Analog modeling method and delamination stress calculation method for eye-shaped structure of optical fiber implanted carbon fiber composite material

Abstract

The invention discloses an analogy modeling method and a delamination stress calculation method for an eye-shaped structure formed when an optical fiber is implanted into a carbon fiber composite material, and the method comprises the steps: obtaining the eye-shaped structure formed when the optical fiber is implanted into the carbon fiber composite material through a microscopic observation technology, and extracting the length-diameter ratio of the eye length to the diameter of the implanted optical fiber in the eye-shaped structure through a computer vision technology; constructing an optical fiber-carbon fiber composite material eye-shaped structure analogy finite element model by utilizing the determined length-diameter ratio, and converting the actual process of implanting the optical fiber into the carbon fiber into a numerical model; normal stress and shear stress are calculated through a finite element simulation analysis method, and prediction of delamination of a structure with a certain length-diameter ratio is completed by using a fracture criterion in fracture mechanics; according to the method, the influence of the optical fiber packaging size, the winding pre-tightening force and the interface resin enrichment structure on stress distribution is comprehensively considered, the influence of optical fiber implantation on the structural performance of the carbon fiber composite material can be quantitatively evaluated, and the structural integration reliability and the design efficiency when the intelligent carbon fiber material is embedded into the optical fiber sensor are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of composite material structural health monitoring, and in particular to an analog modeling method and a delamination stress calculation method for an eye-like structure of fiber-optic implanted carbon fiber composite material. Background Technology

[0002] Fiber Bragg grating sensors have been widely used for strain monitoring and health assessment of composite material structures due to their small size, strong anti-interference ability, and ability to perform distributed measurements. However, when optical fibers are implanted into the interior of composite materials as foreign objects, they can significantly alter the local microstructure of carbon fiber composites, forming typical "eye-like" resin-rich regions, which in turn leads to degradation of mechanical properties, especially a decrease in interlaminar bond strength.

[0003] Existing research has shown that this eye-like structure is a mechanically weak point, prone to delamination or shear failure. However, a quantitative correlation model between its morphological parameters and failure stress is currently lacking. Therefore, establishing a method to predict local failure stresses in this type of structure to support sensor placement design and composite structure reliability assessment is a problem that needs to be solved at this stage. To address these issues, a solution is proposed below. Summary of the Invention

[0004] The purpose of this invention is to provide an analog modeling method for the eye-like structure of fiber-optic implanted carbon fiber composite materials and a method for calculating delamination stress. This method integrates computer vision recognition technology and finite element analysis technology, and achieves accurate prediction of interlaminar separation and shear failure by mapping the actual microstructure into an analytical numerical simulation model.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A method for analogous modeling of an eye-like structure implanted in carbon fiber composite material and a method for calculating delamination stress, comprising the following steps: S1: The eye-like structure formed by fiber optic implantation into carbon fiber composite material was obtained through microscopic observation; S2: Extract the length L of the eye-like structure and the diameter D of the encapsulated optical fiber using computer vision technology, and define the aspect ratio δ=L / D; S3: Combine experimental data to statistically analyze the influence of fiber diameter and winding tension on the eye structure, and form a database of fiber-optic embedded carbon fiber composite materials; S4: Construct a three-dimensional finite element simulation model of fiber-carbon fiber composite material-resin based on structural parameters extracted from the fiber-optic embedded carbon fiber composite material database; S5: For products requiring delamination risk prediction, extract the diameter, winding tension, and material parameters of the implanted optical fiber, and import them into a pre-established database of fiber-embedded carbon fiber composite materials. The database matches the closest sets of data parameters, and then performs mathematical interpolation on these parameters to obtain the model scaling factor between the product to be predicted and the database products. Using a computer image scaling algorithm, the three-dimensional finite element model corresponding to the best-matching parameters is scaled to the previously obtained model scaling factor, thus obtaining the three-dimensional structural model of the fiber-embedded fiber of the product for which delamination risk needs to be predicted.

[0006] S6: Apply loads to the three-dimensional finite element model according to the application scenario, including force loads, pressure loads, temperature loads, and fatigue loads. Simulate the maximum interlaminar normal stress P1 and shear stress P2 of the bonding surface using the finite element method. S7: Based on fracture mechanics theory, the maximum interlaminar normal stress P1 and shear stress P2 are compared with the allowable values ​​of the material to determine whether interlaminar delamination or shear failure has occurred.

