Method, system and equipment for predicting fatigue life of composite material patching and repairing structure

Abstract

The invention belongs to the technical field of computer simulation, and particularly discloses a method, a system and equipment for predicting the fatigue life of a composite material patching and repairing structure. The prediction method comprises the following steps: establishing a composite laminated plate fatigue damage analysis method in combination with an improved Hashin criterion, finite element analysis, a strength degradation model, a rigidity degradation model and a Camanho material parameter degradation model; fatigue life prediction analysis is carried out on the non-porous laminated plate and the porous laminated plate by using the method; and comparing a prediction result with a test result, and verifying the effectiveness of the established composite material laminated plate fatigue damage analysis method. On the basis, a composite material fatigue damage analysis method and a cohesion unit are combined, and a repair structure fatigue life prediction model is established. The fatigue life prediction method for the repair structure is provided by taking the composite material patching and repairing structure as a research object, and has certain engineering practical significance and better practical value.

Description

Technical Field

[0001] The present invention relates to a method, system and device for predicting the fatigue life of a composite patch repair structure, belonging to the technical field of computer simulation. Background Art

[0002] Advanced composite materials have been widely used in the aerospace field due to their excellent mechanical properties, but the disadvantages of composite materials are also obvious. Its impact toughness is low, and the damage after low-speed impact will not appear on the surface of the structure, and it is difficult to detect these damages by naked-eye observation. These invisible damages may lead to a sharp decline in the structural strength. The fatigue damage analysis and life prediction of composite materials have always been the focus and difficulty in the field of composite material mechanics research.

[0003] After years of research, composite material repair technology has also developed greatly. The patch repair technology is the main direction of composite material structure repair. The damaged part can be quickly repaired with a patch. Patch repair can be carried out by bonding a pre-cured composite patch and an adhesive to the damaged structure. This kind of repair can be applied to a unilateral plane or slightly curved surface. The pre-cured composite patch has the advantages of high strength, stiffness, low density and relatively easy surface treatment. Patch repair is a simple structure repair method and has been widely used in the composite material structure repair work. When carrying out patch repair on a composite material structure, it is required that the repaired structure has high static strength and good fatigue resistance. However, there are few studies on the fatigue damage analysis and life prediction of composite patch repair structures. Studying the fatigue life prediction method of the patch repair structure has certain engineering practical significance and good practical value. Summary of the Invention

[0004] The present invention combines the improved Hashin criterion, finite element analysis, strength degradation model, stiffness degradation model, and Camanho material parameter degradation model to establish a fatigue damage analysis method for composite laminates; uses this method to respectively carry out fatigue life prediction analysis on unperforated laminates and perforated laminates; compares the prediction results with the test results to verify the effectiveness of the established fatigue damage analysis method for composite laminates; on this basis, combines the composite material fatigue damage analysis method and cohesive elements to establish a fatigue life prediction model for the patch repair structure. The present invention takes the composite patch repair structure as the research object and proposes a fatigue life prediction method, which has certain engineering practical significance and good practical value.

[0005] The purpose of the present invention is to overcome the technical defects existing in the prior art, propose a fatigue life prediction method for a composite patch repair structure, combine the composite material fatigue damage analysis method and cohesive elements to establish a fatigue life prediction model for the patch repair structure, and achieve the purpose of predicting the fatigue life of the composite patch repair structure.

[0006] The present invention specifically adopts the following technical solutions: A fatigue life prediction method for a composite patch repair structure, comprising the following steps:

[0007] Step SS1: Establish a fatigue damage analysis method for composite laminates by combining the improved Hashin criterion, finite element analysis, strength degradation model, stiffness degradation model, and Camanho material parameter degradation model;

[0008] Step SS2: Use the method in Step SS1 to perform fatigue life prediction and analysis on unperforated laminates and perforated laminates respectively;

[0009] Step SS3: Compare the prediction results with the test results to verify the effectiveness of the established fatigue damage analysis method for composite laminates;

[0010] Step SS4: Combine the fatigue damage analysis method for composite laminates and cohesive elements to establish a fatigue life prediction model for the patch repair structure.

[0011] Further, in the above prediction method, Step SS1 specifically includes: In terms of failure judgment, the improved three-dimensional Hashin criterion is mainly adopted. The failure modes determined by this criterion are mainly divided into seven categories: fiber fracture fatigue failure, fiber compression fatigue failure, matrix cracking fatigue failure, matrix compression fatigue failure, matrix-fiber shear fatigue failure, interlaminar tensile fatigue failure, and matrix compression fatigue failure. This criterion introduces the remaining strength model into the original three-dimensional Hashin criterion. This improved Hashin criterion has good judgment and prediction for matrix and fiber fatigue damage.

