Damage detection and classification in composite structure after water-jet cutting using computed tomography and wavelet analysis

The proposed method of processing of X-ray Computed Tomography (CT) data is based on its three-dimensional (3D) wavelet analysis, which allows for detection and localization of sudden changes in voxels of CT data array. The applied wavelet transform can be considered as filtering using sets of low-pass and high-pass filters over directions of a domain. The internal damage, which initially has different spectrum than the healthy regions of a structure, are emphasized after the wavelet analysis and depending on its intensity in the CT data array the wavelet coefficients become different for them. The tests were performed on the carbon fibre reinforced composite plate. The water-jet method was used for cutting of a circular hole inside. During the cutting process several delaminations in various layers occurred. Moreover, during the manufacturing process several air pockets in the matrix appeared. Application of the proposed processing algorithm allows not only for detection and localization of internal damage but also its classification by a type. It is possible due to analysing the magnitude of wavelet coefficients after wavelet-based decomposition and characteristic shape and dimensions of various types of damage. This allows for automation of the examination process.