Towards an efficient characterization of the viscoelastic properties of anisotropic media based on the ultrasonic polar scan: experiments and numerical modelling

Composite materials (e.g. CFRP) are more and more used for critical components in several industrial sectors (e.g. aerospace, automotive,…). Their complex and often anisotropic nature makes it difficult to accurately determine their material properties or to detect internal damages that may have occurred during manufacturing or material loading. To resolve these challenges, the Ultrasonic Polar Scan (UPS) technique has been introduced. In a UPS experiment, a fixed material spot is insonified at a multitude of incidence angles (θ,φ) and the transmission amplitude as well as the arrival time are subsequently measured [1-2]. Mapping these quantities on a polar diagram gives rise to a local fingerprint of the visco-elasticity of the investigated material. In the present study, we propose a novel two stage inversion scheme which is able to infer both the elastic and the viscous properties of the complex (anisotropic) media. In the first step, we solve the inverse problem of determining the elastic constants of the medium from cross-sections of time-of-flight UPS recordings (Figure 1a). The second stage handles a similar inverse problem, but now operates on the amplitude recordings of a UPS experiment and uses the elasticity values obtained in step one to inversely determine the viscous part of the viscoelastic tensor (Figure 1b). The developed characterization scheme has been employed on both virtual (numerical) experiments, to test the effectiveness of the method, and on actual experimental UPS recordings on CFRP plates.