RU2320987C1 - Method of determining service life of part - Google Patents

Abstract

FIELD: nondestructive testing.

SUBSTANCE: method comprises exciting natural elastic acoustical vibration inside the part by means of short-term striking on the part and recording and analyzing the parameters of the acoustical vibration. The rate of decaying of the logarithmic envelop of the main mode of vibration is used as an informative parameter.

EFFECT: enhanced precision.

1 cl, 6 dwg

Description

The invention relates to the field of diagnostics of the condition of parts of components and assemblies and can be used to assess the residual life of parts, in particular blades of gas turbine aircraft engines.

During the operation of various parts and devices due to aging of materials, their residual life is reduced. In this regard, it is very urgent to assess the residual resource of parts. One possible solution is acoustic diagnostics.

A known method of controlling the defectiveness of the product (see AS SU No. 1552091 for 1990, class G01N 29/04), which consists in the fact that it stimulates forced oscillations using an external harmonic force with a varying frequency, measure the amplitude of the forced oscillations in the resonance region, measure the width of the recorded resonant peak, which characterizes the Q factor of resonance Q≈ and the energy loss in the material of the part, and it is used to judge the defectiveness of the product. However, the considered method has several disadvantages that limit its use. Firstly, for testing, expensive equipment is required, including a continuously tunable sine wave generator based on a magnetodynamic converter. Secondly, due to the high quality factor of the resonators (Q≈10000), high-precision measurements are required to determine the relative width of the resonant peaks. Finally, due to the use of a consistent measurement procedure, product diagnostics take considerable time.

A known method for determining the defectiveness of the blades of a turbine wheel (see US, Pat. No. 6629463 for 2001, class G01N 29/04), consisting in the fact that in the part by impact impact their own elastic acoustic vibrations are excited, then they are measured using a spectral analyzer the frequencies of the first three modes of induced oscillations and by their values judge the defectiveness of the product. The disadvantage of this method is its low sensitivity, since the frequency of the modes of natural vibrations slightly change during the aging of the part.

A known method for detecting defects in parts by acoustic diagnostics (see US Pat. JP No. 3456965 for 2000, class G01N 29/12), which by the nature of the application of acoustic diagnostics can be used as a prototype. When conducting tests in this way in a controlled part by shock, they produce their own damped acoustic vibrations, pick them up with a microphone and analyze the shape of the acoustic wave. The presence of a defect in the part leads to an excess of the amplitude ratio of the nth and (n + k) th maxima of the acoustic wave, which characterizes the damping decrement of the induced oscillations. However, this method has several disadvantages. Firstly, to accurately measure the amplitudes of the wave peaks, a high signal sampling frequency is required. Secondly, the method used gives satisfactory results only in the case of unimodal oscillations, since with multimodal oscillations due to the occurrence of beats, the accuracy of the attenuation estimate is unsatisfactory. Finally, it should be noted the significant sensitivity of the considered method to noise, which sharply reduces the accuracy of diagnostics.

Thus, the disadvantages of all the considered methods are either an unsatisfactory reflection of the aging process of the material of the part, as a result of which they do not provide sufficient accuracy for estimating its residual life, or the need to use expensive equipment and high-precision measurements that require significant time and significantly increase the cost of the diagnostic procedure.

The objective of the invention is the implementation of the technical result, which consists in increasing the accuracy of determining the resource of parts: residual - used and full - new, as well as using a more sensitive and noise-free parameter characterizing the aging of the material - the attenuation rate of the logarithmic envelope of the main or several modes of natural vibrations emitted using narrowband filtering. At the same time, the diagnostics of the part resource is significantly simplified and accelerated.

The technical result is achieved by the fact that in the method for determining the residual life of a part by acoustic diagnostics, in which intrinsic elastic acoustic vibrations are excited by a short-term shock action, their parameters are recorded and analyzed, and the attenuation rate of the logarithmic envelope of the main oscillation mode is detected and used, expressed in dB / s, and the residual resource of the part being checked is judged by the experimental calibration dependence of the speed of anija logarithmic envelope of oscillations of the fundamental mode of use, obtained for study kit of parts.

