Biaxial strain sensor and glass edge internal multi-directional stress measurement device

Abstract

This application discloses a bidirectional strain sensor and a multi-directional stress measurement device inside a glass frame, relating to the field of stress measurement technology. The device includes: an encapsulation layer, a substrate layer, and a first wavy strip. The first wavy strip is located between the encapsulation layer and the substrate layer. A first wavy optical fiber is embedded within the first wavy strip. A normal stress grating and two first shear stress gratings are arranged in the center band of the first wavy optical fiber. The normal stress grating is horizontal, and the two first shear stress gratings are symmetrically arranged and tilted. This application utilizes this bidirectional strain sensor to sense normal stress perpendicular to the glass plane and shear stress parallel to the glass plane, thereby obtaining relevant stress data based on the sensor's sensing signals.

Description

Technical Field

[0001] This application relates to the field of stress measurement technology, and in particular to a bidirectional strain sensor and a multi-directional stress measurement device inside a glass frame. Background Technology

[0002] As a critical component for flight safety, the windshield must possess sufficient structural strength and service life. However, during actual assembly and service, cracks frequently appear in the edge areas of the windshield, posing a significant threat to flight safety. The windshield exhibits significant stress concentration in the frame area; residual stress and assembly stress during assembly are major causes of cracks in this area. During flight, it is also susceptible to internal pressurization and external aerodynamic loads.

[0003] Currently, the photoelastic test method is mostly used to measure the stress of aircraft windshields. However, the existing photoelastic test method is mostly static or offline measurement, which cannot monitor the dynamic stress changes of helicopters in real time during assembly and service. Summary of the Invention

[0004] In view of this, this application proposes a bidirectional strain sensor and a multi-directional stress measurement device inside a glass frame.

[0005] In a first aspect, this application provides a bidirectional strain sensor, comprising: an encapsulation layer, a substrate layer, and a first wavy strip; The first wavy strip is located between the encapsulation layer and the substrate layer. The first wavy strip is embedded with a first wavy optical fiber. The center band of the first wavy optical fiber is provided with a normal stress grating and two first shear stress gratings. The normal stress grating is horizontal, and the two first shear stress gratings are symmetrically arranged and tilted.

[0006] In one embodiment, the first wavy optical fiber has a symmetrical structure, and the normal stress grating is located at the midpoint of the symmetry of the first wavy optical fiber.

[0007] In one embodiment, the horizontal distances between the two first shear stress gratings and the normal stress grating are L / 4, where L is the horizontal distance from the peak to the trough of the center band.

[0008] In one embodiment, the center band of the first wavy optical fiber is the band with the highest height and the longest horizontal length.

[0009] In one embodiment, the first corrugated strip includes an upper polymer layer, a lower polymer layer, and the first corrugated optical fiber; The upper polymer layer is bonded to the encapsulation layer, the lower polymer layer is bonded to the substrate layer, and the first wavy optical fiber is located between the upper polymer layer and the lower polymer layer.

[0010] In one embodiment, the bidirectional strain sensor further includes: a second wavy strip; The second wavy strip is embedded with a second wavy optical fiber, which is intersected with the first wavy optical fiber. Two second shear stress gratings are symmetrically arranged on the center band of the second wavy optical fiber, and the two second shear stress gratings are tilted.

[0011] In one embodiment, the second wavy optical fiber is arranged perpendicularly to the first wavy optical fiber.

[0012] Secondly, this application also provides a multi-directional stress measuring device inside a glass frame, the multi-directional stress measuring device inside a glass frame comprising: an optical fiber sensing string, a transmission optical fiber, a fiber optic grating demodulator, and a processing module. The fiber optic sensing string is located inside the edge of the windshield and includes a plurality of bidirectional strain sensors as described in any one of claims 1 to 7, wherein the plurality of bidirectional strain sensors on the fiber optic sensing string are connected in series. The fiber optic sensing string is connected to the fiber optic demodulator via the transmission fiber; The fiber optic grating demodulator is used to transmit scanning light into the transmission fiber and simultaneously receive reflected light signals from the transmission fiber, and to determine the wavelength offset of the reflection center of each grating in each of the bidirectional strain sensors based on the reflected light signals. The processing module is connected to the fiber optic grating demodulator and is used to determine the strain information of each bidirectional strain sensor based on the wavelength offset of the reflection center of each grating in each bidirectional strain sensor.

