Composite structures widely used in advanced sectors as in the automotive and aeronautical fields, during their useful life are usually subject to dynamic events responsible for apparently invisible failures which, over time, extend and severely compromise their performance. In this regard, a huge amount of experimental results, also validated by theoretical considerations, is available on the behaviour to damage caused by low velocity impacts (LVI) on laminate systems in polymeric composite and on their residual strength. However, until now the research interest has been mainly focused on thin composite laminates (less than 4 mm) and only very few experimental works are available concerning thick laminates (thickness higher than 4 mm) generally used in the skin of airplane wings, stringers, highly loaded components. This study aims to investigate simulated defects in carbon fiber reinforced polymers (CFRP) and of the damage deriving from LVI events, particularly peculiar to structures with higher bending stiffness such as thick ones and, therefore, to fill the current knowledge gap for a more appropriate use of the latter. To this end, thick carbon epoxy resin composite laminates, kindly supplied by Leonardo SpA and impacted at the Department of Industrial Engineering of the University of Naples Federico II, will be systematically investigated with well-established skills on infrared thermography, air coupled ultrasonic tests and shearography at the Institute of Applied Science and Intelligent Systems of the National Research Council. The combined results for both panels with simulated defects and impacted panels provided an accurate description of the different defects present in the thick panels involved in their damage process.

Composite honeycomb sandwich samples are commonly used because they offer a high strength-to-weight ratio, making them ideal for lightweight and durable structures. However, ensuring their structural integrity is essential for safety and performance. Multimodal NDT (Non-Destructive Testing) inspection and characterization of composite honeycomb sandwich samples is a critical process in various industries, including aerospace, automotive, and civil engineering. The use of NDT techniques makes it possible to verify the quality of the composite material and identify any defects. In this context, we provide a comparison of several techniques as nondestructive methods on a sample of interest to the aerospace industry and evaluates the parameters of their use: shearography, infrared thermography and laser ultrasonic. Using nondestructive testing techniques, it is possible to check the quality of composite materials and identify any programmed flaws. These techniques allow for frequent inspections without compromising the integrity of the material. This helps ensure the safety and reliability of products using composite materials. From the preliminary results it is evident that the combined use of the described non-destructive testing (NDT) techniques can significantly improve the reliability and accuracy of the quality control process for a wide variety of materials and defects.

Manufacturing processes in the aerospace context, although strictly supervised and inspected, can sometimes create internal defects in the final components. This paper presents a wavelet-based method for the non-destructive detection of these unwanted defects. By opportunely inspecting the components using laser ultrasonic technology, it is possible to detect defective parts. The wavelet analysis allows us to extract significant and distinctive features (signatures) from the ultrasonic data. As the computed signatures of defective areas differ from the non-defective ones, it is possible to discern these areas effectively. Different machine learning methods for comparing signatures are proposed. High detection accuracies (>97%) have been achieved by investigating one specimen with six different defects. The obtained results allow us to affirm that the proposed approach looks promising and suitable for this purpose, and thus needs further investigations.

Non destructive inspection (NDI) is a widely used method for quality control and materials inspection across various industries, especially in the aerospace field where the introduction of composite materials has revolutionized inspection techniques. In addition, in-service ultrasonic inspection (UT) is also used for preventive maintenance purposes. One of the biggest challenges of such techniques is the need to use a coupling medium, which can often be a critical issue. For this reason, considerable effort has been made in the aerospace field in recent years to employ innovative techniques that do not require the use of coupling media. One of the proposed techniques is Laser Ultrasonic Non-Destructive Testing (LUNDT), which is recognized as a promising method due to its rapid scanning speed, non-contact inspection, coupling-agent independence, and ability to inspect complex shapes. Today, the primary focus is not on generating ultrasound in the material, but rather on how to receive and interpret it. In recent years, several companies have attempted to provide their own solutions in this field. In this study, the utilized solution is based on an all-optical akinetic sensor, which has demonstrated the most promising results. With this technology, we performed a series of analyses on aerospace components of interest, including those made of composite and metallic materials.

This article highlights the importance of continuous flights and sustainable maintenance techniques to maintain competitiveness in the aviation industry. Structural components represent a significant portion of overall maintenance costs, and advanced nondestructive inspection techniques can help reduce maintenance time and associated costs. With the increasing use of composite structures in aircraft, it is essential to understand the possible types of defects that can occur and to use techniques the appropriate nondestructive techniques (NDT) for their identification and characterization. Comprehensive knowledge of possible defects and proper application of NDT techniques can help simplify maintenance operations and ensure sustainable and safe aircraft operations. The use of NDT techniques makes it possible to verify the quality of the composite material and identify any defects. This allows timely action to correct any problems and ensure maximum reliability and durability of the material. In this context, this paper provides a comparison of several techniques as nondestructive methods on a sample of interest to the aerospace industry and evaluates the parameters of their use: shearography, thermography and ultrasound.