Semak P. Evaluation the condition of the material surface layers by measuring the velocity of surface Rayley waves withdifferent frequencies

The dissertation work is aimed at solving important scientific and technical problems of materials and designs diagnostics, namely – development of methods for estimating the inhomogeneous near-surface layer of material for thickness based on measuring the propagation speed of Rayleigh waves with different frequencies. An analytical review and systematic analysis of literature sources about modern methods and means of measuring the parameters of surface acoustic Rayleigh waves was done. Restriction on the use of surface acoustic Rayleigh waves of different frequencies to determine the parameters of inhomogeneous near-surface layers in thickness was set. It is estimated the thickness of the material layer, which can be characterized by determining the velocity of the Rayleigh wave of a certain frequency. This analysis is based on the depth distribution of the Rayleigh wave energy. A criterion is proposed according to which wave velocity is determined by a layer of material with a thickness of 0.6 λ (λ is the wavelength). To ensure the required resolution of measuring of changes in the surface acoustic Rayleigh wave parameters in thickness, it is justified the use of long-term probing radio pulses, which are narrowband. The width of the allowable spectrum of Rayleigh wave acoustic pulse and its connection with depth separation are analyzed. It is shown that for high separation it is necessary to use probing acoustic pulses with duration one and half orders of magnitude for the period of high-frequency signal filling. A method for measuring the velocity of surface acoustic Rayleigh waves based on the use of long-term probing radio pulses has been developed. Rigidly connected piezoelectric transducers are used to measure the speed of Rayleigh surface acoustic waves, and the measurement is performed by determining the time offset of the probing signal relative to the reference sinusoidal signal. To determine the distribution of surface layer parameters by thickness based on probing surface acoustic Rayleigh waves with different frequencies, the inverse problem is solved, which includes determining the effective penetration depth of the surface acoustic Rayleigh wave and the algorithm for determining surface layer thickness parameters which is based on velocity changes of acoustic surface Rayleigh wave with different frequency. This method has been tested on two types of control objects - sills and objects with abrasive blasting, which confirmed the manufacturability and efficiency of its use. A method for studying the parogon material has been developed and local sections of the parogon in which the Rayleigh wave velocity decreases have been identified, and the dependence of this decrease on the wave frequency is also observed. The presence of degradation processes in these areas was also confirmed by metallographic studies. A method for optimizing the technology of the metal abrasive blasting by the frequency dependence of the surface acoustic Rayleigh wave velocity is developed. Based on the research, it is shown that the main changes in the metal occurred in the near-surface layer with a thickness of not more than 0,2 mm in the next treatment modes: compressed air pressure 0,6 MPa, abrasive flow diameter 2 mm, distance from the nozzle to the treatment surface 10 cm . Developed technologies for assessing the metal condition were used in a small state enterprise "Gazothermik" (Lviv) in the form of a method for evaluating the results of abrasive blasting on the magnitude of the Rayleigh waves. The proposed technologies, which are based on determining the speed of Rayleigh waves of different frequencies, were implemented at the enterprise "Techmal" (Lviv). They were used to determine the changes in the state of the metal surface layers under the action of shot blasting in order to improve its strength characteristics, as well as to optimize the technological regime.