High-order modal test method based on piezoelectric crystal excitation

Abstract

The invention provides a high-order modal test method based on piezoelectric crystal excitation. The high-order modal test method comprises the steps that 1, a piezoelectric vibration exciter is matched through the frequency range of blade simulation; 2, a modal test platform is built, and surface treatment is conducted on a modal test piece; 3, modeling of a three-dimensional laser vibration measurement system is carried out; 4, performing high-frequency excitation and vibration acquisition on the three-dimensional laser vibration measurement system; according to the method, remote high-precision automatic multi-measuring-point arrangement, measured blade three-dimensional model scanning modeling and point-by-point automatic vibration measurement in the blade high-order modal test are completed through the three-dimensional laser Doppler scanning technology, and measurement of modal parameters such as the blade high-order modal shape and the modal frequency is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of aeroengines, and in particular to a high-order modal test method based on piezoelectric crystal excitation. Background Art

[0002] As the model development process continues to deepen, fatigue fracture or corner loss problems continue to occur in compressor rotor and stator blades. The reason for the fracture and corner loss of compressor rotor and stator blades is mostly fatigue damage caused by high-order angular vibration. Therefore, it is extremely important to obtain high-order modes of blades and conduct high-order fatigue tests on blades, which can provide technical support for high-order fatigue failures of blades.

[0003] Traditional exciters can be divided into mechanical, electro-hydraulic, electric and other types according to the driving principle. They can meet the test requirements of the low-order modal part of the aircraft engine blades, but there are still some shortcomings in the ability to test the high-order modal parameters of the blades, mainly manifested in the insufficient high-order excitation capability, and the excitation frequency capability of the existing exciters is difficult to reach above 10kHz, the main reason is the matching problem of high-order excitation energy and excitation frequency. Summary of the invention

[0004] In view of this, the present invention provides a high-order modal test method based on piezoelectric crystal excitation to achieve the purpose of realizing high-order high-cycle fatigue testing of aircraft engine blades.

[0005] The present invention provides the following technical solution: a high-order modal test method based on piezoelectric crystal excitation, comprising: step 1, matching the piezoelectric exciter through the frequency range of blade simulation; step 2, building a modal test platform and performing surface treatment on the modal test piece; step 3, modeling a three-dimensional laser vibrometer system; step 4, performing high-frequency excitation and vibration collection on the three-dimensional laser vibrometer system; step 5, performing high-order modal identification according to the collection result of step 4.

[0006] Furthermore, step 1 includes: determining the influence of piezoelectric crystal selection, layout, installation, fixing method and blade excitation point position on the measured vibration response through the frequency range of blade simulation; matching the power amplifier and piezoelectric exciter according to the influence of the measured vibration response.

[0007] Furthermore, step 2 includes: installing the piezoelectric crystal excitation device and the modal test piece on the modal test platform; facing the three-dimensional laser vibration measurement system to the modal test piece; and connecting the power amplifier to the three-dimensional laser vibration measurement system.

[0008] Furthermore, step 2 also includes: wiping the surface of the modal test piece clean, and after the surface is dry, spraying a spray for enhancing reflectivity on the surface to be tested.

[0009] Further, step 3 includes: step 3.1, establishing a three-dimensional space coordinate system of the modal test piece; step 3.2, arranging measurement points on the modal test piece; step 3.3, scanning the measurement points in step 3.2 to generate a three-dimensional model of the modal test piece.

[0010] Furthermore, step 3.1 includes: establishing two-dimensional calibration points and making the two-dimensional calibration points cover the measurement positions of the modal test piece; and establishing a linear relationship between the pixel position on the computer image and the swing angle of the laser scanning mirror.

[0011] Furthermore, step 3.1 also includes: performing three-dimensional calibration on the main probe of the three-dimensional laser vibrometer system; calibrating the left laser head and the right laser head of the three-dimensional laser vibrometer system based on the calibration point of the main probe, and converging the main probe, the left laser head and the right laser at the same point; repeating the above steps to calibrate a set number of calibration points, and selecting three of the calibration points to complete the coordinate system definition.

