A method and system for predicting the strength of a hybrid connection of glue and screw considering nail insertion damage

Abstract

The present invention relates to a method and system for predicting the strength of adhesive-screw hybrid connections considering nail damage, belonging to the field of CFRP connections. The method includes constructing a three-dimensional finite element model of interference nails in a CFRP adhesive-screw hybrid connection structure based on the tensile strength, shear strength, structural dimensions of the connection structure, contact properties, loads, and boundary conditions; based on the above model, type I fracture energy, and type II fracture energy, performing damage analysis according to the contact stresses between the interference bolts, adhesive layer, and the hole wall of the CFRP to determine the damage distribution and stiffness reduction model; constructing a tensile damage model of the CFRP adhesive-screw hybrid connection structure according to the damage distribution; and performing stress analysis on it according to the failure criterion and stiffness reduction model to determine the tensile strength. The present invention effectively analyzes and predicts the tensile strength of the CFRP adhesive-screw hybrid connection structure, reducing the material cost and preparation cycle of the test method.

Description

Technical Field

[0001] The present invention relates to the field of CFRP connections, and particularly to a method and system for predicting the strength of a bonded-screw hybrid connection considering pin damage. Background Art

[0002] The bonded-screw hybrid connection structure is usually used in the assembly process of composite material integral structures. In recent years, with the continuous in-depth research on the performance of composite materials, it has been found that interference connection can not only improve the fatigue performance of the connection structure, but also effectively improve the problem of low bolt bearing efficiency in the bonded-screw hybrid connection structure. However, before installation, the diameter of the pin rod of the interference bolt is larger than the hole diameter, and mechanical external force is required for installation. Due to the low elongation and non-uniformity of composite materials, the extrusion of the bolt causes different degrees of damage to the composite material hole wall along the axial and circumferential directions, resulting in a substantial change in the contact relationship between the bolt and the hole wall; the excessive axial friction force and radial extrusion force also cause a high degree of stress concentration in the adhesive layer in the interference area, and the cohesive damage inside it accelerates the crack initiation and propagation of the adhesive layer under the action of external load, leading to premature failure of the connection structure.

[0003] From the research status at home and abroad, it can be seen that the existing research on the installation process of interference bolt connection structures mainly focuses on the damage forms and stress distributions of composite materials, and most of the research is mainly based on experimental methods. However, the relevant research on the performance degradation of the adhesive layer after curing under the action of interference and its influence on the bearing strength of the connection structure is relatively lacking. The finite element method is a method for studying the strength of carbon fiber reinforced polymer (CFRP) bonded-screw hybrid connection structures. However, in the prediction of the bearing strength of relevant composite material connection structures, the damage caused to the connection part during the installation of fasteners is ignored, especially the stress concentration and cohesive damage of the adhesive layer height are not considered, resulting in inaccurate assembly contact relationships between the bolt, the adhesive layer and the hole wall. The stress fields of the adhesive layer and the composite material hole wall and the assembly contact relationship have an important impact on the tensile strength of the connection structure, and the existing prediction results are not accurate enough. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and system for predicting the strength of a bonded-screw hybrid connection considering pin damage, effectively analyze and predict the tensile strength of a carbon fiber reinforced composite material bonded-screw hybrid connection structure, and reduce the material cost and preparation cycle of the experimental method.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A method for predicting the strength of a bonded-screw hybrid connection considering pin damage, comprising:

[0007] Obtain the tensile strength, shear strength, mode I fracture energy, and mode II fracture energy of the adhesive layer;

[0008] Construct a three-dimensional finite element model of interference pins for a carbon fiber reinforced composite adhesive-bolt hybrid connection structure according to the tensile strength, the shear strength, the structural dimensions of the connection structure, the contact properties of the connection structure, the load of the connection structure, and the boundary conditions of the connection structure; the connection structure includes carbon fiber reinforced composites, the adhesive layer, and interference bolts; the contact properties include the friction coefficient;

[0009] Based on the three-dimensional finite element model of interference pins for the carbon fiber reinforced composite adhesive-bolt hybrid connection structure, the mode I fracture energy, and the mode II fracture energy, perform damage analysis according to the contact stress between the interference bolts, the adhesive layer, and the hole wall of the carbon fiber reinforced composite to determine the damage distribution and the stiffness reduction model;

[0010] Construct a tensile damage model for the carbon fiber reinforced composite adhesive-bolt hybrid connection structure according to the damage distribution;

[0011] Perform stress analysis on the tensile damage model of the carbon fiber reinforced composite adhesive-bolt hybrid connection structure according to the failure criterion and the stiffness reduction model to determine the tensile strength.

[0012] Optionally, the obtaining of the tensile strength, shear strength, mode I fracture energy, and mode II fracture energy of the adhesive layer specifically includes:

[0013] Conduct a tensile test on the adhesive layer to obtain the tensile strength;

[0014] Conduct a shear test on the adhesive layer to obtain the shear strength;

[0015] Conduct a double cantilever beam test on the adhesive layer to obtain the mode I fracture energy;

[0016] Conduct a three-point bending test on the adhesive layer to obtain the mode II fracture energy.

[0017] Optionally, the constructing of the three-dimensional finite element model of interference pins for the carbon fiber reinforced composite adhesive-bolt hybrid connection structure according to the tensile strength, the shear strength, the structural dimensions of the connection structure, the contact properties of the connection structure, the load of the connection structure, and the boundary conditions of the connection structure specifically includes:

[0018] Construct a three-dimensional geometric model according to the structural dimensions of the connection structure, the contact properties of the connection structure, and the boundary conditions of the connection structure;

[0019] Determine the displacement of the interference pin according to the load of the connection structure;

[0020] Determine the stress-strain constitutive relationship of the carbon fiber reinforced composite according to the tensile strength and the shear strength;

[0021] Construct a three-dimensional finite element model of the interference pin in the adhesive-screw hybrid connection structure of carbon fiber reinforced composite materials based on the three-dimensional geometric model, the interference pin displacement, and the stress-strain constitutive relationship of the carbon fiber reinforced composite materials.

