Methods for predicting, detecting, and evaluating the microcrack defect response of carbon fiber reinforced composite hydrogen storage cylinders

Abstract

A method for predicting, detecting, and evaluating the response of carbon fiber reinforced composite hydrogen storage cylinders to microcrack defects. This method includes the following steps: (1) establishing a micromechanical model of real microcrack defects; (2) establishing a digital twin model of the cylinder containing microcrack defects to predict the impact of defects on the cylinder's mechanical behavior; (3) using laser shear speckle interferometry to detect the response characteristics of the cylinder under internal pressure loading; and (4) evaluating the impact of microcrack defects on the cylinder's structural performance. Unlike existing defect models, this invention considers both fiber layer bending and interlayer delamination caused during cylinder manufacturing, establishing a micromechanical model of real microcrack defects. This enables the prediction of the structural performance of cylinders containing numerous randomly located and dispersed microcrack defects. Laser shear speckle interferometry is used for efficient and reliable detection of the cylinder. Based on this method, the prediction, detection, and evaluation of the response of composite gas cylinders to microcrack defects can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of structural mechanical analysis and nondestructive testing of fiber-reinforced composite materials, and specifically relates to a method for predicting, detecting and evaluating the microcrack defect response of carbon fiber reinforced composite hydrogen storage cylinders. Background Technology

[0002] With increasing global focus on clean energy and sustainable development, high-pressure gaseous hydrogen, as the most mature hydrogen storage technology currently available, is widely used in fields such as hydrogen fuel cell vehicles. As the required hydrogen storage density increases, the pressure of on-board high-pressure gaseous hydrogen storage has increased from 35 MPa to 70 MPa, thus placing higher demands on the safety and reliability of on-board hydrogen storage cylinders.

[0003] Carbon fiber reinforced composite hydrogen storage cylinders possess advantages such as light weight, high hydrogen storage density, and good fatigue resistance, making them a core technology and development focus for hydrogen fuel cell vehicles. These cylinders undergo an integrated molding process involving impregnation, winding, and curing. Inappropriate curing can lead to significant residual stress, resulting in microcracks. Curved structures and variable thickness sections may also exhibit microcracks under interlaminar stress. Industrial CT inspections of aluminum alloy-lined carbon fiber fully wound cylinders (Type III) from various domestic companies revealed that all cylinders, before entering service, already exhibited numerous randomly located and dispersed microcracks (such as...) in the end caps, transition sections, and cylindrical shell sections of the composite material layer. Figure 1 (As shown). Random microcracks located in the composite material layer are the most prevalent type of manufacturing defect. These defects vary in severity and are spatially unevenly distributed within the composite layer, causing complex local mechanical characteristics and reducing the consistency of the gas cylinder's mechanical properties. Microcracks severely weaken the strength in the thickness direction of the gas cylinder and may even trigger hydrogen permeation, leading to catastrophic structural failure. Due to the wide distribution and small scale of microcracks, traditional modeling methods for finite element analysis (FEM) of gas cylinders containing microcracks generated during the manufacturing process are difficult to implement, resulting in highly complex mesh generation at the defect locations. While CT inspection can obtain the morphology of the defects, it still cannot quantitatively predict, detect, or assess the degradation of the gas cylinder's mechanical properties caused by these defects. Summary of the Invention

[0004] This invention aims to overcome the shortcomings of existing research methods by proposing a method for predicting, detecting, and evaluating the microcrack defect response of carbon fiber reinforced composite hydrogen storage cylinders. To solve the above problems, the solution of this invention is:

[0005] A method for predicting, detecting, and evaluating the microcrack defect response of carbon fiber reinforced composite hydrogen storage cylinders, comprising the following steps:

[0006] Step 1: Establish a micromechanical model of a real microcrack defect;

[0007] Step 2: Establish a digital twin model of the gas cylinder containing microcrack defects and predict the impact of the defects on the mechanical behavior response of the gas cylinder;

[0008] Step 3: Use laser shear speckle interferometry to detect the response characteristics of the gas cylinder under internal pressure loading;

[0009] Step 4: Evaluate the impact of microcrack defects on the structural performance of the gas cylinder.

[0010] Step 1 specifically includes:

[0011] Unlike existing micromechanical models of defects, the micromechanical model of microcrack defects established in this invention comprehensively considers fiber bending and interlayer delamination, and is more consistent with the geometric characteristics of real microcracks in actual production processes (such as...). Figure 2 (As shown).

