Composite material subsequent damage judgment method and equipment based on maximum equivalent displacement and medium

Abstract

The invention discloses a method and equipment for judging subsequent damage of a composite material based on maximum equivalent displacement and a medium, and relates to the technical field of mechanical simulation analysis of the composite material. Determining the corresponding current maximum equivalent displacement when the current strain unit of the composite material reaches the limit strain in the current analysis step; comparing the current maximum equivalent displacement with a current damage judgment threshold value corresponding to the current analysis step; and determining a next damage judgment threshold value corresponding to the next analysis step based on the comparison result. The method is used for solving the problem that in the prior art, the precision is poor when subsequent damage judgment is conducted on the composite material, and the accuracy of damage judgment is improved through the dynamic damage judgment threshold value.

Description

Technical Field

[0001] This application relates to the technical field of composite material mechanical simulation analysis, and in particular to a method, device and medium for judging subsequent damage of composite materials based on the maximum equivalent displacement. Background Technique

[0002] Currently, composite materials are being more and more widely used in high-tech fields such as aerospace, high-speed rail, and new energy vehicles. During the service process of composite materials, damage often occurs due to factors such as loads and environments. At present, the damage of composite materials can be effectively measured through experiments, but there are problems of high cost and low efficiency.

[0003] With the development of computer technology, the use of numerical simulation methods to predict the mechanical behavior of composite materials has gradually emerged. However, the existing technology can only predict the first damage of composite materials, and the judgment criterion of the first damage is still used in the continuous damage numerical model of composite materials, resulting in low accuracy in judging the subsequent damage of composite materials. Summary of the Invention

[0004] In view of the above problems and technical requirements, the applicant of this application proposes a method, device and medium for judging subsequent damage of composite materials based on the maximum equivalent displacement, so as to solve the problem of poor accuracy in judging subsequent damage of composite materials in the existing technology, and realize improving the accuracy of damage judgment by using a dynamic damage judgment threshold.

[0005] An embodiment of this application provides a method for judging subsequent damage of composite materials based on the maximum equivalent displacement, and the method includes:

[0006] When it is determined that the composite material meets the preset conditions, determine the current maximum equivalent displacement corresponding to the current strain unit of the composite material reaching the ultimate strain at the current analysis step, where the preset conditions include: the composite material is subjected to an external force, the composite material has been damaged and the composite material has not failed;

[0007] Compare the current maximum equivalent displacement with the current damage judgment threshold corresponding to the current analysis step;

[0008] When it is determined that the current maximum equivalent displacement is greater than the current damage judgment threshold, update the current maximum equivalent displacement to the next damage judgment threshold corresponding to the next analysis step; when it is determined that the current maximum equivalent displacement is less than or equal to the current damage judgment threshold, retain the current damage judgment threshold as the next damage judgment threshold corresponding to the next analysis step; and perform subsequent damage judgment of the composite material based on the next damage judgment threshold until the composite material is not subjected to an external force and / or fails.

[0009] According to the subsequent damage discrimination method of composite materials based on the maximum equivalent displacement according to an embodiment of the present application, before determining the current maximum equivalent displacement corresponding to the current strain element of the composite material reaching the ultimate strain when it is determined that the composite material meets the preset conditions, it further includes:

[0010] Obtain the damage variable corresponding to the composite material under the external force;

[0011] Judge whether the damage variable is greater than zero;

[0012] When it is determined that the damage variable is greater than zero, it is determined that the composite material has been damaged;

[0013] When it is determined that the damage variable is less than or equal to zero, it is determined that the composite material has not been damaged.

[0014] According to the subsequent damage discrimination method of composite materials based on the maximum equivalent displacement according to an embodiment of the present application, obtaining the damage variable corresponding to the composite material under the external force includes:

[0015] Obtain the damage variable based on the first calculation formula;

[0016] Among them, the first calculation formula includes:

[0017]

[0018] Among them, I = ft, fc, mt, mc, d I ∈[0,1], d ft represents the fiber tensile damage variable, d fc represents the fiber compressive damage variable, d mt represents the matrix tensile damage variable, d mc represents the matrix compressive damage variable, represents the equivalent displacement corresponding to the failure of the composite material, δ I,eq represents the current equivalent displacement, Initial failure equivalent displacement.

[0019] According to the subsequent damage discrimination method of composite materials based on the maximum equivalent displacement according to an embodiment of the present application, after it is determined that the composite material has been damaged, it further includes:

[0020] Judge whether the current strain element is damaged again;

[0021] When it is determined that there is no re-damage, update the stress and stiffness;

[0022] In the case of determining that re - damage has occurred, use the damage evolution model for damage evolution, and determine whether the fiber tensile damage variable is greater than or equal to 1; in the case of determining that the fiber tensile damage variable is greater than or equal to 1, delete the current strain element, and update the stress and stiffness; in the case of determining that the fiber tensile damage variable is less than 1, update the stress and stiffness.

