A design method and system for a high-temperature preload sensor for fasteners

Abstract

This invention discloses a design method and system for a high-temperature preload sensor for fasteners. Step 1 involves the preliminary design and manufacturing of the preload sensor. Step 2 involves a room-temperature calibration test of the preload sensor in a pressure testing machine. Step 3 involves a high-temperature calibration test of the preload sensor in a high-temperature environmental chamber and a pressure testing machine, performing temperature-zero point calibration and temperature-sensitivity calibration based on the input load, the intermediate temperature of the high-temperature calibration test, and the sensor's operating limit temperature. During temperature-zero point calibration and temperature-sensitivity calibration, the theoretical result data set calculated by the theoretical formula of the high-temperature preload sensor for fasteners is compared with the data set collected by the data acquisition instrument. Step 4 involves comparing the data set comparison results if the error is within 10%, and using the collected data as the calibration result. This invention clarifies the relationship between temperature, sensor material properties, strain gauges, and signal output.

Description

Technical Field

[0001] This invention belongs to the field of detection or calibration technology for instruments used to measure force, specifically a design method and system for a high-temperature preload sensor for fasteners. Background Technology

[0002] Fasteners are currently used in a wide range of industries, including machinery, metallurgy, and mold making. Various types of fasteners can be found in construction, railways, bridges, ships, aerospace, and special equipment.

[0003] When connecting different parts into a whole, the preload of fasteners affects the stiffness and load-bearing capacity of the connection joint, and thus the overall mechanical properties of the structure. In industries with high requirements for structural safety, the preload of fasteners used to connect critical parts must be directly and accurately measured to ensure the safety and reliability of their operation and use.

[0004] At room temperature, the preload of fasteners decreases slowly over time. However, in high-temperature environments, the preload decreases significantly due to factors such as the expansion of the fasteners themselves and the connected components, leading to a reduction in strength. This is especially true for structures using high-strength bolts and grooved rivets, which provide high preload to the connected components. The substantial loss of preload at high temperatures has a significant impact on structural safety. Therefore, measuring the preload of fasteners at high temperatures is particularly important.

[0005] The main challenges in designing high-temperature preload sensors include: 1. The complex mechanism by which temperature affects sensor signal output, making it difficult to clarify the relationship between temperature and sensor signal output, a major reason why high-temperature preload sensors cannot be implemented. 2. High-temperature preload sensors are more complex to design than room-temperature preload sensors, necessitating a systematic design methodology to reduce design difficulty, simplify the design process, and optimize the use of sensor materials. 3. Calibration tests are required before the sensor leaves the factory to ensure its performance meets usage requirements. The main difficulties in calibrating high-temperature preload sensors include: ① Long heating and holding times in high-temperature furnaces, resulting in significantly longer calibration times compared to room-temperature calibration. ② More factors affecting accuracy during high-temperature calibration than during room-temperature calibration. To eliminate the influence of random factors, there is currently no better method than repeated testing, further extending the calibration time. 4. Since temperature alters the properties of sensor materials and strain gauges, the selection of suitable high-temperature preload sensor materials and high-temperature resistant strain gauges directly affects the performance of the high-temperature preload sensor.

[0006] Therefore, in order to solve the above problems, it is urgent to propose a design method and system for high-temperature preload sensors for fasteners. Summary of the Invention

[0007] To address the problems existing in the background art, the present invention provides a design method for a high-temperature preload sensor for fasteners, characterized by comprising:

[0008] Step 1. Conduct preliminary design and manufacturing of the preload sensor;

[0009] Step 2. Perform a room temperature calibration test on the preload sensor in a pressure testing machine. After the sensor is preloaded three times to stabilize the relationship between the sensor load and the strain measured by the strain gauge, load the sensor through the pressure testing machine and collect the sensor output signal at the same time. Obtain the functional relationship between the sensor output signal data and the load of the pressure testing machine under room temperature conditions to complete the room temperature calibration test.

[0010] Step 3. Conduct high-temperature calibration tests on the preload sensor in a high-temperature environment chamber and pressure testing machine. Perform temperature-zero point calibration and temperature-sensitivity calibration based on the input load, the intermediate temperature of the high-temperature calibration test, and the sensor's operating limit temperature.

[0011] During temperature-zero point calibration and temperature-sensitivity calibration, the theoretical result data set calculated by the theoretical formula of the fastener high temperature preload sensor and the data set collected by the data acquisition instrument are compared.

[0012] Step 4. If the error of the data set comparison results is within 10%, the collected data will be used as the calibration result.

