High-density strain sensing optical cable, forming method thereof and monitoring system

Abstract

The invention discloses a high-density strain sensing optical cable, a forming method thereof and a monitoring system. The optical cable comprises a sheath layer, at least one reinforcing piece and a ribbon optical fiber arranged in the sheath layer. The ribbon optical fiber is composed of a plurality of parallel sensing optical fibers and at least one dyed fiber, and each sensing optical fiber is provided with a Bragg grating. And the Bragg gratings on any two adjacent sensing optical fibers are arranged in a staggered manner in the axial direction of the optical cable. According to the invention, the distribution density of sensing points is greatly improved in a staggered tape combining manner on the basis of not changing the existing demodulation technology, and meanwhile, the requirements of light weight, high flame retardance, low toxicity and high strain transmission efficiency in airborne application are met through a specific optical cable structure design; the technical problem that a traditional sensing scheme cannot give consideration to high density, multiple sites and navigability is solved, and a high-precision and high-reliability solution is provided for aircraft structure health monitoring.

Description

Technical Field

[0001] This invention relates to the field of fiber optic grating sensing technology, specifically to a high-density strain sensing optical cable and its formation method and monitoring system. Background Technology

[0002] As a major modern mode of transportation, the structural safety of aircraft is of paramount importance. During long-term service, critical load-bearing components of aircraft are susceptible to potential damage such as microcracks due to fatigue loads, which, if not detected in time, could lead to serious accidents. Current aircraft maintenance methods rely on periodic non-destructive testing and visual inspections, which are inherently lagging and unable to capture damage in real time. Furthermore, with the growth of fleet size and flight frequency, they are insufficient to meet the demands for real-time and precise monitoring.

[0003] Therefore, the introduction of online real-time structural health monitoring (SHM) technology has become a development trend in the aerospace field. Fiber Bragg grating (FBG) sensors, due to their high sensitivity and resistance to electromagnetic interference, are considered to have great application prospects in the aerospace field; for example, Chinese patents affirm their application potential in aircraft structural health monitoring. However, the application of traditional fiber optic sensing technology to aircraft structures faces challenges. The stress field distribution of aircraft structures is complex, requiring a large number of sensing points with high spatial resolution. The traditional method of connecting multiple FBGs with a single fiber has insufficient spatial resolution, while deploying multiple independent fibers or multiple electrical sensors involves complex wiring and other problems, which contradicts aircraft design principles.

[0004] In summary, there is an urgent need for new sensing optical cable solutions that can meet the stringent requirements of high density and multiple locations to improve the practicality and effectiveness of aircraft structural health monitoring systems. Summary of the Invention

[0005] The purpose of this application is to overcome the above-mentioned technical deficiencies and propose a high-density strain sensing optical cable, its formation method and monitoring system, to solve the technical problem that existing optical fiber sensing cables cannot simultaneously meet the requirements of high-density sensing, lightweight and airworthiness for airborne applications.

[0006] To achieve the above-mentioned technical objectives, this application adopts the following technical solution: In a first aspect, this application provides a high-density strain-sensing optical cable, comprising: Sheath layer; At least one reinforcing member is disposed within the sheath layer; The fiber is provided in the sheath layer and includes multiple sensing fibers arranged in parallel and at least one dyed fiber. The dyed fiber is arranged in parallel with the multiple sensing fibers and each sensing fiber is provided with at least one Bragg grating distributed along its axis. In this configuration, the Bragg gratings on any two adjacent sensing optical fibers are staggered relative to each other along the axial direction of the parallel fiber.

[0007] In some embodiments of this application, a dyed fiber is provided on each side of the optical fiber, and the dyed fiber is a different color from the sensing optical fiber.

[0008] In some embodiments of this application, the reinforcing member comprises galvanized steel wire with a diameter of 0.2 mm to 0.4 mm.

[0009] In some embodiments of this application, the outer surface of the sheath layer is provided with anti-slip stripes or a rough structure.

[0010] In some embodiments of this application, the Bragg gratings on two adjacent sensing optical fibers are arranged at equal distances along the axial direction.

[0011] In some embodiments of this application, the number of the plurality of sensing optical fibers is 4-24.

[0012] Secondly, this application provides an aircraft structural health monitoring system, including a grating demodulator and a high-density strain sensing optical cable as described in any embodiment of the first aspect, wherein the grating demodulator is connected to the high-density strain sensing optical cable.

