High-temperature dynamic strain measurement method based on thin film strain gauge

Abstract

The invention belongs to the technical field of high-temperature thin film sensors, provides a high-temperature dynamic strain measurement method based on a thin film strain gauge, and is used for solving the problems that a traditional contact strain gauge is difficult to assemble, the surface structure of a part is damaged, and the accuracy is poor. The method comprises the following steps: firstly, arranging a film strain gauge and a temperature sensor on the surface of a test piece, and synchronously acquiring time-domain resistance signals and temperature information in the vibration process of the test piece; then, converting the time-domain resistance signal into a frequency-domain resistance signal by adopting spectral analysis, taking the resistance amplitude at the zero frequency as the initial resistance of the thin film strain gauge, and taking the resistance amplitude at the resonant frequency of the test piece as the resistance response quantity of the thin film strain gauge; and finally, determining a strain factor of the film strain gauge according to the temperature information, and calculating the dynamic strain of the test piece based on the initial resistance, the resistance response amount and the strain factor of the film strain gauge. On the basis, the strain measurement error is remarkably reduced, and the accuracy of dynamic strain measurement is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature thin film sensors, and specifically provides a high-temperature dynamic strain measurement method based on a thin film strain gauge. Background Art

[0002] In the fields of aerospace, automobile, energy, metallurgy, etc., the operating temperature and strength of high-temperature components are getting higher and higher, and the working conditions are getting closer and closer to the material performance limit; high-temperature components working in a high-temperature and high-load environment for a long time are very likely to be damaged or even broken, seriously affecting production safety; among the many causes of damage to high-temperature components, vibration is an important factor causing component damage, and the stress caused by vibration will aggravate the wear between components and accelerate structural failure; in this context, dynamic strain signal vibration analysis of high-temperature components has become an important part of related fault analysis and health monitoring.

[0003] Among various strain testing and monitoring methods, traditional contact strain gauges are usually installed on the surface of the specimen by embedding or slotting, and have been widely used in related scenarios, but there are problems such as difficult assembly, damage to the surface structure of the component, and poor accuracy. Therefore, new thin film strain gauges have been proposed and developed. Thin film strain gauges are mainly prepared by direct integration on the surface of the component through thin film deposition technologies such as magnetron sputtering and electron beam evaporation. The thickness and size are much smaller than traditional contact strain gauges. They have the characteristics of high integration, fast and sensitive response, accurate measurement, long fatigue life, etc., and have significant advantages in strain measurement. Summary of the invention

[0004] The purpose of the present invention is to propose a high-temperature dynamic strain measurement method based on a thin film strain gauge to solve the problems of difficult assembly, damage to the surface structure of components, and poor accuracy of traditional contact strain gauges. The present invention utilizes the fast and sensitive response characteristics of the thin film strain gauge to collect the resistance change of the thin film strain gauge, and obtains the dynamic strain of the specimen after frequency domain analysis; the present invention can not only obtain the frequency spectrum distribution of the dynamic strain of the specimen, but also use frequency domain analysis technology to reduce or eliminate the interference of factors such as ambient temperature fluctuations and high temperature zero drift on the dynamic strain measurement, thereby significantly improving the accuracy of dynamic strain measurement without taking measures such as temperature compensation and zero point compensation.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A high temperature dynamic strain measurement method based on a thin film strain gauge, characterized by comprising the following steps:

[0007] A thin film strain gauge and a temperature sensor are arranged on the surface of the specimen;

[0008] During the vibration of the specimen, the time domain resistance signal and temperature information are acquired synchronously by the resistance signal acquisition device and the temperature signal acquisition device;

[0009] The time domain resistance signal is converted into the frequency domain resistance signal by spectrum analysis, the resistance amplitude at zero frequency is taken as the initial resistance of the thin film strain gauge, and the resistance amplitude at the resonant frequency of the specimen is taken as the resistance response of the thin film strain gauge;

[0010] The strain factor of the thin film strain gauge is determined according to the temperature information, and the dynamic strain of the specimen is calculated based on the initial resistance, resistance response and strain factor of the thin film strain gauge.

[0011] Furthermore, the sampling rate of the resistance signal acquisition device is twice or more of the resonant frequency of the test piece.

[0012] Furthermore, the spectrum analysis uses Fourier transform, specifically discrete Fourier transform, fast Fourier transform, short-time Fourier transform, Z transform, wavelet transform and other methods.

