Study on pulsed phase analysis of depth measurement for infrared thermal wave nondestructive evaluation

Pulsed infrared thermal wave nondestructive evaluation has been widely used in various materials' R&D, quality supervise, detection and evaluation. Furthermore, based on pulse infrared thermal wave thermography experiment, a new signal analyze method called pulse phase thermography was introduced by changing the temporal signal to frequency field through Fourier transform. The pulse signal consists of various frequencies information and different thermal wave frequency reaches corresponding depth in the material. According to the relation of thermal wave's frequency to conduction depth, pulse phase thermography method can detect the depth of defects. The intuitionistic thermograph result is the phase information of each pixel in frequency field, through that the defect's size, location can be well distinguished. In order to solve the depth detection, two standard flat bottom holes samples made of aluminum and steel were studied. By analyzing the experimental results, it showed the theoretical depth value and actual depth relations, which can provide an assistant way for subsurface defects detection of material and structure. In that case, given a standard sample with artificial defects, the products made of the same material can be well detected and evaluated. At the same time, corresponding to the pulse infrared thermal wave thermography, phase thermographs with the phase information have higher sensitivity to the defects, and do not influence with the ununiformity of the light heating.