Method for studying the effect of random hole geometry deviations on the strength of aircraft panel joint structures

Abstract

The application discloses a method for researching the influence of random hole geometric deviation on the strength of an aircraft wall plate connecting structure, and relates to the field of advanced composite material connection, and comprises the following steps: determining a characterization parameter of hole geometric deviation of a composite material strip-hole laminated plate test piece; establishing a simulation model of a composite material single-nail connecting structure plug-nail connection without hole geometric deviation; based on the characterization parameter and the simulation model of the composite material single-nail connecting structure plug-nail connection without hole geometric deviation, a simulation model of a composite material single-nail connecting structure interference plug-nail process is established; a simulation model of a composite material connecting structure tensile load is established; based on the simulation model of the composite material connecting structure tensile load, a probability distribution graph of the strength change value of the structure is established, and the strength distribution trend under different geometric deviations is determined; and based on the strength distribution trend under different geometric deviations, a new composite material hole making deviation design criterion is constructed. The application can improve the hole making precision of the connecting hole, and reduce the manufacturing difficulty and cost.

Description

Technical Field

[0001] This invention relates to the field of advanced bonding technology for composite materials, and in particular to a method for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures. Background Technology

[0002] Bolted connections are widely used in various engineering structures due to their simple structure, easy disassembly, and low cost, and still hold an important position in the manufacturing of modern aircraft using advanced composite materials. However, each mechanical connection hole in an aircraft panel connection structure compromises material integrity, affecting the strength of the mechanical connection and thus the overall service performance of the aircraft panel. This is mainly due to stress concentration at the hole edges, micro-damage to the hole walls, and the precision of the hole-making geometry, especially for composite material components. Therefore, the precision of the hole-making and the assembly quality are key factors affecting the reliability and service strength of aircraft panel structural components.

[0003] CFRP (Chemical Fluorescent Reinforced Polymer) is a typical difficult-to-machine material. CFRP laminates are non-metallic materials with non-homogeneity, anisotropy, and high hardness, exhibiting extremely low interlayer bonding strength. During machining, defects such as delamination, splitting, radial extrusion, and subsurface damage easily occur. The material fracture is primarily brittle fracture of the fibers, and the friction between the carbon fibers and the tool edge leads to rapid tool dulling and short tool life. These characteristics make the hole-making process of CFRP structures extremely difficult, and the hole-making accuracy is hard to guarantee. In actual assembly production, due to uncontrollable factors such as hole-making equipment, personnel, and environment, the geometric accuracy of composite material holes exhibits a random distribution within a certain error threshold range. The finite element method (FEM) is a method for predicting assembly damage and strength of composite material connection structures. Because it does not require extensive destructive testing, it allows for simulation analysis of the structural loading process at minimal cost.

[0004] The current state of research both domestically and internationally shows that existing studies on bolted connection structures considering the influence of hole geometry deviations mainly focus on predicting the mechanical properties of composite material connection structures under the given upper limit of hole geometry error in the manufacturing process. However, in predicting the load-bearing capacity of related composite material connection structures, the traditional method of strictly controlling hole accuracy to ensure structural load-bearing performance is undoubtedly an excessive constraint on the manufacturing accuracy of composite material connection structures, while also increasing the requirements for hole-making technology and significantly increasing production costs. Summary of the Invention

[0005] The purpose of this invention is to provide a method for studying the influence of random hole geometric deviation on the strength of aircraft panel connection structures. Based on the influence of random hole geometric deviation on the strength of aircraft panel composite connection structures, a new composite material hole deviation design criterion suitable for actual aircraft panel assembly production is constructed to improve the hole making accuracy of connection holes.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A method for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures includes:

[0008] Considering the randomness in the actual composite material assembly process, characterization parameters for the hole geometric deviation of the composite perforated laminate specimen are determined; the hole geometric deviation includes: hole position deviation, hole diameter deviation, and hole perpendicularity deviation.

[0009] Based on the structural dimensions, contact properties, loads, and boundary conditions of carbon fiber composite materials and bolts, a simulation model of a single-nail connection structure of composite materials under non-porous geometric deviations is established.

[0010] Based on the characterization parameters and the simulation model of the single-nail connection structure of composite material under the non-porous geometric deviation, a simulation model of the interference insertion process of the single-nail connection structure of composite material is established.

[0011] Based on the simulation model of the interference pin insertion process of the composite single nail connection structure, a simulation model of tensile load of composite connection structure is established based on the deformation and material damage state of the connection structure output by the simulation model of the interference pin insertion process of the composite single nail connection structure.

[0012] Based on the tensile load simulation model of the composite material connection structure, a probability distribution map of the structural strength variation value is established to determine the strength distribution trend under different geometric deviations.

[0013] Based on the strength distribution trend under different geometric deviations, and combined with the hole-making quality criteria for aircraft panels, a new design criterion for hole-making deviations in composite materials is constructed.

[0014] Optionally, the characterization parameters of the hole position deviation are as follows:

[0015] t∈[0,T], a∈[0,2π]

[0016] Where T represents the maximum upper limit of the hole position deviation required by the hole design, t represents the length of the random hole position deviation vector in actual production, and a represents the angle between the hole position deviation vector and the x-axis.

[0017] The parameters characterizing the aperture deviation are as follows:

[0018] r∈[-ΔR,+ΔR]

[0019] Where ΔR represents the upper limit of the absolute value of the hole diameter deviation required by the hole design, and r represents the random hole diameter deviation value in actual production;

[0020] The parameters characterizing the hole perpendicularity deviation are as follows:

[0021] b∈[0,2π], c∈[0,C]

[0022] Where C represents the maximum upper limit of the hole perpendicularity deviation required by the hole design, c represents the angle value of the random hole perpendicularity deviation in actual production, and b represents the angle between the projection of the hole axis direction on the xy plane and the x-axis.

[0023] Optionally, based on the structural dimensions, contact properties, loads, and boundary conditions of the carbon fiber composite material and the bolts, a simulation model of the composite single-nail connection structure with insert pins under non-porous geometric deviations is established, specifically including:

[0024] A three-dimensional geometric model of the bolt is established, and a three-dimensional geometric model of the composite material laminate structure is established based on the structural dimensions, contact properties, loads and boundary conditions of the carbon fiber composite material and the bolt.

[0025] Based on the actual composite material assembly conditions, the carbon fiber composite laminate and base are restricted to three degrees of freedom in the movement direction and three degrees of freedom in the rotation direction. The bolts are restricted to five degrees of freedom except for the movement in the z direction, and a pin displacement load is applied. Under the above restrictions, the influence of hole-making damage on the degradation of material properties is considered to establish the stress-strain constitutive relationship of carbon fiber composite material.

