A New Ultrasonic Immersion Technique to Retrieve Anisotropic Stiffness Matrix for Dispersion Curves Algorithms

Abstract

Dispersion curve algorithms require the material properties of the anisotropic medium in which the ultrasonic guided-waves (GW) propagate as input. These material properties are currently obtained through ASTM standard mechanical testing procedures. Practice shows that researchers limit themselves to determining the E11 , E22 , G12 and ν12 , while the other engineering constants are then based on assumptions such as: E33 = E22 . The engineering constants are subsequently converted to the stiffness matrix using the relation between the elastic constants. The calculated stiffness matrix is used as input in the dispersion curve algorithm, however, the predicted results may vary significantly from those obtained experimentally due to the assumption. A more accurate method of determining the stiffness matrix is desired. In this research, the stiffness matrix components are determined non-destructively using a modified through-transmission ultrasonic immersion technique. Based on the existence of planes of symmetry within an orthotropic material, the stiffness matrix retrieval process was divided into parts to reduce the complexity of the process and increase the accuracy of the solution. As last, The group velocity dispersion curves are calculated analytically with the material properties from both the ASTM standards and the ultrasonic immersion technique. Both predicted results were compared to experimentally obtained velocities reported in the literature.