[0012] Furthermore, step 4 includes: setting the output signal source voltage value, transmitting the signal source to the power amplifier via the data line, inputting the signal source amplified by the power amplifier into the piezoelectric crystal excitation device, the piezoelectric crystal excitation device vibrates accordingly according to the input signal source waveform, thereby realizing the excitation of the modal test piece; and using the three-dimensional laser vibration measurement system to collect the three-dimensional vibration response signal of the modal test piece point by point.

[0013] Furthermore, step 5 includes: analyzing vibration data of all measuring points, fitting frequency response functions of the measuring points, analyzing modal data using modal identification methods such as polynomial fitting method, and obtaining modal parameters.

[0014] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above technical solutions adopted by the present invention include at least:

[0015] The three-dimensional laser Doppler scanning technology is used to complete the remote high-precision automatic multi-measurement point arrangement in the high-order modal test of the blade, the three-dimensional model scanning and modeling of the measured blade, and the automatic vibration measurement point by point to realize the measurement of the modal parameters such as the high-order modal vibration shape and modal frequency of the blade.

[0016] According to the size of the fixed end of the excitation blade, the blade root is fixed to the piezoelectric exciter by designing a work fixture. The torque of the bolt fixing is determined by the installation frequency of the blade. Generally, when the torque reaches A value or above, the installation frequency of the blade remains unchanged. Therefore, the fixing torque of the bolts of both must be greater than A value by more than 10%.

[0017] The spatial coordinate system of the blade under test is established in the software, and the piezoelectric exciter system is used to provide excitation of waveforms such as sine frequency sweep. The three-dimensional laser scanning technology is used to complete the remote high-precision automatic multi-measurement point arrangement in the high-order modal test of the blade, the three-dimensional model of the blade under test is scanned and modeled, and the vibration is automatically measured point by point.

[0018] Combining the piezoelectric crystal exciter system and 3D laser scanning vibration measurement technology, the piezoelectric crystal exciter system is used to provide stable excitation of waveforms such as sine frequency sweep, and the 3D laser scanning technology is used to realize the measurement point arrangement and 3D model establishment. Based on high-density measurement points, high-precision 3D models and high excitation frequency range, the high-order modal test of the blade is completed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is a schematic diagram of the process of the present invention;

[0021] Figure 2 It is the relationship diagram between the 2D calibration laser point and the mouse point;

[0022] Figure 3 It is a schematic diagram of three-dimensional calibration;

[0023] Figure 4 It is a schematic diagram of the measurement point arrangement;

[0024] Figure 5 It is a schematic diagram of the three-dimensional model. DETAILED DESCRIPTION

[0025] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0026] The following describes the implementation methods of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0027] like Figure 1 As shown, an embodiment of the present invention provides a high-order modal test method based on piezoelectric crystal excitation, which specifically includes:

[0028] Step 1: Match the piezoelectric exciter according to the frequency range of blade simulation;

[0029] Step 2: Build a modal test platform and perform surface treatment on the modal test piece;

[0030] Step 3: Model the three-dimensional laser vibration measurement system;

[0031] Step 4: Perform high-frequency excitation and vibration acquisition on the three-dimensional laser vibration measurement system;

[0032] Step 5: Perform high-order modal identification based on the acquisition results of Step 4.

[0033] The specific content of the above Step 1 is as follows:

[0034] Based on the frequency range of blade simulation, determine the type selection, layout, installation and fixing methods of piezoelectric crystals, etc., and the influence of the blade excitation point position on the measured vibration response. Absorb the theory of piezoelectric crystal drive, match a power amplifier with high power, large excitation voltage and relatively small impedance, match the developed piezoelectric exciter, and verify the working reliability and practicability of the entire exciter system. During specific implementation, the developed piezoelectric exciter mainly consists of a base, a piezoelectric stack, and an inertial mass, and is connected by pre-tightening bolts to prevent the piezoelectric ceramics from being damaged by tension.

[0035] It should be noted that on the working platform of the piezoelectric crystal exciter, the platform mounting holes and the pressing block for fixing the blade root are designed according to the tenon size of a certain aero-engine blade;

[0036] Step 2 includes:

[0037] 2.1 Fix the modal test platform, fix and constrain the modal test platform, which is used to fix the piezoelectric crystal excitation device and ensure that it has sufficient stiffness.

