Nondestructive inspection of aerospace composite laminate using thermal image processing
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Nondestructive inspection of aerospace composite laminate using thermal image processing K. Sreeshan1,4 · R. Dinesh2 · K. Renji3 Received: 12 December 2019 / Accepted: 1 October 2020 © Springer Nature Switzerland AG 2020
Abstract In this work, a novel image segmentation method in thermographic images using the computer vision algorithm, active contours, is presented. These studies were done on thermal images obtained from pulse thermography. Many aerospace components are made of composite laminates. De-bonds/de-laminations set in during the manufacturing or in-service stages of these materials. Identification of de-bonds in composite laminates is a difficult task and faces many challenges when it is done through the processing of thermographic images. The first challenge is to get an accurate seed point to be used in active contours. In this study, the seed points for active contours were obtained from the moving averages of the pixel values taken along the region of interest lines. It is shown that the active contours with the help of seed points identified through this method are able to distinguish the de-bonds. The experimental results, supported by segmentation metrics, suggest that the segmentation method used here outperforms some earlier results which were based on the combination of Gabor filters, watershed models and divide-and-conquer methods such as subdivision of images. Keywords Active contours · Feature extraction · Noise removal · ROIL · Thermal imaging
1 Introduction Aerospace structures use materials that are lightweight but possess high strength and stiffness. Composite materials are the ones used to satisfy the above requirements. The composites are made out of different materials having different physical properties, but in combination give the required properties. The composite laminates consist of various layers made of different materials stacked at different angles. Glass fiber-reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP) are some of the commonly used materials used in aerospace structures. The main drawback of structures made of such materials is the presence of inbuilt defects caused during their manufacturing and also during in-service operations [1]. De-lamination or de-bonding is the more frequently seen
defect, in which some layers of the laminate get displaced from the others. Detecting these defects and undertaking corrective measures is very essential while using composites. Visual inspection alone is not of much help in identifying them due to the fact that the defects can occur in between the layers. Therefore, scientific techniques, that do not cause damage to the material, are needed to identify them. Nondestructive testing (NDT) is a testing and analysis technique to evaluate the properties of a material, component, structure or system for characteristic discontinuities or differences without causing any damage to the original material or part. These methods are based on the use of signals in different domains like X-rays, eddy currents, shearogra
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