Aircraft blade detection probe and method based on flexible double-frequency differential eddy current

Abstract

The invention aims to provide an aircraft blade detection probe and method based on flexible double-frequency differential eddy current, and relates to the technical field of nondestructive testing, when defect detection of an aircraft blade is carried out, a flexible substrate can be adaptively attached to a complex curved surface of the blade; the double-frequency excitation coil cooperatively works through high frequency and low frequency and respectively captures surface micro-cracks and subsurface corrosion defects, and when differential signal amplitude fluctuation occurs in the differential receiving coil, it can be judged that abnormal damage exists in a corresponding blade area; if the coil induction signal is kept stable and unchanged, the corresponding area is in a normal state, and the geometric characteristics of the damaged part can be quantitatively analyzed by observing the numerical range of the amplitude change; specifically, the intensity of signals output by the induction lines and the integrity of the blade structure are in positive correlation, and the larger the fluctuation value is, the more serious the damage degree is.

Description

Technical Field

[0001] The present invention relates to the technical field related to non-destructive testing, and in particular to an aircraft blade detection probe and method based on flexible dual-frequency differential eddy current. Background Art

[0002] Aircraft blades, as the core rotating components of aircraft propulsion systems, are subject to harsh operating conditions. Rotating at frequencies exceeding 100,000 revolutions per minute in ultra-high-temperature and ultra-high-pressure combustion gases, they are constantly subjected to a complex combination of mechanical loads: high-intensity centrifugal effects, unstable aerodynamic shocks, and cyclical thermal expansion and contraction stresses. The interplay of these complex factors can easily lead to structural defects such as stress cracks at the root joint, aging and fracture of the base material, delamination and failure of the surface protective coating, and accumulated deformation at high temperatures. These potential damages can significantly impact the reliable operation of the propulsion system and are directly related to the safety performance of the aircraft. Therefore, it is essential to establish a quality monitoring system that covers the entire product life cycle. Using dynamic testing and intelligent diagnostic technologies, a systematic condition assessment of turbine components is conducted during the testing phase of new components and in actual use.

[0003] Aircraft blades are typically manufactured from high-performance alloy materials, and their quality inspection primarily utilizes non-destructive methods such as eddy current testing, ultrasonic testing, penetrant testing, and X-ray testing. Traditional eddy current testing, however, suffers from complex three-dimensional contours that create blind spots in the detection area, particularly in areas with multi-curvature features such as the root meshing area and end profiles. Ultrasonic testing's accuracy in identifying fine cracks is limited by the anisotropy of the material's crystal structure, and it struggles to capture microscopic damage in specific directions. Liquid penetrant testing requires rigorous surface pretreatment, and its effectiveness plummets in coating structures or with hidden defects. Penetrant testing not only suffers from lengthy operating cycles and low economic efficiency, but also from the fuzzy imaging characteristics of closed fatigue cracks. Existing technology systems struggle to meet the actual needs of aircraft blade monitoring.

[0004] Traditional eddy current testing technology faces two core challenges: First, the compatibility of the probe structure with curved surfaces. Rigid probes, using hard substrates, struggle to conform tightly to the complex curved surfaces of blades, leading to blind spots. Flexible probes, while adaptable, suffer from electromagnetic performance drift caused by mechanical deformation and insufficient high-frequency detection capabilities. Second, there are inherent contradictions inherent in single-frequency excitation. While high-frequency testing is highly sensitive to surface microcracks, it struggles to detect deep defects due to the skin effect. Low-frequency testing can penetrate deep into the material, but is susceptible to interference from lift-off noise and material inhomogeneities, significantly reducing the signal-to-noise ratio. These issues severely restrict the accuracy and reliability of aircraft blade defect detection. Summary of the Invention

[0005] The first purpose of the present invention is to provide a flexible and adaptive eddy current detection probe to solve the problems that existing rigid probes cannot conform to complex surfaces, flexible probes have poor high-frequency performance and insufficient anti-interference ability, and to design a deformable, highly stable dual-frequency differential probe to achieve high-precision detection of the entire blade area.

