A method for optimizing a continuous fiber reinforced metal matrix composite open-hole plate lap joint structure

Abstract

The present application belongs to the field of composite structure optimization, and specifically relates to a continuous fiber reinforced metal matrix composite open-hole plate lap joint structure optimization method, which comprises the following steps: obtaining the stress-strain curve of the continuous fiber reinforced metal matrix composite and the titanium alloy sheath, and then determining the elastic constant and strength parameter of the two materials; based on the elastic constant and strength parameter, establishing the gradual damage constitutive relation of the composite material; based on the actual service condition, establishing the finite element model of the open-hole plate single shear lap joint structure; defining the ply sequence of the open-hole plate lap joint structure in the finite element model as a design variable, establishing the finite element model of multiple different ply sequences, respectively performing stress distribution and damage evolution analysis, and obtaining the optimal ply sequence; and according to the optimal ply sequence, optimizing the geometric parameters of the open-hole plate lap joint structure. The present application can effectively solve the problems of high cost and long cycle faced by the preparation and experimental research of the continuous fiber reinforced metal matrix composite plate.

Description

Technical Field

[0001] This invention belongs to the field of composite material structure optimization, specifically a method for optimizing the overlapping structure of perforated plates in continuous fiber reinforced metal matrix composites. Background Technology

[0002] Continuous fiber reinforced metal matrix composites (CFMCCs) have shown broad application prospects in high-tech fields such as aerospace due to their high specific strength, high specific modulus, excellent high-temperature mechanical properties, and corrosion resistance. Facing the stringent requirements for lightweight and high-temperature durability of skin structures in the extreme service environments of high-speed aircraft, these composite materials are considered ideal candidate materials for high-speed aircraft skin structures. The lap joint structure of composite materials is crucial for its transformation from a material to an engineering structure, but it is also a weak point in composite structures; therefore, the design and analysis of composite lap joint structures are of great significance.

[0003] Perforated mechanical connections, with their simple structure, superior shear resistance, and convenient assembly and maintenance, have become one of the most commonly used and reliable splicing methods. However, in practical applications of composite materials, the presence of perforations can severely disrupt the continuity of long fibers, altering the load transfer path and causing stress concentration, resulting in complex stress distribution and failure zones around the perforations. Therefore, the application of perforated composite plates in practical engineering remains somewhat limited.

[0004] Publication No. CN120756182A proposes a method for preparing an ultrathin SiC fiber-reinforced Ti-based composite material laminate, mainly addressing issues such as uneven fiber distribution, severe warping, and difficulty in ensuring flatness during the preparation process. It does not address the optimization design of the SiC fiber-reinforced titanium-based composite material plate structure. Publication No. CN119141877A proposes a continuous fiber 3D printing path planning method for perforated composite material plates, focusing on minimizing printing spacing through fiber path planning. It does not address improving the stress concentration phenomenon around the holes in the perforated plate. Publication No. CN109676010A proposes a processing method for connecting holes in carbon fiber composite material plates, addressing the influence of hole geometry on stress concentration in the perforated plate. It does not address optimizing the lap performance from the perspective of plate structure design.

[0005] Currently, research on the overall connection performance of composite perforated plate lap structures under complex stress conditions is insufficient. Existing technologies fail to fully consider the structural characteristics of composite materials, cannot accurately predict the stress distribution and failure modes of composite perforated plate lap structures, and lack systematic design and optimization methods. Summary of the Invention

[0006] The purpose of this invention is to provide an optimized design method for the lap joint structure of perforated plates made of continuous fiber reinforced metal matrix composites. This method solves the problem of stress concentration in perforated plate connectors to a certain extent, improves the load-bearing capacity of perforated plate connectors, and optimizes the structural parameters so that the composite material has good mechanical properties under tensile loads.

[0007] The technical solution adopted by this invention to achieve the above objectives is: a method for optimizing the lap joint structure of a perforated plate made of continuous fiber reinforced metal matrix composite material, comprising the following steps:

[0008] Step S1: Obtain the stress-strain curves of the continuous fiber reinforced metal matrix composite and the cladding through mechanical property testing, and then determine the elastic constants and strength parameters of the two materials;

[0009] Step S2: Based on the elastic constants and strength parameters, establish the asymptotic damage constitutive relation of the composite material. The constitutive relation is used to distinguish between fiber-dominated failure mode and matrix-dominated failure mode.

[0010] Step S3: Based on actual service conditions, establish a finite element model of the perforated plate single shear lap joint structure;

[0011] Step S4: Define the ply sequence of the perforated plate overlap structure in the finite element model as a design variable, establish finite element models with different ply sequences, perform stress distribution and damage evolution analysis respectively, and determine the optimal ply sequence.

[0012] Step S5: Optimize the geometric parameters of the perforated plate overlap structure according to the optimal layup sequence.

[0013] In step S1, the mechanical property test includes: quasi-static uniaxial tensile test, quasi-static uniaxial compression test and shear test;

[0014] The elastic constants include: longitudinal elastic modulus, transverse elastic modulus, shear modulus, and Poisson's ratio;

[0015] The strength parameters include: longitudinal tensile strength, longitudinal compressive strength, transverse tensile strength, transverse compressive strength, and shear strength.

