Numerical Simulation of Metal Defect Detection Based on Laser Ultrasound

Abstract

The noncontact and wide-band characteristics of the ultrasonic signal excited by the laser make it widely used in nondestructive detection. In this paper, the finite element method is used to simulate multiple ultrasonic signal modes and the responses of them to metal defects. The simulation shows that the changes of excited Rayleigh-wave (RW) and shear-wave (SW) can be used to research the surface crack and internal defect of the sample respectively. By analyzing the reflected wave of RW and SW at the inspection point, the effects of surface crack and internal defect on the ultrasonic signals of the two modes are quantitatively compared. The results show that the time delay of the Rayleigh echo has a linear relationship to the width and transverse position of the crack, and the peak-valley difference of Rayleigh echo at the inspection point and the crack depth can also be fitted linearly. In addition, the Y component displacement of the bottom reflected SW also decays with the change of the internal defect. This simulation model provides a theoretical basis for further experimental verification basis.

3D Reconfigurable Vectorial Holography via a Dual‐Layer Hybrid Metasurface Device

“…45°LP to no image and on to 120°LP. The imaging efficiency (𝜂) of each state is further calculated as [66] 𝜂= ∑ U 2 out ∕ ∑ U 2 input , where U input represents the radiation fields of RTM at a sampling point, U out represents the output complex-amplitude field at a sampling point on the specific z-axis plane (imaging plane) and ∑ represents the summing of energy of all sampling points on the specific z-axis plane. The simulated of "1", "9", "2", "0", "2", "0", "2", "3", "H", "I", and "T" are 17.32%, 24.35%, 16.70%, 16.39%, 19.90%, 21.60%, 18.76%, 15.75%, 25.21%, 12.05%, and 17.63%, respectively.…”

“…When z 3 = 230 mm, the VMHs switch from “0” to no image and on to “T”, accompanied by a change of the SoP from 135° & 45° LP to no image and on to 120° LP. The imaging efficiency ( η ) of each state is further calculated as [ 66 ] $$\eta {\mathrm{ = }}{{\sum {{\mathrm{U}}_{{\mathrm{out}}}^2} } \mathord{/ {\vphantom {{\sum {{\mathrm{U}}_{{\mathrm{out}}}^2} } {\sum {{\mathrm{U}}_{{\mathrm{input}}}^2} }}} \kern-\nulldelimiterspace} {\sum {{\mathrm{U}}_{{\mathrm{input}}}^2} }}$$, where U input represents the radiation fields of RTM at a sampling point, U out represents the output complex‐amplitude field at a sampling point on the specific z ‐axis plane (imaging plane) and ∑ represents the summing of energy of all sampling points on the specific z ‐axis plane. The simulated η of “1”, “9”, “2”, “0”, “2”, “0”, “2”, “3”, “H”, “I”, and “T” are 17.32%, 24.35%, 16.70%, 16.39%, 19.90%, 21.60%, 18.76%, 15.75%, 25.21%, 12.05%, and 17.63%, respectively.…”

Development of a novel signal restoration algorithm to eliminate the distorted components in space charge measurement excited by femtosecond laser irradiation

“…However, in these research studies, it was found that the introduction of optical means was accompanied by the introduction of the distorted component, and the charge signals were distorted. Some researchers have pointed out that the heat accumulation effect induced by laser irradiation can lead to the generation of ultrasonic waves in materials [18,19]. Moreover, the space charge evolution characteristics under electromagnetic radiation can be very different, which may lead to more space charge accumulation and other problems [20,21].…”

Numerical simulation of angled surface crack detection based on laser ultrasound

“…Zhou used the method of fitting the transmission coefficient and reflection coefficient of the Rayleigh wave to quantitatively identify surface-breaking cracks [28]. Wang proved that the peak-to-valley difference of the Rayleigh echo and the crack depth can be linearly fitted [29]. Most of the research only focuses on a specific defect characteristic, which requires systematic quantitative research.…”