A propeller self-calibratable composite material strain testing system and method

Abstract

The application discloses a self-calibration strain testing system and method for propeller composite materials, and solves the problems of high-precision measurement and real-time calibration of dynamic strain under a complex flow field environment. The system core comprises a linear fiber grating sensor array attached to the surface of the propeller blade and a fiber demodulator integrated in the propeller hub. The sensors are arranged symmetrically along the span, and two infrared transmitting / receiving devices in each pair intersect at the center O of the hub to form a global reference when positioned accurately. A single sensor is installed through a double-shaft flexible hinge and integrated with a shape memory alloy (SMA) wire driving mechanism, which can realize independent micro-motion calibration in the span direction and the chord direction according to the offset of the infrared intersection. The sensor is provided with an internal failure alarm, which is filled with gallium-indium-tin alloy through hollow glass microbeads. The alarm is triggered only when >= 3 microbeads are broken to form a conductive path, thereby avoiding false alarms. The anti-electromagnetic interference module solves the problem of dynamic strain monitoring of the large-deformation composite propeller under high pressure, low temperature and strong electromagnetic environment.

Description

Technical Field

[0001] This invention relates to the field of strain testing of propeller materials, and in particular to a self-calibrating composite material strain testing system for propellers. Background Technology

[0002] As a core component of marine engineering equipment and ship propulsion systems, large-deformation composite propellers play a crucial role in ensuring navigation efficiency, reducing energy consumption, and enhancing structural safety through their dynamic strain performance. Accurately acquiring dynamic strain data of propellers during actual operation is a key prerequisite for optimizing design, assessing lifespan, and ensuring reliable operation. However, current testing technologies face numerous bottlenecks in practical applications, severely hindering the development of related fields. In laboratory environments, high-speed imaging and laser Doppler measurement technologies, with their advantages of high precision and non-contact measurement, can accurately capture the deformation characteristics of propellers. These technologies rely on stable environments and controllable conditions provided by specific facilities such as circulating water tanks, achieving deformation measurement through tracking feature points on the propeller surface or analyzing Doppler frequency shifts. However, when the scenario shifts to lake trials or sea trials, the limitations of these methods become apparent. The openness and complexity of the field environment make it difficult to deploy fixed measurement facilities, and factors such as unstable natural water flow and lighting conditions make it difficult to guarantee the image quality of high-speed cameras, while laser Doppler measurement signals are easily interrupted by interference. Therefore, these laboratory techniques cannot be effectively implemented during lake or sea trials, resulting in a near-complete lack of dynamic strain data for propellers under real-world operating conditions. This severely impacts the accurate evaluation and optimized design of their actual performance. While strain gauges can provide some strain information, each gauge requires an independent cable to connect to the data acquisition equipment. This not only physically limits the number of measurement points (too many cables lead to complex installation, difficult maintenance, and increased risk of signal interference) but also fails to meet the demands of large-deformation composite propellers for multi-point, high-density strain monitoring. Furthermore, in the deep-sea environment, sensors are prone to displacement, affecting detection accuracy. Existing systems rely on manual calibration, which cannot compensate for installation deviations and environmental disturbances in real time, resulting in low efficiency. Sensor failures lack effective early warning systems, often leading to global data distortion due to single-point faults, and resulting in high maintenance costs. Summary of the Invention

[0003] The main objective of this invention is to provide a self-calibration system and method for strain testing of composite materials in propellers, using a fitted symmetrical linear FGB sensor. This system mounts the testing equipment to the tail of the propeller, with linearly arranged and spatially symmetrically fitted gratings on the surface. Dynamic performance is measured as the system rotates synchronously with the propeller. The propeller blades are made of composite materials, and the sensor and optical fiber are embedded in the blades to ensure the accuracy of dynamic performance testing. This invention aims to provide an efficient, accurate, and reliable technical means for dynamic strain testing of large deformation composite material propellers, promoting technological progress and engineering applications in related fields.