[0012] Further, in the above prediction method, Step SS1 specifically further includes: The fatigue damage analysis process of the composite laminate is reflected in the material constitutive change process of the commercial software finite element analysis, realizing the simulation of the fatigue failure propagation and evolution in the composite laminate structure, and predicting the fatigue life of the structure. The corresponding calculation process is as follows: Establish a finite element model according to the loading, displacement constraints, material properties, geometric parameters, ply layup, etc. of the research object, and complete the initialization of material parameters; Increase the number of load cycles, establish a finite element equation, and solve to obtain the stress; Combine the calculated stress and the degraded strength parameters to perform fatigue failure judgment. If failure occurs, further reduce the stiffness according to the failure model. If no failure occurs, degrade the strength and stiffness according to the obtained stress and number of load cycles; Judge whether the structure fails, or whether the overall life reaches infinity. If the conditions are met, output the fatigue life of the structure. If not, continue to increase the number of cycles and repeat the previous steps until the fatigue life of the structure is output.

[0013] Furthermore, in the above prediction method, the step SS3 specifically includes: predicting the fatigue life of the unperforated laminate and the perforated laminate, and comparing with the test values. The results show that the predicted value of the fatigue life of the unperforated laminate is within twice the error band, and the predicted value of the fatigue life of the perforated laminate is within three times the error band, indicating that the established fatigue progressive damage method can be well applied to the fatigue analysis and life prediction of composite laminates.

[0014] Furthermore, in the above prediction method, the step SS4 specifically includes: The cohesive element is a phenomenological model developed by combining damage mechanics and linear elastic fracture mechanics, which can be well applied to the simulation of the adhesive layer in the composite adhesive repair structure, and the prediction results have high accuracy. As Figure 2 shown, the cohesive element is constructed by two corresponding surfaces of the upper and lower adhesive body units connected to it. The adhesive layer is generally thin, so the node distance on the upper and lower surfaces of the cohesive element is also very small. The crack propagation mode in the adhesive layer is as Figure 3 shown, and can be divided into: Mode I opening crack propagation, Mode II sliding crack propagation, and Mode III tearing crack propagation. For the cohesive element in the figure, the stress in the e3(n) direction initiates Mode I crack propagation, and the shear stresses in the e1(n) and e2(n) directions initiate Mode II and Mode III crack propagation. 8 nodes are taken at typical positions on the element, and each node has three degrees of freedom. Each group in the node combinations 1-5, 2-6, 3-7, 4-8 will generate a normal displacement component: δ n , and two in-plane shear displacement components: δ s , δ t . The three displacement components have three corresponding cohesive forces: t n , t s , t n .

[0015] Thus, the constitutive equation of the adhesive layer can be obtained as follows:

[0016]

[0017] In the formula, K nn , K ss , K tt are the stiffness coefficients of the adhesive layer, which can be calculated by the following formula:

[0018]

[0019] In the formula, E n is the elastic modulus of the adhesive layer, and T is the thickness of the adhesive layer.

[0020] Even further, in the above prediction method, the step SS4 specifically further includes: The adhesive layer failure criterion is defined as follows:

[0021]

[0022] In the formula, is the interfacial strength corresponding to the failure of the adhesive layer in three modes separately.

[0023] Furthermore, in the above prediction method, the step SS4 specifically further includes: The degradation model of the adhesive layer material parameters is shown as the following formula:

[0024]

[0025] In the formula, G1, G2, and G3 are the unit strain energies, and G 1C , G 2C , G 3C are the unit critical strain energy release rates.

[0026] Based on the above prediction method, the present invention also proposes a fatigue life prediction system for a composite patch repair structure, including:

[0027] 1) A model construction module, which combines the damaged structure, the patch structure, and the cohesive elements to construct a mathematical analysis model of the composite patch repair structure;

[0028] 2) A fatigue damage analysis module for the composite patch repair structure, which combines the established fatigue damage analysis method for the composite patch repair structure and the cohesive elements to establish a fatigue damage analysis model for the patch repair structure;

[0029] 3) A fatigue life prediction module for the composite patch repair structure, which uses the fatigue damage analysis module for the composite patch repair structure to simulate the fatigue failure propagation and evolution of the composite patch repair structure, and predict the fatigue life of the patch repair structure.

