涡流热成像裂纹检测中的形状大小影响分析

Analysis of influencing factors of geometry size in crack inspection using eddy current thermography

涡流热成像无损检测技术可以对金属表面裂纹进行快速、准确的检测,但是不同的线圈、试件以及裂纹大小对检测效果影响很大。通过建立感应加热二维模型,选取裂纹处与非缺陷处温差作为特征量,对不同组成部分形状大小对涡流热成像检测的影响规律进行了数值模拟;对比分析了不同裂纹深度下温差随体积深度比的变化规律,采用数据拟合方法研究了相似裂纹检测规律,并提取出试件形状以及线圈形状对检测效果的影响曲线;最后进行了涡流热成像试验验证。结果表明:当裂纹深度较大时,体积深度比影响规律可分为上升阶段、平稳阶段和下降阶段;相似裂纹间温差变化符合二次变化规律;涡流热成像技术可有效检测超大或超厚试件表面裂纹;减小线圈提离、曲率和线径的大小有助于增强检测效果。实际检测过程中,可据此针对不同被检试件采用不同线圈,提高检测能力。

The surface crack of metallic materials can be detected efficiently and accurately with eddy current thermography. The detect results vary a lot with the change of coil size,specimen size and crack size. In this paper,a two-dimension model for induction heating is built,and the temperature difference between crack and non-defect is selected to analyze the geometry influence rules of eddy current thermography. Different sizes of specimens with defects of different widths and heights detected by different coils are numerically investigated. Finally,the eddy current thermography test is conducted. The test results demonstrated that the influence rule of volumedepth ratio can be divided into rising phase,stationary phase and decline phase when the crack height is big enough. The temperature difference for similar cracks conforms to the secondary change rule. Eddy current thermography can achieve an efficient detection for surface crack in large or super thick specimen. The decrease of lift-off,curvature and radius of coil can enhance the detection performance. In practical applications,the detection capability can be improved by utilizing different coils for corresponding specimens.