[0013] In one embodiment, when the bidirectional strain sensor includes a second wavy strip, adjacent bidirectional strain sensors on the fiber optic sensing string are connected to the first wavy fiber by a first transmission fiber and to the second wavy fiber by a second transmission fiber.

[0014] In one embodiment, one of the fiber optic sensing strings is disposed on two adjacent sides of a windshield.

[0015] The bidirectional strain sensor proposed in this application has the following advantages over related technologies: 1. The bidirectional strain sensor of this application includes: an encapsulation layer, a substrate layer, and a first corrugated strip. By sandwiching the first corrugated strip, which embeds a first corrugated optical fiber, between the encapsulation layer and the substrate layer, and utilizing the synergistic constraint of the encapsulation layer and the substrate layer and the flexible adaptation characteristics of the corrugated structure, the sensor is given the core advantages of small size and flexibility. This allows it to accurately adapt to the narrow space inside the windshield frame. It can be directly embedded and distributed at the bonding point between the frame and the glass edge, so that the sensor and the glass or windshield frame form a stable structural whole. This fundamentally avoids the problem of decreased measurement accuracy caused by space limitations and complex paths of external measurement methods.

[0016] 2. By setting a horizontal normal stress grating and two symmetrically tilted first shear stress gratings in the center band of the first wavy optical fiber, and by differentiating the orientation of the gratings, different gratings are given specific stress-sensitive directions. When complex stress is applied to the sensor, the sensor can sense the normal stress perpendicular to the glass plane and the shear stress parallel to the glass plane. Then, based on the sensor signal, relevant stress data can be obtained, thereby realizing real-time online monitoring of stress dynamic changes throughout the assembly and service of helicopter windshields. This effectively makes up for the technical shortcomings of static or offline measurement in existing photoelastic experimental methods. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a bidirectional strain sensor in one embodiment of this application; Figure 2 This is a schematic diagram of the structure of the first wavy strip in one embodiment of this application; Figure 3 This is a coordinate schematic diagram of the normal stress grating and the first shear stress grating in one embodiment of this application. Figure 4 This is a schematic diagram of the intersection structure of the first wavy strip and the second wavy strip in one embodiment of this application; Figure 5 This is a schematic diagram of the structure of a multi-directional stress measuring device inside a glass frame in one embodiment of this application; Figure 6 This is a schematic diagram of the application environment of a bidirectional strain sensor in one embodiment of this application.

[0019] Explanation of reference numerals in the attached figures: 1-Encapsulation layer, 2-Base layer, 3-First wavy strip, 30-First wavy optical fiber, 301-Normal stress grating, 302-First shear stress grating, 31-Upper polymer layer, 32-Lower polymer layer, 4-Second wavy strip, 401-Second shear stress grating, 100-Fiber optic sensing string, 200-Transmission optical fiber, 300-Fiber Bragg grating demodulator, 400-Processing module. Detailed Implementation

[0020] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0023] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0024] In some embodiments, such as Figure 1 and Figure 2As shown, the present application provides a bidirectional strain sensor, comprising: an encapsulation layer 1, a substrate layer 2, and a first wavy strip 3.

[0025] The first wavy strip 3 is located between the encapsulation layer 1 and the substrate layer 2. The first wavy strip 3 is embedded with a first wavy optical fiber 30. The center band of the first wavy optical fiber 30 is provided with a normal stress grating 301 and two first shear stress gratings 302. The normal stress grating 301 is in a horizontal state, and the two first shear stress gratings 302 are symmetrically arranged and in an inclined state.

[0026] The encapsulation layer 1 and the base layer 2 can be soft elastomers (modulus in the kPa range) to serve as a protective structure, allowing the bidirectional strain sensor to be installed between the outer and middle layers of the windshield. The first corrugated strip 3, except for the first corrugated optical fiber 30, can be made of a rigid, high-elasticity-modulus polymer to protect and support the first corrugated optical fiber 30. The encapsulation layer 1 and the base layer 2 form a clamping structure, stably constraining the first corrugated strip 3 between them. This provides protection and fixation for the embedded first corrugated optical fiber 30 without affecting the flexible deformation characteristics of the corrugated structure, ensuring that the optical fiber responds synchronously to the stress deformation of the windshield frame.