[0006] The second purpose of the present invention is to propose a dual-frequency collaborative defect classification method to overcome the contradiction between depth and sensitivity of single-frequency detection. Through synchronous excitation and intelligent analysis of high and low frequency signals, surface microcracks and subsurface corrosion can be simultaneously identified, thereby improving the comprehensiveness and reliability of defect detection.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A flexible dual-frequency differential eddy current-based aircraft blade detection probe comprises an electromagnetic shielding layer, two sets of dual-frequency excitation coils, and two sets of differential receiving coils. The dual-frequency excitation coils comprise a first excitation coil and a second excitation coil. The first excitation coil and the second excitation coil are coplanarly and symmetrically arranged vertically. The two sets of dual-frequency excitation coils are coplanarly and symmetrically arranged horizontally, and the two sets of differential receiving coils are located between the first excitation coil and the second excitation coil. The two sets of differential receiving coils are coplanarly and symmetrically arranged vertically, and the two sets of differential receiving coils are differentially connected to the two sets of dual-frequency excitation coils respectively. The dual-frequency excitation coils and the differential receiving coils are processed on a flexible substrate, and the electromagnetic shielding layer is covered on the outside of the dual-frequency excitation coils and the differential receiving coils to shield external electromagnetic interference.

[0009] Furthermore, the flexible substrate is made of a composite of multiple layers of flexible high-temperature resistant materials, and has excellent deformation recovery properties and wide temperature range adaptability. An insulating protective layer is provided on the surface of the flexible substrate to enhance environmental tolerance.

[0010] Furthermore, in the dual-frequency excitation coil, the first excitation coil adopts a precision etching process to form a micro-helical structure, and the efficient utilization of the skin effect is achieved by optimizing the line width of the first excitation coil and the spacing between the inspected blade; the first excitation coil adopts a coplanar layout with the second excitation coil to achieve electromagnetic field synergy, enhance the magnetic field penetration depth, and combine electromagnetic simulation to avoid frequency interference.

[0011] Furthermore, the electromagnetic shielding layer adopts a flexible conductive medium to construct a multi-layer shielding structure, and the electromagnetic shielding layer is provided with a window matching the detection area composed of two groups of dual-frequency excitation coils and two groups of differential receiving coils, and the edge adopts a gradual transition design to reduce the edge magnetic field distortion.

[0012] Furthermore, the probe is excited by the first excitation coil and the second excitation coil at the same time, and the two detection coils receive the signals at the same time.

[0013] Furthermore, the number of turns of the dual-frequency excitation coil is increased as much as possible while meeting the manufacturing process requirements.

[0014] A method for detecting aircraft blades based on flexible dual-frequency differential eddy current includes the following steps:

[0015] Step 1: Connect the first excitation coil and the second excitation coil in the probe to the high-frequency and low-frequency excitation sources respectively, and connect the two differential detection coils to the data acquisition module;

[0016] Step 2: Fix the probe to the actuator at the end of the multi-degree-of-freedom robotic arm. First, take a defect-free standard blade as a reference, apply a preset dual-frequency excitation signal, and record the baseline amplitude and phase values ​​of the differential signal in each area. Then, use a force feedback sensor to adjust the contact pressure between the probe and the blade surface to ensure that the flexible substrate fully adapts to the curved surface and eliminates lift-off interference.

[0017] Step 3: According to the material characteristics of the blade being inspected, the high-frequency excitation frequency band and the low-frequency sweep range of the dual-frequency excitation coil are set. At the same time, in order to optimize the signal-to-noise ratio, the input signal is passed through the power amplifier.

[0018] Step 4: Synchronously start the high-frequency continuous wave and low-frequency sweep signals, drive the dual-frequency excitation coil through the power amplifier to generate a composite magnetic field, and at the same time, the differential receiving coil captures the eddy current response signal in real time and uploads the output signal to the analysis terminal.