[0013] The theoretical formula for the high-temperature preload sensor for fasteners is:

[0014]

[0015] In the formula: F t —Theoretical preload at temperature t℃;

[0016] A – Cross-sectional area of ​​the strain gauge mounting groove;

[0017] E t —The elastic modulus of the elastomer at a temperature of t℃;

[0018] ΔR——The change in total resistance in the sensor circuit caused by the theoretical preload at a temperature of t℃;

[0019] R0—The total resistance of the sensor circuit when the temperature is normal;

[0020] K t —The sensitivity coefficient of the sensor at a temperature of t℃;

[0021] t is the intermediate temperature of the high-temperature calibration test, 100≤t≤600.

[0022] The temperature-zero point calibration process includes: the high-temperature environment chamber sequentially heats the internal sensors to each integer multiple of the intermediate temperature of the high-temperature calibration test until the sensor's operating limit temperature; the data acquisition instrument sequentially collects the sensor outputs as temperature-zero point output data at each temperature and enters the collection result data group.

[0023] The temperature-sensitivity calibration process includes: the high-temperature environment chamber sequentially heats the internal sensors to each integer multiple of the intermediate temperature of the high-temperature calibration test until the sensor's operating limit temperature; the pressure testing machine applies a load to the sensor to simulate preload; after the data stabilizes, the data acquisition instrument sequentially collects the sensor output as temperature-sensitivity output data at each temperature and enters the collected result data group; and the pressure machine is unloaded.

[0024] When the sensor's operating limit temperature is not an integer multiple of the intermediate temperature of the high-temperature calibration test, the results are collected again at the sensor's operating limit temperature during the temperature-zero point calibration and the temperature-sensitivity calibration.

[0025] The data set comparison includes two comparison forms; the first form is to compare the test load and the theoretical calculated load under the same temperature and the same sensor output; the second form is to compare the collected sensor output and the theoretical calculated output under the same temperature and the same load, wherein the theoretical calculated output is calculated by the relative change value of resistance in the formula based on the actual circuit conditions.

[0026] In step 4, if the error exceeds 10%, return to step 3 to perform the same second high-temperature calibration test;

[0027] If either of the following two situations occurs after the second high-temperature calibration test, it is considered a systematic error. In this case, return to step 1 to improve the preliminary design and restart the design process. Otherwise, use the newly collected data as the calibration result:

[0028] Scenario 1: The error still exceeds 10%.

[0029] Scenario 2: The sensor signal output strength at high temperatures does not meet the acquisition requirements.

[0030] Step 1 includes:

[0031] Step 11. Determine the material properties of the sensor elastomer, the strain gauge model, and the dimensions of the sensor elastomer;

[0032] Step 12. Calculate the output sensitivity of the sensor at room temperature. If the sensitivity meets the usage requirements and the acquisition requirements of the data acquisition instrument, the process ends. If it does not meet the requirements, the relevant parameters of the materials to be used need to be re-determined.

[0033] Step 13. Produce and assemble the preload sensor.

[0034] The formula for calculating the sensor output in step 12 is as follows:

[0035]

[0036] In the formula: E u —The output voltage of the bridge;

[0037] E i —The excitation voltage of the bridge;

[0038] G f —Strain gauge sensitivity coefficient;

[0039] N—bridge strain amplification factor;

[0040] e – elastic strain.

[0041] A fastener high-temperature preload sensor design system is also provided, characterized in that the design system includes: an input module, a sensor output calculation module, a high-temperature calibration test module, and a signal data comparison module, wherein the input module is connected to the high-temperature calibration test module and the sensor output calculation module respectively;

[0042] The sensor output calculation module calculates the sensor's output sensitivity at room temperature based on the parameters input by the input module during the design phase.

[0043] The high-temperature calibration test module is connected to the pressure testing machine, the high-temperature environmental chamber, and the signal data comparison module. Based on the input load, the intermediate temperature of the high-temperature calibration test, and the sensor's operating limit temperature, it performs temperature-zero point calibration and temperature-sensitivity calibration. During temperature-zero point calibration, the high-temperature calibration test module simultaneously sends information to the signal data comparison module and the high-temperature environmental chamber; the data collected by the acquisition instrument is sent to the signal data comparison module to enter the result data group. During temperature-sensitivity calibration, the high-temperature calibration test module simultaneously sends information to the signal data comparison module, the pressure testing machine, and the high-temperature environmental chamber; the data collected by the acquisition instrument is sent to the signal data comparison module to enter the result data group.

[0044] The signal data comparison module is connected to the sensor via the acquisition instrument. During each high-temperature calibration test, it calculates the error between the results collected by the acquisition instrument and the results calculated by the theoretical formula of the fastener high-temperature preload sensor in the signal data comparison module. The signal data comparison module outputs the error and the results collected by the acquisition instrument.