[0013] Furthermore, the dynamic strain of the specimen is specifically:

[0014]

[0015] Among them, ε represents the dynamic strain of the specimen, R0 represents the initial resistance of the thin film strain gauge, GF represents the gauge factor of the thin film strain gauge, It represents the resistance response of the thin film strain gauge.

[0016] Furthermore, the thin film strain gauge adopts a high temperature thin film strain gauge, including: a structural transition layer, an insulating layer, a strain sensitive functional layer and a protective layer which are stacked in sequence from bottom to top on the surface of the specimen.

[0017] Based on the above technical solution, the beneficial effects of the present invention are:

[0018] The present invention provides a method for measuring dynamic strain signals based on a thin film strain gauge, which has the following advantages:

[0019] 1) The present invention transforms the dynamic strain information obtained by the thin film strain gauge from the time domain to the frequency domain, and obtains the spectrum distribution of the dynamic strain through the frequency domain analysis method, which is helpful to analyze the comprehensive effects of multiple frequency dynamic strains on the specimen, and makes the analysis of the periodicity, harmonics and frequency characteristics of the dynamic strain signal easier and more intuitive, solving the problem that the traditional strain measurement and analysis method cannot process the strain signal in the time domain when multiple dynamic strains exist at the same time;

[0020] 2) After the present invention converts the dynamic strain signal obtained by the thin film strain gauge into the frequency domain, it is easier to identify and remove the interference noise brought by the outside world. In a complex and harsh working environment, it can significantly reduce the strain measurement error and improve the accuracy of dynamic strain measurement;

[0021] 3) The present invention uses a frequency domain analysis method to directly determine the initial resistance of the thin film strain gauge. Compared with the traditional strain analysis method that relies on temperature compensation, circuit structure, etc. for compensation, the present invention is more convenient and accurate in obtaining the initial resistance (resistance zero point) of the thin film strain gauge at high temperature without temperature compensation, thereby eliminating the measurement error caused by inaccurate temperature compensation and improving the dynamic strain measurement accuracy in a high temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the process of a high temperature dynamic strain measurement method based on a thin film strain gauge in an embodiment of the present invention.

[0023] Figure 2 Schematic diagram of the structure of the thin film strain gauge on the surface of the specimen in an embodiment of the present invention.

[0024] Figure 3 4 is a system block diagram of a signal acquisition system in an embodiment of the present invention.

[0025] Figure 4 It is a time domain information diagram of the thin film strain gauge in an embodiment of the present invention.

[0026] Figure 5 It is a frequency domain information diagram of the thin film strain gauge in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0028] This embodiment provides a high temperature dynamic strain measurement method based on a thin film strain gauge. The specific process is as follows: Figure 1 As shown, the following steps are included:

[0029] Step 1. Prepare a high temperature thin film strain gauge on the surface of the alloy specimen;

[0030] Firstly, an alloy specimen is used as a substrate, and the surface of the specimen is polished, cleaned and blown dry; then, a NiCrAlY transition layer film is prepared on the surface of the specimen by magnetron sputtering technology, and then the specimen is placed in a quartz boat and placed in a vacuum quartz tube furnace for thermal oxidation to form a thermally grown oxide layer (TGO), and then an Al2O3 insulating layer is prepared on the surface of the TGO layer by radio frequency magnetron reactive sputtering; then, a FeCrAl 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 specimen on which the FeCrAl functional sensitive layer has been prepared by radio frequency magnetron reactive sputtering, so as to improve the high-temperature oxidation resistance of the sensitive functional layer, thereby obtaining a FeCrAl high-temperature thin film strain gauge with a total thickness of less than 50 microns;

[0031] Step 2. Collect the resistance signal of the thin film strain gauge on the surface of the specimen;

[0032] For thin film strain gauges, a specific lead connection method is required to connect the strain gauge to the resistance monitoring circuit; in this embodiment, high temperature platinum paste and platinum leads are used to achieve this, such as Figure 2 As shown, specifically:

[0033] First, apply high-temperature platinum slurry to the surface of the electrode area of ​​the thin film strain gauge; then, use a pure platinum wire with a diameter of 75 microns to embed into the applied platinum slurry and place it on a heating table set at a temperature of 150°C for 30 minutes to complete the initial curing; finally, place the specimen in a high-temperature furnace and heat it to 1000°C at a rate of 5°C / min and keep it warm for 2 hours to complete the final curing and realize the lead connection of the thin film strain gauge;