[0022] Optionally, based on the three-dimensional finite element model of the interference pin in the adhesive-screw hybrid connection structure of carbon fiber reinforced composite materials, the mode I fracture energy, and the mode II fracture energy, perform damage analysis according to the contact stress between the interference bolt, the adhesive layer, and the hole wall of the carbon fiber reinforced composite material to determine the damage distribution and the stiffness reduction model, specifically including:

[0023] Perform stress analysis on the adhesive layer in the three-dimensional finite element model of the interference pin in the adhesive-screw hybrid connection structure of carbon fiber reinforced composite materials using the quadratic stress failure criterion to determine the damage condition of the adhesive layer; the damage condition includes damage occurring and no damage occurring;

[0024] When the damage condition of the adhesive layer is damage occurring, determine the stiffness reduction of the adhesive layer in the stiffness reduction model according to the damage variable and the displacement of the adhesive layer;

[0025] Determine the damage distribution according to the mode I fracture energy and the mode II fracture energy;

[0026] Perform stress analysis on the carbon fiber reinforced composite material in the three-dimensional finite element model of the interference pin in the adhesive-screw hybrid connection structure of carbon fiber reinforced composite materials using the maximum stress criterion and the three-dimensional Hashin failure criterion to determine the damage condition of the carbon fiber reinforced composite material;

[0027] When the damage condition of the carbon fiber reinforced composite material is damage occurring, determine the stiffness reduction of the carbon fiber reinforced composite material in the damage stiffness reduction model according to the damage stiffness matrix.

[0028] A strength prediction system for the adhesive-screw hybrid connection considering pin damage, including:

[0029] An acquisition module for acquiring the tensile strength, shear strength, mode I fracture energy, and mode II fracture energy of the adhesive layer;

[0030] A three-dimensional finite element model construction module for the interference pin in the adhesive-screw hybrid connection structure of carbon fiber reinforced composite materials, which is used to construct a three-dimensional finite element model of the interference pin in the adhesive-screw hybrid connection structure of carbon fiber reinforced composite materials according to the tensile strength, the shear strength, the structural dimensions of the connection structure, the contact properties of the connection structure, the load of the connection structure, and the boundary conditions of the connection structure; the connection structure includes carbon fiber reinforced composite materials, the adhesive layer, and interference bolts; the contact properties include the friction coefficient;

[0031] Damage analysis module, which is used to perform damage analysis based on the three-dimensional finite element model of interference pinning of the adhesive-bolt hybrid connection structure of carbon fiber reinforced composite materials, the type I fracture energy and the type II fracture energy, and determine the damage distribution and stiffness reduction model according to the contact stress between the interference bolt, the adhesive layer and the hole wall of the carbon fiber reinforced composite material;

[0032] Tensile damage model construction module for the adhesive-bolt hybrid connection structure of carbon fiber reinforced composite materials, which is used to construct a tensile damage model for the adhesive-bolt hybrid connection structure of carbon fiber reinforced composite materials according to the damage distribution;

[0033] Stress analysis module, which is used to perform stress analysis on the tensile damage model of the adhesive-bolt hybrid connection structure of carbon fiber reinforced composite materials according to the failure criterion and the stiffness reduction model, and determine the tensile strength.

[0034] Optionally, the acquisition module specifically includes:

[0035] Tensile strength acquisition unit, which is used to obtain the tensile strength by performing a tensile test on the adhesive layer;

[0036] Shear strength acquisition unit, which is used to obtain the shear strength by performing a shear test on the adhesive layer;

[0037] Type I fracture energy acquisition unit, which is used to obtain the type I fracture energy by performing a double cantilever beam test on the adhesive layer;

[0038] Type II fracture energy acquisition unit, which is used to obtain the type II fracture energy by performing a three-point bending test on the adhesive layer.

[0039] Optionally, the three-dimensional finite element model construction module for the interference pinning of the adhesive-bolt hybrid connection structure of carbon fiber reinforced composite materials specifically includes:

[0040] Three-dimensional geometric model construction unit, which is used to construct a three-dimensional geometric model according to the structural dimensions of the connection structure, the contact properties of the connection structure and the boundary conditions of the connection structure;

[0041] Interference pin displacement determination unit, which is used to determine the interference pin displacement according to the load of the connection structure;

[0042] Carbon fiber reinforced composite stress-strain constitutive relation determination unit, which is used to determine the stress-strain constitutive relation of carbon fiber reinforced composite materials according to the tensile strength and the shear strength;

[0043] Three-dimensional finite element model construction unit for the interference pinning of the adhesive-bolt hybrid connection structure of carbon fiber reinforced composite materials, which is used to construct a three-dimensional finite element model for the interference pinning of the adhesive-bolt hybrid connection structure of carbon fiber reinforced composite materials according to the three-dimensional geometric model, the interference pin displacement and the stress-strain constitutive relation of carbon fiber reinforced composite materials.

[0044] Optionally, the damage analysis module specifically includes:

[0045] An adhesive layer damage determination unit, configured to perform stress analysis on the adhesive layer in the three-dimensional finite element model of the interference pin of the carbon fiber reinforced composite adhesive-screw hybrid connection structure according to the secondary stress failure criterion, and determine the damage condition of the adhesive layer; the damage condition includes damage occurring and no damage occurring;

[0046] An adhesive layer stiffness reduction determination unit, configured to determine the adhesive layer stiffness reduction in the stiffness reduction model according to the damage variable and the displacement of the adhesive layer when the damage condition of the adhesive layer is damage occurring;

[0047] A damage distribution determination unit, configured to determine the damage distribution according to the mode I fracture energy and the mode II fracture energy;

[0048] A carbon fiber reinforced composite damage determination unit, configured to perform stress analysis on the carbon fiber reinforced composite in the three-dimensional finite element model of the interference pin of the carbon fiber reinforced composite adhesive-screw hybrid connection structure according to the maximum stress criterion and the three-dimensional Hashin failure criterion, and determine the damage condition of the carbon fiber reinforced composite;

[0049] A carbon fiber reinforced composite stiffness reduction determination unit, configured to determine the carbon fiber reinforced composite stiffness reduction in the damage stiffness reduction model according to the damage stiffness matrix when the damage condition of the carbon fiber reinforced composite is damage occurring.

