红外锁相法热波检测技术及缺陷深度测量

Thermal wave detection and defect depth measurement based on lock-in thermography

研究了红外锁相法热波检测技术的原理、缺陷深度测量及在蜂窝夹层结构及焊接构件检测中的应用。建立了二维热传导有限差分模型,采用该模型计算了强度按正弦规律变化的热流引起试件表面温度变化的历程,基于锁相法提取了有缺陷与无缺陷处的准稳态温度变化,并计算了二者的相位差。然后,建立了热波在试件中传导的热-电等效模型,利用该模型对红外锁相法热波检测技术进行了仿真研究,得到了缺陷深度和反射热波与入射热波相位差之间的关系。最后,采用红外锁相法热波检测技术对模拟缺陷的蜂窝夹层结构试件和实际焊接构件进行了无损检测试验。结果显示,有限差分模型和热-电等效模型计算有缺陷与无缺陷处的相位差与试验结果基本一致,偏差<5%,表明采用红外锁相法热波检测技术能够快速、准确地获得缺陷大小、位置等,该技术也适用于有复杂曲面结构的构件。

The principle of a lock-in thermography for non-destructive tests was researched and the evaluation,defect depth measurement and its application to the detection of honeycomb structure materials and welding bearings were introduced.A Finite Difference Model（FDM）of 2D heat conduction was established and it then was used to compute the temperature variety process on the surface of samples under the condition of sine law modulated heat flux.The lock-in processing method was applied to extract the quasi-steady state temperature variety of the defect and non-defect regions and the phase differences between them was computed.Furthermore,a thermal-electronic equivalence modeling was established by analog to the fundamental laws of heat and electricity,and it was used to simulate the lock-in thermography.The relation between defect depth and phase difference of both incident and reflected thermal waves was obtained.Finally,non-destructive tests were carried out on a honeycomb structure sample with simulated defects and a real welding bearing by the lock-in thermography.Experimental results indicate that the phase deference between defect and non-defect regions obtained by the finite difference model and thermal-electrical equivalence modeling is close to the experimental result,and the bias error is less than 5% as well.The lock-in thermography can rapidly and exactly detect defect sizes and positions,and can be also used in the measurement for the curve surface of a structure.