[0023] According to the subsequent damage discrimination method for composite materials based on the maximum equivalent displacement in an embodiment of the present application, after determining that the composite material has not been damaged, it further includes:

[0024] Determine whether the current strain element has suffered the first damage;

[0025] In the case of determining that the first damage has not occurred, update the stress and stiffness;

[0026] In the case of determining that the first damage has occurred, use the damage evolution model for damage evolution, and determine whether the fiber tensile damage variable is greater than or equal to 1; in the case of determining that the fiber tensile damage variable is greater than or equal to 1, delete the current strain element, and update the stress and stiffness; in the case of determining that the fiber tensile damage variable is less than 1, update the stress and stiffness.

[0027] According to the subsequent damage discrimination method for composite materials based on the maximum equivalent displacement in an embodiment of the present application, before determining the current maximum equivalent displacement corresponding to the current strain element of the composite material reaching the ultimate strain at the current analysis step when it is determined that the composite material meets the preset conditions, it further includes:

[0028] Based on the constitutive relationship created in advance, calculate the material stress corresponding to the current strain element of the composite material;

[0029] Based on the material stress and the preset damage determination criterion, perform damage determination on the current strain element. According to the subsequent damage discrimination method for composite materials based on the maximum equivalent displacement in an embodiment of the present application, the constitutive relationship includes:

[0030]

[0031] Where, Δ = 1 - d f d m ν 12 ν 21 -d m ν 23 ν 32 -d f ν 13 ν 31 -2d f d m ν 21 ν 32 ν13 ;

[0032] Among them, C d represents the damage stiffness matrix, d i (i = f, m) represents the damage variable, d f =(1 - d ft )(1 - d fc ) represents the fiber damage variable, d m =(1 - d mt )(1 - d mc ) represents the matrix damage variable, d ft represents the fiber tensile damage variable, d fc represents the fiber compressive damage variable, d mt represents the matrix tensile damage variable, d mc represents the matrix compressive damage variable, E ii (i = 1, 2, 3) represents the elastic modulus in the i direction, v ij (i, j = 1, 2, 3) represents the Poisson's ratio in the ij direction, G ij (i, j = 1, 2, 3) represents the shear modulus in the ij direction.

[0033] According to the subsequent damage discrimination method of composite materials based on the maximum equivalent displacement in an embodiment of the present application, damage determination of the current strain unit is performed based on the material stress and a preset damage determination criterion, including:

[0034] Performing initial damage determination on the current strain unit based on the material stress and the damage determination criterion;

[0035] Among them, the damage determination criterion includes four failure modes, and the four failure modes include: fiber tensile failure mode, fiber compressive failure mode, matrix tensile failure mode, and matrix compressive failure mode;

[0036] The fiber tensile failure mode includes:

[0037]

[0038] σ 11 >= 0;

[0039] Among them, F ft represents the first damage initial value corresponding to the fiber stretching failure mode, σ 11 represents the normal stress corresponding to the first principal direction, X T represents the tensile strength in the fiber direction, σ 12 represents the shear stress corresponding to the 12 direction, S 12 represents the shear strength in the 12 direction, σ 13 represents the shear stress corresponding to the 13 direction, S 13Denote the shear strength in the 13 direction, and α denote the shear failure coefficient, where 0 ≤ α ≤ 1;

[0040] Fiber compression failure mode, including:

[0041]

[0042] σ 11 ≤ 0;

[0043] Among them, F fc denotes the second initial damage value corresponding to the fiber compression failure mode, and X C denotes the compressive strength in the fiber direction;

[0044] Matrix tensile failure mode, including:

[0045]

[0046] σ 22 + σ 33 ≥ 0;

[0047] Among them, F mt denotes the third initial damage value corresponding to the matrix tensile failure mode, σ 22 denotes the normal stress corresponding to the second principal direction, σ 33 denotes the normal stress corresponding to the third principal direction, Y T denotes the transverse tensile strength, S 23 denotes the shear strength in the 23 direction, σ 23 denotes the shear stress corresponding to the 23 direction;

[0048] Matrix compression failure mode, including:

[0049]

[0050] σ 22 + σ 33 < 0;

[0051] Among them, F mc denotes the fourth initial damage value corresponding to the matrix compression failure mode, Y C denotes the transverse compressive strength.

[0052] The embodiment of the present application also provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, the steps of the method for discriminating subsequent damage of a composite material based on the maximum equivalent displacement as described in any one of the above are implemented.

[0053] The embodiment of the present application also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the method for discriminating subsequent damage of a composite material based on the maximum equivalent displacement as described in any one of the above are implemented.