[0050] According to the specific embodiments provided by the present invention, the following technical effects are disclosed by the present invention:

[0051] The present invention obtains the tensile strength, shear strength, mode I fracture energy and mode II fracture energy of the adhesive layer; constructs a three-dimensional finite element model of the interference pin of the carbon fiber reinforced composite adhesive-screw hybrid connection structure according to the tensile strength, the shear strength, the structural dimensions of the connection structure, the contact properties of the connection structure, the load of the connection structure and the boundary conditions of the connection structure; based on the three-dimensional finite element model of the interference pin of the carbon fiber reinforced composite adhesive-screw hybrid connection structure, the mode I fracture energy and the mode II fracture energy, perform damage analysis according to the contact stress between the interference bolt, the adhesive layer and the hole wall of the carbon fiber reinforced composite, determine the damage distribution and the stiffness reduction model; construct a tensile damage model of the carbon fiber reinforced composite adhesive-screw hybrid connection structure according to the damage distribution; perform stress analysis on the tensile damage model of the carbon fiber reinforced composite adhesive-screw hybrid connection structure according to the failure criterion and the stiffness reduction model, and determine the tensile strength. Effectively analyze and predict the tensile strength of the carbon fiber reinforced composite adhesive-screw hybrid connection structure, and reduce the material cost and preparation cycle of the test method. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0053] Figure 1 It is a flowchart of the method for predicting the adhesive - screw hybrid connection strength considering pin damage provided by the present invention in practical applications;

[0054] Figure 2 It is a schematic diagram of the interference pin structure provided by the present invention;

[0055] Figure 3 It is a schematic diagram of the three - dimensional finite - element model of the interference pin provided by the present invention;

[0056] Figure 4 It is a schematic diagram of the press - pin force - displacement curve during the interference pin process provided by the present invention;

[0057] Figure 5 It is a schematic diagram of the tensile finite - element model of the adhesive - screw hybrid connection structure of carbon fiber - reinforced composite material considering pin damage provided by the present invention;

[0058] Figure 6 It is a schematic diagram of the tensile load - displacement curve provided by the present invention;

[0059] Figure 7 It is a flowchart of the method for predicting the adhesive - screw hybrid connection strength considering pin damage provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0060] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0061] The purpose of the present invention is to provide a method and system for predicting the adhesive - screw hybrid connection strength considering pin damage, effectively analyze and predict the tensile strength of the adhesive - screw hybrid connection structure of carbon fiber - reinforced composite materials, and reduce the material cost and preparation cycle of the test method.

[0062] To make the above - mentioned objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0063] As shown Figure 7 in the figure, a method for predicting the strength of a bonded-screw hybrid connection considering nail insertion damage provided by the present invention includes:

[0064] Step 701: Obtain the tensile strength, shear strength, mode I fracture energy, and mode II fracture energy of the adhesive layer.

[0065] Step 701 specifically includes: performing a tensile test on the adhesive layer to obtain the tensile strength; performing a shear test on the adhesive layer to obtain the shear strength; performing a double-cantilever beam test on the adhesive layer to obtain the mode I fracture energy;

[0066] performing a three-point bending test on the adhesive layer to obtain the mode II fracture energy.

[0067] Step 702: Construct a three-dimensional finite element model of interference nail insertion for a carbon fiber reinforced composite bonded-screw hybrid connection structure according to the tensile strength, the shear strength, the structural dimensions of the connection structure, the contact properties of the connection structure, the load of the connection structure, and the boundary conditions of the connection structure; the connection structure includes a carbon fiber reinforced composite, the adhesive layer, and an interference bolt; the contact properties include the friction coefficient.

[0068] Step 702 specifically includes:

[0069] Construct a three-dimensional geometric model according to the structural dimensions of the connection structure, the contact properties of the connection structure, and the boundary conditions of the connection structure; determine the interference nail displacement according to the load of the connection structure; determine the stress-strain constitutive relationship of the carbon fiber reinforced composite according to the tensile strength and the shear strength; construct a three-dimensional finite element model of interference nail insertion for a carbon fiber reinforced composite bonded-screw hybrid connection structure according to the three-dimensional geometric model, the interference nail displacement, and the stress-strain constitutive relationship of the carbon fiber reinforced composite.

[0070] Step 703: Based on the three-dimensional finite element model of interference nail insertion for the carbon fiber reinforced composite bonded-screw hybrid connection structure, the mode I fracture energy, and the mode II fracture energy, perform damage analysis according to the contact stress between the interference bolt, the adhesive layer, and the hole wall of the carbon fiber reinforced composite to determine the damage distribution and the stiffness reduction model.

[0071] Step 703 specifically includes:

[0072] Perform stress analysis on the adhesive layer in the three-dimensional finite element model of interference nail insertion for the carbon fiber reinforced composite bonded-screw hybrid connection structure by using the quadratic stress failure criterion to determine the damage condition of the adhesive layer; the damage condition includes damage occurring and no damage occurring.

[0073] When the damage condition of the adhesive layer is damage, determine the stiffness reduction of the adhesive layer in the stiffness reduction model according to the damage variable and the displacement of the adhesive layer.

[0074] Determine the damage distribution according to the mode I fracture energy and the mode II fracture energy.

[0075] Perform stress analysis on the carbon fiber reinforced composite material in the three-dimensional finite element model of interference plugging of the adhesive-bolt hybrid connection structure of carbon fiber reinforced composite material by using the maximum stress criterion and the three-dimensional Hashin failure criterion, and determine the damage condition of the carbon fiber reinforced composite material.

[0076] When the damage condition of the carbon fiber reinforced composite material is damage, determine the stiffness reduction of the carbon fiber reinforced composite material in the damage stiffness reduction model according to the damage stiffness matrix.

[0077] Step 704: Construct a tensile damage model for the adhesive-bolt hybrid connection structure of carbon fiber reinforced composite material according to the damage distribution.

[0078] Step 705: Perform stress analysis on the tensile damage model of the adhesive-bolt hybrid connection structure of carbon fiber reinforced composite material according to the failure criterion and the stiffness reduction model, and determine the tensile strength.

[0079] In order to overcome the deficiencies of existing prediction methods that ignore the true stress state and damage distribution of the adhesive layer after the installation of interference bolts, and are unable to establish an accurate contact relationship between the bolt, the adhesive layer, and the composite material hole wall, the present invention provides a specific processing process in the practical application of a prediction method for the strength of an adhesive-bolt hybrid connection considering plug damage. This method can effectively analyze and predict the tensile strength of the adhesive-bolt hybrid connection structure of carbon fiber reinforced composite material, reduce the material cost and preparation cycle of the test method, and is used to optimize the assembly process and promote the development of advanced connection technologies.

