Bidirectional strain sensor and glass frame internal multidirectional stress measuring device

Abstract

The invention provides a bidirectional strain sensor and a glass frame internal multidirectional stress measurement device, and relates to the technical field of stress measurement, and the bidirectional strain sensor comprises a packaging layer, a substrate layer, and a first wave-shaped belt. The first wave-shaped belt is located between the packaging layer and the substrate layer, a first wave-shaped optical fiber is embedded in the first wave-shaped belt, a normal stress grating and two first shear stress gratings are arranged on a central wave band on the first wave-shaped optical fiber, the normal stress grating is in a horizontal state, and the two first shear stress gratings are symmetrically arranged and are in an inclined state. The normal stress perpendicular to the glass plane and the shear stress parallel to the glass plane can be sensed through the bidirectional strain sensor, so that related stress data can be obtained based on sensing signals of the sensor.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of stress measurement, in particular to a bidirectional strain sensor and a multi-directional stress measurement device for the inside of a glass frame. BACKGROUND

[0002] As a key component of flight safety, the windshield glass must have sufficient structural strength and service life. However, during actual assembly and service, cracks often occur in the edge area of the windshield glass, which becomes an important hidden danger threatening flight safety. The windshield glass has obvious stress concentration in the frame area. During assembly, residual stress and assembly stress are important reasons for cracks in the frame area, and during flight, the windshield glass is also easily affected by internal pressurization and external aerodynamic load.

[0003] At present, the stress measurement of the windshield glass of an airplane mostly adopts the photoelastic experiment method, and the existing photoelastic experiment method is mostly static or offline measurement, which cannot realize real-time online monitoring of the dynamic change of the stress of the helicopter during assembly and service. SUMMARY

[0004] Therefore, the application provides a bidirectional strain sensor and a multi-directional stress measurement device for the inside of a glass frame.

[0005] In a first aspect, the application provides a bidirectional strain sensor, comprising: a packaging layer, a substrate layer and a first wave-shaped strip. The first wave-shaped strip is located between the packaging layer and the substrate layer, and a first wave-shaped optical fiber is embedded in the first wave-shaped strip. A central wave band on the first wave-shaped optical fiber is provided with a normal stress grating and two first shear stress gratings. The normal stress grating is in a horizontal state, and the two first shear stress gratings are symmetrically arranged and in an inclined state.

[0006] In an embodiment, the first wave-shaped optical fiber is of a symmetric structure, and the normal stress grating is located at the symmetric midpoint of the first wave-shaped optical fiber.

[0007] In an embodiment, the horizontal distance between the two first shear stress gratings and the normal stress grating is L / 4, wherein L is the horizontal distance from the wave peak to the wave trough of the central wave band.

[0008] In an embodiment, the central wave band of the first wave-shaped optical fiber is the wave band with the highest height and the longest horizontal length.

[0009] In an embodiment, the first wave-shaped strip comprises an upper polymer layer, a lower polymer layer and the first wave-shaped optical fiber. The upper polymer layer is attached to the encapsulation layer, the lower polymer layer is attached to the substrate layer, and the first wave-shaped optical fiber is located between the upper polymer layer and the lower polymer layer.

[0010] In an embodiment, the bidirectional strain sensor further comprises: a second wave-shaped belt; The second wave-shaped belt is embedded with a second wave-shaped optical fiber, the second wave-shaped optical fiber is arranged in a cross manner with the first wave-shaped optical fiber, and two second shear stress gratings are symmetrically arranged on a central wave band of the second wave-shaped optical fiber, and the two second shear stress gratings are in an inclined state.

[0011] In an embodiment, the second wave-shaped optical fiber is arranged in a perpendicular manner with the first wave-shaped optical fiber.

[0012] In a second aspect, the application further provides a glass frame internal multi-directional stress measurement device, comprising: a fiber sensing string, a transmission optical fiber, a fiber grating demodulator, and a processing module. The fiber sensing string is located inside the edge of the windshield, and comprises a plurality of bidirectional strain sensors according to any one of claims 1 to 7, and the plurality of bidirectional strain sensors on the fiber sensing string are connected in series. The fiber sensing string is connected to the fiber grating demodulator through the transmission optical fiber. The fiber grating demodulator is used to emit scanning light to the transmission optical fiber, and synchronously receive reflected light signals from the transmission optical fiber, and determine the wavelength shift of each grating reflection center in each bidirectional strain sensor according to the reflected light signals. The processing module is connected to the fiber grating demodulator, and is used to determine the strain information of the position of each bidirectional strain sensor according to the wavelength shift of each grating reflection center in each bidirectional strain sensor.