[0045] The sensor is made of 17-4PH material.

[0046] The beneficial effects of this invention are as follows:

[0047] 1. The fastener high-temperature preload sensor design method proposed in this invention simplifies the design process of such sensors, reduces design difficulty, and optimizes material usage;

[0048] 2. During the calibration process, the theoretical verification formula of the sensor high-temperature calibration test is used to verify the parameters, which reduces the number of tests at intermediate temperatures in each high-temperature calibration test, greatly reducing the total number of high-temperature calibration tests for the newly designed sensor and saving time and costs in the production process.

[0049] 3. The theoretical verification formula of the high temperature calibration test clarifies the relationship between temperature, sensor material properties, strain gauge and signal output, which can eliminate random errors in the calibration process and improve the accuracy of calibration results, thus providing key support for the accurate measurement of high temperature preload of fasteners. Attached Figure Description

[0050] Figure 1 This is a flowchart illustrating an embodiment of the design method for a high-temperature preload sensor for fasteners according to the present invention.

[0051] Figure 2 This is a connection diagram of an embodiment of the fastener high-temperature preload sensor design system of the present invention;

[0052] Figure 3 This is a schematic diagram of the preload sensor in an embodiment of the present invention;

[0053] Figure 4 This is a schematic diagram of the preload sensor in an embodiment of the present invention, omitting the encapsulation shell.

[0054] Figure 5 K represents the high-temperature sensitivity coefficient of the strain gauge in this embodiment of the invention. t Decrease curve with temperature;

[0055] Figure 6 This is a schematic diagram of the fitting results of the elastic modulus reduction coefficient at high temperature of 17-4PH in an embodiment of the present invention;

[0056] Figure 7 This is a comparison chart of the calculation results before and after simplification of the theoretical formula for the high-temperature preload sensor of fasteners in this embodiment of the invention.

[0057] Among them, 1-sealing plate, 2-encapsulation shell, 3-elastomer, 5-upper end of encapsulation shell, 6-lower end of encapsulation shell, 7-upper edge of sealing plate, 9-strain gauge adhesive groove, 10-bottom end of elastomer, 11-lead inlet, 16-strain gauge lead, 17-high temperature strain gauge. Detailed Implementation

[0058] The present invention will be further described in detail below with reference to the accompanying drawings.

[0059] like Figure 1 The embodiment of the present invention shown includes a design method comprising:

[0060] Step 1. Conduct preliminary design and manufacturing of the preload sensor; Step 1 specifically includes:

[0061] Step 11. Determine various parameters, including: the properties of the sensor elastomer material (elastic modulus, yield strength, Poisson's ratio); the strain gauge model (including size and sensitivity coefficient, where size affects the size of the strain gauge mounting groove, which in turn affects the overall size of the sensor, and the strain gauge sensitivity coefficient is related to the sensor measurement accuracy); the sensor elastomer dimensions (mainly including cross-sectional area and axial dimension), and the specific dimensions of other components.

[0062] Step 12. Calculate the output sensitivity of the sensor at room temperature. If the sensitivity meets the usage requirements and the acquisition requirements of the data acquisition instrument, the process ends. If it does not meet the requirements, the relevant parameters such as the materials used need to be re-determined (the adjustment principle is to increase the elastic strain under unit load, the main idea is to reduce the cross-sectional area of ​​the elastic body, or to select a metal material with a small elastic modulus, etc.).

[0063] The output calculation formula for the sensor used in this embodiment is as follows:

[0064]

[0065] In the formula: E u —The output voltage of the bridge;

[0066] E i —The excitation voltage of the bridge;

[0067] G f —Strain gauge sensitivity coefficient;

[0068] N—bridge strain amplification factor;

[0069] e – elastic strain.

[0070] Step 13. After producing and assembling the preload sensor, prepare to conduct calibration tests.

[0071] Step 2. Perform a room temperature calibration test on the preload sensor in a pressure testing machine:

[0072] After the sensor is preloaded three times to eliminate the instability of the relationship between the sensor load and the strain measured by the strain gauge, the sensor is loaded through a pressure testing machine while the sensor output signal is collected. The functional relationship between the sensor output signal data and the pressure testing machine load under normal temperature (20℃) conditions is obtained, and the normal temperature calibration test is completed.

[0073] Step 3. Perform high-temperature calibration tests on the preload sensor in a high-temperature environmental chamber and pressure testing machine:

[0074] Temperature-zero calibration and temperature-sensitivity calibration are performed based on the input load, the intermediate temperature of the high-temperature calibration test, and the sensor's operating limit temperature (which depends on the material of the least heat-resistant component).