[0007] Preferably, in step S3, under the same preload, based on the aspect ratio δ and the known fiber diameter D, the length of the eye structure corresponding to all different fiber diameters is obtained, and a database is established.

[0008] Preferably, under the same preload, the eye-shaped structure with any fiber diameter implanted in carbon fiber composite material has the same aspect ratio. Using a computer image scaling algorithm, the model is scaled according to the aspect ratio to obtain the eye-shaped structure model with other fiber diameters implanted in carbon fiber composite material.

[0009] As a preferred option, based on the Gaussian function f(x) = Establish a model of the eye structure; Image processing was performed on cross-sectional micrographs of optical fibers implanted in carbon fiber composite materials. A coordinate system was established with the center of the optical fiber in the image as the origin. Five feature points were extracted, namely the left and right end points of the eye structure, the curve peak, and the two inflection points on the left and right sides of the peak. Gaussian curve sampling was performed, and the Gaussian function was linearized using the logarithmic method. Finally, the optimal Gaussian function curve was obtained by using the polynomial regression fitting method, thereby obtaining the contour curve of the eye structure.

[0010] The curve above is f1(x) = , The lower curve is f2(x) = - , Where c is the standard deviation of the fitted curve, which can also be used to evaluate the width of the eye-shaped contour. The upper and lower curves form the outer contour of the eye-shaped structure. The curve is compared with the observed actual contour. If the comparison is correct, it is used for subsequent modeling.

[0011] Preferably, in step S6, the method of whether the maximum normal stress and the maximum shear stress of the adhesive surface exceed the vertical tensile strength and shear strength is used to predict the factors affecting the risk of delamination, thereby determining whether the composite material will delaminate.

[0012] As a preferred approach, the extracted structural parameters are used to construct a three-dimensional finite element simulation model of the fiber-carbon fiber composite material-resin. The steps include using the curve f1(x) on the eye-like structure = The lower curve f2(x) = - Create a two-dimensional graphic. A three-dimensional composite material layup model is established in simulation software, with N layers in the X direction, each layer having a thickness of t. The carbon fiber composite material has a length of L0 and a width of W0, and the optical fiber has a diameter of D and a length of L. f Embedded eye-like structure geometry fitted based on aspect ratio δ; Set the elastic modulus and Poisson's ratio to match the material parameters; define the contact type between carbon fiber, resin, and optical fiber; design the axial load as F, and apply n different loading conditions F1, F2...F1. n Static analysis was performed; a temperature load condition T was added, and a finite element model was established for analysis.

[0013] Preferably, the criterion for delamination of the adhesive surface is: When P1≥σ z临界 Or P2≥τ xy临界 When this occurs, it is determined that interlaminar separation or shear failure has occurred; The σ z临界 and τ xy临界 These represent the tensile strength and shear strength in the vertical direction of the cured resin material, respectively.

[0014] Preferably, the method is applicable to the health monitoring design, embedded fiber optic layout, and structural reliability assessment of wet-formed carbon fiber wound composite containers.

[0015] The beneficial effects of this invention are as follows: This method comprehensively considers the influence of optical fiber packaging size, winding preload and interface resin enrichment structure on stress distribution, and can quantitatively evaluate the impact of optical fiber implantation on the structural performance of carbon fiber composite materials, effectively improving the structural integration reliability and design efficiency when smart carbon fiber materials are embedded in optical fiber sensors. Attached Figure Description

[0016] Figure 1 These are comparative photographs of the eye-shaped structure under different package diameters under standard preload, as shown in the examples. Figure 2 This is a finite element modeling assembly drawing for an example. Figure 3The graph shows the relationship between the maximum interlayer stress and the tensile stress in the example. Detailed Implementation

[0017] The following description is merely a preferred embodiment of the present invention, and the scope of protection is not limited to this embodiment. All technical solutions falling within the scope of the present invention should be protected by the present invention. Identical components are indicated by the same reference numerals.

[0018] like Figures 1 to 3 As shown, an analogy modeling method and delamination stress calculation method for an eye-like structure of fiber-optic implanted carbon fiber composite material include the following steps: Step 1: Database Construction Database Construction: Metal capillary-encapsulated optical fibers with encapsulation diameters of 0.3mm, 0.4mm, 0.5mm, and 0.6mm were selected and vertically embedded into T700 carbon fiber layers pre-impregnated with GXC120 resin during wet layup. A standard pre-tension force of 15N was applied to obtain typical eye-like structure images. The measured eye-like structure length L was extracted using computer vision technology, and the corresponding aspect ratio δ=L / D was calculated. δ1, δ2, δ3, and δ4 were 24.6, 25.53, 24.74, and 24.18, respectively, showing relatively uniform variation. The average aspect ratio was taken as 24.5. Based on this aspect ratio, the eye-like structure lengths corresponding to all different fiber diameters under standard tension can be extrapolated to establish a database of aspect ratios for different diameters under standard tension.

