Self-calibration composite material strain test system and method for propeller

Abstract

The invention discloses a self-calibration strain test system and method for a propeller composite material, and solves the problems of high-precision measurement and real-time calibration of dynamic strain in a complex flow field environment. The core of the system comprises a linear fiber grating sensor array attached to the surface of a blade and an optical fiber demodulator integrated on a propeller hub, sensors are symmetrically arranged in the spanwise direction, and infrared transmitting / receiving devices in pairs intersect at the circle center O of the propeller hub when positioning is accurate, so that a global reference is formed; a single sensor is installed through a double-shaft flexible hinge, a shape memory alloy (SMA) wire driving mechanism is integrated, and spanwise / chordwise independent micro-motion calibration can be achieved according to infrared intersection point offset. A failure alarm is arranged in the sensor, gallium-indium-tin alloy is filled in hollow glass beads, alarm is triggered only when more than or equal to 3 beads are broken to form a conductive path, false alarm is avoided, and the problem of dynamic strain monitoring of the large-deformation composite propeller in high-pressure, low-temperature and strong-electromagnetic-interference environments is solved through the anti-electromagnetic-interference module.

Description

Technical Field

[0001] The present invention relates to the field of propeller material strain detection, and in particular to a self-calibrating composite material strain testing system for a propeller. Background Art

[0002] As a core component of marine engineering equipment and ship propulsion systems, the dynamic strain performance of large-deformation composite propellers is crucial for ensuring navigation efficiency, reducing energy consumption, and improving structural safety. Accurately acquiring dynamic strain data during actual propeller operation is a key prerequisite for optimizing design, assessing lifespan, and ensuring reliable operation. However, current testing technologies face numerous bottlenecks in practical application, severely hindering the development of related fields. In laboratory settings, high-speed video and laser Doppler measurement techniques, with their high precision and non-contact measurement advantages, can accurately capture propeller deformation characteristics. These techniques rely on the stable and controllable conditions provided by specific facilities such as circulating water tanks. They measure deformation by tracking characteristic points on the propeller surface or analyzing Doppler frequency shifts. However, the limitations of these methods become apparent when the scenario shifts to lake or sea trials. The openness and complexity of field environments make it difficult to deploy fixed measurement equipment. Furthermore, factors such as natural water flow and unstable lighting conditions make high-speed video images difficult to maintain, and laser Doppler measurement signals are susceptible to interference and interruption. Therefore, these laboratory techniques cannot be effectively implemented during lake or sea trials, resulting in almost no dynamic strain data for propellers under real operating conditions, seriously affecting the accurate evaluation and optimization of their actual performance. When using strain gauges for testing, although strain information can be obtained to a certain extent, each strain gauge requires an independent cable to connect to the data acquisition equipment. This not only physically limits the number of measurement points (excessive cables make installation complicated and maintenance difficult, and increase the risk of signal interference), but also makes it difficult to meet the needs of large-deformation composite propellers for multi-point, high-density strain monitoring. At the same time, in deep-sea environments, sensors are prone to displacement, affecting detection accuracy. Existing systems rely on manual calibration and cannot compensate for installation deviations and environmental disturbances in real time, resulting in low efficiency. There is also a lack of effective early warning for sensor failure, and single-point failures often cause global data distortion, resulting in high maintenance costs. Summary of the Invention

[0003] The primary objective of this invention is to provide a self-calibration system and method for strain testing composite propellers using a symmetrical linear FGB sensor. This system utilizes a test device mounted on the propeller's tail, with linearly arranged and spatially symmetrically applied gratings applied to the surface. Dynamic performance testing is performed during synchronous propeller rotation. The propeller blades are manufactured from composite materials, and the sensors and optical fibers are embedded within the blades to ensure accurate dynamic performance testing. This method aims to provide an efficient, accurate, and reliable technical means for dynamic strain testing of large-deformation composite propellers, thereby promoting technological advancement and engineering applications in related fields.

