Method for calculating heat output of adhesive medium-temperature strain gauge

Abstract

The invention relates to a heat output calculation method for a pasted medium-temperature strain gauge. The method comprises the following steps: decomposing heat output strain; simulation analysis is carried out, and the influence coefficient of the adhesive is calculated; a test is carried out, and a strain gauge resistance temperature coefficient is calibrated; carrying out a test, and calibrating the linear expansion coefficient of the strain gauge; and calculating the thermal output of the strain gauge of the tested piece material. According to the method, through the steps of strain gauge thermal output decomposition, thermal output parameter calibration, thermal output calculation and the like, the thermal output strain of a tested piece material is calculated only through two times of strain tests, and a thermal output test of the tested piece material is omitted.

Description

Technical Field

[0001] The invention relates to a method for calculating the thermal output of a pasted medium-temperature strain gauge, and belongs to the field of structural thermal strength testing. Background Art

[0002] The thermal strength of structures under thermal and mechanical environments is an important strength problem faced by high-speed reentry vehicles. Among them, the strain measurement of adhesive medium-temperature strain sensors has encountered some problems in current engineering applications: medium-temperature strain measurement sensors include concepts such as indicated strain, stress strain, and thermal output strain. The current conventional practice is to directly measure the indicated strain of the sensor, obtain the thermal output strain through thermal output tests, and obtain the stress strain through calculations. When the same type of strain gauge is applied to structural strain measurement of different materials, thermal output experiments are required, which will have an adverse impact on test resources and test time. Summary of the invention

[0003] 1. Technical issues to be resolved

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention proposes a method for calculating the thermal output of an adhesive medium-temperature strain gauge. The method calculates the thermal output strain of the test piece material with only two strain tests through the steps of strain gauge thermal output decomposition, calibration of thermal output parameters and thermal output calculation, thereby eliminating the thermal output test of the test piece material.

[0005] (II) Technical solution

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

[0007] S1. Thermal output strain decomposition;

[0008] S2. Carry out simulation analysis and calculate the influence coefficient of adhesive;

[0009] S3. Carry out tests to calibrate the resistance temperature coefficient of the strain gauge;

[0010] S4. Carry out tests to calibrate the linear expansion coefficient of the strain gauge;

[0011] S5. Calculate the heat output of the strain gauge of the test piece material.

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

[0013]

[0014] In the above formula (1):

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

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

[0017] k t 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.

[0022] In the above step S2, a finite element model of the strain gauge adhesive is established, and a rectangular shell unit is used to simulate the strain gauge adhesive, wherein the shell unit thickness attribute is the strain gauge adhesive thickness, and half of the strain gauge adhesive thickness is set as the offset, that is, the strain gauge adhesive grid position is on its bottom surface, and the length and width are the length and width of the strain gauge adhesive, respectively. A hexahedral body unit is used to simulate the test piece under test, and its length dimension is more than 10 times the length dimension of the adhesive. The connection between the nodes of the strain gauge adhesive and the test piece under test is simulated by a common node, and the three translational degrees of freedom and three rotational degrees of freedom of all nodes of one end face of the test piece under test are constrained. A forced deformation in the length direction of the strain gauge is applied to all nodes of the other end face. The positive strains of the upper and lower surfaces of the shell unit of the strain gauge adhesive are extracted from the finite element static strength analysis results, and the influence coefficient γ of the adhesive is 胶 The calculation formula is as follows:

[0023]

[0024] In the above formula (2):

[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 above step S3, a suspended strain gauge is used to measure the indicated strain within the applicable temperature range of the medium-temperature strain gauge to obtain the resistance temperature coefficient α of the strain gauge material; a 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 use limit temperature range of the strain gauge; the strain gauge is suspended in a temperature box, and the temperature is slowly increased from room temperature at a heating rate of 1°C / s, and the indicated strain of the strain gauge corresponding to each temperature value is measured. 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): 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, and the indicated strain of the medium-temperature strain gauge within the applicable temperature range is measured to obtain the linear expansion coefficient β2 of the strain gauge; the strain gauge is attached 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 use limit temperature range of the strain gauge; the test piece is placed in a temperature box in a free expansion state, and the temperature is slowly increased from room temperature at a heating rate of 1°C / s, 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 To calibrate the linear expansion coefficient of the test piece;

[0034] ε t标 To calibrate the indicated strain of the test piece.

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

[0036] (III) Beneficial effects

[0037] The invention discloses a method for calculating the thermal output of an adhesive medium-temperature strain gauge. The method calculates the thermal output strain of a test piece material with only two strain tests through the steps of strain gauge thermal output decomposition, thermal output parameter calibration and thermal output calculation, thereby eliminating the thermal output test of the test piece material.

[0038] Instruction Manual

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

[0040] A method for calculating the thermal output of a bonded medium-temperature strain gauge comprises the following steps:

[0041] S1. Thermal output strain decomposition;

[0042] S2. Carry out simulation analysis and calculate the influence coefficient of adhesive;

[0043] S3. Carry out tests to calibrate the resistance temperature coefficient of the strain gauge;

[0044] S4. Carry out tests to calibrate the linear expansion coefficient of the strain gauge;

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

[0046] In the above step S1, the strain gauge thermal output is decomposed into the following expression:

[0047]

[0048] In the above formula (1):

[0049] ε t is the heat output of the strain gauge;

[0050] γ 胶 is the influence coefficient of adhesive;

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

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

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

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

[0055] ΔT is the temperature change.