[0075] During temperature-zero point calibration and temperature-sensitivity calibration, the theoretical result data set calculated by the theoretical formula of the fastener high temperature preload sensor and the data set collected by the data acquisition instrument are compared.

[0076] The theoretical formula for the high-temperature preload sensor for fasteners is as follows, and the calibration results are theoretically verified using this formula:

[0077]

[0078] In the formula: F t —Theoretical preload at temperature t℃;

[0079] A – Cross-sectional area of ​​the strain gauge mounting groove;

[0080] E t —The elastic modulus of the elastomer at a temperature of t℃;

[0081] ΔR——The change in total resistance in the sensor circuit caused by the theoretical preload at a temperature of t℃;

[0082] R0—The total resistance value in the sensor circuit when the temperature is normal (20℃);

[0083] K t —The sensitivity coefficient of the sensor at a temperature of t℃.

[0084] In this embodiment, heat preservation is performed before each high-temperature calibration;

[0085] In this embodiment, the data set comparison includes two comparison forms; the first form is: comparing the test load and the theoretically calculated load under the same temperature and the same sensor output; the second form is: comparing the collected sensor output and the theoretically calculated output under the same temperature and the same load, wherein the theoretically calculated output is calculated by the relative change value of resistance in the formula based on the actual circuit conditions.

[0086] In this embodiment, the intermediate temperature of the high-temperature calibration test is t℃, 100≤t≤600, specifically 100℃, 200℃, 300℃, 400℃ and 500℃, and the sensor's operating limit temperature is 600℃.

[0087] The temperature-zero point calibration in this embodiment includes: the high-temperature environment chamber sequentially heats the internal sensors to each integer multiple of the intermediate temperature of the high-temperature calibration test until the sensor's operating limit temperature, and the sensor outputs sequentially collected by the data acquisition instrument are used as temperature-zero point output data at each temperature and entered into the collection result data group.

[0088] The temperature-sensitivity calibration in this embodiment includes: heating the sensor inside the high-temperature environmental chamber sequentially to each integer multiple of the intermediate temperature of the high-temperature calibration test until the sensor's operating limit temperature; applying a load to the sensor using a pressure testing machine to simulate preload; after the data stabilizes, the sensor outputs sequentially collected by the data acquisition instrument are used as the temperature-sensitivity output data at each temperature and entered into the collected result data group; the pressure machine is then unloaded. The sensor's operating limit temperature is taken as the intermediate temperature of the high-temperature calibration test when heated to that temperature.

[0089] In this embodiment, if the sensor's operating limit temperature is not an integer multiple of the intermediate temperature of the high-temperature calibration test, the sensor's operating limit temperature is set to the intermediate temperature of the high-temperature calibration test, and the results are collected again. At the same time, the theoretical formula of the fastener high-temperature preload sensor is used to perform corresponding calculations and data group comparisons for this result collection.

[0090] Step 4. If the error is within 10%, the collected data is used as the calibration result and proceeds to Step 5;

[0091] If the error exceeds 10%, return to step 3 to perform the same second high-temperature calibration test. After the second high-temperature calibration test, if one of the following two situations occurs, it is considered a systematic error (such as unreasonable sensor elastomer size design), return to step 1 to improve the preliminary design and restart the design process; otherwise, use the newly collected data as the calibration result and proceed to step 5. The two situations are:

[0092] Scenario 1: The error in the results still exceeds 10% after repeated trials.

[0093] Scenario 2: The sensor signal output strength at high temperatures does not meet the acquisition requirements (usually depends on the minimum effective recognition value of the acquisition instrument);

[0094] Step 5. Complete the high-temperature calibration test and design process. During subsequent use, install a fastener in the center of the elastomer. The fastener passes through the center of the elastomer and is clamped between the upper and lower end faces.

[0095] like Figure 2 The design system shown includes: an input module, a sensor output calculation module, a high-temperature calibration test module, and a signal data comparison module, wherein the input module is connected to the high-temperature calibration test module and the sensor output calculation module respectively;

[0096] The input module is used to input design data, including: sensor elastomer material properties, strain gauge model, sensor elastomer dimensions, and specific dimensions of other components;

[0097] The sensor output calculation module calculates the sensor's output sensitivity at room temperature based on the parameters input by the input module during the design phase.

