Abstract
Application of surface and subsurface waves for control of objects with a double-layer structure allows to extend possibilities of diagnostics of their physico-mechanical properties. The purpose of work was to determine conditions and offer recommendations providing measuring of ultrasonic velocity and amplitude of the former modes in protective layers and in basis of object at one-sided access to its surface.The analysis of an acoustic path of a measuring system in relation to ultrasonic evaluation of the objects having the restricted sizes and the protective coating according to velocity data of the surface and subsurface waves propagation is made. On the basis of representations of beam acoustics the dependences connecting a wavelength of the excited surface and subsurface modes, thickness and width of a controlled object, acoustic base of a sounding are defined. There are to provide a condition leveling of the influence of an acoustical noise created by the reflected and accompanying waves on parameters of acoustic signal with the given quantity of oscillations in an impulse.The principle opportunity is shown and conditions for determination of velocity of subsurface body waves in the base material which is under a protective coating layer are established. For these purposes on the basis of use of the block of ultrasonic probes the optimum scheme of a sounding is offered and the analytical expression for calculation of required velocity considering varying of thickness of a covering is received.The method of acoustical measuring realized by a direct and reverse sounding of the objects with small aperture and angle probes was analysed and formulas for determination of speed of subsurface wave under protective layer of the wedge form have been got. An ultrasonic device is suggested for the excitationreception of subsurface waves with different speed in objects (on 20–35 %) using for the acoustic concordance of environments of metallic sound duct as a wedge. Possibility of leveling of interference in a protective layer to control efects in basis of material by a volume wave by creation of supporting echo-signal of longitudinal wave of the set frequency and entered normally to the surface of object was studied.
Highlights
The method of acoustical measuring realized by a direct and reverse sounding of the objects with small aperture and angle probes was analysed and formulas for determination of speed of subsurface wave under protective layer of the wedge form have been got
An ultrasonic device is suggested for the excitationreception of subsurface waves with different speed in objects using for the acoustic concordance of environments of metallic sound duct as a wedge
При этом смещается вниз и максимум плотности энергии подповерхностных объемных волн (ПВ), локализованный в окрестности луча, идущего от источника волн под углом αm, и расположенный на расстоянии от поверхности z ≈ xctgαm [4]
Summary
При этом изменение акустической базы L производится путем перемещения одного из ПЭП вдоль оси x образцов разной толщины. A b Рисунок 3 – Экспериментальные зависимости амплитуды продольной подповерхностной волны от длины акустической базы, измеренные на образцах стальных пластин на частоте 1 МГц (а) и 5 МГц (b): hλ = ∞ (1, 4); 1,6 (2); 1 (3); 8,5 (5); 4,7 (6) Figure 3 – Experimental dependences of amplitude of longitudinal subsurface wave on length of acoustic base measured on the specimens of the steel plates when ultrasonic frequency is of 1 MHz (а) and 5 MHz (b): hλ = ∞ (1, 4); 1,6 (2); 1 (3); 8,5 (5); 4,7 (6). Данные исследований поясняются на рисунке 4, где приведены экспериментальные зависимости нормализованной амплитуды зондирующей волны ПВ от безразмерной акустической базы Lλ, измеренные на образцах стальных пластин разной толщины.
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