Detection and Characterization of Artificial Porosity and Impact Damage in Aerospace Carbon Fiber Composites by Pulsed and Line Scan Thermography

Nondestructive testing (NDT) of composite materials is of paramount importance to the aerospace industry. Several NDT methods have been adopted for the inspection of components during production and all through the aircraft service life, with infrared thermography (IRT) techniques, such as line scan thermography (LST) and pulsed thermography (PT), gaining popularity thanks to their rapidity and versatility. On one hand, LST is an attractive solution for the fast inspection of large and complex geometry composite parts during production. On the other hand, PT can be employed for the characterization of composite materials, e.g., the determination of thermal diffusivity and defect depth estimation. In this study, the use of LST with an uncooled microbolometer camera is explored for the identification of artificially produced porosity and barely visible impact damage (BVID) on academic samples. The performance of LST is quantitatively assessed with respect to PT (considered the gold standard in this case) using a high-definition cooled camera through the contrast-to-noise ratio (CNR) criterium. It is concluded that, although in most cases the measured CNR values were higher for PT than for LST (as expected since a high-definition camera and longer acquisition times were used), the majority of the defects were clearly detected (CNR >= 2.5) by LST without the need of advanced signal processing, proving the suitability of LST for the inspection of aerospace composite components. Furthermore, the deepest defect investigated herein (z approximate to 3 mm) was detected solely by LST combined with signal processing and spatial filtering (CNR = 3.6) and not by PT (since pulse heating was not long enough for this depth). In addition, PT was used for the determination of the thermal diffusivity of all samples and the subsequent depth estimation of porosity and damaged areas by pulsed phase thermography (PPT).

Automated summary

Nondestructive testing (NDT) is crucial in the aerospace industry, and infrared thermography (IRT) techniques such as line scan thermography (LST) and pulsed thermography (PT) are popular due to their speed and versatility. LST is suitable for quickly inspecting large and complex composite parts during production, while PT is used for characterizing composite materials. Results show that although PT generally had higher contrast-to-noise ratio (CNR) values than LST, the majority of defects were clearly detected by LST without advanced signal processing, proving its suitability for inspecting aerospace composite components. Furthermore, PT was used to determine thermal diffusivity and estimate the depth of porosity and damaged areas.