[0026] Based on the three-dimensional geometric model of the bolt and the three-dimensional geometric model of the composite material laminate structure, and according to the contact stress between the bolt and the hole wall of the composite material, the three-dimensional Hashin failure criterion is used to perform stress analysis and material failure judgment on the carbon fiber composite material unit, and a simulation model of the single nail connection structure of the composite material without hole geometric deviation is established.

[0027] Optionally, based on the characterization parameters and the simulation model of the composite single-nail connection structure under the non-porous geometric deviation, a simulation model of the interference insertion process of the composite single-nail connection structure is established, specifically including:

[0028] The characterization parameters are randomly assigned values ​​based on the determined hole geometry deviation type;

[0029] A numerical model coordinate system is established, and the assigned characterization parameters in the material model coordinate system are converted to the global coordinate system using the coordinate transformation projection matrix. A simulation model of the interference nail insertion process of the composite single nail connection structure is then established.

[0030] Optionally, a tensile load simulation model of the composite material connection structure is established based on the deformation of the connection structure and the material damage state output by the simulation model of the interference insertion process of the composite single-nail connection structure, specifically including:

[0031] Establish motion coupling reference points for the upper and lower laminates in the composite material laminate structure, restrict the degrees of freedom of the upper and lower laminates, add static tension positions to the upper laminate and apply bolt preload, set the upper and lower laminates in the composite material laminate structure to a predefined field, and complete the setting operation.

[0032] Based on the aforementioned settings, the deformation and material damage states of the connection structure are selected, and the stress state and damage distribution brought about during the insertion process are imported to establish a tensile three-dimensional model that inherits the force field of the insertion pin.

[0033] Stress analysis was performed on the tensile three-dimensional model to establish a simulation model of tensile load on the composite material connection structure.

[0034] Optionally, based on the tensile load simulation model of the composite material connection structure, a probability distribution map of the structural strength variation values ​​is established to determine the strength distribution trend under different geometric deviations, specifically including:

[0035] Load-displacement curves were plotted based on the simulation results of the tensile load simulation model of the composite material connection structure.

[0036] Extract the ultimate load from all load-displacement curves;

[0037] Based on the variation value of the structural ultimate load in the simulation model of the composite single-nail connection structure under the ultimate load and the non-porous geometric deviation, the simulation model of the pin connection is based on the ultimate load variation value.

[0038] A probability histogram of structural strength variation values ​​is established based on the ratio of the variation value to the ultimate load of the reference structure.

[0039] Based on the probability histogram of the structural strength variation values, the Monte Carlo method is used to determine the strength distribution trend under different geometric deviations.

[0040] This invention also provides a system for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures, comprising:

[0041] The characterization parameter determination module is used to determine the characterization parameters of the hole geometric deviation of the composite perforated laminate specimen, taking into account the randomness in the actual composite material assembly process; the hole geometric deviation includes: hole position deviation, hole diameter deviation and hole perpendicularity deviation.

[0042] The first model building module is used to build a simulation model of the single-nail connection structure of composite material under the condition of no hole geometric deviation, based on the structural dimensions, contact properties, load and boundary conditions of carbon fiber composite material and bolts.

[0043] The second model building module is used to establish a simulation model of the interference insertion process of the composite single nail connection structure based on the characterization parameters and the simulation model of the insertion connection of the composite single nail connection structure under the non-porous geometric deviation.

[0044] The third model building module is used to establish a tensile load simulation model of the composite material connection structure based on the connection structure deformation and material damage state output by the simulation model of the interference pin insertion process of the composite single nail connection structure.

[0045] The probability distribution map building module for structural strength variation values ​​is used to build a probability distribution map of structural strength variation values ​​based on the tensile load simulation model of the composite material connection structure, and to determine the strength distribution trend under different geometric deviations.

[0046] A novel composite material hole-making deviation design criterion construction module is used to construct a novel composite material hole-making deviation design criterion based on the strength distribution trend under different geometric deviations and in combination with the aircraft panel hole-making quality criteria.

[0047] Optionally, the first model construction module specifically includes:

[0048] The three-dimensional geometric model building unit is used to establish the three-dimensional geometric model of the bolt, and to establish the three-dimensional geometric model of the composite material laminate structure based on the structural dimensions, contact properties, load and boundary conditions of the carbon fiber composite material and the bolt.

[0049] The stress-strain constitutive relationship establishment unit for carbon fiber composite materials is used to restrict the three degrees of freedom in the movement direction and the three degrees of freedom in the rotation direction of the carbon fiber composite laminate and the base according to the actual composite assembly conditions, restrict the five degrees of freedom of the bolt except for the movement in the z direction, and apply the pin displacement load. Under the above restrictions, the influence of hole-making damage on the degradation of material properties is considered to establish the stress-strain constitutive relationship of carbon fiber composite materials.

[0050] The first model building unit is used to establish a simulation model of the composite material single nail connection structure based on the three-dimensional geometric model of the bolt and the three-dimensional geometric model of the composite material laminate structure. According to the contact stress between the bolt and the hole wall of the composite material, the three-dimensional Hashin failure criterion is used to perform stress analysis and material failure judgment on the carbon fiber composite material unit, and establish a simulation model of the single nail connection structure of the composite material without hole geometric deviation.

[0051] Optionally, the second model building module specifically includes:

[0052] The assignment unit is used to randomly assign values ​​to the characterization parameters according to the determined hole geometry deviation type;

[0053] The second model establishment unit is used to establish the numerical model coordinate system. It uses the coordinate transformation projection matrix to convert the assigned characterization parameters in the material model coordinate system into the global coordinate system, and establishes a simulation model of the interference nail insertion process of the composite single nail connection structure.

[0054] Optionally, the third model building module specifically includes:

[0055] The setting operation completion unit is used to establish motion coupling reference points for the upper and lower laminates in the composite material laminate structure, restrict the degrees of freedom of the upper and lower laminates, add static tension positions to the upper laminate and apply bolt preload, set the upper and lower laminates in the composite material laminate structure to a predefined field, and complete the setting operation.

[0056] The extrusion 3D model building unit is used to select the deformation and material damage state of the connection structure based on the set operation, import the stress state and damage distribution brought about by the insertion process, and build an extrusion 3D model that inherits the force field of the insertion.

[0057] The third model building unit is used to perform stress analysis on the tensile three-dimensional model and establish a tensile load simulation model of the composite material connection structure.

