Simulation method for crack propagation of hole edge crack of aviation fastener based on independent meshing

Abstract

The application provides an aviation fastener hole edge crack propagation simulation method based on independent mesh division, relates to the technical field of aerospace structure integrity evaluation, and comprises the following steps: S1, establishing a fastener connection structure global background mesh model; S2, describing independent crack geometric positions based on a level set function; S3, introducing an enhancement item, and constructing an approximation function of a displacement field of any point in a unit; S4, extracting an interaction integral and a dynamic compound stress intensity factor; S5, judging whether the crack propagates or not, and selecting an updated level set function; S6, entering a next time step and repeating S2 to S5 until a preset termination condition is reached, and obtaining hole edge crack dynamic propagation simulation information. The application completely decouples crack geometry and the background mesh, does not require any mesh redrawing throughout the process, saves preprocessing and mesh division time for a three-dimensional model containing a complex contact algorithm, and greatly improves the calculation efficiency.

Description

Technical Field

[0001] This invention relates to the field of aerospace structural integrity assessment technology, specifically to a method for simulating crack propagation at the hole edge of aerospace fasteners based on independent mesh generation. Background Technology

[0002] In the aerospace field, high-strength aluminum alloys (such as 2024-T3 and 7075-T6) are extensively used in critical structures of aircraft, such as fuselage skin and wing panels, and are connected by fasteners such as rivets or bolts. Due to geometric abrupt changes, significant stress concentration occurs at the edges of fastener holes. During aircraft service, under the dynamic effects of aerodynamic loads, engine vibrations, and alternating pressurized loads, microcracks are highly susceptible to initiation at the hole edges, gradually evolving into multi-source fatigue cracks and even dynamic instability fractures, posing safety hazards.

[0003] To address the dynamic propagation of cracks at the edge of holes in aerospace fasteners, traditional methods typically employ the finite element method (FEM) for crack propagation simulation. However, the FEM often relies on mesh remapping or mesh bonding during crack path evolution, making it difficult to efficiently handle the dynamic propagation of multiple cracks at the edge of complex holes.

[0004] However, the traditional finite element method also faces the following serious technical bottlenecks when dealing with crack propagation problems involving fasteners: 1. Computational disaster caused by mesh remapping: Traditional finite element methods require that the crack surface and fastener hole boundary must completely coincide with the boundary of the finite element mesh. When simulating the dynamic propagation of multiple cracks at the hole edge, every tiny step forward of the crack requires remapping the complex 3D mesh containing fastener contact nonlinearities. This is computationally unacceptable when dealing with high-frequency time steps of dynamic loads.

[0005] 2. Difficulty in simulating multi-source damage interference: In fastener arrays, there are often multiple cracks that propagate simultaneously, interfere with each other, or even merge. Traditional mesh technology has great difficulty in handling such complex topological changes.

[0006] 3. Distortion in capturing dynamic response: Frequent mesh remapping introduces numerical damping and energy dissipation during dynamic solving, resulting in severe distortion of the reflection and transmission of high-frequency stress waves between the fastener and the hole wall, making it impossible to accurately calculate the dynamic stress intensity factor. Summary of the Invention

[0007] To address the shortcomings of the prior art, the present invention aims to provide a method for simulating the crack propagation at the hole edge of aerospace fasteners based on independent mesh generation. This method can completely decouple the crack geometry evolution from the background mesh topology, thus solving the problem of excessive computational load caused by mesh re-division in the prior art.