[0016] The fiber-dominant failure mode is determined using the following failure criteria:

[0017]

[0018] in, The tensile failure strain is in the fiber direction. For fiber-direction compressive failure strain, For the actual strain in the fiber direction, when Exceeding the threshold Failure occurs at times;

[0019] The corresponding formula for calculating the fiber damage factor is:

[0020]

[0021] in, This represents the fiber-direction elastic modulus component. This represents the fracture energy corresponding to fiber-dominated failure. As a fiber damage factor, Let be the base of the natural logarithm, and be a mathematical constant.

[0022] The matrix-dominant failure mode is determined using the following failure criteria:

[0023]

[0024] in, The strain at which transverse tensile failure occurs. For transverse compressive failure strain, For shear failure strain, For the actual lateral strain, when Exceeding the threshold Failure occurs at times;

[0025] The corresponding formula for calculating the matrix damage factor is:

[0026]

[0027] in, This is the transverse elastic modulus component. This represents the fracture energy corresponding to matrix-dominant failure. It is a matrix damage factor.

[0028] In the asymptotic damage constitutive relation, the stiffness matrix of the composite material is reduced based on the fiber damage factor and the matrix damage factor, and the reduced modulus matrix is:

[0029]

[0030] in, As a fiber damage factor, As a matrix damage factor, , , , , , , , , These are the components of the stiffness matrix when the material is undamaged. This represents a symmetric matrix.

[0031] The establishment of the finite element model of the perforated plate single shear lap joint structure includes the following steps:

[0032] Step S3-1: Discretize the perforated plate overlap structure into a hexahedral element mesh, wherein the cladding region uses an eight-node hexahedral reduced integral element, and the composite material region uses an eight-node hexahedral non-coordinated element.

[0033] Step S3-2: Assign isotropic elastic constitutive properties to the cladding unit, assign the established asymptotic damage constitutive relation to the composite material unit, and define the principal directions of the material for the composite material unit according to the layup angle.

[0034] Step S3-3: Set surface-to-surface contact pairs between the screw and the hole wall, and between the washer and the plate surface, with the friction coefficient set to 0.5; set binding constraints between the fixture and the plate end;

[0035] Step S3-4: Apply a full displacement fixed constraint to the left end clamp, and apply a uniaxial tensile displacement load or force load along the overlap direction to the right end clamp;

[0036] Step S3-5: Use the static universal analysis step, enable the large deformation geometric nonlinearity option, and set the initial increment step, minimum increment step, and maximum increment step.

[0037] The finite element model has the following structure: upper plate, lower plate, screws, left end clamp, and right end clamp;

[0038] Both the upper and lower plates are rectangular plates, arranged opposite each other and partially overlapping to form an overlap area. A circular hole is opened in the center of each plate, and the circular hole of the upper plate and the circular hole of the lower plate are coaxially aligned in the overlap area.

[0039] The screws pass through the round holes in the upper plate and the lower plate to rivet and fix the upper plate and the lower plate together.

[0040] Each plate consists of an outer sheath and a central composite material layer. The sheath is made of titanium alloy and completely covers the outer surface of the composite material layer.

[0041] The composite material layer is a SiC fiber-reinforced titanium matrix composite material, and it contains four layers, each with an adjustable angle.

[0042] The left end clamp is held at the left end of the upper plate, and the right end clamp is held at the right end of the lower plate; wherein, the left end clamp is used to apply a fixing constraint, and the right end clamp is used to apply a tensile load along the overlap direction;

[0043] The clamps and screws are set as rigid bodies in the finite element model.

[0044] In step S4, there are several different layup sequences, including the following three overlap sequences:

[0045] Overlap sequence I: The upper slab layer laying sequence is as follows The layering sequence of the lower slab is as follows: ;

[0046] Overlap sequence II: The upper slab layer laying sequence is as follows The layering sequence of the lower slab is as follows: ;

[0047] Overlap sequence III: The upper slab layer laying sequence is as follows The layering sequence of the lower slab is as follows: ;

[0048] Among them, the 0° layer fibers are arranged along the load direction, and the 90° layer fibers are arranged perpendicular to the load direction.

[0049] Step S4 includes the following steps:

[0050] Step S4-1: Apply the same boundary conditions and tensile loads to the finite element model for each layup sequence to complete the solution calculation of the static general analysis step;

[0051] Step S4-2: Extract the load-displacement curves of the connectors for each layup sequence from the calculation results, and record the ultimate load value as an evaluation index of bearing capacity.

[0052] Step S4-3: Output the stress cloud map of the connector under each layup sequence, extract the stress distribution along the fiber direction of the 0° layup and the stress distribution perpendicular to the fiber direction of the 90° layup, and identify the stress concentration area;

[0053] Step S4-4: Output the damage cloud map of the connector under each layup sequence, and extract the distribution and evolution process of damage factors along the fiber direction and damage factors perpendicular to the fiber direction;

[0054] Step S4-5: Compare the ultimate load values ​​of different ply sequences, and determine the ply sequence corresponding to the one with the largest ultimate load as the optimal ply sequence;

[0055] Step S4-6: For the optimal layup sequence, analyze the distribution patterns of damage factors along the fiber direction and damage factors perpendicular to the fiber direction, and determine the starting position, propagation path, and temporal relationship of damage occurrence between different boards.