[0013] In some embodiments of this application, the two ends of the multiple sensing optical fibers in the parallel fiber are connected end to end to form a series optical link.

[0014] In some embodiments of this application, multiple sensing fibers in the parallel fiber are respectively connected to multiple channels of the grating demodulator to form a parallel optical link.

[0015] Thirdly, this application also provides a method for forming a high-density strain-sensing optical cable, applicable to the high-density strain-sensing optical cable described in any embodiment of the first aspect, comprising the following steps: Bragg grating arrays are fabricated on multiple sensing optical fibers, and physical marks are applied at the center of each Bragg grating. Multiple sensing optical fibers are arranged side by side with at least one dyed fiber and at least one reinforcing member, and aligned with the first physical mark on each optical fiber, so that they are staggered at equal distances. Under the condition of controlling the tension of each optical fiber to be consistent, the tape and sheath are extruded and formed.

[0016] Compared with the prior art, the beneficial technical effects of the technical solution provided in this application include: By integrating multiple sensing fibers inscribed with Bragg gratings into a single optical cable in a staggered manner, the minimum grating spacing limitation determined by the demodulator performance in traditional single-fiber sensing technology has been overcome. This structure macroscopically forms an equivalent high-density grating array, improving the spatial resolution of sensing points without altering existing demodulation techniques and equipment. Simultaneously, the integrated cable structure, combining an aerospace-grade sheath and reinforcements to enhance mechanical performance, significantly simplifies wiring and installation on aircraft structures, reducing installation difficulty. It also ensures the cable's overall lightweight design, high flame retardancy, low toxicity, and excellent strain transfer efficiency. This guarantees the accuracy of strain measurements, perfectly meeting the comprehensive requirements of high precision, fast response, high density, and high reliability for aircraft structural health monitoring. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this application, the accompanying drawings used in the embodiments will be briefly described below: Figure 1 This is a schematic diagram of the longitudinal section of a high-density strain sensing optical cable in an embodiment of this application; Figure 2 This is a schematic cross-sectional view of a high-density strain sensing optical cable according to an embodiment of this application; Figure 3 This is a schematic diagram of the connection of a high-density strain sensing optical cable in an embodiment of this application; Figure 4 This is a connection diagram of another high-density strain sensing optical cable in an embodiment of this application; Figure 5 This is a structural schematic diagram of a high-density strain sensing optical cable according to an embodiment of this application; Figure 6 This is a test effect diagram of a high-density strain sensing optical cable in an embodiment of this application; Figure 7 This is a test result diagram of another high-density strain sensing optical cable in the embodiments of this application.

[0018] Figure label: 1-Sheath layer; 2-Strengthening element; 3-Paired optical fiber; 4-First dyed fiber; 5-Second dyed fiber; 6-Sensing optical fiber; 7-Bracket grating. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] Those skilled in the art will understand that, in this specification, the term "comprising" is an open-ended expression, meaning that the stated feature is present but other features are excluded. Directional terms such as "upper," "lower," "left," and "right" refer to exemplary directions based on the accompanying drawings. Features specified as "first" or "second" implicitly include one or more of that feature. Singular expressions can also be used in plural forms. "Multiple" means two or more. The terms "installed," "connected," and "linked" can refer to a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection via an intermediate medium, and it can be a connection within two components. Furthermore, "linked" can include wireless connections.

[0021] The purpose of this application is to overcome the above-mentioned technical deficiencies and propose a high-density strain sensing optical cable, its formation method and monitoring system, to solve the technical problem that existing optical fiber sensing cables cannot simultaneously meet the requirements of high-density sensing, lightweight and airworthiness for airborne applications.

[0022] To achieve the above-mentioned technical objectives, this application adopts the following technical solution: Reference Figures 1-7 This embodiment provides a high-density strain-sensing optical cable. The cable, from the outside in, comprises a sheath layer 1, at least one reinforcing member 2, and a parallel-ribbed optical fiber 3. Both the reinforcing member 2 and the parallel-ribbed optical fiber 3 are encased within the sheath layer 1. The sheath layer 1 is made of a low-smoke halogen-free (LSZH) thermoplastic material (such as thermoplastic polyurethane TPU or polyolefin) through an extrusion molding process. This material not only possesses good flexibility and abrasion resistance, ensuring good adhesion to the structure when the optical cable is bonded to a curved surface for efficient strain transfer, but more importantly, it meets the stringent requirements of the aerospace industry regarding material flame retardancy and smoke toxicity during combustion.

