Abstract
Barely visible impact damage (BVID) is one of the most dangerous types of structural damage in composites, since in most practical cases the application of advanced non-destructive testing (NDT) methods is required to detect and identify it. Due to its character of propagation, there are minor signs of structural damage on a surface, while the internal damage can be broad and complex both in the point of view of fracture mechanisms and resulting geometry of damage. The most common NDT method applied e.g., in aircraft inspections is ultrasonic testing (UT), which enables effective damage detection and localization in various environments. However, the results of such inspections are usually misestimated with respect to the true damage extent, and the quantitative analysis is biased by an error. In order to determine the estimation error a comparative analysis was performed on NDT results obtained for artificially damaged carbon fiber-reinforced composite structures using two UT methods and X-ray computed tomography (CT). The latter method was considered here as the reference one, since it gives the best spatial resolution and estimation accuracy of internal damage among the available NDT methods. Fusing the NDT results for a set of pre-damaged composite structures with various energy values of impact and various types of impactor tips applied for introducing damage, the evaluation of estimation accuracy of UT was possible. The performed analysis allowed for evaluation of relations between UT and X-ray CT NDT results and for proposal of a correcting factor for UT results for BVID in the analyzed composite structures.
Highlights
Composite structures are characterized by high resistance to loads oriented along fiber direction.Unlike metals, composites allow easier forming of non-ruled surfaces with large sizes
It can be noticed that some parts of damage near the bottom surface of the specimens were not detected using ultrasonic testing (UT) methods, which is due to a reduction of heights of echoes from these damage regions resulting from the distance traveled by the ultrasonic wave as well as resulting from a reflection of the most part of this wave from delaminations located above
The authors presented the results of fusion of non-destructive testing results of carbon fiber-reinforced polymeric (CFRP) structures with Barely visible impact damage (BVID) using two modes of UT, B- and C Scans, as well as X-ray computed tomography (CT) used here as the reference method
Summary
Composite structures are characterized by high resistance to loads oriented along fiber direction. The authors of [26] fused the results of two other NDT methods: IRT and shearography, which significantly reduced the measurement error and improved quantification ability of impact damage in tested carbon fiber-reinforced polymeric (CFRP) structures In this approach, the authors used UT in a C-Scan mode for validation purposes. Several applications of fusion of results of various NDT methods are presented in literature, this approach in structural inspection remain open for new solutions and has a great potential in the enhancement of ability of damage detection and quantification This motivated the authors of the following study to apply such a concept in the evaluation of accuracy of estimation of damage extent in composite structures with BVID. The presented approach is useful especially in correcting the damage extent in the considered specimens obtained directly from UT, and further evaluation of a structural residual life, including its prediction for structures being in operation as well as modeling the structural life in CFRP structures subjected to BVID
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