[0058] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0059] This invention provides a method for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures. Considering the randomness of actual composite material assembly processes, characterization parameters for hole geometric deviations in composite perforated laminate specimens are determined. Based on the structural dimensions, contact properties, loads, and boundary conditions of carbon fiber composite materials and bolts, a simulation model of a composite single-nail connection structure with insert pins under hole-free geometric deviations is established. Based on the characterization parameters and the simulation model of the composite single-nail connection structure with insert pins under hole-free geometric deviations, a simulation model of the interference insertion process of the composite single-nail connection structure is established. Based on the deformation and material damage state of the connection structure output by the simulation model of the interference insertion process of the composite single-nail connection structure, a simulation model of the tensile load of the composite connection structure is established. Based on the tensile load simulation model of the composite connection structure, a probability distribution map of structural strength variation values ​​is established to determine the strength distribution trend under different geometric deviations. Based on the strength distribution trend under different geometric deviations, combined with the hole-making quality criteria for aircraft panels, a novel composite hole-making deviation design criterion is constructed. This invention addresses the impact of random hole geometric deviations on the structural load-bearing performance during the assembly of composite panel connection structures in actual aircraft. It constructs a novel design criterion for hole deviations in composite materials, thereby eliminating the excessive requirements for hole precision imposed by traditional research methods, optimizing assembly connection process parameters, reducing manufacturing difficulty and cost, and lowering the material cost and preparation cycle of experimental methods. This provides a basis for optimizing process design schemes and promotes the development of advanced composite material connection technologies. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0061] Figure 1 A flowchart of a method for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures provided by this invention;

[0062] Figure 2 A detailed flowchart of the method for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures provided by this invention;

[0063] Figure 3 A schematic diagram illustrating the parameterized characterization of hole geometric deviation;

[0064] Figure 4 Schematic diagram of the dimensions of the composite material interference pin structure;

[0065] Figure 5Schematic diagram of a simulation model of interference pin connection in composite material connection structure;

[0066] Figure 6 Schematic diagram of tensile load model for composite material connection structure;

[0067] Figure 7 Schematic diagram of tensile load-displacement curve of composite material interference connection structure without hole position deviation;

[0068] Figure 8 Probability distribution of the variation value of the bearing limit of the composite material interference connection structure when the hole position deviation T = 0.05 mm. Detailed Implementation

[0069] 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.

[0070] The purpose of this invention is to provide a method for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures, so as to improve the hole-making accuracy of connection holes while reducing manufacturing difficulty and cost.

[0071] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0072] Example 1

[0073] like Figures 1-2 As shown, the present invention provides a method for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures, comprising the following steps:

[0074] S1: Considering the randomness in the actual composite material assembly process, determine the characterization parameters for the hole geometric deviation of the composite perforated laminate specimen; the hole geometric deviation includes: hole position deviation, hole diameter deviation, and hole perpendicularity deviation, such as... Figure 3 As shown.

[0075] Furthermore, step S1 specifically includes:

[0076] Step S11: Hole position deviation represents the deviation between the actual composite material hole and the designed hole in a two-dimensional plane perpendicular to the hole axis. Therefore, a vector is used to represent the deviation between the center of the deviation hole and the center of the standard hole, with the length of the vector and the angle between the vector and the x-axis used as characterizing parameters for the hole position deviation. This can be expressed as:

[0077] t∈[0,T],a∈[0,2π]

[0078] Where T represents the maximum upper limit of the hole position deviation required by the hole design, t represents the length of the random hole position deviation vector in actual production, and a represents the angle between the hole position deviation vector and the x-axis.

[0079] Step S12: Hole diameter deviation represents the deviation in hole diameter when the actual composite material hole and the designed hole are concentric. Therefore, a scalar r is used to represent the deviation between the center of the deviation hole and the center of the standard hole. This can be expressed as:

[0080] r∈[-ΔR,+ΔR]

[0081] Where ΔR represents the upper limit of the absolute value of the hole diameter deviation required by the hole design, and r represents the random hole diameter deviation value in actual production.

[0082] Step S13: Hole perpendicularity deviation represents the angular deviation between the actual composite material hole axis direction and the normal direction of the sheet material. Therefore, the angle between the hole axis and the z-axis and the angle between the projection of the hole axis onto the xy-plane and the x-axis are used as characterizing parameters for hole perpendicularity deviation. This can be expressed as:

[0083] b∈[0,2π],c∈[0,C]

[0084] Where C represents the maximum upper limit of the hole perpendicularity deviation required by the hole design, c represents the angle value of the random hole perpendicularity deviation in actual production, and b represents the angle between the projection of the hole axis direction on the xy plane and the x-axis.

[0085] S2: Based on the structural dimensions, contact properties, loads, and boundary conditions of carbon fiber composite materials and bolts, a simulation model of a composite single-nail connection structure with insert pins under hole-free geometric deviations is established. Specifically, this includes: establishing a three-dimensional geometric model of the bolts; establishing a three-dimensional geometric model of the composite laminate structure based on the structural dimensions, contact properties, loads, and boundary conditions of the carbon fiber composite materials and bolts; restricting the three degrees of freedom of movement and three degrees of freedom of rotation of the carbon fiber composite laminate and base according to actual composite assembly conditions; restricting the five degrees of freedom of bolt movement except for the z-direction and applying insert pin displacement loads; and, under the above constraints, considering the influence of hole-making damage on material property degradation, establishing a stress-strain constitutive relationship for the carbon fiber composite material; based on the three-dimensional geometric model of the bolts and the three-dimensional geometric model of the composite laminate structure, and according to the contact stress between the bolt and the composite hole wall, using the three-dimensional Hashin failure criterion to perform stress analysis and material failure judgment on the carbon fiber composite unit, thus establishing a simulation model of a composite single-nail connection structure with insert pins under hole-free geometric deviations.

[0086] Furthermore, the simulation model is parameterized, and a simulation model of a composite material single-nail connection structure with pin connection under pore-free geometric deviation is constructed by writing a Python modeling program.

[0087] S21: Establish a three-dimensional geometric model of the carbon fiber composite material and the bolt according to the requirements of ASTM D-5961. Since the length of the bolt shank is greater than the thickness of the laminate of the connection structure, the threaded part is ignored, and the bolt is simplified into a "T" shaped solid model.

[0088] S22: The carbon fiber composite material uses reduced integral hexahedral elements C3D8R, with enhanced hourglass control to reduce mesh distortion. Metal bolts are set as rigid bodies for easier subsequent interference calculations. Based on actual composite assembly conditions, the carbon fiber composite laminate and base are restricted to three translational directions and three rotational directions. The bolts are restricted to five degrees of freedom except for the z-direction, and pin displacement loads are applied.