[0013] In an embodiment, when the bidirectional strain sensor comprises a second wave-shaped belt, a first transmission optical fiber is used to connect the first wave-shaped optical fiber and a second transmission optical fiber is used to connect the second wave-shaped optical fiber between two adjacent bidirectional strain sensors on the fiber sensing string.

[0014] In an embodiment, one fiber sensing string is arranged in two adjacent frames of a windshield.

[0015] The bidirectional strain sensor of the application has the following beneficial effects relative to the related art: 1. The bidirectional strain sensor of the application comprises: a packaging layer, a substrate layer and a first wave-shaped band, by sandwiching the first wave-shaped band with the first wave-shaped optical fiber between the packaging layer and the substrate layer, using the cooperative constraint of the packaging layer and the substrate layer and the flexible adaptation characteristics of the wave-shaped structure, the core advantages of small volume and flexibility are given to the sensor, which can accurately adapt to the narrow space inside the windshield frame, can be directly embedded and distributed in the adhesion between the frame and the glass edge, so that the sensor and the glass or windshield frame form a stable structural whole, fundamentally avoiding the problem of measurement accuracy decline caused by space limitation and complex path of external measurement means.

[0016] 2. By setting the normal stress grating in the horizontal state and the two first shear stress gratings arranged symmetrically and obliquely in the center wave band of the first wave-shaped optical fiber, different gratings are given specific stress sensitive directions by the differential design of the grating orientation, when complex stress acts on the sensor, the sensor can sense the normal stress perpendicular to the glass plane and the shear stress parallel to the glass plane, and then the related stress data can be obtained based on the signal of the sensor, so that the real-time online monitoring of the dynamic change of stress in the whole process of helicopter windshield assembly and service can be realized, and the technical short board of static or offline measurement of the existing photoelastic experiment method is effectively made up. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the application or the related art, the drawings needed to be used in the embodiment or related art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creating laborious work.

[0018] Figure 1 It is a structural schematic diagram of the bidirectional strain sensor in an embodiment of the application. Figure 2 It is a structural schematic diagram of the first wave-shaped band in an embodiment of the application. Figure 3 It is a coordinate schematic diagram of the normal stress grating and the first shear stress grating in an embodiment of the application. Figure 4 It is a cross structure schematic diagram of the first wave-shaped band and the second wave-shaped band in an embodiment of the application. Figure 5 It is a structural schematic diagram of the multidirectional stress measurement device inside the glass frame in an embodiment of the application. Figure 6 It is an application environment schematic diagram of the bidirectional strain sensor in an embodiment of the application.

[0019] Explanation of reference signs: 1 - cladding layer, 2 - substrate layer, 3 - first corrugated strip, 30 - first corrugated fiber, 301 - normal stress grating, 302 - first shear stress grating, 31 - upper polymer layer, 32 - lower polymer layer, 4 - second corrugated strip, 401 - second shear stress grating, 100 - fiber sensing string, 200 - transmission fiber, 300 - fiber grating demodulator, 400 - processing module. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0021] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0022] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise explicitly specified and limited.

[0023] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection", "fixing" and the like should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0024] In some embodiments, as Figure 1 and Figure 2As shown, the bidirectional strain sensor provided by the application comprises a packaging layer 1, a substrate layer 2 and a first wavy band 3.

[0025] The first wavy band 3 is located between the packaging layer 1 and the substrate layer 2, and a first wavy optical fiber 30 is embedded in the first wavy band 3. A central wave segment on 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 packaging layer 1 and the substrate layer 2 can be soft elastomers (modulus kPa level) and are used as protective structures, so that the bidirectional strain sensor can be installed between the outer glass and the middle glass of the windshield glass. The first wavy band 3 can be made of a rigid high-elastic modulus polymer except for the first wavy optical fiber 30, so as to protect and support the first wavy optical fiber 30. The packaging layer 1 and the substrate layer 2 form a clamping structure to stably constrain the first wavy band 3 therebetween, which not only provides protection and fixation for the embedded first wavy optical fiber 30, but also does not affect the flexible deformation characteristics of the wavy structure, and ensures that the optical fiber can respond synchronously with the stress deformation of the frame of the windshield glass.

