RU2234690C2 - Instruments and equipment shock test method - Google Patents

Abstract

FIELD: testing facilities.

SUBSTANCE: invention relates to methods of carrying out shock tests of equipment and instruments of complex articles. Proposed method comes to setting standard action in form of shock spectrum of accelerations, forming shock spectrum of acceleration in points of fastening of objects under testing by synthesizing shock excitation signal by means of elementary signals modulated in amplitude by half-sinusoid so that shock spectrum of summary resulting signal approximates required shock spectrum of accelerations at random degree of accuracy, and loading of abject under test with impulse, thus obtained. Basing on shock spectrum of accelerations, transfer functions from all sources of shock actions on article to places of attachment of equipment are determined and then maximum shock spectrum of accelerations from all sources of shock action for places of attachment of equipment is determined after which main carrier frequencies are discriminated from transfer functions and maximum shock spectrum of accelerations and damping factors in places of attachment of equipment are determined by said frequencies after which shock impulse of acceleration is formed according to definite dependence. Shock spectrum, thus formed, coincides with required standard shock spectrum of accelerations on carrier frequencies and differ from required spectrum within the limits of tolerable error.

EFFECT: possibility of complete accounting of mechanical properties of tested articles.

2 dwg

Description

Shock impacts are one of the types of mechanical stresses that affect the instruments and equipment of various machines during operation. To date, there are various approaches to conducting impact tests. Three basic methods are used to simulate impact effects. In the first method, the impact effect acting on the product under its operating conditions is accurately simulated. Complex impact is often replaced with simpler, but suitable for reproducing in the laboratory. For example, impact tests, presented in the form of simple acceleration pulses (half-wave sine wave, rectangular, triangular pulses, etc.). The second test method is to simulate the reaction of the product to impact. In this case, the type of impact during operation is not important, but it is important what reaction in the product caused this effect.

Under the reaction of the product is understood either the shock spectrum of accelerations, or some transitional characteristic. Recently, the most widespread tests (and the specification of standard loads) for impacts, presented in the form of a shock spectrum of accelerations. Such tests are most often carried out by reproducing shock loading on electrodynamic vibration stands using the method of amplitudes of elementary signals or the method of transfer function. (Testing technique. - A reference book in two books edited by V.V. Klyuyev. M., Mechanical Engineering, 1982, Book 1, pp. 334-337.

The essence of the method of reproducing the shock spectrum by the transfer function is to determine the given waveform in the application of the iterative procedure. The shock excitation signal is corrected using the transfer function of the system, which is a combination of the electrodynamic pathogen, mounting device and the test object. Then find the function of the Fourier transform of the given impact on the output of the system, which is divided by the transfer function of the test system, and produce the inverse Fourier transform of the obtained ratio, which gives the desired input effect in the time domain.

When synthesizing a shock excitation signal using elementary signals (prototype), the test method reduces to excitation of elementary signals, each of which consists of an odd number of half-cycles and is amplitude-modulated by a half-sine wave.

Each signal may be delayed relative to another signal.

When synthesizing a shock signal, it is necessary to determine the signal amplitudes so that the shock spectrum of the total signal approximates the shock spectrum of a given shock with an arbitrary degree of accuracy. As a first approximation, we take the shock spectrum with the frequency of the elementary signal equal to the frequency of its semi-sinusoidal envelope.

A significant disadvantage of these methods is the following. Often tests have to be carried out on the simplest impulses due to the inability to reproduce the required shock acceleration spectrum (USE), as a result of which it is necessary to overload the tested equipment in part of the frequency range in order to withstand the amplitude of the USU in the entire range. On the other hand, the shock spectrum does not unambiguously determine how the change in shock acceleration in time affects the object.

For example, a control system, adopted for autonomous testing of instruments and equipment, may contain spectrum components that are filtered out by the structure, or may not contain frequency components, on which a significant part of the impact energy is concentrated. This is because the algorithm for obtaining the control system implemented in the test method (prototype) under consideration does not take into account the features of the actual loading of the test object during operation. Any complex mechanical system is always a set of narrow-band resonators and broad-band filters.

The proposed solution will eliminate the above disadvantages.