[0098] The high-temperature calibration test module is connected to the pressure testing machine, the high-temperature environmental chamber, and the signal data comparison module. Based on the input load, the intermediate temperature of the high-temperature calibration test, and the sensor's operating limit temperature, it performs temperature-zero point calibration and temperature-sensitivity calibration. During temperature-zero point calibration, the high-temperature calibration test module simultaneously sends information to the signal data comparison module and the high-temperature environmental chamber; the data collected by the acquisition instrument is sent to the signal data comparison module to enter the result data group. During temperature-sensitivity calibration, the high-temperature calibration test module simultaneously sends information to the signal data comparison module, the pressure testing machine, and the high-temperature environmental chamber; the data collected by the acquisition instrument is sent to the signal data comparison module to enter the result data group.

[0099] The signal data comparison module is connected to the sensor via the acquisition instrument. During each high-temperature calibration test, it calculates the error between the results collected by the acquisition instrument and the results calculated by the theoretical formula of the fastener high-temperature preload sensor in the signal data comparison module. The signal data comparison module outputs the error and the results collected by the acquisition instrument.

[0100] An embodiment of the complete process of designing a high-temperature preload sensor using the design method of this invention is given below, including:

[0101] Step 11 (Sensor Size Design): Design the inner diameter of the elastic body force-bearing platform 3 based on the fastener diameter, the outer diameter of the elastic body force-bearing platform 3 based on the fastener head size, and the overall axial thickness of the sensor based on the fastener length. Here, an M12 pull-out grooved rivet is used as an example, with the following dimensions and mechanical properties: rivet head diameter 23mm, rivet shank diameter 12.5-13.1mm, rivet shank riveting thickness 38.1-44.5mm, and preload force not less than 54kN at room temperature. To ensure the sensor's axial force is applied, the inner diameter of the elastic body force-bearing platform 3 should not be too large; therefore, it is selected as 14mm. The outer diameter of the elastic body force-bearing platform 3 is selected as 40mm, and the overall axial thickness of the sensor is selected as 40mm.

[0102] Step 12 (Sensor signal output calculation, i.e., sensor sensitivity output calculation): Calculate the sensor signal output in a normal temperature environment based on the selected dimensions. The selected sensor material is 17-4PH, whose elastic modulus at 20℃ is 1.9 × 10⁻⁶. 5MPa, Poisson's ratio 0.27, yield strength 1250 MPa at 20℃. A high-temperature strain gauge, model ZC-NC-G1262-120, was selected, with a sensitivity coefficient of 2.6 and a bridge strain amplification factor of 2.54. Calculations show that the cross-sectional area of ​​the bonding groove 9 for the sensor's elastic strain gauge is 1102 mm². 2 The strain under a 54kN load is 2.3×10⁻⁶. -4 The formula for calculating the sensor output of a full-bridge circuit is as follows:

[0103]

[0104] In the formula: E u —The output voltage of the bridge;

[0105] E i —The excitation voltage of the bridge;

[0106] G f —Strain gauge sensitivity coefficient;

[0107] N—bridge strain amplification factor;

[0108] e—elastic strain;

[0109] Calculations show that the theoretical output of the circuit is 0.43mV / V, which meets the requirements of the signal acquisition instrument. At the same time, the elastic body stress is 49MPa, which meets the strength requirements. Therefore, the size is reasonable, but the signal output is too small. If the signal output is to be increased, the signal can be enhanced by a signal amplification instrument or the outer diameter of the elastic body can be reduced to increase its strain.

[0110] Step 13 (Component Production and Assembly of the Preload Sensor): Design the dimensions of the sealing plate 1, encapsulation shell 2, and bottom end 10 of the elastomer according to the sensor's elastomer dimensions; process the sensor according to the design dimensions and attach the high-temperature strain gauge; then install as follows... Figure 3 and Figure 4 The sensor shown is as follows: Specifically, the sealing plate 1 installed on the upper outer side of the elastomer is fixed to the elastomer 3 via the upper edge 7 of the sealing plate. The sealing plate 1 is fixed to the outer side of the upper end 5 of the encapsulation shell. The outer edge of the sealing plate 1 is fixed to the encapsulation shell. The lower end 6 of the encapsulation shell is fixed to the elastomer base 10. The elastomer base 10 and the inner elastomer 3 are an integral structure. The sealing plate 1, the encapsulation shell and the elastomer base 10 form a cavity to protect the internal high-temperature strain gauge 17 and strain gauge lead wire 16. Four strain gauge pasting grooves 9 of the same size are evenly distributed along the outer periphery of the elastomer 3. The high-temperature strain gauge is pasted on the strain gauge pasting groove. The strain gauge lead wire 16 extending from the high-temperature strain gauge 17 enters from the lead wire inlet 11 set on the end face of the elastomer base 10 and extends out from the lead wire outlet on the side of the elastomer base 10.

