RU2369850C1 - Method of determining damping characteristics of multilayer devices during impact action - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: present invention relates to impact testing and can be used mainly in high-intensity impact tests for various devices, comprising multilayer devices in form of, for example stacks of plates made from composite materials, honeycomb panels etc. The method of determining damping characteristics of multilayer devices during impact action involves applying impact action on the test device using a pyrotechnic device, measuring momentum and determining dynamic reaction of the test device using accelerometres and strain sensors. The strain wave is first generated in a waveguide without the test object. After that by analysing amplitude spectra and shock spectra of accelerations, a conclusion can be made on damping characteristics of the multilayer device. A damping model is made first from material of the layers of the multilayer device. Impact action is then generated in the waveguide without the test object, while measuring amplitude of shocks from the minimum, produced by the test equipment, to the maximum operating levels. Further, the multilayer device is then tested in several stages, loading one its layers on each stage. Amplitude of shocks on each stage is varied from minimum values, produced by the test equipment, to maximum operational levels, after which the direction of the impact action on the multilayer device is changed to the opposite and all stages of testing the multilayer device are repeated. By analysing the vibration record and strain record, amplitude spectra and shock spectra of accelerations, the damping model of material of the layers of the multilayer devices and the device as a whole is applied using a given formula.

EFFECT: increased accuracy of determining damping mechanism and its numerical characteristics.

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Description

The present invention relates to the field of impact tests and can be used primarily for testing high-intensity impacts of various devices incorporating multilayer devices in the form, for example, of packs of plates made of composite materials, honeycomb panels, etc.

The most general approach to determining the damping properties, which consists in exciting vibrations in the test sample, measuring the exciting force applied at a given point, determining the dynamic response using accelerometers and strain gauges, and then comparing the amplitude-frequency characteristics before and after the shock absorber is formulated in the book: A. Nashif et al. Damping of oscillations, p. 190, - M .: Mir, 1988.

For carrying out shock tests, various methods are used, which are described in patent materials: SU 1249363 A1, SU 1518691 A1, SU 18H276 A1 and several others. The closest is the "Impact Test Method" according to the patent of the Russian Federation No. 224909 C2. The method of impact tests, which consists in impact on the device under test using a shared pyrotechnic device, measuring the force impulse and determining the dynamic response of the device under test using accelerometers and deformation sensors, whereby a deformation wave is created in the waveguide without an installed test object, after which analysis of amplitude spectra and shock spectra of accelerations make a conclusion about the damping properties of a multilayer device.

The disadvantages of this test method include the fact that for determining the damping mechanisms in multilayer structures (such as a sandwich) made of various materials, the integral damping value (for example, a decrease in the acceleration amplitude during the passage of a shock wave through a device) can vary greatly under different influences. This difference is explained by various damping mechanisms that are implemented in different materials at different levels of impact.

The present invention is to improve the accuracy of determining the damping mechanism and its numerical characteristics.

This task is achieved by first developing damping models in the materials of the layers of the multilayer device, then creating shock effects in the waveguide without an installed test object, changing the amplitudes of the impacts from the minimum reproducible by the test equipment to the maximum operational levels, then testing the multilayer device in several stages loading at each stage one of its layers, while the amplitudes of the impacts at each stage are changed from the minimum values, produced by testing equipment to the maximum operational levels, after which they change the direction of impact on the multilayer device to the opposite and repeat all stages of testing the multilayer device, and, based on the analysis of vibration programs and tensograms of amplitude spectra and shock spectra of accelerations, adopt a damping model in the materials of layers of multilayer devices and devices as a whole according to the formula

, и

, and

where L _m - "m" damping model, in which the Δ value is minimal;

Δ is the difference between the calculated and experimental values;

"ω" is the circular frequency;

I is the number of shock impact ranges;

"i" is the number of the impact range;

J is the number of tests (design cases);

"j" is the number of tests (design case);

T is the number of reference points in time;

H is the number of frequency ranges;

"η" is the number of frequency ranges;