[0054] The method, device and medium for discriminating subsequent damage of a composite material based on the maximum equivalent displacement provided by the embodiment of the present application determine the current maximum equivalent displacement corresponding to the current strain element of the composite material reaching the ultimate strain at the current analysis step when it is determined that the composite material meets the preset conditions; compare the current maximum equivalent displacement with the current damage determination threshold corresponding to the current analysis step; when it is determined that the current maximum equivalent displacement is greater than the current damage determination threshold, update the current maximum equivalent displacement to the next damage determination threshold corresponding to the next analysis step; when it is determined that the current maximum equivalent displacement is less than or equal to the current damage determination threshold, retain the current damage determination threshold as the next damage determination threshold corresponding to the next analysis step. The present application determines the maximum equivalent displacement based on the actual situation of the composite material in different analysis steps during the subsequent damage process of the composite material, and dynamically determines the damage determination threshold based on the maximum equivalent displacement, improving the accuracy of damage determination. Description of the Drawings

[0055] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0056] Figure 1 is one of the flowcharts of the method for discriminating subsequent damage of a composite material based on the maximum equivalent displacement provided by the embodiment of the present application;

[0057] Figure 2 is a schematic diagram of the change of the dynamic damage determination threshold provided by the embodiment of the present application;

[0058] Figure 3 is another flowchart of the method for discriminating subsequent damage of a composite material based on the maximum equivalent displacement provided by the embodiment of the present application;

[0059] Figure 4 is a graph of force vs. time of the composite material under different impact energies provided by the embodiment of the present application;

[0060] Figure 5 is a graph of force vs. displacement of the composite material under different impact energies provided by the embodiment of the present application;

[0061] Figure 6It is a schematic structural diagram of an electronic device provided by an embodiment of the present application. Detailed implementation manners

[0062] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present invention.

[0063] To be able to clearly illustrate the present application, the continuous damage of composite materials is further described as follows:

[0064] Composite materials have complex failure modes, such as fiber fracture, matrix cracking, and fiber / matrix interface debonding, etc. Therefore, it is necessary to establish effective constitutive models, failure criteria, and damage evolution methods to predict the damage initiation and evolution process of composite materials under specific loads.

[0065] In the numerical model of continuous damage of composite materials, when the damage initiation criterion determines that a certain element has suffered the first damage, the discrimination of the subsequent damage of this element will affect the evolution and development of its damage, and thus have an important impact on the damage accumulation process of the entire material. At present, there is no clear method to distinguish the damage conditions of damaged and undamaged elements.

[0066] The numerical simulation of continuous damage of composite materials often includes a large number of analysis steps. In each analysis step, the elements will call the material subroutine for damage analysis, including determining whether the element has suffered damage in this analysis step. The damage initiation criteria adopted in the analysis mainly discriminate the first damage of the elements that have not suffered damage. For the damage initiation criterion in stress form, when an element meets the initial damage condition and enters the damage stage in a certain analysis step, its stiffness decreases, and the strain required for the damaged element to meet the original damage condition again in the subsequent analysis step increases greatly, so that the damage condition of the element in this analysis step is difficult to trigger, resulting in an overestimation of the element performance and affecting the calculation accuracy.

[0067] Therefore, it is necessary to establish a reasonable and effective standard to discriminate the subsequent damage of damaged elements to adapt to this continuous damage analysis with multiple analysis steps.

[0068] The embodiment of the present application provides a method for discriminating the subsequent damage of composite materials based on the maximum equivalent displacement. This method can be applied to intelligent terminals and can also be applied to servers. Some examples in the embodiments of the present application are not used to limit the protection scope of the present application, and will not be elaborated one by one hereafter. The specific implementation of this method is as Figure 1 shown:

[0069] Step 101: When it is determined that the composite material meets the preset conditions, determine the current maximum equivalent displacement corresponding to the current strain element of the composite material reaching the ultimate strain under the current analysis step.

[0070] Among them, the preset conditions include: the composite material is subjected to an external force, the composite material has been damaged and the composite material has not failed.

[0071] Among them, the composite material being subjected to an external force includes: the strain element of the composite material is subjected to an external force at the current moment; the composite material having been damaged includes: the composite material has suffered initial damage, or, the composite material has suffered initial damage and subsequent damage.

[0072] Step 102: Compare the current maximum equivalent displacement with the current damage determination threshold corresponding to the current analysis step.

[0073] Among them, the current damage determination threshold is obtained from the previous analysis step.

[0074] Step 103: When it is determined that the current maximum equivalent displacement is greater than the current damage determination threshold, update the current maximum equivalent displacement to the next damage determination threshold corresponding to the next analysis step; when it is determined that the current maximum equivalent displacement is less than or equal to the current damage determination threshold, retain the current damage determination threshold as the next damage determination threshold corresponding to the next analysis step; and based on the next damage determination threshold, perform subsequent damage determination of the composite material until the composite material is no longer subjected to an external force and / or fails.

[0075] Specifically, for each strain element in each analysis step, the above steps are iterated, and finally the damage evolution result of the entire process of the composite material can be obtained.

