SU1244527A1 - Method of dynamic testing of articles - Google Patents

Abstract

This invention relates to a testing technique. The purpose of the invention is to beat the accuracy of imitating the operational loads of a product from repeated shocks. The method consists in preliminarily measuring the eigenfrequencies of critical elements of the product when vibrating excitation of the product at several levels, at which the maximum levels of critical elements of the product correspond to the levels of predetermined shock spectra of the product from a predetermined mode of repeated shocks. Then, the coefficients of structural damping and acceleration of critical elements when the product is struck with shocks with amplifiers corresponding to the amplitudes of a given multiple shock mode are determined. After that, the product is subjected to narrow-band vibration with a variable. frequency, the level of which in the subbands of natural frequencies is set in accordance with the coefficients of structural damping on. these frequencies. The method allows to simulate the operational loads of the product from repeated shocks. 1 hp f-ly, 7 ill. (L N9 4 4ib JV Yu Chae go / na

Description

to

15

20

112AA527

This invention relates to a test technique, in particular to a method for dynamic testing of products.

The purpose of the invention is to improve the accuracy of simulating the operational loads of a product from repeated shocks by first measuring its own frequencies and structural damping coefficients of critical elements at load levels corresponding to the levels of a given mode of repeated shocks.

Fig. 1 shows the amplitude-frequency characteristics of the tested product at various levels and the envelope of the shock spectra of a given mode of repeated shocks; FIG. 2 shows vibration excitation levels when measuring natural frequencies; FIG. 3 is a diagram of the loading of the product by shock loads; in FIG. 4 — impulses of shock loading of the product; FIG. 3 shows a typical oscillogram of the damping oscillatory process of the K-th critical element when the product is excited by impacts; 6 shows the amplitude-frequency characteristics of the product with narrowband vibration, the shock spectrum and the envelope of the shock spectra of the product for a given mode of repeated shocks; Fig. 7 shows the dependence of the acceleration on the frequency of the narrow-band vibration, with the help of which the number of cycles of vibration is determined at the last stage.

The method is carried out as follows.

The eigenfrequencies of critical elements of the product are preliminarily measured by vibrating excitation of the product at several levels (Fig. 2, at which the maximum levels 1 and 2 of vibration of the critical elements of the product correspond to the levels of predetermined shock spectra (envelope 3) of the product from a predetermined multiple-impact mode. The fig shows a typical picture obtained at the initial stage of testing.

one

Pins corresponding to the amplitudes of a given mode of multi-strikes, and durations equal to the half-periods of natural oscillations of critical elements.

Shock effects are used as reference effects, which allow to determine the energy dissipation during elastic oscillations of the product and its elements. The shape of the pulses can be half-sine or close to it.

In figure 1 it can be seen that for definite. To reduce the structural damping parameters, 6 shock pulses with durations ((Fig. 4) determined by dependency are required:

.

moreover, K 1-6.

The test article is equipped with a system for measuring dynamic processes, such as accelerations. At the product, LIIs record the damped oscillatory processes occurring in the critical elements of the product under the action of impulses of shock accelerations on it with certain higher characteristics. The resulting oscillograms of damped oscillations plot the envelope curves, as shown in 4ig.5.

Allocated plot vibrational

35 of the process (FIG. 3) from time t to time t, it is possible to determine the coefficient of the structural damping of the K th critical element using the formula: AW

40

P.,

AO

45

de 0)

A "JSC

i KCtw-to)

 k

K-th natural frequency

critical element;

oscillation amplitude

critical element at the moment

of time

the amplitude of this

element at the moment to.

where through

f

G.

f i

with s

denoted by the fixed natural frequencies of the coggy elements of the product.

 The coefficients of con50 are measured. Next, the product is exposed to narrow-band vibration with a variable frequency, the level of which in the subbands of the natural frequencies is set in accordance with the coefficient of damping and the acceleration of critical elements at excitation at these frequencies. The level A of the product 4 fixed on vibration is set according to the ratio of the mass 3, by strikes (see FIG. 3) with ammonium:

five

0

Pins corresponding to the amplitudes of a given mode of multi-strikes, and durations equal to the half-periods of natural oscillations of critical elements.

Shock effects are used as reference effects, which allow to determine the energy dissipation during elastic oscillations of the product and its elements. The shape of the pulses can be half-sine or close to it.

In figure 1 it can be seen that for definite. To reduce the structural damping parameters, 6 shock pulses with durations ((Fig. 4) determined by dependency are required:

.

moreover, K 1-6.

The test article is equipped with a system for measuring dynamic processes, such as accelerations. On the product, LII records damped oscillatory processes occurring in the critical elements of the product, under the action of impulses of shock accelerations on it with certain characteristics. The resulting oscillograms of damped oscillations plot the envelope curves, as shown in 4ig.5.

