Detection and Evaluation of Surface Defects Based on Critical Frequency Method by Laser Ultrasonic

The time–frequency analysis by smooth Pseudo-Wigner-Ville distribution (SPWVD) is utilized for the double-line laser ultrasonic signal processing, and the effective detection of the metal surface defect is achieved. The double-line source laser is adopted for achieving more defects information. The simulation model by using finite element method is established in a steel plate with three typical metal surface defects (i.e. crack, air hole and surface scratch) in detail. Besides, in order to improve the time resolution and frequency resolution of the signal, the SPWVD method is mainly used. In addition, the deep learning defect classification model based on VGG convolutional neural network (CNN) is set up, also, the data enhancement method is adopted to extend training data and improve the defects detection properties. The results show that, for different types of metal surface defects with sub-millimeter size, the classification accuracy of crack, air holes and scratch surface are 94.6%, 94% and 94.6%, respectively. The SPWVD and CNN algorithm for processing the laser ultrasonic signal and defects classification supplies a useful way to get the defect information, which is helpful for the ultrasonic signal processing and material evaluation.

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An Approach to Size Sub-Wavelength Surface Crack Measurements Using Rayleigh Waves Based on Laser Ultrasounds

Sensors ◽

10.3390/s20185077 ◽

2020 ◽

Vol 20 (18) ◽

pp. 5077

Author(s):

Haiyang Li ◽

Qianghua Pan ◽

Xiaotong Zhang ◽

Zhiwu An

Keyword(s):

Theoretical Analysis ◽

Rayleigh Wave ◽

Surface Crack ◽

Rayleigh Waves ◽

Critical Frequency ◽

Experimental Results ◽

Notch Depth ◽

Frequency Method ◽

Threshold Phenomenon ◽

Sub Wavelength

In this paper, the interaction of a broadband Rayleigh wave generated by a laser and an artificial rectangular notch is analyzed theoretically and experimentally. For the theoretical analysis, a Gaussian function is adopted to analyze the modulation of notch depth on the frequency spectrum via reflection and transmission coefficients. By the finite element method, the Rayleigh wave generated by pulsed laser beam irradiation and its scattering waves at cracks are calculated. A curve with a slope close to 4 fitted by crack depth and critical wavelength of the threshold phenomenon is obtained by the wavelet transform and Parseval’s theorem according to simulated and experimental results. Based on this relationship, the critical frequency at which the threshold phenomenon happens due to energy transformation of transmission/reflection Rayleigh waves is adopted to determine the size of sub-wavelength surface crack. The experimental results of artificial notch depth estimation on aluminum alloy specimens consistent with theoretical analysis validates the usefulness of the critical frequency method based on a broadband Rayleigh wave generated by laser ultrasonic.

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The critical-frequency method of measuring upper-atmospheric ionization

Proceedings of the Physical Society ◽

10.1088/0959-5309/51/1/311 ◽

1939 ◽

Vol 51 (1) ◽

pp. 81-92 ◽

Cited By ~ 14

Author(s):

E V Appleton ◽

R Naismith ◽

L J Ingram

Keyword(s):

Critical Frequency ◽

Frequency Method ◽

Atmospheric Ionization

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Laser ultrasonic measurement of surface defects based on ratio method

10.1117/12.694443 ◽

2006 ◽

Author(s):

Gang Li ◽

Hedong Yu ◽

Guoping Zhang

Keyword(s):

Surface Defects ◽

Ultrasonic Measurement ◽

Ratio Method ◽

Laser Ultrasonic

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Some further measurements of upper atmospheric ionization

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1935.0129 ◽

1935 ◽

Vol 150 (871) ◽

pp. 685-708 ◽

Cited By ~ 59

Keyword(s):