[0030] The beneficial effects achieved by the present invention: First, the present invention establishes a fatigue damage analysis method for the intact structure composite laminate. By comparing the fatigue life prediction value obtained by this method with the test value, the effectiveness of the method is verified; Second, in terms of the application object, different from the traditional prediction of the intact structure, the present invention conducts fatigue life prediction on the new structure after patching and repairing the damaged structure. Since new repair structures need to be introduced after the intact structure is damaged, and there is also a cementing cooperation relationship between the newly added repair structure and the damaged structure, the present invention combines the established fatigue damage analysis method for the intact structure composite laminate and the cohesive elements to establish a fatigue life prediction model for the patched and repaired structure after damage, and realizes the fatigue life prediction of the patched and repaired structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the flowchart of the fatigue life prediction method for the patch repair structure of the present invention;

[0032] Figure 2 It is a schematic diagram of the cohesion unit;

[0033] Figure 3 It is a schematic diagram of typical crack propagation;

[0034] Figure 4 It is a flowchart of progressive damage analysis during fatigue process;

[0035] Figure 5 It is a hole-free laminated plate for fatigue life prediction;

[0036] Figure 6 It is a finite element model of the hole-free laminated plate;

[0037] Figure 7 It is a comparison between the predicted value and the experimental value of the fatigue life of the hole-free laminated plate;

[0038] Figure 8 It is a specimen for tension-tension fatigue test;

[0039] Figure 9 It is a specimen for compression-compression fatigue test;

[0040] Figure 10 It is the tension-tension fatigue damage evolution under the 80%σ b working condition;

[0041] Figure 11 It is the tension-tension fatigue damage evolution under the 70%σ b working condition;

[0042] Figure 12 It is a comparison between the predicted value and the experimental value of the fatigue life under the compression-compression load of the perforated plate;

[0043] Figure 13 It is the compression-compression fatigue damage evolution under the 90%σ b working condition;

[0044] Figure 14 It is the compression-compression fatigue damage evolution under the 80%σ b working condition;

[0045] Figure 15 It is the compression-compression fatigue damage evolution under the 70%σ b working condition;

[0046] Figure 16 It is the compression-compression fatigue damage evolution under the 60%σ b working condition;

[0047] Figure 17 It is a schematic diagram of the dimensions of the patch repair structure. Specific implementation method

[0048] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below in combination with the specification drawings or specific implementation cases. It should be noted that some (but not all) of the disclosed examples are shown in the drawings. In fact, many different examples can be described and these examples should not be construed as limited to the examples set forth herein. On the contrary, these examples are described so as to more clearly demonstrate the positive effects of the present invention, and those parts not elaborated in detail in the text are regarded as well-known technologies or conventional technical means in the art.

[0049] Embodiment 1: A method for predicting the fatigue life of a composite patch repair structure, comprising the following steps:

[0050] Step SS1: Establish a fatigue damage analysis method for composite laminates by combining the improved Hashin criterion, finite element analysis, strength degradation model, stiffness degradation model, and Camanho material parameter degradation model;

[0051] Step SS2: Use the method in Step SS1 to perform fatigue life prediction analysis on unperforated laminates and perforated laminates respectively;

[0052] Step SS3: Compare the prediction results with the test results to verify the effectiveness of the established fatigue damage analysis method for composite laminates;

[0053] Step SS4: Combine the fatigue damage analysis method for composite laminates and cohesive elements to establish a fatigue life prediction model for the patch repair structure.

[0054] As a preferred embodiment, Step SS1 specifically includes: In terms of failure judgment, the improved three-dimensional Hashin criterion is mainly used. This criterion introduces the residual strength model into the original three-dimensional Hashin criterion. This improved Hashin criterion has better judgment and prediction for matrix and fiber fatigue damage.

[0055] As a preferred embodiment, the step SS1 specifically further includes: reflecting the fatigue damage analysis process of the composite laminate into the material constitutive change process of the commercial software finite element analysis, realizing the simulation of the fatigue failure propagation and evolution in the composite laminate structure, and predicting the fatigue life of the structure. The corresponding calculation process is as follows: establish a finite element model according to the loading, displacement constraints, material properties, geometric parameters, ply layup, etc. of the research object, and complete the initialization of material parameters; increase the number of load cycles, establish a finite element equation, and solve to obtain the stress; combine the calculated stress and the degraded strength parameters to judge fatigue failure. If failure occurs, further reduce the stiffness according to the failure model. If no failure occurs, degrade the strength and stiffness according to the obtained stress and the number of load cycles; judge whether the structure fails or the overall life reaches infinity. If the conditions are met, output the fatigue life of the structure. If not, continue to increase the number of cycles and repeat the previous steps until the fatigue life of the structure is output.