[0080] As Figure 1 shown, in this embodiment, taking ERGO7200 structural adhesive, T700 / TED-85 carbon fiber reinforced composite material (lay-up sequence is [0 / 45 / -45 / 90] 3s ) and Ti6Al4V bolt material as examples, a prediction method for the strength of an adhesive-bolt hybrid connection considering plug damage is provided, including the following steps:

[0081] I. Conduct tensile tests, shear tests, double cantilever beam tests, and three-point bending tests on the adhesive layer specimens respectively to obtain the tensile strength, shear strength, mode I and mode II fracture toughness of the adhesive layer, and on this basis, establish a bilinear cohesive constitutive model of the adhesive layer.

[0082] 1.1 According to the requirements in ASTM-D2095, conduct a tensile test to obtain the normal tensile strength Specifically, specimens with a length of 40 mm and a width of 13 mm were designed, adhesively bonded in the center, with an adhesive layer thickness of 12 mm. A tensile test was conducted, and the ultimate load was obtained as 1248 N. Therefore, the tensile strength of the adhesive layer was 8 MPa.

[0083] 1.2 According to the requirements in ASTM-D3165, a tensile test was conducted to obtain the strength in the shear direction and Specifically, specimens with a length of 190.5 mm and a width of 25 mm were designed, adhesively bonded on the top and bottom, and the overlapping area was 343 mm 2 , and a shear test was conducted. The ultimate load was obtained as 6174 N. Therefore, the two shear strengths of the adhesive layer and were 18 MPa. What was obtained in Step 1.1 and Step 1.2 were the maximum tensile strength and shear strength that the adhesive layer could withstand.

[0084] 1.3 According to the HB 7402-96 test standard and the HB 7403-96 test standard, a double-cantilever beam test and a three-point bending test were conducted. From Formulas (1) and (2), it was obtained that A double-cantilever beam test was conducted to obtain the mode I fracture energy of the adhesive layer A three-point bending test was conducted to obtain the mode II fracture energy of the adhesive layer The calculation formulas are as follows:

[0085]

[0086]

[0087] Where:

[0088]

[0089]

[0090] Where, P I 、P II are the external loads; a is the crack length of the adhesive layer; χ is the correction coefficient of the crack length; h is the thickness of the adhesive layer; b is the width of the adhesive layer specimen; E 11 is the elastic modulus of the adhesive layer in the x direction; E 22 is the elastic modulus of the adhesive layer in the y direction; G 13 is the shear modulus in the xoz plane of the adhesive layer, and Γ is an intermediate parameter.

[0091] The bilinear stress-strain constitutive model of the adhesive layer satisfies the following expression:

[0092] [t n t s tt T = K[δ n δ s δ t T (5)

[0093]

[0094] where K is the stiffness matrix of the adhesive layer, t n , t s , t t are the stress components of the adhesive layer in the normal direction and two shear directions respectively; K n , K s , K t are the stiffnesses of the adhesive layer in the normal direction and two shear directions respectively, which are known, and the two shear directions are the stiffnesses in the 13 direction and 23 direction of the adhesive layer; δ n , δ s , δ t are the relative displacement components of the adhesive layer in the normal direction and two shear directions respectively, and their parameters are shown in Table 1:

[0095] Table 1 Adhesive layer material parameters

[0096]

[0097]

[0098] Mode III fracture energy cannot be effectively measured through experiments. Usually

[0099] II. According to the structural dimensions, contact properties, loads and boundary conditions of the carbon fiber reinforced composite material, adhesive layer and interference bolt, use the ABAQUS finite element software to establish a three-dimensional finite element model of the interference inserted nail for the carbon fiber reinforced composite material adhesive-bolt hybrid connection structure, and construct the stress-strain constitutive relationship of the carbon fiber reinforced composite material. The tensile strength and shear strength obtained in Step 1 provide parameter inputs for the adhesive layer model in Step 2.

[0100] 2.1 The structure required in ASTM D-5961 is as Figure 2 shown, and its dimensional parameters are shown in Table 2. Figure 2 In (a) is the schematic diagram of the adhesive layer structure, Figure 2 in (b) is the schematic diagram of the interference bolt structure, Figure 2 in (c) is the schematic diagram of the carbon fiber composite laminate structure. Use the ABAQUS software to establish a three-dimensional geometric model of the carbon fiber reinforced composite material, adhesive layer and bolt, as Figure 3 ​​As shown. According to the requirements in ASTM D-5961, a three-dimensional geometric model of carbon fiber reinforced composite material, adhesive layer and bolt was established using ABAQUS software. Since the length of the smooth rod of the bolt is greater than the laminated thickness of the connection structure, the threaded part was ignored and the bolt was simplified into a "T"-shaped solid model. Its parameters are shown in Table 3, and the identification names of each three-dimensional geometric model were set. The identification name of the adhesive layer was set as ADHESIVE-1; the identification names of the carbon fiber reinforced composite material were set as PLANE-1 and PLANE-2; the identification name of the bolt was set as BOLT-1.

[0101] Table 2 Dimension parameters of CFRP adhesive-bolt hybrid connection structure

[0102]

[0103] L a 、W a 、e a 、r a are the width, length, distance from the hole center to one end and radius of the adhesive layer respectively. R is the diameter of the bolt. L p 、W p 、e p 、r are the length, width, distance from the hole center to one end and radius of the CFRP laminate respectively, with the unit of mm.

[0104] Table 3 Material parameters of Ti6Al4V bolt

[0105]

[0106] E is the elastic modulus of the bolt and V is the Poisson's ratio.

[0107] 2.2 In the property module, set the maximum tensile strength, shear strength and mode I, mode II fracture energies of the adhesive layer to establish a bilinear stress-strain constitutive model. The cohesive element COH3D8 was used for the adhesive layer, and the reduced integration hexahedron element C3D8R was used for the carbon fiber reinforced composite material and the bolt. And enhanced hourglass control was set to reduce mesh distortion.

[0108] 2.3 In the assembly, surface-to-surface tie constraints were used between the adhesive layer and the upper and lower composite laminates. Frictional relationships were established between the bolt and the adhesive layer and the carbon fiber reinforced composite material respectively. The master surface and the slave surface were defined, and the friction coefficient and "hard" contact were added in the contact properties.

[0109] 2.4 Restrict the degrees of freedom of the three translational directions and the three rotational directions of the carbon fiber reinforced composite material and the base according to the actual test conditions, and restrict the five degrees of freedom of the bolt except for the translational degree of freedom in the z direction; establish an interference pin displacement in the load module. Among them, the interference pin displacement is 8.5 mm.

