Classification of Cracks in Composite Structures Subjected to Low-Velocity Impact Using Distribution-Based Segmentation and Wavelet Analysis of X-ray Tomograms.

Angelika Wronkowicz-Katunin,Jernej Klemenc,Andrzej Katunin,Marko Nagode

doi:10.3390/s21248342

Angelika Wronkowicz-Katunin, Jernej Klemenc + Show 2 more

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The problem of characterizing the structural residual life is one of the most challenging issues of the damage tolerance concept currently applied in modern aviation. Considering the complexity of the internal architecture of composite structures widely applied for aircraft components nowadays, as well as the additional complexity related to the appearance of barely visible impact damage, prediction of the structural residual life is a demanding task. In this paper, the authors proposed a method based on detection of structural damage after low-velocity impact loading and its classification with respect to types of acting stress on constituents of composite structures using the developed processing algorithm based on segmentation of 3D X-ray computed tomograms using the rebmix package, real-oriented dual-tree wavelet transform and supporting image processing procedures. The presented algorithm allowed for accurate distinguishing of defined types of damage from X-ray computed tomograms with strong robustness to noise and measurement artifacts. The processing was performed on experimental data obtained from X-ray computed tomography of a composite structure with barely visible impact damage, which allowed better understanding of fracture mechanisms in such conditions. The gained knowledge will allow for a more accurate simulation of structural damage in composite structures, which will provide higher accuracy in predicting structural residual life.

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Carbon fiber reinforced polymer (CFRP) composites, which are increasingly widespread in numerous industrial branches, found their primary applications in aircraft and aerospace vehicles due to their excellent strength-to-mass ratio, resistance to corrosion and numerous chemical agents, flexible forming and manufacturing capabilities, etc
The most dangerous type of impact damage from an operational point of view is the so-called barely visible impact damage (BVID), which appears at low-velocity impact (LVI) loading and results in extended internal damage that is often not recognizable on a surface
Having defined three possible orientations in the tested composite structure, it is essential to select a tool which allows distinguishing cracks of these orientations. This step of the algorithm was based on the 2D real oriented dual-tree wavelet transform (DTWT), which reveals appropriate directional selectivity together with the low noise level during decomposition

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Carbon fiber reinforced polymer (CFRP) composites, which are increasingly widespread in numerous industrial branches, found their primary applications in aircraft and aerospace vehicles due to their excellent strength-to-mass ratio, resistance to corrosion and numerous chemical agents, flexible forming and manufacturing capabilities, etc Despite their numerous advantages, one of the main problems of these materials during operation is their susceptibility to impact loading (see e.g., [1,2,3]). The most dangerous type of impact damage from an operational point of view is the so-called barely visible impact damage (BVID), which appears at low-velocity impact (LVI) loading and results in extended internal damage that is often not recognizable on a surface. Cracks and delaminations resulting from LVI can cause significant reductions in numerous properties of the material, mainly compressive strength and resistance to buckling [5,6], which are the key parameters of composite structures in aviation

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