ε _ijn (t _ξ ) - experimental values of strains in the "i" range of impacts at the "ξ" point in time during the "J" test at the "n" control point;

- расчетные значения в "i" диапазоне ударных воздействий в "ξ" момент времени при "J" испытании в "n" точке контроля;

- calculated values in the "i" range of impacts at the "ξ" point in time during the "J" test at the "n" control point;

- норма по деформациям;

- rate of deformation;

N is the number of control points for deformations;

"n" is the number of the deformation control point;

Θ _ijη is the weight coefficient for deformations;

экспериментальные значения ускорений в "i" диапазоне ударных воздействий в "ζ" момент времени при "J" испытании;

experimental values of accelerations in the "i" range of impacts at the "ζ" point in time during the "J"test;

- расчетные значения ускорений в "i" диапазоне ударных воздействий в "ζ" момент времени при "J" испытании в "k" точке контроля;;

- calculated values of accelerations in the "i" range of impacts at the "ζ" point in time during the "J" test at the "k" control point ;;

- весовой коэффициент по ускорениям;

- weighting coefficient for accelerations;

- норма по ускорению;

- rate of acceleration;

K is the number of control points for acceleration;

"k" is the number of the control point for acceleration;

"ζ" - number of time reference for accelerations;

- экспериментальные значения амплитудного спектра в "i" диапазоне ударных воздействий в "η" частотном диапазоне при "J" испытании в "k" точке контроля;

- experimental values of the amplitude spectrum in the "i" range of impacts in the "η" frequency range during the "J" test at the "k" control point;

- расчетные значения амплитудного спектра в "i" диапазоне ударных воздействий в "η" частотном диапазоне при "J" испытании в "k" точке контроля;

- calculated values of the amplitude spectrum in the "i" range of impacts in the "η" frequency range for the "J" test at the "k" control point;

- норма по амплитудному спектру;

- the norm in the amplitude spectrum;

- весовой коэффициент по амплитудному спектру;

- weight coefficient in the amplitude spectrum;

- экспериментальные значения ударного спектра ускорений в "i" диапазоне ударных воздействий в "η" частотном диапазоне при "J" испытании в "k" точке контроля;

- experimental values of the shock spectrum of accelerations in the "i" range of impacts in the "η" frequency range during the "J" test at the "k" control point;

- расчетные значения ударного спектра ускорений в "i" диапазоне ударных воздействий в "η" частотном диапазоне при "J" испытании в "k" точке контроля;

- calculated values of the shock spectrum of accelerations in the "i" range of impacts in the "η" frequency range during the "J" test at the "k" control point;

- норма по ударному спектру ускорений;

- the norm on the shock spectrum of accelerations;

- весовой коэффициент по ударному спектру ускорений.

- weight coefficient for the shock spectrum of accelerations.

The essence of the invention is illustrated as follows.

When impacted on sandwich-type multilayer devices made of various materials, various damping mechanisms can be implemented in the materials. It is especially important to identify these mechanisms and obtain numerical values of damping for a device when analyzing impacts on structures using finite element modeling methods.

For example, steels behave linearly over a sufficiently large segment of the “dress-strain” diagram, and here we can apply the classical model of viscous friction, when the scattering is proportional to the speed of motion. The logarithmic decrement of oscillations in this case is from hundredths to tenths of a unit. The hysteretic damping mechanism (viscoelastic friction) is often implemented in composite materials such as carbon plastics.

Under the effects of high intensity, damping models are significantly complicated. For example, in the installation area of pyrotechnic devices, damping is represented as combined pseudo-viscosity (as the sum of linear pseudo-viscosity and Neumann-Richtmeier pseudo-viscosity).

Those. At the first stage of obtaining the damping characteristics of devices, it is necessary to adopt a damping model, within which damping characteristics will be determined. There can be several models: both for different materials, and for different ranges of impact effects.