Solar Eclipse ◽

Seasonal Variations ◽

Critical Frequency ◽

Ultra Violet ◽

Frequency Method ◽

Ultra Violet Light ◽

Violet Light ◽

South East England ◽

Atmospheric Ionization ◽

Maximum Ionization

In a previous communication an account was given of some measurements of upper atmospheric ionization in south-east England made by the critical frequency method. These measurements were confined principally to the Kennelly-Heaviside region (region E) and showed that the maximum ionization at that level in the ionosphere exhibits a diurnal and seasonal variation such as may be explained in terms of a solar ionizing agency travelling rectilinearly. It was found, for example, that the ionization reaches a maximum about noon, falls off rapidly as sunset approaches, and continues to decrease less rapidly during the night. A short time before ground sunrise a minimum of ionization is attained, after which the value increases rapidly until the noon maximum is again reached. In the same communication reasons were advanced, based on the radio measurements made by one of us during the solar eclipse of 1927, for believing the ionizing agency for this region to be ultra-violet light from the sun, as opposed to the view then prevailing that a neutral stream of corpuscles was the effective agent, and it was pointed out that the solar eclipse of August 31, 1932, visible in Canada, provided an excellent opportunity for deciding the matter. Using the same critical-frequency method, Dr. J. T. Henderson working at Vankleek Hill, Ontario, was able to set the question beyond doubt and it may now be regarded as established that ultra-violet light is the principal ionizing agency for the Kennelly-Heaviside region. The present communication deals with further measurements made in south-east England by the critical-frequency method in which it is applied to the study of diurnal and seasonal variations in ionization in the upper ionized region (region F) as well as in region E. Since 1932, many workers in different parts of the world have adopted the critical-frequency method for the measurement of maximum ionization content and it is hoped that, in due course, the results of a world-wide survey of the diurnal and seasonal variations in ionospheric conditions will be available. Meanwhile, we are able to compare our present results with those we have previously obtained and also with those obtained in America at places of lower latitude.

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Laser ultrasonic testing for near-surface defects inspection of 316L stainless steel fabricated by laser powder bed fusion

China Foundry ◽

10.1007/s41230-021-1063-1 ◽

2021 ◽

Vol 18 (4) ◽

pp. 360-368

Author(s):

Ting Dai ◽

Xiao-jian Jia ◽

Jun Zhang ◽

Jin-feng Wu ◽

Yi-wei Sun ◽

...

Keyword(s):

Stainless Steel ◽

Ultrasonic Testing ◽

316L Stainless Steel ◽

Surface Defects ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Laser Ultrasonic ◽

Near Surface ◽

Powder Bed ◽

Defects Inspection

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Laser ultrasonic surface defects detection method based on 2D-CNN

Journal of Applied Optics ◽

10.5768/jao202142.0107002 ◽

2021 ◽

Vol 42 (1) ◽

pp. 149-156

Author(s):

XU Zhixiang ◽

◽

GUAN Shouyan ◽

YANG Fan ◽

...

Keyword(s):

Surface Defects ◽

Detection Method ◽

Laser Ultrasonic

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Research on laser ultrasonic surface defect identification based on a support vector machine

Science Progress ◽

10.1177/00368504211059038 ◽

2021 ◽

Vol 104 (4) ◽

pp. 003685042110590

Author(s):

Chao Chen ◽

Xingyuan Zhang

Keyword(s):

Support Vector Machine ◽

Surface Defect ◽

Surface Defects ◽

Support Vector ◽

Laser Ultrasound ◽

Defect Depth ◽

Laser Ultrasonic ◽

Defect Identification ◽

Different Depths ◽

Quantitative Identification

To solve the problem of difficult quantitative identification of surface defect depth during laser ultrasonic inspection, a support vector machine-based method for quantitative identification of surface rectangular defect depth is proposed. Based on the thermal-elastic mechanism, the finite element model for laser ultrasound inspection of aluminum materials containing surface defects was developed by using the finite element software COMSOL. The interaction process between laser ultrasound and rectangular defects was simulated, and the reflected wave signals corresponding to defects of different depths under pulsed laser irradiation were obtained. Laser ultrasonic detection experiments were conducted for surface defects of different depths, and multiple sets of ultrasonic signal waveform were collected, and several feature vectors such as time-domain peak, center frequency peak, waveform factor and peak factor were extracted by using MATLAB, the quantitative defect depth identification model based on support vector machine was established. The experimental results show that the laser ultrasonic surface defect identification model based on support vector machine can achieve high accuracy prediction of defect depth, the regression coefficient of determination is kept above 0.95, and the average relative error between the true value and the predicted value is kept below 10%, and the prediction accuracy is better than that of the reflection echo method and BP neural network model.

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