The inventive method of impact testing of equipment and equipment of complex products is to set the standard impact in the form of a shock spectrum of accelerations, the formation at the points of attachment of the test object (equipment or other equipment) shock spectrum of accelerations. The impact is generated by synthesizing a shock excitation signal using elementary signals modulated in amplitude by a half-sine wave in such a way that the shock spectrum of the total resulting signal approximates the necessary shock spectrum of accelerations with an arbitrary degree of accuracy. Then, shock loading of the test object with the received impulse is carried out. It differs from the known test methods in that the shock functions of the accelerations determine the transfer functions from all sources of impact on the product to the attachment points of the apparatus and equipment. Then, the maximum shock spectrum of accelerations from all sources of shock for the places of attachment of equipment and equipment is obtained, after which the main carrier frequencies are extracted from the transfer functions and the maximum shock spectrum of accelerations and the attenuation coefficients are determined from these frequencies at the points of attachment of equipment and equipment. Next, form an acceleration shock pulse according to the formula

where ψ (t) is the shock pulse of acceleration;

A _i - acceleration amplitude at the i-th frequency (carrier);

ω _i = 2πf _i — intrinsic circular vibration frequency (carrier);

f _i is the natural frequency of the oscillations (carrier);

φ _i is the phase shift;

δ _i = lnζ _i ,

δ _i - logarithmic decrement of oscillations;

ζ _i is the attenuation coefficient;

i is the number of the current carrier frequency;

m is the number of carrier frequencies;

t is the duration of the shock pulse.

so that the shock spectrum formed coincides with the required normative shock spectrum of accelerations at the carrier frequencies, and in the rest of the spectrum it differs from the required spectrum within the margin of error.

The essence of the proposed solutions can be explained as follows. The shock spectrum of accelerations is the frequency conversion of the acceleration function from time to time (Doyar OP The algorithm for calculating the shock spectrum, in the collection. Dynamics of systems. Numerical methods for studying dynamic systems, Nistru, Kishenev, 1982). This is an integral characteristic, which includes both the reaction of the device (equipment) to impact, and the reaction of structural elements on which this equipment is installed. When passing an impact from the point of its origin to the attachment point, part of the impact energy is dissipated in the structure due to structural damping, friction, etc. But in addition to dissipating the impact energy in the structure at resonant frequencies, the effect of increasing the amplitude of the impact can occur. The control system for electrodynamic stands (only they can reproduce signals with a duration of less than 1 ms, as well as their combinations) should form a signal that would provide the necessary USU. Actually, the number of signals from which a test action can be formed is small. The error in signal formation is determined by how closely these frequencies correspond to real ones. Therefore, the most energy-consuming frequency components must be used to generate the signal. You can evaluate this with the help of transfer functions according to USU.

The concept of the transfer function is widely used in technology (see, for example, “Vibrations in technology.” Reference in 6 volumes, volume 5. Measurements and tests. M., Mechanical Engineering, 1981, p. 42. We use this concept in relation to shock The transfer function N (ω) according to the USD is understood here as the ratio of the USU at the point of impact to the USU at the control point:

where ω is the circular oscillation frequency, and τ ₀ (ω), τ _i (ω), the control unit at the point of impact and the control unit at the control point, respectively.

The transfer functions can be obtained either by calculation or experimentally, for example, on a dynamic prototype of the investigated product, for example, a spacecraft (SC), during design qualification, when instruments and equipment are still being developed, or on SC analogs.

There can be several sources of impact on a spacecraft: pyrotechnic devices, triggering and fixing of various mechanical devices, etc. The formation of the normative shock spectrum of accelerations involves the allocation of the maximum values of the control system in each frequency range. Then, usually, the envelope of the shock spectrum is constructed. At the same time, a part of the actions can already be set in the form of ready-made control devices (for example, the effect of a rocket on a spacecraft). Tests involving the creation of the required control system using transfer functions that take into account the features of the test circuit (equipment, type of stand, etc.), or using various iterative procedures, do not take into account the real frequency ranges in which the main energy of the shock is transferred. This approach significantly distorts the real picture of loading: the effect may not have the resonant frequencies that will be realized during the spacecraft operation. Obtaining transfer functions from all sources of shock influences shows at what frequencies the real device will be loaded. Carrier frequencies are here understood to be the natural frequencies of vibrations of a complex product (for example, a spacecraft), on which the bulk of the energy of the impact is transferred.