[0056] In step S5, the geometric parameters include the section thickness of the perforated plate connector, which includes the following steps:

[0057] Step S5-1: Based on the optimal layup sequence, establish a reference finite element model of the perforated plate single shear lap joint structure, wherein the connectors in the reference finite element model have an initial section thickness;

[0058] Step S5-2: Define the section thickness as an optimization variable, set multiple different section thickness values, establish corresponding finite element models and perform tensile load simulation, and extract the bearing capacity and damage evolution characteristics of the connectors under each model;

[0059] Step S5-3: Compare the bearing capacity under different section thicknesses to determine the optimal section thickness that improves bearing capacity and damage tolerance;

[0060] Step S5-4: Optimize the section thickness while keeping the total thickness of the connector unchanged, and locally or overall thicken the connecting section area;

[0061] Step S5-5: Perform finite element analysis on the optimized structure to confirm the effects of stress concentration mitigation and load-bearing capacity improvement;

[0062] Steps S5-6: Based on the optimal layup sequence and optimized section thickness, prepare test specimens for mechanical property testing to verify the effectiveness of the optimized design.

[0063] The present invention has the following beneficial effects and advantages:

[0064] 1. This invention provides an optimized design method for the lap joint structure of perforated plates made of continuous fiber reinforced metal matrix composites. By establishing a finite element model of single-shear lap joint of perforated plates made of continuous fiber reinforced metal matrix composites, accurate prediction from lap joint sequence to lap joint performance is achieved, and the method is verified through experiments. Furthermore, this model is used to further establish the relationship between section thickness and load-bearing capacity, and combined with a multi-objective optimization method, the connection stability of the lap joint structure of perforated plates made of continuous fiber reinforced metal matrix composites is effectively improved.

[0065] 2. This invention can effectively solve the problems of high cost and long cycle in the preparation and experimental research of continuous fiber reinforced metal matrix composite plates, and also solve the problem that the stress concentration caused by the opening of continuous fiber reinforced metal matrix composite plates makes it difficult to optimize the lap joint performance. Attached Figure Description

[0066] Figure 1 This is a schematic diagram of the process for optimizing the design of the lap joint structure of a perforated plate made of continuous fiber reinforced metal matrix composite material according to the present invention.

[0067] Figure 2 This diagram illustrates a single-shear lap joint and the layup sequence.

[0068] Figure 3The stress distribution of each layer of plate A is shown when the intermediate layer is 0° / 0°; among them, (a) is the stress distribution diagram of plate A S11 when the intermediate layer is 0° / 0°, (b) is the stress distribution diagram of plate A S22 when the intermediate layer is 0° / 0°, (c) is the stress distribution diagram of plate A S12 when the intermediate layer is 0° / 0°, and (d) is the stress distribution diagram of plate A Mises when the intermediate layer is 0° / 0°.

[0069] Figure 4 The stress distribution of each layer of plate B is shown when the intermediate layer is 0° / 0°; (a) corresponds to the stress distribution diagram of plate B S11 when the intermediate layer is 0° / 0°, (b) corresponds to the stress distribution diagram of plate B S22 when the intermediate layer is 0° / 0°, (c) corresponds to the stress distribution diagram of plate B S12 when the intermediate layer is 0° / 0°, and (d) corresponds to the stress distribution diagram of plate B Mises when the intermediate layer is 0° / 0°.

[0070] Figure 5 Damage factors along the fiber direction of the intermediate layer connector of overlapping sequence II under different loads; among them, (a) is the damage factor distribution along the fiber direction when the tensile displacement D=0.068 mm, (b) is the damage factor distribution along the fiber direction when the tensile displacement D=0.124 mm, (c) is the damage factor distribution along the fiber direction when the tensile displacement D=0.129 mm, (d) is the damage factor distribution along the fiber direction when the tensile displacement D=0.148 mm, (e) is the damage factor distribution along the fiber direction when the tensile displacement D=0.157 mm, and (f) is the damage factor distribution along the fiber direction when the tensile displacement D=0.188 mm.

[0071] Figure 6 The damage factors in the interlayer connector of the overlapping sequence II perpendicular to the fiber direction are shown below. Among them, (a) is the distribution of damage factors perpendicular to the fiber direction when the tensile displacement D = 0.019 mm, (b) is the distribution of damage factors perpendicular to the fiber direction when the tensile displacement D = 0.028 mm, (c) is the distribution of damage factors perpendicular to the fiber direction when the tensile displacement D = 0.038 mm, (d) is the distribution of damage factors perpendicular to the fiber direction when the tensile displacement D = 0.078 mm, (e) is the distribution of damage factors perpendicular to the fiber direction when the tensile displacement D = 0.081 mm, and (f) is the distribution of damage factors perpendicular to the fiber direction when the tensile displacement D = 0.092 mm.