[0012] (1.1) A representative volume element (RVE) model of microcrack defects coupled with fiber bending and interlayer delamination was established. The representative volume element of the microcrack defect was divided into several narrow bands along the x-direction. The fiber bending in each narrow band has approximately the same out-of-plane deflection angle. t is the interlayer delamination thickness, reflecting the degree of interlayer delamination.

[0013] (1.2.a) First, for interlayer interface peeling, a first-step homogenization is performed along the z-direction using a progressive homogenization method within each narrow band. The equivalent stiffness coefficient is obtained after the progressive homogenization process. The expression:

[0014]

[0015] In the formula, For characteristic functions, <·> Y For the averaging operator, h,i,j,k,l,m,n=1,2,3.

[0016] (1.2.b) The equivalent stiffness coefficient can be obtained. Analytical solution:

[0017]

[0018] (1.2.c) For fiber-reinforced anisotropic materials, the equivalent stiffness matrix obtained by asymptotic homogenization [D] ▲ There are 9 non-zero equivalent stiffness coefficients in it, which can be expressed as:

[0019]

[0020] (1.3.a) For fiber bending, a second homogenization step is performed along the x-direction on the narrow strip after the first homogenization. First, the stiffness matrix [D] of each narrow strip caused by the out-of-plane offset due to fiber bending is calculated according to equation (4). ▲ ] k :

[0021]

[0022] Where k and θ k These represent the narrowband number and its off-plane deflection angle, respectively, where m is the total number of narrowbands. This is the narrowband transformation matrix.

[0023] (1.3.b) The stress is continuous and the deformation is coordinated at the interface where adjacent narrow bands are continuous. The equivalent stiffness matrix of the microcrack defect can be calculated by equation (5) [D]. * ]:

[0024]

[0025] in, and The equivalent stiffness matrix [D] is obtained by asymptotic homogenization along the z-direction in the first step. ▲ The submatrix of ]; and The equivalent stiffness matrix [D] is obtained by homogenizing along the x-direction in the second step. * The submatrix of ].

[0026] Step 2 specifically includes:

[0027] (2.1) Based on the statistical information of microcrack defects in gas cylinders, the equivalent stiffness matrix of different microcrack defects is calculated by the method provided in step 1.

[0028] (2.2) Establish a digital twin model of the gas cylinder containing microcracks, and assign the equivalent stiffness matrix calculated in (2.1) as a material property to the corresponding mesh element (e.g., Figure 3 As shown in the figure, this achieves mechanically equivalent defect modeling, greatly improving modeling efficiency and reducing computational costs.

[0029] (2.3) By applying loads and constraints to the digital twin model containing microcracks and defects established above according to the actual working conditions, the impact of microcracks and defects on the structural performance of the gas cylinder can be predicted.

[0030] Step 3 specifically includes:

[0031] (3.1) Scheme for laser shearing speckle interferometry of gas cylinder (e.g.) Figure 4As shown, the shearing can be achieved by: using a Michelson interference optical path, introducing shearing amount using an optical wedge prism, using a birefringent prism, etc., setting the shearing amount and shearing direction of the laser shearing speckle interference device, and adjusting the laser irradiation on the surface of the gas cylinder being tested.

[0032] (3.2) During the pressurization / depressurization process of the gas cylinder, the test gas cylinder is image acquired and analyzed using a laser shear speckle interferometry device, and the evolution process of shear fringes in the test area on the surface of the gas cylinder is output.

[0033] (3.3) The phase map of the image can be obtained by unwrapping the collected shear fringe pattern. According to the shear amount in different directions, the relationship between the phase difference and the displacement gradient can be obtained, as shown in Equation (6):

[0034]

[0035] in, Let λ be the phase difference, λ be the laser wavelength, and δx / δy be the shearing amount in the corresponding direction. Integrating along the shearing direction yields the out-of-plane displacement of the measured area of ​​the gas cylinder.

[0036] Step 4 specifically includes:

[0037] (4.1) Based on the prediction results of the digital twin model of the gas cylinder with microcrack defects obtained in step 2 above, compare it with the finite element model of the ideal gas cylinder without defects to obtain the first assessment of the performance degradation of the real gas cylinder.

