Development of ultrasound inversion methods for characterising features in 3D woven composite materials

There is an increasing interest in the use of 3D woven composites in applications that require improved strength-to-weight ratios. In addition, the use of these structures helps to reduce CO2 emissions. Woven composites offer many benefits including many possible architectures with high ratios of strain to failure. Woven composites are structures made by interlacing some continuous fibres (known as wefts) in one direction and other continuous fibres (known as warps) in a perpendicular direction. In the case of 3D woven composites, the third direction is reinforced by other continuous fibres known as binder. This study deals with the development of ultrasound inversion methods to characterize features in 3D woven composite materials. The study focuses on orthogonal weave-type only. Both theoretical (simulated) and measured data are analysed and used to calculate features such as the warps, wefts, and binder locations. The analytical-signal response, including the definition of three instantaneous parameters, is analysed and their capabilities to calculate the warp, weft and binder locations are demonstrated. These instantaneous parameters are the instantaneous amplitude, phase and frequency. The simulated data is obtained from a 3D time domain Finite Element model whereas the measured data is acquired from scanning a built specimen using an ultrasound immersion tank. The inversion techniques developed in this study can be extended to other 3D woven weave-types.