A high-temperature strain measurement method based on a thin film strain sensor

Abstract

The present application belongs to the technical field of high-temperature thin film sensor, and specifically provides a high-temperature strain measurement method based on a thin film strain sensor. The present application adopts a high-temperature base point method, specifically a thin film strain analysis method taking the initial resistance of a thin film strain gauge at a to-be-measured temperature as a base point, a high-temperature resistance drift as compensation, and a high-temperature resistance change as a parameter. This method does not need to consider the strain gauge resistance temperature effect and the visual strain error (thermal output) caused by the difference between the sensitive grid and the material linear expansion coefficient of the tested piece, avoids the signal error caused by the thermal output of the high-temperature strain sensor, and does not need to perform temperature compensation on the thermal output data in application, only resistance drift compensation is needed. In summary, the present application takes the high-temperature base point as the calculation base point of the resistance change value, simultaneously compensates the resistance drift at high temperature, effectively reduces the error, improves the measurement precision, and at the same time, verifies the effectiveness of the measurement result through the signal post-processing function, and improves the application range.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature thin-film sensor technology, and relates to thin-film strain sensors, specifically providing a high-temperature strain measurement method based on a thin-film strain sensor. Background Technology

[0002] Strain sensors (also known as strain gauges) can detect mechanical signals such as strain and deformation, and convert these signals into electrical signals such as resistance, voltage, or capacitance for information transmission, processing, and display. Resistive strain sensors work through the resistive strain effect. The principle is that the resistance of a strain-sensitive material changes with mechanical deformation or force. By establishing a mapping relationship between resistance and strain, the magnitude of the mechanical deformation or force can be deduced from the change in resistance.

[0003] With advancements in manufacturing technology and the development of high-temperature and corrosion-resistant materials, thin-film strain sensors that meet the testing requirements of high-temperature environments are being used in high-temperature components of aerospace (such as engine turbine blades). Unlike traditional patch strain gauges, thin-film strain sensors do not require adhesives, grooving, or welding. They are directly deposited onto the surface of the component under test using vacuum deposition technologies such as magnetron sputtering and electron beam evaporation. This method does not damage the surface morphology and structure of the component under test, does not change its mechanical properties and lifespan, and does not affect the flow field distribution in high-velocity environments.

[0004] Traditional strain measurement methods for thin-film strain sensors typically involve connecting the strain sensor to an equal-arm Wheatstone bridge, such as... Figure 1 As shown, a single-arm connection is adopted. When the bridge is balanced (R g =R2=R3=R4), output voltage U0=0; however, when there is strain ε, the bridge balance is disrupted, resulting in a corresponding output voltage U0; based on the sensitivity coefficient K and the output voltage U0 and input voltage U i The strain ε is calculated and expressed as: However, in high-temperature strain measurement, the strain measured by the strain gauge is not the true strain of the specimen. On the one hand, due to the temperature effect of the strain gauge resistance and the difference in linear expansion coefficients between the strain gauge's sensing grid and the test specimen material, thin-film strain gauge measurements suffer from apparent strain error (thermal output). On the other hand, the strain gauge's sensing grid may experience zero-point resistance drift at high temperatures due to structural changes such as crystallization and segregation. Therefore, strain measurements using strain gauges should undergo temperature compensation and measurement error correction. When measuring strain at high temperatures, temperature compensation and error analysis are generally performed based on calibration data such as the thermal output and resistance drift characteristics of the thin-film strain gauge, specifically expressed as: ε T =ε m -ε a -ε d , where ε T For realistic response, ε mThe strain ε is measured by the strain sensor. a For the heat output from room temperature to high temperature, ε d This is for high-temperature strain drift; after the high-temperature strain gauge is calibrated to obtain the heat output within a certain temperature range and the zero-point drift at the temperature to be measured, the true strain of the specimen can be calculated.