[0110] 2.5 Establish the stress-strain constitutive relationship of carbon fiber reinforced composite materials. The carbon fiber reinforced composite materials are modeled as transversely isotropic materials, and their stress-strain constitutive relationship can be expressed as:

[0111]

[0112] Where:

[0113] C 11 = E 11 (1 - v 23 v 32 ) / Δ (8)

[0114] C 22 = E 22 (1 - v 13 v 31 ) / Δ (9)

[0115] C 33 = E 33 (1 - v 12 v 21 ) / Δ (10)

[0116] C 12 = E 11 (v 21 + v 31 v 23 ) / Δ (11)

[0117] C 23 = E 22 (v 32 + v 12 v 31 ) / Δ (12)

[0118] C 13 = E 11 (v 31 + v 21 v 32 ) / Δ (13)

[0119] C 44 = 2G 12 (14)

[0120] C 55 = 2G 23 (15)

[0121] C 66 = 2G 13 (16)

[0122] Δ = 1 / (1 - v 12 v 21 - v 23 v 32-v 13 v 31 -2v 21 v 32 v 13 ) (17)

[0123] In the formula, σ n and σ t are the normal stress components (σ 11 , σ 22 , σ 33 ) and the shear stress components (σ 12 , σ 13 , σ 23 ) respectively; ε n and ε t are the normal strain components (ε 11 , ε 22 , ε 33 ) and the shear strain components (ε 12 , ε 13 , ε 23 ) respectively; C ij = C ji (i, j = 1, 2,... 6); and C ij is the stiffness coefficient.

[0124] E1, E2, and E3 are the elastic moduli of the carbon fiber reinforced composite material, G 12 , G 13 , G 23 are the shear moduli of the carbon fiber reinforced composite material, v12, v13, and v23 are the Poisson's ratios of the carbon fiber reinforced composite material, where the subscripts 12, 13, and 23 represent the 12 - direction, 13 - direction, and 23 - direction of the carbon fiber reinforced composite material respectively; and v ij = v ji , (i, j = 1, 2,... 6). Δ is an intermediate parameter.

[0125] The parameters of the T700 / TED - 85 carbon fiber reinforced composite material are shown in Table 4.

[0126] Table 4 Material parameters and strength of T700 / TED - 85

[0127]

[0128] X T is the fiber tensile strength, X C is the fiber compressive strength, Y T is the in - plane matrix tensile strength, Y C is the in - plane matrix compressive strength, Z T is the out - of - plane matrix tensile strength, Z C is the out - of - plane matrix compressive strength, S 12 and S13 、S 23 is the shear strength, with the unit of MPa.

[0129] III. Combining with the three-dimensional finite element model in Step II, based on the contact stress between the bolt, the adhesive layer, and the composite material hole wall, use the corresponding material failure criterion to conduct damage analysis on each adhesive layer and carbon fiber reinforced composite material element to determine whether the element is damaged. If damaged, use the corresponding stiffness reduction model to reduce the current material stiffness and update the stress; if not damaged, the element stiffness remains unchanged.

[0130] 3.1 Conduct stress analysis on the adhesive layer element, and use the quadratic stress failure criterion to determine whether the adhesive layer element is damaged. The criterion is as follows:

[0131]

[0132] In the formula, the symbol <> is the Macaulay bracket, indicating that the compressive load will not cause damage to the adhesive layer. and are the normal tensile strength of the adhesive layer and the shear strengths in the 1-3 and 2-3 directions respectively; t n 、T s 、t t are the current normal stress of the adhesive layer under tensile load and the shear stresses in the 1-3 and 2-3 directions respectively. If Fa≥1, the adhesive layer element is damaged; if F a <1, the adhesive layer element is not damaged.

[0133] 3.2 If the adhesive layer element is damaged and cracks occur, use the mixed-mode B-K criterion based on fracture toughness to predict the combined propagation effect of the three crack forms:

[0134]

[0135] G T =G I +G II (20)

[0136] In the formula, are the fracture energies of Mode I and Mode II respectively; G I 、G II are the current fracture energies of Mode I and Mode II respectively; is the total fracture energy; G T is the current total fracture energy, that is, the sum of the current fracture energies of Mode I and Mode II when the adhesive layer material is damaged; η is an empirical parameter, and let η = 1.

[0137] Reduce the stiffness of the adhesive layer element:

[0138] K i =(1 - D)K (21)

[0139] The stress-strain constitutive relationship of the adhesive layer element after damage is as follows:

[0140]

[0141] Where:

[0142]

[0143]

[0144] In formula (24), i = n, s, t; D is the damage variable; K i is the stiffness matrix of the adhesive layer element after damage; is the initial displacement when the adhesive layer element is damaged; is the displacement when the adhesive layer element completely fails; is the actual displacement of the adhesive layer element; δ1, δ2, and δ3 are the normal displacement of the adhesive layer element and the displacements in the 13 and 23 directions of the adhesive layer, respectively.

[0145] 3.3 Considering the shear nonlinear behavior of carbon fiber reinforced composite materials, the stress analysis of carbon fiber reinforced composite material elements is carried out by combining the maximum stress criterion and the three-dimensional Hashin failure criterion:

[0146] (1) Fiber tensile failure (σ 11 ≥0):

[0147]

[0148] (2) Fiber compressive failure (σ 11 <0):

[0149]

[0150] (3) In-plane matrix tensile failure (σ 22 +σ 33 ≥0):

[0151]

[0152] (4) In-plane matrix compressive failure (σ 22 +σ 33 <0):

[0153]

[0154] (5) Out-of-plane matrix tensile failure (σ 33 ≥0):

[0155]

[0156] (5) Out-of-plane matrix compressive failure ((σ33 <0):

[0157]

[0158] Wherein, σ 11 , σ 22 , σ 33 are the principal stresses in the x, y, and z directions respectively; σ 12 , σ 13 , σ 23 are the in-plane shear stresses in the corresponding directions; X c , X t , Y c , Y t , Z c , Z t are 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 are the shear ultimate strengths in the corresponding directions; when F ft , F fc , F mt , F mc , F nt , F nc ≥1, damage occurs to the carbon fiber reinforced composite material element; otherwise, the element is undamaged.

