Abstract
Abstract. This paper presents research into a method of processing thermal images aimed at detecting and characterizing material defects, or non-uniformities, of the internal structure of materials. Active thermography was chosen as the NDT method. Hidden defects were revealed by analysing the temperature field of the tested material's front surface which was externally excited with heating lamps. Background removal and image segmentation were applied to the last thermogram in the sequence recorded at the end of the heating phase. The paper focuses on the quality of determining lateral dimensions of subsurface flaws in a polymethylmethacrylate slab with bottom holes drilled to imitate flaws. The following accuracy-affecting factors were taken into account: defect depth, emissivity of the inspected surface as an input, user-set parameter for the IR camera, type of filtering used to eliminate the effect of non-uniformity when heating the object surface with an external source, and global and local thresholding as a segmentation method used for defect detection and sizing.
Highlights
At present, materials such as composites and multi-layered or honeycomb structures have been used ever more widely due to good physical properties in relation to low weight
Objects are inspected for hidden structural defects by using some widely accepted NDT techniques, e.g. radiographic or ultrasound methods as well as active thermography
The following factors are taken into account: defect depth, emissivity ε of the inspected surface as an input, user-set parameter for the IR camera, filter B coefficient value, and the type of filtered contrast applied to process the image with FC or relative incremental filtered contrast (RIFC)
Summary
Materials such as composites and multi-layered or honeycomb structures have been used ever more widely due to good physical properties in relation to low weight. Their application in very demanding industry sectors, such as aerospace, naval or automotive industry, makes rigorous examination of all the parts necessary in both the production phase and later operation. Non-destructive testing relies on a great number of analytical techniques to evaluate the properties of a material, component, or system without inflicting damage. This characteristic becomes especially valuable when production lines cannot be stopped for testing. Objects are inspected for hidden structural defects by using some widely accepted NDT techniques, e.g. radiographic or ultrasound methods as well as active thermography
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