The emergence and propagation of solitary waves is investigated for carbon fibre reinforced polymer using numerical simulations for Non-Destructive Testing (NDT) purposes. The simulations are done with the Chebyshev collocation method. The simplest laminate model is used for the periodical structure of the material from which dispersion will arise. Classical and nonclassical nonlinearities are introduced in the constitutive equation. The balance of the dispersion and nonlinearity is analysed by studying the shape-changing effects of the medium on the initial input pulse and the possibility of solitary wave propagation is considered. Future applications of solitary waves for nonlinear medical imaging and NDT of materials are discussed.

Guided wave tomography is an effective non-destructive method for mapping corrosion damage in thin-walled metal structures. Its efficiency and accuracy depend on the choice of a suitable forward model and inversion method. Current techniques mainly use acoustic forward models that, while computationally efficient, are approximate and fail to accurately represent wave propagation in physical experiments, making them less suitable for inversion. This study investigates the performance of Mindlin plate theory, which accounts for through-thickness shear deformations, enabling the modeling of flexural modes in a two-dimensional (2-D) plane. The scattering of $A_0$ mode Lamb waves from defects of varying depth, width, and shape is analyzed using finite difference and pseudospectral simulations for 2-D and three-dimensional (3-D) defects, respectively. Results from the Mindlin model are compared to finite element model simulations. It is found that Mindlin plate theory accurately represents smooth defect scattering, but is less accurate for sharp-edged defects.

A finite element method simulation of a carbon fibre reinforced polymer block is used to analyse the nonlinearities arising from a contacting delamination gap inside the material. The ultrasonic signal is amplified and nonlinearities are analysed by delayed Time Reversal -- Nonlinear Elastic Wave Spectroscopy signal processing method. This signal processing method allows to focus the wave energy onto the receiving transducer and to modify the focused wave shape, allowing to use several different methods, including pulse inversion, for detecting the nonlinear signature of the damage. It is found that the small crack with contacting acoustic nonlinearity produces a noticeable nonlinear signature when using pulse inversion signal processing, and even higher signature with delayed time reversal, without requiring any baseline information from an undamaged medium.

Various nonlinear methods have been investigated in recent years offering improvements of over conventional B-mode in medical imaging and non-destructive testing (NDT) [1]. The most common include harmonic and overtone generation, inter-modulation product generation and resonant frequency shift, also known as Nonlinear Elastic Wave Spectroscopy (NEWS) methods. Furthermore, new optimized excitations such as Nonlinear Time Reversal (TR) based methods are needed and, thanks to the analysis of symmetry properties of cross-correlation generated functions, a wide range of innovation are classified within TR-NEWS methods [2]. This work proposes to unite the frequency-modulated constant-wave scatterer localization with TR-NEWS principles to enable the localization of scatterers distant from the transducers and the analysis of their nonclassical nonlinearity which often can be caused by microdamage or cracking. In this paper, using the found frequency of the defect, the delayed TR–NEWS can be leveraged to periodically excite the damaged region with the focused ultrasound. Resonance excitation results show potential for enhancing the wave motion more than a simple focused waves [3]. Thanks to the complexity of the acoustical propagation in a complex medium, the physical interpretation of the cross-correlation function used during the TR-NEWS analysis can be easily understood in terms of the acoustic energy focused in space and in time.