[0038] 2.2 Install the piezoelectric crystal excitation device, use installation bolts or screws to firmly install the piezoelectric crystal excitation device on the modal test platform, and ensure that the installation has sufficient stiffness.

[0039] 2.3 Install the test piece, design a fixture to firmly fix the modal test piece (such as a blade) on the working platform of the piezoelectric crystal excitation device, and ensure that its installation has sufficient stiffness.

[0040] 2.4 Install the three-dimensional laser vibration measurement system, connect the power supply of the three-dimensional laser vibration measurement system to a 220V power supply, use signal connection wires to connect the three probes of the three-dimensional laser vibration measurement system to the system, and use a tripod, etc. to firmly support the three probes of the three-dimensional laser vibration measurement system, and place the left probe, the middle probe and the right probe in a "pin" shape; the middle probe is directly opposite the measured blade, and the left and right probes are placed at an acute angle to the middle probe.

[0041] 2.5 Test cable connection: Use a data signal line to connect the input terminal of the above-mentioned specific high-power amplifier and the signal output terminal of the signal generator of the three-dimensional laser vibrometer system, and input the random signal generated by the signal generator into the above-mentioned high-power amplifier. The signal generator is not limited to the random signal or sinusoidal signal generated by the three-dimensional laser vibrometer system; connect the output terminal of the above-mentioned specific high-power amplifier to the signal input terminal of the piezoelectric crystal excitation device; input the amplified random signal to the piezoelectric crystal excitation device, and based on the piezoelectric inverse effect, drive the above-mentioned piezoelectric crystal exciter to generate a vibration excitation source for modal testing.

[0042] 2.6 Surface treatment of the modal test piece: After wiping the surface of the modal test piece clean and drying it, spray a spray that enhances reflectivity on the surface to be tested, so that the acquired signal is clear and the surface measurement points are accurately located.

[0043] Step 3 includes:

[0044] 3.1 Establish the three-dimensional space coordinate system of the test piece. The specific steps are as follows:

[0045] 3.1.1 Two-dimensional calibration,The vibration measurement system consists of three independent high-precision laser interferometers, with a minimum velocity resolution of 0.01um / s and a measurement frequency range of DC to 100kHz.

[0046] During the test, the three laser beams are controlled by a computer to always focus on the same position of the target, so that the speed values ​​in three different directions can be measured at one measuring point.

[0047] The main laser scanning head is equipped with a high-precision interferometer that can receive and transmit lasers, a laser source, a distance sensor, an XY orthogonal scanning mirror and an HD camera.

[0048] The additional scanning head (left probe, right probe) is used for 3D vibration auxiliary measurement. Except for the camera and distance sensor, the other accessories are the same as the main probe. The laser point moves through the deflection of the scanning mirror in the laser head, and the scanning mirror is driven by the built-in swing motor of the laser head. Within a certain deflection range, the deflection angle is linearly related to the input voltage. In the modal test, the high-definition camera built into the main probe transmits the image of the object to be measured to the 3D laser vibration measurement system test software in real time. The entire test process is always performed on the computer screen. In order to establish the correspondence between the pixel position on the computer image and the swing angle of the laser scanning mirror, so that the display point on the computer screen is consistent with the actual test point, the laser head needs to be calibrated in two dimensions.

[0049] Two-dimensional calibration Figure 2As shown, drag the cursor to establish two-dimensional calibration points on the blade image. The calibration points should cover the blade measurement position. Before two-dimensional calibration, the laser point and the computer mouse point are not well correlated, and there is a distance difference. As the calibration proceeds, the mouse point will establish a linear relationship with the deflection angle of the scanning mirror in the laser head. The correspondence between the pixel position on the computer image and the swing angle of the laser scanning mirror can be completed through interpolation calculation. The more calibration points there are, the more accurate the position of the laser point controlled by the software will be. After the calibration is completed, the laser point and the mouse point can completely overlap. Figure 2 From left to right are the figures before calibration, during calibration and after calibration.

[0050] 3.1.2 Three-dimensional calibration, in order to test the accurate speed value in three dimensions, three independent laser beams must coincide on the surface of the object being measured, the beams must be focused, and there must be enough angle to separate the optical axis of the scanning head. Through three-dimensional calibration, the system can determine the position and direction of each laser head relative to other laser heads and the test object, and determine the user-defined measurement coordinate system.

