A method and system for predicting the constant amplitude fatigue life of a woven ceramic matrix composite

Abstract

The application provides a braided ceramic matrix composite equal-amplitude fatigue life prediction method and system, wherein the method considers two important factors of internal fiber bundle composite material friction and wear of the braided ceramic matrix composite, simulates a fatigue damage process of the braided ceramic matrix composite under equal-amplitude cyclic load from the perspective of interface wear degradation of the fiber bundle composite material; in combination with an interface slip model and an interface shear stress degradation model of the fiber / binder in the fiber bundle composite material, cumulative slip distance and cumulative stress between the fiber / binder are introduced, and high-precision fatigue life prediction of the braided ceramic matrix composite is realized.

Description

Technical Field

[0001] This invention belongs to the field of fatigue life prediction technology for composite materials, and particularly relates to a method and system for predicting the constant amplitude fatigue life of braided ceramic matrix composite materials. Background Technology

[0002] Complex woven ceramic matrix composites possess excellent properties such as high specific strength, high specific modulus, high temperature resistance, corrosion resistance, and low density, making them widely needed in high-temperature protection systems for aerospace vehicles. During their service life, these materials gradually suffer component damage and even failure due to factors such as loads and the environment, with fatigue damage being one of the main failure modes. This fatigue failure poses a significant threat to aircraft and is a common failure mode in aircraft protection system structures. Therefore, accurately predicting the fatigue life of complex woven ceramic matrix composites is crucial for eliminating potential hazards, developing health repair plans, and extending service life.

[0003] The application of ceramic matrix composites in aero-engines primarily addresses the issue of predicting their strength and lifespan under fatigue loads. Currently, traditional fatigue life prediction methods and models are mainly used for metallic materials; no mature fatigue life prediction method has been developed for complex braided ceramic matrix composites. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a method and system for predicting the constant amplitude fatigue life of woven ceramic matrix composites.

[0005] In a first aspect, the present invention provides a method for predicting the constant-amplitude fatigue life of braided ceramic matrix composites, comprising:

[0006] Construct a unit cell finite element model of braided ceramic matrix composites;

[0007] Obtain the relative cumulative slip distance and cumulative stress between fibers and matrix in the braided ceramic matrix composite during the current cycle;

[0008] The fiber / matrix interface shear stress in the current cycle is determined based on the relative cumulative slip distance between the fiber and the matrix.

[0009] The coefficient of friction between fiber bundle composite materials in the current cycle is determined based on the cumulative stress between the fiber and the matrix.

[0010] Obtain the initial displacement values ​​of each node in the unit cell finite element model of the braided ceramic matrix composite material under a given strain load;

[0011] The stiffness matrix of each fiber bundle interface element in the unit cell finite element model is constructed based on the shear stress at the fiber / matrix interface, the friction coefficient between fiber bundle composite materials, and the initial values ​​of displacement at each node within the current cycle.

[0012] The overall stiffness matrix of the unit cell finite element model is constructed based on the stiffness matrices of the interface elements of each fiber bundle in the unit cell finite element model.

[0013] Apply periodic displacement boundary conditions to transform and reduce the total stiffness matrix of the unit cell finite element model in order to determine the displacement increment of each free node in the unit cell finite element model.

[0014] The displacement increments of all nodes are determined based on the displacement increments of each free node.

[0015] The displacement increment of each node is added to the displacement of each node in the current period to obtain the updated displacement of each node.

[0016] The stress of each fiber bundle interface element is determined based on the updated node displacements.

[0017] Determine whether the updated displacement vectors of each node are all less than the set threshold;

[0018] If they are not all less than the set threshold, the stiffness matrix of each fiber bundle interface element in the unit cell finite element model is reconstructed based on the fiber / matrix interface shear stress, the friction coefficient between fiber bundle composite materials and the initial value of each node displacement in the current cycle.

[0019] If all values ​​are less than the set threshold, then determine whether the stress of each fiber bundle interface unit is greater than the fiber strength.

[0020] If the strength is greater than the fiber strength, the braided ceramic matrix composite is determined to have failed as a whole, and the number of cycles N corresponding to the current cycle is taken as the fatigue life of the braided ceramic matrix composite.

[0021] If the strength is not greater than the fiber strength, then increase the cycle number N corresponding to the current cycle by n cycles; where one cycle is one period.

[0022] Determine if the N+n loops are greater than or equal to the preset maximum number of loops;

[0023] If the number of cycles is not greater than or equal to the preset maximum number of cycles, the cycle corresponding to the N+nth cycle will be taken as the current cycle, and the relative cumulative slip distance and cumulative stress between the fibers and matrix of the braided ceramic matrix composite material will be obtained again.

[0024] If the maximum number of cycles is greater than or equal to the preset maximum number of cycles, then the preset maximum number of cycles will be used as the fatigue life of the braided ceramic matrix composite material.