[0019] Step 5: Use digital filters to extract high-frequency amplitude signals and low-frequency phase signals, compare the high-frequency signal drop with the baseline threshold, determine the crack location and expansion trend, analyze the low-frequency phase spectrum offset, and estimate the corrosion depth based on the impedance model.

[0020] Compared with the existing technology, the technical solution of this application has the following beneficial effects:

[0021] The present invention adopts a layout of flexible substrate, dual-frequency excitation coil and differential receiving coil, breaking through the fitting limitations of traditional rigid probes on complex curved surfaces, eliminating the interference of lift-off effect, and ensuring the stability and consistency of curved surface detection; through the coordinated work of high and low frequencies of the dual-frequency excitation coil, the contradiction between depth and sensitivity of single-frequency technology is overcome, and it can not only capture sub-surface cracks, but also identify corrosion and fatigue damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the coil layout of the flexible dual-frequency differential eddy current probe of the present invention;

[0023] Figure 2 Schematic diagram of the structure of the flexible dual-frequency differential eddy current probe of the present invention;

[0024] Figure 3This is a flow chart of the detection method of the flexible dual-frequency differential eddy current probe of the present invention;

[0025] Figure 4 This is a schematic diagram of the flexible dual-frequency differential eddy current probe of the present invention being fitted to the blade being inspected;

[0026] Figure 5 This is a line graph of the test results of the best embodiment of the present invention.

[0027] In the figure: flexible substrate-1, dual-frequency excitation coil-2, first excitation coil-21, second excitation coil-22, differential detection coil-3, electromagnetic shielding layer-4, subsurface corrosion-5, surface crack-6, blade-7, connecting rod-8, probe as a whole-9, probe cross section-10. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0029] Example 1:

[0030] like Figure 1-2 As shown, an aircraft blade detection probe based on flexible dual-frequency differential eddy current of the present invention includes a flexible substrate 1, two sets of dual-frequency excitation coils 2, two sets of differential receiving coils 3 and an electromagnetic shielding layer 4; the dual-frequency excitation coil 2 includes a first excitation coil 21 and a second excitation coil 22; the first excitation coil 21 and the second excitation coil 22 are arranged coplanarly and symmetrically in the vertical direction; the two sets of dual-frequency excitation coils 2 are arranged coplanarly and symmetrically in the left and right direction, and the two sets of differential receiving coils 3 are located between the first excitation coil 21 and the second excitation coil 22, and the two sets of differential receiving coils 3 are arranged coplanarly and symmetrically in the vertical direction, and the two sets of differential receiving coils 3 are differentially connected to the two sets of dual-frequency excitation coils 2 respectively;

[0031] In this embodiment, the first excitation coil 21 and the second excitation coil 22 are used to generate a high-frequency magnetic field and a low-frequency magnetic field, respectively. The first excitation coil 21 is formed into a micro-helical structure using a precision etching process, and the line width and spacing of the first excitation coil 21 are optimized to achieve efficient utilization of the skin effect. The second excitation coil 22 is arranged coplanar and symmetrically with the first excitation coil 21 to achieve electromagnetic field synergy and enhance the penetration depth of the magnetic field. The first excitation coil 21 and the second excitation coil 22 are arranged coplanar to achieve electromagnetic field synergy, and electromagnetic simulation is combined to avoid frequency interference.

[0032] In this embodiment, the differential detection coil 3 is used to collect the difference in eddy current response signals; the output end of the differential receiving coil 3 is connected to a differential amplifier to suppress common-mode noise, and the line spacing of the differential receiving coil 3 matches the excitation field distribution characteristics generated by the dual-frequency excitation coil 2;

[0033] In this embodiment, the electromagnetic shielding layer 4 is made of flexible conductive material and covers the outside of the dual-frequency excitation coil 2 and the differential receiving coil 3 to shield external electromagnetic interference; the electromagnetic shielding layer 4 is provided with a window that matches the detection area formed by the two sets of dual-frequency excitation coils 2 and the two sets of differential receiving coils 3, and the edge of the window adopts a gradual transition design to reduce the edge magnetic field distortion.