[0089] S23: Establish the stress-strain constitutive relationship for carbon fiber composites, considering the impact of pore-forming damage on material property degradation. This can be expressed as:

[0090]

[0091] In the formula, σ n σ t These are the normal stress component and the shear stress component, respectively; ε n ε t These are the normal strain component and the shear strain component, respectively; C n C t The stiffness is measured in the normal and shear directions.

[0092] S24: Combining the three-dimensional finite element model, based on the contact stress between the bolt and the composite material hole wall, and considering the shear nonlinear behavior of the carbon fiber composite material, the three-dimensional Hashin failure criterion is used to perform stress analysis and material failure judgment on the carbon fiber composite material element.

[0093] (1) Fiber tensile failure (σ 11 ≥0):

[0094]

[0095] (2) Fiber compression failure (σ) 11 <0):

[0096]

[0097] (3) In-plane matrix tensile failure (σ 22 +σ 33 ≥0):

[0098]

[0099] (4) In-plane matrix compression failure (σ 22 +σ 33 <0):

[0100]

[0101] (5) Out-of-plane matrix tensile failure (σ 33 ≥0):

[0102]

[0103] (6) Out-of-plane matrix compression failure (σ 33 <0):

[0104]

[0105] In the formula, σ 11 σ 22 σ 33 These are the principal stresses in the x, y, and z directions, respectively; σ 12 σ 13 σ 23 These represent the in-plane shear stresses in the corresponding directions; X c X t Y c Y t Z c Z t These represent the tensile and compressive ultimate strengths in the x, y, and z directions, respectively, with the subscript t indicating tension and c indicating compression; S 12 S 13 S 23 These represent the shear limit strength in the corresponding directions; when F ft F fc F mt F mc F nt F nc When the value is ≥1, the carbon fiber composite unit is damaged; otherwise, the unit is not damaged.

[0106] S25: After performing damage analysis on each carbon fiber composite element using material failure criteria, determine whether the element has been damaged. If damaged, apply the corresponding stiffness reduction model to reduce the current material stiffness and update the stress; if no damage occurs, the element stiffness remains unchanged; establish a composite material damage model. Damage stiffness reduction matrix C related to damage variables. d It is expressed as follows:

[0107]

[0108] Where: b1 = 1 - d f b2 = 1 - d m b3 = 1 - d s

[0109] Three independent damage variables were considered: d f d m d s ;d f Indicates degradation in fiber orientation; d m Indicates degradation along the direction perpendicular to the fiber; d s This indicates a degradation in shear properties parallel to the fiber direction. The relationship is as follows:

[0110] d f =1-(1-d) FT (1-d) FC )

[0111] d m =1-(1-d) MT (1-d) MC )

[0112] d s =1-(1-d) f (1-smt×d) MT (1-smc×d) MC )

[0113] In the formula, d FT d FC d represents the damage variable in the fiber's tensile and compressive directions. MT d MC represents the damage variables in the tensile and compressive directions of the matrix; smt and smc are coefficients representing the loss of shear modulus due to tensile and compressive failure of the matrix.

[0114] S26: After modeling is completed, the model is transformed into a runnable algorithm program by writing a Python modeling program, and a simulation model of the single nail connection structure of composite material under non-porous geometric deviation is constructed.

[0115] S3: Based on the characterization parameters and the simulation model of the composite single-nail connection structure under the non-porous geometric deviation, establish a simulation model of the interference insertion process of the composite single-nail connection structure. Specifically, this includes: randomly assigning values ​​to the characterization parameters according to the determined hole geometric deviation type; establishing a numerical model coordinate system; using a coordinate transformation projection matrix to convert the assigned characterization parameters in the material model coordinate system to the global coordinate system; and establishing a simulation model of the interference insertion process of the composite single-nail connection structure.

[0116] Furthermore, a randomized parameter program is used to randomly assign values ​​to the hole geometric deviations (hole position deviation, hole diameter deviation, and hole perpendicularity deviation) to simulate the actual geometric state of the composite material holes during actual assembly production. Based on the model in step S2, the program parameters are corrected, the generated random hole geometric deviation parameters are input, and a batch modeling algorithm is written. Finally, the program is run to generate a large number of sample data of the pin connection model with random hole geometric deviations. After the batch simulation model of the composite material single-pin connection structure interference pin insertion process is analyzed, the deformation and damage are output respectively, and the pin insertion process restart data is saved.

[0117] S31: Based on the determined hole geometry deviation type, perform parameter initialization. Given the number of sample data models N and the maximum upper limit of hole geometry deviation (T, R, C), use the random function to assign random values ​​to the hole geometry deviation. This can be expressed as:

[0118] Hole position deviation: random(t,a)in t∈[0,T],a∈[0,2π];

[0119] Aperture deviation: random(r)in r∈[-ΔR,+ΔR];

[0120] Hole perpendicularity deviation: random(b,c)inb∈[0,2π],c∈[0,C];

[0121] In the formula, T represents the upper limit of the maximum value of the hole position deviation required by the hole design, ΔR represents the upper limit of the maximum value of the absolute value of the hole diameter deviation required by the hole design, and C represents the upper limit of the maximum value of the hole perpendicularity deviation required by the hole design.

[0122] S32: Based on the reference numerical model program in step S2, perform parameter correction on the Python program. Geometric feature identification and insertion are performed on the hole position deviation parameters t and a, hole diameter deviation parameter r, and hole perpendicularity deviation parameters b and c, respectively. A numerical model coordinate system is established, and the hole geometric deviation parameters in the material model coordinate system are converted to the global coordinate system using a coordinate transformation projection matrix. A batch modeling program is then written.

[0123] The two-dimensional coordinate transformation relationship of hole position deviation can be expressed as:

[0124]

[0125] In the formula Represents the global coordinate system With the material model coordinate system The relative translation transformation matrix of a two-dimensional plane. This represents the relative rotation transformation matrix between the global coordinate system and the material coordinate system in a two-dimensional plane.

[0126] The two-dimensional coordinate transformation relationship of aperture deviation can be expressed as:

[0127]

[0128] In the formula Represents the global coordinate system With the material model coordinate system The relative translation transformation matrix of a two-dimensional plane.

[0129] The three-dimensional coordinate transformation relationship of the hole perpendicularity deviation can be expressed as:

[0130]

[0131]

[0132]

[0133] In the formula Represents the global coordinate system With the material model coordinate system The relative translation transformation matrix of a three-dimensional plane. This represents the relative rotation transformation matrix between the global coordinate system and the material coordinate system in three-dimensional space along the x-axis. This represents the relative rotation transformation matrix between the global coordinate system and the material coordinate system in three-dimensional space along the y-axis. This represents the relative rotation transformation matrix between the global coordinate system and the material coordinate system in three-dimensional space along the z-axis.