[0025] Further, determining the fiber / matrix interface shear stress within the current cycle based on the relative cumulative slip distance between the fiber and matrix includes:

[0026] The fiber / matrix interface shear stress τ in the Nth period is calculated using the following formula. i (N):

[0027]

[0028] in, denoted as the initial shear stress at the fiber / matrix interface before fatigue begins; e is the natural constant; ω is the numerical value of the relationship between the relative cumulative slip distance ∑δ between the fiber and the matrix and the shear stress; λ is the stable value of ∑δ as a function of the number of cycles. This represents the final steady-state shear stress at the fiber / matrix interface during the fatigue process.

[0029] Further, determining the inter-fiber bundle composite friction coefficient within the current cycle based on the cumulative stress between the fiber and matrix includes:

[0030] The coefficient of friction μ(N) between fiber bundle composite materials in the Nth cycle is calculated using the following formula:

[0031]

[0032] Where μ0 is the friction coefficient between fiber bundle composite materials before fatigue begins; e is the natural constant; μ ∞ ω1 is the final steady-state coefficient between fiber bundle composite materials during fatigue; ω1 is the fitting parameter for the friction coefficient as a function of the number of cycles; and λ1 is the fitting parameter for the number of experimental cycles.

[0033] Furthermore, the application of periodic displacement boundary conditions to transform and reduce the overall stiffness matrix of the unit cell finite element model to determine the displacement increments of each free node in the unit cell finite element model includes:

[0034] Construct the boundary condition expression for periodic displacement:

[0035]

[0036] Among them, u j+ The displacement of the boundary surface perpendicular to the positive x-axis; u j- This represents the displacement of the boundary surface perpendicular to the negative x-axis. Δx represents the average strain per unit cell; Δx is the coordinate difference between relative points.

[0037] Furthermore, the step of constructing the stiffness matrix of each fiber bundle interface element in the unit cell finite element model based on the fiber / matrix interface shear stress, the friction coefficient between fiber bundle composite materials, and the initial values ​​of displacement at each node within the current period includes:

[0038] The stiffness matrix K of each fiber bundle interface element in the unit cell finite element model is constructed. m expression:

[0039] K m =F m / dm ;

[0040] Among them, F m d is the nodal force matrix; m Let be the nodal displacement matrix.

[0041] Secondly, the present invention provides a constant-amplitude fatigue life prediction system for braided ceramic matrix composite materials, comprising:

[0042] The first building module is used to build a unit cell finite element model of the braided ceramic matrix composite material;

[0043] The first acquisition module is used to acquire the relative cumulative slip distance and cumulative stress between the fibers and matrix of the braided ceramic matrix composite material in the current cycle;

[0044] The first determining module is used to determine the fiber / matrix interface shear stress in the current cycle based on the relative cumulative slip distance between the fiber and the matrix.

[0045] The second determining module is used to determine the friction coefficient between fiber bundle composite materials in the current cycle based on the cumulative stress between the fiber and the matrix.

[0046] The second acquisition module is used to acquire the initial values ​​of the displacements of each node in the unit cell finite element model of the braided ceramic matrix composite material under a given strain load.

[0047] The second construction module is used to construct the stiffness matrix of each fiber bundle interface element in the unit cell finite element model based on the fiber / matrix interface shear stress, the friction coefficient between fiber bundle composite materials and the initial values ​​of each node displacement in the current cycle.

[0048] The third construction module is used to construct the total stiffness matrix of the unit cell finite element model based on the stiffness matrix of each fiber bundle interface element of the unit cell finite element model.

[0049] The third determination module is used to apply periodic displacement boundary conditions and transform and reduce the total stiffness matrix of the unit cell finite element model in order to determine the displacement increment of each free node in the unit cell finite element model.

[0050] The fourth determining module is used to determine the displacement increment of all nodes based on the displacement increment of each free node;

[0051] The displacement update module is used to add the displacement increment of each node to the displacement of each node in the current period to obtain the updated displacement of each node.

[0052] The fifth determination module is used to determine the stress of each fiber bundle interface element based on the updated displacement of each node;

[0053] The first judgment module is used to determine whether the updated displacement vectors of each node are all less than the set threshold.

[0054] The fourth construction module is used to reconstruct the stiffness matrix of each fiber bundle interface element in the unit cell finite element model based on the fiber / matrix interface shear stress, the friction coefficient between fiber bundle composite materials, and the initial value of each node displacement in the current period, when the first judgment module determines that the updated node displacement vectors are not all less than the set threshold.

[0055] The second judgment module is used to determine whether the stress of each fiber bundle interface unit is greater than the fiber strength when the first judgment module determines that the updated displacement vectors of each node are all less than the set threshold.

[0056] The sixth determining module is used to determine the overall failure of the braided ceramic matrix composite material when the stress of each fiber bundle interface unit is greater than the fiber strength as determined by the second determining module, and to take the cycle number N corresponding to the current cycle as the fatigue life of the braided ceramic matrix composite material.

[0057] The cycle number increment module is used to increase the cycle number N corresponding to the current cycle by n cycles if the second judgment module determines that the stress of each fiber bundle interface unit is not greater than the fiber strength; where one cycle is one period.

