Enhanced infrared sparse pattern extraction and usage for impact evaluation of basalt-carbon hybrid composites by pulsed thermography

Nowadays, infrared thermography, as a widely used non-destructive testing method, is increasingly studied for impact evaluation of composite structures. Sparse pattern extraction is attracting increasing attention as an advanced post-processing method. In this paper, an enhanced sparse pattern extraction framework is presented for thermographic sequence processing and defect detection. This framework adapts cropping operator and typical component extraction as a preprocessing step to reduce the dimensions of raw data and applies sparse pattern extraction algorithms to enhance the contrast on the defect area. Different cases are studied involving several defects in four basalt-carbon hybrid fiber-reinforced polymer composite laminates. Finally, comparative analysis with intensity distribution is carried out to verify the effectiveness of contrast enhancement using this framework

Real-time thermography system for composite welding:Undamaged baseline approach

The aerospace industry's current focus on recyclable materials and low-cost processes has accelerated research and implementation of thermoplastics matrix composites (TPC). In the last decades, researchers have researched weldability of these materials as a valid alternative to conventional mechanical fastening and adhesives, for improving the strength of the joint. Automatic induction welding of carbon fiber TPCs is one of the most promising techniques due to its numerous benefits, such as elevated energy efficiency and highly localised heat. As for all the manufacturing techniques, the importance of efficiently detecting the presence of defects during TPCs welding has pushed the need for automated real-time non-destructive evaluation (NDE) systems. This paper focuses on the development of an efficient NDE technique able to detect the presence of alterations and defects in real-time during the welding process. This technique relies on Infrared (IR) active thermography inspections performed using the induction welding heat as the source and an undamaged baseline methodology to detect differences in the heat field. The procedure was experimentally analysed by means of an apparatus capable of automatic welding of samples, performing the real-time NDE during the process. Results show the efficiency of the method to localise the damaged area and characterise the defects during the welding. The undamaged baseline methodology was proven to better clarify shape and location of defects, allowing for an efficient detection of damaged samples and areas where more detailed inspections can be performed after the welding process by means of the same IR apparatus.</p

Defect Detection in Delaminated Glass-Fibre/Epoxy Composite Plates Using Local Defect Resonance Based Vibro-Thermography Technique

In the present scenario, composites are widely used for various applications in the field of aerospace, automobile, marine, sports, construction and electrical industries. The need of damage inspection for these composite structures has been of great importance. Complicated defects like delaminations present in the composite laminates can be detected effectively using nonlinear acoustic wave spectroscopy (NAWS). One of the NAWS techniques of detecting the delamination is based on intensification of vibration amplitudes at the delamination location, known as local defect resonance (LDR) technique. In this chapter, a numerical investigation for detecting delamination in glass fibre reinforced polymer (GFRP) composite based on vibrothermography technique will be discussed. A single periodic LDR frequency excitation is used to excite the GFRP plate, resulting in a local temperature rise at delamination region due to frictional heating at the damage interface. An explicit dynamic temperature displacement analysis will be carried out for a specific time period of LDR excitation. Subsequently, a heat transfer analysis will be performed to observe the temperature difference at top surface of the delaminated GFRP plate. Thus a numerical investigation will be carried out based on LDR excitation for high contrast imaging of delamination in composite materials using vibro-thermography

Non-Destructive Techniques for the Condition and Structural Health Monitoring of Wind Turbines: A Literature Review of the Last 20 Years

A complete surveillance strategy for wind turbines requires both the condition monitoring (CM) of their mechanical components and the structural health monitoring (SHM) of their load-bearing structural elements (foundations, tower, and blades). Therefore, it spans both the civil and mechanical engineering fields. Several traditional and advanced non-destructive techniques (NDTs) have been proposed for both areas of application throughout the last years. These include visual inspection (VI), acoustic emissions (AEs), ultrasonic testing (UT), infrared thermography (IRT), radiographic testing (RT), electromagnetic testing (ET), oil monitoring, and many other methods. These NDTs can be performed by human personnel, robots, or unmanned aerial vehicles (UAVs); they can also be applied both for isolated wind turbines or systematically for whole onshore or offshore wind farms. These non-destructive approaches have been extensively reviewed here; more than 300 scientific articles, technical reports, and other documents are included in this review, encompassing all the main aspects of these survey strategies. Particular attention was dedicated to the latest developments in the last two decades (2000–2021). Highly influential research works, which received major attention from the scientific community, are highlighted and commented upon. Furthermore, for each strategy, a selection of relevant applications is reported by way of example, including newer and less developed strategies as well

Modal-based vibrothermography using feature extraction with application to composite materials

This research focuses on the development of a damage detection algorithm based on modal testing, vibrothermography, and feature extraction. The theoretical development of mathematical models is presented to illustrate the principles supporting the associated algorithms, through which the importance of the three components contributing to this approach is demonstrated. Experimental tests and analytical simulations have been performed in laboratory conditions to show that the proposed damage detection algorithm is able to detect, locate, and extract the features generated due to the presence of sub-surface damage in aerospace grade composite materials captured by an infrared camera. Through tests and analyses, the reliability and repeatability of this damage detection algorithm are verified. In the concluding observations of this article, suggestions are proposed for this algorithm’s practical applications in an operational environment

Enhanced composite plate impact damage detection and characterisation using X-Ray refraction and scattering contrast combined with ultrasonic imaging

Ultrasonic imaging and radiography are widely used in the aerospace industry for non-destructive evaluation of damage in fibre-reinforced composites. Novel phase-based X-ray imaging methods use phase effects occurring in inhomogeneous specimens to extract additional information and achieve improved contrast. Edge Illumination employs a coded aperture system to extract refraction and scattering driven signals in addition to conventional absorption. Comparison with ultrasonic immersion C-scan imaging and with a commercial X-ray CT system for impact damage analysis in a small cross-ply carbon fibre-reinforced plate sample was performed to evaluate the potential of this new technique. The retrieved refraction and scattering signals provide complementary information, revealing previously unavailable insight on the damage extent and scale, not observed in the conventional X-ray absorption and ultrasonic imaging, allowing improved damage characterisation

Non-destructive testing for carbon-fiber-reinforced plastic (CFRP) using a novel eddy current probe

Abstract(#br)Carbon-fiber-reinforced plastic (CFRP) is of low conductivity and has a layered structure. High-frequency transmitter-receiver (T-R) probes are widely chosen to inspect CFRPs using eddy current testing (ECT). However, in these works, the variation in the distance between the probe and test sample can cause a larger signal than that caused by defects and may cover up the defect. The detection sensitivity was also reduced by random noise resulting from lift-off change. To address these issues, it is meaningful to design a probe which can overcome the effect of lift-off variation and meanwhile offer high sensitivity to defects in CFRPs. In this study, a T-R probe with a special structure for detection of CFRPs was developed. The probe contains an 8-shaped transmitter coil (TX coil) and a circular receiver coil (RX coil), which is placed on a line equidistant from the two parts of the transmitter coil. Theoretically, regardless of how the lift-off changes, the output signal is always 0 if the azimuth of the probe agrees with one of the fiber orientations of an intact CFRP. Experimental studies demonstrate that the proposed probe is insensitive to lift-off compared with a traditional T-R probe and offers high sensitivity to defects. For defect detection, in-plane waviness can be detected with the proposed probe. Quantitative experiments for crack detection were performed. The cracks were clearly visualized in the scanning images. The length and location of the cracks can also be estimated from the scanning images