[0134] S33: Input the N sets of random hole geometric deviation parameters generated in step S31 into the batch modeling program in step S32, run the parametric modeling program, and generate a large number of composite material connection structure model data sample sets with random hole geometric deviations.

[0135] S34: After the simulation model of the interference insertion process of the batch composite single nail connection structure is analyzed, the deformation and material damage state of the connection structure are output and packaged into the insertion process restart data for cross-stage model analysis.

[0136] S4: Based on the deformation and material damage state of the connection structure output by the simulation model of the interference insertion process of the composite single-nail connection structure, a tensile load simulation model of the composite connection structure is established. Specifically, this includes: establishing motion coupling reference points for the upper and lower laminates in the composite laminate structure, restricting the degrees of freedom of the upper and lower laminates, adding a static tension position to the upper laminate and applying bolt preload, setting a predefined field for the upper and lower laminates in the composite laminate structure, and completing the setting operation; based on the setting operation, selecting the deformation and material damage state of the connection structure, importing the stress state and damage distribution brought about by the insertion process, and establishing a tensile three-dimensional model inheriting the insertion force field; performing stress analysis on the tensile three-dimensional model to establish a tensile load simulation model of the composite connection structure.

[0137] Furthermore, based on the restart database of the pin connection process model, the unit equivalent stress and damage distribution obtained in step S3 are inherited, and the composite laminate lap structure model with geometric deformation field and physical damage field is imported. The corresponding loads and boundary conditions are applied to establish a tensile load simulation model of composite joint structure and construct the basic dataset of Monte Carlo analysis method.

[0138] S41: Establish a three-dimensional geometric model of the carbon fiber composite material and the bolt. The deformed composite laminate is imported from the simulation results file of the stud connection in step S2. A three-dimensional model inheriting the geometric deformation field of the stud is established to complete the dynamic transfer and evolution process of the geometric field. Since the mechanical behavior of the bolt is not considered, an "I"-shaped bolt model is established instead of a "T"-shaped bolt model.

[0139] S42: Establish motion coupling reference points for the upper and lower composite plates and restrict their degrees of freedom. Add static tensile displacement to the upper composite plate and apply bolt preload. To avoid conflicts in bolt cross-section properties, set the bolt cross-section properties to default during mesh generation.

[0140] S43: Read the simulation result file of the pin connection in step S3, set the predefined field for the upper and lower composite plates, select the result of the last analysis step of the pin simulation model, import the stress state and damage distribution brought about by the pin insertion process, and establish a tensile three-dimensional model that inherits the pin force field.

[0141] S44: Combining the composite material properties, failure criteria, and stiffness reduction model from step S2, perform stress analysis on the above tensile three-dimensional model to determine whether each composite material unit has been damaged or has undergone stiffness reduction, and establish a damage model.

[0142] S5: Based on the tensile load simulation model of the composite material connection structure, establish a probability distribution map of the structural strength variation value, and determine the strength distribution trend under different geometric deviations.

[0143] After the tensile load simulation model of the batch composite single-nail connection structure was completed, the load-displacement curves of each simulation result were plotted, and the tensile strength of the structure was extracted and statistically analyzed. Following the statistical principles of the Monte Carlo method, a probability distribution map of the structural strength variation under a given geometric deviation was established, and the strength distribution trend under different geometric deviations was analyzed.

[0144] Furthermore, step S5 specifically includes:

[0145] S51: After the batch simulation model calculations are completed, output the displacement and support reaction force along the loading direction at the motion coupling reference point according to the result file, and plot the load-displacement curve of the simulation results. Repeat the operation until all models have completed the output of results.

[0146] S52: Extract the ultimate load Fi from all load-displacement curves, and calculate the change in the ultimate load ΔF of the structure compared to the model without geometric deviation. i The ratio to the ultimate load F0 of the reference structure. The ratio ΔF is calculated statistically. i The distribution trend and pattern of / F0 were analyzed, and a probability histogram of structural strength variation values ​​was established.

[0147] S53: Based on the probability histogram in step S52, use the Monte Carlo method to analyze the statistical results and obtain the intensity distribution trend under a given geometric deviation.

[0148] S6: Based on the strength distribution trend under different geometric deviations, and combined with the hole-making quality criteria for aircraft panels, a new design criterion for hole-making deviations in composite materials is constructed.

[0149] Based on the analysis results in step S5, and combined with the quality criteria for hole making in aircraft panels, a new design criterion for hole making deviation of composite materials suitable for actual aircraft panel assembly production is constructed.

[0150] Example 2

[0151] To better understand the method in Embodiment 1, this embodiment provides a specific example.

[0152] This embodiment uses T300 / TED-85 carbon fiber composite material (layout sequence [0 / 45 / -45 / 90]3s) and Ti6Al4V bolt material as examples, with a hole position deviation T = 0.1mm and a number of groups N = 500. Other geometric deviations (hole diameter deviation, hole perpendicularity deviation) are similar. The more groups N, the higher the accuracy of the results, but the higher the calculation cost.

[0153] I. Considering the randomness in the actual composite material assembly process, the hole position deviation of the composite perforated laminate specimen is characterized by parameters.

[0154] Hole position deviation represents the deviation of the actual composite material hole from the designed hole in a two-dimensional plane perpendicular to the hole axis. Therefore, a vector is used to represent the deviation between the center of the deviation hole and the center of the standard hole, with the length of the vector and the angle between the vector and the x-axis used as characterizing parameters of the hole position deviation. This can be expressed as:

[0155] t∈[0,T],a∈[0,2π]

[0156] Where T represents the maximum upper limit of the hole position deviation required by the hole design, t represents the length of the random hole position deviation vector in actual production, and a represents the angle between the hole position deviation vector and the x-axis.

[0157] II. Based on the structural dimensions, contact properties, loads, and boundary conditions of carbon fiber composite materials and bolts, a simulation model of a composite single-nail connection structure with insert connections under pore-free geometric deviations is established. Simultaneously, the simulation model is parameterized, and a reference numerical model for the simulation of the composite single-nail connection structure with insert connections is constructed using a Python modeling program.

[0158] 2.1 The structure and dimensions required by ASTM D-5961 are as follows: Figure 4 As shown, the composite laminates are named PLATE1 & PLATE2, the metal bolts are named BOLT, and the washers are named BASEPLATE. A three-dimensional geometric model of the carbon fiber composite laminates and bolts was created using Abaqus software. Since the length of the bolt shank is greater than the thickness of the laminate in the connection structure, the threaded portion is ignored, and the bolt is simplified to a "T" shape. Its material parameters are shown in Table 1. Geometric errors caused by the actual hole-making process are not considered when modeling the composite laminates. The simulation model of the single-nail interference connection structure for composite materials is shown below. Figure 5 As shown.