[0058] The third judgment module is used to determine whether the N+n loops are greater than or equal to the preset maximum number of loops;

[0059] The third acquisition module is used to take the period corresponding to the N+nth cycle as the current cycle and reacquire the relative cumulative slip distance and cumulative stress between the fibers and matrix of the braided ceramic matrix composite material when the third judgment module determines that the N+n cycles are not greater than or equal to the preset maximum number of cycles.

[0060] The seventh determination module is used to determine the fatigue life of the braided ceramic matrix composite material when the third judgment module determines that N+n cycles are greater than or equal to the preset maximum number of cycles.

[0061] Furthermore, the first determining module includes:

[0062] The first calculation unit is used to calculate the fiber / matrix interface shear stress τ in the Nth cycle according to the following formula. i (N):

[0063]

[0064] in, denoted as the initial shear stress at the fiber / matrix interface before fatigue begins; e is the natural constant; ω is the numerical value of the relationship between the relative cumulative slip distance ∑δ between the fiber and the matrix and the shear stress; λ is the stable value of ∑δ as a function of the number of cycles. This represents the final steady-state shear stress at the fiber / matrix interface during the fatigue process.

[0065] Furthermore, the second determining module includes:

[0066] The second calculation unit is used to calculate the friction coefficient μ(N) between fiber bundle composite materials in the Nth cycle according to the following formula:

[0067]

[0068] Where μ0 is the friction coefficient between fiber bundle composite materials before fatigue begins; e is the natural constant; μ ∞ ω1 is the final steady-state coefficient between fiber bundle composite materials during fatigue; ω1 is the fitting parameter for the friction coefficient as a function of the number of cycles; and λ1 is the fitting parameter for the number of experimental cycles.

[0069] Furthermore, the third determining module includes:

[0070] The first building block is used to construct the expression for the periodic displacement boundary conditions:

[0071]

[0072] Among them, u j+ The displacement of the boundary surface perpendicular to the positive x-axis; u j- This represents the displacement of the boundary surface perpendicular to the negative x-axis. Δx represents the average strain per unit cell; Δx is the coordinate difference between relative points.

[0073] Furthermore, the second building module includes:

[0074] The second building block is used to construct the stiffness matrix K of each fiber bundle interface element in the unit cell finite element model. m expression:

[0075] K m =F m / d m ;

[0076] Among them, F m d is the nodal force matrix; m Let be the nodal displacement matrix.

[0077] This invention provides a method and system for predicting the fatigue life of braided ceramic matrix composites under constant amplitude cyclic loading. The method considers two important factors: friction and wear between the fiber bundles within the braided ceramic matrix composite. It simulates the fatigue damage process of the braided ceramic matrix composite under constant amplitude cyclic loading from the perspective of interfacial wear degradation between the fiber bundles. By combining the fiber / matrix interfacial slip model and the fiber / matrix interfacial shear stress degradation model in the fiber bundle composite, and introducing the cumulative slip distance and cumulative stress between the fibers and the matrix, high-precision prediction of the fatigue life of the braided ceramic matrix composite is achieved. The life prediction model used in this invention employs a micromechanical model, calculated based on experimental results of fiber bundle composites at corresponding temperatures. This model can accurately reflect the damage condition inside the braided material, and the predicted fatigue life is within four times the dispersion band, meeting the fatigue life design requirements of aero-engine structural components. Attached Figure Description

[0078] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0079] Figure 1 A flowchart illustrating a method for predicting the constant amplitude fatigue life of braided ceramic matrix composites provided in an embodiment of the present invention;

[0080] Figure 2 The embodiment of the present invention provides a finite element model diagram of a 2D braided ceramic matrix composite unit cell;

[0081] Figure 3 The fatigue SN curve provided for embodiments of the present invention;

[0082] Figure 4 This is a divergence curve diagram for fatigue life prediction provided in an embodiment of the present invention;

[0083] Figure 5 This is a schematic diagram of a braided ceramic matrix composite constant amplitude fatigue life prediction system provided in an embodiment of the present invention. Detailed Implementation

[0084] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0085] The target structure of this invention is any one of the (2D, 2.5D and 3D) braided type unit cell structures. This invention uses a 2D braided type unit cell as an example for illustration.

[0086] Fatigue tests were conducted on fiber bundle composite materials, and the data are shown in Table 1. Figure 3 As shown, the curve of fatigue hysteresis secant stiffness as a function of the number of cycles is obtained. By establishing the mapping relationship between the hysteresis secant stiffness obtained from experiments and numerical simulations, the relationship of interface shear stress as a function of the number of cycles and the degradation formula of the friction coefficient between fiber bundle composite materials are indirectly obtained.

[0087] Table 1 Fatigue test data

[0088]

[0089] In one embodiment, such as Figure 1 As shown, this embodiment of the invention provides a method for predicting the constant-amplitude fatigue life of braided ceramic matrix composites, including:

[0090] Step 101: Construct a unit cell finite element model of the braided ceramic matrix composite material.

