CN108663411A - A kind of temperature-compensation method of electromechanics impedance structure damage monitoring - Google Patents

Abstract

The invention discloses a temperature compensation method for monitoring damage of an electromechanical impedance structure. First, through the measurement and analysis of the impedance (admittance) signal of the tested object, the influence of temperature changes on its impedance signal is studied. Both the real part and the imaginary part of the impedance spectrum of the measured structure drift in a certain direction with the change of temperature. Secondly, the temperature compensation algorithm based on the minimum RMSD is used to compensate the reference signal, and the frequency and amplitude compensation amount of the reference signal are curve-fitted to obtain the relationship between temperature and the two compensation amounts, that is, the temperature compensation amount fitting curve of the reference signal . Finally, the temperature compensation amount fitting curve of the reference signal is used for compensation of different temperature monitoring signals. This effective and quantitative temperature compensation algorithm based on electromechanical impedance technology can realize the compensation of damage impedance (admittance) signals in any experimental temperature range, and improves the accuracy of damage location and quantification based on electromechanical impedance technology in structural health monitoring. .

Description

A Temperature Compensation Method for Electromechanical Impedance Structural Damage Monitoring

technical field

The invention relates to a temperature compensation method for damage monitoring of electromechanical impedance structures, and belongs to the technical fields of nondestructive testing technology and structural health monitoring.

Background technique

With the continuous development of science, technology and industry, various materials are more and more widely used in engineering structures, mechanical structures are becoming more and more complex, and equipment functions are becoming more and more perfect. At the same time, the requirements for materials and structures are also increasing. higher. Structural health monitoring is a very active research field in mechanical and structural engineering, and the research in this field has a wide and far-reaching engineering background. Once the material is damaged, the structural health is compromised. The decline of the bearing capacity of the structure during the service period is defined as the damage of the structure. The decline of the structural bearing capacity is generally caused by the damage of the structural components and their connectors. The damage of all load-bearing structures during the service period is gradually formed. If the damage gradually formed during the service period of the structure cannot be detected in time, it will endanger the overall structural safety of the project, and even lead to major accidents, endangering the life and property of personnel. Therefore, it is of great significance to implement health status monitoring and fault diagnosis for the structure and key components of important engineering facilities to prolong the life of engineering facilities and ensure production safety.

The electromechanical impedance method is a new type of structural health monitoring method that has emerged in recent years. Because of its high sensitivity to defect detection and convenient and fast signal acquisition and processing, it has been widely used in the field of structural health monitoring. The piezoelectric element in electromechanical impedance structural health monitoring can be pasted on the surface of the structure or placed inside the structure. It can be used as a driver for signal excitation and as a sensor for signal monitoring. Affected by the electromechanical coupling between the piezoelectric element and the structure, different degrees of structural damage will lead to different electrical responses of the piezoelectric element, that is, different electromechanical impedance signals. In structural health monitoring, the judgment of structural damage can be realized by analyzing the changes of electromechanical impedance response signals.

However, in the actual application process, since the temperature will change the properties of the structure, the adhesive layer, and the piezoelectric element, the application of electromechanical impedance technology for structural health monitoring is easily affected by the ambient temperature, and accurate monitoring results cannot be obtained. Especially when the initial damage of the structure occurs, the monitoring data is inaccurate due to the instability of the surrounding environment, and the initial damage of the structure is ignored. Initial damage that is allowed to deepen over time can have more serious consequences.

Contents of the invention

In order to solve the above problems in the prior art, the present invention proposes a temperature compensation method for monitoring damage of electromechanical impedance structures.

The purpose of the present invention is to design and propose an effective and quantitative temperature compensation algorithm based on the minimum RMSD to eliminate the impact of the ambient temperature on the monitoring results during the monitoring process, in view of the fact that the structural health monitoring technology based on the electromechanical impedance method is easily disturbed by environmental temperature factors. Impact.