[0056] As a preferred embodiment, the step SS3 specifically includes: predicting the fatigue life of the unperforated laminate and the perforated laminate, and comparing it with the test values. The results show that the predicted fatigue life value of the unperforated laminate is within twice the error band, and the predicted fatigue life value of the perforated laminate is within three times the error band, indicating that the established fatigue progressive damage method can be well applied to the fatigue analysis and life prediction of composite laminates.

[0057] As a preferred embodiment, the step SS4 specifically includes: The cohesive element is a phenomenological model developed by combining damage mechanics and linear elastic fracture mechanics, and can be well applied to the simulation of the adhesive layer in the composite adhesive repair structure, and the prediction results have high accuracy. As Figure 2 shown, the cohesive element is constructed by two corresponding surfaces of the upper and lower bonded body units connected to it. The adhesive layer is generally thin, so the node distance on the upper and lower surfaces of the cohesive element is also very small. The crack propagation mode in the adhesive layer is as Figure 3 shown, and can be divided into: Mode I opening crack propagation, Mode II sliding crack propagation, and Mode III tearing crack propagation. For the cohesive element in the figure, the stress in the e3(n) direction initiates Mode I crack propagation, and the shear stresses in the e1(n) and e2(n) directions initiate Mode II and Mode III crack propagations. Each of the 8 nodes on the element has three degrees of freedom. Each group of node combinations 1-5, 2-6, 3-7, 4-8 will generate a normal displacement component: δ n , two in-plane shear displacement components: δ s , δ t . The three displacement components have three corresponding cohesive forces: t n , t s , t n .

[0058] The constitutive equation of the adhesive layer can be obtained as follows:

[0059]

[0060] In the formula, K nn , K ss , K tt are the stiffness coefficients of the adhesive layer and can be calculated by the following formula:

[0061]

[0062] In the formula, E n is the elastic modulus of the adhesive layer, and T is the thickness of the adhesive layer.

[0063] As a preferred embodiment, the step SS4 specifically further includes: the failure criterion of the adhesive layer is defined as follows:

[0064]

[0065] In the formula, are the interfacial strengths corresponding to the failure of the adhesive layer in three modes separately.

[0066] As a preferred embodiment, the step SS4 specifically further includes: the degradation model of the adhesive layer material parameters is shown in the following formula:

[0067]

[0068] In the formula, G1, G2, and G3 are the unit strain energies, and G 1C , G 2C , G 3C are the unit critical strain energy release rates.

[0069] The present invention proposes a fatigue life prediction method for a composite patch repair structure. As Figure 1 shown, this method is used to predict the fatigue life of the composite patch repair structure. First, a fatigue damage analysis method for the composite laminate is established, and the corresponding calculation process is as Figure 4 shown. The analysis process of this method is reflected in the change process of the material constitutive in the commercial software finite element analysis, realizing the simulation of the fatigue failure propagation and evolution in the composite laminate structure, and predicting the fatigue life of the structure. The analysis steps are as follows.

[0070] 1. Establish a finite element model according to the loading, displacement constraints, material properties, geometric parameters, layup, etc. of the research object, and complete the initialization of material parameters;

[0071] 2. Increase the number of load cycles, establish a finite element equation, and solve to obtain the stress;

[0072] 3. Combine the calculated stress and the degraded strength parameters to judge fatigue failure. If failure occurs, further reduce the stiffness according to the failure model. If no failure occurs, degrade the strength and stiffness according to the obtained stress and the number of load cycles.

[0073] 4. Judge whether the structure fails or the overall life reaches infinity. If the conditions are met, output the fatigue life of the structure. If not, continue to increase the number of cycles and repeat steps 2, 3, and 4 until the fatigue life of the structure is output.

[0074] In this embodiment, during the fatigue process stress analysis, under the action of fatigue loads, the material properties of the composite laminate structure degenerate due to cumulative fatigue damage. The decrease in stiffness causes the stiffness matrix to change, and the structure stress is redistributed. At the same time, the structure strength is degraded, and the regions that meet the failure judgment criteria after the degradation of stiffness and strength are damaged, and the fatigue damage region expands. Repeat this process until no new fatigue damage occurs. In each fatigue loading cycle, the stress analysis follows this iterative calculation process. As this calculation process is repeated continuously, until the entire structure loses its load-bearing capacity and is completely damaged.