[0019] Step 2: Model Selection and Import of Composite Materials under Loading Environment To determine whether the GXC120 resin-T700 carbon fiber composite layer with embedded optical fiber will delaminate in a uniform loading environment ranging from 100MPa to 1000MPa, a metal capillary-encapsulated optical fiber with an encapsulation diameter of 0.3mm was selected and vertically implanted into the pre-impregnated carbon fiber layer during the wet layup process. With a standard preload of 15N, and based on an aspect ratio of 24.5 and an encapsulation diameter of 0.3mm, the corresponding Gaussian-fitted eye structure model was exported from the database.

[0020] Step 3: Finite element modeling and tensile force loading Based on the two-dimensional graphic of the eye structure, a three-dimensional finite element model was created using finite element simulation software, with the following parameters set: Carbon fiber composite layer: material orientation 90°, layer thickness 0.2mm, one layer above and one layer below the optical fiber; total dimensions are 20mm long and 2mm wide; import the corresponding material parameters; Fiber optic model: Solid model, encapsulation diameter 0.25mm, embedding length 2mm; import corresponding material parameters; The morphology of the eye-like structure in the resin-rich region was modeled based on optical image sampling results: the shape was based on a Gaussian fitting curve; the corresponding material parameters were imported; and the modeling was performed sequentially. Delamination failure of carbon fiber resin composites mainly occurs in the destruction of the resin matrix. The tensile strength of GXC120 resin is 80 MPa and the shear strength is 5 MPa. Contact conditions: The carbon fiber layer is fully bonded to the optical fiber and resin; Boundary conditions: Apply tensile stress increasing from 100MPa to 1000MPa at one end, in the direction of the fiber axis, i.e., the positive direction of the Y-axis; fix the other end or apply equal opposing tensile stress to simulate force balance; activate the large deformation and weak spring stability control module.

[0021] Step 4: Analysis of Stress Results on Adhesive Surface After the model is solved, the normal stress of the adhesive surface, i.e. the Z-axis direction, has the maximum value near the resin separation endpoint and gradually weakens outward; the shear stress, i.e. the XY plane direction, is symmetrically distributed on both sides of the eye-shaped structure, with equal magnitude and opposite direction; the maximum stress value is statistically analyzed and data under different loading conditions are recorded.

[0022] Step 5: Application of Criteria and Failure Prediction GXC120 resin critical normal tensile strength σ z临界 =80MPa, shear strength τ xy临界 =5MPa, from Figure 3 As can be seen from the data, during the entire loading process, the interlaminar tensile stress was less than 80 MPa and the shear stress was less than 5 MPa, neither of which exceeded the limit value.

[0023] Step 6, Conclusion: Under this parameter configuration, the implantation of optical fiber into the T700 carbon fiber layer of GXC120 resin will not cause delamination or shear failure, and has a safety margin.

[0024] The specific embodiments described above further illustrate the technical problems, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for analogous modeling of an eye-like structure implanted in a fiber optic carbon fiber composite material and a method for calculating delamination stress, characterized in that, Includes the following steps, S1: The eye-like structure formed by fiber optic implantation into carbon fiber composite material was obtained through microscopic observation; S2: Extract the length L of the eye-like structure and the diameter D of the encapsulated optical fiber using computer vision technology, and define the aspect ratio δ=L / D; S3: Combine experimental data to statistically analyze the influence of fiber diameter and winding tension on the eye structure, and form a database of fiber-optic embedded carbon fiber composite materials; S4: Construct a three-dimensional finite element simulation model of fiber-carbon fiber composite material-resin based on structural parameters extracted from the fiber-optic embedded carbon fiber composite material database; S5: For products that need to predict delamination risk, extract the diameter, winding tension, and material parameters of the implanted optical fiber and import them into a pre-established database of fiber-embedded carbon fiber composite materials. The database matches the closest sets of data parameters, and then performs mathematical interpolation on these parameters to obtain the model scale coefficient between the product to be predicted and the products in the database. Using a computer image scaling algorithm, the three-dimensional finite element model corresponding to the best matching parameters is scaled up to the previously obtained model scale coefficient, thereby obtaining the three-dimensional structural model of the fiber-embedded fiber of the product to be predicted for delamination risk. S6: Apply loads to the three-dimensional finite element model according to the application scenario, including force loads, pressure loads, temperature loads, and fatigue loads. Simulate the maximum interlaminar normal stress P1 and shear stress P2 of the bonding surface using the finite element method. S7: Based on fracture mechanics theory, the maximum interlaminar normal stress P1 and shear stress P2 are compared with the allowable values ​​of the material to determine whether interlaminar delamination or shear failure has occurred.