[0004] A composite material strain testing system for a propeller includes a fiber grating (FBG) sensor array and a fiber demodulator. The fiber grating (FBG) sensor array can sense strain and temperature and convert the changes into changes in the central wavelength of the fiber grating (FBG). The fiber demodulator is installed in the propeller hub and can collect and demodulate spectral signals, analyze the wavelength of the fiber grating (FBG), and thus obtain the structural strain and temperature changes of the propeller. The fiber grating (FBG) sensor array is linearly arranged along the surface of each blade. Each blade has more than five single fiber grating (FBG) sensors connected in series linearly to form the fiber grating sensor array. The corresponding sequence of single fiber grating sensors on each blade are spatially symmetrically arranged in the same plane and are paired. Each pair is provided with an infrared emitting device and an infrared receiving device. When accurately positioned, the infrared rays of each pair intersect at a point O, the center of a circle. Each fiber grating sensor is provided with a micro-displacement automatic adjustment mechanism. When the fiber grating sensor is offset, it can automatically calibrate according to the shifted infrared intersection point. Each fiber grating sensor is also provided with a failure alarm.

[0005] Each fiber Bragg grating (FBG) sensor in the FBG sensor array functions as a light reflection filter. Multiple FBG sensors of different wavelengths are connected in series, each assigned a bandwidth so that wavelength drift remains within that bandwidth throughout its operating range. Each FBG sensor is mounted to the blade surface via a biaxial flexure hinge. This hinge allows for independent micro-movement of the sensor in both spanwise and chordwise directions. A shape memory alloy (SMA) wire is integrated into the sensor tip to drive the hinge's deformation, achieving displacement adjustment.

[0006] The failure alarm contains hollow glass microspheres coated with a metallic conductive film and filled with liquid metal. When ruptured, these microspheres form a conductive path, triggering a damage alarm and ceasing infrared transmission or reception. The hollow glass microspheres are 50-100μm in diameter and have a density of 100-300 microspheres per mm³. The liquid metal is a gallium-indium-tin alloy, ensuring that at least three microspheres must rupture before the alarm is triggered.

[0007] The optical fiber demodulator mainly consists of two parts: the optoelectronic processing part and the power supply part. The optoelectronic processing part contains optoelectronic components and optical circuits, and the power supply part provides stable power supply for the instrument.

[0008] The optoelectronic processing module includes a broadband light source and driver, a spectrum analysis module, an AD converter, an FPGA control unit, a DSP digital signal processing unit, a communication interface circuit, and an optical switch array. The broadband light source outputs broadband light with a wavelength range of 1510 nm to 1590 nm. The light source driver implements constant current drive and constant temperature control of the broadband light source to ensure its normal operation. At the same time, the output light intensity of the broadband light source can be digitally controlled by the DSP. The light output by the broadband light source enters the optical switch array through a circulator and completes time-sharing measurement of multiple sensors through time-division multiplexing. The reflected light from the fiber grating sensor passes through the circulator to the spectrum analysis module.

[0009] The spectral analysis module converts the optical signal output by the sensor into a pixel voltage signal. After entering the spectral analysis module, the optical signal passes through the collimating lens and is irradiated on the volume phase grating. After passing through the volume phase grating, the refraction angles of light of different wavelengths are different, and finally, light of different wavelengths are finally projected onto the linear detector at different positions. Light of different wavelengths is received by pixels at different positions of the linear detector, ultimately achieving the purpose of spectral measurement. The CCD chip has a built-in temperature sensor for temperature compensation of wavelength signal measurement; the AD converter mainly converts the voltage output by the spectral analysis module into a digital quantity. The FPGA control unit is used to realize the drive control of the spectral analysis module and control the AD converter to realize the acquisition of pixel voltage signals; the DSP digital signal processing unit obtains the pixel information collected by the FPGA, intercepts several pixel voltage values ​​corresponding to each sensor, and fits them to calculate the spectral center wavelength value corresponding to each sensor, and then calculates the temperature value according to the sensor calibration curve; the wireless communication module is used to output the final measurement results to the data acquisition and editing unit.

[0010] The power supply part consists of EMI filtering and protection circuit, DC / DC module, and output filtering circuit.

[0011] The system also includes an anti-interference demodulation system, including a magnetically shielded spectroscopy module and a ring optical fiber network. The spectroscopy module uses a double-layer Permalloy shielding shell.