[0008] Specifically, on the one hand, the present invention provides a method for simulating the crack propagation at the hole edge of aerospace fasteners based on independent mesh generation, which includes the following steps: S1: Establish a global background mesh model for the fastener connection structure; S2: In the mesh model established in S1, the geometric location of independent cracks is described based on the level set function; S3: Based on the geometric position in S2, identify the background element traversed by the zero isosurface of the level set function, introduce an enhancement term into the standard finite element displacement field, and construct an arbitrary point within the element. displacement field Approximation function: ; In the formula: Here, represents the standard finite element shape function; I represents the set of nodes for conventional elements, where i is the node number in set I; J represents the set of nodes for crack surface jump reinforcement, where j is the node number in set J; and K represents the set of nodes for crack tip reinforcement, where k is the node number in set K. Number the crack tip enhancement function; For conventional nodal displacement degrees of freedom; This is the Heaviside step function, used to describe the displacement jump on both sides of the crack surface; Increase the degree of freedom for the corresponding jump; For the asymptotic enhancement function at the crack tip; Increase the degree of freedom at the crack tip; S4: Displacement field based on S3 Extract the dynamic composite stress intensity factor of the interaction integral under dynamic load and the fastener hole edge crack; S5: Dynamic composite stress intensity factor obtained from S4 Calculate the equivalent dynamic stress intensity factor : ; Equivalent dynamic stress intensity factor The crack propagation is compared with the material's dynamic fracture toughness or a preset propagation threshold to determine whether the crack has propagated: if no propagation has occurred, the current level set function remains unchanged; if propagation has occurred, the crack initiation angle and the crack propagation increment within the current time step are calculated. The crack propagation increment proceeds along the direction determined by the initiation angle. Update the crack leading edge position and update the level set function; S6: Based on the updated level set function, proceed to the next time step and repeat S2 to S5 until the preset termination condition is reached, and finally obtain the simulation information of dynamic crack propagation at the hole edge.

[0009] Furthermore: In S1, the method for establishing a global background mesh model of the fastener connection structure includes: establishing a hexahedral or tetrahedral solid element background mesh based on the geometric dimensions of the aerospace aluminum alloy panel and the fastener; Local mesh refinement is performed in the region containing fastener holes, initial cracks are ignored during mesh generation, and an elastoplastic constitutive model of the aluminum alloy material and dynamic frictional contact properties between the fastener and the hole wall are defined.

[0010] Furthermore: In S2, the methods for describing the geometric location of independent cracks based on level set functions include: S21: Orthogonal horizontal set functions are used to independently describe the geometric location of the hole edge crack without changing the background mesh; S22: Define the first level set function Represents any point within the structural domain The sign distance of the normal band to the crack surface, the second level set function Point The orthogonal distance to the plane perpendicular to the tangent at the crack tip and passing through the crack tip; if ,and If, then it is positioned as a crack surface; if ,and Then it is located at the crack tip.

[0011] Furthermore: In S3, the crack tip asymptotic enhancement function Based on the definition of linear elastic fracture mechanics: ; In the formula, and These are local polar coordinates with the crack tip as the origin; To increase the degree of freedom at the tip.

[0012] Furthermore, in S4, the method for extracting the dynamic composite stress intensity factor of the interaction integral and the fastener hole edge crack under dynamic load includes: considering inertial force and damping force in each time step of the explicit or implicit dynamic time integral, solving the system dynamic equation; extracting the dynamic composite stress intensity factor of the fastener hole edge crack from the independent background mesh based on the dynamic interaction integral method; wherein, the interaction integral domain is set in several layers of elements around the crack tip.

[0013] Furthermore: In S5, the crack propagation initiation angle Determined by the maximum circumferential stress criterion: ; In the formula, These are Type I and Type II dynamic stress intensity factors, respectively.

[0014] Furthermore: In S5, the crack propagation increment The calculation method is as follows: ; In the formula, The material expansion coefficient, This is the current time step; It is the equivalent dynamic stress intensity factor; The preset expansion threshold; The material expansion coefficient; This represents the current time step.

[0015] Furthermore, in S5, the updated level set function is used to re-identify the set of element nodes J that are completely penetrated by the crack surface and the set of element nodes K that contain the crack tip, providing input for reconstructing the enhanced displacement field in the next time step.

[0016] Furthermore, in S6, the simulation information for dynamic propagation of cracks at the hole edge includes the dynamic propagation path of the crack at the hole edge, the crack length evolution curve, the dynamic stress intensity factor evolution curve, the crack penetration state, and the dynamic residual strength variation law of the fastener connection structure.

