Fibre direction and stacking sequence measurement in carbon fibre composites using Radon transforms of ultrasonic data

Stacking sequence and, more generally, fibre orientation, are critical parameters in fibrous composite materials since they govern mechanical performance. This paper presents a method, based on the ultrasonic pulse-echo non-destructive technique, that can map the stacking sequence in unidirectional carbon-fibre composites. In-plane fibre orientation is measured using a Radon-transform method applied to local 2D images extracted from the 3D dataset formed from a 2D scan of pulse-echo responses. The ability to align these local 2D images to the plies in the region being assessed makes this technique suitable even in laminates where out-of-plane ply wrinkling is present. The Radon-transform method is shown to provide interpretable stacking-sequence maps, allowing ply lay-up sequence and both in-plane waviness and out-of-plane wrinkling to be visualised and quantified.