[0004] A composite material strain testing system for propellers includes a fiber Bragg grating sensor array and a fiber demodulator. The fiber Bragg grating sensor array can sense strain and temperature and convert the changes into changes in the center wavelength of the fiber Bragg grating. The fiber demodulator, installed in the propeller hub, can acquire and demodulate spectral signals, resolve the wavelength of the fiber Bragg grating, and thus obtain the structural strain and temperature changes of the propeller. The fiber Bragg grating sensor array is linearly attached to the surface of each propeller blade. Each blade has more than five individual fiber Bragg grating sensors connected in series to form the fiber Bragg grating sensor array. The individual fiber Bragg grating sensors in corresponding sequences on each blade are spatially symmetrically arranged in pairs on the same plane. Each pair is equipped with an infrared emitting device and an infrared receiving device. When the positioning is accurate, the infrared rays of each pair intersect at a point O. Each fiber Bragg grating sensor is equipped with a micro-displacement automatic adjustment mechanism, which can automatically calibrate according to the intersection point of the displaced infrared rays when the fiber Bragg grating sensor is offset. Each fiber Bragg grating sensor is equipped with a failure alarm.

[0005] In the fiber Bragg grating sensor array, each fiber Bragg grating acts as a light reflection filter. Multiple fiber Bragg grating sensors with different wavelengths are connected in series, with each sensor allocated a bandwidth to ensure that the wavelength drift of each sensor remains within that bandwidth throughout its operating range. Each fiber Bragg grating sensor is mounted to the blade surface via a biaxial flexible hinge, which allows for independent micro-motion of the sensor in both the spanwise and chordwise directions. A shape memory alloy (SMA) filament is integrated at the sensor end to drive the deformation of the flexible hinge, thereby achieving displacement adjustment.

[0006] The fault alarm contains hollow glass microspheres. The inner wall of each microsphere is coated with a conductive metal film and filled with liquid metal. When the microsphere ruptures, it creates a conductive path, triggering a fault alarm and stopping the transmission or reception of infrared radiation. The hollow glass microspheres in the fault alarm have a diameter of 50-100μm and a density of 100-300 microspheres / mm³. The liquid metal is a gallium indium tin alloy, and the alarm is only triggered when at least three microspheres rupture.

[0007] The fiber optic demodulator mainly consists of two parts: the optoelectronic processing section and the power supply section. The optoelectronic processing section includes optoelectronic components and optical circuits, while the power supply section provides a stable power supply for the instrument.

[0008] The optoelectronic processing module includes a broadband light source and driver, a spectral 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 provides constant current and temperature control for the broadband light source, ensuring its normal operation. The output light intensity of the broadband light source can be digitally controlled via the DSP. The light output from the broadband light source enters the optical switch array through a circulator, and time-division multiplexing is used to perform time-division measurements on multiple sensors. The reflected light from the fiber Bragg grating sensor is processed by the spectral analysis module through the circulator.

[0009] The spectral analysis module converts the light signal output from the sensor into a pixel voltage signal. After entering the spectral analysis module, the light signal passes through a collimating lens and illuminates a volume phase grating. Different wavelengths of light refract at different angles after passing through the volume phase grating, resulting in different wavelengths of light ultimately landing at different positions on the linear detector. Different wavelengths of light are received by pixels at different positions on 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 from the spectral analysis module into a digital quantity. The FPGA control unit is used to drive and control the spectral analysis module and control the AD converter to acquire pixel voltage signals. The DSP digital signal processing unit acquires the pixel information collected by the FPGA, extracts several pixel voltage values ​​corresponding to each sensor, and fits them to calculate the spectral center wavelength value corresponding to each sensor. Then, it calculates the temperature value based on 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 section consists of EMI filtering and protection circuits, a DC / DC module, and an output filtering circuit.

[0011] The system also includes an anti-interference demodulation system, which includes a magnetically shielded spectral module and a ring fiber optic network. The spectral module uses a double-layer permalloy shielding shell.

[0012] Self-calibration methods for composite material strain testing systems include:

[0013] S1. Initial positioning: When the propeller is stationary, infrared rays converge at a point by symmetrically arranging fiber optic grating sensors 11;

[0014] S2. Offset Detection: When the intersection point shifts, it is detected that the sensor has shifted.