[0072] Figure 7 The diagrams are for the optimization schemes; (a) is a diagram of the optimization scheme with added shims, and (b) is a diagram of the optimization scheme with increased thickness. Detailed Implementation

[0073] 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.

[0074] Currently, aerospace vehicle components typically employ composite material designs to ensure lightweight structures. However, bolted connections introduce stress concentration, becoming weak points in the structure and limiting their application in aerospace and other fields. This invention utilizes a combination of finite element analysis and experimental methods to achieve synchronous and coordinated optimization of the overlapping sequence and connection structure. It designs a continuous fiber-reinforced metal matrix composite perforated plate overlapping structure, resolving stress concentration issues and improving the load-bearing capacity and connection capability of the composite perforated plate overlapping structure.

[0075] This invention designs an optimization method for the lap joint structure of perforated plates made of continuous fiber reinforced metal matrix composites, see [link to relevant documentation]. Figure 1 This includes the following steps:

[0076] Step S1: Obtain the stress-strain curves of the continuous fiber reinforced metal matrix composite and the titanium alloy sheath through mechanical property testing, and then determine the elastic constants and strength parameters of the two materials;

[0077] Step S2: Based on the elastic constants and strength parameters, establish the asymptotic damage constitutive relation of the composite material. The constitutive relation is used to distinguish between fiber-dominated failure mode and matrix-dominated failure mode.

[0078] Step S3: Based on actual service conditions, establish a finite element model of the perforated plate single shear lap joint structure;

[0079] Step S4: Define the ply sequence of the perforated plate overlap structure in the finite element model as a design variable, establish finite element models with different ply sequences, perform stress distribution and damage evolution analysis respectively, and determine the optimal ply sequence.

[0080] Step S5: Optimize the geometric parameters of the perforated plate overlap structure according to the optimal layup sequence.

[0081] Example:

[0082] This embodiment uses the example of optimizing the design of a perforated plate structure of a single-shear lap composite material with tensile load to illustrate the present invention in detail.

[0083] I. Obtaining Material Performance Parameters

[0084] First, following step S1, quasi-static uniaxial tensile, quasi-static uniaxial compression, and shear tests were designed for the continuous fiber reinforced metal matrix composite and its sheath to obtain its stress-strain curves. Combining the experimental data with literature experience, the material property parameters of the composite material and its components are obtained as follows:

[0085] Table 1 Material properties of components in continuous fiber reinforced metal matrix composites

[0086]

[0087] II. Establishing a Finite Element Model

[0088] Establishing a finite element model of a perforated plate single shear lap joint structure includes the following steps:

[0089] Step S3-1: Discretize the perforated plate overlap structure into a hexahedral element mesh, wherein the cladding region uses an eight-node hexahedral reduced integral element, and the composite material region uses an eight-node hexahedral non-coordinated element.

[0090] Step S3-2: Assign isotropic elastic constitutive properties to the cladding unit, assign the established asymptotic damage constitutive relation to the composite material unit, and define the principal directions of the material for the composite material unit according to the layup angle.

[0091] Step S3-3: Set surface-to-surface contact pairs between the screw and the hole wall, and between the washer and the plate surface, with the friction coefficient set to 0.5; set binding constraints between the fixture and the plate end;

[0092] Step S3-4: Apply a full displacement fixed constraint to the left end clamp, and apply a uniaxial tensile displacement load or force load along the overlap direction to the right end clamp;

[0093] Step S3-5: Use the static universal analysis step, enable the large deformation geometric nonlinearity option, and set the initial increment step, minimum increment step, and maximum increment step.

[0094] In this embodiment, a finite element model of a single shear overlap of a perforated plate is established using finite element software. The specific steps are as follows:

[0095] like Figure 2 As shown. The specific structure of the finite element model in this embodiment is as follows:

[0096] The model includes: an upper plate (plate A), a lower plate (plate B), screws, a left-end clamp, and a right-end clamp. Both the upper and lower plates are rectangular plates with geometric dimensions of 32mm (length) × 16mm (width) × 0.8mm (thickness), and a 4mm diameter circular hole in the center. The upper and lower plates are positioned opposite each other, partially overlapping to form an overlap area, and then the upper plate (A) and lower plate (B) are riveted together using 4mm diameter screws. The circular holes in the upper and lower plates are coaxially aligned within the overlap area to allow the screws to pass through. To ensure coaxiality during the stretching process, the clamps and screws are set as rigid bodies to improve computational efficiency.

[0097] The sheath and composite plate were treated as isotropic and anisotropic materials, respectively. Each plate consisted of two sheath layers (M region) and a central four-layer composite material layer (C region), with the thickness consistent with the experimental plate. The ply angle of the plate was achieved using the Composite Layup function. Furthermore, a transition mesh was used to improve computational accuracy and reduce computation time; the sheath and composite plate used hexahedral C3D8R and C3D8I elements, respectively, to suppress the hourglass effect. A tie connection was established between the fixture and the plate, and a fixed load and a tensile load of 300 MPa were applied to the left and right fixtures, respectively. The analysis step type was selected as a static general analysis step to obtain the stress, state, and damage state of each element. The post-processing module was then used to extract the load and displacement curves at the reference point and fit them to a load-displacement curve using a function.