[0034] In this embodiment, the flexible substrate 1 is made of a composite of multiple layers of flexible high-temperature resistant materials, and the surface is covered with an insulating protective layer. It has excellent deformation recovery characteristics and adaptability to a wide temperature range; it breaks through the limitations of traditional rigid probes on the fitting of complex curved surfaces, eliminates the interference of the lift-off effect, and ensures the stability and consistency of curved surface detection.

[0035] Example 2:

[0036] like Figure 1-3 As shown, according to embodiment 1, a method for detecting aircraft blades based on flexible dual-frequency differential eddy current of the present invention includes the following steps:

[0037] The first step is to prepare and calibrate the probe. The first excitation coil 21 and the second excitation coil 22 in the probe are connected to the high-frequency and low-frequency excitation sources respectively, and the two sets of differential receiving coils 3 are connected to the data acquisition module. The probe is fixed to the end effector of the multi-degree-of-freedom robotic arm. A defect-free standard blade is first taken as a reference. A preset dual-frequency excitation signal is applied, and the baseline amplitude and phase value of the differential signal in each area are recorded. The contact pressure between the probe and the blade surface is adjusted through the force feedback sensor to ensure that the flexible substrate 1 adapts to the curved surface completely and eliminates lift-off interference.

[0038] The second step is to set the excitation signal. Based on the material properties of the blade being inspected, the high-frequency excitation frequency band and low-frequency sweep range of the dual-frequency excitation coil 2 are set. At the same time, to optimize the signal-to-noise ratio, the input signal is passed through a power amplifier. Then, signal acquisition and processing can be carried out. The high-frequency continuous wave and low-frequency sweep signals are started synchronously. The power amplifier drives the excitation coil to generate a composite magnetic field. At the same time, the differential receiving coil captures the eddy current response signal in real time and uploads the output signal to the analysis terminal. The high-frequency amplitude signal and low-frequency phase signal are extracted through a digital filter. The high-frequency signal drop is compared with the baseline threshold to determine the crack location and expansion trend. The low-frequency phase spectrum offset is analyzed, and the corrosion depth is estimated by combining the impedance model.

[0039] Finally, defect determination and analysis are performed. The amplitude change of the high-frequency component is used to identify surface defects, and the phase delay of the low-frequency component is used to determine sub-surface defects.

[0040] Example 3:

[0041] According to Examples 1-2, this example is a specific result obtained from a first example. Taking a certain type of aircraft engine blade as an example, the blade material is titanium alloy, and there are microcracks on the surface and corrosion defects on the subsurface. The probe and detection method of the present invention are used for detection;

[0042] like Figure 1 As shown, subsurface corrosion 5 is replaced by a cylinder and set to a new material; surface crack 6 is a rectangle with a length of 1mm, a width of 3mm, and a depth of 1mm, and its material is set to air to represent the crack. Both faults are located on a rectangle with a length of 100mm, a width of 40mm, and a depth of 4mm, representing blade 7, and its material is set to titanium with an electrical conductivity of 5.8e6 s / m and a relative magnetic permeability of 1.0002.

[0043] like Figure 4 As shown, in the specific example, the probe preparation also includes a blade 7, a connecting rod 8, a probe body 9, and a probe cross section 10. The probe is fixed to the end of the robot arm with the connecting rod 8, and a non-defective aircraft blade 7 is calibrated to record the baseline signal; the probe body 9 is cut along the probe cross section 10 to obtain the following. Figure 2 The structure shown includes a dual-frequency excitation coil 2, a differential receiving coil 3, an electromagnetic shielding layer 4 and a flexible substrate 1;

[0044] like Figure 5 As shown, the excitation frequency of the first excitation coil 21 is set to 10 MHz, and the excitation frequency of the first excitation coil 21 is 1 kHz to 100 kHz. Then, the probe is moved on the surface of the blade 7 to collect the differential signal. The high-frequency amplitude signal and the low-frequency phase signal are extracted by a digital filter. Finally, the red is the amplitude ratio and the blue is the phase in the figure. It is found that the high-frequency signal has a significant decrease in a certain area on the blade surface, and the low-frequency phase signal is delayed in a certain area on the blade subsurface.