The technical solution adopted in the present invention is a temperature compensation method for monitoring damage of electromechanical impedance structures. First, the structure is composed of a high and low temperature test chamber 1, a computer 3, a precision impedance analyzer 2, a test piece 4 and a piezoelectric ceramic sheet 5. In the health monitoring system, the high and low temperature test chamber 1 is connected to the precision impedance analyzer 2, and the precision impedance analyzer 2 is connected to the computer 3; the test piece 4 and the piezoelectric ceramic sheet 5 are installed in the high and low temperature test chamber 1.

Use the structural health monitoring system to monitor the original impedance (admittance) signal of the non-destructive tested object within a certain temperature range, and obtain the original impedance by observing and analyzing the original impedance (admittance)-frequency curve of the non-destructive tested object at different temperatures (admittance) signal changes with temperature. The original impedance signal of different tested parts varies with temperature. As the temperature rises, the real part of the impedance signal of the non-destructive tested part drifts regularly to different frequency regions, and at the same time, it also changes in the amplitude direction, and The amplitude changes at the resonant peak are more obvious; the imaginary part of the impedance signal of the non-destructive test piece increases with the temperature, and the imaginary part of the impedance spectrum also drifts regularly in the frequency range, and the drift law is more obvious than the real part. When the electromechanical impedance signal is affected by temperature changes, it will drift in the direction of frequency and amplitude, and the greater the temperature change, the greater the signal drift.

Secondly, after determining the change law of the impedance signal with temperature, in order to better characterize the damage degree of the structure, the root mean square deviation (Root Mean Square Deviation, RMSD) was introduced as the damage index for the analysis and processing of the impedance signal , to realize the identification of quantitative and localized structural damage. Impedance signals drift regularly with temperature. Eliminating the influence of temperature on the impedance signal is actually to effectively move the frequency and amplitude of the impedance spectrum to a position at a specified temperature, so as to achieve the effect of temperature compensation. Since the signal drifts in the direction of frequency and amplitude, it is necessary to compensate the frequency and amplitude separately, and find the minimum RMSD to determine the optimal frequency and amplitude between the actual monitored impedance signal and the reference impedance signal. The compensation amount, the optimal compensation amount is used for the compensation of the impedance signal, so as to eliminate the drift of the impedance characteristic caused by the temperature change. Then through the method of linear fitting, the linear relationship fitting curves of the optimal compensation value of frequency and amplitude and temperature are obtained. Using this linear fitting relationship and the best compensation value to bring the previously collected impedance signals of non-destructive specimens at different temperatures, the frequency and the compensated impedance signal are obtained, and the temperature compensation of the impedance signal is realized.

Finally, using the structural health monitoring system based on electromechanical impedance technology built in the early stage, within a certain temperature range, the impedance signal measurement and data acquisition of the tested parts with different types or different degrees of structural defects in actual working conditions are carried out. In order to obtain the impedance signal of the tested piece at different temperatures, use the linear relationship between the best frequency compensation value and the amplitude best compensation value and temperature obtained by the temperature compensation algorithm to fit the curve, and the impedance signal of the damaged tested piece Perform frequency and amplitude compensation, and then realize temperature compensation for the structural health monitoring results based on the electromechanical resistance method.

The advantages of the present invention are: the effective and quantitative temperature compensation algorithm based on the electromechanical impedance technology can quickly extract the change law of the electromechanical impedance monitoring signal affected by temperature, and then realize the impedance (admittance) signal of the tested piece in any temperature range The compensation in terms of frequency and amplitude can also compensate the structural damage monitoring signal obtained in the actual working conditions, effectively reducing and avoiding the influence of temperature on the monitoring results, and greatly improving the structural health based on electromechanical impedance technology. Accuracy of lesion localization and quantification in monitoring.

Description of drawings

Figure 1 is a schematic diagram of a structural health monitoring system based on the electromechanical resistance method.

Figure 2 is a graph of the real part of the impedance of the non-destructive test piece at different temperatures.

Figure 3 is a flow chart of an effective quantitative temperature compensation algorithm.

Fig. 4 is a fitting curve diagram of the linear relationship between the optimal frequency compensation value and temperature.

Fig. 5 is a curve diagram of the real part of the impedance of the non-destructive tested object after compensation.

Figure 6 is a histogram of the damage index of the tested piece before and after compensation.