[0023] Reference Figure 1 and Figure 2 The parallel fiber 3 is the core sensing unit of this invention, which consists of multiple sensing fibers 6 arranged in parallel and at least one dyed fiber (as shown in Figures 4 and 5). Each sensing fiber 6 is a standard single-mode communication fiber, with one or more Bragg gratings 7 etched along its length. Each Bragg grating 7 acts as an independent sensing unit, capable of reflecting light signals of a specific wavelength, the reflected wavelength of which drifts with changes in axial strain and temperature of the fiber.

[0024] The key technical feature of this invention is that, in the parallel fiber 3, the Bragg gratings 7 on any two adjacent sensing fibers 6 are staggered relative to each other in the axial (length direction) direction of the parallel fiber 3. For example... Figure 2As shown, if the grating spacing on a single sensing fiber 6 is d_single, by paralleling n such fibers and staggering them axially by a fixed distance (d_single / n), the final optical cable will macroscopically exhibit a sensing point spacing d_actual that is reduced to d_single / n. For example, if the grating spacing of a single fiber is 1 meter, by paralleling 10 fibers at equal distances, the overall grating spacing can be reduced to 0.1 meters. In this way, the grating spacing distribution of the paralleled fibers can be increased to a maximum of 2 centimeters, achieving a significant increase in sensing point density.

[0025] The working principle of this invention is based on fiber optic grating sensing technology and time-division / wavelength-division multiplexing (TDM / WDM) technology. The grating demodulator operates by emitting broadband optical pulses into the fiber and receiving narrowband optical pulses reflected back from each Bragg grating 7. The demodulator determines the physical location of the corresponding grating 7 by measuring the arrival time of each reflected pulse and calculates the strain / temperature at that location by analyzing its spectral center wavelength. Limited by the high-speed A / D sampling frequency and laser pulse interval within the demodulator, there must be a minimum time interval t0 between two adjacent reflected pulses that the instrument can resolve. This t0 is a constant determined by the instrument's hardware performance. This results in the minimum resolvable spacing d between two physical gratings on the same fiber link needing to satisfy the formula: d = Vc × t0 / 2, where Vc is the transmission speed of the optical signal in the silica fiber (approximately 2 x 10^8 m / s). This is the fundamental reason for the limited sensing density of traditional single-fiber sensors. This invention uses a "staggered parallel" method to arrange n sensing optical fibers 6 side-by-side in space. Physically, they are n independent optical paths (or connected in series through fusion splicing into a single long optical path), but in macroscopic applications, they are treated as a single optical cable. Since the gratings on different fibers are staggered in axial position, from the perspective of the entire optical cable, the actual distribution interval d_actual of its sensing points satisfies the formula: d_actual = d_single / n. Thus, even though the grating interval d_single on a single fiber is still limited by the minimum resolution distance d of the demodulator, by increasing the number of parallel fibers n, the actual sensing density can be easily increased by n times, thereby overcoming hardware limitations.

[0026] Existing demodulation technology, namely wavelength division multiplexing (WDM), has a minimum spacing limitation (due to pulse width) when identifying gratings. Therefore, although a very dense number of gratings can be written on a single optical fiber during the writing process, the demodulation system cannot identify them, resulting in defects at the application end. Therefore, in the actual use of optical cables, we also adopted a method of multiple optical fibers in parallel (a common technique in communication fibers). On this basis, we deliberately staggered the grating points on each optical fiber. This has the advantage that, for the demodulator, the signal interval transmitted by each grating is still large and can be identified. Spatially, the staggered gratings significantly improve the spatial density, enabling the application of high-density strain gauge optical cables based on existing demodulation technology. The reliability of this method has also been proven in the actual signal acquisition process.