[0027] It is understandable that, from a mechanical deformation perspective, shear stress will cause the corrugated optical fiber to undergo "tangential bending deformation." However, this deformation is "strain canceled out" at the midpoint. Therefore, a horizontal normal stress grating 301 is set in the center band of the first corrugated optical fiber 30. This normal stress grating 301 avoids bending caused by shear force, allowing it to primarily measure the bending deformation and film deformation caused by normal stress at that location. Furthermore, since the grating axis is sensitive to the direction perpendicular to the glass plane (i.e., the expected direction of normal stress), it can measure the normal stress perpendicular to the glass plane caused by compression or tension. The first shear stress grating 302 is set at a specific tilt angle on the first corrugated strip 3. Its grating axis is sensitive to the shear direction parallel to the glass plane, allowing it to measure the shear stress caused by interlayer misalignment, etc. The symmetrical arrangement of the first shear stress grating 302 provides a mechanical compensation basis for subsequent data processing. It can reduce the interference of stress in other directions besides the shear direction by setting it symmetrically, and finally accurately extract the pure stress data in the shear direction, so as to achieve independent and accurate measurement of normal stress and shear stress.

[0028] The aforementioned bidirectional strain sensor includes an encapsulation layer 1, a base layer 2, and a first wavy strip 3. By sandwiching the first wavy strip 3, which has an embedded first wavy optical fiber 30, between the encapsulation layer 1 and the base layer 2, the sensor is given the core advantages of small size and flexibility by utilizing the synergistic constraint of the encapsulation layer 1 and the base layer 2 and the flexible adaptation characteristics of the wavy structure. This allows the sensor to accurately adapt to the narrow space inside the windshield frame and can be directly embedded and distributed at the edge of the frame and the glass. This allows the sensor to form a stable structural whole with the glass or windshield frame, fundamentally avoiding the problem of decreased measurement accuracy caused by space limitations and complex paths of external measurement methods. Meanwhile, by setting a horizontal normal stress grating 301 and two symmetrically tilted first shear stress gratings 302 in the center band of the first wavy optical fiber 30, the different orientations of the gratings give each grating a specific stress-sensitive direction. When complex stress is applied to the sensor, the sensor can sense the normal stress perpendicular to the glass plane and the shear stress parallel to the glass plane. Then, based on the sensor's sensing signal, relevant stress data can be obtained, thereby enabling real-time online monitoring of stress dynamic changes throughout the assembly and service of helicopter windshields. This effectively makes up for the technical shortcomings of existing photoelastic experimental methods for static or offline measurement.

[0029] In some embodiments, such as Figure 2 As shown, the first wavy optical fiber 30 has a symmetrical structure, and the normal stress grating 301 is located at the midpoint of the symmetry of the first wavy optical fiber 30.

[0030] It is understandable that the first wavy optical fiber 30 adopts a symmetrical structural design, with its wave shape distributed in a mirror-symmetrical manner along the central axis. This structural characteristic allows the tangential bending deformation generated on both sides of the fiber to form a precise mirror cancellation effect when shear stress is applied to the sensor. That is, the bending deformation on both sides of the symmetry is equal in magnitude and opposite in direction, ultimately achieving complete cancellation of shear strain at the symmetrical midpoint of the fiber, effectively avoiding cross-interference of shear deformation on normal stress measurement. The normal stress grating 301 is deliberately set at this symmetrical midpoint, which fully utilizes the mechanical property of shear strain cancellation at the midpoint. In addition, the normal stress grating 301 itself is horizontal, and its axis is specifically sensitive to the direction of normal stress perpendicular to the glass plane. This allows the grating to completely get rid of the deformation interference caused by shear stress and focus on capturing the normal strain perpendicular to the glass plane generated by compression or tension, and then accurately convert it into normal stress data. At the same time, it complements the two symmetrically tilted first shear stress gratings 302, ensuring the independence and accuracy of normal stress measurement.

[0031] In some embodiments, such as Figure 3As shown, the horizontal distances between the two first shear stress gratings 302 and the normal stress grating 301 are L / 4, where L is the horizontal distance from the peak to the trough of the center band.

