A method for calculating the heat output of a bonded medium temperature strain gauge

Abstract

The present application relates to a kind of sticking type medium temperature strain gauge heat output calculation method, comprising the following steps: heat output strain decomposition;Carry out simulation analysis, calculate the influence coefficient of adhesive;Carry out test, and the resistance temperature coefficient of strain gauge is calibrated;Carry out test, and the linear expansion coefficient of strain gauge is calibrated;The heat output of the material strain gauge of the test piece is calculated.The method is through strain gauge heat output decomposition, calibrates heat output parameter and heat output calculation etc., only uses twice strain test, and the heat output strain of test piece material is calculated, and the heat output test of test piece material is saved.

Description

TECHNICAL FIELD

[0001] The application relates to a method for calculating thermal output of a pasting type medium-temperature strain gauge, and belongs to the field of structural thermal strength test. BACKGROUND

[0002] The structural thermal strength problem in a force-thermal environment is an important strength problem faced by a high-speed reentry aircraft, and strain measurement of a pasting type medium-temperature strain sensor encounters some problems in current engineering application. The medium-temperature strain measurement sensor comprises concepts of indicated strain, stress strain, thermal output strain and the like. Currently, the conventional method is to directly measure the indicated strain of the sensor, obtain the thermal output strain through a thermal output test, and obtain the stress strain through calculation. The same type of strain gauge needs to be used for strain measurement of structures made of different materials, and a thermal output test needs to be conducted, which is not conducive to test resources and test time. SUMMARY

[0003] (I) Technical problem to be solved

[0004] In view of the above problems in the prior art, the application provides a method for calculating thermal output of a pasting type medium-temperature strain gauge. The method comprises the steps of thermal output decomposition of a strain gauge, calibration of thermal output parameters and thermal output calculation, and only two strain tests are needed to calculate the thermal output strain of a test piece material, so that the thermal output test of the test piece material is omitted.

[0005] (II) Technical scheme

[0006] A method for calculating thermal output of a pasting type medium-temperature strain gauge comprises the following steps.

[0007] S1. Thermal output strain decomposition;

[0008] S2. Simulation analysis is conducted to calculate the influence coefficient of the adhesive;

[0009] S3. A test is conducted to calibrate the temperature coefficient of resistance of the strain gauge;

[0010] S4. A test is conducted to calibrate the linear expansion coefficient of the strain gauge;

[0011] S5. Thermal output of the strain gauge of the test piece material is calculated.

[0012] In the step S1, the thermal output of the strain gauge is decomposed into the following expression:

[0013]

[0014] In the formula (1), the following applies:

[0015] ε t is the thermal output of the strain gauge;

[0016] γ胶 γ is the influence coefficient of the adhesive;

[0017] k t k is the sensitivity coefficient of the strain gauge;

[0018] α is the resistance temperature coefficient of the strain gauge material;

[0019] β1 is the linear expansion coefficient of the material of the test piece;

[0020] β2 is the linear expansion coefficient of the strain gauge material;

[0021] ΔT is the temperature change amount.

[0022] In the step S2, a finite element model of the strain gauge adhesive is established, a rectangular shell element is used to simulate the strain gauge adhesive, wherein the shell element thickness attribute is the strain gauge adhesive thickness, half of the strain gauge adhesive thickness is set as the bias amount, i.e. the strain gauge adhesive grid position is at the bottom surface, the length and width are the length and width of the strain gauge adhesive respectively, a hexahedron element is used to simulate the test piece, the length dimension is more than 10 times of the adhesive length dimension, the connection between the nodes of the strain gauge adhesive and the test piece is simulated by the common nodes, 3 translational degrees of freedom and 3 rotational degrees of freedom of all the nodes of one end surface of the test piece are constrained, the forced deformation in the length direction of the strain gauge is applied to all the nodes of the other end surface, the normal strain on the upper and lower surfaces of the strain gauge adhesive shell element is extracted from the finite element static strength analysis result, and then the influence coefficient γ of the adhesive is obtained. 胶 The calculation formula is as follows:

[0023]

[0024] In the above formula (2), ε

[0025] ε x上 is the normal strain on the upper surface of the strain gauge adhesive shell element;

[0026] ε x下 is the normal strain on the lower surface of the strain gauge adhesive shell element.

[0027] In the step S3, the indicated strain of the strain gauge within the applicable temperature range of the medium temperature strain gauge is measured to obtain the resistance temperature coefficient α of the strain gauge material; at least 5 temperature values are selected from room temperature to the limit temperature range of the strain gauge, the strain gauge is placed in the oven, the temperature is slowly increased at a rate of 1℃ / s from room temperature, the indicated strain of the strain gauge corresponding to each temperature value is measured, and the resistance temperature coefficient α of the strain gauge is obtained by the following formula:

[0028] α = ε 空 k t / ΔT (3)

[0029] In the above formula (3): ε 空 is the indicated strain of the suspended strain gauge.