[0027] It can be understood that, from the perspective of mechanical deformation, shear stress will cause the wavy optical fiber to produce “tangential bending deformation”, but this deformation has “strain offset” at the midpoint. Therefore, the normal stress grating 301 in the horizontal state is arranged on the central wave segment of the first wavy optical fiber 30, so as to avoid the bending caused by shear force, and make the normal stress grating 301 mainly measure the bending deformation and film deformation caused by the normal stress at the position. Since the grating axis is perpendicular to the vertical direction of the glass plane (i.e., the expected normal stress direction), the normal stress caused by extrusion or stretching perpendicular to the glass plane can be measured. The first shear stress grating 302 is arranged on the first wavy band 3 at a certain inclined angle, and the grating axis is sensitive to the shear direction parallel to the glass plane, so that the shear stress caused by interlayer dislocation can be measured. The symmetric arrangement of the first shear stress grating 302 provides a mechanical compensation basis for subsequent data processing, which can reduce the interference of stress in other directions except the shear direction through symmetric arrangement, and finally accurately extract the pure stress data in the shear direction, so as to realize independent and accurate measurement of the normal stress and the shear stress.

[0028] The bidirectional strain sensor comprises a packaging layer 1, a substrate layer 2 and a first wave-shaped strip 3, the first wave-shaped strip 3 in which the first wave-shaped optical fiber 30 is embedded is clamped between the packaging layer 1 and the substrate layer 2, the small volume and flexible core advantages of the sensor are given by the cooperative constraint of the packaging layer 1 and the substrate layer 2 and the flexible adaptation characteristics of the wave-shaped structure, which can accurately adapt to the narrow space inside the windshield glass frame, can be directly embedded and distributed in the adhesion between the frame and the glass edge, and the sensor and the glass or the windshield glass frame form a stable structure as a whole, which fundamentally avoids the problem of measurement accuracy reduction caused by space limitation and complex path of external measurement means. At the same time, by setting the normal stress grating 301 in the horizontal state and the two first shear stress gratings 302 arranged in a symmetrical and inclined manner in the central wave band of the first wave-shaped optical fiber 30, the different gratings are given specific stress sensitive directions by the differential design of the grating orientation, when the complex stress acts on the sensor, the sensor can sense the normal stress perpendicular to the glass plane and the shear stress parallel to the glass plane, and then the related stress data can be obtained based on the sensing signal of the sensor, so that the real-time online monitoring of the stress dynamic change in the whole process of helicopter windshield glass assembly and service can be realized, and the technical short board of the existing photoelastic experiment method static or offline measurement is effectively made up.

[0029] In some embodiments, as shown in Figure 2 The first wave-shaped optical fiber 30 is a symmetrical structure, and the normal stress grating 301 is located at the symmetry midpoint of the first wave-shaped optical fiber 30.

[0030] It can be understood that the first wave-shaped optical fiber 30 adopts a symmetrical structure design, and the wave shape is mirror-symmetrically distributed along the central axis. This structural characteristic makes the tangential bending deformation generated on both sides of the optical fiber when the shear stress acts on the sensor form an accurate mirror cancellation effect, that is, the bending deformation on both sides of the symmetry is equal in size and opposite in direction, and finally the shear strain at the symmetry midpoint of the optical fiber is completely cancelled out, effectively avoiding the cross interference of shear deformation on the normal stress measurement. The normal stress grating 301 is specially set at the symmetry midpoint, which fully utilizes the mechanical characteristics of shear strain cancellation at the midpoint, and the normal stress grating 301 itself is in a horizontal state, and its axial direction is sensitive to the normal stress direction perpendicular to the glass plane, so that the grating can completely get rid of the deformation interference caused by shear stress, and focus on capturing the normal strain perpendicular to the glass plane caused by extrusion or stretching, and then accurately convert it into normal stress data, while forming a functional complement with the two first shear stress gratings 302 arranged in a symmetrical and inclined manner, ensuring the independence and accuracy of the normal stress measurement.