[0032] It is understandable that, due to the symmetrical structure of the first wavy fiber 30, the tangential bending deformation generated under shear stress is gradually distributed from the crest to the trough. The midpoint of the symmetry (where the normal stress grating 301 is located) has no shear strain due to the mirror cancellation of deformation on both sides. The midpoint between the crest and the midpoint, and between the midpoint and the trough (i.e., L / 4 from the midpoint) is precisely the region where shear strain is most significant and stable. This avoids the strain cancellation effect at the midpoint and is far from the measurement distortion problems that may be caused by the concentrated deformation at the crest and trough. Simultaneously, the two first shear stress gratings 302 are located symmetrically at L / 4 positions on both sides of the normal stress grating 301. Combined with their tilted sensitive direction design, they can simultaneously capture the shear strain signals on both sides of the symmetry. This not only ensures the sensitivity and stability of shear stress measurement but also, through the calibration of the symmetrical signal in subsequent data processing, further eliminates the influence of normal stress and other directional interference signals. Together with the normal stress grating 301, they form a precise spatial layout and functional division, ultimately achieving independent, high-precision synchronous measurement of normal stress and shear stress.

[0033] In some embodiments, such as Figure 1 and Figure 2 As shown, the center band of the first wavy optical fiber 30 is the highest in height and the longest in horizontal length.

[0034] It is understandable that the central band of the first wavy fiber 30 is the highest and longest horizontal band. The highest height means that the wave amplitude of this band is the largest, which allows it to produce more significant and easily captured mechanical deformation when subjected to normal or shear stress, thus improving the sensitivity of the grating to weak stress signals. The longest horizontal length design provides ample space for the rational layout of the core grating, which can stably accommodate the normal stress grating 301 located at the midpoint of symmetry, and ensure that the horizontal distance between the two first shear stress gratings 302 and the normal stress grating 301 is precisely controlled at L / 4, perfectly matching the gradual distribution law of shear strain from the peak to the trough, so that the shear grating is exactly in the region where the shear strain is most significant and stable.

[0035] Furthermore, as the core measurement area of ​​the optical fiber, the large-size design of the center band can reduce the interference of uneven deformation in the edge band on the measurement, making the stress transmission in this band more uniform and direct. This ensures that the normal stress grating 301 can focus on capturing the stress signal perpendicular to the glass plane, and the two shear gratings can synchronously acquire shear strain signals at symmetrical positions. Through subsequent data processing, interference is eliminated, ultimately achieving high-sensitivity, high-precision independent synchronous measurement of normal stress and shear stress. This lays a key structural foundation for the accurate analysis of complex stress fields.

[0036] In some embodiments, such as Figure 2 As shown, the first wavy strip 3 includes an upper polymer layer 31, a lower polymer layer 32, and a first wavy optical fiber 30.

[0037] The upper polymer layer 31 is bonded to the encapsulation layer 1, the lower polymer layer 32 is bonded to the substrate layer 2, and the first wavy optical fiber 30 is located between the upper polymer layer 31 and the lower polymer layer 32.

[0038] Both the upper polymer layer 31 and the lower polymer layer 32 can be made of rigid, high-elasticity polymers (such as polyimide, with a modulus in the GPa range). The upper polymer layer 31 serves as a protective layer and provides mechanical support, while the lower polymer layer 32 can be bonded to the substrate layer 2 to provide interfacial stability.

[0039] It is understandable that the first wavy strip 3 adopts a sandwich-like composite structure of an upper polymer layer 31, a lower polymer layer 32, and a first wavy optical fiber 30. This achieves a stable integration of the optical fiber and the sensor as a whole, while the flexibility of the polymer material ensures the sensor's flexibility, perfectly adapting to the narrow installation environment inside the windshield frame. The upper and lower polymer layers 32 not only provide physical protection for the first wavy optical fiber 30, preventing it from being affected by external factors such as friction and impact during assembly and service, but also ensure that the stress of the windshield frame can be efficiently and without distortion transferred to the grating area on the optical fiber through the synergistic deformation characteristics of the polymer, optical fiber, encapsulation layer 1, and base layer 2. At the same time, the clamping effect of the two polymer layers can fix the relative spatial arrangement of the normal stress grating 301 and the two first shear stress gratings 302, preventing the measurement accuracy from decreasing due to grating displacement.

