Nondestructive testing method of heterogeneous property of solid material

Abstract

The invention discloses a nondestructive testing method of heterogeneous property of a solid material, which comprises the steps of: detecting N surface acoustic wave signals excited by laser and spreading different distances, wherein N is not less than 2; processing data of the obtained N surface acoustic wave signals for spreading different distances, i.e., firstly, carrying out discrete Fourier transform on each signal to convert the signal into an amplitude spectrum and a phase spectrum to obtain N amplitude values Ai (i=1, ......, N) and N phase values relevant to wave spreading distance xi under each frequency component, wherein the phase is a function of the distance xi; fitting the relationship of the phase and the distance under each frequency into a line through a least square method; and obtaining a dispersion curve according to the phase speed value Cf of each frequency so as to reflect the heterogeneous property of the solid material, wherein the phase speed of each frequency is C, f is frequency and k is a gradient of the line. The invention increases the frequency range, thereby improving the spatial resolution of the heterogeneous property of a detection material; meanwhile, the surface acoustic waves are excited in a non-contact manner under a thermoelastic mechanism therefore, superheating is avoided, and nondestructive testing is realized.

Description

Technical field [0001] The invention belongs to a technology for non-destructive diagnosis of non-uniform properties in solids, and particularly relates to a non-destructive detection method for non-uniform properties of solid materials. Background technique [0002] When ultrasonic waves propagate in inhomogeneous materials, they will have frequency dispersion and cause energy loss based on frequency changes. The non-uniformity of materials, such as grain structure, deposited film or layered structure, is the main cause of sound wave dispersion, which is manifested in the gradual distortion of the ultrasonic wave. In order to achieve non-destructive testing of material properties that change with depth, thickness testing of films, coatings, etc., and similar problems, it is necessary to measure the dispersion curve with the highest possible accuracy. [0003] Existing methods for measuring dispersion in non-uniform materials are based on detecting two broadband surface acoustic w...

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Problems solved by technology

In this paper, the laser source distributed by the thermal grid needs to be modulated by a high-precision spatial phase modulator through control software. On the one hand, the equipment cost is high, and on the other hand, there are special requirements for the laser to ensure the excitation efficiency. The general nanosecond laser does not Applicable; only detecting narrow-band signals with fixed propagation distances and different center frequencies for calculation and analysis of phase velocity has large errors, and sufficient measurement reliability cannot be guaranteed

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