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

[0032] It can be understood that, since the first wave-shaped optical fiber 30 is a symmetrical structure, the tangential bending deformation caused by the shear stress gradually changes from the peak to the trough. The symmetrical midpoint (where the normal stress grating 301 is located) has no shear strain because the deformations on both sides cancel each other out. The middle position from the peak to the trough (i.e., L / 4 from the midpoint) is exactly the area where the shear strain is most significant and stable, avoiding the strain cancellation effect at the midpoint and the measurement distortion problem caused by deformation concentration at the peak and trough. At the same time, the two first shear stress gratings 302 are located at the symmetrical positions L / 4 on both sides of the normal stress grating 301, and combined with the design of the sensitive direction of their inclination, they can synchronously capture the shear strain signals on both sides of the symmetry. This not only ensures the sensitivity and stability of the shear stress measurement, but also further eliminates the influence of normal stress and other direction interference signals through the calibration of symmetrical signals in subsequent data processing, forming a precise spatial layout and functional division with the normal stress grating 301, and finally realizing independent and high-precision synchronous measurement of normal stress and shear stress.

[0033] In some embodiments, as shown in FIGS. 1A and 1B, the first wave-shaped optical fiber 30 is a wave-shaped optical fiber with a central wave band. Figure 1 and Figure 2 As shown, the central wave band of the first wave-shaped optical fiber 30 is the wave band with the highest height and the longest horizontal length.

[0034] It can be understood that the central wave band of the first wave-shaped optical fiber 30 is the wave band with the highest height and the longest horizontal length. The highest height means that the wave amplitude of this wave band is the largest, so that it can produce more significant and easier-to-catch mechanical deformation when subjected to normal stress or shear stress, improving the perception sensitivity of the grating to weak stress signals. The design of the longest horizontal length provides sufficient space for the reasonable layout of the core grating, which can not only stably accommodate the normal stress grating 301 located at the symmetrical midpoint, but also ensure that the horizontal distance between the two first shear stress gratings 302 and the normal stress grating 301 is accurately controlled at L / 4, perfectly matching the gradual distribution rule of shear strain from the peak to the trough, so that the shear grating is exactly in the area where the shear strain is most significant and stable.

[0035] In addition, as the core measurement area of the optical fiber, the large size design of the central wave band can also reduce the interference of uneven deformation of the edge wave band on the measurement, make the stress transmission in the wave band more uniform and direct, ensure 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 collect the shear strain signals at the symmetric positions, eliminate the interference through subsequent data processing, and finally realize the independent and synchronous measurement of the normal stress and shear stress with high sensitivity and high precision, which lays a key structural foundation for the accurate analysis of complex stress field.

[0036] In some embodiments, as shown in Figure 2 The first wave-shaped band 3 includes an upper polymer layer 31, a lower polymer layer 32, and a first wave-shaped optical fiber 30.

[0037] The upper polymer layer 31 is attached to the packaging layer 1, the lower polymer layer 32 is attached to the substrate layer 2, and the first wave-shaped optical fiber 30 is located between the upper polymer layer 31 and the lower polymer layer 32.

[0038] The materials of the upper polymer layer 31 and the lower polymer layer 32 can be rigid high-elastic modulus polymers (such as polyimide, modulus GPa level). The upper polymer layer 31 serves as a protective layer and can provide mechanical support, and the lower polymer layer 32 can be bonded to the substrate layer 2 to provide interface stability.

[0039] It can be understood that the first wave-shaped band 3 adopts a sandwich composite structure of the upper polymer layer 31, the lower polymer layer 32, and the first wave-shaped optical fiber 30, which can realize the stable integration of the optical fiber and the sensor as a whole, and also ensures the flexibility of the sensor through the flexible characteristics of the polymer material, perfectly adapting to the narrow installation environment inside the windshield glass frame. The upper and lower polymer layers 32 not only can form physical protection for the first wave-shaped optical fiber 30 to avoid its being affected by external factors such as friction and impact during assembly and service, but also can ensure that the stress of the windshield glass frame can be efficiently and distortionlessly transmitted to the grating area on the optical fiber through the synergistic deformation characteristics of the polymer, the optical fiber, the packaging layer 1, and the substrate layer 2. Meanwhile, the clamping action of the two polymer layers can fix the relative spatial layout of the normal stress grating 301 and the two first shear stress gratings 302, avoiding the decrease of measurement accuracy caused by the displacement of the gratings.

