Drilling and riveting point layout optimization method for damage repair of aerospace composite material components

Abstract

The application discloses a kind of drilling and riveting point layout optimization methods for aeronautical composite material component damage repair, belong to composite material repair technical field, the method includes: the layered damage site is detected and damage influence is evaluated and marks the depth, position and shape of layered damage area;Irregularly shaped layered defect area is equivalent to regular shape;Composite material layered damage riveting repair finite element simulation model is established, and a plurality of initial point layouts are generated through ABAQUS / Python secondary development interface, the strength and stiffness of damage repair structure are solved;The rivet fastener layout is iteratively optimized by genetic optimization algorithm, and the optimal layout scheme of riveting repair of damaged composite material is obtained.The method can be aimed at any shape of composite material internal layered damage, optimize the arrangement mode of fastener in drilling and riveting repair, maximize the strength and stiffness of damaged composite material structure, reduce the number of rivets, reduce the additional weight of structure.

Description

Technical Field

[0001] This invention belongs to the field of composite material repair technology, specifically, it relates to a method for optimizing the layout of drilling and riveting points for the repair of damage to aerospace composite material components.

[0002] Research Background

[0003] Composite materials possess advantages such as high specific strength and stiffness, strong fatigue and impact resistance, and long service life, making them widely used in aircraft manufacturing. However, unlike metal components, composite components have relatively weak interlaminar strength. During the manufacturing process, due to the dispersion of layup quality, resin-rich areas are easily formed, leading to differences in interlaminar shrinkage during curing and making delamination defects highly likely. Simultaneously, incomplete curing of the material, the introduction of foreign particles, and uneven heating in equipment can also cause interlaminar debonding, resulting in interlaminar damage or crack sources in composite panels from the outset of service. Furthermore, existing interlaminar defects and damage can further expand under extreme operating conditions. These delamination damages significantly reduce the overall strength and stiffness of the structure, severely weakening the flight performance of military aircraft and posing significant safety hazards during service.

[0004] Composite material components have high molding process requirements, are expensive, and have long molding cycles. Directly scrapping and replacing defective or damaged composite material panels for military aircraft would not only increase manufacturing costs but also increase the difficulty and duration of aircraft repair and maintenance. This would fail to meet wartime requirements for rapid response, simple repair methods, and high reliability, severely weakening the aircraft's formation combat capability and battlefield survivability. Previous exploration and practice by technicians have shown that drilling and riveting holes within the delamination damage areas and their envelopes of composite material panels can suppress delamination damage propagation, increase the overall strength and stiffness of the panels and assembly structure, and thus extend the structure's service life. However, the location of initial interlaminar defects and cracks, as well as service load-induced interlaminar damage, is highly random. The resulting delamination areas vary in location, depth, size, and properties, increasing the difficulty of drilling and riveting repairs. Currently, maintenance personnel mainly rely on experience to arrange drilling and riveting points, often failing to achieve optimal configuration. For layers of various shapes and locations, traditional empirical methods may fail to effectively control the spread of the layers or result in overly dense point arrangements, leading to localized stress concentration. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for optimizing the layout of drilling and riveting points for the repair of damaged aerospace composite components. This method can optimize the arrangement of rivets and fasteners during drilling and riveting repair for internal delamination damage in aerospace composite components of any shape, thereby maximizing the restoration of the strength and stiffness of the damaged composite structure, reducing the number of rivets, and reducing the additional weight of the structure.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution: a method for optimizing the layout of drilling and riveting points for the repair of damaged aerospace composite components, comprising the following steps:

[0007] Step 1: Use non-destructive testing technology to detect the depth, location and shape of delamination damage inside aerospace composite components, mark the outline of the damaged area, and select rivets and fasteners of appropriate size.

[0008] Step 2: By calling the internal function in the OpenCV algorithm library, the marked damage region contour is converted into a contour convex hull. The center coordinates, semi-major axis and semi-minor axis lengths and rotation angle of the minimum envelope ellipse of the damage region contour are calculated based on the contour convex hull. The minimum envelope ellipse is used to simplify the damage region contour.

[0009] Step 3: Based on the structural characteristics, material properties, location of delamination damage, and minimum envelope ellipse of the aerospace composite component, establish a finite element calculation model of the aerospace composite component with delamination damage, and set boundary conditions according to the fit relationship between the rivet fastener and the aerospace composite component and the structural load characteristics.

[0010] Step 4: Set the initial conditions for the genetic optimization algorithm: Using the installation position and quantity of rivet fasteners as design variables, the aerospace composite component with delamination damage is divided using the grid method, and the design variables of the rivet fasteners are encoded using binary vectors; the compressive stiffness and structural ultimate strength of the damaged composite laminate structure are used as optimization objectives to establish a riveting repair quality evaluation function.