[0098] III. Realization of Asymptotic Damage Constitutive Relations

[0099] Based on the significant anisotropy of continuous fiber-reinforced metal matrix composites, this invention employs a linear asymptotic damage failure analysis method, implementing the constitutive relation using a UMAT subroutine written in Fortran. This method fully considers the difference in mechanical properties of the composite material along and perpendicular to the fiber direction, clarifying that the material exhibits two failure modes: fiber-dominated and matrix-dominated. The specific failure criteria and damage factor calculation formulas are as follows:

[0100] 1) Fiber-dominated failure criterion:

[0101]

[0102] in, The tensile failure strain is in the fiber direction. For fiber-direction compressive failure strain, For the actual strain in the fiber direction, when Exceeding the threshold Failure occurs at times;

[0103] The corresponding formula for calculating the fiber damage factor is:

[0104]

[0105] in, This represents the fiber-direction elastic modulus component. This represents the fracture energy corresponding to fiber-dominated failure. As a fiber damage factor, Let be the base of the natural logarithm, and be a mathematical constant.

[0106] 2) The matrix-dominant failure mode is determined using the following failure criteria:

[0107]

[0108] in, The strain at which transverse tensile failure occurs. For transverse compressive failure strain, For shear failure strain, For the actual lateral strain, when Exceeding the threshold Failure occurs at times;

[0109] The corresponding formula for calculating the matrix damage factor is:

[0110]

[0111] in, This is the transverse elastic modulus component. This represents the fracture energy corresponding to matrix-dominant failure. It is a matrix damage factor.

[0112] Modulus matrix after stiffness reduction:

[0113]

[0114] in, As a fiber damage factor, As a matrix damage factor, , , , , , , , , These are the components of the stiffness matrix when the material is undamaged. This represents a symmetric matrix.

[0115] The stress calculation formula is:

[0116]

[0117] in, This is the stress tensor (or equivalent stress vector), representing the actual stress in a material under damaged conditions. This is the stiffness matrix (modulus matrix) after damage. For strain tensor, This refers to matrix multiplication.

[0118] The strain at each component reference point is substituted into the corresponding failure criterion to determine the failure status of the reference point. Based on the failure status, the macroscopic elastic constants of the composite material are reduced by combining the fiber-dominated failure model, the matrix-dominated failure model, and the stiffness reduction matrix, and the initial macroscopic elastic constants of stiffness are replaced. The above failure analysis process is written into a UMAT subroutine for macroscopic asymptotic failure analysis of composite materials using the Fortran language.

[0119] IV. Analysis of Layer Sequence Optimization

[0120] Three overlapping sequences were designed for the perforated plate structure, including:

[0121] Overlap sequence I: The upper slab layer laying sequence is as follows The layering sequence of the lower slab is as follows: ;

[0122] Overlap sequence II: The upper slab layer laying sequence is as follows The layering sequence of the lower slab is as follows: ;

[0123] Overlap sequence III: The upper slab layer laying sequence is as follows The layering sequence of the lower slab is as follows: ;

[0124] In this arrangement, the 0° layer fibers are arranged along the load direction, while the 90° layer fibers are arranged perpendicular to the load direction. Table 2 shows the load values ​​for three different overlapping sequences. The results indicate that the load-bearing capacity decreases from strongest to weakest in the order of II, I, and III. That is, the closer the 0° layer is to the overlapping interface in the overlapping area and the greater its number, the stronger the load-bearing capacity of the connector.

[0125] Table 2 Simulation results for three different overlapping sequences

[0126]

[0127] As shown in Table 2, the load-bearing capacity from strongest to weakest is II, I, and III. That is, the closer the 0° layer is to the overlap interface in the overlap area and the more numerous they are, the stronger the load-bearing capacity of the connector. Therefore, overlap sequence II is determined to be the optimal layup sequence.

[0128] Further analysis of the stress distribution of the connectors under lap sequence II, such as... Figure 3 and Figure 4As shown, the results indicate that large-area stress concentrations occur along the fiber direction in both the 0° and 90° layers. The 0° layer composite material bears the main tensile load, while the 90° layer bears the load perpendicular to the force direction. Since the strength of continuous fiber reinforced metal matrix composites along the longitudinal direction (along the fiber direction) is much greater than that in the transverse direction (perpendicular to the fiber direction), the transverse direction is usually the failure point. This deficiency can be compensated for by the cross design of the 0° and 90° layers, thereby improving the overall structural strength. The comparison of the maximum stress values ​​along the fiber direction of connectors with different overlapping sequences is shown in Table 3.

[0129] Table 3. Maximum stress values ​​along the fiber direction for connectors with three different lap sequences.