[0017] Furthermore, in S6, the preset termination conditions include reaching a preset number of load cycles, crack penetration, dynamic instability, or residual strength falling below a preset strength threshold.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention completely decouples crack geometry from the background mesh, eliminating the need for any mesh remapping during the complex process of multiple crack initiation and convergence at the edge of fastener holes. For 3D models involving complex contact algorithms, it can save more than 80% of preprocessing and mesh generation time, breaking through mesh dependence and significantly improving computational efficiency.

[0019] 2. By maintaining a uniform and constant background mesh, this invention avoids the numerical oscillations of the mass matrix and stiffness matrix caused by mesh mapping in traditional methods, and can capture the transmission of stress waves between aluminum alloy plates and fasteners and the dynamic response of crack tips with high precision.

[0020] 3. By introducing level set functions, this invention makes it extremely simple to track the merging behavior of two or more cracks. Only Boolean operations need to be performed on multiple level set functions to ensure accurate multi-distance loss interference analysis, which greatly improves the accuracy of aerospace structural tolerance design.

[0021] 4. By introducing an asymptotic enhancement function at the crack tip, this invention can describe the asymptotic characteristics of the displacement field near the crack tip, enabling the enhanced finite element solution to reflect the stress singularity at the crack tip and improving the description accuracy of the displacement and stress fields near the crack tip. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of an independent mesh model of a multi-source crack in an aerospace fastener connection structure in an embodiment of the present invention; Figure 2 This is a schematic diagram of the distribution of crack unit reinforcement nodes and the range of influence of shape functions in aluminum alloy materials in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the geometric description principle of fastener hole edge cracks based on level set functions in an embodiment of the present invention. Figure 4 This is a flowchart illustrating the dynamic crack propagation and interaction integral calculation process in an embodiment of the present invention. Figure 5 This is a schematic diagram of the topology update of the fastener hole edge double crack intersection and merging in an embodiment of the present invention. Detailed Implementation

[0023] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0024] like Figure 4 and Figure 5 As shown, this invention provides a method for simulating the dynamic propagation of hole edge cracks in aerospace fasteners based on independent mesh generation, which includes the following steps: wherein, Figure 4 The cyclical process from dynamic solution, fracture parameter extraction to level set update is shown; Figure 5 The process of two cracks at the edge of a fastener hole propagating towards each other, approaching each other, converging, and completing topological merging is illustrated to demonstrate the ability of this method to handle crack penetration and crack merging without remapping the background mesh.

[0025] S1: Establish the global background mesh model of the fastener connection structure: Based on the geometry of the aerospace aluminum alloy panels and fasteners, a background mesh of hexahedral or tetrahedral solid elements is established. Local mesh refinement is performed in key areas of interest, including fastener holes, but the presence of initial cracks is completely ignored during mesh generation. An elastoplastic constitutive model of the aluminum alloy material and the dynamic frictional contact properties between the fasteners and the hole walls are defined.

[0026] S2: Geometric description of independent cracks based on level set functions: In the mesh model established in S1, orthogonal level set functions are used to independently describe the geometric location of the hole edge crack without changing the background mesh. The first level set function is defined. Represents any point within the structural domain The sign distance of the normal band to the crack surface; define the second level set function. Point The orthogonal distance to the plane perpendicular to the tangent at the crack tip and passing through the crack tip.

[0027] By satisfying and To accurately locate the crack surface under the required conditions, and to meet the following conditions. and Locate the crack tip.