[0040] In addition, the light and thin characteristics of the polymer layer will not increase the overall volume of the sensor, and the mechanical adaptability of its elastic modulus to the optical fiber and the glass frame can reduce the energy loss in the stress transmission process, so that the normal stress grating 301 can accurately capture the compression or tensile stress perpendicular to the glass plane, and the two shear stress gratings can stably perceive the shear strain parallel to the glass plane, and finally ensure the independent and high-precision synchronous measurement of the normal stress and shear stress of the sensor.

[0041] In some embodiments, as shown in Figure 4 The bidirectional strain sensor further comprises a second wave-shaped band 4.

[0042] The second wave-shaped band 4 is embedded with a second wave-shaped fiber, which is arranged in cross with the first wave-shaped fiber 30, and two second shear stress gratings 401 are symmetrically arranged on the central wave band of the second wave-shaped fiber, and the two second shear stress gratings 401 are in an inclined state.

[0043] It can be understood that the newly added second wave-shaped band 4 of the bidirectional strain sensor is clamped between the packaging layer 1 and the base layer 2 together with the first wave-shaped band 3, which continues the composite structure design of the upper and lower polymer layers 32 clamping the wave-shaped fiber, which not only guarantees the core characteristics of small overall volume and flexibility of the sensor, which is suitable for the narrow installation environment of the windshield glass frame, but also builds an orthogonal shear stress measurement dimension through the cross layout of the second wave-shaped fiber and the first wave-shaped fiber 30.

[0044] The shear measurement direction of the first wave-shaped fiber 30 and the shear measurement direction of the second wave-shaped fiber are crossed with each other, which can comprehensively cover the shear stress component parallel to the glass plane. At the same time, the two second shear stress gratings 401 symmetrically arranged on the central wave band of the second wave-shaped fiber are in an inclined state, which continues the mechanical design logic of symmetrically canceling out, uses the inclination angle to give the gratings the pertinence sensitivity to the target shear direction, and through the symmetric arrangement, the average value can be obtained in subsequent data processing, which plays the role of mutual calibration and mutual inspection of the effectiveness of the gratings, reduces the interference of normal stress and other non-target direction stress, and accurately extracts the stress data of the corresponding shear direction. The structure design is complementary to the first wave-shaped band 3, and the horizontal normal stress grating 301 on the first wave-shaped fiber 30 focuses on capturing the normal stress perpendicular to the glass plane, and the shear gratings of the first and second wave-shaped fibers accurately measure the shear stress in two orthogonal directions, respectively, and finally realize the comprehensive, independent and high-precision synchronous measurement of three-dimensional stress components, which provides more complete key data support for analyzing the distribution rule of the complex stress field of the windshield glass during assembly and service and tracing the crack initiation mechanism. At the same time, the cross layout and the collaborative design of the double wave-shaped bands strengthen the response sensitivity of the sensor to stress deformation in different directions, ensure that the stress is transmitted without distortion, and further improve the reliability of dynamic real-time monitoring.

[0045] In some embodiments, as shown in Figure 4 The second wave-shaped fiber is arranged perpendicularly to the first wave-shaped fiber 30.

[0046] It can be understood that the first wavy optical fiber 30 corresponds to a shear measurement direction which is 90° perpendicular to the shear measurement direction of the second wavy optical fiber, and can comprehensively cover all shear stress components (i.e., X and Y shear stresses) parallel to the glass plane, completely solving the problem that a single direction shear measurement cannot capture multi-directional shear action in a complex stress field. At the same time, this perpendicular layout forms a perfect functional complement with the first wavy band 3: the horizontal normal stress grating 301 on the first wavy optical fiber 30 focuses on capturing the normal stress (Z direction) perpendicular to the glass plane, and the shear gratings of the first and second wavy optical fibers independently measure the shear stresses (X and Y directions) in two orthogonal directions, respectively, ultimately achieving comprehensive, non-missing, high-precision synchronous measurement of three-dimensional stress components (normal + two-direction orthogonal shear). Moreover, the vertically arranged double wavy bands do not interfere with each other in the stress transmission process, and can both capture weak stress signals through the high-sensitivity deformation response of the wavy structure, ensuring the reliability and data accuracy of dynamic real-time monitoring.