[0015] S3. Automatic adjustment: When the horizontal offset exceeds the limit (> set threshold), drive the SMA and flexible hinge for fine adjustment until the intersection point returns to normal.

[0016] S4. Damage Detection: When the hollow glass microsphere inside the fault alarm 114 breaks, a conductive path is formed, which triggers the damage alarm and indicates that the sensor is damaged and needs to be replaced.

[0017] Beneficial Technical Effects: 1. **Integrated Design:** Embedding sensors and optical fibers onto the blade ensures accurate dynamic performance testing, making dynamic strain testing of large-deformation composite propellers efficient, accurate, and reliable. 2. **Further Enhancement:** Connecting multiple fiber Bragg grating sensors of different wavelengths in series yields better results. 3. **Symmetrical Layout and Baseline Calibration:** Sensors are linearly bonded and symmetrically arranged on the blade surface, with pairs of infrared sensors converging at the hub center to construct a dynamic reference point. This enables high-density strain monitoring, significantly improving the stability of the reference point compared to traditional layouts. It provides a precise data foundation for modal analysis and also forms a calibration base point, providing a reference for automatic calibration. 4. **Intelligent Self-Calibration Mechanism:** A dual-axis flexible hinge combined with shape memory alloy drive allows for independent micro-motion of the sensors. It detects infrared point offset in real time and automatically calibrates, quickly correcting installation deviations and environmental disturbances. This achieves high-precision measurement under dynamic operating conditions, significantly improving the real-time performance and accuracy of strain monitoring. 5. High-reliability design: The failure alarm utilizes a hollow glass microsphere and liquid metal design to detect sensor damage in real time and trigger an alarm, effectively isolating single-point failures; the demodulator is miniaturized and integrated into the propeller hub sealing cavity, reducing cable connections, improving signal transmission reliability, and adapting to extreme deep-sea environments. 6. The anti-electromagnetic interference module solves the problem of dynamic strain monitoring of large-deformation composite material propellers under high pressure, low temperature, and strong electromagnetic environments. Attached Figure Description

[0018] Figure 1 Schematic diagram of the installation location of the composite material strain testing system;

[0019] Figure 2 Schematic diagram of symmetrical infrared calibration arrangement;

[0020] Figure 3 Schematic diagram of a symmetrically arranged fiber Bragg grating sensor structure;

[0021] Figure 4 The main modules of an optical fiber demodulator; Detailed Implementation

[0022] like Figure 1-3As shown, a self-calibrating composite material strain testing system for propellers includes a fiber Bragg grating sensor array 1 and a fiber demodulator 2. The fiber Bragg grating sensor array 1 can sense strain and temperature and convert the changes into changes in the center wavelength of the fiber Bragg grating. The fiber demodulator 2, installed in the propeller hub, can acquire and demodulate spectral signals, resolve the wavelength of the fiber Bragg grating, and thus obtain the structural strain and temperature changes of the propeller. The fiber Bragg grating sensor array 1 is linearly attached to the surface of each propeller blade, with more than five individual fiber Bragg grating sensors 1 on each blade. A fiber Bragg grating sensor array 1 is formed by a series of linear components. Individual fiber Bragg grating sensors 11 on each blade are spatially symmetrically arranged in the same plane and are paired up. Each pair is equipped with an infrared transmitter 111 and an infrared receiver 112. When the positioning is accurate, the infrared rays of each pair intersect at a point O. Each fiber Bragg grating sensor 11 is equipped with a micro-displacement automatic adjustment mechanism 113, which can automatically calibrate according to the intersection point of the displaced infrared rays when the fiber Bragg grating sensor 11 is offset. Each fiber Bragg grating sensor 11 is equipped with a failure alarm 114.

[0023] In the fiber Bragg grating sensor array 1, each fiber Bragg grating is a light reflection filter. Multiple fiber Bragg grating sensors 11 with different wavelengths are connected in series. Each sensor is allocated a bandwidth so that the wavelength drift of each sensor is within that bandwidth throughout the entire operating range.