[0130]

[0131] Figure 5 and Figure 6 The damage evolution of the intermediate layer in overlapping sequence II is shown. SDV3 and SDV4 represent the damage factors along the fiber direction and perpendicular to the fiber direction, respectively. The results indicate that fiber damage mainly occurs around the holes. Damage along the fiber direction in plate A appears before that in plate B, indicating that plate A fails before plate B along the fiber direction. However, damage along the perpendicular fiber direction in plate A appears simultaneously with that in plate B, and its damage distribution becomes symmetrical with increasing load, suggesting that the damage evolution processes along the perpendicular fiber direction are similar for both.

[0132] The specific steps for the layup optimization analysis in this embodiment are as follows:

[0133] In step S4, the stress distribution and damage evolution are analyzed, and the specific steps are as follows:

[0134] Step S4-1: Apply identical boundary conditions and tensile loads (left end fixed, right end applied displacement load) to the finite element model of each layup sequence (I, II, III) to complete the solution calculation of the static general analysis step until the preset termination condition (such as maximum displacement or complete failure) is reached.

[0135] Step S4-2: Extract the load-displacement curves of the connectors for each ply sequence from the calculation results. The load is obtained from the support reaction force at the reference point of the right-end clamp, and the displacement is obtained from the displacement at the reference point of the right-end clamp. Record the ultimate load value (the load corresponding to the highest point of the curve) as an evaluation index of the load-bearing capacity.

[0136] Step S4-3: Output the stress contour map of the connector for each layup sequence. Extract the stress distribution along the fiber direction for the 0° layup (S11) and the stress distribution perpendicular to the fiber direction for the 90° layup (S22), respectively, and identify stress concentration areas (usually located near the hole edge and overlap interface). Compare the stress peak values ​​and distribution patterns of different layup sequences.

[0137] Step S4-4: Output damage contour maps for connectors under each layup sequence. Extract the distribution and evolution of damage factors along the fiber direction (SDV3) and perpendicular to the fiber direction (SDV4). Observe the damage initiation location (hole edge, interlayer, etc.), damage propagation path, and final failure mode.

[0138] Step S4-5: Compare the ultimate load values ​​of the three layup sequences and determine the layup sequence with the largest ultimate load as the optimal layup sequence. In this embodiment, layup sequence II has the largest ultimate load (4756.32N), and is therefore determined as the optimal layup sequence.

[0139] Step S4-6: For the optimal layup sequence (II), further analyze the distribution patterns of damage factors along the fiber direction and damage factors perpendicular to the fiber direction. Determine the starting position of fiber damage (usually at the edge of the hole along the fiber direction), the propagation path (along the fiber direction or laterally), and the temporal relationship of damage occurrence between different boards (e.g., damage along the fiber direction in board A occurs before that in board B, while damage in the perpendicular direction occurs simultaneously). Figure 5 , Figure 6 As shown.

[0140] V. Experimental Verification

[0141] Based on the overlap sequence II [90°, 90°, 0°, 0°]-[0°, 0°, 90°, 90°], two test samples of perforated plate connectors were prepared. A tensile rate of 1 mm / min was set in the finite element model for simulation, and actual tensile tests were conducted. Connector-1 completely fractured, with the crack propagating at a 90° angle perpendicular to the tensile direction and deflecting at the edge. Connector-2, although not completely fractured, lost its load-bearing capacity. The average load-bearing capacity of the two samples was 4520.10 N, with an error of 5.2% compared to the finite element simulation result of 4756.32 N, verifying the effectiveness of the finite element model.

[0142] VI. Geometric Parameter Optimization

[0143] Following step S5, the thickness of the section was optimized. Two optimization schemes were designed:

[0144] Option ①: such as Figure 7 As shown in (a), a gasket of the same length and material as the connecting section is added at the connection, and its thickness is the same as that of the single-layer plate; the interface between the gasket and the screw and the mother plate is defined as surface-to-surface contact, and the coefficient of friction is set to 0.5.

[0145] Option 2: such as Figure 7As shown in (b), the thickness of the connecting section plate is increased, and the total thickness of the connector remains consistent in both schemes; the thickened part is constrained with the original plate by setting a Tie, ensuring that the two are regarded as a whole.

[0146] Step S5-1: Based on the optimal layup sequence (II), establish the baseline finite element model of the perforated plate single shear lap joint structure. The connectors in the baseline finite element model have initial section thicknesses. All other parameters of the model are identical to those before.

[0147] Step S5-2: Define the section thickness as an optimization variable. Set multiple different section thickness values. Establish corresponding finite element models for each model and perform tensile load simulation. Extract the load-bearing capacity and damage evolution characteristics of the connectors under each model.

[0148] Step S5-3: Compare the load-bearing capacity under different section thicknesses. Plot the "thickness-ultimate load" curve to analyze the trend of load-bearing capacity with thickness. Taking into account both the increase in load-bearing capacity and the cost of structural weight gain, determine the optimal section thickness that significantly improves load-bearing capacity and damage tolerance.

