Method of detecting defects in flexible structure

FIELD: analyzing or investigating of materials.

SUBSTANCE: method comprises exciting several modes of natural vibration of the reference structure and the structure to be analyzed, determining one of the observation parameter for the reference structure and structure to be analyzed at the first point, determining observation parameter at the second point for each of the structures, and determining the mode of structure vibration at the second point as a ratio of the value of the observation parameter at this point to the value of the observation parameter at the first point. The defect is detected from the difference of natural mode of vibration at the second point of the reference structure and the structure to be analyzed.

EFFECT: simplified method.

2 dwg

 

The invention relates to active acoustic methods of control of elastic structures using forced mechanical vibrations, and can find application in mechanical engineering, in particular the aircraft engine industry.

The main characteristics of natural vibrations of the structure (modal parameters) are the natural frequencies, its own mode shapes and damping factors. Own forms of vibrations of an elastic body are determined with the accuracy up to a constant multiplier. When you define your own mode shapes can we assume that the value of this form (i.e. the value of the parameter monitoring fluctuations in the construction of this form) at some point And design is one. Then the value of the own mode shapes of the structure at any point is equal to the ratio of the value of the parameter monitoring at the point in time when the oscillations of construction of this form to the value of the observation at point A.

There is a method of detecting defects in material elastic design, which excite oscillations of the reference and test designs, choose from several forms of oscillation, measured for these forms of resonant frequencies of structures, and on the occurrence of a defect is judged by the difference of the values of the resonant frequencies of the reference and test structures (is.Palestin, Weebly, Schwabichin and others, edited by Nepalese. "Acoustic methods of testing metals", M., engineering, 1989, p.98, 102).

The disadvantage of this method is that the resonant frequency is an integral characteristic of elastic design, i.e. describes the design as a whole and not its individual points, and change the resonant frequency it is possible to judge the occurrence of the defect, but it is impossible to determine the place of its occurrence. In addition, with the development of the defect resonance frequency varies slowly. All this leads to low reliability of detection of a defect in the material of the elastic structure.

Also there is a method of detecting defects in material elastic design, which excite oscillations of the reference and study design, choose a few of their own forms of vibrations on the selected mode shapes define one of the monitoring parameters for the reference and study design at the point of observation. As a diagnostic sign of use is equivalent to mass (the Description of the invention to the patent of Russian Federation №2190207, IPC 7 G01N 19/08, 29/00, Appl. 07.12.99,, publ. 27.09.02,)

According to this method measure the coefficients of internal friction, the real part of the dynamic compliance at frequencies of excitation, static compliance and determine equivalent to the mass.

The disadvantages of this method include the fact that for the determination of equivalent mass, you need to measure the dynamic flexibility of the design. The procedure of such measurement involves measuring not only the amplitude changes of parameter observations (vibratory displacement, velocity, acceleration, vipranarayana), but the magnitude of the exciting impact that is often impossible for various reasons, in particular due to the unavailability of the required locations of the sensors.

The invention solves the problem of the use of defects in the material of the elastic structure as a diagnostic sign of the parameter for the calculation of which does not require measurement of dynamic compliance of the design, and hence the magnitude of the exciting action.

To achieve this, the technical result in the implementation of the method for detecting defects choose some of their own shapes, excite vibrations of the reference and study design for each of the selected forms, and when these fluctuations determine one of the monitoring parameters for the reference and test structures in the first observation point.

New in the proposed method is that for each of these structures determine the parameter observations in the second point, about Radelet is its own mode shapes of the structure at the second point as the ratio of the parameter value of the observation at this point to the value of observations in the first point, and on occurrence of a defect is judged by the difference of the values of its own waveform at the second point of reference and study design.

The proposed method is illustrated by drawings, where

figure 1 shows a sample without defect;

figure 2 - sample with a defect.

The method is as follows.

Choose a few of their own shapes, excite vibrations of the reference and study design for each of the selected forms. When these fluctuations determine the value of the observations for the reference and test structures in two points: the first point and the second point C. as a parameter monitoring use of vibratory displacement, velocity, acceleration or vipranarayana. Parameter values survey (vibratory displacement, velocity, acceleration, vipranarayana) fluctuations in the structure on its own form of measure, for example, vibro-measuring the complex AWDI-1. Determine the value of its own mode shapes of the structure at point b as the ratio of the parameter value of the observation at point b to the value of the observation at point A. On the occurrence of a defect is judged by the difference of the values of its own waveform reference and study design.

EXAMPLE

Considered its own form of fluctuations in the fixed reference is brazza (figure 1) and the sample with the defect (figure 2). In the calculations, the samples were fixed at the wide end. When this area of the samples oscillations (the working part of the sample), was a rectangular beam size 0,110×0,015×0,0025 m based computing ANSYS defines its own form of oscillations of the reference sample and the sample with the defect. The defect was simulated by changing the elastic modulus of the material in the area of its occurrence (figure 2). This is considered the first two transverse mode shapes and defines the following values: y1(A), y2(A) the amplitude of a reference sample on its first and second form;- the amplitude of a sample with a defect in his first and second shape; I1(In1),- amplitude point In1the reference sample and the sample with the defect on the first form;2(In2),- amplitude point In2the reference sample and the sample with a defect in the second form. On the basis of the results obtained the following values of the mode shapes,reference sample and,sample with defect:

(first form)

(the second form).

Analysis of the results shows that the changes of the amplitudes of the points B1and In2if any defect is:

(first form)

(the second form).

If we accept the criterion of defect detection change diagnostic symptom of not less than 10%, then the defect can be considered detected.

The proposed solution allows to simplify the method for detecting defects by eliminating the need to measure the magnitude of the exciting impact that is often impossible for various reasons, in particular due to the unavailability of the required locations of the sensors.

Method of detecting defects in material elastic design, in which choose some of their own shapes, excite vibrations of the reference and study design for each of the selected forms, and when these fluctuations determine one of the monitoring parameters for the reference and test structures in the first observation point, characterized in that for each of these structures determine the parameter of the observation in the second observation point, determine the value of the own waveform design in W is Roy point as the ratio of the parameter value of the observation at this point to the value of observations in the first point, and on occurrence of a defect is judged by the difference of the values of its own waveform at the second point of reference and study design.



 

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