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A method for detecting cracks by laser thermal imaging

A detection method and thermal imaging technology, applied in the field of crack detection based on laser thermal imaging, can solve the problems of many point lasers, different detection sensitivity, complex design, etc., and achieve the effect of high detection efficiency

Active Publication Date: 2022-04-15
CHINA JILIANG UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

During fractional laser detection, the spot is generally stationary during detection, so the detection sensitivity is significantly different with the distance from the spot, and the test results have strong non-uniformity
Moreover, if the crack position happens to expand along the direction of heat flow, such as passing through the center of the spot, or just on the symmetry line between the two spots, it is easy to miss detection.
The moving device can be omitted based on the point-matrix laser detection system, but the number of point lasers is large, or a single high-power laser and complex optical devices are used to generate point laser arrays, and the design is relatively more complicated

Method used

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  • A method for detecting cracks by laser thermal imaging
  • A method for detecting cracks by laser thermal imaging
  • A method for detecting cracks by laser thermal imaging

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Experimental program
Comparison scheme
Effect test

Embodiment approach 1

[0028] The basic structure of the test system is as follows: figure 1 As shown: there is a crack 2 on the surface of the sample 1 to be tested, the laser 3 projects the laser light 4 onto the sample surface, and the laser 4 heats the sample 1 to cause a facing heat flow 5; the thermal imager 6 is located above the sample 1, and observes and records the evolution of the temperature field on the surface of the sample 1, And the data is transmitted to the data analysis software 7; the laser 3 is installed on the displacement stage 8, which can perform one-dimensional scanning, so that the laser 4 continuously scans and heats the surface of the sample 1 .

[0029] The surface condition of sample 1 is as follows figure 2 As shown, the laser 4 used for thermal excitation during the test is composed of 18 spot spots 411-419, 421-429, each of which has a diameter of about 1 mm; among them, 9 spot spots 411-419 are arranged in a line array L1 at equal intervals. The distance between ...

Embodiment approach 2

[0052] The basic structure of the test system is as follows: image 3 As shown: there is a crack 2 on the surface of the cylindrical sample 11 to be tested, the laser 14 projects the laser 16 to the sample surface, and the laser 15 projects the laser 17 to the sample surface; laser heating causes heat flow 5; the thermal imager 6 is located above the sample 1, and the observation record The evolution of the surface temperature field of the sample 11, and the data is transmitted to the data analysis software 7; the cylindrical sample 11 is placed on the cylindrical drum 12 and the drum 13, and the drum 12 and the drum 13 rotate at the same speed at a constant speed, so that the cylindrical sample 11 is rotated at the same speed. The linear speed rotates at a constant speed to realize the laser thermal imaging scanning detection of the entire outer surface of the sample 11.

[0053] The surface condition of sample 11 is as follows Figure 4 As shown, the outer circular surface ...

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Abstract

The invention discloses a method for detecting cracks by laser thermal imaging. In the present invention, the laser spot is two groups of point spots arranged in parallel line arrays, and the two line arrays are staggered by a certain distance along the line length direction. When performing scanning detection, each point spot generates heat flow in parallel scanning direction and vertical scanning direction, and cracks in all directions near the spot can be detected. If the crack is parallel to the scanning direction and it is just located in the center of a certain spot, or the crack is located on the symmetrical line of the center of two adjacent spot spots of a certain line array, the crack will not be caused when the line array spot scans past. The temperature is abnormal, but when another line array spot scans, it will definitely cause temperature abnormality, so as to detect cracks. With the laser spot design of the present invention, cracks in special positions and directions will not be missed, and this scanning detection method only needs to perform one-dimensional scanning, and the detection efficiency is high.

Description

technical field [0001] The invention relates to a non-destructive detection method for surface cracks, in particular to a crack detection method based on laser thermal imaging. Background technique [0002] Laser thermal imaging is a non-destructive detection method mainly aimed at surface and near-surface cracks. The basic principle is that localized laser heating causes surface-to-face heat transfer. When there is a crack on the heat transfer path, due to the high thermal resistance caused by the air gap at the crack, This leads to anomalies in the spatial distribution or time variation of the temperature on both sides of the crack. [0003] The spatial distribution mode of spot power density during laser thermal imaging detection has a great influence on the detection effect. Currently common laser modes include: point laser, line laser, and fractional laser. [0004] Spot laser heating can cause heat transfer in all directions at the same time, so except for cracks tha...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G01N25/72
CPCG01N25/72
Inventor 侯德鑫叶树亮
Owner CHINA JILIANG UNIV