[0045] like Figure 1 The presence of a subsurface corrosion defect 5 can be determined based on the low-frequency phase delay, and the presence of a surface crack defect 6 can be determined based on the high-frequency signal amplitude reduction.

[0046] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. An aircraft blade detection probe based on flexible dual-frequency differential eddy current, characterized in that: It includes an electromagnetic shielding layer, two groups of dual-frequency excitation coils and two groups of differential receiving coils; the dual-frequency excitation coils include a first excitation coil and a second excitation coil; the first excitation coil and the second excitation coil are arranged in a coplanar manner; the two groups of dual-frequency excitation coils and the two groups of differential receiving coils are arranged symmetrically, and the two groups of differential receiving coils are differentially connected to the two groups of dual-frequency excitation coils respectively; the dual-frequency excitation coils and the differential receiving coils are processed on a flexible substrate, and the electromagnetic shielding layer is covered on the outside of the dual-frequency excitation coils and the differential receiving coils to shield external electromagnetic interference.

2. The aircraft blade detection probe based on flexible dual-frequency differential eddy current according to claim 1, characterized in that: The flexible substrate is made of a composite of multiple layers of flexible high-temperature resistant materials, has excellent deformation recovery properties and wide temperature range adaptability, and an insulating protective layer is provided on the surface of the flexible substrate.

3. The aircraft blade detection probe based on flexible dual-frequency differential eddy current according to claim 1, characterized in that: In the dual-frequency excitation coil, the first excitation coil is a micro-helical structure.

4. The aircraft blade detection probe based on flexible dual-frequency differential eddy current according to claim 1, characterized in that: The electromagnetic shielding layer adopts a flexible conductive medium to construct a multi-layer shielding structure. The electromagnetic shielding layer is provided with a window matching the detection area composed of two groups of dual-frequency excitation coils and two groups of differential receiving coils, and the window edge adopts a gradual transition design.

5. The aircraft blade detection probe based on flexible dual-frequency differential eddy current according to claim 1, characterized in that: The probe is excited by the first excitation coil and the second excitation coil at the same time, and is received by the two detection coils at the same time.

6. The detection method of an aircraft blade detection probe based on flexible dual-frequency differential eddy current according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: Connect the first excitation coil and the second excitation coil in the probe to the high-frequency and low-frequency excitation sources respectively, and connect the two differential detection coils to the data acquisition module; Step 2: Fix the probe to the actuator at the end of the multi-degree-of-freedom robotic arm. Take a defect-free standard blade as a reference, apply a preset dual-frequency excitation signal, and record the baseline amplitude and phase values ​​of the differential signal in each area. The contact pressure between the probe and the blade surface is adjusted through a force feedback sensor to ensure that the flexible substrate fully adapts to the curved surface and eliminates lift-off interference. Step 3: According to the material characteristics of the blade being inspected, the high-frequency excitation frequency band and the low-frequency sweep range of the dual-frequency excitation coil are set. At the same time, in order to optimize the signal-to-noise ratio, the input signal is passed through the power amplifier. Step 4: Synchronously start the high-frequency continuous wave and low-frequency sweep signals, drive the dual-frequency excitation coil through the power amplifier to generate a composite magnetic field, and at the same time, the differential receiving coil captures the eddy current response signal in real time and uploads the output signal to the analysis terminal. Step 5: Use digital filters to extract high-frequency amplitude signals and low-frequency phase signals, compare the high-frequency signal drop with the baseline threshold, determine the crack location and expansion trend, analyze the low-frequency phase spectrum offset, and estimate the corrosion depth based on the impedance model.

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