[0005] Therefore, it is evident that the traditional bridge method uses the room-temperature resistance of the strain gauge as a baseline, and temperature compensation must be performed based on the thermal output performance of the strain gauge when measuring high-temperature strain. However, for thin-film strain sensors, the resistance values ​​between different batches, the thermal output from room temperature to a predetermined temperature, and the resistance drift at different temperatures generally vary significantly, making them incompatible with the traditional bridge method. This is especially true for high-temperature thin-film strain sensors, which operate at even higher temperatures (up to 1000℃) and exhibit greater thermal output. Metal alloy thin-film strain sensors, such as PdCr and FeCrAl, etc., Figure 2 As shown, after heating to different temperatures and holding at those temperatures, the resistance drift is relatively small, while the thermal output of the strain sensor is relatively large. Furthermore, traditional bridge-type strain signal measurement systems typically only accept standard strain gauges with common resistance values ​​such as 120Ω, 350Ω, and 1000Ω. Excessive deviation in resistance value will cause the bridge to become unbalanced and unable to perform measurements. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned deficiencies in the background technology by proposing a high-temperature baseline measurement method for high-temperature thin-film strain sensors. Specifically, this method employs a high-temperature baseline method, which uses the initial resistance of the thin-film strain gauge at the test temperature as the baseline, the high-temperature resistance drift as compensation, and the high-temperature resistance change as a parameter for thin-film strain analysis. This method eliminates the need to consider the temperature effect of the strain gauge resistance and the apparent strain error (thermal output) caused by the difference in linear expansion coefficients between the sensitive grid and the test material. It avoids signal errors caused by the thermal output of the high-temperature strain sensor. Furthermore, it eliminates the need for temperature compensation of the thermal output data in application; only resistance drift compensation is required. Simultaneously, the validity of the measurement results is verified through signal post-processing, thus expanding the application range.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A high-temperature strain measurement method based on a thin-film strain sensor, characterized by comprising the following steps:

[0009] Step 1. Set the high-temperature baseline;

[0010] Temperature signals of the area to be measured are acquired using thermocouples, and a time window t is set. c Real-time calculation time window t c The average historical temperature is calculated, and the difference between the current temperature and this average value is determined. If the difference is less than a preset threshold T, the temperature is considered zero. yWhen the to-be-tested region reaches a constant temperature state, record the resistance value R0 of the film strain sensor at the current time as a high-temperature base point, and record the temperature value T at the current time as a constant temperature;

[0011] Step 2. Calculate the resistance drift rate and complete drift compensation;

[0012] After the to-be-tested region reaches a constant temperature state, set a time window Δt, and calculate the resistance drift rate D within the time window Δt at the constant temperature; collect the resistance value R of the film strain sensor in real time t , complete drift compensation according to the resistance drift rate D, and obtain the compensated resistance value R D ;

[0013] Step 3. Calculate the real-time strain value;

[0014] According to the strain factor GF value of the film strain sensor at the constant temperature and the resistance drift rate D, calculate the resistance difference ΔR t,D between the compensated resistance value R t and the high-temperature base point R0, and further calculate the real-time strain value ε t measured by the film strain sensor;

[0015] Step 4. Calculate the real-time stress;

[0016] According to the elastic modulus Y value of the substrate of the film strain sensor at the constant temperature and the real-time strain value ε, calculate the real-time stress σ t measured by the film strain sensor.

[0017] Further, in step 2, the resistance drift rate D is expressed as:

[0018]

[0019] wherein R t0 represents the starting resistance value of the film strain sensor within the specified time window Δt, and R t0+Δt represents the terminal resistance value of the film strain sensor within the specified time window Δt.

[0020] Further, in step 2, the compensated resistance value R D is expressed as:

[0021]

[0022] wherein t s is the sampling interval time of the resistance value of the film strain sensor.

[0023] Further, in step 3, the real-time strain value ε t is specifically expressed as: ΔR t = Rt,D -R0.

[0024] Further, in step 4, the real-time stress σ t Specifically represented as: σ t =Y·ε t .