[0159] Table 1 Material parameters of Ti6Al4V bolts

[0160]

[0161] Note: E is the elastic modulus of the bolt, and υ is Poisson's ratio.

[0162] 2.2 The carbon fiber composite material uses reduced integral hexahedral elements C3D8R, and reinforced hourglass control is implemented to reduce mesh distortion. The metal bolts are set as rigid bodies to facilitate subsequent calculation of interference.

[0163] 2.3 Based on the actual test conditions, the carbon fiber composite material and the base are restricted to three translational directions and three rotational directions. The bolts are restricted to five degrees of freedom except for the z-direction. An interference pin displacement of 8.5 mm is established in the load module.

[0164] 2.4 Carbon fiber composites are modeled as transversely isotropic materials, and the stress-strain constitutive model parameter relationship can be expressed as:

[0165]

[0166] In the formula, σ n σ t These are the normal stress component and the shear stress component, respectively; ε n ε t These are the normal strain component and the shear strain component, respectively; C n C t The stiffness is measured in the normal and shear directions.

[0167] 2.5 Combining the three-dimensional finite element model, based on the contact stress between the bolt and the composite material hole wall, the three-dimensional Hashin failure criterion is used to perform stress analysis on the carbon fiber composite element. The material failure criterion is used to perform damage analysis on each carbon fiber composite element to determine whether the element is damaged. If damaged, the corresponding stiffness reduction model is used to reduce the current material stiffness and update the stress; if there is no damage, the element stiffness remains unchanged; a composite material damage model is established. The strength parameters of T300 carbon fiber composite material are shown in Table 2.

[0168] Table 2 Mechanical properties of T300 composite materials

[0169]

[0170] Note: X T X represents the fiber tensile strength. C Y represents the fiber compressive strength. T Y represents the in-plane tensile strength of the matrix. C S is the in-plane matrix compressive strength. 12 S 13 S 23 Shear strength, in MPa.

[0171] 2.6 After modeling is completed, an executable algorithm program is generated.

[0172] Third, a randomized parameter program is used to randomly assign values ​​to the hole position deviation parameters, simulating the actual geometric state of the composite material holes during actual assembly production, i.e., random(t,a)in t∈[0,T],a∈[0,2π]. Based on the above reference model, the modeling program parameters are modified, and the generated random hole geometric deviation parameters t and a are input. A batch modeling algorithm based on Python is written. Finally, this program is run in Abaqus to generate a large number of pin connection model data samples with random hole position deviations. After the batch composite material single-pin connection structure interference pin insertion process simulation model has been analyzed, the deformation and damage are output respectively, and the pin insertion process restart data is saved.

[0173] Fourth, based on the restart database of the interference pin model, import composite laminate lap structure models with geometric deformation fields and physical damage fields into Abaqus. On this basis, establish a tensile load simulation model of the composite joint structure and construct the basic dataset for the Monte Carlo method.

[0174] 4.1 A three-dimensional geometric model of the carbon fiber composite material and bolts was established using Abaqus software. The composite laminate was imported from the simulation results file of the stud connection, and a three-dimensional model inheriting the geometric deformation field of the studs was established to complete the dynamic transfer and evolution process of the geometric field. Since the elastoplastic damage of the bolts was not considered, an "I"-shaped bolt model was established to replace the "T"-shaped bolt model, and a tensile load model of the composite material connection structure was constructed, as follows. Figure 6 As shown.

[0175] 4.2 The metal bolts and composite materials use the same material properties as the composite material structure pin connection simulation model established in step two.

[0176] 4.3 Apply loads and boundary conditions, establish motion coupling reference points for the upper and lower composite plates, and restrict the degrees of freedom of the upper and lower composite plates. Add a static tensile displacement of 5mm to the upper composite plate. Apply bolt preload; to avoid conflicts in bolt section properties, set the bolt section properties to default in the mesh module.

[0177] 4.5 Read the simulation result file of the pin connection, set the predefined field for the upper and lower composite plates, select the result of the last analysis step of the pin simulation model, import the stress state and damage distribution brought about by the pin insertion process, and establish a tensile three-dimensional model that inherits the pin force field.

[0178] 4.6 Combining the failure criteria and stiffness reduction model in step two, stress analysis is performed on the tensile model of the above composite material interference connection structure to determine whether each composite material unit is damaged or undergoes stiffness reduction, and a damage model is established.

[0179] V. After the tensile load simulation model of the batch composite single-nail connection structure is analyzed, the load-displacement curves of each simulation result are plotted, and the tensile strength of the structure is extracted and statistically analyzed. Following the statistical principles of the Monte Carlo method, a probability distribution diagram of the structural strength variation under a given geometric deviation is established. The strength distribution trend under different geometric deviations is analyzed, and a new composite material hole-making deviation design criterion suitable for actual assembly production is constructed.

[0180] 5.1 After the batch simulation model calculations are completed, output the displacement and support reaction force along the loading direction at the motion coupling reference point according to the result file, and plot the load-displacement curve of the simulation results. Repeat the operation until all models have completed the output of results. Figure 7 The figure shows the load-displacement curves output by the composite material interference connection structure without hole position deviation.

[0181] 5.2 Extract the ultimate load Fi from all load-displacement curves, and calculate the change in the ultimate load ΔF of the structure compared to the model without geometric deviation. i The ratio to the ultimate load F0 of the reference structure. The ratio ΔF is calculated statistically. i The distribution trend and pattern of / F0 were analyzed, and a probability histogram of structural strength variation values ​​was established. Figure 8 The diagram shows the probability distribution of the load-bearing limit of the composite material interference connection structure when the hole position deviation T = 0.1 mm.

[0182] 5.3 Based on the probability histogram in 5.3, the Monte Carlo method is used to analyze the statistical results, establishing the relationship between the change in the maximum load-bearing capacity of the structure and the criterion under a given maximum hole position deviation value. Figure 8 The results show that, with a confidence level of 99.55%, the maximum hole position deviation T = 0.1 mm will not reduce the overall tensile bearing capacity of the structure by more than 25%; with a confidence level of 83.77%, the maximum hole position deviation T = 0.1 mm will not reduce the overall tensile bearing capacity of the structure by more than 15%.

[0183] VI. Based on the analysis results in step five, and combined with the quality criteria for hole making in aircraft panels, a new design criterion for hole making deviation of composite materials suitable for actual assembly production is constructed.