[0056] See also Figure 1 In the above step S2, a finite element model of the strain gauge adhesive is established, and a rectangular shell element is used to simulate the strain gauge adhesive, wherein the shell element thickness attribute is the strain gauge adhesive thickness, and half of the strain gauge adhesive thickness is set as the offset, that is, the strain gauge adhesive grid position is on its bottom surface, and the length and width are the length and width of the strain gauge adhesive, respectively. A hexahedral body element is used to simulate the test piece, and its length dimension is more than 10 times the length dimension of the adhesive. The connection between the nodes of the strain gauge adhesive and the test piece is simulated by a common node, and the three translational degrees of freedom and three rotational degrees of freedom of all nodes of one end face 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 face. The positive strains of the upper and lower surfaces of the strain gauge adhesive shell element are extracted from the finite element static strength analysis results, and the influence coefficient γ of the adhesive is 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 is the normal strain on the lower surface of the strain gauge adhesive shell element.

[0061] In the above step S3, a suspended strain gauge is used to measure the indicated strain within the applicable temperature range of the medium-temperature strain gauge to obtain the resistance temperature coefficient α of the strain gauge material; a 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 use limit temperature range of the strain gauge; the strain gauge is suspended in a temperature box, and the temperature is slowly increased from room temperature at a heating rate of 1°C / s, and the indicated strain of the strain gauge corresponding to each temperature value is measured. The resistance temperature coefficient α of the strain gauge is obtained by the following formula:

[0062] α=ε 空 k t / ΔT (3)

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

[0064] In the above step S4, a test piece with a known linear expansion coefficient is used as a calibration test piece, and the indicated strain of the medium-temperature strain gauge within the applicable temperature range is measured to obtain the linear expansion coefficient β2 of the strain gauge; the strain gauge is attached 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 use limit temperature range of the strain gauge; the test piece is placed in a temperature box in a free expansion state, and the temperature is slowly increased from room temperature at a heating rate of 1°C / s, 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:

[0065]

[0066] In the above formula (4):

[0067] β 1标 To calibrate the linear expansion coefficient of the test piece;

[0068] ε t标 To calibrate the indicated strain of the test piece.

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

Claims

1. A method for calculating the thermal output of a bonded medium-temperature strain gauge, characterized in that: The following steps are involved: S1. Thermal output strain decomposition; S2. Carry out simulation analysis and calculate the influence coefficient of adhesive; S3. Carry out tests to calibrate the resistance temperature coefficient of the strain gauge; S4. Carry out tests to calibrate the linear expansion coefficient of the strain gauge; S5. Calculate the heat output of the strain gauge of the test piece material.

2. The method for calculating the thermal output of the adhesive medium-temperature strain gauge according to claim 1, characterized in that: In the above step S1, the strain gauge thermal output is decomposed into the following expression: In the above formula (1): ε t is the heat output of the strain gauge; γ 胶 is the influence coefficient of 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 material of the test piece; β2 is the linear expansion coefficient of the strain gauge material; ΔT is the temperature change.

3. The method for calculating the thermal output of the adhesive medium-temperature strain gauge according to claim 2, characterized in that: In the above step S2, a finite element model of the strain gauge adhesive is established, and a rectangular shell unit is used to simulate the strain gauge adhesive, wherein the shell unit thickness attribute is the strain gauge adhesive thickness, and half of the strain gauge adhesive thickness is set as the offset, that is, the strain gauge adhesive grid position is on its bottom surface, and the length and width are the length and width of the strain gauge adhesive, respectively. A hexahedral body unit is used to simulate the test piece under test, and its length dimension is more than 10 times the length dimension of the adhesive. The connection between the nodes of the strain gauge adhesive and the test piece under test is simulated by a common node, and the three translational degrees of freedom and three rotational degrees of freedom of all nodes of one end face of the test piece under test are constrained. A forced deformation in the length direction of the strain gauge is applied to all nodes of the other end face. The positive strains of the upper and lower surfaces of the shell unit of the strain gauge adhesive are extracted from the finite element static strength analysis results, and the influence coefficient γ of the adhesive is 胶 The calculation formula is as follows: In the above formula (2): ε x上 is the normal strain on the upper surface of the strain gauge adhesive shell element; ε x下 is the normal strain on the lower surface of the strain gauge adhesive shell element.

4. The method for calculating the thermal output of the adhesive medium-temperature strain gauge according to claim 3, characterized in that: In the above step S3, a suspended strain gauge is used to measure the indicated strain within the applicable temperature range of the medium-temperature strain gauge to obtain the resistance temperature coefficient α of the strain gauge material; a 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 use limit temperature range of the strain gauge; the strain gauge is suspended in a temperature box, and the temperature is slowly increased from room temperature at a heating rate of 1°C / s, and the indicated strain of the strain gauge corresponding to each temperature value is measured. The resistance temperature coefficient α of the strain gauge is obtained by the following formula: a=e 空 k t / ΔT (3) In the above formula (3): 空 is the indicated strain of the suspended strain gauge.

5. The method for calculating the thermal output of the adhesive medium-temperature strain gauge according to claim 4, characterized in that: In the above step S4, a test piece with a known linear expansion coefficient is used as a calibration test piece, and the indicated strain of the medium-temperature strain gauge within the applicable temperature range is measured to obtain the linear expansion coefficient β2 of the strain gauge; the strain gauge is attached 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 use limit temperature range of the strain gauge; the test piece is placed in a temperature box in a free expansion state, and the temperature is slowly increased from room temperature at a heating rate of 1°C / s, 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: 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.

6. The method for calculating the thermal output of the adhesive medium-temperature strain gauge according to claim 5, characterized in that: In the above step S5, the γ obtained in steps S2 to S4 is 胶 Substituting the values ​​of α, β2 and the linear expansion coefficient β1 of the test piece into formula (1) can obtain the heat output of the test piece.

Images