RU2732469C1 - Method for detection of gas turbine engine blade crack - Google Patents

Abstract

FIELD: fault detection.SUBSTANCE: invention can be used for non-destructive testing of gas turbine engines blades. Essence of the invention consists in the fact that by means of impact action the self-elastic acoustic oscillations are excited in the blade. Spectral analysis is used to register and record their frequency. Additionally, for the investigated stage the experimental dependence of the natural oscillation frequency is constructed from the installation point of the receiving device for conversion of mechanical vibrations into an electrical signal and allowable spread of oscillations of defect-free blades is determined, when beyond the boundaries of which there is determined presence of a crack of the blade.EFFECT: technical result is simplification of gas turbine engine blades control.1 cl, 3 dwg

Description

The invention can be used in the fuel and energy and machine-building industries.

The invention relates to methods of non-destructive testing and can be used for diagnostics of products of complex geometry, in particular, gas turbine engine blades, according to the parameters of their oscillations.

There is a known method for monitoring the defectiveness of a product, which consists in the fact that by means of shock action in a solid, elastic vibrations are excited at natural frequencies and their amplitudes are measured. At the natural frequencies, the time realization of elastic vibrations is recorded, which is divided into successive time intervals, and the Fourier transform is calculated in each of them. In the obtained spectrum, the maximum amplitude is determined, which is compared with the maximum amplitude of elastic vibrations in the first time interval, and the amplitude spectrum is calculated from the obtained normalized time sequence of maximum amplitudes, from which the second-order finite differences are determined. The maximum value of the second-order difference is taken as the coefficient of the presence of a crack, by exceeding the threshold value determined on the basis of measurements of a defect-free solid, the presence of cracks is judged (RF Patent No. 2274857, IPC: G01N 29/04).

The disadvantage of this method is the need to use expensive equipment and high-precision measurements, which require significant time and significantly increase the cost of the diagnostic procedure.

There is a known method for monitoring the defectiveness of an object, which consists in the fact that forced vibrations are excited in a controlled object, the frequency of forced vibrations is changed until resonant vibrations in the object occur, the parameters of these vibrations are measured, which are selected as the upper and lower frequencies corresponding to a given response amplitude, the ratio these frequencies, which is used to judge the defectiveness of the product (USSR author's certificate No. 1552091, IPC: G01N 29/04).

The disadvantages of this method is the inability to control with sufficient reliability objects, the hardening of which is not uniform in depth.

The closest in technical essence and the achieved result to the claimed method for detecting a crack in a gas turbine engine blade is a method for detecting cracks in a solid, which consists in the fact that elastic vibrations are excited in a solid by means of a shock effect at natural frequencies and their amplitudes are measured, on the basis of which the coefficient of the presence of a crack is determined, by exceeding a threshold value determined on the basis of measurements of a defect-free solid, the presence of cracks is judged taken as a prototype (Patent for invention of the Russian Federation No. 2219538, IPC: G01N 29/04).

The disadvantage of the known method for detecting cracks in a solid is the generation of waves at combination frequencies. To obtain waves at combination frequencies, a monochromatic ultrasonic wave is excited in a solid, and a crack is detected due to waves caused by the nonlinear interaction of an ultrasonic wave on it and oscillations at natural frequencies, and this requires the use of a monochromatic signal generator, an ultrasonic signal power amplifier, piezoelectric of the emitter and the laborious operation of gluing the emitter to the surface of a solid body, which leads to the complication and rise in the cost of the method.

The objective of this invention is to extend the service life of a gas turbine engine blades and, as a consequence, to increase economic performance during the repair and operation of a gas turbine engine.

The technical result in the implementation of this method is to exclude the possibility of fatigue failure and breakage of the blades of a gas turbine engine.