[0091] like Figure 2 As shown, a unit cell finite element model of braided ceramic matrix composite material was constructed using ANSYS APDL.

[0092] Step 102: Obtain the relative cumulative slip distance and cumulative stress between the fibers and matrix of the braided ceramic matrix composite material in the current cycle.

[0093] The relative cumulative slip distance ∑δ between the fiber and the matrix is ​​obtained from experimental measurements, while the cumulative stress ∑σ can be obtained directly from the results of each simulation calculation.

[0094] The values ​​of each empirical parameter in the interface shear stress degradation formula were determined by fitting experimental data.

[0095] By conducting linear reciprocating friction tests on fiber bundle composites, the friction coefficient and wear law between fiber bundle composites in braided ceramic matrix composites were measured, thereby determining the values ​​of each parameter in the friction coefficient degradation model between fiber bundle composites.

[0096] Step 103: Determine the fiber / matrix interface shear stress in the current cycle based on the relative cumulative slip distance between the fiber and the matrix.

[0097] For example, the fiber / matrix interface shear stress τ in the Nth cycle is calculated according to the following formula. i (N):

[0098]

[0099] in, denoted as the initial shear stress at the fiber / matrix interface before fatigue begins; e is the natural constant; ω is the numerical value of the relationship between the relative cumulative slip distance ∑δ between the fiber and the matrix and the shear stress; λ is the stable value of ∑δ as a function of the number of cycles. This represents the final steady-state shear stress at the fiber / matrix interface during the fatigue process.

[0100] Step 104: Determine the friction coefficient between fiber bundle composite materials in the current cycle based on the cumulative stress between the fiber and the matrix.

[0101] For example, the coefficient of friction μ(N) between fiber bundle composite materials in the Nth cycle is calculated according to the following formula:

[0102]

[0103] Where μ0 is the friction coefficient between fiber bundle composite materials before fatigue begins; e is the natural constant; μ ∞ ω1 is the final steady-state coefficient between fiber bundle composite materials during fatigue; ω1 is the fitting parameter for the friction coefficient as a function of the number of cycles; and λ1 is the fitting parameter for the number of experimental cycles.

[0104] Step 105: Obtain the initial displacement values ​​of each node in the unit cell finite element model of the braided ceramic matrix composite material under a given strain load.

[0105] Step 106: Construct the stiffness matrix of each fiber bundle interface element in the unit cell finite element model based on the fiber / matrix interface shear stress, the friction coefficient between fiber bundle composite materials, and the initial values ​​of each node displacement within the current cycle.

[0106] The stiffness matrix of each element is derived from the principle of virtual displacement, which leads to the nodal force matrix F. m and nodal displacement matrix d m The relationship is obtained. For example, the stiffness matrix K of each fiber bundle interface element in the unit cell finite element model is constructed. m expression:

[0107] K m =F m / d m .

[0108] Step 107: Construct the overall stiffness matrix of the unit cell finite element model based on the stiffness matrices of the interface elements of each fiber bundle in the unit cell finite element model.

[0109] The global stiffness matrix is ​​formed by superimposing each element in the stiffness matrix of each element according to its subscript, and this superposition must be performed in the same global coordinate system.

[0110] Step 108: Apply periodic displacement boundary conditions to transform and reduce the total stiffness matrix of the unit cell finite element model in order to determine the displacement increment of each free node in the unit cell finite element model.

[0111] For example, this step includes:

[0112] Construct the boundary condition expression for periodic displacement:

[0113]

[0114] Among them, u j+ The displacement of the boundary surface perpendicular to the positive x-axis; u j- This represents the displacement of the boundary surface perpendicular to the negative x-axis. Δx represents the average strain per unit cell; Δx is the coordinate difference between relative points.

[0115] Step 109: Determine the displacement increment of all nodes based on the displacement increment of each free node.

[0116] Step 1010: Add the displacement increment of each node to the displacement of each node in the current period to obtain the updated displacement of each node.

[0117] Step 1011: Determine the stress of each fiber bundle interface element based on the updated node displacements.

[0118] Based on the finite element theory, the strain and stress of each fiber bundle interface element are calculated according to the nodal displacement.

[0119] Step 1012: Determine whether the updated displacement vectors of each node are all less than the set threshold.

[0120] Step 1013: If all values ​​are not less than the set threshold, then the stiffness matrix of each fiber bundle interface element in the unit cell finite element model is reconstructed based on the fiber / matrix interface shear stress, the friction coefficient between fiber bundle composite materials, and the initial values ​​of each node displacement within the current cycle.

[0121] Step 1014: If all values ​​are less than the set threshold, then determine whether the stress of each fiber bundle interface unit is greater than the fiber strength.

[0122] The failure status of each fiber bundle interface unit is determined based on the fiber random fracture model. The fiber random fracture model generates h random numbers p for any small segment using a uniformly distributed random number generator. j , 1≤j≤h(0≤p j ≤1). P(Λ) j ) represents the probability that a certain segment contains a defect of level j. For a certain segment, when p j <P(Λ) jIf the stress distribution is equal to the strength distribution of the most severe defect, then the fiber segment has a level j defect. The strength of this fiber segment is equal to the strength of the most severe defect. By comparing the stress distribution with the strength distribution of the fiber, the complete failure process of the fiber can be simulated.