In the figure: 1-high and low temperature test chamber, 2-precision impedance analyzer, 3-computer, 4-tested piece, 5-piezoelectric ceramic sheet.

Detailed ways

In order to make the technical solutions and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the drawings in the embodiments of the present invention:

The invention proposes an effective quantitative temperature compensation method for monitoring the structural damage of electromechanical impedance. Firstly, the structural health monitoring system based on the electromechanical impedance method is used to collect and analyze the impedance signal of the tested object. Taking the aluminum alloy beam structure as an example, the influence of temperature change on the impedance signal of the aluminum beam is studied. It was found that both the real part and the imaginary part of the impedance spectrum of the tested piece drifted in a certain direction with the change of temperature. Through calculation, curve fitting is carried out on the compensation amount of impedance spectrum at different temperatures. It is found that the compensation amount of impedance spectrum has a linear relationship with the temperature change. Then, the temperature control experiments were carried out on the aluminum beams under three different damage conditions, and the results proved that the small damage will not cause a large shift in the impedance spectrum, so the compensation curve without damage can be used to correct the damage. Time monitoring signal for temperature compensation. Finally, the compensation curve of the impedance signal of the non-destructive aluminum beam is used to perform temperature compensation on the impedance signal under three different damage conditions, and the compensation effect is ideal, which can effectively realize the evaluation of the structural damage condition. Specifically include the following steps:

S1: Use the structural health monitoring system, as shown in Figure 1, to detect the impedance signal of the non-destructive aluminum beam specimen within a certain temperature range. For example, collect the corresponding initial impedance signals at different temperatures, and select the impedance signal at the normal temperature T ₀ of the experimental environment as the reference signal Z(f). Through observation and analysis, it can be concluded that the real part of the impedance spectrum of the non-destructive aluminum beam drifts to the low frequency region regularly with the increase of temperature, and the drift in the amplitude direction also changes, and the amplitude change at the resonance peak is relatively large. Obviously, as shown in Figure 2.

S2: After determining the change law of the impedance signal with temperature, eliminating the influence of temperature on the impedance spectrum is actually to effectively move the frequency and amplitude of the impedance spectrum to a position at a specified temperature, thereby achieving temperature compensation. Use the method of finding the minimum root mean square deviation (RMSD) to determine the optimal compensation amount △f and △Z between the monitoring impedance signal and the reference impedance signal in frequency and amplitude, and use the compensation amount for the monitoring signal Compensation is a temperature compensation algorithm based on the minimum RMSD. The flow chart of the algorithm is shown in Figure 3. The expression of RMSD is

In the formula, Z _i,1 - the impedance value of the reference signal of the structure;

Z _i,2 ——impedance value after structure change;

n——is the number of data points.

In view of the situation that the impedance signal caused by the ambient temperature drifts in the frequency and amplitude directions at the same time, it is necessary to compensate the frequency and amplitude separately. First, the impedance spectrum is compensated in the frequency direction, and the impedance signal at temperature T ₀ is used as the reference signal to realize the temperature compensation of the frequency of the impedance signal at other temperatures. Using the linear fitting method, the fitting curve △f(t) of the linear relationship between the frequency optimal compensation amount △f and the temperature T is obtained. By bringing △f(t) into the initial impedance signal Z, the frequency-compensated signal Z(f)=Z(f+△f(t)) is obtained, and the frequency compensation of the impedance signal is realized. Fig. 4 is a fitting curve diagram of the linear relationship between the optimal frequency compensation value and temperature.

S3: Similarly, the minimum RMSD algorithm is used to determine the impedance amplitude compensation signal at different temperatures to obtain the amplitude compensation amount ΔZ. Through the linear fitting method, the linear relationship fitting curve △Z(t) of the amplitude compensation amount △Z and the temperature T is obtained. By bringing △Z(t) into the impedance signal after frequency compensation in the previous step, the signal after amplitude compensation and frequency compensation Z(f)=Z(f+△f(t))+△Z(t), The amplitude compensation and frequency compensation of the impedance signal are realized. Fig. 5 is a curve diagram of the real part of the impedance of the non-destructive tested object after compensation. At the same time, the RMSD of the impedance signal before and after compensation is calculated separately, which also reflects the effectiveness of the temperature compensation algorithm, as shown in Figure 6.

