Arvi Ravasoo

Nondestructive characterization of materials with variable properties

SummaryMaterials with continuous variable properties in time and space are considered. The possibility of nondestructive characterization of these materials on the basis of nonlinear longitudinal wave propagation data is discussed on the basis of recent results. The model direct and inverse problems are solved. The utilization of obtained results enables one to solve several nondestructive material characterization problems.

Nonlinear Acoustic Nondestructive Evaluation (NDE): Qualitative and Quantitative Effects

The recent results in constructing the mathematical basis of nonlinear acoustic techniques for nondestructive evaluation (NDE) of inhomogeneous materials are discussed. These include microstructural materials and materials with weakly or strongly changing properties of specimens (structural elements) under inhomogeneous prestress. The idea is to extract additional information from nonlinear and dispersive effects of wave propagation. Novel concepts are introduced: (i) the analysis of dispersive effects; (ii) the analysis of two counter-propagating nonlinear waves.

The Perturbation Technique for Wave Interaction in Prestressed Material

Perturbation theory is a collection of methods for the systematic analysis of the global behavior of solutions to differential and difference equations. It is most useful when the first step reveals the important features of the solution and the remaining ones give small corrections. This is illustrated by the solution to the problem of interaction of longitudinal waves in an elastic material with inhomogeneous plane prestrain. The perturbative solution to the governing equation is expanded in a series with a small parameter that characterizes the small strain. The obtained solution that is global in space and time and local in the small parameter is analyzed in detail. Utilization of the solution in practical applications of ultrasonic nondestructive material characterization is discussed on the basis of numerical simulation data.

Counterpropagating Ultrasonic Waves for Inhomogeneous Materials Characterization

The interaction of two counterpropagating waves in an inhomogeneously prestressed material (a structural element) and in a physically nonlinear material with essentially changing continuous properties is studied theoretically. The influence of the parameters of a two-parametric prestressed state and the exponentially changing material properties on the profiles of boundary oscillations, evoked in the specimen with two parallel boundaries by the counterpropagating waves is clarified. Algorithms for qualitative and quantitative ultrasonic nondestructive characterization of two-parametric prestress and for qualitative characterization of essentially and exponentially changing properties of the elastic material with quadratic nonlinearity are proposed. Utilization of these algorithms in practical applications of ultrasonic nondestructive characterization of inhomogeneous materials is illustrated on the basis of numerical simulation data.

Nonlinear Acoustic NDE – Qualitative and Quantitative Effects

The recent results in constructing the mathematical basis of nonlinear acoustic techniques for NDE of inhomogeneous materials are discussed. These include microstructural materials and materials with weakly or strongly changing properties of specimens (structural elements) under inhomogeneous prestress. The idea is to extract additional information from nonlinear and dispersive effects of wave propagation. Novel concepts are introduced: (i) the analysis of dispersive effects; (ii) the analysis of two counter-propagating nonlinear waves.

Ultrasonic Wave Interaction for NDE of Inhomogeneous Prestress in Materials

The problem of ultrasonic nondestructive evaluation (NDE) of inhomogeneous prestress field is studied theoretically for an elastic material and plane strain. The nonlinear effects of ultrasonic wave propagation and interaction are shown to be additional sources of information for NDE. A model problem of simultaneous propagation of two ultrasonic longitudinal waves in physically nonlinear elastic material undergoing two-parametric prestress state is solved. The corresponding analytical solution is derived. Results of numerical simulations lead to the conclusion that it is possible to propose an algorithm for NDE of the inhomogeneous prestress field on the basis of the recorded data of boundary oscillations evoked by simultaneous propagation of two ultrasonic waves. The analysis of the oscillating boundary profiles permits to determine qualitatively the presence of prestress in the material and to distinguish special cases of the prestress state, for example, to evaluate quantitatively the parameters of the prestress.Copyright