[0159] 3.4 When damage occurs to the carbon fiber reinforced composite material element, the material damage stiffness matrix will be activated, and a damage variable is introduced to characterize the damage process. When the material is undamaged, the damage variable is 0; when damage occurs, the damage variable will increase monotonically, and when it reaches 1, it indicates that the material has completely failed. The damage stiffness matrix C d is expressed as follows:

[0160]

[0161] Then the stress-strain constitutive relationship of the carbon fiber reinforced composite material element after damage is:

[0162]

[0163] Wherein:

[0164] b1 = 1 - d f (33)

[0165] b2 = 1 - d m (34)

[0166] b3 = 1 - d s (35)

[0167] Three independent damage variables are considered: d f , d m , d s ; d f represents the degradation in the fiber direction; d m represents the degradation along the direction perpendicular to the fiber; d s represents the degradation of the shear performance parallel to the fiber direction. The relationships are as follows:

[0168] d f = 1 - (1 - d FT )(1 - d FC ) (36)

[0169] d m = 1 - (1 - d MT )(1 - d MC ) (37)

[0170] d s = 1 - (1 - d f )(1 - smt × d MT )(1 - smc × d MC ) (38)

[0171] In the formulas, d FT , d FC are the damage variables in the fiber tension and compression directions; d MT , d MC are the damage variables in the matrix tension and compression directions; smt and smc are the coefficients of the shear modulus loss caused by matrix tension and compression failures.

[0172] IV. Combine the interference pin displacement in 2.4 to judge whether the pinning process is over. If the pinning process is not over, increase the pinning load, return to step III, and continue the stress analysis; if the pinning process is over, the model stops the analysis; the interference pin displacement is a fixed value set by humans. When analyzing, the model divides the pin displacement into several small displacements according to the complexity of the model and then conducts the analysis. After each small displacement analysis is completed, the model will judge whether the entire analysis process is over. If not, it will continue the analysis until all the small displacements are analyzed, and then the model will automatically stop the analysis.

[0173] V. After the three-dimensional finite element model of the interference pinning of the carbon fiber reinforced composite adhesive-bolt hybrid connection structure stops the analysis, compare the press-fit force-displacement curve, as Figure 4 shown, to verify the accuracy of the friction coefficient; the damage distribution of the elements is calculated and obtained in step III, and then the equivalent stress of each adhesive layer element and carbon fiber reinforced composite element in its finite element results is extracted.

[0174] 6. Based on the three-dimensional anisotropic progressive damage model in Step 3, i.e., the criteria in 3.1 and 3.3, inherit the equivalent stress and damage distribution of the elements obtained in Step 5, establish the corresponding load and boundary conditions, and construct a tensile damage model for the adhesive-bolt hybrid connection structure of carbon fiber reinforced composites; as Figure 5 shown. The load refers to the bolt pre-tightening force in 6.2; the boundary conditions refer to the operation settings in 6.4.

[0175] 6.1 Read the equivalent stress and damage distribution of the adhesive layer and carbon fiber reinforced composite elements obtained in Step 5, and associate the equivalent stress and damage distribution of their elements in the predefined field according to the identification names of the adhesive layer and carbon fiber reinforced composites in 2.1.

[0176] 6.2 Since the elastoplastic damage of the bolt is not considered, refer to the structural dimensions of each component in 2.1, establish an "I"-shaped bolt model, replace the "T"-shaped bolt model, and apply the bolt pre-tightening force in the load module; in order to avoid conflicts in the bolt cross-section properties, set the bolt cross-section properties to the default in the mesh module.

[0177] 6.3 In the contact module, establish the friction property between the bolt and the adhesive layer and composite material hole wall elements that inherit the equivalent stress and damage, add "hard" contact, and take the friction coefficient as 0.1.

[0178] 6.4 In the load and boundary module, establish the kinematic coupling reference points for the upper and lower laminates, restrict the 6 degrees of freedom of the kinematic coupling reference point of the lower laminate, restrict 5 degrees of freedom except the x-direction at the kinematic coupling reference point of the upper laminate, and add a quasi-static tensile displacement. Specifically, in the load and boundary module, establish the kinematic coupling reference points RP-1 and RP-2 for the upper and lower laminates, restrict the degrees of freedom of the upper and lower laminates, and add a 3.5 mm quasi-static tensile displacement at the reference point RP-1.

[0179] 7. Combine the failure criterion and stiffness reduction model in Step 3 to perform stress analysis on the tensile damage model of the adhesive-bolt hybrid interference connection structure of carbon fiber reinforced composites in Step 6, and judge whether each adhesive layer element and composite material element is damaged or undergoes stiffness reduction. The present invention includes two stages: the interference bolt insertion process + the tensile process after the insertion is completed. These two processes correspond to two different finite element models respectively, so two judgments are required, but the criteria are the same. Moreover, the elements in the second tensile model inherit the stress and damage of the first model, and then perform stress analysis again under the action of the tensile load, so as to obtain damage and stiffness reduction, and finally reach the overall failure of the structure.

[0180] VIII. Determine whether the damage of each adhesive layer unit and composite material unit causes the failure of the connection structure. If the connection structure does not fail, increase the tensile load and return to step VII; if the connection structure fails, the model stops analyzing. At this time, the tensile load is the tensile strength of the carbon fiber reinforced composite adhesive-bolt hybrid interference connection structure, output the tensile load-displacement curve, as Figure 6 shown. The prediction effect is shown in Table 5, and the prediction error of the tensile strength of the carbon fiber reinforced composite adhesive-bolt hybrid interference connection structure is 3.21%. Among them, the judgment of the failure of the connection structure is determined by the Abaqus software to iteratively calculate the element stiffness by itself. When the element is damaged, the stiffness will be reduced. The normal stiffness is reduced to 0, but the element stiffness appears negative during the tensile process, which makes the software unable to assemble the element stiffness matrix and the analysis will stop automatically. At this time, it is considered that the connection structure has failed.

[0181] Table 5 Comparison between Tensile Test and Prediction Results

[0182]

[0183] The present invention also provides a prediction system for the strength of an adhesive-bolt hybrid connection considering the damage of the dowel pin, including:

[0184] An acquisition module for acquiring the tensile strength, shear strength, mode I fracture energy, and mode II fracture energy of the adhesive layer.

[0185] A three-dimensional finite element model construction module for an interference dowel pin of a carbon fiber reinforced composite adhesive-bolt hybrid connection structure, which is used to construct a three-dimensional finite element model for an interference dowel pin of a carbon fiber reinforced composite adhesive-bolt hybrid connection structure according to the tensile strength, the shear strength, the structural dimensions of the connection structure, the contact properties of the connection structure, the load of the connection structure, and the boundary conditions of the connection structure; the connection structure includes carbon fiber reinforced composite materials, the adhesive layer, and interference bolts; the contact properties include the friction coefficient.