[0027] Reference Figure 4 , Figure 5 , Figure 6 and Figure 7 The applicant actually manufactured a sample optical cable with a width of 5 mm, a thickness of 1.2 mm, and a weight of only 15 g / m, demonstrating its compact and lightweight characteristics. Testing showed that its strain transfer efficiency was no less than 90%. In a verification experiment, two identical optical cables were respectively attached to the upper and lower surfaces of a 1.2-meter-long aluminum alloy tube. When a load was applied above the central area of ​​the aluminum alloy tube, the upper surface cable was compressed, while the lower surface cable was stretched. Figure 6 The strain distribution of the strain-sensing optical cable installed under the aluminum alloy beam was disclosed. Figure 7 The strain distribution of a strain-sensing optical cable installed above an aluminum alloy beam is shown. It can be seen that the upper surface exhibits a linearly decreasing negative strain from the center to both sides, while the lower surface exhibits a symmetrical positive strain, with excellent symmetry in the data from both sides. The sensing point density in the experiment was 8 cm² / point, and the test results accurately reflect the actual strain variation trend of the beam, demonstrating the excellent sensing performance and reliability of the optical cable.

[0028] By integrating multiple sensing optical fibers in a staggered manner into a protective sheath that meets airworthiness requirements, this invention achieves a significant increase in sensing point density without relying on demodulator hardware upgrades. At the same time, it solves a series of engineering problems in airborne applications, such as complex wiring, increased weight, and difficult installation, providing an ideal sensor carrier for high-resolution, distributed, online real-time health monitoring of critical structural areas of aircraft.

[0029] One dyed fiber is provided on each side of the parallel fiber 3, such as... Figure 1The first dyed fiber 4 and the second dyed fiber 5 are different colors, for example, one is blue and the other is orange. These dyed fibers can be ordinary single-mode communication optical fibers, and in addition to color marking, they can also perform some communication transmission functions.

[0030] By using different colored markers on both sides of the optical fiber, clear and unambiguous directional guidance is provided for on-site installation and cabling. When attaching the optical cable to the aircraft structure, construction workers can easily identify the "left" and "right" or "up" and "down" of the cable, effectively preventing the cable from twisting along its axis. This ensures that the radial position of all sensor gratings remains consistent, guaranteeing the accuracy and comparability of measurement data and greatly improving installation efficiency and reliability.

[0031] The reinforcing member 2 is preferably a galvanized steel wire with a diameter in the range of 0.2 mm to 0.4 mm. This reinforcing member is covered together with the sheath layer 1 and the optical fiber 3 during the optical cable extrusion molding process.

[0032] Using galvanized steel wire as a reinforcing component significantly enhances the overall tensile strength of the optical cable, enabling it to resist unexpected tensile forces during installation and service, protecting the fragile internal optical fibers from damage. Furthermore, the steel wire also functions as a "tear cord," allowing for easy and neat removal of the sheath when the cable end needs to be treated or the sheath layer needs to be peeled off to splice the internal optical fibers. This simplifies termination operations and improves construction convenience.

[0033] The outer surface of the sheath layer 1 may be provided with anti-slip stripes or roughened. For example, fine longitudinal or grid-like grooves may be machined on the sheath extrusion die, so that the surface of the formed sheath has corresponding raised stripes.

[0034] By incorporating stripes or a roughened structure on the outer surface of the sheath, the contact area and mechanical interlocking force between the optical cable and the adhesive (such as aerospace-grade epoxy) are increased. This significantly improves the bonding strength and shear strength between the optical cable and the surface of the monitored aircraft structure, thereby ensuring that the strain of the aircraft structure can be efficiently and non-destructively transferred to the sensing optical fiber inside the cable. The strain transfer efficiency can be consistently maintained above 90%, guaranteeing the accuracy and high fidelity of the measurement results.

[0035] The Bragg gratings 7 on two adjacent sensing optical fibers 6 are staggered at equal distances along the axial direction.

[0036] By employing an equidistant, staggered arrangement, the sensing points along the entire length of the optical cable are uniformly distributed. This uniform, high-density grid greatly facilitates subsequent data processing and analysis. For example, spatial difference calculations can be easily performed to obtain strain gradients, or Fourier transforms can be performed to analyze the wavelength components of strain. This is crucial for advanced applications such as damage identification, localization, and load inversion.

[0037] The number of the multiple sensing optical fibers 6 can be selected according to specific application requirements, typically ranging from 4 to 24.

[0038] The invention offers a flexible range of fiber optic cable numbers, making the optical cable highly customizable. For general monitoring areas, a smaller number of fibers (e.g., 4 or 8) can be used to balance cost and density; for critical stress concentration areas such as wing roots and landing gear connections, a larger number of fibers (e.g., 16 or 24) can be used to achieve extremely high spatial resolution and enable precise detection of minute damage.

