RU2287794C2 - Method of testing impact for impact effect - Google Patents

Abstract

FIELD: test equipment.

SUBSTANCE: object to be tested is fixed onto table of resilient resonator, which is mounted onto platform of bed to be subject to impact impulse effect. One or several resilient resonators are mounted additionally between table of resonator and tested object depending on required range and level of frequencies excited in object; rigidity of resonators increases from platform to tested object. Natural frequencies of system formed by platform and resonators are tuned to frequencies which correspond to preliminary calculated minimums of Fourier amplitude spectrum of impact pulse reproduced by bed.

EFFECT: widened operational abilities.

4 dwg

Description

The invention relates to the field of testing equipment, in particular to testing objects for impact loads.

At present, the modes of autonomous shock testing of devices are mainly assigned in the form of single shock impulses of acceleration of a half-sinusoidal shape, the parameters of which in peak value can reach 100,000 m / s ² or more with a minimum impact duration of 0.2 · 10 ^-3 s or less . Impact resistance tests to such loads are especially important for elements containing piezocrystals, etc. However, existing industry-known equipment for testing an object for impact impacts has limited operational capabilities for reproducing shock pulses both in terms of maximum peak value and their minimum duration.

In this regard, there was a need to develop a method that allows to expand the range and increase the level of frequencies excited in the test objects on existing designs of shock stands with their ultimate operational capabilities, which will improve the quality of testing their impact resistance.

In the field of testing equipment, a widespread method of testing an object for impact, which, for example, is implemented in a hammer-type shock stand [1]. This method consists in the fact that the test object, mounted on the platform of the free fall copra, is dropped from a certain height and in the process of interaction of the platform with the stop (shaper) is subjected to the action of a single pulse of acceleration acceleration. The main limitation of the operational capabilities of free fall copra is the maximum platform discharge height, which depends on the height of the laboratory room.

It is known that in order to increase the response of structural elements at their own frequencies, it is necessary to increase the peak value of shock acceleration, and to expand the range of frequencies excited in the product, reduce the duration of exposure. However, as a rule, due to the presence of plastic deformations of materials in the contact zone of the platform with an emphasis, one more restriction appears associated with the reproduction of the maximum minimum possible duration of a shock acceleration pulse. Thus, a disadvantage of the known method is that, having the limiting parameters of the shock acceleration pulse formed by the stand, it becomes difficult to expand the range of frequencies excited in the product and increase the reaction of its elements.

A known method of testing an object for impact, implemented in the invention under the name "Stand for testing products for the effects of damped oscillations" [2].

According to this method, the closest in technical essence and adopted for the prototype, the test object is mounted on the table of an elastic resonator mounted on the platform of the stand, which is subjected to a shock acceleration pulse. In this case, the reaction of the resonator table is alternating decaying oscillations of a certain frequency. However, according to [3], the response of an elastic resonator to an input action in the form of a half-sinusoidal acceleration pulse can be transformed into a single shock acceleration pulse with an increase in peak value compared to the input action, provided that the natural frequency of the system (platform and resonator with the test person) object) is equal to:

,

,

where ƒ _p is the intrinsic purity of the system formed by the platform and the resonator with the test object;

τ _I - the duration of the input impact.

Thus, the presence on the platform of the stand of the resonator with the test object (according to the technical solution [2]) tuned to the required frequency allows us to transform the shock pulse of the input action with amplitude A _in and duration τ _in into a single shock pulse with increased amplitude A _p > A _in and a shorter duration τ _p <τ _vx , while maintaining a constant velocity drop per stroke, i.e.

where A _in - input shock pulse;

And _p is the shock pulse with increased amplitude.

This allows you to slightly expand the range of frequencies excited in the test object and increase the response of elements at these frequencies, which, along with a positive effect, is also a disadvantage of the prototype, since there is no possibility of further increasing the range and level of frequencies excited in the test object.

Thus, the object of the present invention is to expand operational capabilities by increasing the range and level of frequencies excited in the test object without changing the limiting parameters of the shock pulse reproduced by the bench.

The problem is solved in that in the method of testing an object for impact, according to which the test object is mounted on a table of an elastic resonator mounted on a platform of the stand, which is subjected to a shock pulse, according to the invention, between the table of the resonator and the test object is additionally set depending on the required range and the level of frequencies excited in the object, one or more sequentially fixed elastic resonators with increasing rigidity from platform to test the desired object, and the eigenfrequencies of the system formed by the platform and the resonators are tuned to frequencies corresponding to the previously calculated minimums of the Fourier amplitude spectrum reproduced by the stand of the ultimate shock pulse.