[0011] Step 5: Using the coded rivet fastener design variables as the initial population, input them into the finite element calculation model through the ABAQUS / Python secondary development interface. Calculate the recovery rate R of the compressive stiffness of the damaged aerospace composite material under each rivet fastener point layout scheme in the initial population. t Structural ultimate strength recovery rate S of damaged aerospace composite materials t and R t and S tThe genetic optimization algorithm is input through the ABAQUS / Python secondary development interface. The repair quality evaluation index is calculated through the repair quality evaluation function. The initial population is iteratively optimized through genetic operators such as selection, crossover, and mutation until the maximum number of iterations is reached, and the final optimized population is obtained.

[0012] Step 6: Sort each rivet and fastener point layout scheme in the final optimized population according to the maintenance quality evaluation index from largest to smallest, and output the rivet and fastener point layout schemes with the top 10% maintenance quality index.

[0013] Furthermore, step 2 includes the following sub-steps:

[0014] Step 2.1: Call the cvtColor() function in the OpenCV algorithm library to convert the image of the marked damaged area contour into a grayscale image, and use the contour function to find the boundary of the damaged area contour of the grayscale image.

[0015] Step 2.2: Approximate the contour boundary of the damaged region as a convex hull using the convexHull() function, obtaining the convex hull point set P = {P1,…,P}. i ,…,P n}, where n represents the number of elements in the convex hull set of the contour, P i Let P be the i-th point in the set of points of the convex hull of the contour. i =(x i ,y i );

[0016] Step 2.3: Calculate the geometric moments of the convex hull based on the point set of the convex hull. And based on the zeroth moment m of the geometric moments 00 First-order moment m 10 and m 01 Find the coordinates c of the center point of the ellipse. x =m 10 / m 00 c y =m 01 / m 00 , where m pq μ represents the (p+q)th order moment of the convex hull, where p and q represent the moments of the convex hull in the x and y dimensions, respectively. x and μ y These are the center coordinates of the convex hull of the contour.

[0017] Step 2.4: Solve for the covariance matrix of the convex hull point set of the contour. Solving for the eigenvalues ​​λ1 and λ2, and the eigenvectors v1 and v2, we obtain the semi-major axis length a and semi-minor axis length b of the ellipse. and The rotation angle of the ellipse is Where Var(x) represents the variance of the convex hull point set along the x-dimensional axis. Var(y) represents the variance of the convex hull point set in the y-axis. Cov(x,y) represents the covariance of the convex hull point set in the x and y dimensions. v1[1] represents the second element of the feature vector v1, and v1[0] represents the first element of the feature vector v1;

[0018] Step 2.5: Establish a coordinate system with the center point coordinates of the ellipse as the origin, and draw the minimum envelope ellipse according to the semi-major axis length a, semi-minor axis length b, and rotation angle to effectively simplify the outline of the damaged area.

[0019] Furthermore, the boundary conditions for the finite element calculation model in step 3 are:

[0020] (1) Establish the contact relationship between aerospace composite material components and rivet fasteners;

[0021] (2) Set the preload of the rivet fasteners;

[0022] (3) Set the loading mode and constraint relationship of aerospace composite material components during the mechanical performance test process.

[0023] Furthermore, the process of setting the design variables in step 4 is as follows: A polar coordinate system is established with the center of the minimum envelope ellipse as the pole O and the minor axis of the minimum envelope ellipse as the polar axis X. The installation positions and quantities of the rivet fasteners are arranged as H = [h1, ..., h...]. m …,h M ], where M represents the number of rivet fasteners, M = card(H); h m This indicates the specific location of the m-th rivet fastener. ρ m Represents the position h in polar coordinates m radius, Represents the position h in polar coordinates m The angle.

[0024] Furthermore, the rivet fastener is installed within the minimum envelope elliptical region, at point h in the polar coordinate system. m radius ρ m satisfy:

[0025]

[0026] Where a is the length of the semi-major axis of the ellipse, b is the length of the semi-minor axis of the ellipse, and c is the semi-focal length of the ellipse.

[0027] Furthermore, the riveting repair quality evaluation function is:

[0028]

[0029] Among them, f t Let M represent the maintenance quality index corresponding to the t-th rivet fastener layout scheme, where M = card(H); and k1 represents R. t The weight value, k2 represents S t The weight value.

[0030] Further, the process of encoding the rivet fastener layout in step 4 is as follows: using the diameter of the rivet fastener as the unit size, the aerospace composite component is divided into several grids using a grid method. Each grid represents a potential rivet fastener connection point, and each grid is numbered starting from the lower left corner, with the numbering starting from 1 and ending at N. Based on the grid diagram of the aerospace composite component, the rivet fasteners are encoded using binary vectors according to their installation position and quantity: S = [w1 w2 ... w N ] T , where S is an N-dimensional vector, and the elements in S are the positions of each cell grid after the grid is divided. If the binary number is 1, it means that a rivet fastener is installed on the grid. If the binary number is 0, it means that no rivet fastener is installed on the grid.