[0025] Further, the high-temperature strain measurement method based on the thin-film strain sensor further comprises the following steps:

[0026] Step 5. Uncertainty verification;

[0027] Set a time window t k , and calculate the average value of the historical stress in the time window t k in real time (taking the current time as t, the average value of the stress from the time t-t k to the current time is calculated), and then calculate the standard deviation s of the historical stress in the time window t k ; the relative standard deviation s A is calculated according to the standard deviation s: ε FS represents the full-scale strain value; the uncertainty u A is calculated according to the relative standard deviation s A : If the uncertainty u A is less than a preset threshold u y , the thin-film strain sensor is in normal working condition, and the measurement result is valid.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] The present application provides a high-temperature strain measurement method based on a thin-film strain sensor, which is used to cope with the special temperature resistance properties of metal-based sensitive materials and the high-temperature application scenarios of thin-film strain sensors, optimizes the traditional room temperature resistance base point method, uses a high-temperature base point as the calculation base point of the resistance change value, simultaneously compensates for the resistance drift at high temperature, effectively reduces the error, improves the measurement accuracy, and verifies the validity of the measurement result through signal post-processing function, and improves the application range. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a structural schematic diagram of a strain sensor single-arm access Wheatstone bridge in the prior art.

[0031] Figure 2 It is a temperature resistance curve diagram of a typical PdCr strain sensor in the prior art.

[0032] Figure 3The flowchart of the high-temperature strain measurement method based on the thin-film strain sensor in the application is shown.

[0033] Figure 4 The temperature and load change curve of the test process in the application is shown. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and beneficial effects of the application more clear, the application is further described in detail below with reference to the drawings and examples.

[0035] The embodiment provides a high-temperature strain measurement method based on a thin-film strain sensor, and the flow thereof is shown in Figure 3 , and specifically includes the following steps:

[0036] Step 1. Setting a high-temperature base point;

[0037] The temperature signal of the to-be-measured region is collected by a thermocouple, a time window t c is set, the average value of the historical temperature in the time window t c is calculated in real time (the current time is recorded as t, and the average value of the temperature from the time t-t c to the current time is calculated), the difference between the temperature value at the current time and the average value is calculated, when the difference is less than a preset threshold T y , it is determined that the to-be-measured region reaches a constant temperature state, the resistance value R0 of the thin-film strain sensor at the current time is recorded as the high-temperature base point, and the temperature value T at the current time is recorded as the constant temperature;

[0038] Step 2. Calculating the resistance drift rate and completing drift compensation;

[0039] After the to-be-measured region reaches the constant temperature state, a time window Δt is set, and the resistance drift rate D in the time window Δt at the constant temperature is calculated:

[0040]

[0041] Wherein, R t0 represents the starting resistance value of the thin-film strain sensor in the specified time window Δt, and R t0+Δt represents the terminal resistance value of the thin-film strain sensor in the specified time window Δt;

[0042] The resistance value R t of the thin-film strain sensor is collected in real time, drift compensation is completed according to the resistance drift rate D, and the resistance value R D after compensation is represented as:

[0043]

[0044] Wherein, t s is the sampling interval time of the resistance value of the thin-film strain sensor;

[0045] Step 3. Calculate the real-time strain value;

[0046] According to the strain factor GF value and the resistance drift rate D of the thin film strain sensor at constant temperature, calculate the compensated resistance value R t,D The resistance difference ΔR of the high-temperature base point R0 t : ΔR t = R t,D -R0, and further calculate the real-time strain value ε measured by the thin film strain sensor t :

[0047] Step 4. Calculate the real-time stress;

[0048] According to the elastic modulus Y value of the substrate of the thin film strain sensor at constant temperature and the real-time strain value ε, calculate the real-time stress σ measured by the thin film strain sensor t : σ t =Y·ε t .