[0184] According to the quality standards for hole drilling in aircraft panels, the hole position tolerance T for composite materials is 0.1 mm. Step five analysis shows that, in actual production, the structural load-bearing capacity is greater than 0.25*F with a 99.55% confidence level. max =3609N, with an 83.77% confidence level, the structure's load-bearing capacity is greater than 0.15*F. max=3609N =2165N. Therefore, when the actual structural load-bearing strength requirement is less than 3600N, the hole tolerance of the connection structure can be appropriately increased to improve efficiency and reduce costs.

[0185] Example 3

[0186] To implement the method corresponding to Embodiment 1 above and achieve the corresponding functions and technical effects, a system for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures is provided below, comprising:

[0187] The characterization parameter determination module is used to determine the characterization parameters of the hole geometric deviation of the composite perforated laminate specimen, taking into account the randomness in the actual composite material assembly process; the hole geometric deviation includes: hole position deviation, hole diameter deviation and hole perpendicularity deviation.

[0188] The first model building module is used to build a simulation model of a composite single-nail connection structure with pin connection under the condition of no hole geometric deviation, based on the structural dimensions, contact properties, load and boundary conditions of carbon fiber composite materials and bolts.

[0189] The second model building module is used to establish a simulation model of the interference insertion process of the composite single nail connection structure based on the characterization parameters and the simulation model of the insertion connection of the composite single nail connection structure under the non-porous geometric deviation.

[0190] The third model building module is used to establish a tensile load simulation model of the composite material connection structure based on the deformation of the connection structure and the material damage state output by the simulation model of the interference insertion process of the single nail connection structure of the composite material.

[0191] The probability distribution map establishment module for structural strength variation values ​​is used to establish a probability distribution map for structural strength variation values ​​based on the tensile load simulation model of the composite material connection structure, and to determine the strength distribution trend under different geometric deviations.

[0192] A novel composite material hole-making deviation design criterion construction module is used to construct a novel composite material hole-making deviation design criterion based on the strength distribution trend under different geometric deviations and in combination with the aircraft panel hole-making quality criteria.

[0193] Furthermore, the first model construction module specifically includes:

[0194] The three-dimensional geometric model building unit is used to establish the three-dimensional geometric model of the bolt, and to establish the three-dimensional geometric model of the composite material laminate structure based on the structural dimensions, contact properties, loads and boundary conditions of the carbon fiber composite material and the bolt.

[0195] The stress-strain constitutive relationship establishment unit for carbon fiber composite materials is used to restrict the three degrees of freedom of movement and the three degrees of freedom of rotation of the carbon fiber composite laminate and the base according to the actual composite assembly conditions, restrict the five degrees of freedom of bolt movement except for the z-direction, and apply the pin displacement load. Under the above restrictions, the influence of hole-making damage on the degradation of material properties is considered to establish the stress-strain constitutive relationship of carbon fiber composite materials.

[0196] The first model building unit is used to establish a simulation model of the composite material single nail connection structure based on the three-dimensional geometric model of the bolt and the three-dimensional geometric model of the composite material laminate structure. According to the contact stress between the bolt and the hole wall of the composite material, the three-dimensional Hashin failure criterion is used to perform stress analysis and material failure judgment on the carbon fiber composite material unit, and establish a simulation model of the single nail connection structure of the composite material without hole geometric deviation.

[0197] Furthermore, the second model building module specifically includes:

[0198] The assignment unit is used to randomly assign values ​​to the characterization parameters according to the determined hole geometry deviation type.

[0199] The second model establishment unit is used to establish the numerical model coordinate system. It uses the coordinate transformation projection matrix to convert the assigned characterization parameters in the material model coordinate system into the global coordinate system, and establishes a simulation model of the interference nail insertion process of the composite single nail connection structure.

[0200] Furthermore, the third model building module specifically includes:

[0201] The setting operation completion unit is used to establish motion coupling reference points for the upper and lower laminates in the composite material laminate structure, restrict the degrees of freedom of the upper and lower laminates, add static tension positions to the upper laminate and apply bolt preload, set the upper and lower laminates in the composite material laminate structure to a predefined field, and complete the setting operation.

[0202] The extrusion 3D model building unit is used to select the deformation and material damage state of the connection structure based on the set operation, import the stress state and damage distribution brought about by the insertion process, and build an extrusion 3D model that inherits the force field of the insertion pin.

[0203] The third model building unit is used to perform stress analysis on the tensile three-dimensional model and establish a tensile load simulation model of the composite material connection structure.

[0204] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0205] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures, characterized in that, include: Considering the randomness in the actual composite material assembly process, we determine the characterization parameters for the hole geometry deviation of the composite perforated laminate specimen. The hole geometric deviations include: hole position deviation, hole diameter deviation, and hole perpendicularity deviation; Based on the structural dimensions, contact properties, loads, and boundary conditions of carbon fiber composite materials and bolts, a simulation model of a single-nail connection structure of composite materials under non-porous geometric deviations is established. Based on the characterization parameters and the simulation model of the composite single-nail connection structure under the non-porous geometric deviation, a simulation model of the interference insertion process of the composite single-nail connection structure is established; specifically, it includes: randomly assigning values ​​to the characterization parameters according to the determined hole geometric deviation type; establishing a numerical model coordinate system, and using a coordinate transformation projection matrix to convert the assigned characterization parameters in the material model coordinate system to the global coordinate system, thereby establishing a simulation model of the interference insertion process of the composite single-nail connection structure. Based on the simulation model of the interference pin insertion process of the composite single nail connection structure, a simulation model of tensile load of composite connection structure is established based on the deformation of connection structure and material damage state of material damage output by the simulation model of interference pin insertion process of composite single nail connection structure. Based on the tensile load simulation model of the composite material connection structure, a probability distribution map of the structural strength variation value is established to determine the strength distribution trend under different geometric deviations. Based on the strength distribution trend under different geometric deviations, and combined with the hole-making quality criteria for aircraft panels, a new design criterion for hole-making deviations in composite materials is constructed.

2. The method for studying the influence of random hole geometric deviation on the strength of aircraft panel connection structure according to claim 1, characterized in that, The characterization parameters for the hole position deviation are as follows: ， Where T represents the maximum upper limit of the hole position deviation required by the hole design, t represents the length of the random hole position deviation vector in actual production, and a represents the angle between the hole position deviation vector and the x-axis. The parameters characterizing the aperture deviation are as follows: in, This represents the upper limit of the absolute value of the hole diameter deviation required by the hole design, and r represents the random hole diameter deviation value in actual production. The parameters characterizing the hole perpendicularity deviation are as follows: ， Where C represents the maximum upper limit of the hole perpendicularity deviation required by the hole design, c represents the angle value of the random hole perpendicularity deviation in actual production, and b represents the angle between the projection of the hole axis direction on the xy plane and the x-axis.