[0031] Furthermore, step 5 includes the following sub-steps:

[0032] Step 5.1: Based on the fact that the rivets and fasteners are installed within the minimum envelope elliptical region, determine the constraints on the number and installation position of the rivets and fasteners, randomly generate design variables as individuals of the rivet and fastener point layout, and combine the individuals of the rivet and fastener point layout to form an initial population.

[0033] Step 5.2: The initial population is input into the finite element calculation model through the ABAQUS / Python secondary development interface. The recovery rate R of the compressive stiffness of the damaged aerospace composite material under each rivet fastener point layout scheme in the initial population is calculated. t Structural ultimate strength recovery rate S of damaged aerospace composite materials t ;

[0034] Step 5.3, R t and S t The data is input into the genetic optimization algorithm through the ABAQUS / Python secondary development interface, and the repair quality evaluation index is calculated through the repair quality evaluation function.

[0035] Step 5.4: Use the roulette wheel selection method to select a set number of individuals from the initial population as parent individuals, perform crossover and mutation, and generate an optimized population;

[0036] Step 5.5: Replace the initial population with the optimized population, and repeat steps 5.2-5.4 until the maximum number of iterations is reached to obtain the final optimized population.

[0037] Furthermore, the specific process of selecting the roulette wheel selection method in step 5.4 is as follows:

[0038] Step 5.4.1: Determine the maintenance quality index f for each rivet fastener location layout scheme in the population based on the riveting repair quality evaluation function. t and the probability of selecting each rivet fastener point layout scheme. Calculate the cumulative probability C of each rivet fastener point layout scheme. t =p1+p2+…+p t Where T is the number of rivet fastener point layout schemes in the population, 1≤t≤T, and initially, C0=0;

[0039] Step 5.4.2: Generate a random number r, r∈[0,1], and search for a population that satisfies condition C based on the random number r. t-1 ≤r≤C t The layout scheme for rivet fastener locations;

[0040] Step 5.4.3: Select rivet fastener point layout schemes by repeatedly generating random numbers until a sufficient number of rivet fastener point layout schemes are selected as parent individuals to participate in crossover and mutation operations.

[0041] Furthermore, the crossover process in step 5.4 is specifically as follows: for two parent individuals S p1 and S p2 Multiple gene positions in the individual's coding were randomly selected for multi-point crossover to obtain two new individuals S. p1 'and S p2 ', where the number and position of intersections are randomly generated. If the position of the rivet fastener in the new individual after intersection is repeated or exceeds the minimum envelope elliptical region, the new individual is deleted.

[0042] The mutation process in step 5.2 is specifically as follows: among the newly generated individuals, random individuals S... p Randomly select r positions i1, i2, ..., i r Invert the binary values ​​at these positions to obtain the new individual S. p If the positions of rivets and fasteners in the mutated updated individual are repeated or exceed the minimum envelope ellipse region, then the new individual is deleted.

[0043] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention simplifies the irregular layered shape measured in engineering by using a minimum envelope ellipse, avoiding the difficulties in constructing finite element models and poor convergence of irregular layered shapes while ensuring the overall structural performance remains unchanged. Simultaneously, based on a genetic optimization algorithm, the discrete variables and distribution positions of the number of rivets and fasteners are discretized, and binary vectors are used to encode the number and position of rivets and fasteners. Through selection, crossover, and mutation, the maintenance quality evaluation index of each rivet and fastener point layout scheme is calculated, forming a final population to seek the global optimal solution. This truly achieves the optimization of the drilling and riveting point layout for the repair of damaged composite material components, maximizing the structural stiffness and strength recovery rate, minimizing the number of rivets, and minimizing the overall weight gain under specified constraints. This invention proposes maintenance quality indicators for composite materials with layered damage and applies a multi-objective optimization algorithm to optimize the rivet and fastener point layout, helping maintenance technicians determine the most practical personalized repair scheme based on actual damage. This method has universality for optimizing the mechanical connection repair process of damaged composite material components. Attached Figure Description

[0044] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the specific embodiments will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0045] Figure 1 This is a flowchart of the drilling and riveting point layout optimization method for the repair of damage to aerospace composite components according to the present invention;

[0046] Figure 2 This is a schematic diagram of the equivalent shape of irregular delamination damage in the aerospace composite material of the present invention;

[0047] Figure 3 This is a schematic diagram of the finite element structure for riveting repair of delamination damage in aerospace composite materials according to the present invention;

[0048] Figure 4 This is a schematic diagram showing the boundary condition settings of the finite element model for riveting repair of delamination damage in aerospace composite materials according to the present invention.

[0049] Figure 5 This is a flowchart illustrating the rivet fastener point arrangement using a genetic optimization algorithm according to the present invention.