[0075] In this embodiment, the degradation of material properties during the fatigue process mainly includes two parts: the degradation of strength and stiffness before failure, and the stiffness reduction after failure. Before failure, the material accumulates fatigue damage under the continuous action of fatigue loads, and parameters such as material strength and stiffness decrease continuously. After failure, that is, when the structure is considered to have lost its load-bearing capacity, the material parameters are reduced according to the failure mode. The specific reduction method uses the Camanho degradation model. The Camanho degradation model directly reduces the corresponding stiffness to a few tenths of the original according to different failure modes, with high calculation efficiency and can reflect the actual failure behavior of the material to a certain extent. Therefore, the present invention adopts the Camanho degradation model, and its specific degradation method is as follows:

[0076] Fiber tensile failure: The damaged element completely loses its load-bearing capacity, and the degradation method of material parameters is: E1, E2, E3, G 12 、G 13 、G S3 、v 12 、v 13 、v 23 Reduced to 0.07 times the initial value.

[0077] Fiber compression failure: The damaged element completely loses its load-bearing capacity, and the degradation method of material parameters is: E1, E2, E3, G 12 、G 13 、G 23 、v 12 、v 13 、v 23Reduced to 0.14 times the initial value.

[0078] Matrix tensile failure: The damaged element loses its lateral load-bearing capacity, and the material parameter degradation method is: E2, G 12 、G 23 Reduced to 0.2 times the initial value.

[0079] Matrix compressive failure: The damaged element loses its lateral load-bearing capacity, and the material parameter degradation method is: E2, G 12 、G 23 Reduced to 0.4 times the initial value.

[0080] Matrix-fiber shear failure: The damaged element loses its shear load-bearing capacity, and the material parameter degradation method is: G 12 、v 12 Reduced to 0.

[0081] Delamination tensile or compressive failure: The damaged element loses its normal load-bearing capacity, and the material parameter degradation method is: E3, G 13 、G 23 、v 13 、v 23 Reduced to 0.

[0082] During the calculation process, to prevent the stiffness matrix from being singular, the situation where the material properties degrade to 0 is replaced by degrading to a very small value, which is taken as 1.0×10 in this invention -6 。

[0083] In this embodiment, the fatigue failure criterion is mainly used to judge the failure of the composite laminate under fatigue load. If the criterion is met, it is considered that the element has fatigue failure. Tserpes et al. widely introduced the residual strength model into the three-dimensional Hashin criterion, and the results showed that this modified Hashin criterion has good judgment and prediction for matrix and fiber fatigue damage. This invention mainly uses the improved form of the fatigue damage criterion proposed by Tserpes to judge the fatigue damage failure of the composite structure. The judgment expressions for each failure mode are as follows:

[0084] Fiber tensile fatigue failure (σ1>0):

[0085]

[0086] Fiber compressive fatigue failure (σ1<0):

[0087]

[0088] Matrix tensile fatigue failure (σ2>0):

[0089]

[0090] Matrix compressive fatigue failure (σ2 < 0):

[0091]

[0092] Matrix-fiber shear fatigue failure (σ1 < 0):

[0093]

[0094] Delamination tensile fatigue failure (σ3 > 0):

[0095]

[0096] Delamination compressive fatigue failure (σ3 < 0):

[0097]

[0098] In Equations (1) to (7), σ 11 , σ 22 , σ 33 , τ 12 , τ 13 , τ 23 are the normal stresses and shear stresses in each direction of the composite laminate. X T (n, R, σ), X C (n, R, σ) are the residual tensile strength and residual compressive strength of the fiber, Y T (n, R, σ), Y C (n, R, σ) are the residual tensile strength and residual compressive strength of the matrix, Z T (n, σ, σ), Z C (n, R, σ) are the residual tensile strength and residual compressive strength in the normal thickness direction, S 12 (n, R, σ), S 13 (n, R, σ), S 23 (n, R, σ) are the residual shear strength. When the stress level at any point within the composite laminate satisfies one of Equations (1) to (7), it is considered that fatigue failure of the corresponding mode occurs at that point, and then the material stiffness is reduced according to the corresponding mode.

[0099] The unperforated laminate for fatigue life prediction in this embodiment is as Figure 5 shown. Combining the fatigue progressive damage analysis method described above, its life is predicted. This unidirectional laminate uses AS4 / 3501-6 composite material, the number of plies of the laminate is 16, and the ply sequence is

[30] 16 .