[0186] A damage analysis module for performing damage analysis based on the three-dimensional finite element model of the interference dowel pin of the carbon fiber reinforced composite adhesive-bolt hybrid connection structure, the mode I fracture energy, and the mode II fracture energy, and determining the damage distribution and stiffness reduction model according to the contact stress between the interference bolt, the adhesive layer, and the hole wall of the carbon fiber reinforced composite material.

[0187] A tensile damage model construction module for a carbon fiber reinforced composite adhesive-bolt hybrid connection structure, which is used to construct a tensile damage model for a carbon fiber reinforced composite adhesive-bolt hybrid connection structure according to the damage distribution.

[0188] A stress analysis module, configured to perform stress analysis on the tensile damage model of the carbon fiber reinforced composite adhesive-bolt hybrid connection structure according to the failure criterion and the stiffness reduction model, and determine the tensile strength.

[0189] As an alternative implementation, the acquisition module specifically includes:

[0190] A tensile strength acquisition unit, configured to perform a tensile test on the adhesive layer to obtain the tensile strength.

[0191] A shear strength acquisition unit, configured to perform a shear test on the adhesive layer to obtain the shear strength.

[0192] A mode I fracture energy acquisition unit, configured to perform a double cantilever beam test on the adhesive layer to obtain the mode I fracture energy.

[0193] A mode II fracture energy acquisition unit, configured to perform a three-point bending test on the adhesive layer to obtain the mode II fracture energy.

[0194] As an alternative implementation, the interference pin three-dimensional finite element model construction module for the carbon fiber reinforced composite adhesive-bolt hybrid connection structure specifically includes:

[0195] A three-dimensional geometric model construction unit, configured to construct a three-dimensional geometric model according to the structural dimensions of the connection structure, the contact properties of the connection structure, and the boundary conditions of the connection structure.

[0196] An interference pin displacement determination unit, configured to determine the interference pin displacement according to the load of the connection structure.

[0197] A carbon fiber reinforced composite stress-strain constitutive relationship determination unit, configured to determine the carbon fiber reinforced composite stress-strain constitutive relationship according to the tensile strength and the shear strength.

[0198] An interference pin three-dimensional finite element model construction unit for the carbon fiber reinforced composite adhesive-bolt hybrid connection structure, configured to construct an interference pin three-dimensional finite element model for the carbon fiber reinforced composite adhesive-bolt hybrid connection structure according to the three-dimensional geometric model, the interference pin displacement, and the carbon fiber reinforced composite stress-strain constitutive relationship.

[0199] As an alternative implementation, the damage analysis module specifically includes:

[0200] An adhesive layer damage condition determination unit, configured to perform stress analysis on the adhesive layer in the interference pin three-dimensional finite element model of the carbon fiber reinforced composite adhesive-bolt hybrid connection structure by using the secondary stress failure criterion, and determine the damage condition of the adhesive layer; the damage condition includes damage occurring and no damage occurring.

[0201] The adhesive layer stiffness reduction determination unit is used to determine the adhesive layer stiffness reduction in the stiffness reduction model according to the damage variable and the displacement of the adhesive layer when the damage condition of the adhesive layer is damage.

[0202] The damage distribution determination unit is used to determine the damage distribution according to the mode I fracture energy and the mode II fracture energy.

[0203] The damage condition determination unit of the carbon fiber reinforced composite material is used to perform stress analysis on the carbon fiber reinforced composite material in the three-dimensional finite element model of the interference pin of the adhesive-bolt hybrid connection structure of the carbon fiber reinforced composite material by using the maximum stress criterion and the three-dimensional Hashin failure criterion, and determine the damage condition of the carbon fiber reinforced composite material.

[0204] The carbon fiber reinforced composite material stiffness reduction determination unit is used to determine the carbon fiber reinforced composite material stiffness reduction in the damage stiffness reduction model according to the damage stiffness matrix when the damage condition of the carbon fiber reinforced composite material is damage.

[0205] The present invention takes into account the degradation of the cohesive performance of the adhesive layer, the interfacial stress state and damage distribution of the composite material hole wall after the installation of the interference bolt, and realizes the accurate prediction of the tensile strength of the connection structure under quasi-static displacement loading.

[0206] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the system disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0207] In this article, specific examples are used to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for predicting the strength of adhesive-screw hybrid connections considering nail insertion damage, characterized in that Including: Obtaining the tensile strength, shear strength, mode I fracture energy, and mode II fracture energy of the adhesive layer; Constructing a three-dimensional finite element model of an interference pin in a carbon fiber reinforced composite adhesive-bolt hybrid connection structure based on the tensile strength, the shear strength, the structural dimensions of the connection structure, the contact properties of the connection structure, the load of the connection structure, and the boundary conditions of the connection structure; the connection structure includes a carbon fiber reinforced composite material, the adhesive layer, and an interference bolt; the contact properties include the friction coefficient; Based on the three-dimensional finite element model of the interference pin in the carbon fiber reinforced composite adhesive-bolt hybrid connection structure, the mode I fracture energy, and the mode II fracture energy, performing damage analysis according to the contact stress between the interference bolt, the adhesive layer, and the hole wall of the carbon fiber reinforced composite material to determine the damage distribution and the stiffness reduction model, specifically including: performing stress analysis on the adhesive layer in the three-dimensional finite element model of the interference pin in the carbon fiber reinforced composite adhesive-bolt hybrid connection structure using the quadratic stress failure criterion to determine the damage condition of the adhesive layer; the damage condition includes damage occurring and no damage occurring; when the damage condition of the adhesive layer is damage occurring, determining the stiffness reduction of the adhesive layer in the stiffness reduction model according to the damage variable and the displacement of the adhesive layer; determining the damage distribution according to the mode I fracture energy and the mode II fracture energy; performing stress analysis on the carbon fiber reinforced composite material in the three-dimensional finite element model of the interference pin in the carbon fiber reinforced composite adhesive-bolt hybrid connection structure using the maximum stress criterion and the three-dimensional Hashin failure criterion to determine the damage condition of the carbon fiber reinforced composite material; when the damage condition of the carbon fiber reinforced composite material is damage occurring, determining the stiffness reduction of the carbon fiber reinforced composite material in the damage stiffness reduction model according to the damage stiffness matrix; Constructing a tensile damage model of the carbon fiber reinforced composite adhesive-bolt hybrid connection structure according to the damage distribution; Performing stress analysis on the tensile damage model of the carbon fiber reinforced composite adhesive-bolt hybrid connection structure according to the failure criterion and the stiffness reduction model to determine the tensile strength.