The next step is to obtain in the waveguide shock parameters from a pyrotechnic device consisting of pyro bolts and a set of inserts of various materials (acoustic filter), which allows varying the magnitude of the shock effect on the waveguide. This stage passes without the device under study, the installation of which at the next stage will allow us to compare vibrograms (acceleration graphs), tensograms (strain graphs), amplitude spectra, showing the distribution of amplitudes of accelerations and deformations in frequency and shock acceleration spectra, showing the maximum possible accelerations at different frequencies .

Consistent impact on different layers of the device allows you to get enough information to build damping models. When analyzing the results, the influence of part of the device layers on damping is excluded.

The essence of the proposed solution is illustrated by drawings, where Figures 1-3 show a shock test bench, which consists of a shock loading device 1 and waveguides 2. The shock source is a split pyrotechnic device 1. Between the shock source 1 and the waveguide 2 a set of liners 3 with different acoustic flexibility is installed, made in the form of glasses on a threaded leg. Between the set of liners 3 and the waveguide 2, a docking device 4 is installed, made in the form of a thick-walled cylinder with a bottom 5. A thread 6 is made on the inner diameter of the cylinder to connect the cylinder with a set of liners, and the bottom has a hole 7 for a bolt 8, while along the edges of the bottom flange 9 is made. The diameter and width of the cylinder flange are equal to the diameter and wall thickness of the waveguide, and at the end of the waveguide 2 there is an insert 10 with a hole with thread 11, the diameter and pitch of which is equal to the diameter and pitch of the bolt. The test object 12 is placed between the docking device 4 and the end face of the waveguide 2. Moreover, the test object 12 is tightly pressed to the ends 13 of the waveguide 2 due to the shoulder 9 of the docking device 4 and the bolt 8. To ensure the transmission of shock directly to the test layer in test object 12 (multilayer device) a cylindrical hole 14 is cut to the desired layer 15.

The very procedure for determining the damping properties of multilayer devices by the formula (*) is performed as follows.

Of course, an element model (CEM) of an impact stand without a multilayer test device and with a multilayer device is built. According to the test results without a device, verification of the design scheme is carried out. Then, a multilayer device model with developed damping models is added to the CEM, and accelerations, deformations, amplitude spectra, and shock acceleration spectra are calculated.

Further, shock tests are carried out in accordance with the algorithm described above. Then, according to the formula (*), the Δ value is calculated for different levels of impacts and models. Formula (*) is based on the ideology of the least squares method (the differences of the squares of the compared quantities are summed). The introduction of standardizing coefficients makes these differences dimensionless, and weighting coefficients make it possible to take into account additional information about the tests and increase the influence on the decision-making of the most important recorded parameters and amplitude-frequency ranges of effects for a particular device. After that, the damping model, at which the minimum Δ value is obtained, is adopted as the damping model of the multilayer device under study.

The considered algorithm for obtaining the minimum Δ value is implemented in the MatLab package in macros written in the Simulink language. But these programs belong to the "know-how" of the invention and are not discussed in further materials of the application.

Practical example

To protect one of the shock-sensitive devices, the circuit board was made of a multilayer material (layers of aluminum, carbon fiber, fiberglass and a central layer of foam). The stand CEM was built in the PATRAN preprocessor, and the calculations were performed in the DYTRAN package. The KEM stand consisted of 6137 nodes and 17217 elements. The layer model was adopted in the form of plates with constant damping. Since the device should be installed in the zone of increased impact (from 2 to 5 thousand g according to USU), the combined pseudo-viscosity model, which is the sum of the quadratic and linear pseudo-viscosities, was taken as the basis of the damping model (see, for example, Applied Solid Mechanics Wednesday / Edited by V.V. Selivanov in 3 volumes, Vol.3, Babkin A.V., Kolpakov V.I. Okhotin, V.N. Selivanov V.V. Numerical methods in problems of explosion physics and shock. - M.: Publishing house of MSTU, 2000.-516 p.)

P - stress, Q - pseudo viscosity

Variable parameters here are: C - linear pseudo-viscosity and C _L- quadratic pseudo-viscosity.