[0049] Further, the high-temperature strain measurement method based on the thin film strain sensor further comprises the following steps:

[0050] Step 5. Uncertainty verification;

[0051] Set a time window t k , and calculate the average value of the historical stress within the time window t k (take the current time as t, then calculate the average value of the stress from the time t-t k to the current time), and further calculate the standard deviation s of the historical stress within the time window t k ; According to the standard deviation s, calculate the relative standard deviation s A : ε FS represents the full-scale strain value; in the relative standard deviation s A , calculate the uncertainty u A : If the uncertainty u A is less than the preset threshold u y , the thin film strain sensor is working normally, and the measurement result is valid.

[0052] Further, the high-temperature thin film strain sensor is prepared by the following steps:

[0053] ​First, high-temperature alloy 4169 is used as a substrate, the substrate is polished, cleaned and dried; then, a NiCrAlY transition layer film is prepared on the surface of the substrate by magnetron sputtering, and then placed in a quartz boat and put into a vacuum quartz tube furnace to form a thermal growth oxide layer (TGO) by thermal oxidation, and then an Al2O3 insulating layer is prepared on the surface of the TGO layer by radio frequency magnetron reactive sputtering; then, a PdCr sensitive functional layer is prepared on the surface of the Al2O3 insulating layer by radio frequency magnetron reactive sputtering using a metal mask; finally, an Al2O3 protective layer is prepared on the surface of the metal substrate sample on which the PdCr functional sensitive layer has been prepared by radio frequency magnetron reactive sputtering, to improve the high-temperature oxidation resistance of the sensitive functional layer, thereby obtaining a PdCr high-temperature thin film strain sensor with a total thickness of less than 50 microns.

[0054] Under the above fixed preparation process, the GF value of the PdCr high-temperature thin film strain gauge prepared and the elastic modulus Y of the high-temperature alloy 4169 substrate are known a priori, as shown in the following table:

[0055] Temperature range / °C 0～200 200～400 400～600 600～800 800～1000 GF 1.78 1.84 1.94 2.03 2.13 Y / Gpa 190 192 194 196 198

[0056] Further, the temperature signal and the resistance value of the thin film strain sensor are obtained by a signal acquisition and processing module, mainly including signal amplification, filtering processing and AD conversion; for signal amplification, a signal generator using a voltage stabilizer or a current stabilizer is used, and an operational amplifier is used to amplify the collected weak signal according to the actual demand gain to improve the signal-to-noise ratio and measurement accuracy; for filtering processing, a low-pass filter is used to remove high-frequency noise, and analog filters such as RC filters and LC filters can be used to remove high-frequency noise and interference components in the signal, retain useful signal parts, and improve signal quality; for AD conversion, a successive approximation type (SAR) or Σ-Δ type AD converter is used, and after the collected analog signal is converted into a digital signal by the AD converter, it is convenient for further digital processing, analysis and storage.

[0057] Further, the above steps 1-4 can be executed by a signal real-time analysis module, and step 5 can be executed by a signal post-processing module; in addition, the signal post-processing module can also realize frequency domain analysis, for measurement conditions with a sampling frequency greater than twice the substrate resonance frequency, after entering the holding stage, the resistance value R t,D after resistance drift compensation is calculated by step 2, the time domain signal (R t,D ) in a certain sampling point is Fourier transformed according to the sampling frequency, the frequency domain data is obtained, and the strain value ε and the stress σ are calculated in turn according to the amplitude R at the maximum amplitude frequency (i.e. at the resonance frequency) by steps 3 and 4.

[0058] The effectiveness of the high-temperature strain measurement method based on the thin film strain sensor provided in the embodiment is verified by testing, and the temperature and load change curve in a typical test process is as shown in the figure Figure 4 The high-temperature resistance base point is set and the high-temperature resistance drift calculation is completed according to the measurement requirements, and then an arbitrary load is applied to realize the real-time strain measurement based on the resistance drift compensation under the high-temperature base point, and finally the real-time stress is calculated; in the embodiment, the time window t c is set to 64 sampling moments, and the threshold T y is set to 5℃, the time window Δt in step 2 is set to 10s, and the time window t k in step 3 is set to 10 sampling moments, and the threshold u y is set to 5%; N moments are randomly selected at the set temperature, and the real-time strain is measured in turn n=1, 2…N; according to the applied strain and the real-time strain , the strain measurement error value ε err % is calculated.