[0111] In this embodiment, four rectangular high-temperature strain gauges are attached to the elastomer, with the attachment directions being: two length directions along the axial direction and two length directions along the circumferential direction.

[0112] Step 2 (Room Temperature Calibration): In a room temperature environment, perform three pre-load cycles; then connect the sensor wires to the signal acquisition instrument and place the sensor in the pressure testing machine. Start the pressure testing machine to apply pressure to the sensor. At this time, the sensor strain gauge and the sensor elastic body undergo synchronous strain, causing a change in the total resistance in the circuit, which in turn generates a changing voltage output signal that is acquired by the acquisition instrument. Record the output signals of the pressure testing machine and the sensor, and repeat the test at least twice. Obtain the correspondence between the sensor output signal data at room temperature and the load value of the pressure testing machine, thus completing the room temperature calibration test.

[0113] Step 3 (High-Temperature Calibration): Temperature-Zero Point Calibration: Place the sensor in a high-temperature environmental chamber and heat it to 100℃ at a rate of 20℃ / min. Record the sensor output for 5 minutes. Continue heating to the next target temperature point and repeat the above operation until the test ends, obtaining the sensor temperature-zero point data. Temperature-Sensitivity Calibration: Place the sensor in a high-temperature environmental chamber and heat it to 100℃ at a rate of 20℃ / min. Then, start the pressure testing machine to apply a pressure of 10-50kN to the sensor and record the sensor output under the corresponding load. Continue heating to the next target temperature point and repeat the above operation until the test ends, obtaining the sensor temperature-sensitivity data. Subtract the corresponding temperature-zero point data from the temperature-sensitivity data to obtain the high-temperature preload sensor calibration result. Compare the calibration test results with the theoretical calculation results in the signal data comparison module. If the error exceeds 10%, the calibration test needs to be performed again.

[0114] The theoretical formula for the high-temperature preload sensor for fasteners of this invention is as follows, and the calibration results can be theoretically verified using the theoretical formula:

[0115]

[0116] In the formula: F t —Theoretical preload at temperature t℃;

[0117] A – Cross-sectional area of ​​the strain gauge mounting groove;

[0118] E t —The elastic modulus of the elastomer at a temperature of t℃;

[0119] ΔR——The change in total resistance in the sensor circuit caused by the theoretical preload at a temperature of t℃;

[0120] R0—The total resistance value in the sensor circuit when the temperature is normal (20℃);

[0121] Kt —The sensitivity coefficient of the sensor at a temperature of t℃.

[0122] Wherein, the cross-sectional area A at the strain gauge bonding groove is usually considered to be the cross-sectional area A of the elastic body at a temperature of t℃. t A t =π[(r1-r1μ) s ε z +r1β s Δ t ) 2 -(r0-r0μ s ε z +r0β s Δ t ) 2 Where: r0 is the inner radius of the sensor; r1 is the outer radius of the sensor; μ s ε is the sensor's Poisson's ratio; z β represents the axial strain of the sensor. s Δ is the coefficient of linear expansion of the sensor; t For temperature changes (compared to room temperature 20℃); Equation (2) above (i.e., the theoretical formula for a high-temperature preload sensor for fasteners) considers the influence of two factors on the cross-sectional area: thermal expansion of the elastic body and deformation under stress at high temperatures. The comparison results before and after formula simplification are as follows: Figure 7 As shown, the simplified formula has an error of less than 2% compared with the original formula. Therefore, the simplified formula can reflect the actual situation of the sensor under high temperature when calculating the cross-sectional area. The proposed formula for theoretical verification eliminates the influence of random errors on the calibration results and improves the accuracy of high temperature calibration.

[0123] To facilitate understanding of Formula 2, the relationship between the change in total resistance of the sensor circuit, the sensor sensitivity coefficient, and the sensor strain is listed below.

[0124] K t : Sensor sensitivity coefficient, ε: Strain at the strain gauge attachment point (aligned with the direction of the strain gauge attachment length, either circumferential or axial).

[0125] In formula (2), the high-temperature sensitivity coefficient K of the sensor t The reduction with temperature is shown in the figure. Figure 5 Its sensitivity coefficient at room temperature (20℃) is 2.6; the sensitivity coefficient at the corresponding temperature point can be obtained by multiplying the room temperature sensitivity coefficient by the reduction factor at the corresponding temperature point.