[0076] The method for subsequent damage discrimination of a composite material based on the maximum equivalent displacement provided by the embodiments of the present application determines the current maximum equivalent displacement corresponding to the current strain element of the composite material reaching the ultimate strain under the current analysis step when it is determined that the composite material meets the preset conditions; compares the current maximum equivalent displacement with the current damage determination threshold corresponding to the current analysis step; when it is determined that the current maximum equivalent displacement is greater than the current damage determination threshold, updates the current maximum equivalent displacement to the next damage determination threshold corresponding to the next analysis step; when it is determined that the current maximum equivalent displacement is less than or equal to the current damage determination threshold, retains the current damage determination threshold as the next damage determination threshold corresponding to the next analysis step. The present application determines the maximum equivalent displacement based on the actual situation of the composite material in different analysis steps during the subsequent damage process of the composite material, and dynamically determines the damage determination threshold based on the maximum equivalent displacement, improving the accuracy of damage determination.

[0077] In a specific embodiment, when it is determined that the composite material meets the preset conditions, before determining the current maximum equivalent displacement corresponding to the current strain element of the composite material reaching the ultimate strain in the current analysis step, based on the constitutive relationship created in advance, calculate the material stress corresponding to the current strain element of the composite material; and determine the damage of the current strain element based on the material stress and the preset damage determination criterion.

[0078] In a specific embodiment, the constitutive relationship is shown in formula (1):

[0079]

[0080] where, Δ = 1 - d f d m ν 12 ν 21 -d m ν 23 ν 32 -d f ν 13 ν 31 -2d f d m ν 21 ν 32 ν 13 ;

[0081] where, C d represents the damage stiffness matrix, d i (i = f, m) represents the damage variable, d f = (1 - d ft )(1 - d fc ) represents the fiber damage variable, d m = (1 - d mt )(1 - d mc ) represents the matrix damage variable, d ft represents the fiber tensile damage variable, d fc represents the fiber compressive damage variable, d mt represents the matrix tensile damage variable, d mc represents the matrix compressive damage variable, E ii (i = 1, 2, 3) represents the elastic modulus in the i direction, v ij (i, j = 1, 2, 3) represents the Poisson's ratio in the ij direction, G ij (i, j = 1, 2, 3) represents the shear modulus in the ij direction.

[0082] where, there is a mapping relationship between the damage stiffness matrix and the material stress. Based on formula (1), the damage stiffness matrix is obtained, and then the material stress is obtained based on this mapping relationship.

[0083] In a specific embodiment, the damage determination basis includes: an initial damage determination criterion.

[0084] In a specific embodiment, the specific implementation of damage determination for the current strain element based on material stress and a preset damage determination basis includes:

[0085] Performing an initial damage determination on the current strain element based on material stress and the damage determination basis to obtain a damage variable.

[0086] Specifically, perform an initial damage determination on the strain element based on material stress and the initial damage determination criterion.

[0087] Specifically, use the Hashin criterion to determine the initiation of damage to the strain element.

[0088] Among them, the initial damage determination criterion includes four failure modes, and the four failure modes include: fiber tensile failure mode, fiber compressive failure mode, matrix tensile failure mode, and matrix compressive failure mode.

[0089] The fiber tensile failure mode is shown in formulas (2) and (3):

[0090]

[0091] σ 11 > = 0................................ (3)

[0092] Among them, F ft represents the first damage initial value corresponding to the fiber tensile failure mode, σ 11 represents the normal stress corresponding to the first principal direction, X T represents the tensile strength in the fiber direction, σ 12 represents the shear stress corresponding to the 12 direction, α 12 represents the shear strength in the 12 direction, σ 13 represents the shear stress corresponding to the 13 direction, S 13 represents the shear strength in the 13 direction, α represents the shear failure coefficient, which is used to determine the influence of shear stress on fiber tensile failure, 0 ≤ α ≤ 1, and in this application, it can be set to 1.

[0093] The fiber compressive failure mode is shown in formula (4) and formula (5):

[0094]

[0095] σ 11 ≤ 0................................ (5)

[0096] Among them, F fc represents the second damage initial value corresponding to the fiber compressive failure mode, X CRepresents the compressive strength in the fiber direction.

[0097] The matrix tensile failure mode is shown in Equations (6) and (7):

[0098]

[0099] σ 22 +σ 33 ≥0……………………………………………………………………(7)

[0100] Wherein, F mt represents the third initial damage value corresponding to the matrix tensile failure mode, σ 22 represents the normal stress corresponding to the second principal direction, σ 33 represents the normal stress corresponding to the third principal direction, Y T represents the transverse tensile strength, S 23 represents the shear strength in the 23 direction, σ 23 represents the shear stress corresponding to the 23 direction.

