SU1067369A1 - Oscillation logarithmic decrement determination method - Google Patents

Abstract

FIRMAN DEFINITION OF LOGO-. RHYTHMECHECK OF THE VIBRATION DECREMENT, consisting in that they excite harmonic oscillations of the system, measure the period of these oscillations, as well as variations in the oscillation parameters over time, and from the indicated values calculate the desired value, characterized in that in order to improve the accuracy and reliability of determining the logarithmic squared value oscillations, and quasi-periodic anharmonic oscillations are excited in the system, two periods of anharmonic oscillations are measured, the time interval between them and the measured D 4 para frames determined value of decrement depending sleDuyu1tsey .iiilli. .2 cL 2ut (when the period of harmonic oscillations of the systems is; the so-called angular oscillations of the system, measured over a period of time.

Description

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The invention relates to a measurement technique and can be used for the investigation of the physicomechanical properties of solids.

A known method for determining the logarithmic decrement of oscillations is that in a small sample having a disk shape, free damped oscillations are excited, for example, using a ball dropped on the sample, the time during which the amplitude of oscillation decreases by a factor, and using the indicated time and natural frequency of oscillation of the sample, the value of the Cl 3 decrement is calculated.

The disadvantages of this method are laboriousness and low accuracy of measurement parameters.

The closest in technical essence and the achieved result to the invention is the method of logarithmic determination: the oscillation decrement, which implies harmonic oscillations of the system, measures the period of these oscillations, as well as changes in time parameters of the oscillations, and from these values calculate the desired , the value of 2.

However, the known method is characterized by a high methodological error in determining the decrement of vibrations.

The purpose of the invention is to improve the accuracy and reliability of the determination of the logarithmic decrement of vibrations.

The goal is achieved by the method of determining the logarithmic decrement of oscillations, which consists in exciting the harmonic oscillations of the system, measuring the period of these oscillations, as well as variations in the oscillation parameters over time and calculating the desired value from the indicated values, and in the system excitating quasi-periodic anharmonic oscillations, measure two periods of anharmonic oscillations, the time interval between them, and determine the value of the decrement from the following ty

To-o)

en

t2):

where TQ is the period of harmonic oscillations of the system; T, T - periods of anharmonic

system vibrations measured. over a period of time. o Figure 1 shows a diagram of a device that implements a method for determining the logarithmic decrement of vibrations; figure 2 - vibro processes damping.

The scheme of the device includes the test sample 1 in the form of a thin film fixed on top of the base 2. The inertial mass 3 is attached to the sample 1. Additionally, a permanent magnet 4 is mounted on the sample 1. In addition, the device has an electromagnetic coil 5 with amplifier 6 and recording equipment consisting of frequency counter 7 and recorder 8.

The method is carried out as follows.

In the test sample 1, harmonic periodic oscillations are excited by means of a twisting of the mass 3 at some given angle. Using a measuring circuit consisting of an electromagnetic coil 5 and recording equipment, a vibrogram of damping of free oscillations is recorded. Then the system is informed of periodic oscillations by turning the inertial mass 3 at the initial twist angle, which ensures the occurrence of anharmonic oscillations in the system, and the Vibrogram is recorded. The period of such oscillations is calculated by the formula

±

rVOALx,

(I

T

about

where t

period of anharmonic oscillations of the system; period of harmonic oscillations of the system;

And the amplitude

max systems;

B is the coefficient of expiration of the geometrical parameters of the sample and its elastic characteristics. Since the oscillation damping occurs in the system; the amplitude decreases with time according to the following dependence

mc, x Lauer (t) - (2) where AJJ is the initial amplitude of oscillation;

f is the constant of oscillation damping time.

Substituted the relation (2) into (1 dd fixed time points

and ± 2 we get

/ 2i,

(31 G

(-)

(four

T. and T, periods of oscillation of the system corresponding to the moments of time -t and t. . Expressions from relations (3) and (4) T, after transformations, we obtain (fgp1 I, - 2 & i .l where At t2 - t (. A typical type of damping vibrogram obtained on the recorder tape (Fig. 2), contains the following notation: vibration damping of free harmonic oscillations "; vibration damping of free anharmonic oscillations S; amplitude of free periodic damping of oscillations A; current time

G. m t; the period of harmonic oscillations of the system T (j; the period of anharmonic oscillations of the system, measured through a period of time (ui) T and T. The log of the values of the periods T., and T with a frequency meter and the measurement of the time interval ui by a vibrogram determine the value of the logarithmic decrement (cG) using the invention allows to increase the accuracy of determining the logarithmic decrement of the oscillations by eliminating instrumental and methodical errors.

Claims (1)

METHOD FOR DEFINING THE LOG-. RHYTHMIC DECREE OF Oscillations, consisting in the fact that harmonic oscillations of the system are excited, measure the period of the indicated oscillations logarithmic decrement of oscillations, quasiperiodic oscillations are also excited in the system. anharmonic oscillations, two periods of anharmonic oscillations are measured, the time interval between them and the measured parameters limit the magnitude of the decrement from the following dependence t (t ² -t ² ) t ^{2 0} Pk x ¹ о> 2 ^2Δ * (t ² -t ² ) t ² \ 2 o) 1 period of harmonic oscillations system; | periods of anharmonic | £ oscillations of the system, measured over a period of time.