[0024] 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 move independently in the spanwise and chordwise directions. A shape memory alloy (SMA) wire is integrated at the end of the sensor 11 to drive the deformation of the flexible hinge and achieve displacement adjustment.

[0025] The fault alarm 114 contains hollow glass microspheres. The inner wall of each microsphere is coated with a conductive metal film and filled with liquid metal. When the microspheres rupture, a conductive path is formed, triggering a fault alarm and stopping the transmission or reception of infrared radiation. The hollow glass microspheres in the fault alarm 114 have a diameter of 50-100μm and a density of 100-300 microspheres / mm³. The liquid metal is a gallium indium tin alloy, ensuring that at least 3 microspheres rupture before triggering the alarm.

[0026] The fiber optic 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, while the power supply part provides a stable power supply for the instrument.

[0027] The optoelectronic processing module includes a broadband light source and driver, a spectral 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 provides constant current and temperature control for the broadband light source, ensuring its normal operation. The output light intensity of the broadband light source can be digitally controlled via the DSP. The light output from the broadband light source enters the optical switch array through a circulator, and time-division multiplexing is used to perform time-division measurements on multiple sensors. The reflected light from the fiber Bragg grating sensor is processed by the spectral analysis module through the circulator.

[0028] The spectral analysis module converts the light signal output from the sensor into a pixel voltage signal. After entering the spectral analysis module, the light signal passes through a collimating lens and illuminates a volume phase grating. Different wavelengths of light refract at different angles after passing through the volume phase grating, resulting in different wavelengths of light ultimately landing at different positions on the linear detector. Different wavelengths of light are received by pixels at different positions on 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 from the spectral analysis module into a digital quantity. The FPGA control unit is used to drive and control the spectral analysis module and control the AD converter to acquire pixel voltage signals. The DSP digital signal processing unit acquires the pixel information collected by the FPGA, extracts several pixel voltage values ​​corresponding to each sensor, and fits them to calculate the spectral center wavelength value corresponding to each sensor. Then, it calculates the temperature value based on the sensor calibration curve. The wireless communication module is used to output the final measurement results to the data acquisition and editing unit.

[0029] The power supply section consists of EMI filtering and protection circuits, a DC / DC module, and an output filtering circuit.

[0030] The system also includes an anti-interference demodulation system, which includes a magnetically shielded spectral module and a ring fiber optic network. The spectral module uses a double-layer permalloy shielding shell.

[0031] Self-calibration methods for composite material strain testing systems include:

[0032] S1. Initial positioning: When the propeller is stationary, infrared rays converge at a point by symmetrically arranging fiber optic grating sensors 11;

[0033] S2. Offset Detection: When the intersection point shifts, it is detected that the sensor has shifted.

[0034] S3. Automatic adjustment: When the horizontal offset exceeds the limit (> set threshold), drive the SMA and flexible hinge for fine adjustment until the intersection point returns to normal.

[0035] S4. Damage Detection: When the hollow glass microsphere inside the fault alarm 114 breaks, a conductive path is formed, which triggers the damage alarm and indicates that the sensor is damaged and needs to be replaced.