[0101] The matrix compressive failure mode is shown in Equations (8) and (9):

[0102]

[0103] σ 22 +σ 33 <0…………………………………(9)

[0104] Wherein, F mc represents the fourth initial damage value corresponding to the matrix compressive failure mode, Y C represents the transverse compressive strength.

[0105] In a specific embodiment, once the initial damage determination criterion is satisfied, the stiffness degradation process of the strain unit is controlled by a damage evolution model, and a fracture energy-based model is adopted.

[0106] The specific implementation of obtaining the damage variable corresponding to the composite material under an external force includes:

[0107] Obtaining the damage variable based on a first calculation formula.

[0108] Wherein, the first calculation formula is shown in Equation (10):

[0109]

[0110] Wherein, I = ft, fc, mt, mc, d I ∈[0,1], d ft represents the fiber tensile damage variable, d fc represents the fiber compressive damage variable, dmt denotes the matrix tensile damage variable, d mc denotes the matrix compressive damage variable denotes the equivalent displacement corresponding to the failure of the composite material, δ I,eq denotes the current equivalent displacement The equivalent displacement at initial failure

[0111] Among them, formula (10) can characterize the damage variables corresponding to different failure modes

[0112] In a specific embodiment, when it is determined that the composite material meets the preset conditions, before determining the current maximum equivalent displacement corresponding to the current strain element of the composite material reaching the ultimate strain in the current analysis step, obtain the damage variable corresponding to the composite material under the external force; determine whether the damage variable is greater than zero; when it is determined that the damage variable is greater than zero, determine that the composite material has been damaged; when it is determined that the damage variable is less than or equal to zero, determine that the composite material has not been damaged

[0113] Specifically, take the fiber damage variable and the matrix damage variable as state variables, and their values are passed as the analysis step progresses. In each analysis step, due to the application of the load, the strain element generates a strain increment

[0114] In a specific embodiment, after determining that the composite material has been damaged, determine whether the current strain element is damaged again; when it is determined that there is no re-damage, update the stress and stiffness; when it is determined that there is re-damage, perform damage evolution using the damage evolution model, and determine whether the fiber tensile damage variable is greater than or equal to 1; when it is determined that the fiber tensile damage variable is greater than or equal to 1, delete the current strain element, and update the stress and stiffness; when it is determined that the fiber tensile damage variable is less than 1, update the stress and stiffness

[0115] In a specific embodiment, after determining that the composite material has not been damaged, determine whether the current strain element is damaged for the first time; when it is determined that there is no first damage, update the stress and stiffness; when it is determined that there is first damage, perform damage evolution using the damage evolution model, and determine whether the fiber tensile damage variable is greater than or equal to 1; when it is determined that the fiber tensile damage variable is greater than or equal to 1, delete the current strain element, and update the stress and stiffness; when it is determined that the fiber tensile damage variable is less than 1, update the stress and stiffness

[0116] Specifically, in order to achieve continuous accumulation of damage, it is necessary to determine whether the mechanical properties of the strain element will further decrease in subsequent analysis steps, so a dynamic damage determination threshold is used for damage determination. And, during the whole process, the maximum equivalent displacement of the strain element shows an upward trend. SeeFigure 2 。

[0117] Among them, in Figure 2 S represents the initial equivalent stress, the initial failure equivalent displacement, represents the previous maximum equivalent displacement, represents the equivalent displacement corresponding to the final failure, δ I,eq represents the current equivalent displacement.

[0118] Next, the present application will be specifically described through Figure 3 as follows:

[0119] Step 301: Calculate the material stress based on the constitutive relationship, and determine the damage of the strain element according to the material stress and the damage judgment criterion.

[0120] Step 302: Judge whether the damage variable is greater than zero. If so, execute Step 303; otherwise, execute Step 309.

[0121] Step 303: Determine that the composite material has been damaged.

[0122] Step 304: Judge whether the current strain element is damaged again. If so, execute Step 305; otherwise, execute Step 308.

[0123] Step 305: Perform damage evolution using the damage evolution model.

[0124] Step 306: Judge whether the fiber tensile damage variable is greater than or equal to 1. If so, execute Step 307; otherwise, execute Step 308.

[0125] Step 307: Delete the current strain element, and update the stress and stiffness.

[0126] Step 308: Update the stress and stiffness.

[0127] Step 309: Determine that the composite material has not been damaged.

[0128] Step 310: Judge whether the current strain element is damaged for the first time. If so, execute Step 305; otherwise, execute Step 308.

[0129] Step 311: Until the composite material is not subjected to external forces and / or fails.