3. The method for studying the influence of random hole geometric deviation on the strength of aircraft panel connection structure according to claim 1, characterized in that, Based on the structural dimensions, contact properties, loads, and boundary conditions of carbon fiber composite materials and bolts, a simulation model of a single-nail connection structure for composite materials under non-porous geometric deviations is established, specifically including: A three-dimensional geometric model of the bolt is established, and a three-dimensional geometric model of the composite material laminate structure is established based on the structural dimensions, contact properties, loads and boundary conditions of the carbon fiber composite material and the bolt. Based on the actual composite material assembly conditions, the carbon fiber composite laminate and base are restricted to three degrees of freedom in the movement direction and three degrees of freedom in the rotation direction. The bolts are restricted to five degrees of freedom except for the movement in the z direction, and a pin displacement load is applied. Under the above restrictions, the influence of hole-making damage on the degradation of material properties is considered to establish the stress-strain constitutive relationship of carbon fiber composite material. Based on the three-dimensional geometric model of the bolt and the three-dimensional geometric model of the composite material laminate structure, and according to the contact stress between the bolt and the hole wall of the composite material, the three-dimensional Hashin failure criterion is used to perform stress analysis and material failure judgment on the carbon fiber composite material unit, and a simulation model of the single nail connection structure of the composite material without hole geometric deviation is established.

4. The method for studying the influence of random hole geometric deviation on the strength of aircraft panel connection structure according to claim 1, characterized in that, Based on the simulation model of the interference insertion process of the composite single-nail connection structure, the tensile load simulation model of the composite connection structure is established according to the deformation of the connection structure and the material damage state output by the simulation model. Specifically, it includes: Establish motion coupling reference points for the upper and lower laminates in the composite material laminate structure, restrict the degrees of freedom of the upper and lower laminates, add static tension positions to the upper laminate and apply bolt preload, set the upper and lower laminates in the composite material laminate structure to a predefined field, and complete the setting operation. Based on the aforementioned settings, the deformation and material damage states of the connection structure are selected, and the stress state and damage distribution brought about during the insertion process are imported to establish a tensile three-dimensional model that inherits the force field of the insertion pin. Stress analysis was performed on the tensile three-dimensional model to establish a simulation model of tensile load on the composite material connection structure.

5. The method for studying the influence of random hole geometric deviation on the strength of aircraft panel connection structure according to claim 1, characterized in that, Based on the tensile load simulation model of the composite material connection structure, a probability distribution map of the structural strength variation values ​​is established to determine the strength distribution trend under different geometric deviations, specifically including: Load-displacement curves were plotted based on the simulation results of the tensile load simulation model of the composite material connection structure. Extract the ultimate load from all load-displacement curves; Based on the change value of the structural ultimate load of the simulation model of the composite single nail connection structure under the ultimate load and the non-porous geometric deviation; A probability histogram of structural strength variation values ​​is established based on the ratio of the variation value to the ultimate load of the reference structure. Based on the probability histogram of the structural strength variation values, the Monte Carlo method is used to determine the strength distribution trend under different geometric deviations.

6. A system for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures, characterized in that, include: The characterization parameter determination module is used to determine the characterization parameters for the hole geometry deviation of composite perforated laminate specimens, taking into account the randomness in the actual composite material assembly process. The hole geometric deviations include: hole position deviation, hole diameter deviation, and hole perpendicularity deviation; The first model building module is used to build a simulation model of the single nail connection structure of composite material under the condition of no hole geometric deviation, based on the structural dimensions, contact properties, load and boundary conditions of carbon fiber composite material and bolts. The second model building module is used to establish a simulation model of the interference insertion process of the composite single-nail connection structure based on the characterization parameters and the simulation model of the insertion connection of the composite single-nail connection structure under the hole-free geometric deviation. Specifically, it includes: an assignment unit, used to randomly assign values ​​to the characterization parameters according to the determined hole geometric deviation type; and a second model building unit, used to establish a numerical model coordinate system, and use a coordinate transformation projection matrix to convert the assigned characterization parameters in the material model coordinate system to the global coordinate system to establish a simulation model of the interference insertion process of the composite single-nail connection structure. The third model building module is used to establish a tensile load simulation model of the composite material connection structure based on the connection structure deformation and material damage state output by the simulation model of the interference pin insertion process of the composite single nail connection structure. The probability distribution map building module for structural strength variation values ​​is used to build a probability distribution map of structural strength variation values ​​based on the tensile load simulation model of the composite material connection structure, and to determine the strength distribution trend under different geometric deviations. A novel composite material hole-making deviation design criterion construction module is used to construct a novel composite material hole-making deviation design criterion based on the strength distribution trend under different geometric deviations and in combination with the aircraft panel hole-making quality criteria.

7. The system for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures according to claim 6, characterized in that, The first model building module specifically includes: The three-dimensional geometric model building unit is used to establish the three-dimensional geometric model of the bolt, and to establish the three-dimensional geometric model of the composite material laminate structure based on the structural dimensions, contact properties, load and boundary conditions of the carbon fiber composite material and the bolt. The stress-strain constitutive relationship establishment unit for carbon fiber composite materials is used to restrict the three degrees of freedom in the movement direction and the three degrees of freedom in the rotation direction of the carbon fiber composite laminate and the base according to the actual composite assembly conditions, restrict the five degrees of freedom of the bolt except for the movement in the z direction, and apply the pin displacement load. Under the above restrictions, the influence of hole-making damage on the degradation of material properties is considered to establish the stress-strain constitutive relationship of carbon fiber composite materials. The first model building unit is used to establish a simulation model of the composite material single nail connection structure based on the three-dimensional geometric model of the bolt and the three-dimensional geometric model of the composite material laminate structure. According to the contact stress between the bolt and the hole wall of the composite material, the three-dimensional Hashin failure criterion is used to perform stress analysis and material failure judgment on the carbon fiber composite material unit, and establish a simulation model of the single nail connection structure of the composite material without hole geometric deviation.

8. The system for studying the influence of random hole geometric deviations on the strength of aircraft panel connection structures according to claim 6, characterized in that, The third model building module specifically includes: The setting operation completion unit is used to establish motion coupling reference points for the upper and lower laminates in the composite material laminate structure, restrict the degrees of freedom of the upper and lower laminates, add static tension positions to the upper laminate and apply bolt preload, set the upper and lower laminates in the composite material laminate structure to a predefined field, and complete the setting operation. The extrusion 3D model building unit is used to select the deformation and material damage state of the connection structure based on the set operation, import the stress state and damage distribution brought about by the insertion process, and build an extrusion 3D model that inherits the force field of the insertion. The third model building unit is used to perform stress analysis on the tensile three-dimensional model and establish a tensile load simulation model of the composite material connection structure.

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