[0028] S3: Constructing the decoupled enhanced displacement field function: Based on the geometric location of the hole-edge crack in S2, background elements traversed by the zero isosurface of the horizontal set function are identified. To reflect the displacement discontinuity of the aluminum alloy at the crack surface and the stress singularity at the crack tip, reinforcement terms are introduced into the standard finite element displacement field. (The last sentence appears to be incomplete and possibly refers to a different element.) displacement field The approximation function is constructed as follows: ; In the formula: These are standard finite element shape functions; These represent the degrees of freedom for conventional nodal displacements. The set of element nodes that are completely penetrated by the crack surface; The function is the Heaviside step function, with a value of 1 on one side of the crack and -1 on the other side. Increase the degree of freedom for the corresponding jump; It is a set of element nodes that contain the crack tip.

[0029] This displacement field approximation function is used to solve for the displacement field u(x) at any point x in a cracked structure, transforming the crack geometry described independently in S2 into a finite element computable displacement field. The purpose of this enhanced displacement field formula is to embed the crack geometry information given in S2 into the finite element approximation space without changing the background mesh topology, so that the displacement field simultaneously possesses the characteristics of displacement discontinuity at the crack surface and the singular field characteristics at the crack tip. The strain, stress, velocity, and acceleration fields can be further obtained from this displacement field.

[0030] For isotropic aerospace aluminum alloys, the asymptotic strengthening function at the crack tip Based on the definition of linear elastic fracture mechanics: ; In the formula, and These are local polar coordinates with the crack tip as the origin; To increase the degree of freedom at the tip.

[0031] Crack tip enhancement basis function The crack tip enhancement term, embedded in the enhanced displacement field approximation function, improves the accuracy of the description of the displacement and stress fields near the crack tip. Its function is to describe the asymptotic characteristics of the displacement field near the crack tip, enabling the enhanced finite element solution to reflect the stress singularity at the crack tip. The local polar coordinates in this function... The crack tip location and local crack direction determined by S2 are used as the basis function for the crack tip enhancement term in the enhanced displacement field approximation function. The displacement field corrected by this enhancement function can be used in S4 to calculate the dynamic interaction integral around the crack tip, thereby obtaining a more accurate dynamic composite stress intensity factor.

[0032] S4: Extraction of dynamic composite stress intensity factor for fastener hole edge cracks from interaction integrals under dynamic loading: Based on the strain, stress, velocity, and acceleration fields obtained in S3, the system dynamic equations are solved by considering inertial forces and damping forces at each time step of the explicit or implicit dynamic time integral (such as Newmark-β).

[0033] Based on the dynamic interaction integral method, the dynamic composite stress intensity factor of fastener hole edge cracks is extracted from an independent background mesh. Considering the dynamic contact of the crack surface, the interaction integral domain is set within several layers of elements surrounding the crack tip.

[0034] S5: Dynamic Evolution and Level Set Update of Multi-Source Cracks First, based on the dynamic composite stress intensity factor obtained from S4 Calculate the equivalent dynamic stress intensity factor : ; When using the stress intensity factor criterion, if the equivalent dynamic stress intensity factor <Preset expansion threshold If the crack has not propagated, the current level set function remains unchanged; if the equivalent dynamic stress intensity factor... >Preset expansion threshold If so, it can be determined that the crack has expanded.

[0035] When using the energy release rate criterion, if G eq <G dc If G eq >G dc If G is positive, then it is determined that the crack has propagated; where G is positive. eq The equivalent dynamic energy release rate is used to characterize the energy release level at the crack tip under dynamic loading; G dc The critical dynamic energy release rate of the material is used as the crack propagation threshold based on the energy release rate criterion.

[0036] After determining that propagation has occurred, calculate the crack initiation angle according to the maximum circumferential stress criterion. And based on the equivalent dynamic stress intensity factor The crack propagation increment is determined by the material propagation parameters and the current time step. Then, starting from the current crack tip, along the crack initiation angle... The determined direction of advance distance This allows us to obtain the updated crack leading edge position and reinitialize or update the level set functions φ and ψ.

[0037] Cracked corner The calculation formula is as follows: ; Cracked corner and equivalent amplitude ΔK eq Both are used after crack propagation, but their functions differ: ΔK eq It is mainly used to determine and calculate the extent of crack propagation, that is, the increment of crack propagation. ; Cracked corner It is mainly used to determine the direction of propagation, that is, the direction angle when the crack front is renewed.