[0130] Next, the present application will be specifically described through a specific example:

[0131] In the simulation, a finite element model of low-velocity impact including a composite gas cylinder, a punch, and a fixture was established in ABAQUS / CAE. The gas cylinder includes a hoop layer, a helical layer, and an EPDM gasket with thicknesses of 1.3 mm, 1.9 mm, and 1.8 mm respectively. The ply orientation of the gas cylinder is [90°4 / (20°2 / -20°2)4 / EPDM], where 90° represents the hoop direction. The inner diameter of the cylinder is 157 mm. In the finite element model, fixed constraints are used to support the fixture, and the X and Y degrees of freedom of the radial section are constrained. Symmetric constraints in the Y direction are applied to the circumferential section. In the experiment, two aluminum alloy fixtures are used to fix the cylinder at a distance of 100 mm to ensure no gap between the fixture and the cylinder. The diameter and mass of the punch are 12.7 mm and 7.5 kg respectively, and drop hammer impact tests on the composite gas cylinder are carried out at energies of 3 J, 5 J, 10 J, and 15 J. T , where 90° represents the hoop direction. The inner diameter of the cylinder is 157 mm. In the finite element model, fixed constraints are used to support the fixture, and the X and Y degrees of freedom of the radial section are constrained. Symmetric constraints in the Y direction are applied to the circumferential section. In the experiment, two aluminum alloy fixtures are used to fix the cylinder at a distance of 100 mm to ensure no gap between the fixture and the cylinder. The diameter and mass of the punch are 12.7 mm and 7.5 kg respectively, and drop hammer impact tests on the composite gas cylinder are carried out at energies of 3 J, 5 J, 10 J, and 15 J.

[0132] Reduced integration three-dimensional solid elements (C3D8R) are assigned to the composite material layer and the EPDM gasket, and bilinear cohesive elements with zero thickness (COH3D8) are used to simulate the interlayer damage behavior between adjacent layers. The discrete mesh consists of 145,600 C3D8R elements and 134,400 COH3D8 elements. Considering the calculation accuracy and efficiency, the mesh near the impact area is refined, and fine elements with a size of 0.9 mm × 0.9 mm are adopted.

[0133] The elastic constant of EPDM is 25 MPa, and the Poisson's ratio is 0.4. The material parameters of the composite material are as follows: Young's modulus (elastic modulus) is E 11 = 134.6 GPa, E 22 = E 33 = 7.65 GPa, shear modulus G 12 = G 13 = 3.68 GPa, G 23 = 3.2 GPa, Poisson's ratio is v 12 = v 13 = 0.298, v 23 = 0.52, strength is X T = 2480 MPa, X C = 952 MPa, Y T = 32.4 MPa, Y C = 138 MPa, S 12 = S 13 = 77.5 MPa, S 23 = 68.6 MPa, fracture energy is G ft = 133 N / mm, G fc = 40 N / mm, G mt = 0.6 N / mm, G mc = 2.1 N / mm.

[0134] The proposed subsequent damage discrimination method also describes the initial damage process of the element. The equivalent stress and equivalent displacement corresponding to the initial damage judged by the Hashin criterion are regarded as the initial equivalent stress and initial equivalent displacement, denoted by S and respectively.

[0135] After the first damage, the stress and stiffness of the element decrease with the linear evolution model until the element reaches the ultimate strain. The maximum equivalent displacement corresponding to the ultimate strain is denoted by which can be updated in subsequent analysis steps and only increases. Figure 2 The condition for triggering subsequent damage is defined using the maximum equivalent displacement as a threshold.

[0136] The process of the punch impacting the gas cylinder with different energies is simulated using ABAQUS / EXPLICT explicit calculation. ABAQUS-VUMAT is strain-driven and performs the Figure 3 steps shown. The progressive failure process of the composite gas cylinder is obtained based on the above process.

[0137] To verify the finite element model and evaluate the influence of the proposed subsequent damage discrimination method on the entire damage evolution process of the composite gas cylinder, the obtained numerical results are compared with the experimental data.

[0138] Figure 4 The force-time curves of the composite cylinder at impact energies of 3 J (corresponding to a), 5 J (corresponding to b), 10 J (corresponding to c), and 15 J (corresponding to d) are shown respectively. The predicted force-time curves are in good agreement with the experimental curves. The errors between the peak forces calculated at the four energies and the experimental results are -1.22%, -3.65%, -2.38%, and -2.12% respectively.

[0139] Among them, the experimental curves are indicated by the black solid lines, and the predicted curves are indicated by the red dashed lines.

[0140] Figure 5 The force-displacement curves at four different impact energies of 3 J (corresponding to a), 5 J (corresponding to b), 10 J (corresponding to c), and 15 J (corresponding to d) are shown respectively. The predicted force-displacement curves are in good agreement with the experimental curves. The errors between the non-recoverable displacements calculated at the four energies and the experimental results are -6.38%, 9.61%, 9.26%, and 8.82% respectively.

[0141] Among them, the experimental curves are indicated by the black solid lines, and the predicted curves are indicated by the red dashed lines.

[0142] In addition, the present application separately compares the experimental and numerical results of the peak force and the maximum displacement under different impact energies. The predicted peak force and maximum displacement are in good agreement with the experimental values at all energies. The errors between the calculated maximum displacements and the experimental results at the four energies are -2.13%, -3.49%, -2.33%, and -1.15% respectively.

