A mode conversion-based algorithm for detecting rectangular notch parameters in plates using Lamb waves

2015 ◽  
Vol 85 (6) ◽  
pp. 793-804 ◽  
Author(s):  
Amin Ghadami ◽  
Mehdi Behzad ◽  
Hamid Reza Mirdamadi
Keyword(s):  
Lamb Waves ◽  
Mode Conversion ◽  
Rectangular Notch

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

scholarly journals Lamb Waves Topological Imaging of Multiple Blind Defects in an Isotropic Plate

2019 ◽  
Vol 24 (2) ◽  
pp. 320-326 ◽  
Author(s):  
Wen-Fa Zhu ◽  
Hai-Yan Zhang Zhang ◽  
Meng-Yun Xu ◽  
Guo-Peng Fan
Keyword(s):  
Lamb Wave ◽  
Isotropic Plate ◽  
Lamb Waves ◽  
Mode Conversion ◽  
Image Resolution ◽  
Imaging Method ◽  
Wave Fields ◽  
Face To Face ◽  
Element Simulation ◽  
Reference Medium

The study investigates the feasibility of the Lamb wave topological imaging method for detecting multiple blindholes in an isotropic plate. The topological imaging method is performed based on the computations of two wave fields, a forward and an adjoint, in the defect-free reference medium using different emitting sources. The image is computed by multiplying the forward and adjoint wave fields together and integrating them over time or frequency. The interferences of multimode aliasing and the scattering effect can thus be eliminated at the defectfree positions with an improved image resolution. To investigate the physical mechanism, the refocusing process of the multimode Lamb waves at the defect positions is presented by a face-to-face comparison between the snapshots of the forward and adjoint wave fields using the finite element simulation. The Lamb wave topological imaging method is numerically and experimentally verified to identify multiple blind-holes in an isotropic aluminium plate. The results demonstrate that the topological imaging method enables the suppression of the sartefacts resulting from the mode conversion and achieve high-resolution imaging of the blind defects

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.

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