[0123] Step 1015: If the strength is greater than the fiber strength, the braided ceramic matrix composite material is determined to have failed as a whole, and the number of cycles N corresponding to the current cycle is taken as the fatigue life of the braided ceramic matrix composite material.

[0124] Step 1016: If the strength is not greater than the fiber strength, increase the cycle number N corresponding to the current cycle by n cycles; where one cycle is one period.

[0125] 'n' represents the increment of the fatigue iteration cycle number in each iteration. To ensure computational accuracy while considering computational efficiency, 'n' can be set to different values ​​at different stages. For example, when the number of iterations is low, 'n' ranges from 1 to 10; subsequently, when the number of iterations is high, 'n' ranges from 100 to 1000.

[0126] Step 1017: Determine whether the N+n loops are greater than or equal to the preset maximum number of loops.

[0127] Step 1018: If the number of cycles is not greater than or equal to the preset maximum number of cycles, then the cycle corresponding to the N+nth cycle is taken as the current cycle, and the relative cumulative slip distance and cumulative stress between the fibers and matrix of the braided ceramic matrix composite material are obtained again.

[0128] Step 1019: If the number of cycles is greater than or equal to the preset maximum number of cycles, then the preset maximum number of cycles is taken as the fatigue life of the braided ceramic matrix composite material.

[0129] This invention provides a method for predicting the fatigue life of braided ceramic matrix composites under constant amplitude cyclic loading. It considers two important factors: friction and wear between the fiber bundles within the braided ceramic matrix composite, simulating the fatigue damage process of the braided ceramic matrix composite under constant amplitude cyclic loading from the perspective of interfacial wear degradation between the fiber bundles. By combining the fiber / matrix interfacial slip model and the fiber / matrix interfacial shear stress degradation model, and introducing the cumulative slip distance and cumulative stress between the fibers and the matrix, high-precision prediction of the fatigue life of braided ceramic matrix composites is achieved. Figure 4 As shown, the life prediction model used in this invention is a micromechanical model, which is calculated based on the test results of fiber bundle composite materials at the corresponding temperature. It can accurately reflect the damage inside the woven material, and the predicted fatigue life is within four times the dispersion band, which meets the fatigue life design requirements of aero-engine structural components.

[0130] Based on the same inventive concept, this invention also provides a constant-amplitude fatigue life prediction system for braided ceramic matrix composites. Since the principle of this system in solving the problem is similar to the above-mentioned constant-amplitude fatigue life prediction method for braided ceramic matrix composites, the implementation of this system can refer to the implementation of the constant-amplitude fatigue life prediction method for braided ceramic matrix composites, and the repeated parts will not be described again.

[0131] In another embodiment, the braided ceramic matrix composite constant-amplitude fatigue life prediction system provided by this invention, such as... Figure 5 As shown, it includes:

[0132] The first building module 10 is used to build a unit cell finite element model of the braided ceramic matrix composite material.

[0133] The first acquisition module 20 is used to acquire the relative cumulative slip distance and cumulative stress between the fibers and matrix of the braided ceramic matrix composite material in the current cycle.

[0134] The first determining module 30 is used to determine the fiber / matrix interface shear stress in the current cycle based on the relative cumulative slip distance between the fiber and the matrix.

[0135] The second determining module 40 is used to determine the friction coefficient between fiber bundle composite materials in the current cycle based on the cumulative stress between the fiber and the matrix.

[0136] The second acquisition module 50 is used to acquire the initial values ​​of the displacements of each node in the unit cell finite element model of the braided ceramic matrix composite material under a given strain load.

[0137] The second construction module 60 is used to construct the stiffness matrix of each fiber bundle interface element in the unit cell finite element model based on the fiber / matrix interface shear stress, the friction coefficient between fiber bundle composite materials, and the initial values ​​of each node displacement within the current cycle.

[0138] The third construction module 70 is used to construct the total stiffness matrix of the unit cell finite element model based on the stiffness matrix of each fiber bundle interface element of the unit cell finite element model.

[0139] The third determining module 80 is used to apply periodic displacement boundary conditions to transform and reduce the total stiffness matrix of the unit cell finite element model in order to determine the displacement increment of each free node in the unit cell finite element model.

[0140] The fourth determining module 90 is used to determine the displacement increment of all nodes based on the displacement increment of each free node.

[0141] The displacement update module 100 is used to add the displacement increment of each node to the displacement of each node in the current period to obtain the updated displacement of each node.

[0142] The fifth determination module 110 is used to determine the stress of each fiber bundle interface element based on the updated displacement of each node.

[0143] The first judgment module 120 is used to determine whether the updated displacement vectors of each node are all less than the set threshold.