[0126] To obtain E tFor specific data, a 17-4PH high-temperature material property test was conducted to obtain the elastic modulus of the material at temperatures of 20℃, 100℃, 200℃, 300℃, 400℃, 500℃, and 600℃. The elastic modulus reduction factor at high temperatures was fitted as shown in Formula 3. The specific values ​​of the coefficients in the formula are shown in Table 1, and the fitting results are shown in [Table 1]. Figure 6 According to formula (3), the predicted value of the elastic modulus of 17-4PH at any temperature point within 600℃ can be obtained. In summary, the theoretical formula and the actual calibration test can be used for dual verification, making the sensor calibration results scientific and reliable.

[0127]

[0128] In the formula: E t —Elastic modulus at high temperature of 17-4PH;

[0129] E0 – Elastic modulus at room temperature (17-4 pH): 1.9 × 10⁻⁶ 5 MPa;

[0130] t — temperature (°C);

[0131] a, b — coefficients.

[0132] Table 1. Values ​​of coefficients in Formula 3

[0133] Temperature t (°C) a b 20≤t<100 0 1 100≤t<500 <![CDATA[-2.4507×10 -4 ]]> 1.0245 500≤t≤600 <![CDATA[-3.0500×10 -3 ]]> 2.4289

[0134] Since step 3 of this embodiment establishes the theoretical verification formula for the high-temperature preload sensor, the preload F at high temperature is... t By establishing a functional relationship between the change in relative resistance of the circuit and the high-temperature preload and the sensor's signal output under rated voltage, the purpose of quickly verifying the calibration test results through theoretical formulas can be achieved. This reduces the number of calibration tests, avoids a large number of repetitive heating and waiting processes during the design process, and saves the total design time.

[0135] Step 4. Since the actual comparison results in this embodiment show an error within 10%, the collected data is used as the calibration result; then proceed to step 5.

[0136] Step 5. Complete the high-temperature calibration test and design process, and print the calibration results on the factory inspection report. During application, install a fastener in the center of the elastomer 3: the fastener passes through the center of the elastomer 3 and is clamped between the upper and lower end faces of the elastomer 3, thus completing the assembly of the preload sensor and the fastener.

Claims

1. A design method for a high-temperature preload sensor for fasteners, characterized in that, include: Step 1. Conduct preliminary design and manufacturing of the preload sensor; Step 2. Perform a room temperature calibration test on the preload sensor in a pressure testing machine. After the sensor is preloaded three times to stabilize the relationship between the sensor load and the strain measured by the strain gauge, load the sensor through the pressure testing machine and collect the sensor output signal at the same time. Obtain the functional relationship between the sensor output signal data and the load of the pressure testing machine under room temperature conditions to complete the room temperature calibration test. Step 3. Conduct high-temperature calibration tests on the preload sensor in a high-temperature environment chamber and pressure testing machine. Perform temperature-zero point calibration and temperature-sensitivity calibration based on the input load, the intermediate temperature of the high-temperature calibration test, and the sensor's operating limit temperature. During temperature-zero point calibration and temperature-sensitivity calibration, the theoretical result data set calculated by the theoretical formula of the fastener high temperature preload sensor and the data set collected by the data acquisition instrument are compared. Step 4. If the error of the data set comparison results is within 10%, then the collected data will be used as the calibration result; Step 1 includes: Step 11. Determine various parameters: sensor elastomer material properties, strain gauge model, sensor elastomer dimensions, and specific dimensions of other components; Step 12. Calculate the output sensitivity of the sensor at room temperature. If the sensitivity meets the usage requirements and the acquisition requirements of the data acquisition instrument, the process ends. If it does not meet the requirements, the relevant parameters such as the materials used need to be re-determined. Step 13. After producing and assembling the preload sensor, prepare to conduct calibration tests; The theoretical formula for the high-temperature preload sensor for fasteners is: In the formula: F t —Theoretical preload at temperature t℃; A – Cross-sectional area of ​​the strain gauge mounting groove; E t —The elastic modulus of the elastomer at a temperature of t℃; ΔR——The change in total resistance in the sensor circuit caused by the theoretical preload at a temperature of t℃; R0—The total resistance of the sensor circuit when the temperature is normal; K t —The sensitivity coefficient of the sensor at a temperature of t℃; t is the intermediate temperature of the high-temperature calibration test, 100≤t≤600.

2. The design method for a high-temperature preload sensor for fasteners according to claim 1, characterized in that, The temperature-zero point calibration process includes: the high-temperature environment chamber sequentially heats the internal sensors to each integer multiple of the intermediate temperature of the high-temperature calibration test until the sensor's operating limit temperature; the data acquisition instrument sequentially collects the sensor outputs as temperature-zero point output data at each temperature and enters the collection result data group. The temperature-sensitivity calibration process includes: the high-temperature environment chamber sequentially heats the internal sensors to each integer multiple of the intermediate temperature of the high-temperature calibration test until the sensor's operating limit temperature; the pressure testing machine applies a load to the sensor to simulate preload; after the data stabilizes, the data acquisition instrument sequentially collects the sensor output as temperature-sensitivity output data at each temperature and enters the collected result data group; and the pressure machine is unloaded.