[0047] In some embodiments, as shown in FIG. 1, the present application also provides a glass frame internal multi-directional stress measurement device, which comprises a fiber sensing string 100, a transmission optical fiber 200, a fiber grating demodulator 300 and a processing module 400. Figure 5

[0048] The fiber sensing string 100 is located inside the edge of the windshield glass and comprises a plurality of two-directional strain sensors according to any one of the above solutions. The plurality of two-directional strain sensors on the fiber sensing string 100 are connected in series. It should be noted that the two-directional strain sensors can be used as independent sensing units, and the independent sensing units are connected by optical fibers. Alternatively, a wavy optical fiber (the first wavy optical fiber 30 or the second wavy optical fiber) comprising a plurality of two-directional strain sensors can be formed on one optical fiber, thereby avoiding the need to set a connection interface.

[0049] The fiber sensing string 100 is connected to the fiber grating demodulator 300 through the transmission optical fiber 200.

[0050] The fiber grating demodulator 300 is used to emit scanning light to the transmission optical fiber 200 and synchronously receive reflected light signals from the transmission optical fiber 200, and determine the wavelength shift of each grating reflection center in each two-directional strain sensor according to the reflected light signals.

[0051] The processing module 400 is connected to the fiber grating demodulator 300 and is used to determine the strain information of the position of each two-directional strain sensor according to the wavelength shift of each grating reflection center in each two-directional strain sensor.

[0052] ​Wherein, the fiber grating string can be laid on the windshield surface of the frame loading area according to a predetermined path (for example, the frame and glass bonding place), and the internal structure of the windshield frame embedded with the bidirectional stress sensor can be as shown in Figure 6 One fiber sensing string 100 is arranged on two adjacent frames of a windshield, and for an aircraft windshield assembly structure including a left windshield and a right windshield, the specific laying path can be that four fiber sensing strings 100 are laid on the left and lower sides of the left windshield frame, the upper and right sides of the left windshield frame, the left and upper sides of the right windshield frame, and the lower and right sides of the right windshield frame, so as to realize distributed and multi-point synchronous measurement of the stress field in the entire frame.

[0053] Before the windshield assembly is assembled, the fiber grating string containing a plurality of bidirectional stress sensors (sensing units) can be laid and positioned according to a predetermined path; then the frame is assembled, filled with sealant, and hardened at room temperature to complete the sealing, so that the entire grating string is permanently embedded in the internal structure of the frame to form an integrated intelligent structure. After the fiber sensing string 100 is installed on the edge surface of the windshield, the structure of the glass itself is not changed, the fiber grating string is led out of the frame through the transmission fiber 200, and connected to the external fiber grating demodulator 300. The fiber grating demodulator 300 emits scanning light to the entire fiber grating string through the transmission fiber 200, and 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 shift (Δλ) of each grating reflection center. The processing module 400 finally determines the strain information of the position of each bidirectional strain sensor according to the wavelength shift of each grating reflection center in each bidirectional strain sensor.

[0054] In application, when the windshield is under the action of assembly and flight load, complex stress is generated in the internal frame. The stress is transmitted to the wave-shaped band of each embedded bidirectional stress sensor through the frame structure. The wave-shaped band is slightly bent and deformed, and the normal stress component is mainly captured by the normal stress grating 301, and the shear stress component is mainly captured by the shear stress grating.

[0055] In the fiber grating sensing, the grating wavelength can be converted into stress by the Bragg grating formula, and the related calculation principle is as follows: In application, the wave-shaped band structure is composed of two layers of polymers and optical fibers with different elastic moduli, and the wave-shaped band structure has a pre-strain wherein the maximum wave length of the center is .

[0056] The equivalent axial stiffness calculation formula of the wave-shaped band is as follows:

[0057] where, represents the upper layer modulus, represents the lower layer modulus, represents the thickness of the corrugated tape, represents the width of the corrugated tape.

