Computational Prediction of Micro-crack Induced Ultrasound Attenuation in CFRP Composites

A computational study is presented of ultrasound attenuation arising from linear elastic scattering by matrix micro-cracking in carbon fiber reinforced polymer (CFRP) composites. The model considers ultrasound propagation in a unidirectionally reinforced laminate containing randomly distributed matrix micro-cracks, configured such that neither the cracked laminate nor wavefield display dependence on the spatial direction of fiber reinforcement. The resulting 2D scattering formulation is solved using the boundary element method (BEM). Scatter-induced ultrasound attenuation is computed using a fully-interacting scattering matrix, as well as approximate multiple scattering formulations. Through comparison to the fully-interacting computation, the validity of level 1 scattering (independent scattering approximation), level 2 scattering (single neighbor interaction), and level 3 scattering (two neighbor interaction) is noted as a function of micro-crack density. A single parameter estimation of attenuation dependence on micro-crack density is obtained by fitting exponential dependence to the fully-interacting scattering results. Additionally, this single parameter is shown to be extracted equally well by fitting over the limited validity range of the independent scattering formulation. When uniform crack morphology is assumed, the exponential fit to the independent scattering approximation yields a practical estimation of micro-crack induced attenuation over the full range of micro-crack density through consideration of forward scattering by a single micro-crack. Comparison of results to limited experimental data, and to an independent alternate computational approach, lends plausibility to the study’s conclusions.