3. The design method for a high-temperature preload sensor for fasteners according to claim 2, characterized in that, When the sensor's operating limit temperature is not an integer multiple of the intermediate temperature of the high-temperature calibration test, the results are collected again at the sensor's operating limit temperature during the temperature-zero point calibration and the temperature-sensitivity calibration.

4. The design method for a high-temperature preload sensor for fasteners according to claim 1, characterized in that, The data set comparison includes two comparison forms; the first form is to compare the test load and the theoretical calculated load under the same temperature and the same sensor output; the second form is to compare the collected sensor output and the theoretical calculated output under the same temperature and the same load, wherein the theoretical calculated output is calculated by the relative change value of resistance in the formula based on the actual circuit conditions.

5. The design method for a high-temperature preload sensor for fasteners according to claim 1, characterized in that, In step 4, if the error exceeds 10%, return to step 3 to perform the same second high-temperature calibration test; If either of the following two situations occurs after the second high-temperature calibration test, it is considered a systematic error. In this case, return to step 1 to improve the preliminary design and restart the design process. Otherwise, use the newly collected data as the calibration result: Scenario 1: The error still exceeds 10%; Scenario 2: The sensor signal output strength at high temperatures does not meet the acquisition requirements.

6. The design method for a high-temperature preload sensor for fasteners according to claim 1, characterized in that, Step 1 includes: Step 11. Determine the material properties of the sensor elastomer, the strain gauge model, and the dimensions of the sensor elastomer; Step 12. Calculate the output sensitivity of the sensor at room temperature. If the sensitivity meets the usage requirements and the acquisition requirements of the data acquisition instrument, the process ends. If it does not meet the requirements, the relevant parameters of the materials to be used need to be re-determined. Step 13. Produce and assemble the preload sensor.

7. The design method for a high-temperature preload sensor for fasteners according to claim 6, characterized in that, The formula for calculating the sensor output in step 12 is as follows: In the formula: E u —The output voltage of the bridge; E i —The excitation voltage of the bridge; G f —Strain gauge sensitivity coefficient; N—bridge strain amplification factor; e – elastic strain.

8. A design system for a high-temperature preload sensor for fasteners, characterized in that, The design system includes: an input module, a sensor output calculation module, a high-temperature calibration test module, and a signal data comparison module, wherein the input module is connected to the high-temperature calibration test module and the sensor output calculation module respectively; The sensor output calculation module calculates the sensor's output sensitivity at room temperature based on the parameters input by the input module during the design phase. The high-temperature calibration test module is connected to the pressure testing machine, the high-temperature environmental chamber, and the signal data comparison module. Based on the input load, the intermediate temperature of the high-temperature calibration test, and the sensor's operating limit temperature, it performs temperature-zero point calibration and temperature-sensitivity calibration. During temperature-zero point calibration, the high-temperature calibration test module simultaneously sends information to the signal data comparison module and the high-temperature environmental chamber; the data collected by the acquisition instrument is sent to the signal data comparison module to enter the result data group. During temperature-sensitivity calibration, the high-temperature calibration test module simultaneously sends information to the signal data comparison module, the pressure testing machine, and the high-temperature environmental chamber; the data collected by the acquisition instrument is sent to the signal data comparison module to enter the result data group. The signal data comparison module is connected to the sensor via a data acquisition instrument. During each high-temperature calibration test, it calculates the error between the results collected by the data acquisition instrument and the results calculated by the theoretical formula of the fastener high-temperature preload sensor within the signal data comparison module. The signal data comparison module outputs the error and the results collected by the data acquisition instrument. The input module is used to input design data, including: sensor elastomer material properties, strain gauge model, sensor elastomer dimensions, and specific dimensions of other components; The theoretical formula for a high-temperature preload sensor for fasteners is: In the formula: F t —Theoretical preload at temperature t℃; A – Cross-sectional area of ​​the strain gauge mounting groove; E t —The elastic modulus of the elastomer at a temperature of t℃; ΔR——The change in total resistance in the sensor circuit caused by the theoretical preload at a temperature of t℃; R0—The total resistance of the sensor circuit when the temperature is normal; K t —The sensitivity coefficient of the sensor at a temperature of t℃.

9. The fastener high-temperature preload sensor design system according to claim 8, characterized in that, The sensor is made of 17-4PH material.

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