[0012] The self-calibration method of the composite material strain testing system includes: S1 initial positioning: When the propeller is stationary, the infrared rays converge at one point by symmetrically arranging the fiber grating sensors 11; S2. Offset detection: When the intersection point is offset, it is detected as sensor offset. S3. Automatic adjustment: When the horizontal deviation exceeds the limit (> the set threshold), the SMA and flexible hinge are driven to fine-tune until the intersection point returns to normal; S4. Damage detection: When the hollow glass beads built into the failure alarm 114 break, a conductive path is formed, which triggers a damage alarm, indicating that the sensor is damaged and needs to be replaced.

[0013] Beneficial technical effects: 1. Fitting design: The sensor and optical fiber are embedded in the blade to ensure the accuracy of dynamic performance detection, making the dynamic strain test of large-deformation composite propellers efficient, accurate and reliable; 2. Using multiple fiber grating sensors of different wavelengths in series can achieve better results. 3. Symmetrical layout and fixed-base calibration: The sensors are linearly fitted and symmetrically arranged on the blade surface, and pairs of infrared rays converge at the center of the hub to construct a dynamic reference point to achieve high-density strain monitoring. Compared with the traditional layout, the uniform stress distribution significantly improves the reference stability, providing an accurate data basis for modal analysis, and also forming a calibration base point, providing a reference for automatic calibration. 4. Intelligent self-calibration mechanism: The dual-axis flexible hinge combined with shape memory alloy drive allows the sensor to micro-move independently, detect the infrared point offset in real time and automatically calibrate, quickly correct installation deviations and environmental disturbances, achieve high-precision measurement under dynamic conditions, and greatly improve the real-time and accuracy of strain monitoring. 5. High-Reliability Design: The failure alarm utilizes hollow glass microspheres and liquid metal to detect sensor damage in real time and trigger an alarm, effectively isolating single points of failure. The demodulator is miniaturized and integrated into the propeller hub's sealed cavity, reducing cable connections and improving signal transmission reliability, making it suitable for extreme deep-sea environments. 6. An anti-electromagnetic interference module addresses the challenge of dynamic strain monitoring for large-deformation composite propellers operating in high-pressure, low-temperature, and strong electromagnetic environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 : Schematic diagram of the installation location of the composite material strain testing system; Figure 2 : Schematic diagram of symmetrically arranged infrared calibration; Figure 3 : Schematic diagram of the symmetrically arranged fiber Bragg grating sensor structure; Figure 4 :The main modules of optical fiber demodulator; DETAILED DESCRIPTION like Figure 1-3As shown, a composite material strain testing system for propeller self-calibration includes a fiber grating sensor array 1 and a fiber demodulator 2. The fiber grating sensor array 1 can sense strain and temperature and convert the changes into changes in the central wavelength of the fiber grating; the fiber demodulator 2 is installed in the hub to realize the acquisition and demodulation of spectral signals, analyze the wavelength of the fiber grating, and then obtain the structural strain and temperature changes of the propeller; the fiber grating sensor array 1 is arranged linearly along the surface of each blade, and each blade has more than five single fiber grating sensors 1 A fiber Bragg grating sensor array 1 is formed by linear series connection. The corresponding sequence of single fiber Bragg grating sensors 11 on each blade are spatially symmetrically arranged in the same plane, and are paired. Each pair is provided with an infrared emitting device 111 and an infrared receiving device 112. When the positioning is accurate, each team of infrared rays intersects at a point O, the center of the circle. Each fiber Bragg grating sensor 11 is provided with a micro-displacement automatic adjustment mechanism 113, which can automatically calibrate according to the shifted infrared intersection point when the fiber Bragg grating sensor 11 is offset. Each fiber Bragg grating sensor 11 is also provided with a failure alarm 114.

[0015] Each fiber Bragg grating in the fiber Bragg grating sensor array 1 is a light reflection filter. Multiple fiber Bragg grating sensors 11 with different wavelengths are connected in series and each sensor is allocated a bandwidth so that the wavelength drift of each sensor in the entire working range is within the bandwidth.

[0016] Each fiber Bragg grating sensor 11 is mounted on the blade surface via a biaxial flexible hinge. The biaxial flexible hinge allows the sensor to independently micro-move in the span and chord directions. A shape memory alloy (SMA) wire is integrated at the end of the sensor 11 to drive the deformation of the flexible hinge to achieve displacement adjustment.