[0038] Cracked corner and crack propagation increment All are composed of dynamic composite stress intensity factors The derivation shows that they share a common origin. Based on the Paris formula or the dynamic fracture criterion based on energy release rate, the equivalent dynamic stress intensity factor amplitude ΔK is calculated based on the amplitude of the dynamic composite stress intensity factor. eq This allows for the determination of the crack propagation increment. ; Then, starting from the current crack tip, along the crack initiation angle... The determined direction of advance distance The updated crack leading edge position is obtained. The level set function is then reinitialized or updated using the convection equation. And ψ. The updated level set function is used to re-identify the set of element nodes J and the set of crack tip reinforcement nodes K that are completely penetrated by the crack surface, thereby providing input for reconstructing the reinforcement displacement field in the next time step.

[0039] S6: Based on the updated level set function, proceed to the next time step and repeat S2 to S5 until the preset termination condition is reached, and finally obtain the simulation information of dynamic crack propagation at the hole edge.

[0040] The preset termination conditions include the process being executed cyclically over time until a preset number of load cycles, crack penetration, dynamic instability, or residual strength falling below a threshold is reached.

[0041] The simulation information on the dynamic propagation of cracks at the hole edge includes the dynamic propagation path of the crack at the hole edge, the crack length evolution curve, the dynamic stress intensity factor evolution curve, the crack penetration state, and the dynamic residual strength variation law of the fastener connection structure.

[0042] Through the above-mentioned cycle of "dynamic solution - fracture parameter extraction - crack propagation - level set update - enhanced set re-identification", the dynamic propagation path of the hole edge crack, the crack length evolution curve, the dynamic stress intensity factor evolution curve, the crack penetration state, and the dynamic residual strength variation law of the fastener connection structure are finally obtained.

[0043] Example Combination Figures 1 to 3 As shown, Figure 1 This is a schematic diagram of an independent mesh model of multi-source cracks in an aerospace fastener connection structure. It shows a regular background mesh and independent crack surfaces interspersed within it, without the need for mesh bonding. Figure 2 This diagram illustrates the distribution of crack element reinforcement nodes and the influence range of shape functions in aluminum alloy materials, distinguishing between conventional nodes, Heaviside step reinforcement nodes, and crack tip analytical reinforcement nodes. Specifically, XFEM Topology Enhancement represents XFEM topology enhancement; Heaviside Nodes represent Heaviside nodes; Crack Tip Nodes represent crack tip nodes; and Heaviside domain represents the Heaviside region. Crack tip domain refers to the area at the tip of a crack. Figure 3 This diagram illustrates the principle of geometric description of fastener hole edge cracks based on level set functions, showing the orthogonal distribution of φ and ψ isosurfaces. Figures 1 to 3 It is understood that the present invention can embed the hole edge crack geometry, crack surface displacement discontinuity and crack tip singular field into the finite element solution space without changing the background mesh topology, thereby providing a stable computational basis for subsequent dynamic stress intensity factor extraction and crack propagation determination.

[0044] This embodiment simulates the dynamic propagation of cracks on both sides of holes in a 7075-T6 aluminum alloy panel containing interference-fit rivets: 1. Parameter definition and mesh initialization: Create a model of the perforated aluminum alloy plate (200mm long, 50mm wide, 6mm hole diameter) and a solid model of the countersunk rivet.

[0045] Material properties: 7075-T6 aluminum alloy, elastic modulus Poisson's ratio ,density Dynamic fracture toughness .

[0046] Background mesh generation: The entire system was meshed using C3D8R (eight-node linearly reduced integral 3D solid element). The mesh size in the hole edge region was controlled at 0.5mm, with a total of approximately 150,000 nodes. The interference between the rivet shank and the hole wall, as well as the "face-to-face" penalty function for frictional contact, were defined.