[0050] Among them, 1. Layered true contour; 2. Minimum envelope elliptical contour; 3. Finite element model of composite panel; 4. Finite element model of adhesive with layered damage; 5. Simplified finite element model of rivet fastener. Detailed Implementation

[0051] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the specific 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.

[0052] like Figure 1 This is a flowchart of the drilling and riveting point layout optimization method for the repair of damaged aerospace composite components according to the present invention. The drilling and riveting point layout optimization method specifically includes the following steps:

[0053] Step 1: Use non-destructive testing technology to detect the depth, location and shape of delamination damage inside aerospace composite components, mark the outline of the damaged area, and determine the thickness, layup and material properties of the damaged composite structure to be repaired by referring to structural drawings or digital models, and select rivets and fasteners of appropriate size.

[0054] Step 2: By calling internal functions in the OpenCV algorithm library, the marked damage region contour is converted into a contour convex hull. Based on the contour convex hull, the center coordinates, semi-major axis and semi-minor axis lengths, and rotation angle of the minimum envelope ellipse of the damage region contour are calculated. The minimum envelope ellipse is used to simplify the damage region contour, ensuring the equivalence of the overall mechanical performance of the structure while avoiding problems such as difficulty in constructing irregular layered regions and poor convergence in subsequent numerical calculation models. Specifically, this includes the following sub-steps:

[0055] Step 2.1: Call the cvtColor() function in the OpenCV algorithm library to convert the image of the marked damaged area contour into a grayscale image, and use the contour function to find the boundary of the damaged area contour of the grayscale image.

[0056] Step 2.2: Approximate the contour boundary of the damaged region as a convex hull using the convexHull() function, obtaining the convex hull point set P = {P1,…,P}. i ,…,P n The convex hull of a contour is the smallest convex polygon containing the contour boundary, where n represents the number of elements in the vertex set of the convex hull, and P... i Let P be the i-th point in the set of points of the convex hull of the contour. i =(x i ,y i );

[0057] Step 2.3: Calculate the geometric moments of the convex hull based on the point set of the convex hull. And based on the zeroth moment m of the geometric moments 00 First-order moment m 10 and m 01Find the coordinates c of the center point of the ellipse. x =m 10 / m 00 c y =m 01 / m 00 , where m pq μ represents the (p+q)th order moment of the convex hull, where p and q represent the moments of the convex hull in the x and y dimensions, respectively. x and μ y These are the center coordinates of the convex hull of the contour. Zeroth moment m 00 The first moment m represents the area enclosed by the convex hull of the contour. 10 and m 01 These represent the centroid positions of the region enclosed by the convex hull in the x and y dimensions, respectively.

[0058] Step 2.4: Solve for the covariance matrix of the convex hull point set of the contour. Solving for the eigenvalues ​​λ1 and λ2, and the eigenvectors v1 and v2, we obtain the semi-major axis length a and semi-minor axis length b of the ellipse. and The rotation angle of the ellipse is Where Var(x) represents the variance of the convex hull point set along the x-dimensional axis. Var(y) represents the variance of the convex hull point set in the y-axis. Cov(x,y) represents the covariance of the convex hull point set in the x and y dimensions. v1[1] represents the second element of the feature vector v1, and v1[0] represents the first element of the feature vector v1;

[0059] Step 2.5: Establish a coordinate system with the center point of the ellipse as the origin. Draw the minimum envelope ellipse based on the semi-major axis length 'a', semi-minor axis length 'b', and rotation angle to effectively simplify the contour of the damaged area, as shown below. Figure 2 As shown, 1 represents the layered true contour, and 2 represents the minimum envelope ellipse contour. It can be seen that the minimum envelope ellipse closely fits the original irregular shape, and the minimum envelope ellipse effectively reflects the geometric information and directionality of the irregular shape.

[0060] Step 3: Based on the structural characteristics, material properties, location of delamination damage, and minimum envelope ellipse of the aerospace composite component, establish a finite element model of the aerospace composite component with delamination damage. To ensure that the simulation results are closer to the actual test results, set boundary conditions according to the rivet fastener fit relationship during actual maintenance and the loading mode of the structure during performance testing.

[0061] (1) Establish the contact relationship between aerospace composite material components and rivet fasteners;

[0062] (2) Set the preload of the rivet fasteners;

[0063] (3) Set the loading mode and constraint relationship of aerospace composite material components during the mechanical performance test process.

[0064] Step 4: Set the initial conditions for the genetic optimization algorithm: Using the installation position and quantity of rivet fasteners as design variables, the aerospace composite component with delamination damage is divided using the grid method, and the design variables of the rivet fasteners are encoded using binary vectors; the compressive stiffness and structural ultimate strength of the damaged composite laminate structure are used as optimization objectives to establish a riveting repair quality evaluation function.

