Investigation of the Space Distribution of the Velocity of Surface Acoustic Waves in Plastically Deformed Steel by the L
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INVESTIGATION OF THE SPACE DISTRIBUTION OF THE VELOCITY OF SURFACE ACOUSTIC WAVES IN PLASTICALLY DEFORMED STEEL BY THE LASER METHOD V. V. Koshovyi,1 О. M. Mokryi,1,2 М. І. Hredil’,1 and І. М. Romanyshyn1
UDC 539.4: 669.778
We study the influence of plastic deformation of St.3 steel on the velocity of Rayleigh surface acoustic waves measured by the method of laser recording. It is shown that plastic strains lead to the formation of anisotropy of the acoustic properties mainly determined, according to the data of evaluation of residual mechanical stresses, by the texture of steel. Keywords: surface acoustic waves, plastic deformation, velocity of surface acoustic waves, internal mechanical stresses.
The acoustic properties (АP) of metals depend on various factors, namely, on their phase composition, imperfections of the structure, level of mechanical stresses, etc. [1, 2]. Since the measurements of AP are nondestructive, this opens broad prospects for the development of nondestructive diagnostics of the state of metals in critical structures aimed at monitoring of their durability in the course of long-term operation, especially under the conditions of exhausted designed service life. At present, it becomes necessary to be able to measure the AP of specimens with spatially inhomogeneous properties. These inhomogeneities can be caused by the processes investigated by acoustic methods including the processes of welding [3, 4], strain hardening [5], forge-rolling [6], hardening [1], plastic deformation [7] (including plastic deformation near the crack tips [8]), etc. We can also mention the measurements of mechanical stresses on the basis of the acoustoelastic effect (which are mainly spatially inhomogeneous) [5, 9, 10]. These investigations require the procedures capable of the local determination of AP. Parallel with tomographic methods and investigation of the scattering characteristics of metals, as one of possible approaches, we can mention the procedure of measuring AP in certain small regions of specimens [1, 11]. The advantage of this approach is explained by the relative simplicity of its realization.
For the efficient realization of the indicated approach, it is reasonable to use surface acoustic Rayleigh waves (SAW) [1–3, 5, 11–13]. As compared with volume waves, SAW have numerous features making them more convenient for the determination of local AP. First of all, this is the possibility of easy localization of the zone of measurements determined by the positions of the exciting and receiving transducers. It is also necessary to mention the possibility of localizing the region of measurements across the thickness of the specimen because the depth of penetration of SAW is determined by their frequency. The capabilities of SAW are substantially extended by the application of laser equipment for their excitation and/or recording [14]. Lasers do not distort acoustic fields and enable one to increase the space resolution and operate in the high-frequency region. However, they somewhat complicate the procedure o
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