The allocation of carrier frequencies can be carried out, for example, as follows. The transfer functions from the shock sources show at what frequencies the shock attenuation is minimal, or it even increases due to resonance phenomena in the structure (transmission coefficients are greater than 1). On the other hand, the impact has peaks also at certain frequencies. When the frequencies of influence and the natural frequencies of the structure coincide, resonances arise. Obviously, these frequencies will always carry the bulk of the impact energy. When spacing the eigenfrequencies of the structure and external influences, we shall refer to the carrier frequencies those frequencies at which the control system is at the fastening points of the equipment at maximum. When there is experimental data on all sources of impact, the maximum USU constructed from all sources will show these frequencies. Sometimes it is impossible to reproduce the impact itself (for example, at the junction of the rocket with the spacecraft, the shock loads are set in the form of a ready-made control system). But the transfer functions from the junction with the rocket to the installation site of the device on the spacecraft make it possible to isolate the frequencies transmitting the impact.

The formation of the test impact, which has the required (standardized) control system and includes frequencies carrying the main energy of the shock, will allow a better quality of this type of test. Thus, a certain fairly formal characteristic (USM) is supplemented by a set of frequencies containing physical meaning. Destruction of equipment usually occurs if an external action produces a resonant response.

After allocating an array of carrier frequencies (and this procedure is poorly formalized and requires a certain amount of experience from the experimenter), various rather easily formalized algorithms for obtaining the necessary effect can be constructed. Consider one of them.

Let there be a certain set of actions A _m (t), m = 1, 2, ..., M.

For each of the impacts, its own shock spectrum is constructed, i.e. it turns out the dependence of acceleration on frequency

The algorithm for computing the control system is considered, for example, in [Doyar O.P. The algorithm for calculating the shock spectrum, in Sat System Dynamics. Numerical methods for the study of dynamical systems, Nistru, Kishenev, 1982].

We now consider the construction of the optimal action A (t)

providing the required accuracy. The construction of such an impact by the method of least squares is impossible. This follows from the fact that the shock spectra are nonlinear in the addition of various effects and, therefore, the smoothness of the derivatives of the shock spectrum with respect to the parameters α _m . Therefore, it seems more appropriate to use the collocation method in the algorithm (see Volkov EA, Numerical Methods. M., Nauka, 1987, 248 pp., 194-196), in which it is necessary to ensure the coincidence of the reference signal (shock spectrum ν * (ω)) with the shock spectrum from the action (shock pulse) A (t) only at a given set of points ω _k , (k = 1, 2, ..., N). The collocation method leads to the solution of a nonlinear system of equations

where k = 1, ..., M.

The solution to the system (*) can be performed in various ways. One of the possible algorithms was implemented in the application package of the measurement processing system, developed on the basis of the Matlab package, version 5.3, by the OBRAS subroutine (inverse spectrum). Given the real capabilities of the test equipment, a solution is sought in a class of functions of the form:

Where

ψ (t) is the shock pulse of acceleration;

A _i - acceleration amplitude at the i-th frequency (carrier);

ω _i = 2πf _i — intrinsic circular vibration frequency (carrier);

f _i is the natural frequency of the oscillations (carrier);

φ _i is the phase shift;

δ _i = lnζ _i ,

δ _i - logarithmic decrement of oscillations;

ζ _i is the attenuation coefficient;

i is the number of the current carrier frequency;

m is the number of carrier frequencies;

t is the duration of the shock pulse.

The attenuation coefficients were obtained from the test results according to the usual algorithm (see, for example, Babakov I.M. Oscillation Theory. M., Nauka, 1968, p. 65).

This greatly simplifies the search for a solution. The algorithm for finding the required function and the developed computer program belong to the know-how of this invention and are not considered in the application materials.

An example of practical implementation.