[0058] The equivalent bending stiffness of the corrugated tape is calculated as follows:

[0059] where, represents the upper layer modulus, represents the lower layer modulus, , , are the top and bottom section moments of inertia about their own centroidal axes, respectively, is the width of the corrugated tape, is the thickness of the corrugated tape, is the cross-sectional area.

[0060] The equivalent elastic modulus of the encapsulation layer and the substrate corresponds to the following formula:

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

[0062] Since the corrugated tape is composed of two layers of polymers with different moduli, the neutral surface position The corresponding calculation formula is as follows:

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

[0064] Based on the above derivation, the normal stress The calculation formula derivation process is as follows: The normal grating output strain at is not sensitive to the tangential stress τ is only the sum of the film strain and the bending strain caused by the normal stress, then The calculation formula of

[0065] Film strain is proportional to the normal stress , then:

[0066] where, is the equivalent elastic modulus of the encapsulation layer and the substrate, a dimensionless correction parameter, reflecting the relative axial stiffness of the corrugated strip structure; another dimensionless correction parameter, mainly used to correct the effect of the finite thickness of the encapsulation layer and the substrate.

[0067] bending strain dependent position , then the bending strain is:

[0068] where, the parameter and Based on the equivalent stiffness:

[0069]

[0070] At , therefore:

[0071] Let

[0072] where, record is the contribution coefficient of the normal pressure at ; record is the contribution coefficient of the normal pressure at , and:

[0073] Therefore, the pressure is:

[0074] Similarly, based on the foregoing derivation, the shear stress τ The calculation formula is as follows: The output strain of the grating strain gauge at is the result of the joint action of the normal stress and the shear stress, and the film strain under the shear force can be ignored, so it is the film strain caused by the normal stress , 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 multi-directional stress measuring device inside the glass frame comprises a fiber sensing string 100, a transmission fiber 200, a fiber grating demodulator 300 and a processing module 400. The fiber sensing string 100 is formed by connecting a plurality of the aforementioned bidirectional strain sensors in series, and the full-coverage monitoring of the stress of the frame is realized by the multi-sensor series layout, solving the problem that single-point measurement cannot reflect the overall stress distribution. The fiber sensing string 100 is connected to the fiber grating demodulator 300 through the transmission fiber 200, the scanning light emitted by the demodulator reaches the grating area of each sensor through the transmission fiber 200, when stress acts on the sensor, the grating reflection center wavelength will shift with the strain, the demodulator synchronously receives the reflected light signal and accurately identifies the wavelength shift of each grating, realizing efficient conversion and real-time collection of stress signals to optical signals; the processing module 400 is linked with the demodulator, based on the wavelength shift of each grating and the corresponding relationship of stress-strain-wavelength, combined with the structural design parameters of the sensor, the normal strain and bidirectional shear strain information of the position of each sensor are directly calculated, without relying on complex theoretical models and assumptions, effectively eliminating cross interference, and finally outputting the full-distributed multi-directional stress data, so as to realize the monitoring of the stress of the glass frame and greatly improve the reliability of the glass frame stress monitoring.

[0084] In some embodiments, in the case where the bidirectional strain sensor comprises a second wave-shaped band 4, the first transmission fiber is used to connect the first wave-shaped fiber 30 and the second transmission fiber is used to connect the second wave-shaped fiber between two adjacent bidirectional strain sensors on the fiber sensing string 100.

[0085] It can be understood that the first transmission fiber serves as a dedicated transmission channel for the first wave-shaped fiber 30 and specially carries the reflected light signals of the horizontal normal stress grating 301 and the first shear stress grating 302 in each sensor, and the second transmission fiber serves as a dedicated transmission channel for the second wave-shaped fiber and specially carries the reflected light signals of the second shear stress grating 401 in each sensor, effectively avoiding the cross-talk that may be generated when signals of different measurement dimensions are transmitted in a single transmission fiber, and ensuring that the reflected center wavelength shift of each grating can be accurately identified by the fiber grating demodulator 300.

