基于脉冲涡流热成像的下表面缺陷评估

摘要

The skin depth of metal materials is very small under high-frequency eddy current incentives,so it can be regarded as surface heating.As it is difficult to capture subsurface defects of the specimen,a longitudinal heat conduction method based on pulsed eddy current thermography was proposed to identify the subsurface defect.Meanwhile,the subsurface defects were quantitatively studied according to the change of curve slope.For ferromagnetic materials and non-ferromagnetic materials,their subsurface defects were studied by the finite element simulation and experiments.Results show that longitudinal heat conduction is greater than lateral heat conduction when length-width ratio of the defect is greater than 2,and the obvious temperature difference on the surface is formed to realize the detection of subsurface defects.According to time points corresponding to linear and nonlinear changes of temperature response curve slope,the relationship between the defect depths is quantitatively analyzed.%针对目前金属材料在高频涡流的激励下,趋肤深度十分小,可视为表面加热,试件下表面缺陷难以被捕捉的现象,提出了基于脉冲涡流热成像纵向热传导的方法来对其下表面缺陷进行识别,同时根据曲线斜率变化来对下表面缺陷进行量化研究.针对铁磁性、非铁磁性材料,通过有限元仿真以及实验验证的方法进行研究.结果表明:当缺陷处横向宽度与剩余厚度之比大于2时,热传导的纵向传导效应会大于横向传导效应,在材料表面形成明显的温度差,从而实现下表面缺陷的检测,并根据温度响应曲线斜率的线性变化与非线性变化所对应的时间点来定量分析缺陷深度之间的关系.