Abstract
In this work, enhanced thermal data processing is developed with experimental procedures, improving visualization algorithm for sub-surface defect detection on industrial composites. These materials are prone to successful infrared nondestructive investigation analyses, since defects are easily characterized by temperature response under thermal pulses with reliable results. Better defect characterization is achieved analyzing data with refined processing and experimental procedures, providing detailed contrasts maps where defects are better distinguished. Thermal data are analyzed for different CFRP specimens with artificial defects and experimental procedures are verified on real structural aeronautical component with internal anomalies due to impact simulation. A better computation method is found to be useful for simultaneous defect detection by means of automatic mapping of absolute contrast, optimized to identify defect boundaries.
Highlights
Internal defects are the major sources of composite failures in FRP structures and originate from manufacturing and/or from in-service events
In active IRT methods, an external stimulus is applied to specimen surface, in order to induce relevant thermal contrasts between regions of interest and these techniques include pulsed thermography (PT) as valid robust technique for checking the integrity of structures [2,3] and consists of rapidly heating the specimen recording the temperature decay curve; the free-defect material conducts heat more efficiently than defective zones, where heat is either absorbed, or reflected, indicating the quality state of the inspected area [4]
For defect presence and size evaluation, a whole C-scan mapping of the damaged area is conducted in the functional direction along the simulated impact, where in Figure 17 are clearly highlighted the delamination distribution and their boundaries
Summary
Internal defects are the major sources of composite failures in FRP structures and originate from manufacturing (delamination, voids, porosity, fiber wrinkles, etc.) and/or from in-service events (impact or fatigue damage, micro-cracks, debonding, delamination, erosion, etc.). In active IRT methods, an external stimulus is applied to specimen surface, in order to induce relevant thermal contrasts between regions of interest and these techniques include pulsed thermography (PT) as valid robust technique for checking the integrity of structures [2,3] and consists of rapidly heating the specimen recording the temperature decay curve; the free-defect material conducts heat more efficiently than defective zones, where heat is either absorbed, or reflected, indicating the quality state of the inspected area [4]. The CDT method represents an interesting and valid ND approach where a previous thermal excitation in an oven allows a uniform temperature through thickness and could be applied on CFRP plates, especially in the case of deeper defects
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