves at the conical point are found, and it is shown that as the wavenumber gets close to zero, considerable group velocity is seen only for material properties supporting a degeneracy or near-degeneracy. The unusual wave propagation and mode conversion of Lamb waves generated at the conical point are elucidated through numerical simulations. Experimental measurements of near conical point Lamb wave interaction with holes in a plate demonstrate that these waves flow around defects while maintaining a constant phase of oscillation across that plate surface.

scholarly journals Partial Energy Transfer Model of Lamb Waves Scattering in Materially Isotropic Waveguides

2021 ◽  
Vol 11 (10) ◽  
pp. 4508
Author(s):  
Pavel Šofer ◽  
Michal Šofer ◽  
Marek Raček ◽  
Dawid Cekus ◽  
Paweł Kwiatoń
Keyword(s):  
Energy Transfer ◽  
Lamb Waves ◽  
Hybrid Approach ◽  
Wave Mode ◽  
Transfer Model ◽  
Material Interface ◽  
Modal Expansion ◽  
Scattering Coefficients ◽  
Expansion Technique ◽  
Partial Energy

The scattering phenomena of the fundamental antisymmetric Lamb wave mode with a horizontal notch enabling the partial energy transfer (PET) option is addressed in this paper. The PET functionality for a given waveguide is realized using the material interface. The energy scattering coefficients are identified using two methods, namely, a hybrid approach, which utilizes the finite element method (FEM) and the general orthogonality relation, and the semi-analytical approach, which combines the modal expansion technique with the orthogonal property of Lamb waves. Using the stress and displacement continuity conditions on the present (sub)waveguide interfaces, one can explicitly derive the global scattering matrix, which allows detailed analysis of the scattering process across the considered interfaces. Both methods are then adopted on a simple representation of a surface breaking crack in the form of a vertical notch, of which a certain section enables not only the reflection of the incident energy, but also its nonzero transfer. The presented results show very good conformity between both utilized approaches, thus leading to further development of an alternative technique.

A baseline-free approach of locating defect based on mode conversion and the reciprocity principle of Lamb waves

Ultrasonics ◽  
2020 ◽  
Vol 102 ◽  
pp. 106063
Author(s):  
Hongbo Jia ◽  
Hongwei Liu ◽  
Zhichun Zhang ◽  
Fuhong Dai ◽  
Yanju Liu ◽  
...  
Keyword(s):  
Lamb Waves ◽  
Mode Conversion ◽  
Reciprocity Principle

scholarly journals Defects Detection and Localization in Underwater Plates Using Laser Laterally Generated Pure Non-Dispersive S0 Mode

2019 ◽  
Vol 9 (3) ◽  
pp. 459 ◽  
Author(s):  
Qingnan Xie ◽  
Chenyin Ni ◽  
Zhonghua Shen
Keyword(s):  
Defect Detection ◽  
Lamb Waves ◽  
Mode Conversion ◽  
High Sensitivity ◽  
Laser Source ◽  
Dispersion Characteristics ◽  
High Attenuation ◽  
Corrosion Defects ◽  
Detection And Localization ◽  
Lateral Excitation

When working in humid environments, corrosion defects are easily produced in metallic plates. For defect detection in underwater plates, symmetric modes of Lamb waves are widely used because of their characteristics including long propagating distance and high sensitivity to defects. In this study, we extend our previous work by applying the laser laterally generated S0 mode to detection and localization of defects represented by artificial notches in an aluminum plate immersed in water. Pure non-dispersive S0 mode is generated in an underwater plate by lateral laser source irradiation and its fd (frequency·thickness) range is selected by theoretical calculation. Using this lateral excitation, the S0 mode is enhanced; meanwhile, the A0 mode is effectively suppressed. The mode-converted A0 mode from the incident S0 mode is used to detect and localize the defect. The results reveal a significantly improved capability to detect defects in an underwater plate using the laser laterally generated S0 mode, while that using A0 is limited due to its high attenuation. Furthermore, owing to the long propagating distance and the non-dispersion characteristics of the S0 generated by the lateral laser source, multiple defects can also be detected and localized according to the mode conversion at the defects.

scholarly journals Air coupled ultrasonic inspection with Lamb waves in plates showing mode conversion

Ultrasonics ◽  
2020 ◽  
Vol 100 ◽  
pp. 105984 ◽  
Author(s):  
Arno Römmeler ◽  
Peter Zolliker ◽  
Jürg Neuenschwander ◽  
Valentin van Gemmeren ◽  
Mario Weder ◽  
...  
Keyword(s):  
Lamb Waves ◽  
Mode Conversion ◽  
Ultrasonic Inspection
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