[0017] Failure alarm 114 contains hollow glass microspheres coated with a metallic conductive film and filled with liquid metal. When ruptured, these microspheres form a conductive path, triggering a damage alarm and ceasing infrared transmission or reception. The hollow glass microspheres in Failure Alarm 114 have a diameter of 50-100μm and a density of 100-300 microspheres per mm³. The liquid metal is a gallium-indium-tin alloy, ensuring that at least three microspheres must rupture before the alarm is triggered.

[0018] The optical fiber demodulator 2 mainly consists of two parts: the optoelectronic processing part and the power supply part. The optoelectronic processing part includes optoelectronic components and optical circuits, and the power supply part provides stable power supply for the instrument.

[0019] The optoelectronic processing module includes a broadband light source and driver, a spectrum analysis module, an AD converter, an FPGA control unit, a DSP digital signal processing unit, a communication interface circuit, and an optical switch array. The broadband light source outputs broadband light with a wavelength range of 1510 nm to 1590 nm. The light source driver implements constant current drive and constant temperature control of the broadband light source to ensure its normal operation. At the same time, the output light intensity of the broadband light source can be digitally controlled by the DSP. The light output by the broadband light source enters the optical switch array through a circulator and completes time-sharing measurement of multiple sensors through time-division multiplexing. The reflected light from the fiber grating sensor passes through the circulator to the spectrum analysis module.

[0020] The spectral analysis module converts the optical signal output by the sensor into a pixel voltage signal. After entering the spectral analysis module, the optical signal passes through the collimating lens and is irradiated on the volume phase grating. After passing through the volume phase grating, the refraction angles of light of different wavelengths are different, and finally, light of different wavelengths are finally projected onto the linear detector at different positions. Light of different wavelengths is received by pixels at different positions of the linear detector, ultimately achieving the purpose of spectral measurement. The CCD chip has a built-in temperature sensor for temperature compensation of wavelength signal measurement; the AD converter mainly converts the voltage output by the spectral analysis module into a digital quantity. The FPGA control unit is used to realize the drive control of the spectral analysis module and control the AD converter to realize the acquisition of pixel voltage signals; the DSP digital signal processing unit obtains the pixel information collected by the FPGA, intercepts several pixel voltage values ​​corresponding to each sensor, and fits them to calculate the spectral center wavelength value corresponding to each sensor, and then calculates the temperature value according to the sensor calibration curve; the wireless communication module is used to output the final measurement results to the data acquisition and editing unit.

[0021] The power supply part consists of EMI filtering and protection circuit, DC / DC module, and output filtering circuit.

[0022] The system also includes an anti-interference demodulation system, including a magnetically shielded spectroscopy module and a ring optical fiber network. The spectroscopy module uses a double-layer Permalloy shielding shell.

[0023] The self-calibration method of the composite material strain testing system includes: S1 initial positioning: When the propeller is stationary, the infrared rays converge at one point by symmetrically arranging the fiber grating sensors 11; S2. Offset detection: When the intersection point is offset, it is detected as sensor offset. S3. Automatic adjustment: When the horizontal deviation exceeds the limit (> the set threshold), the SMA and flexible hinge are driven to fine-tune until the intersection point returns to normal; S4. Damage detection: When the hollow glass beads built into the failure alarm 114 break, a conductive path is formed, which triggers a damage alarm, indicating that the sensor is damaged and needs to be replaced.

Claims

1. A self-calibrating composite material strain testing system for a propeller, comprising a fiber grating (FBG) sensor array and a fiber interrogator. The FBG sensor array can sense strain and temperature and convert the changes into changes in the central wavelength of the FBG. The fiber interrogator, installed in the propeller hub, can collect and demodulate spectral signals, resolve the wavelength of the FBG, and thus obtain the structural strain and temperature changes of the propeller. The FBG sensor array is arranged linearly along the surface of each blade. Each blade has at least five individual FBG sensors connected in series to form a FBG sensor array 1. The corresponding sequence of individual FBG sensors on each blade are spatially symmetrically arranged in the same plane and are paired. Each pair is provided with an infrared transmitter and an infrared receiver. When accurately positioned, the infrared rays of each pair intersect at a point O at the center of a circle. Each FBG sensor is provided with an automatic micro-displacement adjustment mechanism. When the FBG sensor deviates, it can automatically calibrate according to the shifted infrared intersection point. Each FBG sensor is also provided with a failure alarm.