[0040] Furthermore, the thin and light nature of the polymer layer does not increase the overall size of the sensor, and its elastic modulus is mechanically compatible with the optical fiber and glass frame, which can reduce energy loss during stress transmission. This allows the normal stress grating 301 to accurately capture compressive or tensile stress perpendicular to the glass plane, while the two shear stress gratings can stably sense shear strain parallel to the glass plane. Combined with the symmetrical layout, interference signals are canceled out, ultimately ensuring that the sensor can independently and with high precision measure normal and shear stress synchronously.

[0041] In some embodiments, such as Figure 4 As shown, the bidirectional strain sensor also includes: a second wavy strip 4.

[0042] The second wavy strip 4 is embedded with a second wavy optical fiber. The second wavy optical fiber is intersected with the first wavy optical fiber 30. Two second shear stress gratings 401 are symmetrically arranged on the center band of the second wavy optical fiber. The two second shear stress gratings 401 are tilted.

[0043] It is understandable that the second wavy strip 4 and the first wavy strip 3 of the bidirectional strain sensor are sandwiched between the encapsulation layer 1 and the base layer 2, continuing the composite structure design of the upper and lower polymer layers 32 holding the wavy optical fiber. This not only ensures the core characteristics of the sensor being small in size and flexible, adapting to the narrow installation environment of the windshield frame, but also constructs an orthogonal shear stress measurement dimension through the cross layout of the second wavy optical fiber and the first wavy optical fiber 30.

[0044] The shear measurement directions of the first wavy fiber 30 and the second wavy fiber intersect, comprehensively covering the shear stress components parallel to the glass plane. Simultaneously, two tilted second shear stress gratings 401, symmetrically arranged in the center band of the second wavy fiber, continue the mechanical design logic of symmetrical cancellation. The tilt angle gives the gratings targeted sensitivity to the target shear direction. Their symmetrical arrangement allows for averaging in subsequent data processing, serving as mutual calibration and verification of grating effectiveness. This reduces interference from normal stress and other non-target direction stresses, accurately extracting stress data corresponding to the shear direction. This structural design complements the first wavy strip 3. The horizontal normal stress grating 301 on the first wavy fiber 30 focuses on capturing the normal stress perpendicular to the glass plane. The shear gratings of the first and second wavy fibers accurately measure the shear stress in two orthogonal directions, ultimately achieving comprehensive, independent, and high-precision synchronous measurement of the three-dimensional stress components. This provides more complete key data support for analyzing the distribution law of complex stress fields during the assembly and service of windshields and tracing the crack initiation mechanism. At the same time, the synergistic design of the cross layout and the double wavy strip enhances the sensor's response sensitivity to stress deformation in different directions, ensuring distortion-free stress transmission and further improving the reliability of dynamic real-time monitoring.

[0045] In some embodiments, such as Figure 4 As shown, the second wavy optical fiber is set perpendicular to the first wavy optical fiber 30.

[0046] It can be understood that the shear measurement direction corresponding to the first wavy fiber 30 is perpendicular to the shear measurement direction of the second wavy fiber at 90°, which can comprehensively cover all shear stress components parallel to the glass plane (i.e., X-direction and Y-direction shear stress), completely solving the problem that single-direction shear measurement cannot capture multi-directional shear action in complex stress fields. At the same time, this vertical layout perfectly complements the first wavy strip 3: the horizontal normal stress grating 301 on the first wavy fiber 30 focuses on capturing the normal stress (Z-direction) perpendicular to the glass plane, while the shear gratings of the first and second wavy fibers independently measure the shear stress in two orthogonal directions (X-direction and Y-direction), ultimately achieving comprehensive, complete, and high-precision synchronous measurement of three-dimensional stress components (normal + bidirectional orthogonal shear). Moreover, the vertically arranged double wavy strips do not interfere with each other during stress transmission, and both can capture weak stress signals through the high-sensitivity deformation response of the wavy structure, ensuring the reliability and accuracy of dynamic real-time monitoring.

[0047] In some embodiments, such as Figure 5 As shown, this application also provides a multi-directional stress measuring device inside a glass frame, which includes: an optical fiber sensing string 100, a transmission optical fiber 200, a fiber optic demodulator 300, and a processing module 400.