2. The method for predicting the strength of the glue-screw hybrid connection considering the damage of the dowel according to claim 1, wherein The obtaining of the tensile strength, shear strength, mode I fracture energy, and mode II fracture energy of the adhesive layer specifically includes: Performing a tensile test on the adhesive layer to obtain the tensile strength; Performing a shear test on the adhesive layer to obtain the shear strength; Performing a double cantilever beam test on the adhesive layer to obtain the mode I fracture energy; Performing a three-point bending test on the adhesive layer to obtain the mode II fracture energy.

3. The method for predicting the strength of the adhesive-screw hybrid connection considering the damage of the dowel pin according to claim 1, wherein The constructing of the three-dimensional finite element model of the interference pin in the carbon fiber reinforced composite adhesive-bolt hybrid connection structure based on the tensile strength, the shear strength, the structural dimensions of the connection structure, the contact properties of the connection structure, the load of the connection structure, and the boundary conditions of the connection structure specifically includes: Constructing a three-dimensional geometric model according to the structural dimensions of the connection structure, the contact properties of the connection structure, and the boundary conditions of the connection structure; Determining the displacement of the interference pin according to the load of the connection structure; Determining the stress-strain constitutive relationship of the carbon fiber reinforced composite material according to the tensile strength and the shear strength; Construct a three-dimensional finite element model of interference pins for a carbon fiber reinforced composite adhesive-bolt hybrid connection structure based on the three-dimensional geometric model, the interference pin displacement, and the stress-strain constitutive relationship of the carbon fiber reinforced composite material.

4. A prediction system for the strength of the glue-screw hybrid connection considering the damage of the dowel pin, characterized in that, It includes: An acquisition module for acquiring the tensile strength, shear strength, mode I fracture energy, and mode II fracture energy of the adhesive layer; A three-dimensional finite element model construction module for interference pins of a carbon fiber reinforced composite adhesive-bolt hybrid connection structure, which constructs a three-dimensional finite element model of interference pins for a carbon fiber reinforced composite adhesive-bolt hybrid connection structure based on the tensile strength, the shear strength, the structural dimensions of the connection structure, the contact properties of the connection structure, the load of the connection structure, and the boundary conditions of the connection structure; the connection structure includes a carbon fiber reinforced composite material, the adhesive layer, and interference bolts; the contact properties include the friction coefficient; A damage analysis module for performing damage analysis based on the three-dimensional finite element model of interference pins for a carbon fiber reinforced composite adhesive-bolt hybrid connection structure, the mode I fracture energy, and the mode II fracture energy, and determining the damage distribution and stiffness reduction model according to the contact stress between the interference bolts, the adhesive layer, and the hole wall of the carbon fiber reinforced composite material; The damage analysis module specifically includes: a damage condition determination unit for the adhesive layer, which performs stress analysis on the adhesive layer in the three-dimensional finite element model of interference pins for a carbon fiber reinforced composite adhesive-bolt hybrid connection structure using the quadratic stress failure criterion to determine the damage condition of the adhesive layer; the damage condition includes damage occurring and no damage occurring; an adhesive layer stiffness reduction determination unit for determining the adhesive layer stiffness reduction in the stiffness reduction model according to the damage variable and the displacement of the adhesive layer when the damage condition of the adhesive layer is damage occurring; a damage distribution determination unit for determining the damage distribution according to the mode I fracture energy and the mode II fracture energy; a damage condition determination unit for the carbon fiber reinforced composite material, which performs stress analysis on the carbon fiber reinforced composite material in the three-dimensional finite element model of interference pins for a carbon fiber reinforced composite adhesive-bolt hybrid connection structure using the maximum stress criterion and the three-dimensional Hashin failure criterion to determine the damage condition of the carbon fiber reinforced composite material; a carbon fiber reinforced composite material stiffness reduction determination unit for determining the carbon fiber reinforced composite material stiffness reduction in the damage stiffness reduction model according to the damage stiffness matrix when the damage condition of the carbon fiber reinforced composite material is damage occurring; A tensile damage model construction module for a carbon fiber reinforced composite adhesive-bolt hybrid connection structure, which constructs a tensile damage model for a carbon fiber reinforced composite adhesive-bolt hybrid connection structure according to the damage distribution; A stress analysis module for performing stress analysis on the tensile damage model of the carbon fiber reinforced composite adhesive-bolt hybrid connection structure according to the failure criterion and the stiffness reduction model to determine the tensile strength.

5. The glue-screw hybrid connection strength prediction system considering nail damage according to claim 4, characterized in that The acquisition module specifically includes: A tensile strength acquisition unit for obtaining the tensile strength by performing a tensile test on the adhesive layer; A shear strength acquisition unit for obtaining the shear strength by performing a shear test on the adhesive layer; The mode I fracture energy acquisition unit is used to obtain the mode I fracture energy by performing a double cantilever beam test on the adhesive layer; The mode II fracture energy acquisition unit is used to obtain the mode II fracture energy by performing a three-point bending test on the adhesive layer.

6. The prediction system for the strength of the glue-screw hybrid connection considering pin damage according to claim 4, wherein The interference pin three-dimensional finite element model construction module for the carbon fiber reinforced composite adhesive-screw hybrid connection structure specifically includes: The three-dimensional geometric model construction unit is used to construct a three-dimensional geometric model according to the structural dimensions of the connection structure, the contact properties of the connection structure, and the boundary conditions of the connection structure; The interference pin displacement determination unit is used to determine the interference pin displacement according to the load of the connection structure; The carbon fiber reinforced composite stress-strain constitutive relation determination unit is used to determine the carbon fiber reinforced composite stress-strain constitutive relation according to the tensile strength and the shear strength; The interference pin three-dimensional finite element model construction unit for the carbon fiber reinforced composite adhesive-screw hybrid connection structure is used to construct an interference pin three-dimensional finite element model for the carbon fiber reinforced composite adhesive-screw hybrid connection structure according to the three-dimensional geometric model, the interference pin displacement, and the carbon fiber reinforced composite stress-strain constitutive relation.

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