[0051] Three-dimensional calibration Figure 3 As shown, first calibrate the main probe in three dimensions. After completion, calibrate the left and right laser heads with the calibration point of the main probe as the standard, so that the three laser beams converge at one point, calibrate 4 to 7 test points, and select three of the calibration points to define the origin, X-axis direction and XY plane to complete the coordinate system definition. After setting the three-dimensional positioning point and assigning the coordinate value, the error between the three scanning points can be calculated by the software. Generally, for small structures, the error within 1mm is acceptable. Figure 3 From left to right in the figure are schematic diagrams of the main probe, left and right probes, and three probes.

[0052] 3.2 Measurement point arrangement. When arranging the measurement points, the number of measurement points should be designed considering the modal order required to be measured, and the measurement points should cover the entire blade to be measured. On the blade image, the measurement points are arranged according to the blade geometry. Generally, the higher the vibration order requirement, the more measurement points are needed, such as Figure 4 shown.

[0053] 3.3 Three-dimensional modeling, the main probe contains a distance sensor to determine the distance of each measuring point on the blade surface relative to the laser source. The three-dimensional modal test will use triangulation to obtain the relative position relationship and XYZ coordinates of each test point based on the two conditions of the XY scanning lens deflection angle determined by the two-dimensional calibration and the distance from the laser source to the blade surface obtained by the ranging laser. Through the three-dimensional coordinates of the measuring point, the test measuring points established in 3.2 are used to automatically scan and generate a 3D morphology scan of the blade, such as Figure 5 shown.

[0054] Step 4 includes:

[0055] 4.1 Excitation, select the appropriate excitation waveform, usually a sinusoidal swept frequency signal, set the output signal source voltage value, the signal source is transmitted to the power amplifier via the data line, the signal amplified by the power amplifier is input to the piezoelectric crystal excitation device, the piezoelectric crystal excitation device vibrates accordingly according to the input signal source waveform to achieve the excitation of the blade.

[0056] 4.2 Automatically collect and use the laser probe of the three-dimensional laser vibrometer system to collect the three-dimensional vibration response signal of the blade; set at least 3 averages for each measuring point, and adjust the output voltage and power amplifier output power through the feedback value to obtain a frequency response function with high signal-to-noise ratio and high quality.

[0057] Repeat the above step 5.2 to automatically complete the vibration response signal measurement of all measuring points point by point.

[0058] The step 5 comprises:

[0059] Analyze the vibration data of all measuring points, fit the frequency response function of the measuring points, use the polynomial fitting method and isomodal identification method to analyze the modal data, and obtain modal parameters such as high-order modal vibration shape and modal frequency.

[0060] The vibration differential equation of a general vibration system is Formula 1;

[0061]

[0062] The measurement point response data x(t) and system excitation data f(t) collected by the three-dimensional laser vibration probe are Fourier transformed to obtain the frequency domain vector values ​​X(ω) and F(ω), and then the frequency response function is obtained as shown in Formula 2:

[0063]

[0064] The modal expansion of the frequency response function is shown in formula 3:

[0065]

[0066] From formula 3, we can see that each element of the frequency response function matrix contains the modal parameters and modal mass m of each order of the vibration system. i , modal stiffness k i , modal damping c i or modal frequency ω 0i , damping ratio ξ i Therefore, to identify these modal parameters, only one element of the frequency response function needs to be obtained; each row or column of the frequency response function contains the modal vectors of each order of the vibration system. Therefore, by identifying a row or a column of elements of the frequency response function, all modal parameters of the vibration system, such as vibration shape, frequency, and damping, can be obtained.

[0067] The three-dimensional laser vibrometer system is used to measure the responses and excitation signals of all measuring points, and a row or a column of parameters of the frequency response function are obtained, so as to solve and identify the modal parameters.