[0038] (4.2) Under the given testing conditions, including laser wavelength, amplification factor, shear amount, shear direction, and pressure level / pressure difference, the stripe pattern of the gas cylinder under test is obtained. Combined with the periodic inspection requirements of the gas cylinder, the test is carried out again under the same testing conditions. By directly comparing the stripe levels of the two tests, the degree of performance degradation of the gas cylinder during its service life can be determined according to Equation (7).

[0039]

[0040] Where n is the stripe level.

[0041] The beneficial effects of this invention are:

[0042] Compared with existing defect models, the micromechanical model of microcrack defects established in this invention considers both fiber layer bending and interlayer delamination caused during gas cylinder manufacturing, establishing a realistic micromechanical model of microcrack defects. This reduces the complexity of modeling fiber-reinforced laminated structures, simplifies model mesh generation, and significantly improves the efficiency of finite element analysis of gas cylinders, enabling the prediction of the structural performance of gas cylinders containing numerous randomly located and dispersed microcrack defects. The defect feature regions detected by laser shear speckle interferometry show a high degree of consistency with the detection results of industrial CT in terms of location and size (e.g., Figure 5 As shown), efficient and reliable inspection of gas cylinders can be achieved. Furthermore, by comparing the finite element analysis results of a digital twin model of a gas cylinder containing microcracks with the inspection results (as shown...),... Figure 6 As shown in the figure, the effectiveness of the method of the present invention is demonstrated. Based on this method, the prediction, detection and evaluation of microcrack defect response of composite gas cylinders can be realized. Attached Figure Description

[0043] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate the invention and are used to explain it, but do not constitute an undue limitation of the invention.

[0044] Figure 1 These are CT images of the composite material hydrogen storage cylinder of the present invention;

[0045] Figure 2 This is a schematic diagram of the micromechanical model of microcrack defects of the present invention;

[0046] Figure 3 This is a schematic diagram of a digital twin model of a gas cylinder containing microcrack defects according to the present invention;

[0047] Figure 4 This is a schematic diagram of an embodiment of the laser shearing speckle interferometry scheme for gas cylinders according to the present invention;

[0048] Figure 5 This is a comparison diagram of the laser shearing speckle interferometry results of the gas cylinder and the results of industrial CT scans according to the present invention;

[0049] Figure 6 This is a comparison diagram of the finite element results and the laser shear speckle interferometry results of this invention;

[0050] Figure 7 This is a flowchart illustrating the implementation of the method of the present invention;

[0051] Figure 8 This is a diagram showing the evolution process of shear stripes and the out-of-plane displacement curve of the present invention. Detailed Implementation

[0052] First, it should be noted that this invention belongs to the field of structural mechanical analysis and nondestructive testing of fiber-reinforced composite materials, and specifically relates to a method for predicting, detecting, and evaluating the microcrack defect response of carbon fiber reinforced composite hydrogen storage cylinders. The applicant believes that, after carefully reading the application documents and accurately understanding the implementation principle and purpose of this invention, and in conjunction with existing known technologies, those skilled in the art can fully utilize the method proposed in this invention. All references in this application document fall within this scope, and the applicant will not list them all further.

[0053] The effects of this invention will be illustrated below with reference to the accompanying drawings and specific implementation examples based on the method described herein. Figure 7 The diagram shows the implementation flowchart of a method for predicting, detecting, and evaluating microcrack defects in carbon fiber reinforced composite hydrogen storage cylinders proposed in this invention.

[0054] A method for predicting, detecting, and evaluating the microcrack defect response of carbon fiber reinforced composite hydrogen storage cylinders includes the following steps:

[0055] Step 1: Establish a micromechanical model of a real microcrack defect;

[0056] (1.1) As Figure 2 The model established is a Representative Volumetric Element (RVE) model of microcrack defects coupled with fiber bending and interlayer delamination. The representative volumetric element of the microcrack defect is divided into several narrow bands along the x-direction. The fiber bending in each narrow band has approximately the same out-of-plane deflection angle, and t is the interlayer delamination thickness, reflecting the degree of interlayer delamination.

[0057] (1.2.a) First, for interlayer interface peeling, a first-step homogenization is performed along the z-direction using a progressive homogenization method within each narrow band. The equivalent stiffness coefficient D is obtained after the progressive homogenization process. ij ▲ kl The expression:

[0058]

[0059] In the formula, For characteristic functions, <·> Y For the averaging operator, h,i,j,k,l,m,n=1,2,3.

