基于对数坐标二阶微分峰值法的感应热成像内部缺陷识别研究

针对感应热成像检测中金属工件内部缺陷检测较为困难的问题，对常用的铁磁材料45#钢和非铁磁材料铝试件进行了研究。提取45#钢和铝试件上宽深比不同缺陷的降温曲线，对其进行归一化对数温度-对数时间拟合并求取二阶微分，利用二阶微分极小峰值时间作为特征量对缺陷深度进行定量。结果表明，对45#钢试件，缺陷宽深比大于等于2时，二阶微分极小峰值所对应的时间与缺陷深度平方呈线性关系，可以用来对缺陷深度进行定量；铝试件处理后降温曲线的二阶微分极小峰值时间不受缺陷深度变化影响，不能作为特征量定量缺陷深度。最后通过实验验证了仿真结果。

Subsurface defects recognition using thermography based on second order differential peak method of logarithmic coordinates

It is difficult to detect subsurface defects on the specimen using thermography. For this problem, different cracks on ferromagnetic 45# steel and non ferromagnetic material aluminum were studied. Cooling curve of different defects on both 45# steel and aluminum were extracted and normalized and then turned into the logarithmic temperature logarithmic time curves to obtain a second order differential curve by fitting, furthermore, the minimum peak time of the second order differential was used as the feature quantity to quantified the defect depth. Results show that, as for 45# steel,when the ratio of width to depth is equal to or larger than 2, the relationship between the time corresponding to the minimum peak of second order differential and the square of depth is linear,its possible to measure the depth of the crack. As for aluminum, the time is independent of the depth, and the depth cannot be measured. Finally, the simulation results were verified by experiment.