Ravasoo A.

APPLICATION OF COUNTERPROPAGATING NONLINEAR WAVES TO INHOMOGENEOUS PRESTRESS CHARACTERIZATION Arvi RAVASOO Centre for Nonlinear Studies, Institute of Cybernetics at Tallinn University of Technology, Akadeemia tee 21, 12618 Tallinn, Estonia, E-mail: arvi@ioc.ee Due to promising perspectives in nondestructive testing (NDT) of materials wave-wave and wave-material interaction is under intensive investigation. The objective of this paper is to demonstrate the possibility to solve the problem of nondestructive evaluation of inhomogeneous prestress in the elastic material on the basis of nonlinear effects of interaction of counterpropagating ultrasonic waves. Counterpropagation of two longitudinal waves in a physically nonlinear inhomogeneously prestressed elastic material (structural element) is studied theoretically. The analytical solution to the nonlinear equation of motion is derived and analyzed. The main attention is paid to the wave induced oscillations on two parallel boundaries of the material. It cleared up that the nonlinear effects of boundary oscillations are sensitive to the values of the parameters of multi-parametric prestressed state of the material. Comparisons of nonlinear boundary oscillation profiles on opposite boundaries enables qualitatively determine the presence of prestress in the material and distinguish the different states of prestress. This is illustrated by the numerical experiment for the case of two-parametric prestressed state. Dependence of the value of local maximum of the nonlinear part of boundary oscillation amplitude on prestress makes it possible to propose the algorithm for quantitative nondestructive evaluation of the parameters of prestress. The algorithm resorts to the plots the local maximum of the nonlinear part of boundary oscillation amplitude versus parameters of the prestressed state. Information obtained from the nonlinear effects of counterpropagation and interaction of ultrasonic waves in inhomogeneously prestressed materials enables to enhance the efficiency of NDT. The research was supported by the Estonian Science Foundation under the grant no. 6018.