[0048] The fiber optic sensing string 100 is located inside the edge of the windshield and includes multiple bidirectional strain sensors as described above, connected in series. It should be noted that the bidirectional strain sensors can be independent sensing units, connected to each other via optical fibers. Alternatively, multiple bidirectional strain sensors can be fabricated on a single optical fiber in a wavy pattern (either the first wavy fiber 30 or the second wavy fiber), thus avoiding the need for connection interfaces.

[0049] The fiber optic sensor string 100 is connected to the fiber optic demodulator 300 via the transmission fiber optic cable 200.

[0050] The fiber optic grating demodulator 300 is used to transmit scanning light to the transmission fiber 200 and simultaneously receive the reflected light signal from the transmission fiber 200, and determine the wavelength offset of the reflection center of each grating in each bidirectional strain sensor based on the reflected light signal.

[0051] The processing module 400 is connected to the fiber optic grating demodulator 300 and is used to determine the strain information of each bidirectional strain sensor based on the wavelength offset of the reflection center of each grating in each bidirectional strain sensor.

[0052] The fiber Bragg grating string can be laid on the windshield surface of the frame loading area according to a predetermined path (e.g., at the bonding point between the frame and the glass), and the internal structure of the windshield frame with embedded bidirectional stress sensors can be as follows: Figure 6 As shown. A fiber optic sensor string 100 is disposed on two adjacent frames of a windshield. For example, for an aircraft windshield assembly structure including a left windshield and a right windshield, the specific laying path can be to lay four fiber optic sensor strings 100 on the left and bottom sides of the left windshield frame, the top and right sides of the left windshield frame, the left and top sides of the right windshield frame, and the bottom and right sides of the right windshield frame, thereby realizing distributed, multi-point synchronous measurement of the stress field inside the entire frame.

[0053] Before assembling the windshield assembly, a fiber Bragg grating string containing multiple bidirectional stress sensors (sensing units) can be laid and positioned according to a preset path. Then, the frame is assembled, sealant is applied, and the sealant is allowed to harden at room temperature, permanently embedding the entire grating string within the frame structure to form an integrated intelligent structure. After the fiber optic sensing string 100 is installed on the edge surface of the windshield without altering the glass's structure, the fiber Bragg grating string is led out of the frame via a transmission fiber optic cable 200 and connected to an external fiber Bragg grating demodulator 300. The fiber Bragg grating demodulator 300 emits scanning light into the entire fiber Bragg grating string via the transmission fiber optic cable 200. The demodulator synchronously receives reflected light signals from each normal stress grating 301 and shear stress grating on the string and accurately measures the wavelength offset (Δλ) at the reflection center of each grating. Finally, the processing module 400 determines the strain information at the location of each bidirectional strain sensor based on the wavelength offset at the reflection center of each grating in each bidirectional strain sensor.

[0054] In applications, when the windshield is subjected to assembly and flight loads, complex stresses are generated within its frame. This stress is transmitted through the frame structure to the corrugated strip of each embedded bidirectional stress sensor. The corrugated strip undergoes slight bending deformation, and the normal stress component is mainly captured by the normal stress grating 301, while the shear stress component is mainly captured by the shear stress grating.

[0055] In fiber Bragg grating sensing, the grating wavelength can be converted into stress using the Bragg grating formula. The relevant calculation principle is as follows: In applications, the wavy ribbon structure consists of two layers of polymers and optical fibers with different elastic moduli. Pre-strain occurs during the formation of the wavy ribbon structure. The maximum wave wavelength at its center ,amplitude .

[0056] The formula for calculating the equivalent axial stiffness of a corrugated belt is as follows:

[0057] in, Indicates the upper-level modulus. Indicates the lower-level modulus. Indicates the thickness of the wavy band. This indicates the width of the wavy band.

[0058] The formula for calculating the equivalent bending stiffness of a corrugated belt is as follows:

[0059] in, Indicates the upper-level modulus. Indicates the lower-level modulus. , , Let be the moments of inertia of the top and bottom sections about their own centroidal axes, respectively. It is the width of the wavy band. The thickness of the wavy band. It is the cross-sectional area.

[0060] The formulas corresponding to the equivalent elastic modulus of the encapsulation layer and the substrate are as follows:

[0061] in, , This represents the elastic modulus of the encapsulation layer and the substrate material. , This indicates the thickness of the encapsulation layer and the substrate.