[0047] 2. Initial damage preset: At the thickness center at symmetrical positions on both sides of the fastener hole, an initial horizontal set function is defined. and Two semi-elliptical initial microcracks, each 1 mm in length, were seamlessly implanted. The background mesh remained unchanged.

[0048] 3. Applying load boundary conditions: An aluminum alloy plate is fixed at one end, while a high-frequency dynamic tensile load of 50Hz is applied to the other end, simultaneously simulating the transient shock wave generated by aircraft pressurization. , Let f be the amplitude of the tensile load, f be the load frequency (50Hz in this embodiment), and t be the time. It is the equivalent load of the transient shock wave.

[0049] 4. Dynamically enhanced solution loop: Step 1: The system reads the displacement field and level set distribution at the current time t and identifies the element cut off by the double crack at the hole edge.

[0050] Step 2: Assemble the stiffness and mass matrices. This is due to the introduction of the Heaviside step function. and crack tip asymptotic enhancement function To ensure the accuracy of numerical integration, Gaussian sub-region integration method should be used for elements containing cracks.

[0051] Step 3: Use the central difference method to solve for the acceleration, velocity and displacement of the current step.

[0052] 5. Fracture determination and crack propagation: Calculate the equivalent stress contour plot. Extract nodal variables around the crack tip and calculate the dynamic stress. Integral, and by dynamic Integral method to obtain composite dynamic stress intensity factor Based on the composite dynamic stress intensity factor Calculate the equivalent dynamic stress intensity factor : ; Equivalent dynamic stress intensity factor The crack propagation is compared with the material's dynamic fracture toughness or a preset propagation threshold to determine whether the crack has propagated: if no propagation has occurred, the current level set function remains unchanged; if propagation has occurred, the crack initiation angle and the crack propagation increment within the current time step are calculated. The crack propagation increment proceeds along the direction determined by the initiation angle. Update the position of the crack leading edge and update the level set function.

[0053] When the cracks on both sides extend towards each other and meet the geometric tolerance, the level set fusion algorithm is triggered to simulate crack penetration.

[0054] 6. Post-processing output: The enhanced solution, which includes additional degrees of freedom, is mapped back onto the regular visualization nodes.

[0055] Outputs the rivet contact stress distribution, hole edge crack three-dimensional propagation surface, and dynamic residual strength curve as they evolve over time.

[0056] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for simulating crack propagation at the hole edge of aerospace fasteners based on independent mesh generation, characterized in that, It includes the following steps: S1: Establish a global background mesh model for the fastener connection structure; S2: In the mesh model established in S1, the geometric location of independent cracks is described based on the level set function; S3: Based on the geometric position in S2, identify the background element traversed by the zero isosurface of the level set function, introduce an enhancement term into the standard finite element displacement field, and construct an arbitrary point within the element. displacement field Approximation function: ； In the formula: Here, represents the standard finite element shape function; I represents the set of nodes for conventional elements, where i is the node number in set I; J represents the set of nodes for crack surface jump reinforcement, where j is the node number in set J; and K represents the set of nodes for crack tip reinforcement, where k is the node number in set K. Number the crack tip enhancement function; For conventional nodal displacement degrees of freedom; This is the Heaviside step function, used to describe the displacement jumps on both sides of the crack surface; Increase the degrees of freedom for the corresponding jumps; For the asymptotic enhancement function at the crack tip; Increase the degree of freedom at the crack tip; S4: Displacement field based on S3 Extract the dynamic composite stress intensity factor of the interaction integral under dynamic load and the fastener hole edge crack; S5: Dynamic composite stress intensity factor obtained from S4 Calculate the equivalent dynamic stress intensity factor : ； Equivalent dynamic stress intensity factor The crack is compared with the material's dynamic fracture toughness or a preset propagation threshold to determine whether it has propagated: if it has not propagated, the current level set function remains unchanged. If crack propagation occurs, calculate the crack initiation angle and the crack propagation increment within the current time step. The crack propagation increment proceeds along the direction determined by the initiation angle. Update the crack leading edge position and update the level set function; S6: Based on the updated level set function, proceed to the next time step and repeat S2 to S5 until the preset termination condition is reached, and finally obtain the simulation information of dynamic crack propagation at the hole edge.