[0060] (1.2.b) The equivalent stiffness coefficient can be obtained. Analytical solution:

[0061]

[0062] (1.2.c) For fiber-reinforced anisotropic materials, the equivalent stiffness matrix [D] obtained by asymptotic homogenization is... ▲There are 9 non-zero equivalent stiffness coefficients in it, which can be expressed as:

[0063]

[0064] (1.3.a) For fiber bending, a second homogenization step is performed along the x-direction on the narrow strip after the first homogenization. First, the stiffness matrix [D] of each narrow strip caused by the out-of-plane offset due to fiber bending is calculated according to equation (4). ▲ ] k :

[0065]

[0066] Where k and θ k These represent the narrowband number and its off-plane deflection angle, respectively, where m is the total number of narrowbands. This is the narrowband transformation matrix.

[0067] (1.3.b) The stress is continuous and the deformation is coordinated at the interface where adjacent narrow bands are continuous. The equivalent stiffness matrix of the microcrack defect can be calculated by equation (5) [D]. * ]:

[0068]

[0069] in, and The equivalent stiffness matrix [D] is obtained by asymptotic homogenization along the z-direction in the first step. ▲ The submatrix of ]; and The equivalent stiffness matrix [D] is obtained by homogenizing along the x-direction in the second step. * The submatrix of ].

[0070] Step 2: Establish a digital twin model of the gas cylinder containing microcrack defects and predict the impact of the defects on the mechanical behavior response of the gas cylinder.

[0071] (2.1) Based on the statistical information of microcrack defects in gas cylinders, the equivalent stiffness matrix of different microcrack defects is calculated by the method provided in step 1.

[0072] (2.2) Establish a digital twin model of the gas cylinder containing microcracks, and assign the equivalent stiffness matrix calculated in (2.1) as a material property to the corresponding mesh element (e.g., Figure 3 (As shown).

[0073] (2.3) By applying loads and constraints to the digital twin model containing microcracks and defects established above according to the actual working conditions, the impact of microcracks and defects on the structural performance of the gas cylinder can be predicted.

[0074] Step 3: Use laser shear speckle interferometry to detect the response characteristics of the gas cylinder under internal pressure loading;

[0075] (3.1) Scheme for laser shearing speckle interferometry of gas cylinder (e.g.) Figure 4 As shown, the shearing can be achieved by: using a Michelson interference optical path, introducing shearing amount using an optical wedge prism, using a birefringent prism, etc., setting the shearing amount and shearing direction of the laser shearing speckle interference device, and adjusting the laser irradiation on the surface of the gas cylinder being tested.

[0076] (3.2) During the pressurization / depressurization process of the gas cylinder, an image acquisition and analysis device is used to measure the shear fringe evolution process of the measured area on the cylinder surface. The acquired shear fringe image can be unwrapped to obtain the phase map of the image. Integration along the shear direction yields the out-of-plane displacement of the measured area surface of the gas cylinder (e.g., ...). Figure 8 (As shown).

[0077] (3.3) The phase map of the image can be obtained by unwrapping the collected shear fringe pattern. According to the shear amount in different directions, the relationship between the phase difference and the displacement gradient can be obtained, as shown in Equation (6):

[0078]

[0079] Step 4: Evaluate the impact of microcrack defects on the structural performance of the gas cylinder.

[0080] (4.1) Based on the prediction results of the digital twin model of the gas cylinder with microcrack defects obtained in step 2 above, compare it with the finite element model of the ideal gas cylinder without defects to obtain the first assessment of the performance degradation of the real gas cylinder.

[0081] (4.2) Under the given testing conditions, including laser wavelength, amplification factor, shear amount, shear direction, and pressure level / pressure difference, the stripe pattern of the gas cylinder under test is obtained. Combined with the periodic inspection requirements of the gas cylinder, the test is carried out again under the same testing conditions. By directly comparing the stripe levels of the two tests, the degree of performance degradation of the gas cylinder during its service life can be determined according to Equation (7).

[0082]

[0083] Where n is the stripe level.

[0084] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly implemented or conceived by those skilled in the art from the disclosure of this invention, regardless of the different ways in which shearing amount is introduced in shear speckle interferometry, should be considered within the scope of protection of this invention.

