Non stationary Infrared Imaging for Non destructive Characterization

Abstract

Infrared non-destructive testing (IRNDT) involves mapping the surface temperature over a test object with the intent of detecting surface and subsurface defects. It is a whole field, non-contact and a nondestructive testing method for defect detection. Since most solids conduct heat, IRNDT has potential for wide use in defect detection in a variety of materials such as metals, composites and semiconductors [1]. IRNDT has numerous applications in aeronautical, space, electrical, electronic and mechanical industries. Of the various possibilities for thermal non destructive testing (TNDT) implementation, IRNDT has gained wide acceptance in non-destructive testing and evaluation (NDT & E). Various methods and techniques have further been developed throughout the world to improve and widen the use of IRT for nondestructive characterization. IRNDT can be carried out either in active mode or in passive mode. Passive thermography involves mapping the temperature profile of a sample surface in the absence of any external heat stimulus. This approach may not provide sufficient temperature contrast over the defect and non-defective regions of the test specimen, especially for defects lying deep inside. In order to reveal these deep defects with a high contrast, active thermography is used. This requires an external thermal stimulus to the inspected specimen in order to obtain significant temperature differences, witnessing the presence of subsurface defects. In active approach, external heat stimulus on to the test sample is provided, whose thermal response is observed. As the characteristics of the external thermal stimulation applied onto the specimen are known (i.e. nature of excitation, its time duration and its band width etc), for a possible qualitative and quantitative characterization of sub-surface defects.