2. The method for simulating crack propagation at the hole edge of aerospace fasteners based on independent mesh generation as described in claim 1, characterized in that: In S1, the method for establishing a global background mesh model of the fastener connection structure includes: establishing a hexahedral or tetrahedral solid element background mesh based on the geometric dimensions of the aerospace aluminum alloy panel and the fastener. Local mesh refinement is performed in the region containing fastener holes, initial cracks are ignored during mesh generation, and an elastoplastic constitutive model of the aluminum alloy material and dynamic frictional contact properties between the fastener and the hole wall are defined.

3. The simulation method for hole edge crack propagation of aerospace fasteners based on independent mesh generation as described in claim 1, characterized in that: In S2, methods for describing the geometric location of independent cracks based on level set functions include: S21: Orthogonal horizontal set functions are used to independently describe the geometric location of the hole edge crack without changing the background mesh; S22: Define the first level set function Represents any point within the structural domain The sign distance of the normal band to the crack surface, the second level set function Point The orthogonal distance to the plane perpendicular to the tangent at the crack tip and passing through the crack tip; if ,and If so, it is located as a crack surface; if ,and Then it is located at the crack tip.

4. The method for simulating crack propagation at the hole edge of aerospace fasteners based on independent mesh generation as described in claim 1, characterized in that: In S3, the asymptotic enhancement function at the crack tip Based on the definition of linear elastic fracture mechanics: ； In the formula, and These are local polar coordinates with the crack tip as the origin; To increase the degree of freedom at the tip.

5. The method for simulating crack propagation at the hole edge of aerospace fasteners based on independent mesh generation as described in claim 1, characterized in that: In S4, the method for extracting the dynamic composite stress intensity factor of the interaction integral and the fastener hole edge crack under dynamic load includes: considering inertial force and damping force in each time step of the explicit or implicit dynamic time integral, solving the system dynamic equation; extracting the dynamic composite stress intensity factor of the fastener hole edge crack from the independent background mesh based on the dynamic interaction integral method; wherein, the interaction integral domain is set in several layers of elements around the crack tip.

6. The method for simulating crack propagation at the hole edge of aerospace fasteners based on independent mesh generation as described in claim 1, characterized in that: In S5, the crack propagation initiation angle Determined by the maximum circumferential stress criterion: ； In the formula, These are Type I and Type II dynamic stress intensity factors, respectively.

7. The method for simulating crack propagation at the hole edge of aerospace fasteners based on independent mesh generation as described in claim 6, characterized in that: In S5, the crack propagation increment The calculation method is as follows: ； In the formula, The material expansion coefficient, This is the current time step; It is the equivalent dynamic stress intensity factor; The preset expansion threshold; The material expansion coefficient; This represents the current time step.

8. The method for simulating crack propagation at the hole edge of aerospace fasteners based on independent mesh generation as described in claim 1, characterized in that: In S5, the updated level set function is used to re-identify the set of element nodes J that are completely penetrated by the crack surface and the set of element nodes K that contain the crack tip, providing input for reconstructing the enhanced displacement field in the next time step.

9. The method for simulating crack propagation at the hole edge of aerospace fasteners based on independent mesh generation as described in claim 1, characterized in that: In S6, the simulation information for dynamic propagation of cracks at the hole edge includes the dynamic propagation path of the crack at the hole edge, the crack length evolution curve, the dynamic stress intensity factor evolution curve, the crack penetration state, and the dynamic residual strength variation law of the fastener connection structure.

10. The method for simulating the crack propagation at the hole edge of aerospace fasteners based on independent mesh generation as described in any one of claims 1-9, characterized in that: In S6, the preset termination conditions include reaching a preset number of load cycles, crack penetration, dynamic instability, or residual strength falling below a preset strength threshold.

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