Laser ultrasonic transmission type time-delay detection method for internal defects of material

Abstract

The invention discloses a laser ultrasonic transmission type time-delay detection method for internal defects of a material. The method comprises the following steps: firstly, enabling pulse laser excited by a laser device to act on the surface of a sample so as to excite ultrasonic body waves; secondly, focusing detection laser on a centering position of excited laser so as to detect ultrasonic body wave signals; thirdly, scanning a two-dimensional moving sample, and carrying out mutual correlation calculation on ultrasonic wave signals obtained at all scanning points by taking ultrasonic bodies with relatively high signal to noise ratios at non-defect position of the sample as reference waves; and finally, calculating the waveform correlation coefficients of the ultrasonic wave signals and time delay values of waveforms with the highest correlation coefficients, so as to finish the detection of the internal defects. The method has high sensitivity and stability to the detection of the internal defects, particularly sub-millimeter microdefects, the accurate positioning and quantification of the internal defects can be realized, and the method is suitable for nondestructive testingof various materials.

Description

Technical field [0001] The invention belongs to the technical field of material non-destructive testing, and specifically relates to a laser ultrasonic transmission time delay detection method for internal defects of materials. Background technique [0002] Internal defects widely exist in various materials and product workpieces. If they are not detected in time, these defects will gradually expand under the action of external force, causing the workpiece to break and fail, which seriously endangers product quality and engineering safety. Therefore, the internal defects of materials Accurate and timely non-destructive testing is essential. However, with the development of industrial automation and intelligence, high-precision, high-speed online inspection, and non-contact inspection have been put forward for non-destructive testing of internal defects. Conventional non-destructive testing methods have been difficult to meet the requirements. Laser ultrasound technology (laser u...

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Problems solved by technology

[0003] However, there are still some technical difficulties in using the existing laser ultrasonic technology to detect internal defects, especially small internal defects at the submillimeter level, which are mainly reflected in two points: First, under the condition of laser non-destructively exciting ultrasonic waves, along the direction perpendicular to the material surface, there are still some technical difficulties. The amplitude of the propagating ultrasonic wave is low, and the signal-to-noise ratio of the defect detection signal is low; secondly, in the process of laser ultrasonic scanning detection, the surface state of the material at different scanning positions is different, and the absorption of the excitation laser and the detection of the laser are different. Signal reception will have a greater impact, resulting in fluctuations in ultrasonic amplitude

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