[0149] In this embodiment, Table 4 shows the calculation results for the two optimization schemes. After adding the shim, the load-bearing capacity of the lap plate decreased by 10.3%. The main reason is that the introduction of the shim increases the surface-to-surface contact area at the joint, requiring the part that originally directly bears the load to also resist contact friction, resulting in more severe stress concentration around the hole and causing premature damage to the hole edge. However, increasing the plate thickness increased the load-bearing capacity of the lap plate by 26.9%. This is mainly because the increased plate thickness significantly increases the load-bearing cross-sectional area of ​​the lap region, mitigating stress concentration at the hole edge; furthermore, the increased net cross-sectional area increases the contact area between the hole inner wall and the screw, resulting in more uniform pressure distribution and delaying the failure process.

[0150] Table 4 Calculation results of the two optimization methods

[0151]

[0152] The results show that the load-bearing capacity of Scheme ① decreased by 10.3% because the introduction of the gasket increased the surface-to-surface contact area, which made the stress concentration around the hole more severe; the load-bearing capacity of Scheme ② increased by 26.9% because the increase in plate thickness significantly increased the load-bearing cross-sectional area of ​​the overlap area, alleviated the stress concentration around the hole, and made the pressure distribution more uniform.

[0153] In summary, the optimization method for the lap joint structure of perforated plates in continuous fiber-reinforced metal matrix composites provided by this invention achieves accurate simulation of the stress state of the connectors under tensile loads by establishing a finite element model. Multi-objective optimization is performed using layup sequence and section thickness as design variables, effectively reducing stress concentration and improving the uniformity and stability of the load-bearing capacity and overall performance of the connectors. This method can significantly shorten the structural development cycle, reduce testing costs, and provide theoretical guidance for the design of composite laminate structures.

[0154] Those skilled in the art will understand that the above description is merely a preferred embodiment of the present invention, and the features described in the various embodiments of this disclosure can be combined or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. This is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for optimizing the lap joint structure of a perforated plate made of continuous fiber reinforced metal matrix composite material, characterized in that, Includes the following steps: Step S1: Obtain the stress-strain curves of the continuous fiber reinforced metal matrix composite and the cladding through mechanical property testing, and then determine the elastic constants and strength parameters of the two materials; Step S2: Based on the elastic constants and strength parameters, establish the asymptotic damage constitutive relation of the composite material. The constitutive relation is used to distinguish between fiber-dominated failure mode and matrix-dominated failure mode. Step S3: Based on actual service conditions, establish a finite element model of the perforated plate single shear lap joint structure; Step S4: Define the ply sequence of the perforated plate overlap structure in the finite element model as a design variable, establish finite element models with different ply sequences, perform stress distribution and damage evolution analysis respectively, and determine the optimal ply sequence. Step S5: Optimize the geometric parameters of the perforated plate overlap structure according to the optimal layup sequence; wherein, the geometric parameters are the section thickness of the perforated plate connector.

2. The method for optimizing the lap joint structure of a perforated plate of a continuous fiber reinforced metal matrix composite material according to claim 1, characterized in that, In step S1, the mechanical property test includes: quasi-static uniaxial tensile test, quasi-static uniaxial compression test and shear test; The elastic constants include: longitudinal elastic modulus, transverse elastic modulus, shear modulus, and Poisson's ratio; The strength parameters include: longitudinal tensile strength, longitudinal compressive strength, transverse tensile strength, transverse compressive strength, and shear strength.

3. The method for optimizing the lap joint structure of a perforated plate of a continuous fiber reinforced metal matrix composite material according to claim 1, characterized in that, The fiber-dominant failure mode is determined using the following failure criteria: ； in, The tensile failure strain is in the fiber direction. For fiber-direction compressive failure strain, For the actual strain in the fiber direction, when Exceeding the threshold Failure occurs at times; The corresponding formula for calculating the fiber damage factor is: ； in, This represents the fiber-direction elastic modulus component. This represents the fracture energy corresponding to fiber-dominated failure. As a fiber damage factor, Let be the base of the natural logarithm, and be a mathematical constant.

4. The method for optimizing the lap joint structure of a perforated plate of a continuous fiber reinforced metal matrix composite material according to claim 1, characterized in that, The matrix-dominant failure mode is determined using the following failure criteria: ； in, The strain is the transverse tensile failure strain. For transverse compressive failure strain, For shear failure strain, For the actual lateral strain, when Exceeding the threshold Failure occurs at times; The corresponding formula for calculating the matrix damage factor is: ； in, This is the transverse elastic modulus component. This represents the fracture energy corresponding to matrix-dominant failure. It is a matrix damage factor.

5. The method for optimizing the lap joint structure of a perforated plate of a continuous fiber reinforced metal matrix composite material according to claim 1, characterized in that, In the asymptotic damage constitutive relation, the stiffness matrix of the composite material is reduced based on the fiber damage factor and the matrix damage factor, and the reduced modulus matrix is: ； in, As a fiber damage factor, As a matrix damage factor, , , , , , , , , These are the components of the stiffness matrix when the material is undamaged. This represents a symmetric matrix.