[0143] Verified by examples, the calculation errors are all within the allowable range of engineering. Therefore, it is reasonable to use the maximum equivalent displacement as the threshold to judge the subsequent damage.

[0144] Based on the ABAQUS software, the present invention develops user subroutines. Taking the Hashin criterion as the initial damage criterion, a method for judging subsequent damage using the maximum equivalent displacement as the threshold is proposed. Through specific example calculations, it is found that this method can accurately predict the progressive damage process of composite gas cylinders, verifying that it is reasonable to use the maximum equivalent displacement as the threshold to judge subsequent damage, providing technical support for the numerical simulation of composite progressive damage.

[0145] The method for judging subsequent damage proposed in the present application after initial damage in the damage initiation criterion judgment unit is used to obtain a more accurate damage accumulation process for the continuous damage numerical simulation of composites. Based on the Hashin criterion, a method for judging subsequent damage with the maximum equivalent displacement as the threshold is proposed. The progressive damage model is integrated into ABAQUS through user-defined material subroutines UMAT / VUMAT. Verified by example calculations, a method for judging subsequent damage using a dynamic threshold that can reflect the instantaneous damage state has obtained satisfactory calculation accuracy.

[0146] Figure 6 An example of a schematic physical structure diagram of an electronic device is shown as Figure 6 shown. The electronic device may include: a processor 601, a communications interface 602, a memory 603, and a communication bus 604. Among them, the processor 601, the communications interface 602, and the memory 603 complete mutual communication through the communication bus 604. The processor 601 can call the logical instructions in the memory 603 to execute the method for judging subsequent damage of composites based on the maximum equivalent displacement.

[0147] In addition, when the logical instructions in the above-mentioned memory 603 are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs that can store program codes.

[0148] On the other hand, the present invention also provides a computer program product. The computer program product includes a computer program stored on a non-transitory computer-readable storage medium. The computer program includes program instructions. When the program instructions are executed by a computer, the computer can execute the subsequent damage discrimination method of composite materials based on the maximum equivalent displacement provided by the above-mentioned various methods.

[0149] On yet another aspect, the present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it is implemented to execute the subsequent damage discrimination method of composite materials based on the maximum equivalent displacement provided by the above-mentioned various embodiments.

[0150] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated. The components shown as units may or may not be physical units, that is, they may be located in one place, or may be distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without creative labor.

[0151] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0152] Finally, it should be noted that the above is only the preferred implementation of the present application, and the present application is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the scope of protection of the present application.

Claims

1. A method for judging subsequent damage of composite materials based on the maximum equivalent displacement, characterized in that The method includes: When it is determined that the composite material meets the preset conditions, determining the current maximum equivalent displacement corresponding to the current strain element of the composite material reaching the ultimate strain in the current analysis step, where the preset conditions include: the composite material is subjected to an external force, the composite material has been damaged and the composite material has not failed; Comparing the current maximum equivalent displacement with the current damage determination threshold corresponding to the current analysis step; When it is determined that the current maximum equivalent displacement is greater than the current damage determination threshold, updating the current maximum equivalent displacement to the next damage determination threshold corresponding to the next analysis step; when it is determined that the current maximum equivalent displacement is less than or equal to the current damage determination threshold, retaining the current damage determination threshold as the next damage determination threshold corresponding to the next analysis step; and performing subsequent damage determination of the composite material based on the next damage determination threshold until the composite material is not subjected to an external force and / or fails.

2. The subsequent damage discrimination method for composite materials based on the maximum equivalent displacement according to claim 1, characterized in that Before determining the current maximum equivalent displacement corresponding to the current strain element of the composite material reaching the ultimate strain in the current analysis step when it is determined that the composite material meets the preset conditions, it further includes: Obtaining the damage variable corresponding to the composite material under the external force; Judging whether the damage variable is greater than zero; When it is determined that the damage variable is greater than zero, determining that the composite material has been damaged; When it is determined that the damage variable is less than or equal to zero, determining that the composite material has not been damaged.

3. The subsequent damage discrimination method for composite materials based on the maximum equivalent displacement according to claim 2, wherein Obtaining the damage variable corresponding to the composite material under the external force includes: Obtaining the damage variable based on the first calculation formula; Wherein, the first calculation formula includes: where I = ft, fc, mt, mc, d I ∈[0, 1], d ft represents the fiber tensile damage variable, d fc represents the fiber compressive damage variable, d mt represents the matrix tensile damage variable, d mc represents the matrix compressive damage variable, represents the equivalent displacement corresponding to the failure of the composite material, δ I,eq represents the current equivalent displacement, the initial failure equivalent displacement.