[0144] The fourth construction module 130 is used to reconstruct the stiffness matrix of each fiber bundle interface element in the unit cell finite element model based on the fiber / matrix interface shear stress, the friction coefficient between fiber bundle composite materials, and the initial value of each node displacement in the current period, when the first judgment module determines that the updated displacement vectors of each node are not less than the set threshold.

[0145] The second judgment module 140 is used to determine whether the stress of each fiber bundle interface unit is greater than the fiber strength when the first judgment module determines that the updated displacement vectors of each node are all less than the set threshold.

[0146] The sixth determining module 150 is used to determine the overall failure of the braided ceramic matrix composite material when the stress of each fiber bundle interface unit is greater than the fiber strength as determined by the second determining module, and to take the cycle number N corresponding to the current cycle as the fatigue life of the braided ceramic matrix composite material.

[0147] The cycle number increment module 160 is used to increase the cycle number N corresponding to the current cycle by n cycles when the second judgment module determines that the stress of each fiber bundle interface unit is not greater than the fiber strength; where one cycle is one period.

[0148] The third judgment module 170 is used to determine whether the N+n loops are greater than or equal to the preset maximum number of loops.

[0149] The third acquisition module 180 is used to take the period corresponding to the N+nth cycle as the current cycle and reacquire the relative cumulative slip distance and cumulative stress between the fibers and matrix of the braided ceramic matrix composite material when the third judgment module determines that the N+n cycles are not greater than or equal to the preset maximum number of cycles.

[0150] The seventh determining module 190 is used to determine the fatigue life of the braided ceramic matrix composite material when the third determining module determines that N+n cycles are greater than or equal to the preset maximum number of cycles.

[0151] For example, the first determining module includes:

[0152] The first calculation unit is used to calculate the fiber / matrix interface shear stress τ in the Nth cycle according to the following formula. i (N):

[0153]

[0154] in, denoted as the initial shear stress at the fiber / matrix interface before fatigue begins; e is the natural constant; ω is the numerical value of the relationship between the relative cumulative slip distance ∑δ between the fiber and the matrix and the shear stress; λ is the stable value of ∑δ as a function of the number of cycles. This represents the final steady-state shear stress at the fiber / matrix interface during the fatigue process.

[0155] For example, the second determining module includes:

[0156] The second calculation unit is used to calculate the friction coefficient μ(N) between fiber bundle composite materials in the Nth cycle according to the following formula:

[0157]

[0158] Where μ0 is the friction coefficient between fiber bundle composite materials before fatigue begins; e is the natural constant; μ ∞ ω1 is the final steady-state coefficient between fiber bundle composite materials during fatigue; ω1 is the fitting parameter for the friction coefficient as a function of the number of cycles; and λ1 is the fitting parameter for the number of experimental cycles.

[0159] For example, the third determining module includes:

[0160] The first building block is used to construct the expression for the periodic displacement boundary conditions:

[0161]

[0162] Among them, u j+ The displacement of the boundary surface perpendicular to the positive x-axis; u j- This represents the displacement of the boundary surface perpendicular to the negative x-axis. Δx represents the average strain per unit cell; Δx is the coordinate difference between relative points.

[0163] For example, the second building module includes:

[0164] The second building block is used to construct the stiffness matrix K of each fiber bundle interface element in the unit cell finite element model. m expression:

[0165] K m =F m / d m .

[0166] Among them, F m d is the nodal force matrix; m Let be the nodal displacement matrix.

[0167] For more detailed information on the working process of each of the above modules, please refer to the relevant content disclosed in the foregoing embodiments, which will not be repeated here.

[0168] In another embodiment, the present invention provides a computer device including a processor and a memory; wherein, when the processor executes a computer program stored in the memory, it implements the steps of the above-described method for predicting the constant amplitude fatigue life of braided ceramic matrix composites.

[0169] For a more detailed explanation of the above method, please refer to the relevant content disclosed in the foregoing embodiments, which will not be repeated here.

[0170] In another embodiment, the present invention provides a computer-readable storage medium for storing a computer program; when the computer program is executed by a processor, it implements the steps of the above-described method for predicting the constant amplitude fatigue life of braided ceramic matrix composite materials.

[0171] For a more detailed explanation of the above method, please refer to the relevant content disclosed in the foregoing embodiments, which will not be repeated here.

[0172] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. The systems, devices, and storage media disclosed in the embodiments are described simply because they correspond to the methods disclosed in the embodiments; relevant details can be found in the method section.

[0173] Those skilled in the art will clearly understand that the techniques in the embodiments of the present invention can be implemented using software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solutions in the embodiments of the present invention, or the parts that contribute to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in various embodiments or certain parts of the embodiments of the present invention.