[0065] The process of setting the design variables in this invention is as follows: A polar coordinate system is established with the center of the minimum envelope ellipse as the pole O and the minor axis of the minimum envelope ellipse as the polar axis X. The installation positions and quantities of the rivet fasteners are arranged as H = [h1, ..., h...]. m …,h M ], where M represents the number of rivet fasteners, M = card(H); h m This indicates the specific location of the m-th rivet fastener. ρ m Represents the position h in polar coordinates m radius, Represents the position h in polar coordinates m To minimize the risk of Type I crack propagation in composite structures with delamination damage under load, a new rivet fastener with the designation i=0, h0, representing the origin of the minimum envelope ellipse for delamination damage, is added. Its position remains fixed during subsequent simulation optimization. The rivet fastener is installed within the minimum envelope ellipse region, i.e., any rivet fastener h... m The point layout will not exceed the boundary of the minimum envelope ellipse, and the point h in the polar coordinate system m radius ρ m satisfy:

[0066]

[0067] Where a is the length of the semi-major axis of the ellipse, b is the length of the semi-minor axis of the ellipse, and c is the semi-focal length of the ellipse.

[0068] In this invention, the riveting repair quality evaluation function must satisfy the requirements of minimizing the number of rivets and fasteners and maximizing the restored stiffness and strength of the damaged structure. Therefore, the riveting repair quality evaluation function is constructed as follows:

[0069]

[0070] Among them, f tLet M represent the maintenance quality index corresponding to the t-th rivet fastener layout scheme, where M = card(H); R t S represents the recovery rate of compressive stiffness of damaged aerospace composite materials under the t-th rivet fastener point layout scheme. t Let R be the structural ultimate strength recovery rate of the damaged aerospace composite material under the t-th rivet fastener point layout scheme, and k1 represent R. t The weight value, k2 represents S t The weight value.

[0071] To discretize the positions of rivet fasteners, the specific process of rivet fastener layout coding is as follows: using the diameter of the rivet fastener as the unit size, the aerospace composite component is divided into several grids using a grid method. Each grid represents a potential rivet fastener connection point, and each grid is numbered starting from the lower left corner, with the numbering starting from 1 and ending at N. Based on the grid diagram of the aerospace composite component, the rivet fasteners are encoded using binary vectors according to their installation position and quantity: S = [w1 w2 ... w N ] T , where S is an N-dimensional vector, and the elements in S are the positions of each cell grid after the grid is divided. If the binary number is 1, it means that a rivet fastener is installed on the grid. If the binary number is 0, it means that no rivet fastener is installed on the grid.

[0072] Step 5: Using the coded rivet fastener design variables as the initial population, input them into the finite element calculation model through the ABAQUS / Python secondary development interface. Calculate the recovery rate R of the compressive stiffness of the damaged aerospace composite material under each rivet fastener point layout scheme in the initial population. t Structural ultimate strength recovery rate S of damaged aerospace composite materials t and R t and S t The genetic optimization algorithm is input through the ABAQUS / Python secondary development interface. Repair quality evaluation indicators are calculated using a repair quality evaluation function. The initial population is iteratively optimized using genetic operators such as selection, crossover, and mutation until the maximum number of iterations is reached, resulting in the final optimized population. Combining finite element analysis with the genetic optimization algorithm allows for the analysis of structural deformation and stress factors in aerospace composite panel structures under load, while simultaneously optimizing the number and location of rivet fasteners. Figure 5 Specifically, it includes the following sub-steps:

[0073] Step 5.1: Based on the fact that the rivets and fasteners are installed within the minimum envelope elliptical region, determine the constraints on the number and installation position of the rivets and fasteners, randomly generate design variables as individuals of the rivet and fastener point layout, and combine the individuals of the rivet and fastener point layout to form an initial population.

[0074] Step 5.2: The initial population is input into the finite element calculation model through the ABAQUS / Python secondary development interface. The recovery rate R of the compressive stiffness of the damaged aerospace composite material under each rivet fastener point layout scheme in the initial population is calculated. t Structural ultimate strength recovery rate S of damaged aerospace composite materials t ;

[0075] Step 5.3, R t and S t The data is input into the genetic optimization algorithm through the ABAQUS / Python secondary development interface, and the repair quality evaluation index is calculated through the repair quality evaluation function.