[0062] Because the wavy band is composed of two layers of polymers with different moduli, the neutral plane position... The corresponding calculation formula is as follows:

[0063] grating position The distance from the neutral surface is:

[0064] Based on the above derivation, normal stress The derivation of the calculation formula is as follows: Normal grating output strain (Quantity obtained) at At the location, for tangential stress τ Insensitive to membrane strain caused only by normal stress and bending strain The sum of them, then The calculation formula is as follows:

[0065] Membrane strain With normal stress If they are directly proportional, then:

[0066] in, It is the equivalent elastic modulus of the encapsulation layer and the substrate. A dimensionless correction parameter reflects the relative axial stiffness of the wavy band structure; Another dimensionless correction parameter is mainly used to correct for the effects of the limited thickness of the encapsulation layer and the substrate.

[0067] Bending strain depends on location Then the bending strain for:

[0068] Among them, parameters and Based on equivalent stiffness:

[0069]

[0070] exist Place, ,therefore:

[0071] make

[0072] Among them, record Normal pressure exist Contribution coefficient at the location; denoted as Normal pressure exist The contribution coefficient at that location, and:

[0073] Therefore, pressure for:

[0074] Similarly, based on the aforementioned derivation, shear stress τ The calculation formula is derived as follows: Grating strain gauge output strain At The strain at this point is the result of the combined action of normal stress and shear stress. Membrane strain is negligible under shear stress; therefore, it is the normal stress that causes the membrane strain. Bending strain and bending stress caused by shear stress sum:

[0075]

[0076] Among them, the shear sensitivity constant for:

[0077] exist Place, Therefore, it can be known that in The output strain of the optical grating strain gauge For shear stress Most sensitive, then:

[0078] make ,but:

[0079] Shear stress for:

[0080] in Normal pressure exist The contribution coefficient at that location is calculated as follows:

[0081] After receiving the wavelength offset signal output by the fiber Bragg grating demodulator 300, the processing module 400 can calculate and determine the strain information of each bidirectional strain sensor based on the algorithm constructed according to the above principle.

[0082] It should be noted that the bidirectional strain sensor provided in this application embodiment can be referred to the description of the bidirectional strain sensor in the foregoing embodiment, and the repeated parts will not be repeated.

[0083] The aforementioned multi-directional stress measurement device inside the glass frame includes: an optical fiber sensor string 100, a transmission optical fiber 200, a fiber optic demodulator 300, and a processing module 400. The optical fiber sensor string 100 is composed of multiple bidirectional strain sensors connected in series. Through the multi-sensor series layout, it achieves full coverage monitoring of stress over the entire frame area, solving the problem that single-point measurement cannot reflect the overall stress distribution. The fiber optic sensing string 100 is connected to the fiber optic grating demodulator 300 via the transmission fiber 200. The scanning light emitted by the demodulator reaches the grating area of ​​each sensor via the transmission fiber 200. When stress is applied to the sensor, the wavelength of the grating reflection center will shift with strain. The demodulator synchronously receives the reflected light signal and accurately identifies the wavelength shift of each grating, realizing efficient conversion and real-time acquisition of stress signal to optical signal. The processing module 400 is linked with the demodulator. Based on the wavelength shift of each grating and the correspondence between stress-strain-wavelength, combined with the structural design parameters of the sensor, it directly calculates the normal strain and bidirectional shear strain information at the location of each sensor. It does not rely on complex theoretical models and assumptions, effectively eliminates cross interference, and finally outputs distributed multi-directional stress data, thereby enabling the monitoring of stress in the glass frame and significantly improving the reliability of glass frame stress monitoring.

[0084] In some embodiments, when the bidirectional strain sensor includes a second wavy strip 4, two adjacent bidirectional strain sensors on the fiber optic sensing string 100 are connected to the first wavy fiber 30 by a first transmission fiber and to the second wavy fiber by a second transmission fiber.

[0085] It is understandable that the first transmission fiber serves as the dedicated transmission channel for the first wavy fiber 30, specifically carrying the reflected light signals of the horizontal normal stress grating 301 and the first shear stress grating 302 in each sensor. The second transmission fiber serves as the dedicated transmission channel for the second wavy fiber, specifically carrying the reflected light signals of the second shear stress grating 401 in each sensor. This effectively avoids crosstalk that may occur when signals of different measurement dimensions are transmitted in a single transmission fiber, ensuring that the reflection center wavelength offset of each grating can be accurately identified by the fiber optic grating demodulator 300.