[0174] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for predicting the constant-amplitude fatigue life of braided ceramic matrix composites, characterized in that, include: Construct a unit cell finite element model of braided ceramic matrix composites; Obtain the relative cumulative slip distance and cumulative stress between fibers and matrix in the braided ceramic matrix composite during the current cycle; The fiber / matrix interface shear stress in the current cycle is determined based on the relative cumulative slip distance between the fiber and the matrix. The coefficient of friction between fiber bundle composite materials in the current cycle is determined based on the cumulative stress between the fiber and the matrix. Obtain the initial displacement values ​​of each node in the unit cell finite element model of the braided ceramic matrix composite material under a given strain load; The stiffness matrix of each fiber bundle interface element in the unit cell finite element model is constructed based on the shear stress at the fiber / matrix interface, the friction coefficient between fiber bundle composite materials, and the initial values ​​of displacement at each node within the current cycle. The overall stiffness matrix of the unit cell finite element model is constructed based on the stiffness matrices of the interface elements of each fiber bundle in the unit cell finite element model. Apply periodic displacement boundary conditions to transform and reduce the total stiffness matrix of the unit cell finite element model in order to determine the displacement increment of each free node in the unit cell finite element model. The displacement increments of all nodes are determined based on the displacement increments of each free node. The displacement increment of each node is added to the displacement of each node in the current period to obtain the updated displacement of each node. The stress of each fiber bundle interface element is determined based on the updated node displacements. Determine whether the updated displacement vectors of each node are all less than the set threshold; If they are not all less than the set threshold, the stiffness matrix of each fiber bundle interface element in the unit cell finite element model is reconstructed based on the fiber / matrix interface shear stress, the friction coefficient between fiber bundle composite materials and the initial value of each node displacement in the current cycle. If all values ​​are less than the set threshold, then determine whether the stress of each fiber bundle interface unit is greater than the fiber strength. If the strength is greater than the fiber strength, the braided ceramic matrix composite is determined to have failed as a whole, and the number of cycles N corresponding to the current cycle is taken as the fatigue life of the braided ceramic matrix composite. If the strength is not greater than the fiber strength, then increase the cycle number N corresponding to the current cycle by n cycles; where one cycle is one period. Determine if the N+n loops are greater than or equal to the preset maximum number of loops; If the number of cycles is not greater than or equal to the preset maximum number of cycles, the cycle corresponding to the N+nth cycle will be taken as the current cycle, and the relative cumulative slip distance and cumulative stress between the fibers and matrix of the braided ceramic matrix composite material will be obtained again. If the maximum number of cycles is greater than or equal to the preset maximum number of cycles, then the preset maximum number of cycles will be used as the fatigue life of the braided ceramic matrix composite material.

2. The method for predicting the constant-amplitude fatigue life of braided ceramic matrix composites according to claim 1, characterized in that, The determination of the fiber / matrix interface shear stress within the current cycle based on the relative cumulative slip distance between the fiber and the matrix includes: The fiber / matrix interface shear stress τ in the Nth period is calculated using the following formula. i (N): in, denoted as the initial shear stress at the fiber / matrix interface before fatigue begins; e is the natural constant; ω is the numerical value of the relationship between the relative cumulative slip distance ∑δ between the fiber and the matrix and the shear stress; λ is the stable value of ∑δ as a function of the number of cycles. This represents the final steady-state shear stress at the fiber / matrix interface during the fatigue process.

3. The method for predicting the constant-amplitude fatigue life of braided ceramic matrix composites according to claim 1, characterized in that, The determination of the inter-fiber bundle composite friction coefficient within the current cycle based on the cumulative stress between the fiber and the matrix includes: The coefficient of friction μ(N) between fiber bundle composite materials in the Nth cycle is calculated using the following formula: Where μ0 is the friction coefficient between fiber bundle composite materials before fatigue begins; e is the natural constant; μ ∞ ω1 is the final steady-state coefficient between fiber bundle composite materials during fatigue; ω1 is the fitting parameter for the friction coefficient as a function of the number of cycles; and λ1 is the fitting parameter for the number of experimental cycles.

4. The method for predicting the constant-amplitude fatigue life of braided ceramic matrix composites according to claim 1, characterized in that, The application of periodic displacement boundary conditions transforms and reduces the overall stiffness matrix of the unit cell finite element model to determine the displacement increments of each free node in the unit cell finite element model, including: Construct the boundary condition expression for periodic displacement: Among them, u j+ The displacement of the boundary surface perpendicular to the positive x-axis; u j- This represents the displacement of the boundary surface perpendicular to the negative x-axis. Δx represents the average strain per unit cell; Δx is the coordinate difference between relative points.

5. The method for predicting the constant-amplitude fatigue life of braided ceramic matrix composites according to claim 1, characterized in that, The stiffness matrix of each fiber bundle interface element in the unit cell finite element model is constructed based on the shear stress at the fiber / matrix interface, the friction coefficient between fiber bundle composite materials, and the initial values ​​of displacement at each node within the current period, including: The stiffness matrix K of each fiber bundle interface element in the unit cell finite element model is constructed. m expression: K m =F m / d m ; Among them, F m d is the nodal force matrix; m Let be the nodal displacement matrix.

