Characterization of the orthotropic viscoelastic tensor of composites using the Ultrasonic Polar Scan

An enhanced two-stage inversion scheme for the determination of the viscoelastic properties of orthotropic plates (e.g. fiber reinforced polymers) based on the pulsed ultrasonic polar scan (P-UPS) is presented. A forward numerical model for the P-UPS is combined with an efficient optimizer routine (particle swarm optimizer, PSO) to inversely extract the complex orthotropic stiffness tensor, as well as the orientation of the main axes of orthotropy. The developed inversion technique is validated on synthetic data, yielding accurate results with small deviations: elasticity tensor <0.5%, viscosity tensor <2% and main axes of orthotropy <0.03°. The inversion procedure has been further applied to analyze actual experimental P-UPS recordings on an aluminum plate as well as a unidirectional [0]8 carbon/epoxy laminate. The obtained inversion results yield complex stiffness parameters which are in close agreement to reported values in literature, and confirms the potential of the UPS technique and its inversion optimization routine as an enhanced NDT technique to quickly and accurately obtain characteristic material properties of composites.