[0076] Step 5.4: Using the roulette wheel selection method, a set number of individuals are selected from the initial population as parent individuals based on the maintenance quality index. Crossover and mutation are then performed to generate an optimized population. This method determines the probability of selection based on the proportion of individuals' maintenance quality index; individuals with better maintenance quality have a higher probability of being selected. Simultaneously, it avoids the optimization result from falling into a local infinite loop, achieving global optimization. Specifically,

[0077] The specific process of choosing a method in roulette is as follows:

[0078] Step 5.4.1: Determine the maintenance quality index f for each rivet fastener location layout scheme in the population based on the riveting repair quality evaluation function. t and the probability of selecting each rivet fastener point layout scheme. Calculate the cumulative probability C of each rivet fastener point layout scheme. t =p1+p2+…+p t Where T is the number of rivet fastener point layout schemes in the population, 1≤t≤T, and initially, C0=0;

[0079] Step 5.4.2: Generate a random number r, r∈[0,1], and search for a population that satisfies condition C based on the random number r. t-1 ≤r≤C t The layout scheme for rivet fastener locations;

[0080] Step 5.4.3: Select rivet fastener point layout schemes by repeatedly generating random numbers until a sufficient number of rivet fastener point layout schemes are selected as parent individuals to participate in crossover and mutation operations.

[0081] The crossover process is as follows: for two parent individuals S p1 and S p2 Multiple gene positions in the individual's coding were randomly selected for multi-point crossover to obtain two new individuals S. p1 'and S p2 ', where the number and position of intersections are randomly generated. If the position of the rivet fastener in the new individual after intersection is repeated or exceeds the minimum envelope elliptical region, the new individual is deleted.

[0082] The mutation process is specifically as follows: among the newly generated individuals, random individuals S... p Randomly select r positions i1, i2, ..., i r Invert the binary values ​​at these positions to obtain the new individual S. p If the positions of the rivets and fasteners in the mutated updated individual are repeated or exceed the minimum envelope ellipse region, then the new individual is deleted.

[0083] Step 5.5: Replace the initial population with the optimized population, and repeat steps 5.2-5.4 until the maximum number of iterations is reached to obtain the final optimized population.

[0084] Step 6: Sort each rivet and fastener point layout scheme in the final optimized population according to the maintenance quality evaluation index from largest to smallest, and output the rivet and fastener point layout schemes with the top 10% of maintenance quality index for selection in the maintenance of damaged aerospace composite components.

[0085] Example

[0086] In this embodiment, the aerospace composite material components with delamination damage and the rivet fasteners used for maintenance are modeled using ABAQUS as finite element methods. Figure 3Among them, 3 is the finite element model of the composite panel, 4 is the finite element model of the adhesive with delamination damage, and 5 is the simplified finite element model of the rivet fastener. The material properties of the composite panel and the rivet fastener are defined by solid element layup, and the C3D8R eight-node hexahedral reduced integral element is used as the element type. All of them use reinforced hourglass control units. The material properties of the adhesive layer are defined by cohesive layup, and the COH3D8 eight-node three-dimensional cohesive element is used as the element type. The mesh of the delamination area and the periphery of the connection hole is refined to ensure the accuracy of the analysis of contact and stress state. Based on the assembly relationship between aerospace composite components and rivet fasteners, a hard contact property is adopted between the aerospace composite components and rivet fasteners. A surface-to-surface contact relationship with sliding friction and limited sliding is established between their contact surfaces. To simplify calculations, the "Bolt load" function in ABAQUS software is used to simulate the clamping force of the rivet fasteners on the connected parts. Actual working conditions are simulated by restricting the degrees of freedom around the composite panel. During the loading process of the riveting repair model, the lower plate end face is fixed, and a compressive displacement load is applied to the upper plate end face. Simultaneously, the lateral displacements on both sides of the specimen are constrained to simulate the constraint effect of lateral expansion of the specimen during actual loading. Figure 4 As shown.

[0087] Based on the finite element calculation model and boundary conditions set above, the optimized layout of rivet fasteners is obtained through the drilling and riveting point layout optimization method of this invention for repairing damage to aerospace composite components. This optimized layout is then used to repair the actual delaminated composite material, as shown in Table 1. In the genetic optimization algorithm, an initial population is set, and the stiffness of the repaired structure using the initial point layout scheme is 58.85 × 10⁻⁶. 6 The strain has a strength of 102.5 kN and is subjected to iterative optimization using a genetic optimization algorithm to obtain the final optimized population. The stiffness of the damage repair structure after the final optimized site layout is 65.24 × 10⁻⁶ N / m. 6 With a strength of 125.5 kN and a stiffness of N / m, compared to the unrepaired state, the stiffness is increased by 23.7% and the strength by 52.3%, while using fewer rivets and fasteners. Therefore, the drilling and riveting point layout optimization method of this invention for the repair of damaged aerospace composite components can optimize the arrangement of rivets and fasteners during drilling and riveting repair for internal delamination damage in aerospace composite components of any shape, maximizing the restoration of the strength and stiffness of the damaged composite structure, reducing the number of rivets, and reducing the additional weight of the structure.

