Use of 3D ultrasound data sets to map the localised properties of fibre-reinforced composites

This thesis documents a programme of work undertaken from mid-2005 to mid-2009 as a part-time PhD, investigating the application of signal-processing methods to ultrasonic non-destructive evaluation (NDE) data from fibre-reinforced composite materials. The aims of the project were: •to push the boundaries of defect detectability by applying knowledge-based filtering methods to remove the response of the structure; •to produce 3D profile maps of various measured parameters to assist in differentiating between defects and structural effects; •to present the NDE information in terms of actual material properties that can be easily interpreted. These aims are linked to specific NDE problems in inhomogeneous materials: •3D characterisation of the material properties and defects in composite materials such as carbon-fibre reinforced plastic (CFRP); •3D mapping of ply wrinkling and fibre orientation in CFRP and glass-fibre reinforced plastic (GFRP). By developing and using a model, it was possible to understand the ultrasonic response of multi-layered structures when the layers themselves comprise both fibres and matrix. Various defects were inserted into the model to determine which parameters from the ultrasonic response would provide good distinction between defect types and enable quantitative 3D profiling of the required material properties. A toolset of signal-processing and image-processing algorithms was used to apply the methods to both simulated and real ultrasonic data from the above NDE problems in order to demonstrate the benefits of the new methods. At various stages through the project a validation process was undertaken to evaluate the methods for use on real composite aerostructures.