The impact on the test object of a shock pulse, the parameters of which are set taking into account the proposed conditions, depending on the required range and the level of frequencies excited in the object, allows you to transform the shock pulse of the input action into a single shock pulse with an increased amplitude and a reduced duration.

The presence in the claimed invention features that distinguish it from the prototype, allows us to consider it appropriate to the condition of "novelty."

New features (additional installation between the resonator table and the test object, depending on the required range and the level of frequencies of one or several successively mounted resonators excited in the object with increasing rigidity from the platform to the test object, the eigenfrequencies of the system formed by the platform and the resonator are tuned to frequencies corresponding to the previously calculated minima of the amplitude Fourier spectrum reproduced by the stand of the ultimate shock pulse, did not reveal enes in the technical solutions of similar purpose. On this basis, it can be concluded according to the claimed invention, the condition of "inventive step".

The invention is illustrated by the following drawings, where

figure 1 shows the amplitude-time dependence of shock pulses of acceleration;

figure 2 - dependence of the amplitude Fourier spectrum of shock acceleration pulses reproduced by the stand;

figure 3 shows the design diagram of a device that implements a method of testing an object for impact;

figure 4 - dependence of the positive and negative shock spectra of the current and aftereffect of acceleration pulses.

Figure 1 shows the amplitude-time dependence of shock pulses of acceleration (where A is the acceleration, t is time):

- limit reproduced by the stand (curve a);

- the response of the resonator to the limit impulse at the frequency of the system formed by the platform and the resonator with the test object equal to the frequency of the first minimum of the amplitude Fourier spectrum of the acceleration limit impulse (curve c);

- reproduced according to the invention in the presence of two series-mounted resonators with increasing rigidity with the natural frequencies of the system formed by the platform and two resonators with the test object equal to the frequencies of the first and second minimum Fourier amplitude spectrum of the acceleration limit pulse (curve c).

Figure 2 shows the dependence of the amplitude Fourier spectrum of shock acceleration pulses reproduced by the stand (where S (f) is the amplitude Fourier spectrum, f is the frequency) obtained by:

- analogue [1] (curve a);

- prototype [2] (curve c);

- the invention (curve c).

Figure 3 shows the design diagram of a device that implements a method of testing an object for impact, where it is indicated:

M ₀ is the mass of the stand platform;

M ₁ is the mass of the table of the first resonator;

M ₂ is the mass of the table of the second resonator with the test object;

C ₁ is the stiffness of the first resonator;

C ₂ is the stiffness of the second resonator;

And ₀ (t) is the input shock pulse of acceleration generated by the stand.

Figure 4 shows plots of positive and negative shock spectra of current and aftereffect acceleration pulses (where R (f) ⁺ - positive shock spectrum, R (f) ^{- -} negative shock spectrum, f - frequency), obtained by:

- analogue [1] (curves 1 _a , 1 _c );

- prototype [2] (curves 2 _a , 2 _c );

- the present invention (curves 3 _a , 3 _c ).

The implementation of the method of testing an object for impact is shown in figure 3 - design scheme with two resonators.

The method is as follows.

The first elastic resonator with rigidity C _{1 is} installed on the stand platform. A second resonator of rigidity C _{2 is} installed on the table of the first resonator, on the table of which the test object is fixed, and the condition C ₂ > C ₁ is fulfilled. Knowing in advance the parameters (peak shock acceleration - A ₀ , duration - τ) and the shape of the shock pulse A ₀ (t) (see Fig. 1, curve a) formed by the bench at the maximum operational capabilities, its amplitude Fourier spectrum is calculated depending on frequency (see figure 2, curve a). At the minimum points of the amplitude Fourier spectrum, the values of the frequencies f ₁ and f ₂ are determined, which must correspond to the eigenfrequencies of the entire system formed by the platform and two resonators with the test object (Fig. 4).

The platform is exposed to a shock pulse A ₀ (t) (see Fig. 1, curve a), which is also transformed by the system into a single acceleration pulse both by the mass of the table of the first resonator A ₁ (t) and by the mass of the table of the second resonator A ₂ (t ), but with an increase in their peak values of acceleration A ₂ > A ₁ > A ₀ and a decrease in durations τ ₂ <τ ₁ <τ ₀ , which allows us to increase the range and level of frequencies excited in the test object (see Fig. 1, curves in , from).