[0088] Table 1: Comparison of Point Layout Results Optimized Using This Method

[0089]

[0090]

[0091] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for optimizing the layout of drilling and riveting points for the repair of damaged aerospace composite components, characterized in that, Includes the following steps: Step 1: Use non-destructive testing technology to detect the depth, location and shape of delamination damage inside aerospace composite components, mark the outline of the damaged area, and select rivets and fasteners of appropriate size. Step 2: By calling the internal function in the OpenCV algorithm library, the marked damage region contour is converted into a contour convex hull. The center coordinates, semi-major axis and semi-minor axis lengths and rotation angle of the minimum envelope ellipse of the damage region contour are calculated based on the contour convex hull. The minimum envelope ellipse is used to simplify the damage region contour. Step 3: Based on the structural characteristics, material properties, location of delamination damage, and minimum envelope ellipse of the aerospace composite component, establish a finite element calculation model of the aerospace composite component with delamination damage, and set boundary conditions according to the fit relationship between the rivet fastener and the aerospace composite component and the structural load characteristics. Step 4: Set the initial conditions for the genetic optimization algorithm: Using the installation position and quantity of rivet fasteners as design variables, the grid method is used to divide the aerospace composite material components with delamination damage, and binary vectors are used to encode the design variables of the rivet fasteners. A quality evaluation function for riveting repair is established with the compressive stiffness and ultimate structural strength of the damaged composite laminate structure as optimization objectives. Step 5: Using the coded rivet fastener design variables as the initial population, input them into the finite element calculation model through the ABAQUS / Python secondary development interface. Calculate the recovery rate R of the compressive stiffness of the damaged aerospace composite material under each rivet fastener point layout scheme in the initial population. t Structural ultimate strength recovery rate S of damaged aerospace composite materials t and R t and S t The genetic optimization algorithm is input through the ABAQUS / Python secondary development interface. The repair quality evaluation index is calculated through the repair quality evaluation function. The initial population is iteratively optimized through genetic operators such as selection, crossover, and mutation until the maximum number of iterations is reached, and the final optimized population is obtained. Step 6: Sort each rivet and fastener point layout scheme in the final optimized population according to the maintenance quality evaluation index from largest to smallest, and output the rivet and fastener point layout schemes with the top 10% maintenance quality index.

2. The method for optimizing the layout of drilling and riveting points for repairing damage to aerospace composite components according to claim 1, characterized in that, Step 2 includes the following sub-steps: Step 2.1: Call the cvtColor() function in the OpenCV algorithm library to convert the image of the marked damaged area contour into a grayscale image, and use the contour function to find the boundary of the damaged area contour of the grayscale image. Step 2.2: Approximate the contour boundary of the damaged region as a convex hull using the convexHull() function, obtaining the convex hull point set P = {P1,…,P}. i ,…,P n }, where n represents the number of elements in the convex hull set of the contour, P i Let P be the i-th point in the set of points of the convex hull of the contour. i =(x i ,y i ); Step 2.3: Calculate the geometric moments of the convex hull based on the point set of the convex hull. And based on the zeroth moment m of the geometric moments 00 First-order moment m 10 and m 01 Find the coordinates c of the center point of the ellipse. x =m 10 / m 00 c y =m 01 / m 00 , where m pq μ represents the (p+q)th order moment of the convex hull, where p and q represent the moments of the convex hull in the x and y dimensions, respectively. x and μ y These are the center coordinates of the convex hull of the contour. Step 2.4: Solve for the covariance matrix of the convex hull point set of the contour. Solving for the eigenvalues ​​λ1 and λ2, and the eigenvectors v1 and v2, we obtain the semi-major axis length a and semi-minor axis length b of the ellipse. and The rotation angle of the ellipse is Where Var(x) represents the variance of the convex hull point set along the x-dimensional axis. Var(y) represents the variance of the convex hull point set in the y-axis. Cov(x,y) represents the covariance of the convex hull point set in the x and y dimensions. v1[1] represents the second element of the feature vector v1, and v1[0] represents the first element of the feature vector v1; Step 2.5: Establish a coordinate system with the center point coordinates of the ellipse as the origin, and draw the minimum envelope ellipse according to the semi-major axis length a, semi-minor axis length b, and rotation angle to effectively simplify the outline of the damaged area.

3. The method for optimizing the layout of drilling and riveting points for repairing damage to aerospace composite components according to claim 1, characterized in that, The boundary conditions for the finite element calculation model in step 3 are: (1) Establish the contact relationship between aerospace composite material components and rivet fasteners; (2) Set the preload of the rivet fasteners; (3) Set the loading mode and constraint relationship of aerospace composite material components during the mechanical performance test process.

4. The method for optimizing the layout of drilling and riveting points for repairing damage to aerospace composite components according to claim 1, characterized in that, The process of setting the design variables in step 4 is as follows: Establish a polar coordinate system with the center of the minimum envelope ellipse as the pole O and the minor axis of the minimum envelope ellipse as the polar axis X. Arrange the installation positions and quantities of the rivet fasteners as H = [h1, ..., h...]. m …,h M ], where M represents the number of rivet fasteners, M = card(H); h m This indicates the specific location of the m-th rivet fastener. ρ m Represents the position h in polar coordinates m radius, Represents the position h in polar coordinates m The angle.