[0086] Meanwhile, the combination of the double-path connection mode and the series layout of multiple bidirectional strain sensors makes the fiber sensing string 100 form a monitoring system of “double independent sensing channels + distributed measuring points”, the demodulator can synchronously receive all the grating reflected light signals from the two transmission fibers, and by distinguishing the signal sources corresponding to the first and second transmission channels, the corresponding grating of each sensor is accurately matched, and the processing module 400 calculates the Z-direction normal strain, X-direction shear strain and Y-direction shear strain of each measuring point based on the wavelength shift of each channel and the structural parameters of the sensor, and finally realizes the synchronous monitoring of the full-distributed three-dimensional stress inside the windshield glass frame.

[0087] Those skilled in the art will appreciate that features recited in the various embodiments of the application can be combined and / or integrated in various combinations, even if such combinations have not been recited in the application. In particular, features recited in the various embodiments of the application can be combined and / or integrated in various combinations without departing from the spirit and teachings of the application. All such combinations and / or integrations are within the scope of the application. The scope of the application should therefore not be limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application should be included in the scope of the application.

Claims

1. A bidirectional strain sensor, characterized by, The application relates to a bidirectional strain sensor. The bidirectional strain sensor comprises a packaging layer, a substrate layer and a first wavy band. The first wavy band is arranged between the packaging layer and the substrate layer, and a first wavy optical fiber is arranged in the first wavy band; a normal stress grating and two first shear stress gratings are arranged on a central wave band of the first wavy optical fiber; the normal stress grating is in a horizontal state; and the two first shear stress gratings are symmetrically arranged and in an inclined state.

2. The bidirectional strain sensor of claim 1, wherein, The first wavy optical fiber is of a symmetric structure, and the normal stress grating is located at a symmetric midpoint of the first wavy optical fiber.

3. The bidirectional strain sensor of claim 2, wherein, The horizontal distance between the two first shear stress gratings and the normal stress grating is L / 4, wherein L is the horizontal distance from a wave peak to a wave trough of the central wave band.

4. The bidirectional strain sensor of claim 1, wherein, The central wave band of the first wavy optical fiber is the wave band with the highest height and the longest horizontal length.

5. The bidirectional strain sensor of claim 1, wherein, The first wavy band comprises an upper polymer layer, a lower polymer layer and the first wavy optical fiber. The upper polymer layer is attached to the packaging layer, the lower polymer layer is attached to the substrate layer, and the first wavy optical fiber is located between the upper polymer layer and the lower polymer layer.

6. The bidirectional strain sensor of claim 1, wherein, The bidirectional strain sensor further comprises a second wavy band. The second wavy band is arranged with a second wavy optical fiber, the second wavy optical fiber is arranged in cross with the first wavy optical fiber, and two second shear stress gratings are symmetrically arranged on a central wave band of the second wavy optical fiber, and the two second shear stress gratings are in an inclined state.

7. The bidirectional strain sensor of claim 6, wherein, The second wavy optical fiber is arranged perpendicularly to the first wavy optical fiber.

8. A multi-directional stress measurement apparatus inside a glass border, characterized by, The multi-directional stress measuring device inside the glass frame comprises a fiber sensing string, a transmission optical fiber, a fiber grating demodulator and a processing module. The fiber sensing string is located inside the edge of the windshield glass and comprises a plurality of bidirectional strain sensors according to any one of claims 1 to 7, and the plurality of bidirectional strain sensors on the fiber sensing string are connected in series. The fiber sensing string is connected to the fiber grating demodulator through the transmission optical fiber. The fiber grating demodulator is used for emitting scanning light to the transmission optical fiber and synchronously receiving reflected light signals from the transmission optical fiber, and the wavelength shift of each grating reflection center in each bidirectional strain sensor is determined according to the reflected light signals. The processing module is connected to the fiber grating demodulator and is used for determining the strain information of the position of each bidirectional strain sensor according to the wavelength shift of each grating reflection center in each bidirectional strain sensor.

9. The glass bezel interior multi-directional stress measurement apparatus of claim 8, wherein, In the case that the bidirectional strain sensor comprises a second wavy band, a first transmission optical fiber is used to connect the first wavy optical fiber and a second transmission optical fiber is used to connect the second wavy optical fiber between two adjacent bidirectional strain sensors on the fiber sensing string.

10. The glass bezel interior multi-directional stress measurement apparatus of claim 8, wherein, One fiber sensing string is arranged on two adjacent frames of a windshield glass.

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