[0039] This embodiment also provides an aircraft structural health monitoring system. The system includes a high-density strain-sensing optical cable as described in any of the foregoing embodiments, and a grating demodulator connected to the optical fiber of the optical cable. The optical cable is laid in the area to be tested on the aircraft structure, and its optical fiber output is connected to the grating demodulator via a connector. The grating demodulator is responsible for generating and transmitting probe light signals, receiving and processing signals reflected from each Bragg grating in the optical cable, calculating the wavelength of each sensing point in real time, and calculating the corresponding strain value based on the wavelength change.

[0040] By combining high-performance sensing optical cables with mature demodulation equipment, a complete, plug-and-play aircraft structural health monitoring solution has been constructed. This system enables large-scale, distributed, real-time strain monitoring of aircraft structures, providing direct and reliable data support for assessing structural integrity, predicting fatigue life, and guiding maintenance decisions.

[0041] Reference Figure 3 In the series connection method, the multiple sensing fibers 6 in the parallel fiber 3 can be fused at both ends of the optical cable, so that they are connected end to end, ultimately forming a single, ultra-long series optical link. For example, for a 12-core optical cable, at the far end, the first fiber can be fused with the second fiber, the third with the fourth, and so on; at the near end, corresponding jumpers are made, ultimately forming a single optical path that originates from the demodulator, traverses all 12 fibers, and returns to the demodulator.

[0042] By using a series configuration, all sensing points within the optical cable can be monitored using only one channel of the grating demodulator. This significantly reduces the required number of demodulator channels, thereby substantially reducing the cost and complexity of the entire monitoring system, making it particularly suitable for cost-sensitive applications or those with extremely limited installation space.

[0043] Reference Figure 4 In the parallel connection method, the multiple sensing optical fibers 6 in the parallel fiber 3 can also be independently connected to multiple different channels of the grating demodulator to form a parallel optical link.

[0044] Using a parallel connection, each sensing fiber is an independent optical path, allowing the demodulator to perform synchronous high-speed scanning of all channels. This scanning frequency is much higher than that of a series long optical path, making it particularly suitable for monitoring dynamic strain responses caused by gusts, flutter, or maneuvering during flight. It can capture high-frequency structural vibration information, providing data for analyzing aircraft dynamic characteristics and aeroelasticity issues.

[0045] This embodiment also provides a method for forming a high-density strain-sensing optical cable, which aims to precisely control the misalignment distance and includes the following steps: Step S1: Fabricate Bragg grating arrays 7 on multiple sensing optical fibers 6 respectively.

[0046] During the process of drawing the sensing fiber 6 and writing the grating in line, a physical mark, such as a black mark with a length of 2-3 cm, is applied to the fiber coating at the center of each Bragg grating 7 based on the time-delay marking technology, to ensure that the grating 7 is precisely located in the center of the black mark.

[0047] Step S2: Arrange the marked multiple sensing optical fibers 6 in parallel with at least one dyed fiber 4 / 5 and at least one reinforcing member 2.

[0048] Before starting the fusion process, carefully align the first physical mark on each optical fiber with the preset equidistant offset. Adjust the pay-off reels of each optical fiber to ensure that the pay-off tension of each fiber is consistent and stable.

[0049] Step S3: Under the condition of controlling the tension of each optical fiber to be consistent, start the parallel belt equipment and sheath extruder to perform parallel belt and sheath extrusion molding.

[0050] The method further includes: during the bonding process, checking the distribution of black marks on the bonding optical fibers at intervals (e.g., every 10 meters) using a machine vision system or manually. When a slight deviation in the position of a mark on a particular optical fiber is detected (the interval becomes larger or smaller), the tension of that fiber is finely adjusted accordingly (decreased or increased). If a large change is detected, production is immediately stopped, the fiber is repositioned, and bonding is restarted.

[0051] Through a closed-loop process control system of "pre-marking - initial alignment - tension control - process inspection - dynamic adjustment," this method achieves precise correlation and locking between macroscopic mechanical processes and micron-level fiber optic grating positions. It effectively solves the problem of misalignment accumulation errors caused by inconsistent fiber lengths in long-distance production, ensuring highly consistent sensor point accuracy throughout the entire optical cable. This provides crucial process assurance for producing high-quality, high-reliability, high-density sensing optical cables.