As an example, consider building a model for the second layer (carbon fiber). The tests were carried out on a shock stand SPI6.3480-0. Impacts ranged from 1000g (a cushioning rod consisting of 5 layers of the following materials was used: textolite-aluminum-steel-aluminum-textolite and steel docking device) to ~ 10000g when a burst bolt was installed in the docking device. Accelerations were recorded at 4 points with ABC052 accelerometers, and deformations at 6 points with KF5 strain gauges. The impact was varied across 8 levels (by changing the set of liners and replacing the burst bolts 8 × 54 with less powerful 8 × 55). At each level, 3 actuation bolts were performed. Registration and processing of measurement results was carried out in the frequency range up to 10 kHz. The total error did not exceed 20%.

Processing the results by the formula (*) allowed us to accept the following pseudo-viscosities: linear pseudo-viscosity - 0.8 and quadratic pseudo-viscosity - 4.

It should be noted that in the frequency range up to 2 kHz, when modeling the entire multilayer device, one can take the values of the VDAMP coefficient (for models in the DYTRAN software package) associated with the critical damping coefficient of ~ 0.00008.

Of the sources of information and patent materials known to the authors, the totality of features similar to the totality of features of the claimed objects is not known.

Claims (1)

A method for determining the damping characteristics of multilayer devices under impact, which consists in impact on the device under test using a shared pyrotechnic device, measuring the momentum of the force and determining the dynamic response of the device under test using accelerometers and deformation sensors, whereby a deformation wave is created in the waveguide without an installed test object after which, based on the analysis of amplitude spectra and shock spectra of accelerations, a conclusion is made on the damping x the properties of the multilayer device, characterized in that first damping models are developed in the materials of the layers of the multilayer device, then shock waves are created in the waveguide without an installed test object, changing the amplitudes of the impacts from the minimum reproducible by the test equipment to the maximum operating levels, then the multilayer device is tested in several stages, loading at each stage one of its layers, while the amplitudes of the impacts at each stage change t of the minimum values reproduced by the test equipment to the maximum operating levels, after which they change the direction of the impact on the multilayer device to the opposite and repeat all the stages of testing the multilayer device, and, based on the analysis of vibration programs and tensograms, amplitude spectra and shock spectra of accelerations, adopt the damping model in materials layers of multilayer devices and the device as a whole according to the formula

, and

where L _m - m damping model, in which the value of A is minimal;
Δ is the difference between the calculated and experimental values;
ω is the circular frequency;
I is the number of shock impact ranges;
i is the number of the shock impact range;
J is the number of tests (design cases);
j is the number of tests (design case);
T is the number of reference points in time;
H is the number of frequency ranges;
η is the number of frequency ranges;
ε _ijn (t _ξ ) - experimental values of strains in the i range of impacts at ξ moment of time during the J test at the n point of control;

- calculated values in the i range of impacts at ξ time point during the J test at the n point of control;

- rate of deformation;
N is the number of control points for deformations;
n is the number of the control point for deformations;
Θ _ijη is the weight coefficient for deformations;

- experimental values of accelerations in the i range of impacts at the ζ moment in time during the J test;

- calculated values of accelerations in the i range of impacts at the ζ point in time during the J test at the k control point;

- weighting coefficient for accelerations;

- rate of acceleration;
K is the number of control points for acceleration;
k is the number of the control point for acceleration;
ζ is the number of the time reference for accelerations;

- experimental values of the amplitude spectrum in the i range of shock effects in the η frequency range for the J test at the k control point;

- calculated values of the amplitude spectrum in the i range of shock effects in the η frequency range for the J test at the k control point;

- the norm in the amplitude spectrum;

- weight coefficient in the amplitude spectrum;

- experimental values of the shock spectrum of accelerations in the i range of impacts in the η frequency range during the J test at the k point of control;

- calculated values of the shock spectrum of accelerations in the i range of impacts in the η frequency range for the J test at the k point of control;

- the norm on the shock spectrum of accelerations;

- weight coefficient for the shock spectrum of accelerations.

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