Allocated plot vibrational

5 of the process (FIG. 3) from time t to time t, it is possible to determine the coefficient of structural vibration of the K-th critical element by the formula: AW

0

P.,

AO

five

de 0)

A "JSC

i KCtw-to)

 k

K-th natural frequency

critical element;

oscillation amplitude

critical element at the moment

of time

the amplitude of this

element at the moment to.

50 Further, the product is exposed to a narrow-band vibration with a variable frequency, the level of which in the subbands of the natural frequencies is set in accordance with the coefficient-A.

where X., having rooted the K-th critical element when the product is excited by blows; n is the structural damping coefficient of the kth critical element.

The entire frequency range can be divided into a number of sub-bands (Fig. 6) within which the narrow-band vibration amplitude is constant, which makes it possible to apply well-known vibration test control methods, for example, to conduct frequency scanning tests within the sub-band with a constant level. Figure 6 also shows the individual amplitude-frequency from Hfeie characteristics of 6 vibrations at different frequencies.

Thus, the expression for A makes it possible to determine the amplitudes of narrow-band vibration, which creates a load of elements on the product, equivalent to a load with repeated shock effects (5 twi x.

The number of vibration cycles at the last stage is set equal to the number of cycles of a given mode of repeated shocks. As can be seen from Fig. 6, because of the narrow bandwidth of the vibration, it is necessary to carry out the tests in such a way as to cover the entire spectrum of the product's own frequencies and operating loads. For this test, several fixed frequencies or a scanning method are carried out with the entire frequency range, the product response range from repeated shocks, and the required number of loading cycles is required. The outcome of the engineering accuracy of the accuracy of -V 10% when determining r the number of loading cycles as a frequency and fjt frequencies, where a certain number of loading cycles occur, the width of the resonance curve is taken to be 0.9 of the maximum amplitude.

The test time at mid-frequency f is defined as follows.

tfc

Njc.

where is the number of repeated shocks given for a given frequency band. The test time is determined by

in the following way:

 - within each frequency interval (shown in FIG. 6 and corresponding to the horizontal sections of the polyline) there is an average frequency fy of the interval (fkg.7);

-determined bandA. frequency resonance curve;

-determines the fu test time using the above formula;

- determine the number of segments of width d, within each frequency interval;

-determines the time of the test within each interval as the sum

test times at frequencies f ,, f

.4Л J

-determines the test time over the entire frequency range as the sum of the times for each interval.

Tests at fixed frequencies f, f, y. ... within the intervals it is advisable to replace with a frequency scan, pass the interval at a constant speed over time

ty t,

I .. -. . ,

If in the frequency range of vibration effects there are no resonant frequencies, it is possible beyond the resonant minimum.,

maximum Gmskocho n one average frequency range

,; / iin + m "ks tjp: 2

The method allows one to carry out tests of large-sized extended products weighing several tons to loads equivalent to repeated mechanical shocks. At the same time, a significant reduction in time and laboriousness of testing, as well as saving labor and material resources associated with the preparation of tests, is provided.

45

Claims (1)

1. The dynamic testing method of the product, consisting in the fact that the own The frequencies of critical elements of the product, vibratory excitation of the product, as well as the coefficients of structural damping, and then the product are exposed to narrow band vibration with a variable frequency, the level of which in the subbands of the natural frequencies is set in accordance with the coefficients of structural damping at these frequencies, characterized by , in order to increase the accuracy of imitation of the operational loads of the product from repeated shocks, vibration excitation of the product when measuring its own Frequencies are conducted at several levels, with KotopHx, the maximum vibration levels of critical elements of the product correspond to the levels of predetermined shock spectra of the product from a given multiple impact mode, then measure the structural damping and acceleration factors of critical elements when the product is excited by strikes with the amplitude, corresponding amplitudes of a given mode of multiple shocks, and long duration spiA2 t m equal to the half-periods of natural oscillations of critical elements, and the level A of the vibration is set according to: . 2nji xit a. " u) j where Ujj is the natural frequency of the K-th critical element; Hz - the acceleration of the K-th critical element when the product is excited by blows; and n is the structural damping coefficient for the K-th critical element. 2, the method according to claim 1, and tl and ch and yu and teM that the number of cycles of vibration in the last stage, set equal to the number of cycles of a given mode of repeated shocks. Frequency (pic f) uf. ffflfm Clever BUT 1244527 Sstavitel V.Meshkovsky Editor L.Pchepinska Tehred I.Popovich Proofreader S.Shekmar Order 3907/45 Circulation 778 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Ra n. 4/5 emb. Production and printing company, Uzhgorod, st. Project, 4