Claims

1. A method for predicting, detecting, and evaluating the microcrack defect response of carbon fiber reinforced composite hydrogen storage cylinders, comprising the following steps: Step 1: Establish a micromechanical model of a real microcrack defect; Step 2: Establish a digital twin model of the gas cylinder containing microcrack defects and predict the impact of the defects on the mechanical behavior response of the gas cylinder; Step 3: Use laser shear speckle interferometry to detect the response characteristics of the gas cylinder under internal pressure loading; Step 4: Evaluate the impact of microcrack defects on the structural performance of the gas cylinder; Step 1 specifically includes: (1.1) A representative volume element (RVE) model of microcrack defects coupled with fiber bending and interlayer interface peeling was established; the representative volume element of the microcrack defect was then... x The direction is divided into several narrow bands, and the fiber bending in each narrow band has approximately the same off-plane deflection angle. t is the interfacial delamination thickness, reflecting the degree of interfacial peeling. (1.2.a) First, for interlayer interface peeling, a progressive homogenization method is used along each narrow band. z The direction is first homogenized; after the asymptotic homogenization process, the equivalent stiffness coefficient is obtained. The expression: （1） In the formula, For characteristic function, For the average operator, ; (1.2.b) Obtain the equivalent stiffness coefficient Analytical solution: （2） (1.2.c) For fiber-reinforced anisotropic materials, the equivalent stiffness matrix obtained by asymptotic homogenization is... There are 9 non-zero equivalent stiffness coefficients, denoted as: （3） (1.3.a) Regarding fiber bending, the narrow band after the first homogenization step... x The direction is homogenized in the second step; first, the stiffness matrix of each narrow strip caused by the out-of-plane offset due to fiber bending is calculated according to equation (4). : （4） in k and θ k These represent the narrowband number and its deflection angle from the surface, respectively. m It is the total number of narrowbands. This is the narrowband transformation matrix; (1.3.b) The stress is continuous and the deformation is coordinated at the interface where adjacent narrow bands are continuous. The equivalent stiffness matrix of the microcrack defect as a whole can be calculated by Equation (5). : （5） in, , and It is the first step along z Equivalent stiffness matrix obtained by asymptotic homogenization of direction The submatrix; , and It is the second step along x Equivalent stiffness matrix obtained by directional homogenization The submatrix; Step 2 specifically includes: (2.1) Based on the statistical information of microcrack defects in gas cylinders, the equivalent stiffness matrix of different microcrack defects is calculated by the method provided in step 1. (2.2) Establish a digital twin model of the gas cylinder containing microcrack defects, and assign the equivalent stiffness matrix calculated in (2.1) as a material property to the corresponding mesh element; (2.3) Apply loads and constraints to the digital twin model of the gas cylinder with microcrack defects established above according to the actual working conditions, and predict the impact of microcrack defects on the structural performance of the gas cylinder. Step 3 specifically includes: (3.1) Implementation scheme of laser shearing speckle interferometry for gas cylinders, the shearing is achieved by: based on Michelson interference optical path, using optical wedge prism to introduce shearing amount, using birefringent prism, and adjusting the laser irradiation on the surface of the gas cylinder under test; (3.2) During the pressurization or depressurization of the gas cylinder, the test gas cylinder is image acquired and analyzed using a laser shear speckle interferometry device, and the evolution process of shear fringes in the test area on the surface of the gas cylinder is output. (3.3) The phase map of the image is obtained by unwrapping the collected shear fringe pattern. Based on the shear amount in different directions, the relationship between the phase difference and the displacement gradient is obtained, as shown in Equation (6): （6） in, For phase difference, The wavelength of the laser. The shear amount is given in the corresponding direction; the out-of-surface displacement of the measured area of ​​the gas cylinder is obtained by integrating along the shear direction. Step 4 specifically includes: (4.1) Based on the prediction results of the digital twin model of the gas cylinder with microcrack defects obtained in step 2 above, compare it with the finite element model of the ideal gas cylinder without defects to obtain the first assessment of the performance degradation of the real gas cylinder. (4.2) Under the given testing conditions, the specific conditions include: laser wavelength, amplification factor, shear amount, shear direction, pressure level or pressure difference, to obtain the stripe pattern of the gas cylinder under test; combined with the periodic inspection requirements of the gas cylinder, the test is carried out again under the same testing conditions, and the degree of performance degradation of the gas cylinder during service is judged directly by comparing the stripe levels of the two tests according to formula (7): （7） in, n The number of stripes represents the stripe order.

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