[0030] In the above step S4, a test piece with a known linear expansion coefficient is used as a calibration test piece to measure the indicated strain of the medium temperature strain gauge in the applicable temperature range, and the linear expansion coefficient β2 of the strain gauge is obtained; the strain gauge is adhered to the calibration test piece by an adhesive, and the temperature value corresponding to the indicated strain of the medium temperature strain gauge is selected, and at least 5 temperature values are selected from room temperature to the limited temperature range of the strain gauge; the test piece is placed in a temperature chamber in a free expansion state, and the temperature is slowly raised at a rate of 1℃ / s from room temperature, and the indicated strain of the strain gauge corresponding to each temperature value is measured, and the linear expansion coefficient β2 of the strain gauge is obtained by the following formula:

[0031]

[0032] In the above formula (4):

[0033] β 1标 is the linear expansion coefficient of the calibration test piece;

[0034] ε t标 is the indicated strain of the calibration test piece.

[0035] In the above step S5, the values of γ 胶 , α, β2 obtained in steps S2 to S4 and the linear expansion coefficient β1 of the test piece are substituted into formula (1) to obtain the heat output of the test piece.

[0036] (III) Beneficial effects

[0037] The adhesive type medium temperature strain gauge heat output calculation method of the present application, through strain gauge heat output decomposition, calibration heat output parameter and heat output calculation steps, only two times of strain test are used to calculate the heat output strain of the test piece material, and the heat output test of the test piece material is omitted.

[0038] Drawings of the specification

[0039] Figure 1 Schematic diagram of the adhesive finite element model modeling method of step S2 of the method of the present application DETAILED DESCRIPTION

[0040] An adhesive type medium temperature strain gauge heat output calculation method, comprising the following steps:

[0041] S1. Heat output strain decomposition;

[0042] S2. Simulation analysis is carried out to calculate the influence coefficient of the adhesive;

[0043] S3. Test is carried out to calibrate the resistance temperature coefficient of the strain gauge;

[0044] S4. Develop a test to calibrate the strain gauge linear expansion coefficient;

[0045] S5. Calculate the strain gauge thermal output of the test piece material.

[0046] In the above step S1, the strain gauge thermal output is decomposed as follows:

[0047]

[0048] In the above formula (1):

[0049] ε t is the strain gauge thermal output;

[0050] γ 胶 is the adhesive influence coefficient;

[0051] k t is the strain gauge sensitivity coefficient;

[0052] α is the strain gauge material resistance temperature coefficient;

[0053] β1 is the test piece material linear expansion coefficient;

[0054] β2 is the strain gauge material linear expansion coefficient;

[0055] ΔT is the temperature change amount.

[0056] Referring to Figure 1 , in the above step S2, a strain gauge adhesive finite element model is established, a rectangular shell element is used to simulate the strain gauge adhesive, the shell element thickness attribute is the strain gauge adhesive thickness, half of the strain gauge adhesive thickness is set as the offset amount, i.e. the strain gauge adhesive grid position is at the bottom surface, the length and width are the length and width of the strain gauge adhesive, a hexahedral element is used to simulate the test piece, the length dimension is more than 10 times the length dimension of the adhesive, the nodes of the strain gauge adhesive are connected to the test piece through co-nodes, 3 translational degrees of freedom and 3 rotational degrees of freedom of all nodes of one end surface of the test piece are constrained, a forced deformation in the length direction of the strain gauge is applied to all nodes of the other end surface, the normal strain on the upper and lower surfaces of the strain gauge adhesive shell element is extracted from the finite element static strength analysis result, and then the adhesive influence coefficient γ 胶 The calculation formula is as follows:

[0057]

[0058] In the above formula (2):

[0059] ε x上 is the normal strain on the upper surface of the strain gauge adhesive shell element;

[0060] ε x下 ε

[0061] In step S3, the indicated strain of the suspended strain gauge is measured within the temperature range of the medium temperature strain gauge to obtain the temperature coefficient of resistance α of the strain gauge material; the temperature value corresponding to the indicated strain of the medium temperature strain gauge is selected, and at least 5 temperature values are selected from room temperature to the limited temperature range of the strain gauge; the strain gauge is suspended and placed in the oven, and the indicated strain of the strain gauge corresponding to each temperature value is measured at a temperature rising rate of 1℃ / s from room temperature, and the temperature coefficient of resistance α of the strain gauge is obtained by the following formula:

[0062] α=ε 空 k t / ΔT (3)

[0063] In formula (3), ε 空 is the indicated strain of the suspended strain gauge.