[0100] Its finite element model is as Figure 6As shown, the model uses three-dimensional solid elements, and a total of 1326 elements are divided. The left end of the unperforated plate is fixed, and tensile fatigue loads of 80%, 75%, 70%, 65%, 60%, and 55% of the static strength σ b are applied to the right end, the stress ratio R is 0.1, and the final failure criterion is that large-area matrix damage occurs in the plate. The comparison between the predicted values and the test values is as Figure 7 shown in and Table 1:

[0101] Table 1 Comparison between the predicted values and the test values of the tensile-tensile fatigue life of the

[30] 16 ply unidirectional laminate under different stress levels

[0102]

[0103]

[0104] From Figure 7 and Table 1, it can be seen that for the unperforated unidirectional laminate, compared with the test values, the predicted values all fall within twice the error band.

[0105] The perforated laminate for which fatigue life prediction is carried out in this embodiment is as Figure 8 and Figure 9 shown, and the material is AS4 / 3501-6. Thomas carried out tensile-tensile fatigue tests on the perforated laminate using Figure 8 , with a stress ratio R = 0.1, and carried out compressive-compressive fatigue tests on the perforated plate in Figure 9 , with a stress ratio R = 10. Among them, the ply sequence of the tensile-tensile fatigue specimen is [0 / 45 / -45 / 90] 3s , and the ply sequence of the compressive-compressive fatigue specimen is [0 / 45 / -45 / 90] 4s . The thickness of each ply in the tensile-tensile fatigue specimen and the compressive-compressive fatigue specimen is 0.146 mm, and the diameter D of the middle damage hole is 6.35 mm. Using the fatigue progressive damage analysis method established above, the tensile-tensile and compressive-compressive fatigue life damage analysis and life prediction of the perforated plate are carried out in the commercial software ABAQUS.

[0106] The left end of the specimen is fixed. For the right end of the tensile-tensile fatigue specimen, fatigue tensile loads of 80% and 70% of the tensile static strength σ b are applied. For the right end of the compressive-compressive fatigue specimen, fatigue compressive loads of 80%, 70%, and 60% of the compressive static strength σ b are applied. For the tensile-tensile fatigue specimen, its failure criterion is that fiber fracture fatigue failure propagates from the hole edge to the edge of the plate; for the compressive-compressive fatigue specimen, its failure criterion is that fiber compressive fatigue failure propagates from the hole edge to the edge of the plate.

[0107] The calculation results of the tension-tension fatigue specimens and the Thomas test results are compared in Table 2 and Figure 10 and Figure 11 as shown below:

[0108] Table 2 Comparison between predicted and experimental tension-tension fatigue life

[0109]

[0110]

[0111] It can be seen from Table 2 that at the load levels of 80%σ b and 70%σ b , the tension-tension fatigue test life of the specimens has all exceeded 1×10 6 . When the simulation cycle number exceeds 1×10 6 , the laminate has not been completely damaged yet. Figure 10 and 11 The results also show that no fatigue damage has occurred in the 0° ply. A small number of fatigue failure elements are generated at the initial moment of fatigue load application for the 45° and -45° plies. As the fatigue load continues to act, only a small number of failure elements are extended by the time of 1×10 6 cycles. For the 90° ply, under the 80%σ b condition, the entire ply is damaged when the maximum fatigue load is first reached. Under the 70%σ b condition, at the initial moment, there are a large number of failure elements at the hole edge. As the fatigue load continues to act, all the elements are damaged when the cycle number exceeds 1×10 6 cycles.

[0112] The fatigue progressive damage calculation of the compression-compression fatigue specimens and the Thomas test results are compared in Table 3 as follows:

[0113] Table 3 Comparison between predicted and experimental compression-compression fatigue life

[0114]

[0115] It can be seen from Table 3 and Figure 12 that compared with the experimental values, most of the results predicted by the fatigue progressive damage model under the compression-compression fatigue condition fall within the three-fold error band. The fatigue damage of the laminate under each condition is as shown in Figure 13 and Figure 14 and Figure 15 and Figure 16As shown. It can be seen from the figure that after the fatigue life of the laminate reaches the limit, the fatigue damage elements of the 0° ply under the compression-compression fatigue condition are often more than those of other plies. Compared with the tension-tension fatigue load, in the initial stage of fatigue loading, relatively more fatigue damage elements are generated in the 90° ply of the structure. Under the compression-compression fatigue load, relatively more damage elements are generated in the 0° ply in the initial stage of fatigue load loading. Under the compression-compression fatigue load, for 70%σ b 、80%σ b 、90%σ b load levels, the 0° ply fails first. Under the 60%σ b load level, that is, after 1×10 6 cycles, the test piece was artificially damaged and the test stopped. The simulation results show that after 1×10 6 cycles, a small number of damage elements are generated at the hole edge of the 0° ply, and a large number of failure elements are generated in other plies, and it is not completely damaged.

