SU1377679A1 - Apparatus for measuring internal friction of solid bodies - Google Patents

Abstract

This invention relates to a measurement technique. Improving the accuracy of measuring the internal friction of solids is due to the fact that test sample 6 oscillates on two film electrodes 9, 10, one of which is grounded, and the other is connected to a voltage source 11. Electrodes 9, 10 and sample 6 form a capacitor , the voltage on which is maintained constant due to the change in the electromotive force of the source 11, due to the change in capacitance between the electrodes 9, 10 and sample 6 on the resistor 15, the constant voltage drops. When the signal at the output of amplifier 12 is zero, the output voltage of the first comparator 17 changes sign and the first pulse shaper 18 produces pulses, the time interval between which is equal to the oscillation period of the sample 6. These pulses drive the saw voltage generator 19, from which the voltage is fed to the input of the second comparator 20 and to the input of the peak detector 21. The second pulse shaper 23 produces pulses that trigger the analog-to-digital converter 13, the output of which is measured The output values of the output signal of the amplifier 12 go to the memory of the computing unit 14, where the determination of the amount of internal friction takes place. 1 il. with S (L 09 O) h QD

Description

The invention relates to a measuring technique and can be used to study the physicomechanical properties of materials from measured parameters of freely damped oscillations.

The aim of the invention is to improve the accuracy of measuring internal friction by increasing the informative value of the signal.

The drawing shows a diagram of the device.

The device for measuring the internal friction comprises guides 1, on which two flat rectangular plates 2 and 3 of dielectric material, on which glass filaments 4 and 5 are fixed, are mounted along the guides 1 in the same plane. which sample 6 underlines in its node lines, two internal film electrodes 7 and 8 are applied to electrostatically excite transverse oscillations of sample 6 and two extreme film electrodes 9 and 10 to measure the maximum velocity before The motion of the part of sample 6 located in the region of the last electrodes. One of the ich extreme electrodes 10 is connected to a source of voltage 11, and the other is grounded. Voltage source 11, amplifier, analog-to-digital converter 13, computing unit 14 are connected in series. Parallel to the input of amplifier 12, a resistor 15 is turned on, and the output of amplifier 12 is connected via a voltage compensation unit I6 to a control input of a source of voltage. The amplifier 12 is also connected to the first., the input of the first comparator 17, the second input of which is grounded. The output of the first comparator 17 is connected to the input of the first driver 18 pulses, the output of the latter is connected to the control input of the driver 19 saw

different voltage, the output of which

connected to the first input of the second comparator 20 and to the input of the peak detector 21, which is through a divider

22 voltage is connected to the second input of the second comparator 20. The output of the latter through the second driver

23 pulses are connected to the control input of the analog-digital converter 13.

The device works as follows.

To excite oscillations in sample 6, an alternating voltage appears on electrodes 7 and 8 and transverse oscillations of sample 6 are excited electrostatically at mechanical resonance frequencies corresponding to the shape of the oscillations.

Measurement of the internal friction is performed after exclusion of the excitation when sample 6 makes freely damped oscillations.

A constant voltage is applied to one of the extreme electrodes 10 from the voltage source 1I. Maintaining a constant voltage U on a capacitor containing two extreme electrodes 9 and 10 and sample 6 is necessary, since this ensures the proportionality of the output signal Up ,, j of the speed of movement of a part of the sample in the region of electrode 10, through the equilibrium position.

In order to maintain a constant voltage and the electromotive force E of the voltage source 11 is changed according to the following law:

E

and + iR,

where and is the constant voltage; R is the resistance of the resistor 15, i, is the current in the circuit ground - electrode 9 - sample 6 - electrode 10 - voltage source 11 - resistor 15 - ground. This is accomplished with the aid of a voltage compensation unit 16, which is controlled by a force-input signal. tel 12.

Due to a change in electrical capacitance between electrodes 9 and 10 and sample 6, a variable voltage drops across resistor 15, which is amplified by amplifier 12. At times when. the signal at the output of amplifier 12 is equal to O, i.e. in moments

Ot | - - f 2ЧГ and cot - I M + 2 (to is the cyclic frequency of the sample 6, n is a positive integer), the output voltage of the first comparator 17 changes its sign. The first driver 18 pulses produces pulses at times V or tot Y + 2 u n, the time interval

between which is equal to the period of oscillation T of sample 6.

These pulses control the operation of the saw-tooth former 19. Between two consecutive pulses from the output of the first shaper 18 pulses, the output voltage of the shaper 19 the sawtooth of its voltage periodically linearly increases to the maximum value and proportional to the period of oscillation of the SRI T of the sample 6. The sawtooth at the output of the shaper 19 of the sawtooth voltage goes to the first the input of the second comparator 20 and the input of the peak detector 21, at the output of which a voltage appears and 5 which, separated by a voltage divider 22 into four, arrives at th input of the second comparator 20. At the instants (j t

 .-sh I j + 2 G „

and oat IT + 2 ir the output voltage of the second comparator 20

not sign. At times wt

+ 2T, the second pulse shaper 23 pulses the pulses, which at these moments trigger the analog-to-digital converter 13. The latter measures the instantaneous value of the output signal of the amplifier 12 proportional to the speed of movement of the portion of sample 6 located in the region of the outer electrodes 9 and .10 through equilibrium position. Measured values w. from the output of the analog-to-digital converter 13 enters the operative memory of the calculating unit 14. In the computing unit 14, two adjacent values Ug, and UBb) K.i4i use the formula

 IT In

and

BULL-1

and

& B1.

the amount of internal friction Q is determined.

50

five

0 5 0

five

Claims (1)

Invention Formula A device for measuring the internal friction of solids, containing two guides on which is movable, the base in the form of two flat rectangular plates of dielectric material, each of which has two film electrodes and one glass filament, characterized by that, for the purpose of measuring accuracy, it is additionally equipped with a peak detector, voltage divider, voltage compensation unit, connected in series by a voltage source, amplifier, pa allele input of which includes a resistor, an analog-to-digital converter and a computing unit connected in series by the first comparator, one input of which is grounded, and the second input is connected to the output of the amplifier, the first pulse shaper, the sawtooth driver, the second comparator and the second pulse shaper, output which is connected to the control input of the analog-digital converter, the input of the peak detector is connected to the output of the sawtooth generator, the output of the peaks Through the voltage divider connected to the second input of the second comparator, the input of the voltage compensation unit is connected to the output of the amplifier, the output of the voltage compensation unit is connected to the control input of the voltage source connected to one of the extreme electrodes, the second extreme electrode grounded