Quantitative detection of surface defect using laser-generated Rayleigh wave with broadband local wavenumber estimation

Rayleigh wave propagation in centrosymmetric materials with micro-stiffness, flexoelectric and micro-inertia effects

A theoretical investigation of Rayleigh waves propagation in polarized media has been carried out using a reformulated flexoelectric theory for isotropic dielectrics with micro-inertia effect. Within this non-classical theory, the internal energy density is the functional of the strain tensor, dilatation gradient, deviatoric part of stretch gradient and rotation gradient tensors, polarization vector, and polarization gradient. The obtained system of governing equations additionally contains three material length-scale parameters to account the micro-stiffness effect, one material constant to capture the micro-inertia effect, two flexoelectric constants to describe the flexoelectric effect and three length scale parameters related to the polarization gradient. To solve the coupled governing equations, the method of Lamé-type potentials for mechanical displacement and electric polarization vectors is used. The influences of various factors such as micro-stiffness, flexoelectricity, electric quadrupoles and micro-inertia effects on the phase velocity of the Rayleigh waves in a homogeneous isotropic half-space are studied. It is found that above effects become significant with the increase of the wavenumber. This study can be important for the investigation of high frequency surface acoustic waves in dielectric materials.

Systematic Evaluation of Ultrasonic In-Line Inspection Techniques for Oil and Gas Pipeline Defects Based on Bibliometric Analysis

The global reliance on oil and gas pipelines for energy transportation is increasing. As the pioneering review in the field of ultrasonic defect detection for oil and gas pipelines based on bibliometric methods, this study employs visual analysis to identify the most influential countries, academic institutions, and journals in this domain. Through cluster analysis, it determines the primary trends, research hotspots, and future directions in this critical field. Starting from the current global industrial ultrasonic in-line inspection (ILI) detection level, this paper provides a flowchart for selecting detection methods and a table for defect comparison, detailing the comparative performance limits of different detection devices. It offers a comprehensive perspective on the latest ultrasonic pipeline detection technology from laboratory experiments to industrial practice.

A novel 3D evaluation method for surface defects using broadband laser-generated Rayleigh waves with wavenumber analysis

To address the issues of large imaging errors for small defects and the difficulty in depth evaluation using local wavenumber estimation for surface defect imaging, a novel three-dimensional (3D) evaluation method for surface defects using broadband laser-generated Rayleigh waves with wavenumber analysis is proposed. A finite element model is established to investigate the interaction between the Rayleigh wave and the surface defect and reveal the wavenumber change mechanism of the non-dispersive Rayleigh wave in the case of defects. It is discovered that when the Rayleigh wave encounters the surface defect, various mode-converted scattered waves are generated, resulting in the appearance of new components with wavenumbers lower than that of the incident Rayleigh wave in the wavenumber domain. Additionally, the maximum amplitude of the Rayleigh wave in the B-scan image increases as the defect depth increases. Based on the simulation analysis, a 3D evaluation method for surface defects is proposed. Firstly, the scattered Rayleigh wave caused by the defect is extracted using frequency-wavenumber analysis. Secondly, a space-frequency-wavenumber analysis is used to determine the local wavenumber of the scattered Rayleigh wave for defect imaging. Finally, the defect depth is estimated by analyzing the maximum amplitude of the Rayleigh wave. A surface defect detection experiment is conducted to verify the effectiveness of the proposed method, and the experimental results demonstrate that the proposed method can suppress noise interference and accomplish high-precision imaging of small surface defects compared to the traditional method. Moreover, the method can establish a linear mapping relationship between the defect depth and the maximum amplitude of the Rayleigh wave for depth evaluation. The research results can provide a potential application for the 3D evaluation of surface defects.

Surface breaking crack sizing method using pulse-echo Rayleigh waves

Surface cracks are common in various industries. Eddy current testing (ECT) is commonly used for crack sizing but necessitates complex calibration standards and a highly trained inspector. Moreover, for large-area inspections, it requires additional scanning arrangements. In recent years the wedge technique-based Rayleigh wave crack sizing method has attracted significant research interest due to its unidirectional excitability. However, Rayleigh wave features generated at crack tips are often weak and masked under noise, and they mostly attenuate before reaching the receiving probe due to the couplant between the wedge-test specimen interface. Consequently, sizing the crack depth is difficult using a pulse-echo setup. This work presents a wedge-free pulse-echo Rayleigh wave method for surface crack sizing using a conventional phased array transducer. Eliminating the wedge removes a couplant layer leading to lower attenuation, enabling the transducer to capture crack tip features. This allows the sizing of surface cracks in pulse-echo using the time-of-flight (ToF) information. Furthermore, leveraging the phased array system, an averaging technique employed to the time trace signals captured by the transducer elements effectively averages out the other wave modes generated at crack geometries by the scattering of Rayleigh waves. This significantly minimizes sizing errors and enhances the signal-to-noise ratio (SNR). The performance of the proposed method is demonstrated through finite element simulations and experiments. Experiments with electric discharged machined (EDM) notches on test specimen surface at various angles and depths mimicking surface-breaking cracks show accurate sizing within a 5% error. The proposed method offers flexibility in performing inspections using a wide frequency range and can be easily applied to different materials using any conventional phased array transducer. This enhances its adaptability for industrial applications in the characterization of surface cracks.