[0116] The calculation results of the above two examples show that the fatigue progressive damage analysis method established by the present invention has good prediction accuracy for the fatigue life of perforated and non-perforated laminates, and can be applied to the fatigue life prediction of composite laminates.

[0117] Combined with the fatigue progressive damage analysis method and cohesive elements, a fatigue life prediction model for the patch repair structure is established. The geometric dimensions of the repair structure are as Figure 17 shown. In this model, the patch and the parent plate both use AS4 / 3501-6 material, and the adhesive layer part uses J-159 material. The parent plate is 152.4 mm long, 38.1 wide, and 3.504 thick, and the ply sequence is [0 / 45 / -45 / 90] 3s , the thickness of each ply of the patch is the same as that of the parent plate, and its ply sequence is [0 / 0 / 0 / 0]. The radius of the patch is 10 mm, and a hole representing damage is reserved in the middle of the parent plate, and its radius is 5 mm.

[0118] It can be seen that the present invention proposes a fatigue life prediction method for a composite patch repair structure. By combining the composite fatigue damage analysis method and cohesive elements, a fatigue life prediction model for the patch repair structure is established to achieve the purpose of predicting the fatigue life of the composite patch repair structure.

[0119] In the specific implementation process, in order to more quickly and simply implement the above-mentioned fatigue life prediction method for the composite patch repair structure, the present invention also provides the following implementable structures:

[0120] A fatigue life prediction system for a composite patch repair structure, the prediction system includes the following functional modules: a fatigue damage analysis module for composite laminates, which establishes a fatigue damage analysis for composite laminates by comprehensively improving the Hashin criterion, finite element analysis, strength degradation model, stiffness degradation model, and Camanho material parameter degradation model;

[0121] A fatigue life prediction module for composite laminates, which uses the fatigue damage analysis module for composite laminates to perform fatigue life prediction and analysis on unperforated laminates and perforated laminates respectively;

[0122] A verification module, which compares the prediction results of the fatigue life prediction module for composite laminates with the test results to verify the effectiveness of the established fatigue damage analysis method for composite laminates;

[0123] A fatigue life prediction module for the patch repair structure, which combines the fatigue damage analysis method for composite laminates and cohesive elements to complete the fatigue life prediction of the patch repair structure.

[0124] The prediction method proposed above in the present invention can also be implemented by a computer device, and the device includes

[0125] A memory for storing executable computer programs;

[0126] A processor, connected to the memory, for retrieving and executing the computer program to implement the fatigue life prediction method for the composite patch repair structure as described above.

[0127] Those skilled in the art should understand that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes.

[0128] The present application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, as well as the combination of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processors of general-purpose computers, special-purpose computers, embedded processors, or other programmable data processing devices to generate a machine, so that the instructions executed by the processors of the computer or other programmable data processing devices generate for implementing in the process Figure 1 one process or multiple processes and / or blocksFigure 1 a device for the functions specified in one or more boxes. These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including an instruction device that implements in the process Figure 1 one process or multiple processes and / or boxes Figure 1 a device for the functions specified in one or more boxes. These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to produce a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one process or multiple processes and / or boxes Figure 1 a device for the functions specified in one or more boxes.

[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the specific implementation manners of the present invention can still be modified or equivalently replaced, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A method for predicting fatigue life of a composite material patch repair structure, characterized in that: The steps include: Step SS1: Establish a fatigue damage analysis method for composite laminates by combining the improved Hashin criterion, finite element analysis, strength degradation model, stiffness degradation model, and Camanho material parameter degradation model; Step SS2: using the method in step SS1 to perform fatigue life prediction analysis on the non-porous laminate and the porous laminate respectively; Step SS3: Compare the prediction results with the test results to verify the effectiveness of the established composite laminate fatigue damage analysis method; Step SS4: Combining the fatigue damage analysis method of composite laminates and the cohesive force unit, a fatigue life prediction model for the patch repair structure is established.

2. The fatigue life prediction method of a composite material patch repair structure according to claim 1, characterized in that: The step SS1 specifically includes: using the improved three-dimensional Hashin criterion to complete failure judgment, and the failure modes determined by the criterion are divided into seven categories: fiber fracture fatigue failure, fiber compression fatigue failure, matrix cracking fatigue failure, matrix compression fatigue failure, matrix fiber shear fatigue failure, interlayer tensile fatigue failure, and matrix compression fatigue failure; this criterion introduces the residual strength model into the original three-dimensional Hashin criterion to realize the judgment and prediction of matrix and fiber fatigue damage.