The possibility of industrial implementation and practical feasibility of achieving the desired technical result when using the invention is illustrated by the following example.

Example.

The limiting acceleration pulse reproduced by the shock stand had the following parameters: the peak value of shock acceleration is A ₀ = 1000 m / s ² and the duration is τ = 0.5 · 10 ^-3 s, which was the input for further calculations (see Fig. 1, curve a). The amplitude Fourier spectrum of this shock pulse was calculated (see Fig. 2, curve a). We determined the frequencies at which the amplitude Fourier spectrum took the minimum values (in our case, zero), they amounted to f ₁ = 3000 Hz and f ₂ = 5000 Hz. By installing one elastic resonator on a platform of mass M ₀ and choosing a stiffness C ₁ such that the natural frequency of the system formed by the platform M ₀ and resonator M ₁ is equal to f ₁ = 3000 Hz, we also obtained on the resonator table when an input shock pulse is applied to the platform a single acceleration pulse with a peak value of A ₁ = 1500 m / s ² with a duration of τ≈0.35 · 10 ^-3 s (see figure 1, curve c). Its amplitude Fourier spectrum (see Fig. 2, curve c) expanded to 5000 Hz, and the shock spectra increased in their level (see Fig. 4, curves 2 _a , 2 _c ) in comparison with the shock spectra of the input action (see 4, (curves 1 _a , 1 _c ).

When an additional resonator M _{2 is} mounted on the table of the first resonator with stiffness C ₂ , which together with stiffness C ₁ provides the natural frequencies of the system formed by the platform M ₀ and resonators M ₁ and M ₂ equal to 3000 Hz and 5000 Hz, the input impact on the table of the second resonator transformed into a single impact with a peak acceleration value of 1900 m / s ² with a duration of ≈0.27 · 10 ^-3 s (see figure 1, curve c). The amplitude spectrum of the Fourier pin widened to 7000 Hz (see FIG. 2, curve a) and shock spectra to the level increased twice or more compared to the spectra of the input impact shock (see FIG. 4, curves 3 _and, 3 _c ).

As a result of the impact, the input shock pulse A ₀ = 1000 m / s ² with a duration τ = 0.5 · 10 ^-3 s (see Fig. 1, curve a) was transformed into a pulse with a peak value A ₁ = 1900 m / s ² with a duration of τ = 0.27 · 10 ^-3 s (see figure 1, curve c).

Thus, the proposed method allowed 1.9 times to increase the amplitude and reduce the duration of the test acceleration pulse.

Further sequential installation of resonators with increased stiffness from the platform to the test object also led to an increase in the peak value of the generated shock acceleration pulse and a decrease in its duration, which made it possible to increase the range and level of frequencies excited in the object.

The present invention made it possible to create a simple method for calculating characteristics of an object for impact testing, which together with existing test methods will allow testing on existing structures of impact stands with their ultimate operational capabilities, expanding the range and increasing the level of frequencies excited in the test objects.

Thus, the information presented indicates the fulfillment of the following set of conditions when using the claimed invention:

- the tool embodying the inventive method in its implementation, is intended to test the object for exposure to peak shock loads on existing structures of shock stands, with their own extreme operational capabilities;

- for the proposed method in the form in which it is described in the claims, the possibility of its implementation using the means and methods described in the application and known prior to the priority date is confirmed.

Therefore, the claimed invention meets the condition of "industrial applicability".

Information sources

[1] - Burago A.N. Stands for testing products for impact. / LDNTP, 1970, p. 13, Fig. 2.

[2] - USSR Copyright Certificate No. 1089445, G 01 M 7/00, publ. 04/30/84 g, prototype.

[3] - Lenk A., Renitz Yu. Mechanical testing of devices and apparatuses. / M., World. 1976, p. 40, FIG. 2.17 (there is no aftereffect).

Claims (1)

The method of testing the object for impact, in which the test object is mounted on a table of an elastic resonator mounted on a platform of the stand, which is subjected to a shock pulse, characterized in that between the table of the resonator and the test object is additionally set depending on the required range and the level of excitation in the object frequencies of one or more sequentially fixed elastic resonators with increasing rigidity from the platform to the test object, and the eigenfrequencies The sys tems of the system formed by the platform and the resonators are tuned to frequencies corresponding to the preliminarily calculated minima of the Fourier amplitude spectrum reproduced by the shock pulse stand.

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