Study On The Detectivity Of The Pulsed Infrared Thermograph

Infrared thermography as a wide-area, rapid, and noncontact nondestructive testing (NDT) method has been widely recognized for many years. It is based on the thermal wave theory, using different heat source to heat the detected samples, Pulsed Infrared Thermography has emerged as the most widely used form of the technique, through the measurement of the surface temperature, the inside information of the sample can be obtained. However, the detectivity of the Pulsed Infrared Thermography has its limitations, fundamental detectivity of a flaw will depend on its size, depth and the distance between two adjacent flaws. In this paper, the theoretical analysis of detectivity of infrared pulsed thermography and criteria to assess the detectivity are discussed, as well as the theoretical testing limit is given for the Pulsed Infrared Thermography, two related experiments are done, one sample is the aluminum plate with back-drilled rectangle flumes, having six flumes in the same size but different depths, the sample is used as the detectivity reference sample, which is used to analysis the relationship between detectivity of the pulsed infrared system and the characters of a flaw. Meanwhile, a second sample is the Sandwiched structures which are composed by a honeycomb core between two multi-layer carbon fiber reinforced plastic (CFRP) facesheets, the structure is widely used in aerospace nowadays, it has flaws in different sizes, depths and distances between two flaws, the second sample is used to study the influence factors of the detectivity of the Pulsed Infrared Thermography. For the CFRP sample, the detectable size, depth, and distances between the flaws are given as a result. From the two different experiments, detectivity of the Infrared Pulsed Thermograhy has been studied.