3. The fatigue life prediction method of a composite material patch repair structure according to claim 1, characterized in that: The step SS1 specifically also includes: the fatigue damage analysis process of the composite laminate is reflected in the material constitutive change process of the commercial software finite element analysis, so as to simulate the fatigue failure extension evolution in the composite laminate structure and predict the fatigue life of the structure. The corresponding calculation process is: according to the load, displacement constraint, material properties, geometric parameters, and ply conditions of the research object, a finite element model is established to complete the material parameter initialization; the number of load cycles is increased, the finite element equation is established, and the stress is obtained by solving; fatigue failure judgment is performed based on the calculated stress and the degraded strength parameters. If failure occurs, the stiffness is further reduced according to the failure model. If failure occurs, the strength and stiffness are degraded according to the obtained stress and the number of load cycles; it is judged whether the structure fails or the overall life reaches infinity. If the conditions are met, the fatigue life of the structure is output. If not, the number of cycles is continued to be increased, and the previous steps are repeated until the fatigue life of the structure is output.

4. The fatigue life prediction method of a composite material patch repair structure according to claim 1, characterized in that: The step SS3 specifically includes: predicting the fatigue life of non-porous laminates and porous laminates, and comparing them with the test values. If the fatigue life prediction value of the non-porous laminate is within a twice error band with the test value, and the fatigue life prediction value of the porous laminate is within a three times error band with the test value, it indicates that the established fatigue asymptotic damage method can be well applied to the fatigue analysis and life prediction of composite laminates, and it is judged that the fatigue damage analysis method of composite laminates is effective, otherwise it is invalid.

5. The fatigue life prediction method of a composite material patch repair structure according to claim 1, characterized in that: In step SS4: the cohesive force unit is constructed by two corresponding surfaces of the upper and lower adhesive body units connected thereto, and the adhesive layer is generally thin, so the node distance on the upper and lower surfaces of the cohesive force unit is also very small; the crack propagation modes in the adhesive layer are divided into: type I opening crack propagation, type II sliding crack propagation, and type III tearing crack propagation; in the cohesive force unit, the stress in the e3(n) direction triggers type I crack propagation, and the shear stress in the e1(n) and e2(n) directions triggers type II and III crack propagation; Take 8 nodes at typical locations on the element, each node has three degrees of freedom, and each of the node combinations 1-5, 2-6, 3-7, 4-8 will produce a normal displacement component: δ n , two in-plane shear displacement components: δ s , δ t ; The three displacement components have three corresponding cohesion forces: t n , t s , t n ; The constitutive equation of the glue layer can be obtained as follows: In the formula, K nn , k ss , k tt is the stiffness coefficient of the adhesive layer, which can be calculated by the following formula: In the formula, E n is the elastic modulus of the adhesive layer, and T is the thickness of the adhesive layer.

6. The fatigue life prediction method of a composite material patch repair structure according to claim 5, characterized in that: In step SS4: the adhesive layer fails in three modes alone, and the corresponding interface strengths are: The failure criterion of the adhesive layer adopts the secondary strength criterion in the form of relative displacement, which is defined as follows: In the formula, It is the interface strength corresponding to the three failure modes of the adhesive layer alone.

7. The fatigue life prediction method of a composite material patch repair structure according to claim 6, characterized in that: In step SS4, under the three crack extension modes, the strain energy release rate of the unit satisfies the critical strain energy release rate of a certain crack, and the corresponding crack extension occurs; the secondary energy criterion is used as the adhesive layer degradation model, as shown in the following formula: In the formula, G1, G2, G3 are unit strain energies, G 1C , G 2C , G 3C is the critical strain energy release rate of the unit.

8. A fatigue life prediction system for composite material patch repair structures, characterized in that: The prediction system includes the following functional modules: 1) Model building module, combining the damaged structure, patch structure and cohesive force unit to build a mathematical analysis model of the composite material patch repair structure; 2) Composite material patch repair structure fatigue damage analysis module, which combines the established composite material patch repair structure fatigue damage analysis method and cohesive force unit to establish a patch repair structure fatigue damage analysis model; 3) Composite material patched and repaired structure fatigue life prediction module, which uses the composite material patched and repaired structure fatigue damage analysis module to simulate the fatigue failure propagation evolution of the composite material patched and repaired structure, and predict the fatigue life of the patched and repaired structure.

9. A computer device implementation, characterized in that: The device comprises: a memory for storing executable computer programs; A processor is connected to the memory and is used to retrieve and execute the computer program to implement the fatigue life prediction method for a composite material patch repair structure as described in any one of claims 1 to 7.

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