Method for detecting flaw through infrared thermography

Abstract

The invention provides a method for detecting a flaw through infrared thermography. The method comprises the following steps that thermal excitation is performed on a detected test piece, time sequence detection thermal images of the surface of the detected test piece in a period of time before, in and after excitation are acquired through a thermal infrared imager; temperature fitting is performed on the temperature rising stage and the temperature lowering stage; the average temperature is derived to take a maximum value to determine an excitation starting time point and an excitation finishing time point in detection to build time references for analyzing a relationship between the flaw and the time; second derivatives of the average temperature are solved to take an extreme value to determine the precise time when a temperature difference occurs; after excitation is finished, the area size of the flaw is detected, and a threshold value coefficient in a half maximum contrast width method is determined to range from 0.5 to 0.7; a contour surface is constructed in time sequence according to a same image grey value, and a three-dimensional flaw reconstruction result is acquired by adopting a projection method. According to the method, high-precision flaw projection reconstruction can be achieved.

Description

technical field [0001] The invention relates to a method for detecting defects by infrared thermal imaging. Background technique [0002] Infrared thermal imaging non-destructive testing technology is a new non-destructive testing technology that has gradually matured with the development of thermal imaging technology. Infrared thermal image detection is to receive the infrared radiation emitted by the object and display it in the form of a thermal image with an infrared thermal imager. When an object has defects, its thermal conductivity is significantly different from that of the object material itself. Under a certain thermal excitation, the defect will affect the heat conduction, resulting in abnormal surface temperature distribution. The infrared thermal imaging camera and other sensing devices are used to measure the surface temperature change of the inspected structure, and then the characteristics of the internal defect are obtained through analysis and processing t...

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Problems solved by technology

The Chinese invention patent "Reconstruction method of infrared thermal wave detection tomographic image" (public number CN1696674A) also studies the depth-based infrared detection tomographic reconstruction method, but only gives the plane tomographic images of flat-bottomed blind hole defects at different depths , does not give the tomographically reconstructed stereoscopic image or its profile, and the detection object is only defects with different depths, and does not consider the problem of defect size extraction, and depth and size are two aspects of defect image reconstruction

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