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, 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 non-destructive 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.
The analysis of innovative materials and processes stands at the frontier of a series of wide-ranging scientific problems and poses stimulating challenges from a scientific as well as technological point of view, by virtue of its connection with various industrial sectors, such as aerospace and aeronautics. In recent years, composite materials have found numerous applications due to their mechanical characteristics and properties, representing the evolution of materials science and technologies by fusing within them the best characteristics of multiple materials. The present work is focused on the characterization of composite materials, using non-destructive techniques (NDT), to check different kinds of defects eventually present for a quality control of the object under observation. Shearography and thermography are used as nondestructive methods. The former, is an optical interferometric method for the detection of surface or sub-surface defects, the latter is a diagnostic technique that, by measuring the infrared radiation emitted by a body, allows to determine its surface temperature and to understand the health status of the investigated object. The results of the shearography technique, including, are complementary to thermographic techniques and allow us to have a complete characterization of the object. Their use offers advantages related to visualization and testing of end products, as well as the noncontact nature, nondestructive and areal working principle, rapid response, high sensitivity, resolution, and accuracy.
Polymeric thin films represent an emerging industrial area driven by their enormous technological and commercial potential in interdisciplinary sectors such as chemistry, material science, engineering, and physics. The large selection in terms of materials/composites and the wide range of technological solutions that could be used for their fabrication could create confusion for the final user requiring a quantitative characterization of their properties. This analysis could be even more complex in the case of functionalized polymeric films such as the samples reported in this work. Here we present how thin polymer films can be wholly characterized by applying a multiplicity of optical methods. Films were realized by a special liquid one-step process. Moreover, such polymer films were functionalized here for the first time by mesoporous silica nanoparticles. The nanoparticles were added to a polymeric matrix. We show that a full characterization was achieved by employing three different microscope techniques, i.e., scanning electron microscope, digital holography (DH), and space-time DH. Exploiting such a multimodal methodology can be of great benefit for characterizing the functionalized polymeric thin films. In fact, multiple characterization in different conditions was possible. The results reported in terms of morphological information, thickness distribution, three-dimensional (3D) mapping, large field of view, high magnification, and super resolution of the zoomed area offer a good solution for testing materials and obtaining a quantitative characterization and whole inspection in the case of complex polymeric samples.
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