3D characterisation of fibre orientation and resulting material properties

Conformance of ply lay-up and local fibre orientation to design is critical in ensuring the performance of composite structures. It has been shown that even very small misalignments of fibres can cause a significant knock-down in strength and stiffness in the important stress directions. A new ultrasonic method has been developed for non-destructive mapping of both out-of-plane ply wrinkling and in-plane fibre waviness. The resultant 3D map of fibre orientation can form the basis of a 3D finite-element model to determine mechanical properties of the actual as-built structure and such a model is demonstrated here. This capability is important not only at manufacture but also in service for mapping material surrounding a defect in order to design a composite repair and then to confirm the integrity of the repair. In the military environment, information about the ply lay-up is not always available for assisting in the design of a repair. Ultrasonic determination of ply lay-up and the thicknesses of the plies will allow customised in-service repairs. Extensive validation work has been carried out on the technique which can be applied to full-waveform ultrasonic data captured in a variety of formats from either single-element or phased array acquisition systems. A programme has commenced to create 3D finite-element meshes and import this 3D fibreorientation information into the cells to determine the stiffness axes. The capabilities, limitations and current status of the technique are presented here.