5. The method for optimizing the layout of drilling and riveting points for repairing damage to aerospace composite components according to claim 4, characterized in that, The rivet fastener is installed within the minimum envelope elliptical region, at point h in the polar coordinate system. m radius ρ m satisfy: Where a is the length of the semi-major axis of the ellipse, b is the length of the semi-minor axis of the ellipse, and c is the semi-focal length of the ellipse.

6. The method for optimizing the layout of drilling and riveting points for repairing damage to aerospace composite components according to claim 1, characterized in that, The riveting repair quality evaluation function is: Among them, f t Let M represent the maintenance quality index corresponding to the t-th rivet fastener layout scheme, where M = card(H); and k1 represents R. t The weight value, k2 represents S t The weight value.

7. The method for optimizing the layout of drilling and riveting points for repairing damage to aerospace composite components according to claim 1, characterized in that, Step 4, the process of encoding the rivet fastener layout, is as follows: Using the diameter of the rivet fastener as the unit size, the aerospace composite component is divided into several grids using a grid method. Each grid represents a potential rivet fastener connection point, and each grid is numbered starting from the lower left corner, with the numbering beginning with 1 and ending at N. Based on the grid diagram of the aerospace composite component, the rivet fasteners are encoded using binary vectors according to their installation position and quantity: S = [w1 w2 ... w N ] T , where S is an N-dimensional vector, and the elements in S are the positions of each cell grid after the grid is divided. If the binary number is 1, it means that a rivet fastener is installed on the grid. If the binary number is 0, it means that no rivet fastener is installed on the grid.

8. The method for optimizing the layout of drilling and riveting points for repairing damage to aerospace composite components according to claim 1, characterized in that, Step 5 includes the following sub-steps: Step 5.1: Based on the fact that the rivets and fasteners are installed within the minimum envelope elliptical region, determine the constraints on the number and installation position of the rivets and fasteners, randomly generate design variables as individuals of the rivet and fastener point layout, and combine the individuals of the rivet and fastener point layout to form an initial population. Step 5.2: The initial population is input into the finite element calculation model through the ABAQUS / Python secondary development interface. The recovery rate R of the compressive stiffness of the damaged aerospace composite material under each rivet fastener point layout scheme in the initial population is calculated. t Structural ultimate strength recovery rate S of damaged aerospace composite materials t ; Step 5.3, R t and S t The data is input into the genetic optimization algorithm through the ABAQUS / Python secondary development interface, and the repair quality evaluation index is calculated through the repair quality evaluation function. Step 5.4: Use the roulette wheel selection method to select a set number of individuals from the initial population as parent individuals, perform crossover and mutation, and generate an optimized population; Step 5.5: Replace the initial population with the optimized population, and repeat steps 5.2-5.4 until the maximum number of iterations is reached to obtain the final optimized population.

9. The method for optimizing the layout of drilling and riveting points for repairing damage to aerospace composite components according to claim 8, characterized in that, The specific process of choosing the roulette wheel selection method in step 5.4 is as follows: Step 5.4.1: Determine the maintenance quality index f for each rivet fastener location layout scheme in the population based on the riveting repair quality evaluation function. t and the probability of selecting each rivet fastener point layout scheme. Calculate the cumulative probability C of each rivet fastener point layout scheme. t =p1+p2+…+p t Where T is the number of rivet fastener point layout schemes in the population, 1≤t≤T, and initially, C0=0; Step 5.4.2: Generate a random number r, r∈[0,1], and search for a population that satisfies condition C based on the random number r. t-1 ≤r≤C t The layout scheme for rivet fastener locations; Step 5.4.3: Select rivet fastener point layout schemes by repeatedly generating random numbers until a sufficient number of rivet fastener point layout schemes are selected as parent individuals to participate in crossover and mutation operations.

10. The method for optimizing the layout of drilling and riveting points for the repair of damaged aerospace composite components according to claim 8, characterized in that, The crossover process in step 5.4 is as follows: For two parent individuals S p1 and S p2 Multiple gene positions in the individual's coding were randomly selected for multi-point crossover to obtain two new individuals S. p1 'and S p2 ', where the number and position of intersections are randomly generated. If the position of the rivet fastener in the new individual after intersection is repeated or exceeds the minimum envelope elliptical region, the new individual is deleted. The mutation process in step 5.2 is specifically as follows: among the newly generated individuals, random individuals S... p Randomly select r positions i1, i2, ..., i r Invert the binary values ​​at these positions to obtain the new individual S. p If the positions of the rivets and fasteners in the mutated updated individual are repeated or exceed the minimum envelope ellipse region, then the new individual is deleted.

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