Abstract
This paper presents a theoretical and finite element (FE) investigation of the generation and propagation characteristics of the fundamental Lamb waves symmetrical mode S0 and anti-symmetrical mode A0 after testing with different types of defects in the plates. The reflection and transmission of Lamb waves at a micro symmetry defect and asymmetry defect are analyzed numerically in the two-dimension (2D) model. Mode conversion of Lamb waves can occur upon encountering the asymmetry discontinuities leading to newly-converted modes apart from wave reflection and transmission. When testing the symmetry defects, the reflection and transmission waves have no modal separation phenomenon. To describe the mode conversion and reflection and transmission degree, and evaluate the micro defect severity, a series of defects are simulated to explore the relationships of defect reflection and transmission with the length and depth of a defect in the 2D FE model. In the three-dimension (3D) FE model, the straight-crest Lamb waves and circular-crest Lamb waves are simulated and researched by contrast analysis. Then the straight-crest Lamb waves are motivated to study the scattering laws of Lamb waves interacting with the circle hole defects and rectangular hole defects. S0 mode and SH0 mode are contained in the scattering waves after S0 mode testing the through holes defects. Corresponding mode energy percentages were analyzed at different micro defect severities changed in different ways. Simulation results illustrated that the modal energy percentages varied in a different character and provided support for the analytically determined results of Lamb waves in the non-destructive testing and evaluation.
Highlights
Lamb waves have been widely explored as a promising inspection tool for non-destructive testing (NDT) and structural health monitoring (SHM) during the past years [1, 2]
Numerical methods such as finite element method (FEM) about defect recognition depends on the systematically analysis of the dispersion characteristics, structural characteristics, attenuation characteristics, reflection and transmission characteristics after Lamb waves testing the defects in the plates, and the research about studying the sensitivity of each Lamb mode to the encountered defects is very important
The circular-crest Lamb waves can be treated as straight-crest Lamb waves before a micro defect when spread over a long distance and meet the micro defects
Summary
Lamb waves have been widely explored as a promising inspection tool for non-destructive testing (NDT) and structural health monitoring (SHM) during the past years [1, 2]. Many other researches had shown the interactions with different types of defects including the hole defects, the surface defects, the vertical cracks, the inclined cracks, corrosion defects, groove defects and other irregular defects [33] These authors combined a finite element method and a modal decomposition to investigate the interaction of Lamb waves with defects, but only considered a single characteristic or a single boundary condition. Due to the complex mode conversion and energy redistribution after testing the micro defects, Lamb wave’s scattering, reflection and transmission characteristics at the defects (or its interactions with the micro defects) is difficult to study in a pure analytical way Numerical methods such as finite element method (FEM) about defect recognition depends on the systematically analysis of the dispersion characteristics, structural characteristics, attenuation characteristics, reflection and transmission characteristics after Lamb waves testing the defects in the plates, and the research about studying the sensitivity of each Lamb mode to the encountered defects is very important. Corresponding mode energy percentages and scattering characteristics were analyzed emphatically by the straight-crest Lamb waves at different micro defect severities changed in different ways
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