This problem is solved due to the fact that the resource of the blades of a gas turbine engine is extended, thanks to the use of a method for detecting a crack in a gas turbine engine blade, including

means for mechanically energizing the blade (for example, a soft-tipped hammer),

a receiving device for converting mechanical vibrations into an electrical signal (for example, an accelerometer),

electronic unit for processing the received signal.

The essence of the present invention lies in the fact that, by means of impact action, elastic vibrations are excited in a solid at natural frequencies and their amplitudes are measured. On the basis of the measurements, the coefficient of the presence of a crack is determined, by the excess of which the threshold value, determined on the basis of measurements of a defect-free solid, is judged on the presence of a crack. According to the invention, in addition, with the help of spectral analysis, the frequency of natural vibrations of a gas turbine engine blade is recorded and recorded, an experimental dependence of the natural vibration frequency of the blade on the installation site of the receiving device for converting mechanical vibrations into an electrical signal and, based on the results of the vibration survey of the gas turbine engine blades and static data processing, the permissible scatter of oscillations of defect-free blades is determined, when going beyond the boundaries of which the presence of a crack is judged.

FIG. 1 shows a diagram of a method for detecting a crack in a gas turbine engine blade, where:

1 - a blade of a gas turbine engine;

2 - means for mechanical excitation of the blade;

3 - receiving device for converting mechanical vibrations into an electrical signal;

4 - electronic unit for processing the received signal.

FIG. 2 shows the installation of a receiving device for converting mechanical vibrations into an electrical signal to a blade of a gas turbine engine in three sections.

FIG. 3 shows the dependences of the natural vibration frequency of the blades on the installation location of the receiving device for converting mechanical vibrations into an electrical signal to a gas turbine engine blade.

The method for detecting a crack in a gas turbine engine blade is carried out as follows.

In the blade (1) of a gas turbine engine, by means of impact action by means of mechanical excitation (2), natural elastic acoustic vibrations are excited. The vibrations are recorded using a receiver for converting mechanical vibrations into an electrical signal (3), connected to the input of the electronic unit for processing the received signal (4).

The measurement of the natural vibration frequency of a gas turbine engine blade is carried out in three sections by installing a device for converting mechanical vibrations into an electrical signal on the blade using a magnet. The reading of the natural frequency is performed in the acceleration measurement mode, since in the velocity and displacement measurement mode, one or two integration is performed. The damped process has a wide frequency spectrum that can go beyond the integration region, and this can lead to unreliable results. With the help of spectral analysis, the frequency of natural vibrations of a gas turbine engine blade is recorded and recorded. For the stage under study, an experimental dependence of the frequency of natural vibrations of the blade on the place of installation of the receiving device for converting mechanical vibrations into an electrical signal is constructed. Based on the results of the vibration examination of the blades of a gas turbine engine and static data processing, the permissible variation of oscillations of defect-free blades is determined, and when it goes beyond the boundaries of which, the presence of a blade crack is judged.

The proposed method for detecting a crack in a gas turbine engine blade makes it possible to exclude the possibility of fatigue failure and blade breakage. Monitoring the technical condition, flaw detection and rejection of the blade according to vibration characteristics increases the reliability, efficiency and safety of gas turbine engine operation and, as a result, leads to improved economic performance.

Claims (1)

A method for detecting a crack in a blade of a gas turbine engine, which consists in the fact that by means of a shock effect, elastic vibrations are excited in a solid at natural frequencies and their amplitudes are measured, on the basis of which the coefficient of the presence of a crack is then determined, by exceeding a threshold value determined on the basis of measurements of a defect-free solid body, they judge the presence of a crack, characterized in that, using spectral analysis, the frequency of natural vibrations of a gas turbine engine blade is recorded and recorded, an experimental dependence of the natural vibration frequency of the blade on the installation site of the receiving device for converting mechanical vibrations into an electrical signal is constructed and, based on the results of the vibration inspection of the blades of a gas turbine engine and static data processing, the permissible variation of oscillations of defect-free blades is determined, when it goes beyond the boundaries of which a crack is judged.

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