Multiscale approach for identification of transverse isotropic carbon fibre properties and prediction of woven elastic properties using ultrasonic identification

In this work the possibility to reverse engineer the transverse isotropic carbon fibre properties from the 3D homogenized elastic tensor of the UD ply for the prediction of woven ply properties is explored. Ultrasonic insonification is used to measure the propagation velocity of both the longitudinally and transversally polarized bulk waves at various symmetry planes of a unidirectional (UD) Carbon/Epoxy laminate. These velocities and the samples' dimensions and density are combined to obtain the full 3D orthotropic stiffness tensor of the ply. The properties are subsequently used to reverse engineer the stiffness tensor, assumed to be transversely isotropic, of the carbon fibres. To this end, four micro-scale homogenization methods are explored: 2 analytical models (Mori-Tanaka and Mori-Tanaka-Lielens), 1 semi-empirical (Chamis) and 1 finite-element (FE) homogenization (randomly distributed fibres in a Representative Volume Element). Next, the identified fibre properties are used to predict the elastic parameters of UD plies with multiple fibre volume fractions. These are then used to model the fibre bundles (yarns) in a meso-scale FE model of a plain woven carbon/epoxy material. Finally, the predicted elastic response of the woven carbon/epoxy is compared to the experimentally obtained elastic stiffness tensor. The predicted and measured properties are in good agreement. Some discrepancy exists between the ultrasonically measured value of the Poisson's ratio and the predicted value. Nonetheless, it is shown that virtual identification and prediction of mechanical properties for woven plies is feasible.