[0064] In step S4, a test piece with a known linear expansion coefficient is used as a calibration test piece to measure the indicated strain of the medium temperature strain gauge within the applicable temperature range to obtain the linear expansion coefficient β2 of the strain gauge; the strain gauge is adhered to the calibration test piece by an adhesive, and the temperature value corresponding to the indicated strain of the medium temperature strain gauge is selected, and at least 5 temperature values are selected from room temperature to the limited temperature range of the strain gauge; the test piece is placed in the oven in a free expansion state, and the indicated strain of the strain gauge corresponding to each temperature value is measured at a temperature rising rate of 1℃ / s from room temperature, and the linear expansion coefficient β2 of the strain gauge is obtained by the following formula:

[0065]

[0066] In formula (4), β

[0067] β 1标 is the linear expansion coefficient of the calibration test piece;

[0068] ε t标 is the indicated strain of the calibration test piece.

[0069] In step S5, the values of γ 胶 , α, β2 obtained in steps S2 to S4 and the linear expansion coefficient β1 of the test piece are substituted into formula (1) to obtain the heat output of the test piece.

Claims

1. A method of calculating the heat output of a bonded mid-temperature strain gauge, characterized by, The method comprises the following steps: S1. thermal output strain decomposition; S2. simulation analysis is carried out to calculate the influence coefficient of the adhesive; S3. test is carried out to calibrate the resistance temperature coefficient of the strain gauge; S4. test is carried out to calibrate the linear expansion coefficient of the strain gauge; S5. the thermal output of the strain gauge of the tested material is calculated; In the above step S1, the thermal output of the strain gauge is decomposed into the following expression: In the above formula (1): ε t Strain gauge heat output; gamma 胶 The influence coefficient of the adhesive; k t is the sensitivity coefficient of the strain gauge α is the resistance temperature coefficient of the strain gauge material; β1 is the linear expansion coefficient of the tested material; β2 is the linear expansion coefficient of the strain gauge material; ΔT is the temperature change.

2. The method according to claim 1, wherein In step S2, a finite element model of the strain gauge adhesive is established, a rectangular shell element is used to simulate the strain gauge adhesive, a half of the thickness of the strain gauge adhesive is set as a bias, i.e. the grid position of the strain gauge adhesive is at the bottom surface, the length and the width are respectively the length and the width of the strain gauge adhesive, a hexahedron element is used to simulate the test specimen, the length dimension is more than 10 times of the length dimension of the adhesive, the connection between the nodes of the strain gauge adhesive and the test specimen is simulated by co-nodes, 3 translational degrees of freedom and 3 rotational degrees of freedom of all nodes of one end surface of the test specimen are constrained, a forced deformation in the length direction of the strain gauge is applied to all nodes of another end surface, the normal strain on the upper and lower surfaces of the shell element of the strain gauge adhesive is extracted in the static strength analysis result of the finite element, and the influence coefficient γ of the adhesive is calculated. 胶 The calculation formula is as follows: In the above formula (2): ε x上 Normal strain on the upper surface of the strain gage adhesive shell unit; ε x下 Normal strain to the lower surface of the strain gage adhesive shell unit.

3. The method according to claim 2, wherein In the above step S3, the resistance temperature coefficient α of the strain gauge material is obtained by measuring the indicated strain of the suspended strain gauge within the applicable temperature range of the medium temperature strain gauge; at least 5 temperature values are selected from room temperature to the limited temperature range of the strain gauge; the strain gauge is slowly warmed from room temperature at a temperature rising rate of 1℃ / s, the indicated strain of the strain gauge corresponding to each temperature value is measured, and the resistance temperature coefficient α of the strain gauge is obtained by the following formula: a = e 空 k t / AT (3) In the above formula (3): ε 空 is the indicated strain of the suspended strain gauge.

4. The method according to claim 3, wherein In the above step S4, a test piece with a known linear expansion coefficient is used as a calibration test piece to measure the indicated strain of the medium temperature strain gauge within the applicable temperature range, and the linear expansion coefficient β2 of the strain gauge is obtained; the strain gauge is pasted on the calibration test piece by the adhesive, at least 5 temperature values are selected from room temperature to the limited temperature range of the strain gauge corresponding to the indicated strain of the medium temperature strain gauge; the test piece is placed in a temperature chamber in a free expansion state, slowly warmed from room temperature at a temperature rising rate of 1℃ / s, the indicated strain of the strain gauge corresponding to each temperature value is measured, and the linear expansion coefficient β2 of the strain gauge is obtained by the following formula: In the above formula (4): β 1标 to calibrate the linear expansion coefficient of the test piece; ε t标 To calibrate the indicated strain of the test piece.

5. The method according to claim 4, wherein In the above step S5, the thermal output of the test piece is obtained by substituting the values of α, β2 and the linear expansion coefficient β1 of the test piece into the formula (1). 胶 In the above step S5, the thermal output of the test piece is obtained by substituting the values of α, β2 and the linear expansion coefficient β1 of the test piece into the formula (1).

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