6. A constant-amplitude fatigue life prediction system for braided ceramic matrix composites, characterized in that, include: The first building module is used to build a unit cell finite element model of the braided ceramic matrix composite material; The first acquisition module is used to acquire the relative cumulative slip distance and cumulative stress between the fibers and matrix of the braided ceramic matrix composite material in the current cycle; The first determining module is used to determine the fiber / matrix interface shear stress in the current cycle based on the relative cumulative slip distance between the fiber and the matrix. The second determining module is used to determine the friction coefficient between fiber bundle composite materials in the current cycle based on the cumulative stress between the fiber and the matrix. The second acquisition module is used to acquire the initial values ​​of the displacements of each node in the unit cell finite element model of the braided ceramic matrix composite material under a given strain load. The second construction module is used to construct the stiffness matrix of each fiber bundle interface element in the unit cell finite element model based on the fiber / matrix interface shear stress, the friction coefficient between fiber bundle composite materials and the initial values ​​of each node displacement in the current cycle. The third construction module is used to construct the total stiffness matrix of the unit cell finite element model based on the stiffness matrix of each fiber bundle interface element of the unit cell finite element model. The third determination module is used to apply periodic displacement boundary conditions and transform and reduce the total stiffness matrix of the unit cell finite element model in order to determine the displacement increment of each free node in the unit cell finite element model. The fourth determining module is used to determine the displacement increment of all nodes based on the displacement increment of each free node; The displacement update module is used to add the displacement increment of each node to the displacement of each node in the current period to obtain the updated displacement of each node. The fifth determination module is used to determine the stress of each fiber bundle interface element based on the updated displacement of each node; The first judgment module is used to determine whether the updated displacement vectors of each node are all less than the set threshold. The fourth construction module is used to reconstruct the stiffness matrix of each fiber bundle interface element in the unit cell finite element model based on the fiber / matrix interface shear stress, the friction coefficient between fiber bundle composite materials, and the initial value of each node displacement in the current period, when the first judgment module determines that the updated node displacement vectors are not all less than the set threshold. The second judgment module is used to determine whether the stress of each fiber bundle interface unit is greater than the fiber strength when the first judgment module determines that the updated displacement vectors of each node are all less than the set threshold. The sixth determining module is used to determine the overall failure of the braided ceramic matrix composite material when the stress of each fiber bundle interface unit is greater than the fiber strength as determined by the second determining module, and to take the cycle number N corresponding to the current cycle as the fatigue life of the braided ceramic matrix composite material. The cycle number increment module is used to increase the cycle number N corresponding to the current cycle by n cycles if the second judgment module determines that the stress of each fiber bundle interface unit is not greater than the fiber strength; where one cycle is one period. The third judgment module is used to determine whether the N+n loops are greater than or equal to the preset maximum number of loops; The third acquisition module is used to take the period corresponding to the N+nth cycle as the current cycle and reacquire the relative cumulative slip distance and cumulative stress between the fibers and matrix of the braided ceramic matrix composite material when the third judgment module determines that the N+n cycles are not greater than or equal to the preset maximum number of cycles. The seventh determination module is used to determine the fatigue life of the braided ceramic matrix composite material when the third judgment module determines that N+n cycles are greater than or equal to the preset maximum number of cycles.

7. The constant-width fatigue life prediction system for braided ceramic matrix composites according to claim 6, characterized in that, The first determining module includes: The first calculation unit is used to calculate the fiber / matrix interface shear stress τ in the Nth cycle according to the following formula. i (N): in, denoted as the initial shear stress at the fiber / matrix interface before fatigue begins; e is the natural constant; ω is the numerical value of the relationship between the relative cumulative slip distance ∑δ between the fiber and the matrix and the shear stress; λ is the stable value of ∑δ as a function of the number of cycles. This represents the final steady-state shear stress at the fiber / matrix interface during the fatigue process.

8. The constant-width fatigue life prediction system for braided ceramic matrix composites according to claim 6, characterized in that, The second determining module includes: The second calculation unit is used to calculate the friction coefficient μ(N) between fiber bundle composite materials in the Nth cycle according to the following formula: Where μ0 is the friction coefficient between fiber bundle composite materials before fatigue begins; e is the natural constant; μ ∞ ω1 is the final steady-state coefficient between fiber bundle composite materials during fatigue; ω1 is the fitting parameter for the friction coefficient as a function of the number of cycles; and λ1 is the fitting parameter for the number of experimental cycles.

9. The constant-width fatigue life prediction system for braided ceramic matrix composites according to claim 6, characterized in that, The third determining module includes: The first building block is used to construct the expression for the periodic displacement boundary conditions: Among them, u j+ The displacement of the boundary surface perpendicular to the positive x-axis; u j- This represents the displacement of the boundary surface perpendicular to the negative x-axis. Δx represents the average strain per unit cell; Δx is the coordinate difference between relative points.

10. The constant-width fatigue life prediction system for braided ceramic matrix composites according to claim 6, characterized in that, The second building module includes: The second building block is used to construct the stiffness matrix K of each fiber bundle interface element in the unit cell finite element model. m expression: K m =F m / d m ; Among them, F m d is the nodal force matrix; m Let be the nodal displacement matrix.

Images