[0052] To achieve co-curing integration with the composite material structure, the sheath layer 1 can be made of high-performance engineering plastics, such as polyetheretherketone (PEEK) or polyimide (PI), which can co-cur and bond with the matrix resin of the aircraft composite component during the curing process. Furthermore, the glass transition temperature (Tg) of the selected sheath material must be higher than the curing temperature of the composite matrix resin. For example, if the curing temperature of the epoxy resin in the composite material is 180°C, then a PEEK material with a Tg greater than 180°C should be selected.

[0053] By employing a special sheath material chemically compatible with the composite matrix, the sensing optical cable can be directly embedded between the prepreg layers during the manufacturing process of composite components, acting as an "intelligent nerve," and cured together with the structure. This "co-curing" technology creates a perfect interface bond without adhesive layers, fundamentally eliminating strain transfer loss and creep aging problems caused by adhesive layers, achieving 100% strain transfer efficiency, greatly improving the long-term accuracy and reliability of monitoring, and representing the highest level of airborne sensor integration.

[0054] To eliminate the cross-influence of temperature changes on strain measurements, the parallel fiber 3 may additionally include a separate temperature compensation fiber arranged parallel to the multiple sensing fibers 6. The Bragg grating on this temperature compensation fiber appears in pairs with the Bragg grating on the sensing fiber 6 along the length direction (i.e., as close as possible in position). Crucially, this temperature compensation fiber is specially treated to decouple it from the axial strain of the optical cable; for example, it is loosely wrapped with a micro-diameter polytetrafluoroethylene (PTFE) tube with an inner diameter slightly larger than the fiber diameter before paralleling, or its surface is coated with a layer of extremely low-modulus silica gel.

[0055] By integrating a precisely aligned, strain-decoupled temperature sensor array into a compact parallel structure, in-situ, real-time temperature compensation for each strain measurement point is achieved. When the optical cable is stretched under stress, the wavelength change of the sensing grating reflects both strain and temperature, while the wavelength change of the "isolated" temperature grating reflects only temperature. Pure strain information can be accurately separated using a simple algorithm (Δλ_strain = Δλ_total - k×Δλ_temp), improving measurement accuracy to the micro-strain (με) level, which is crucial for accurately assessing the static and quasi-static loads on structures.

[0056] To enable intelligent management of the sensor, a passive RFID chip can be periodically encapsulated at the end of the sheath layer 1 or along its length. This chip pre-stores the optical cable's unique serial number, a detailed grating wavelength / position mapping table, production date, batch number, and installation information (which can be written during installation).

[0057] By integrating the sensor fiber optic cable with the Internet of Things (IoT) and giving it a unique "digital ID card," automatic identification, rapid traceability, and intelligent management of sensor information throughout the aircraft's entire lifecycle are achieved. Line maintenance personnel no longer need to consult cumbersome paper diagrams or databases; they can simply scan the cable with a handheld RFID reader to instantly obtain the entire "file" of that section of fiber optic cable and its precise location on the aircraft. This greatly improves the efficiency and accuracy of maintenance work and reduces the risk of human error.

[0058] A hybrid fiber design can be adopted. Of the multiple sensing fibers 6, one part is a standard single-mode fiber used to measure axial strain; the other part is a polarization-maintaining fiber (PMF), on which Bragg gratings are inscribed along its fast or slow axis.

[0059] By integrating different types of sensing fibers within a single optical cable, a leap from one-dimensional strain measurement to two-dimensional stress state monitoring has been achieved. Standard single-mode fiber's FBG measures axial strain, while polarization-maintaining fiber's FBG is sensitive to lateral stress (i.e., pressure perpendicular to the fiber axis). When the optical cable is subjected to lateral compression, the birefringence effect of the polarization-maintaining fiber changes, causing a shift in the wavelength interval between its two reflection peaks on the fast and slow axes. By monitoring this change in peak splitting interval, lateral stress can be quantitatively measured. This allows a single optical cable to simultaneously acquire axial tension / compression and lateral pressure information, providing an unprecedented data dimension for more accurate assessment of the multiaxial stress state of structures and identification of impact damage (such as dents caused by tool drops).

[0060] The present invention also provides a method for identifying aircraft structural damage based on the optical cable described in any of the foregoing embodiments. The method includes: The high-density strain sensing optical cable is installed in a critical area of ​​the aircraft structure, and the wavelength data of all Bragg gratings 7 are collected in real time using a grating demodulator. The discrete strain distribution curve ε(x) along the optical cable path is obtained by conversion.