2. The system according to claim 1, wherein: Each fiber Bragg grating in the fiber Bragg grating sensor array is a light reflection filter. Multiple fiber Bragg grating sensors with different wavelengths are used in series, and each sensor is assigned a bandwidth so that the wavelength drift of each sensor in the entire working range is within the bandwidth.

3. The system according to claim 1, wherein: Each fiber grating sensor is mounted on the blade surface through a biaxial flexible hinge. The biaxial flexible hinge allows the sensor to micro-move independently in the span and chord directions. A shape memory alloy wire is integrated at the end of the sensor to drive the deformation of the flexible hinge to achieve displacement adjustment.

4. The system according to claim 1, characterized in that: The failure alarm has built-in hollow glass microspheres. The inner wall of the microspheres is coated with a metal conductive film and filled with liquid metal. When they break, a conductive path is formed, which triggers a damage alarm and stops transmitting or receiving infrared.

5. The system according to claim 4, characterized in that: The failure alarm has built-in hollow glass microbeads with a diameter of 50-100μm and a density of 100-300 particles / mm³. The liquid metal is a gallium-indium-tin alloy, ensuring that at least three beads must rupture before the alarm is triggered.

6. The system according to claim 1, wherein: The optical fiber demodulator mainly consists of two parts: the optoelectronic processing part and the power supply part. The optoelectronic processing part contains optoelectronic components and optical circuits, and the power supply part provides stable power supply for the instrument.

7. The system according to claim 6, characterized in that: The optoelectronic processing module includes a broadband light source and driver, a spectrum analysis module, an AD converter, an FPGA control unit, a DSP digital signal processing unit, a communication interface circuit, and an optical switch array. The broadband light source outputs broadband light with a wavelength range of 1510 nm to 1590 nm. The light source driver implements constant current drive and constant temperature control of the broadband light source to ensure its normal operation. At the same time, the output light intensity of the broadband light source can be digitally controlled by the DSP. The light output by the broadband light source enters the optical switch array through a circulator and completes time-sharing measurement of multiple sensors through time-division multiplexing. The reflected light from the fiber grating sensor passes through the circulator to the spectrum analysis module.

8. The system according to claim 7, characterized in that: The spectral analysis module converts the optical signal output by the sensor into a pixel voltage signal. After entering the spectral analysis module, the optical signal passes through the collimating lens and is irradiated on the volume phase grating. After passing through the volume phase grating, the refraction angles of light of different wavelengths are different, and finally, light of different wavelengths are projected onto different positions of the linear detector. Light of different wavelengths is received by pixels at different positions of the linear detector, ultimately achieving the purpose of spectral measurement. The CCD chip has a built-in temperature sensor for temperature compensation of wavelength signal measurement; the AD converter mainly converts the voltage output by the spectral analysis module into a digital quantity, and the FPGA control unit is used to realize the drive control of the spectral analysis module and control the AD converter to realize the acquisition of pixel voltage signals; the DSP digital signal processing unit obtains the pixel information collected by the FPGA, intercepts several pixel voltage values ​​corresponding to each sensor, and fits them to calculate the spectral center wavelength value corresponding to each sensor, and then calculates the temperature value according to the sensor calibration curve; The wireless communication module is used to output the final measurement results to the data acquisition and editing unit.

9. The system according to claim 6, wherein the power supply part is composed of an EMI filtering and protection circuit, a DC / DC module, and an output filtering circuit.

10. The composite material strain testing system self-calibration method according to claims 1-9 comprises: S1. Initial positioning: When the propeller is stationary, symmetrically arrange the fiber grating sensors so that the infrared rays converge at a single point. S2. Offset detection: When the intersection point is offset, it is detected as sensor offset. S3. Automatic Adjustment: If the horizontal deviation exceeds the limit, the shape memory alloy wire and flexible hinge are fine-tuned until the intersection returns to its original position. S4. Damage Detection: When the hollow glass beads inside the failure alarm break, a conductive path is formed, triggering a damage alarm, indicating that the sensor is damaged and needs to be replaced.

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