[0034] The thin film strain gauge on the surface of the specimen is connected to an external resistance signal acquisition device through lead connection, such as Figure 3 As shown, the time domain resistance information of the thin film strain gauge when the specimen vibrates is obtained and recorded by the resistance signal acquisition device, and the temperature information of the specimen is synchronously acquired by the temperature sensor; in this embodiment, the resonant frequency of the specimen is 284 Hz, the temperature of the specimen is 600°C, the acquisition frequency of the resistance signal acquisition device is set to 4800 Hz, and the acquired time domain resistance signal is as follows Figure 4 As shown; it should be noted that the resonant frequency of the specimen can be known a priori through the existing technology in this field;

[0035] Step 3. Convert the collected time domain resistance signal into a frequency domain amplitude signal through spectrum analysis;

[0036] Fourier transform is used to convert the time domain resistance signal into the frequency domain resistance signal, such as Figure 5 As shown, the horizontal axis is the frequency and the vertical axis is the resistance amplitude; in this embodiment, the frequency domain resistance signal has four peaks at 0 Hz, 50 Hz, 150 Hz and 284 Hz respectively;

[0037] Step 4. Obtain effective dynamic strain information through resistance response type;

[0038] The resistance amplitude at zero frequency is taken as the initial resistance (resistance zero point) of the thin film strain gauge in the unstressed state, and the resistance amplitude at the resonant frequency of the specimen is taken as the resistance response of the thin film strain gauge due to dynamic strain, and the peak values ​​at other frequencies are the power frequency noise response; in this embodiment, the peak values ​​at 50 Hz and 150 Hz are the power frequency noise response; the peak value at a frequency of 284 Hz corresponds to the resistance response of the thin film strain gauge due to dynamic strain, specifically 0.83 Ω; the peak value at 0 Hz corresponds to the initial resistance of the thin film strain gauge in the unstressed state, specifically 906.48 Ω;

[0039] Step 5. Calculate the dynamic strain of the specimen based on the temperature information and the effective dynamic strain information;

[0040] The strain factor of the thin film strain gauge is determined according to the temperature information, and the dynamic strain of the specimen is calculated based on the initial resistance, resistance response and strain factor of the thin film strain gauge, which is specifically expressed as:

[0041]

[0042] Among them, ε represents the dynamic strain of the specimen, that is, the measurement result; R0 represents the initial resistance of the thin film strain gauge, GF represents the gauge factor of the thin film strain gauge, It represents the resistance response of the thin film strain gauge;

[0043] In this embodiment, the strain factor of the thin film strain gauge at 600°C is 2, that is, GF=2. It should also be noted that the strain factor of the thin film strain gauge at a specified temperature can be known a priori through the prior art in the art; accordingly, R0=906.48Ω, ΔR f =0.83Ω, the calculated dynamic strain is: ε=457.8μ, thus completing the high temperature dynamic strain measurement.

[0044] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A high temperature dynamic strain measurement method based on a thin film strain gauge, characterized in that: The following steps are involved: A thin film strain gauge and a temperature sensor are arranged on the surface of the specimen; During the vibration of the specimen, the time domain resistance signal and temperature information are acquired synchronously by the resistance signal acquisition device and the temperature signal acquisition device; The time domain resistance signal is converted into the frequency domain resistance signal by spectrum analysis, the resistance amplitude at zero frequency is taken as the initial resistance of the thin film strain gauge, and the resistance amplitude at the resonant frequency of the specimen is taken as the resistance response of the thin film strain gauge; The strain factor of the thin film strain gauge is determined according to the temperature information, and the dynamic strain of the specimen is calculated based on the initial resistance, resistance response and strain factor of the thin film strain gauge.

2. The high temperature dynamic strain measurement method based on thin film strain gauge according to claim 1 is characterized in that: The sampling rate of the resistance signal acquisition device is twice or more of the resonant frequency of the test piece.

3. The high temperature dynamic strain measurement method based on thin film strain gauge according to claim 1 is characterized in that: The spectrum analysis uses Fourier transform, specifically one of discrete Fourier transform, fast Fourier transform, short-time Fourier transform, Z transform, and wavelet transform.

4. The high temperature dynamic strain measurement method based on thin film strain gauge according to claim 1 is characterized in that: The dynamic strain of the specimen is: Among them, ε represents the dynamic strain of the specimen, R0 represents the initial resistance of the thin film strain gauge, GF represents the gauge factor of the thin film strain gauge, It represents the resistance response of the thin film strain gauge.

5. The high temperature dynamic strain measurement method based on thin film strain gauge according to claim 1, characterized in that: The thin film strain gauge comprises: a structural transition layer, an insulating layer, a strain sensitive functional layer and a protective layer which are stacked in sequence from bottom to top on the surface of the specimen.

Images