For the dynamic model of the device weighing 57 kg, it was necessary to conduct stand-alone impact tests specified in the form of shock acceleration spectra shown in the drawings.

Figure 1 shows the following USU:

1 - generalized USU obtained from various sources of shock effects on the spacecraft;

2 - normalized control system from the launch vehicle.

Figure 2 shows the transmission coefficient from the attachment point from one of the spacecraft CA (pyrozamka) to the device in question.

Based on the results of frequency tests of the spacecraft dynamic layout, transfer functions were obtained from the shock sources on the spacecraft to the attachment points of the instrument in question and 6 main frequencies were allocated:

2 frequencies determined the shock loading from the LV (~ 1.1-1.2 and 1.8-1.9 kHz),

3 frequencies determined the shock loading from the spacecraft’s own means (~ 2.7-2.9, 3.3-3.4 and 3.7-4.1 kHz),

and one carrier frequency determined the loading of the spacecraft when mechanical devices of solar batteries were triggered (~ 650-700 Hz).

According to the above algorithm, an effect was found that generates the necessary CSS.

In figure 1, under the number 3 shows the USU found by the considered algorithm.

The resulting CSS is generated by exposure

y = 100e ^-α1t sinω ₁ t + 463e ^-α2t sinω ₂ t;

where τ ₁ = 150, τ ₂ = 450; δ = ln2.

It should be noted that of the six initially selected reference frequencies to create a test mode that could be reproduced by the VEDS-10000 vibration stand, four frequencies were omitted. This was done due to the impossibility of the control system of the stand to correctly reproduce the load at 6 frequencies.

Two frequencies were left that determined the maximum load in the frequency range under consideration. Figure 1 shows two groups of frequencies f ₁ -f ₃ and f ₄ -f ₆ (ω _i = 2πf _i ). One of them corresponds to the effect of the launch vehicle and one corresponds to the operation of the spacecraft’s pyromedicines. The transmission coefficient (figure 2) shows that in the frequency range 2.4-3.6 kHz there is a resonance (Ko <1).

It should be noted that the resulting effect overlaps the control system from the LV in the frequency range up to 2 kHz (this was an additional requirement of the customer of the device, which was implemented using strict requirements on the accuracy of the control system implementation), and the effects of more than 1 kHz are filtered out by the design at fairly short distances. Those. the regulatory requirement for shock loading of the device from the LV in the frequency range of 1-2 kHz is clearly overstated. But even an inflated USU is implemented at frequencies at which the real energy of the impact is transferred.

Evaluation by the energy method of such loading shows that approximately 80% of the impact energy is determined by 2 of these frequencies.

Claims (1)

The method of impact tests of apparatus and equipment, which consists in setting the normative impact in the form of an acceleration shock spectrum, forming at the attachment points of the acceleration shock spectrum test object by synthesizing the shock excitation signal using elementary signals modulated in amplitude by a half-sine wave so that the total impact spectrum the signal approximated the necessary shock spectrum of accelerations with an arbitrary degree of accuracy, and loading the test object with the received impulse, characterized in that the shock functions of the accelerations determine the transfer functions from all sources of impact on the product to the points of attachment of equipment and equipment, then get the maximum shock spectrum of accelerations from all sources of shock for places of attachment of equipment and equipment, after from which the main carrier frequencies are distinguished from the transfer functions and the maximum shock spectrum of accelerations and the attenuation coefficients are determined from these frequencies estah fastening apparatus and equipment, whereupon a shock acceleration pulse form by the formula:

where ψ (t) is the shock pulse of acceleration; And _i is the acceleration amplitude at the i-th frequency (carrier); ω _i = 2πf _i — intrinsic circular vibration frequency (carrier); f _i is the natural frequency of the oscillations (carrier); φ _i is the phase shift;

δ _i = lnζ _i ; δ _i - logarithmic decrement of oscillations; ζ _i is the attenuation coefficient; i is the number of the current carrier frequency; m is the number of carrier frequencies; t is the shock pulse action time; so that the shock spectrum formed coincides with the required normative shock spectrum of accelerations at the carrier frequencies, and in the rest of the spectrum it differs from the required spectrum within the margin of error.

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