SU754250A1 - Device for measuring fatigue durability of engineering structures - Google Patents

Description

one

The device relates to the measurement technique and is designed to measure and predict the fatigue life of engineering structures.

A device for measuring fatigue life of machine-building structures exposed to random loads is known, comprising a recorder and a serially connected strain-to-electric converter, an amplifier, a unit for measuring the root-mean-square value, a non-linear conversion unit and a filter with tunable frequency response [Ϊ].

A disadvantage of the known device is low accuracy due to measurement errors in the restructuring of the frequency response of the filter.

The purpose of the invention is to improve the accuracy of measurement.

This is achieved by the fact that the device is equipped with a reference voltage source, serially connected by a differentiation unit, a second RMS measurement unit, a second non-second unit.

2

linear conversion and a sensor, the output of which is connected to the recorder input, the second input of it with the output of the first nonlinear conversion unit, and the third with the reference voltage source, and the input of the differentiator connected to the output of the amplifier.

The drawing shows the block diagram of the device.

The device contains a source of reference voltage 1, a serially connected converter 2 of deformation into an electrical signal, an amplifier .3, a unit 4 measuring the root-mean-square value, a resistive divider 5, a block b of a nonlinear pre-20 formation, a series-connected differentiation unit 7, a second block 8 measuring the root-mean-square . the second nonlinear conversion unit 9, the adder 10, the transistor 11. The second input of the adder 10 is connected to the output of the first nonlinear conversion unit 6, and the third to the source 1 ′ of the reference voltage, the input of the differentiation unit 7 30 to the output of the amplifier 3. ·

3

754250

four

Resistive divider 5 contains τη resistors 12, 13 ... 14. Blocks 6 and 9 of nonlinear conversion are identical and contain operational amplifiers 15 and 16, the feedback circuit of which includes nonlinear elements · 17 and 18 with a logarithmic conversion characteristic, which is given by resistors 19 and 20 and nonlinear elements 17 and 18. Adder 10 contains operational an amplifier 21, summing resistors 22 and 23, and a feedback resistor 24. The outputs of blocks 6 and 9 of the nonlinear conversion are connected to the inverting input 25 of the operational amplifier 21 through summing resistors 22 and 23.

The source 1 of the reference voltage is connected to the non-inverting input 26 of the operational amplifier 21.

The device works as follows.

To the input of the amplifier 3 from the deformation converter 2, a signal-analogue of the dynamic stresses arising on the tested product is fed into the electrical signal. From the output of amplifier 3, the signal enters two parallel circuits. The first circuit unit 4 measures the rms value, the resistive divider 5, unit 6 non-linear conversion performs the signal conversion on the law

where _1st - the output voltage at the output of block 6;

t is the coefficient specified by block 5;

56 is the rms value of the signal at the output of block 4.

The second circuit - the differentiation unit 7, the second measurement unit of the measurement of the rms value and the nonlinear conversion unit 9 - performs the signal conversion according to the law

^ 2eh ⁼

where 1½ is the output voltage of you ’* block 9;

5ώ - the rms value of the derivative of the signal at the output of block 8.

The received signals and _1v1X and and _2b1x ³ come along with the voltage

and _{ai | x} = Food. source 1 of the reference voltage to the input of the adder, the output of which produces a signal proportional to £ d a- (t £ d 56 + · Un $ 6), which is recorded by the recorder 11.

The use of the proposed device will improve the accuracy of the measurements, since there is no filter with a tunable frequency response, which introduces significant errors.

Claims (1)

Claim 20 Device for measuring the fatigue life of engineering structures under random loads, containing the recorder and sequentially -c converter connected ^£ tions deformation into an electric signal, an amplifier unit rms measurement nonlinear transformation unit, characterized in that, in order to increase the accuracy of measurement, it is provided with a reference voltage, series connected differentiating unit, the second measuring unit rms second block 35 nonlinear conversion and an adder, the output of which is connected to the input of the recorder, its second input with the output of the nonlinear conversion unit, and the third with the source 40 of the reference voltage, and the input of the differentiator is connected to the output of the amplifier.