Depth and Angle Evaluation of Oblique Surface Cracks Using a Support Vector Machine Based on Seven Parameters

Abstract

To intelligently and quickly verify the depths and angles of oblique surface cracks using the laser ultrasound technique, a crack geometry information evaluation method using a support vector machine (SVM) is proposed. The relationships between several parameters—which are based on transmitted waves and reflected waves containing crack geometry information in the time domain, frequency domain and time–frequency domain, and crack size—are presented in detail. To decide which feature parameters are involved in the SVM model, two selection standards are proposed according to the correlations between feature parameters and crack size and between the feature parameters themselves. Finally, a seven-feature-parameter SVM model which has an excellent ability to classify oblique crack depths and angles is built. The results of simulations using the finite element method (FEM) and experimental data show that seven parameters based on the SVM model are available for the oblique surface crack depth and angle evaluation and can be used to nondestructively detect natural cracks.

Laser Ultrasonic Automatic Detection Method for Surface Microcracks on Metallic Cylinders

“…In fact, cracks are not always perpendicular to the sample surface. Li et al [21] used a seven-feature parameter support vector machine (SVM) model to intelligently and quickly identify the depths and angles of oblique surface cracks. Zeng et al [22] used the finite element method to investigate the relationship between the crack orientation and the LU spectrum.…”

A Sensitive Frequency Range Method Based on Laser Ultrasounds for Micro-Crack Depth Determination

“…The crack depth is a key parameter to evaluate the mechanical properties of materials. The ultrasonic-detection method has the advantages of non-pollution, available wave types, and abundant acoustic phenomenon, and the Rayleigh wave in particular is very sensitive to surface cracks, making it a good tool to quantitatively test the surface crack’s depth [ 1 , 2 ]. However, the coupling between the transducer and the tested material limits the application of the traditional Rayleigh-wave method in severe environments such as high temperature, high pressure, and high corrosion to accomplish quantitative testing of surface cracks.…”