[0061] Spatial differentiation (or difference) is performed on the collected discrete strain distribution ε(x) data to obtain the strain gradient distribution dε / dx.

[0062] A damage alarm threshold is established. The strain gradient distribution is monitored in real time. When the absolute value of the strain gradient |dε / dx| at a certain location x0 continuously or instantaneously exceeds the preset threshold, the system determines that there is significant stress concentration at location x0, marks it as a suspected damage point, and triggers an alarm.

[0063] This method pioneers a new paradigm for directly "diagnosing" damage using high-density strain data. The physical essence of structural damage (such as cracks) is the creation of extreme stress concentration in localized areas, which inevitably produces a sharp abrupt change in the strain distribution curve—a very large strain gradient. The optical cable of this invention provides the high-density data required for such gradient calculation. By monitoring anomalies in the strain gradient, which serves as a damage "indicator," rapid, automatic alarms and precise location of early damage, such as microcrack initiation, can be achieved. This elevates structural health monitoring from merely "sensing" loads to a higher level of proactively "diagnosing" damage.

[0064] Compared with the prior art, the beneficial technical effects of the technical solution provided in this application include: This invention provides an aircraft structural health monitoring sensing solution that integrates high density, lightweight, high reliability, ease of integration, and intelligence. Through an innovative staggered and integrated structural design, it overcomes the bottlenecks of existing technologies. Its diverse implementation methods and extended functions can meet application needs at different levels, from composite material co-curing integration to multi-dimensional stress monitoring and intelligent damage diagnosis. It has significant technical advantages and immense application value in improving flight safety, optimizing maintenance strategies, and reducing total lifecycle costs.

[0065] Those skilled in the art will understand that the steps, measures, and schemes in the various operations, methods, processes, and procedures discussed in this application can be alternated, modified, rearranged, decomposed, combined, or deleted.

[0066] The specific embodiments described above do not constitute a limitation on the scope of protection of this application. Any other corresponding changes and modifications made based on the technical concept of this application should be included within the scope of protection of the claims of this application.

Claims

1. A high-density strain-sensing optical cable, characterized in that, include: Sheath layer; At least one reinforcing member is disposed within the sheath layer; The fiber is provided in the sheath layer and includes multiple sensing fibers arranged in parallel and at least one dyed fiber. The dyed fiber is arranged in parallel with the multiple sensing fibers and each sensing fiber is provided with at least one Bragg grating distributed along its axis. In this configuration, the Bragg gratings on any two adjacent sensing optical fibers are staggered relative to each other along the axial direction of the parallel fiber.

2. The high-density strain sensing optical cable according to claim 1, characterized in that, A dyed fiber is provided on each side of the optical fiber, and the dyed fiber is a different color from the sensing optical fiber.

3. The high-density strain sensing optical cable according to claim 1, characterized in that, The reinforcing member comprises galvanized steel wire with a diameter of 0.2mm-0.4mm.

4. The high-density strain sensing optical cable according to claim 1, characterized in that, The outer surface of the sheath layer is provided with anti-slip stripes or a rough structure.

5. The high-density strain sensing optical cable according to claim 1, characterized in that, The Bragg gratings on two adjacent sensing optical fibers are staggered at equal distances along the axial direction.

6. The high-density strain sensing optical cable according to claim 1, characterized in that, The number of the multiple sensing optical fibers is 4-24.

7. A monitoring system, characterized in that, It includes a grating demodulator and a high-density strain sensing optical cable as described in any one of claims 1-6, wherein the grating demodulator is connected to the high-density strain sensing optical cable.

8. The monitoring system according to claim 7, characterized in that, The two ends of the multiple sensing optical fibers in the parallel optical fiber are connected end to end to form a series optical link.

9. The monitoring system according to claim 7, characterized in that, The multiple sensing fibers in the parallel fiber are respectively connected to multiple channels of the grating demodulator, forming a parallel optical link.

10. A method for forming a high-density strain-sensing optical cable, characterized in that, Includes the following steps: Bragg grating arrays are fabricated on multiple sensing optical fibers, and physical marks are applied at the center of each Bragg grating. Multiple sensing optical fibers are arranged side by side with at least one dyed fiber and at least one reinforcing member, and aligned with the first physical mark on each optical fiber, so that they are staggered at equal distances. Under the condition of controlling the tension of each optical fiber to be consistent, the tape and sheath are extruded and formed.

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