6. The method for optimizing the lap joint structure of a perforated plate of a continuous fiber reinforced metal matrix composite material according to claim 1, characterized in that, The establishment of the finite element model of the perforated plate single shear lap joint structure includes the following steps: Step S3-1: Discretize the perforated plate overlap structure into a hexahedral element mesh, wherein the cladding region uses an eight-node hexahedral reduced integral element, and the composite material region uses an eight-node hexahedral non-coordinated element. Step S3-2: Assign isotropic elastic constitutive properties to the cladding unit, assign the established asymptotic damage constitutive relation to the composite material unit, and define the principal directions of the material for the composite material unit according to the layup angle. Step S3-3: Set surface-to-surface contact pairs between the screw and the hole wall, and between the washer and the plate surface, with the friction coefficient set to 0.5; set binding constraints between the fixture and the plate end; Step S3-4: Apply a full displacement fixed constraint to the left end clamp, and apply a uniaxial tensile displacement load or force load along the overlap direction to the right end clamp; Step S3-5: Use the static universal analysis step, enable the large deformation geometric nonlinearity option, and set the initial increment step, minimum increment step, and maximum increment step.

7. The method for optimizing the lap joint structure of a perforated plate of a continuous fiber reinforced metal matrix composite material according to claim 1, characterized in that, The finite element model has the following structure: upper plate, lower plate, screws, left end clamp, and right end clamp; Both the upper and lower plates are rectangular plates, arranged opposite each other and partially overlapping to form an overlap area. A circular hole is opened in the center of each plate, and the circular hole of the upper plate and the circular hole of the lower plate are coaxially aligned in the overlap area. The screws pass through the round holes in the upper plate and the lower plate to rivet and fix the upper plate and the lower plate together. Each plate consists of an outer sheath and a central composite material layer. The sheath is made of titanium alloy and completely covers the outer surface of the composite material layer. The composite material layer is a SiC fiber-reinforced titanium matrix composite material, and it contains four layers, each with an adjustable angle. The left end clamp is held at the left end of the upper plate, and the right end clamp is held at the right end of the lower plate; wherein, the left end clamp is used to apply a fixing constraint, and the right end clamp is used to apply a tensile load along the overlap direction; The clamps and screws are set as rigid bodies in the finite element model.

8. The method for optimizing the lap joint structure of a perforated plate of a continuous fiber reinforced metal matrix composite material according to claim 1, characterized in that, In step S4, there are several different layup sequences, including the following three overlap sequences: Overlap sequence I: The upper slab layer laying sequence is as follows The layer sequence of the lower plate is as follows: ; Overlap sequence II: The upper slab layer laying sequence is as follows The layer sequence of the lower plate is as follows: ; Overlap sequence III: The upper slab layer laying sequence is as follows The layer sequence of the lower plate is as follows: ; Among them, the 0° layer fibers are arranged along the load direction, and the 90° layer fibers are arranged perpendicular to the load direction.

9. The method for optimizing the lap joint structure of a perforated plate of a continuous fiber reinforced metal matrix composite material according to claim 1, characterized in that, Step S4 includes the following steps: Step S4-1: Apply the same boundary conditions and tensile loads to the finite element model for each layup sequence to complete the solution calculation of the static general analysis step; Step S4-2: Extract the load-displacement curves of the connectors under each layup sequence from the calculation results, and record the ultimate load value as an evaluation index of bearing capacity. Step S4-3: Output the stress cloud map of the connector under each layup sequence, extract the stress distribution along the fiber direction of the 0° layup and the stress distribution perpendicular to the fiber direction of the 90° layup, and identify the stress concentration area; Step S4-4: Output the damage cloud map of the connector under each layup sequence, and extract the distribution and evolution process of damage factors along the fiber direction and damage factors perpendicular to the fiber direction; Step S4-5: Compare the ultimate load values ​​of different ply sequences, and determine the ply sequence corresponding to the one with the largest ultimate load as the optimal ply sequence; Step S4-6: For the optimal layup sequence, analyze the distribution patterns of damage factors along the fiber direction and damage factors perpendicular to the fiber direction, and determine the starting position, propagation path, and temporal relationship of damage occurrence between different boards.

10. The method for optimizing the lap joint structure of a perforated plate of a continuous fiber reinforced metal matrix composite material according to claim 1, characterized in that, Step S5 includes the following steps: Step S5-1: Based on the optimal layup sequence, establish a reference finite element model of the perforated plate single shear lap joint structure, wherein the connectors in the reference finite element model have an initial section thickness; Step S5-2: Define the section thickness as an optimization variable, set multiple different section thickness values, establish corresponding finite element models and perform tensile load simulation, and extract the bearing capacity and damage evolution characteristics of the connectors under each model; Step S5-3: Compare the bearing capacity under different section thicknesses to determine the optimal section thickness that improves bearing capacity and damage tolerance; Step S5-4: Optimize the section thickness while keeping the total thickness of the connector unchanged, and locally or overall thicken the connecting section area; Step S5-5: Perform finite element analysis on the optimized structure to confirm the effects of stress concentration mitigation and load-bearing capacity improvement; Steps S5-6: Based on the optimal layup sequence and optimized section thickness, prepare test specimens for mechanical property testing to verify the effectiveness of the optimized design.

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