The anisotropic propagation of ultrasonic guided waves in composite materials and implications for practical applications.

Ultrasonic guided wave propagation in anisotropic attenuative materials like CFRP (carbon fibre reinforced polymer) is much more complicated than in isotropic materials. Propagation phenomena need to be understood and quantified before reliable NDE (Non-destructive Evaluation)/SHM (Structural Health Monitoring) inspection systems can be realized. The propagation characteristics: energy velocity, dispersion, mode coupling, energy focusing factor and attenuation are considered in this paper. Concepts of minimum resolvable distance and sensitivity maps are extended to anisotropic attenuative materials in order to provide the means for comparison of different guided wave modes in composite materials. The paper is intended to serve as a framework for evaluating and comparing different modes and choosing the optimum operating conditions (frequency, sensor layout) for possible NDE/SHM applications on composite materials. Fundamental guided wave modes in the low frequency regime for highly anisotropic CFRP plates are investigated experimentally and theoretically and the implications for NDE/SHM are discussed.