[0086] Meanwhile, this dual-path connection method, combined with the series layout of multiple bidirectional strain sensors, enables the fiber optic sensing string 100 to form a monitoring system of "dual independent sensing channels + distributed measuring points". The demodulator can simultaneously receive all the grating reflected light signals transmitted from the two transmission optical fibers. By distinguishing the signal sources corresponding to the first and second transmission channels, it accurately matches the corresponding grating of each sensor. The processing module 400 then calculates the Z-direction normal strain, X-direction shear strain and Y-direction shear strain of each measuring point based on the wavelength offset of each channel and the structural parameters of the sensor. Finally, it realizes the synchronous monitoring of three-dimensional stress distributed throughout the entire interior of the windshield frame.

[0087] Those skilled in the art will understand that the features described in the various embodiments of this application can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this application. In particular, the features described in the various embodiments of this application can be combined and / or combined in various ways without departing from the spirit and teachings of this application. All such combinations and / or combinations fall within the scope of this application. Therefore, the scope of this application should not be limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A bidirectional strain sensor, characterized in that, include: Encapsulation layer, substrate layer, first wavy strip, and second wavy strip; The first wavy strip is located between the encapsulation layer and the substrate layer. The first wavy strip is embedded with a first wavy optical fiber. The center band of the first wavy optical fiber is provided with a normal stress grating and two first shear stress gratings. The normal stress grating is horizontal, and the two first shear stress gratings are symmetrically arranged and tilted. The first wavy optical fiber has a symmetrical structure, and the normal stress grating is located at the midpoint of the symmetry of the first wavy optical fiber; the horizontal distances between the two first shear stress gratings and the normal stress grating are L / 4 respectively, and the central band of the first wavy optical fiber is the band with the highest height and the longest horizontal length; where L is the horizontal distance from the peak to the trough of the central band. The first wavy strip includes an upper polymer layer, a lower polymer layer, and a first wavy optical fiber; the upper polymer layer is bonded to the encapsulation layer, the lower polymer layer is bonded to the substrate layer, and the first wavy optical fiber is located between the upper polymer layer and the lower polymer layer; The second wavy strip is embedded with a second wavy optical fiber, which is intersected with the first wavy optical fiber. Two second shear stress gratings are symmetrically arranged on the center band of the second wavy optical fiber, and the two second shear stress gratings are tilted.

2. The bidirectional strain sensor as described in claim 1, characterized in that, The second wavy optical fiber is arranged perpendicularly to the first wavy optical fiber.

3. A multi-directional stress measuring device for the interior of a glass frame, characterized in that, The multi-directional stress measurement device inside the glass frame includes: an optical fiber sensing string, a transmission optical fiber, a fiber optic demodulator, and a processing module. The fiber optic sensing string is located inside the edge of the windshield and includes a plurality of bidirectional strain sensors as described in any one of claims 1 to 2, wherein the plurality of bidirectional strain sensors on the fiber optic sensing string are connected in series. The fiber optic sensing string is connected to the fiber optic demodulator via the transmission fiber; The fiber optic grating demodulator is used to transmit scanning light into the transmission fiber and simultaneously receive reflected light signals from the transmission fiber, and to determine the wavelength offset of the reflection center of each grating in each of the bidirectional strain sensors based on the reflected light signals. The processing module is connected to the fiber optic grating demodulator and is used to determine the strain information of each bidirectional strain sensor based on the wavelength offset of the reflection center of each grating in each bidirectional strain sensor.

4. The multi-directional stress measuring device inside the glass frame as described in claim 3, characterized in that, In the case where the bidirectional strain sensor includes a second wavy strip, two adjacent bidirectional strain sensors on the optical fiber sensing string are connected to the first wavy fiber by a first transmission optical fiber, and connected to the second wavy fiber by a second transmission optical fiber.

5. The multi-directional stress measuring device inside the glass frame as described in claim 3, characterized in that, One of the aforementioned fiber optic sensing strings is disposed on two adjacent sides of a windshield.

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