[0068] The present invention is mainly used for high-order modal tests of blades. It uses a piezoelectric exciter system to provide excitations of waveforms such as sine frequency sweeps, and uses three-dimensional laser scanning technology to complete remote high-precision automatic multi-measurement point arrangement in high-order modal tests of blades, scan and model the three-dimensional model of the tested blade, and automatically measure vibration point by point to achieve the measurement of modal parameters such as high-order modal vibration shape and modal frequency of blades and stress distribution of blades. The maximum number of measurement points arranged is 512×512, and the speed measurement accuracy is 0.01um / s, which solves the problem of low modeling accuracy and low measurement accuracy of high-order vibration shape caused by a small number of measurement points in ordinary test methods. After the test parameters are set, automated testing is realized, which greatly improves the test efficiency and reduces manpower and time costs. The measured results are more in line with the three-dimensional simulation vibration shape of the blade, realizing the unification of the actual measurement and simulation model, supporting the correction of the simulation calculation model and the measurement of the strain in the high-order area of ​​the blade.

[0069] At the same time, the present invention is also applicable to high-order modal testing and high-order fatigue testing of blades or components in various fields.

[0070] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A high-order modal test method based on piezoelectric crystal excitation, characterized in that: include: Step 1, matching the piezoelectric exciter with the frequency range of the blade simulation; Step 2: Build a modal test platform and perform surface treatment on the modal test piece; Step 3: Modeling a three-dimensional laser vibration measurement system; Step 4, performing high-frequency excitation and vibration collection on the three-dimensional laser vibrometer system; Step 5: Perform high-order modal identification based on the acquisition results of step 4.

2. The high-order modal test method based on piezoelectric crystal excitation according to claim 1 is characterized in that: The step 1 comprises: Through the frequency range of blade simulation, determine the influence of piezoelectric crystal selection, layout, installation, fixing method and blade excitation point position on the measured vibration response; The power amplifier and piezoelectric exciter are matched based on the impact of the measured vibration response.

3. The high-order modal test method based on piezoelectric crystal excitation according to claim 2 is characterized in that: The step 2 comprises: Install the piezoelectric crystal excitation device and the modal test piece on the modal test platform; Place the three-dimensional laser vibrometer system directly on the modal test piece; Connect the power amplifier to the 3D laser vibrometer system.

4. The high-order modal test method based on piezoelectric crystal excitation according to claim 3 is characterized in that: The step 2 further comprises: wiping the surface of the modal test piece clean, and after the surface is dry, spraying a spray for enhancing reflectivity on the surface to be tested.

5. The high-order modal test method based on piezoelectric crystal excitation according to claim 4 is characterized in that: The step 3 comprises: Step 3.1, establish the three-dimensional space coordinate system of the modal test piece; Step 3.2, arranging the measuring points of the modal test piece; Step 3.3: Scan the measuring points in step 3.2 to generate a three-dimensional model of the modal test piece.

6. The high-order modal test method based on piezoelectric crystal excitation according to claim 5 is characterized in that: The step 3.1 comprises: Establishing two-dimensional calibration points and making the two-dimensional calibration points cover the measurement positions of the modal test piece; A linear relationship is established between the pixel position on the computer image and the swing angle of the laser scanning mirror.

7. The high-order modal test method based on piezoelectric crystal excitation according to claim 6 is characterized in that: The step 3.1 also includes: Carry out three-dimensional calibration of the main probe of the three-dimensional laser vibrometer system; The left laser head and the right laser head of the 3D laser vibrometer system are calibrated based on the calibration point of the main probe, and the main probe, the left laser head and the right laser are converged at the same point; Repeat the above steps to calibrate the set number of calibration points, and select three of them to complete the coordinate system definition.

8. The high-order modal test method based on piezoelectric crystal excitation according to claim 7 is characterized in that: The step 4 comprises: The output signal source voltage value is set, and the signal source is transmitted to the power amplifier via the data line. The signal source amplified by the power amplifier is input into the piezoelectric crystal excitation device, and the piezoelectric crystal excitation device vibrates accordingly according to the input signal source waveform to realize the excitation of the modal test piece; The three-dimensional vibration response signal of the modal test piece is collected point by point using a three-dimensional laser vibrometer system.

9. The high-order modal test method based on piezoelectric crystal excitation according to claim 8, characterized in that: The step 5 comprises: Analyze the vibration data of all measuring points, fit the frequency response function of the measuring points, use the modal identification method such as polynomial fitting method to analyze the modal data, and obtain the modal parameters.

Images