The proposed method is based on the fact that the number of internal defects (dislocations) increases in the structure of the material during its aging. When mechanical vibrations are excited in a part, part of the vibrational energy is converted into thermal energy, as a result of which the vibration damping rate in such parts increases.

The application of the proposed method can improve the accuracy of determining the residual life of parts, reduce the complexity and reduce the time of diagnosis, thereby significantly saving on material costs during testing. Due to the isolation of the oscillation mode using narrow-band filtering, the presence of additive noise has little effect on the attenuation measurement procedure, which significantly increases the measurement accuracy. In addition, due to the slow variation of the envelope of the vibrational mode over time, a high sampling rate is not required to ensure measurement accuracy, as in the case of a method based on the direct analysis of the vibrational mode or acoustic wave or vibrational mode in the time domain.

In the case of excitation of several modes of natural vibrations in the investigated part, its residual life of the part can be determined by the dependence of the attenuation of the logarithmic envelopes of several modes caused by mechanical vibrations. As a result of this, the influence of the noise component during measurements can be reduced and a more accurate prediction of the residual life can be obtained.

The invention is illustrated by drawings, where:

figure 1 is a spectrum of one of the recorded signals, where the arrow indicates the main mode of oscillation, the frequency of which is 2652 Hz;

figure 2 - the main mode of oscillation of a new blade, selected using narrow-band filtering;

figure 3 - the main mode of oscillation of the same blades susceptible to aging on a vibrating stand;

4 is a logarithmic envelope of the selected main oscillation mode of a new blade;

5 is a logarithmic envelope of the selected main mode of oscillation of the scapula after operating time on a vibration stand;

6 is an experimental calibration dependence of the decay rate of the logarithmic envelope of the main vibration mode from the value of the operating time, where:

V is the decay rate of the logarithmic envelope (dB / s);

N is the operating time, measured by the number of cycles of alternating load of a certain intensity applied to the part;

Nsize - operating time corresponding to the moment of destruction of the part;

Vism. - the measured decay rate of the logarithmic envelope;

Nost. - residual resource of the part;

Nost = Nsize-N.

For experimental confirmation of the results of the proposed method for determining the residual life of a part by acoustic diagnostics, a batch of compressor blades of a gas turbine aircraft engine was investigated. In the investigated blades of the batch, the shock acoustic waves excited their own acoustic vibrations in the blade and entered data into the computer through the MD-71 microphone. Then, the spectra of the recorded signals were determined by software, the main mode of oscillations was isolated with a narrow-band filter, and its logarithmic envelope was found. We studied blades from one batch of manufacture (new and subjected to aging (production) on a vibration stand for 20 million cycles with a specific load of σ = 40 kg / mm ² .

When comparing the results of the work (see Figs. 4 and 5), it was found that from the influence of the operating time, the decay rate of the logarithmic envelope of the main mode of the blade’s own vibrations increased from 7.19 dB / s to 12.1 dB / s, that is, in 1, 68 times. This meant that the aging of the material was accompanied by an increase in the number of mechanical defects accelerating the damping of natural vibrations, and testified to the high sensitivity of the selected parameter to the life of the part.

Thus, the relationship between the attenuation rate of the logarithmic envelope of the mode of natural vibrations of the part and its residual life was experimentally confirmed.

From the foregoing, it follows that the proposed method provides sufficient accuracy for determining the residual life of the part and reduces labor costs for the operation.

Claims (2)

1. A method for determining the residual life of a part by acoustic diagnostics, in which intrinsic elastic acoustic vibrations are excited by a short-term shock action, their parameters are recorded and analyzed, characterized in that the attenuation rate of the logarithmic envelope of the main vibration mode and the residual are detected and used as an informative parameter the resource is judged by the experimental calibration dependence of the attenuation rate of the logarithmic attenuation obtained for the test batch bending oscillations of the fundamental mode of use. 2. The method according to claim 1, characterized in that the assessment of the residual life of the part is carried out according to the measurement results of the attenuation rates of several modes of natural oscillations.

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