Claims

1. A self-calibrating composite material strain testing system for propellers, comprising a fiber Bragg grating sensor array and a fiber demodulator. The fiber Bragg grating sensor array senses strain and temperature and converts the changes into changes in the center wavelength of the fiber Bragg grating. The fiber demodulator, installed in the propeller hub, can acquire and demodulate spectral signals, resolve the wavelength of the fiber Bragg grating, and thus obtain the structural strain and temperature changes of the propeller. The fiber Bragg grating sensor array is linearly attached to the surface of each propeller blade. Each propeller blade has five or more individual fiber Bragg grating sensors connected in series to form the fiber Bragg grating sensor array. The individual fiber Bragg grating sensors in corresponding sequences on each propeller blade are spatially symmetrically arranged in the same plane and paired in pairs. Each pair is equipped with an infrared emitting device and an infrared receiving device. When the positioning is accurate, each pair of infrared rays intersects at a point O. Each fiber Bragg grating sensor is equipped with a micro-displacement automatic adjustment mechanism. When the fiber Bragg grating sensor shifts, it automatically calibrates based on the infrared intersection of the shifted points. Each fiber Bragg grating sensor has a failure alarm. 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 connected in series, and each sensor is allocated a bandwidth so that the wavelength drift of each sensor remains within that bandwidth throughout the entire operating range. The system also includes an anti-interference demodulation system, which includes a magnetically shielded spectral module and a ring fiber network. The spectral module uses a double-layer permalloy shielding shell. Each fiber Bragg grating sensor is mounted on the blade surface via a biaxial flexible hinge. The biaxial flexible hinge allows the sensor to move independently in the spanwise and chordwise directions. A shape memory alloy wire is integrated at the end of the sensor to drive the deformation of the flexible hinge and achieve displacement adjustment.

2. The composite material strain testing system according to claim 1, characterized in that: The fault alarm has a built-in hollow glass microsphere. The inner wall of the microsphere is coated with a metal conductive film and filled with liquid metal. When it breaks, it forms a conductive path, which triggers the fault alarm and stops transmitting or receiving infrared signals.

3. The composite material strain testing system according to claim 2, characterized in that: The failure alarm contains hollow glass microspheres with a diameter of 50-100μm and a density of 100-300 microspheres / mm³. The liquid metal is a gallium indium tin alloy, ensuring that at least 3 microspheres must break before the alarm is triggered.

4. The composite material strain testing system according to claim 1, characterized in that: The fiber optic demodulator consists of two parts: an optoelectronic processing module and a power supply section. The optoelectronic processing module includes optoelectronic components and optical circuits, while the power supply section provides a stable power supply for the instrument.

5. The composite material strain testing system according to claim 4, characterized in that: The optoelectronic processing module includes a broadband light source and driver, a spectral 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 provides constant current and temperature control for the broadband light source, ensuring its normal operation. The output light intensity of the broadband light source is digitally controlled by the DSP. The light output from the broadband light source enters the optical switch array through a circulator, and time-division multiplexing is used to perform time-division measurements on multiple sensors. The reflected light from the fiber Bragg grating sensor enters the spectral analysis module through a circulator.

6. The composite material strain testing system according to claim 5, characterized in that: The spectral analysis module converts the light signal output by the sensor into a pixel voltage signal. After entering the spectral analysis module, the light signal passes through a collimating lens and illuminates a volume phase grating. Different wavelengths of light refract at different angles after passing through the volume phase grating, resulting in different wavelengths of light ultimately being projected onto different positions of the linear detector. Different wavelengths of light are 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 converts the voltage output by the spectral analysis module into a digital quantity. The FPGA control unit is used to drive and control the spectral analysis module and control the AD converter to acquire pixel voltage signals. The DSP digital signal processing unit acquires the pixel information collected by the FPGA, extracts several pixel voltage values ​​corresponding to each sensor, fits and calculates the spectral center wavelength value corresponding to each sensor, and then calculates the temperature value based on the sensor calibration curve. The wireless communication module is used to output the final measurement results to the data acquisition and editing unit.

7. The composite material strain testing system according to claim 4, wherein the power supply section consists of an EMI filter and protection circuit, a DC / DC module, and an output filter circuit.

8. The self-calibration method for the composite material strain testing system according to any one of claims 1-7 includes: S1. Initial positioning: When the propeller is stationary, infrared rays converge at a single point by symmetrically arranging fiber optic grating sensors; S2. Offset Detection: When the intersection point shifts, it is detected that the sensor has shifted; S3. Automatic Adjustment: When the horizontal offset exceeds the limit, the shape memory alloy wire and flexible hinge are driven for fine adjustment until the intersection point returns to its original position; S4. Damage Detection: When the hollow glass microsphere inside the fault alarm breaks, a conductive path is formed, which triggers the damage alarm and indicates that the sensor is damaged and needs to be replaced.

Images