4. The subsequent damage discrimination method of composite materials based on the maximum equivalent displacement according to claim 2, characterized in that After determining that the composite material has been damaged, it further includes: Judging whether the current strain element is damaged again; When it is determined that there is no re-damage, updating the stress and stiffness; When it is determined that there is re-damage, performing damage evolution using the damage evolution model, and judging whether the fiber tensile damage variable is greater than or equal to 1; when it is determined that the fiber tensile damage variable is greater than or equal to 1, deleting the current strain element, and performing stress and stiffness updates; when it is determined that the fiber tensile damage variable is less than 1, performing stress and stiffness updates.

5. The subsequent damage discrimination method for composite materials based on the maximum equivalent displacement according to claim 2, wherein After determining that the composite material has not been damaged, it further includes: Judging whether the current strain element is damaged for the first time; When it is determined that there is no first damage, updating the stress and stiffness; When it is determined that there is first damage, performing damage evolution using the damage evolution model, and judging whether the fiber tensile damage variable is greater than or equal to 1; when it is determined that the fiber tensile damage variable is greater than or equal to 1, deleting the current strain element, and performing stress and stiffness updates; when it is determined that the fiber tensile damage variable is less than 1, performing stress and stiffness updates.

6. The subsequent damage discrimination method for composite materials based on the maximum equivalent displacement according to any one of claims 1-5, characterized in that Before determining the current maximum equivalent displacement corresponding to the current strain element of the composite material reaching the ultimate strain in the current analysis step when it is determined that the composite material meets the preset conditions, it further includes: Calculating the material stress corresponding to the current strain element of the composite material based on the pre-created constitutive relationship; Performing damage determination on the current strain element based on the material stress and the preset damage determination basis.

7. The method for judging subsequent damage of a composite material based on the maximum equivalent displacement according to claim 6, wherein The constitutive relationship includes: where Δ = 1 - d f d m ν 12 ν 21 -d m ν 23 ν 32 -d f ν 13 ν 31 -2d f d m ν 21 ν 32 ν 13 ; Among them, C d represents the damage stiffness matrix, d i (i = j, m) represents the damage variable, d f =(1 - d ft )(1 - d fc ) represents the fiber damage variable, d m =(1 - d mt )(1 - d mc ) represents the matrix damage variable, d ft represents the fiber tensile damage variable, d fc represents the fiber compressive damage variable, d mt represents the matrix tensile damage variable, d mc represents the matrix compressive damage variable, E ii (i = 1, 2, 3) represents the elastic modulus in the i direction, v ij (i, j = 1, 2, 3) represents the Poisson's ratio in the ij direction, G ij (i, j = 1, 2, 3) represents the shear modulus in the ij direction.

8. The subsequent damage discrimination method of composite materials based on the maximum equivalent displacement according to claim 6, characterized in that Judging the damage of the current strain unit based on the material stress and a preset damage judgment basis, including: Performing an initial damage judgment on the current strain unit based on the material stress and the damage judgment basis; Wherein, the damage judgment basis includes four failure modes, and the four failure modes include: fiber tensile failure mode, fiber compressive failure mode, matrix tensile failure mode, and matrix compressive failure mode; The fiber tensile failure mode includes: σ 11 >= 0; Among them, F ft represents the first damage initial value corresponding to the fiber stretching failure mode, σ 11 represents the normal stress corresponding to the first principal direction, X T represents the tensile strength in the fiber direction, σ 12 represents the shear stress corresponding to the 1-2 direction, α 12 represents the shear strength in the 1-2 direction, σ 13 represents the shear stress corresponding to the 1-3 direction, S 13 represents the shear strength in the 1-3 direction, α represents the shear failure coefficient, 0 ≤ σ ≤ 1; The fiber compressive failure mode includes: σ 11 ≤0; Among them, F fc represents the second initial damage value corresponding to the fiber compression failure mode, and X C represents the compressive strength in the fiber direction; The matrix tensile failure mode includes: σ 22 +σ 33 ≥0; Among them, F mt represents the third initial damage value corresponding to the matrix tensile failure mode, σ 22 represents the normal stress corresponding to the second principal direction, σ 33 represents the normal stress corresponding to the third principal direction, Y T represents the transverse tensile strength, S 23 represents the shear strength in the 2-3 direction, σ 23 represents the shear stress corresponding to the 2-3 direction; The matrix compressive failure mode includes: σ 22 +σ 33 < 0; Among them, F mc represents the fourth initial damage value corresponding to the matrix compression failure mode, and Y C represents the transverse compression strength.

9. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the program, the steps of the composite material subsequent damage discrimination method based on the maximum equivalent displacement as described in any one of claims 1 to 8 are implemented.

10. A non-transitory computer-readable storage medium storing a computer program thereon, characterized in that, When the computer program is executed by the processor, the steps of the composite material subsequent damage discrimination method based on the maximum equivalent displacement as described in any one of claims 1 to 8 are implemented.

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