[0059]

[0060] In summary, the measurement error value of the high-temperature strain measurement method based on the thin film strain sensor provided in the embodiment is 1.5%, which proves the effectiveness of the application, and has the advantages of high measurement precision and small measurement error.

[0061] The above is only a specific embodiment of the application, any feature disclosed in the specification can be replaced by other equivalent or similar purpose alternative features unless specifically stated; all features disclosed, or steps in all methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A high-temperature strain measurement method based on a thin-film strain sensor, characterized in that, Includes the following steps: Step 1. Set the high-temperature baseline; Temperature signals of the area to be measured are acquired using thermocouples, and a time window t is set. c Real-time calculation time window t c The average historical temperature is calculated, and the difference between the current temperature and this average value is determined. If the difference is less than a preset threshold T, the temperature is considered zero. y When the measured area reaches a constant temperature, the resistance value R0 of the thin film strain sensor at the current moment is recorded as the high temperature baseline, and the temperature value T at the current moment is recorded as the constant temperature. Step 2. Calculate the resistance drift rate and perform drift compensation; After the area to be measured reaches a constant temperature, a time window Δt is set, and the resistance shift rate D within the time window Δt at a constant temperature is calculated; the resistance value R of the thin-film strain sensor is acquired in real time. t Drift compensation is performed based on the resistance drift rate D, and the compensated resistance value R is obtained. D ; Step 3. Calculate the real-time strain value; Based on the strain factor GF and resistivity D of the thin-film strain sensor at constant temperature, the compensated resistance value R is calculated. t,D The resistance difference ΔR between the high-temperature base point R0 and the base point R0 t Then, the real-time strain value ε measured by the thin-film strain sensor is calculated. t ; Step 4. Calculate real-time stress; Based on the elastic modulus Y of the substrate of the thin-film strain sensor at a constant temperature and the real-time strain value ε, the real-time stress σ measured by the thin-film strain sensor is calculated. t .

2. The high-temperature strain measurement method based on a thin-film strain sensor according to claim 1, characterized in that, In step 2, the resistance offset rate D is expressed as: Among them, R t0 R represents the initial resistance value of the thin-film strain sensor within a specified time window Δt. t0+Δt This represents the termination resistance value of the thin-film strain sensor within a specified time window Δt.

3. The high-temperature strain measurement method based on a thin-film strain sensor according to claim 1, characterized in that, In step 2, the compensated resistance value R D Represented as: Among them, t s This is the sampling interval for the resistance value of the thin-film strain sensor.

4. The high-temperature strain measurement method based on a thin-film strain sensor according to claim 1, characterized in that, In step 3, the real-time strain value ε t Specifically, it is expressed as follows: ΔR t =R t,D -R0.

5. The high-temperature strain measurement method based on a thin-film strain sensor according to claim 1, characterized in that, In step 4, the real-time stress σ t Specifically, it is represented as: σ t =Y·ε t .

6. The high-temperature strain measurement method based on a thin-film strain sensor according to claim 1, characterized in that, It also includes the following steps: Step 5. Uncertainty verification; Set time window t k Real-time calculation time window t k Average value of historical stress within (Let the current time be t, then calculate the time tt) k The average stress up to the current moment is used to calculate the time window t. k The standard deviation s of the historical stress within the range; the relative standard deviation s is calculated from the standard deviation s. A : ε FS This represents the full-scale strain value; based on the relative standard deviation s A The uncertainty u is calculated. A : If the uncertainty u A Less than the preset threshold u y If the thin-film strain sensor is working properly, then the measurement result is valid.

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