2. The optical fiber implanted carbon fiber composite eye structure analogous modeling method and delamination stress calculation method according to claim 1, characterized in that, In step S3, under the same preload, based on the aspect ratio δ and the known fiber diameter D, the length of the eye structure corresponding to all different fiber diameters is obtained, and a database is established.

3. The optical fiber-embedded carbon fiber composite eye-like structure analogous modeling method and delamination stress calculation method according to claim 1, characterized in that, Under the same preload, eye-shaped structures with any fiber diameter implanted in carbon fiber composite material have the same aspect ratio. Using a computer image scaling algorithm, the model is scaled according to the aspect ratio to obtain eye-shaped structure models with other fiber diameters implanted in carbon fiber composite material.

4. The optical fiber implanted carbon fiber composite eye structure analogous modeling method and delamination stress calculation method according to claim 1, characterized in that, The contour curve of the eye structure in analog modeling is based on the Gaussian function f(x) = The fitting method is as follows: Image processing is performed on the cross-sectional micrographs after the optical fiber is implanted into the carbon fiber composite material. A coordinate system is established with the center of the optical fiber in the image as the origin. Five feature points are extracted, namely the left and right end points of the eye structure, the curve peak, and the two inflection points on the left and right sides of the peak. Gaussian curve sampling is performed, and the Gaussian function is linearized using the logarithmic method. Finally, the optimal Gaussian function curve is obtained by using the polynomial regression fitting method, thereby obtaining the contour curve of the eye structure. The curve above is f1(x) = , The lower curve is f2(x) = - , Where c is the standard deviation of the fitted curve. The upper and lower curves form the outer contour of the eye-like structure. The curves are compared with the observed actual contours. If the comparison is correct, the curves are used for subsequent modeling.

5. The optical fiber implanted carbon fiber composite eye structure analogous modeling method and delamination stress calculation method according to claim 1, characterized in that, In step S6, the method of whether the maximum normal stress and maximum shear stress of the adhesive surface exceed the vertical tensile strength and shear strength is used to predict the influencing factors of delamination risk, thereby determining whether delamination of the composite material will occur.

6. The optical fiber-embedded carbon fiber composite eye-like structure analogous modeling method and delamination stress calculation method according to claim 1, characterized in that, The extracted structural parameters are used to construct a three-dimensional finite element simulation model of fiber-carbon fiber composite material-resin. The steps include using the curve f1(x) on the eye-shaped structure as an example. The lower curve f2(x) = - A two-dimensional graphic is created, and a three-dimensional composite material layup model is built in simulation software. This model has N layers in the X direction, each with a thickness of t. The carbon fiber composite material has a length of L0 and a width of W0, and the optical fiber has a diameter of D and a length of L. f Embedded eye-like structure geometry fitted based on aspect ratio δ; Set the elastic modulus and Poisson's ratio to match the material parameters; define the contact type between carbon fiber, resin, and optical fiber; design the axial load as F, and apply n different loading conditions F1, F2...F1. n Perform static analysis; Add a temperature load condition T and establish a finite element model for analysis.

7. The optical fiber implanted carbon fiber composite eye-like structure analogous modeling method and delamination stress calculation method according to claim 1, characterized in that, The criterion for delamination of the adhesive surface is: When P1≥σ z临界 Or P2≥τ xy临界 When this occurs, it is determined that interlaminar separation or shear failure has occurred; The σ z临界 and τ xy临界 These represent the tensile strength and shear strength in the vertical direction of the cured resin material, respectively.

8. The optical fiber implanted carbon fiber composite eye structure analogous modeling method and delamination stress calculation method according to any one of claims 1-7, characterized in that, The method is applicable to the health monitoring design, embedded fiber optic layout, and structural reliability assessment of wet-formed carbon fiber wound composite containers.

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