S4: Treat loading defects, single-hole defects and double-hole defects on the tested aluminum beam specimens, and collect their electromechanical impedance signals for observation and analysis. Similarly, use the temperature compensation algorithm based on the minimum RMSD Compensate the impedance signals at different temperatures to obtain the optimal compensation amount of frequency and amplitude and the fitting curve of the compensation amount. From this, it can be known that the impedance compensation fitting curves of the three different damages and the compensation fitting curves without damage The trend is very close, and the drift of the impedance spectrum due to the influence of temperature is basically the same. The compensation fitting curve when there is no damage can be used to perform temperature compensation on the monitoring signal when there is damage, and the compensation amount obtained in the previous step can be realized. The fitted curve is used to compensate any on-line real-time monitoring signal.

Claims (1)

1. a kind of temperature-compensation method of electromechanics impedance structure damage monitoring, it is characterised in that：First, by high-low temperature test chamber, Computer, precise impedance analyzer, test specimen and piezoelectric ceramic piece composed structure health monitoring systems, high-low temperature test chamber and Precise impedance analyzer interconnects, precise impedance analyzer and computer interactive connection；Test specimen and piezoelectric ceramic piece peace In high-low temperature test chamber；

The original impedance signal for acquiring lossless test specimen in certain temperature range using structural healthy monitoring system, passes through sight Original impedance-the frequency curve for examining and analyzing lossless test specimen under different temperatures obtains original impedance signal and varies with temperature Rule；The rule that the original impedance signal of different test specimens varies with temperature is different, lossless tested with the raising of temperature The impedance signal real part of test specimen regularly drifts about to different frequency area, while also being changed in amplitude direction, and in resonance Amplitude variation is more apparent at peak；Lossless test specimen impedance signal imaginary part is increased with temperature, and impedance spectrum imaginary part then equally exists Occur regularly to drift about in frequency range, and moving tracks are more more obvious than real part；When electromechanical impedance signal is become by temperature When the influence of change, it can drift about in frequency and amplitude direction, and the bigger signal drift amount of temperature change is bigger；

Secondly, it after being determined that impedance signal varies with temperature rule, in order to preferably characterize the degree of injury of structure, introduces Root-mean-square-deviation RMSD is as damage index, for the analysis and processing to impedance signal, realize to the quantitative of structural damage with The identification of positioning；With the variation of temperature regular drift can occur for impedance signal；Influence of the temperature to impedance signal is eliminated, Practical is exactly by effectively being moved with amplitude to impedance spectral frequency, the position under assigned temperature being moved into, to reach To the effect of temperature-compensating；Since signal has drift in frequency and amplitude direction, need respectively to carry out frequency and amplitude Compensation is found minimum RMSD and be can determine between the impedance signal of actual monitoring and reference impedance signal in frequency and amplitude The optimal compensation amount is used for the compensation of impedance signal, to eliminate the impedance characteristic caused by temperature change by optimal compensation rate Drift；Again by the method for linear fit, the linear pass of frequency the optimal compensation value and amplitude the optimal compensation value and temperature is obtained It is matched curve；Lossless test specimen under the different temperatures previously acquired is brought into using this linear fit relationship and the optimal compensation value to hinder Antinoise signal realizes the temperature-compensating of impedance signal to get the impedance signal arrived after frequency and compensation；

Finally, right in certain temperature range using the structural healthy monitoring system based on electromechanical resistance technique built early period The test specimen progress impedance signal measurement and data that different type or different degrees of fault of construction are generated in actual condition are adopted Collection；To obtain the impedance signal of test specimen under different temperatures, the frequency obtained using previously passed temperature compensation algorithm is most The linear relationship matched curve of good offset and amplitude the optimal compensation value and temperature, the impedance signal to damaging test specimen carry out Frequency and amplitude compensation, and then realize the temperature-compensating to the monitoring structural health conditions result based on the anti-method of electrical equipment unit.