A near-field dynamic damage calculation method considering anisotropy of timber structures

Abstract

The application discloses a kind of considering wood structure anisotropy near-field dynamic damage calculation method, first the wood structure entity model to be simulated is dispersed into a series of space particles, the spatial coordinates of particle are generated;Obtain the parameters of wood, and as the input of prediction model;Based on spatial coordinates, the constitutive relation of wood anisotropy model is constructed, the size of near-field domain is set, the range of bond force is determined;Determine initial boundary condition, and apply external force using uniform speed loading;Using explicit iteration method, real-time update particle position, velocity, acceleration and other physical and mechanical information, while using critical elongation bond breaking criterion to describe damage cracking;Output displacement results, damage results at different times, and record the position and time of damage and cracking, obtain crack propagation path at different times.The application macroscopically characterizes the anisotropy of wood, simplifies the steps, and can effectively predict and analyze the mechanical behavior and damage problem of wood structure under load.

Description

Technical Field

[0001] This invention belongs to the field of wood and wood structure damage simulation technology, specifically involving a method for predicting and analyzing the damage behavior of wood structures based on near-field dynamics theory and considering the anisotropic characteristics of wood. Background Technology

[0002] Wood damage occurs when wood cracks and deforms under the combined effects of external forces and environmental factors, either individually or in combination, ultimately leading to failure and complete destruction, severely impacting its mechanical properties. For the sake of service life and safety, fracture analysis of wood and practical engineering structures is essential. Wood is an anisotropic material, exhibiting greater nonlinearity and variability compared to concrete and steel. Its crack propagation involves complex and progressive failure modes, making the dynamic response and damage deformation of wood structures more complex and unpredictable. The occurrence of cracks represents a material discontinuity problem. Traditional mechanical theories, such as those related to elasticity, assume continuity in their theoretical framework, which presents numerous limitations when studying discontinuous issues like cracks.

[0003] Peridynamics (PD) is a newly emerging mechanical theory system based on the concept of nonlocal interactions. It avoids the singularity problems arising from differentiation at discontinuities and provides a natural description of crack propagation. In its early stages, it was mainly applied to traditional problems in isotropic materials, including crack propagation in brittle materials and fracture in concrete structures. In recent years, it has been further applied to describe failure problems in more complex anisotropic materials. However, the use of peridynamics to study the mechanical properties and damage of timber structures still requires further exploration. To leverage the unique advantages of peridynamics in analyzing discontinuous problems and to more effectively and efficiently guide future engineering practices, it is necessary to develop an easy-to-implement model and algorithm that considers the anisotropy of timber structures, effectively predicting damage while simplifying the process as much as possible. Summary of the Invention

[0004] The purpose of this invention is to innovatively propose a near-field dynamic damage calculation method that considers the anisotropy of wood structures, macroscopically characterizing the anisotropy of wood and simplifying the process. By introducing the constitutive relation of the wood anisotropy model into near-field dynamics theory, the constitutive forces between particles are decomposed into two types of forces, changing the bond stiffness in different directions of the wood. This numerical method can effectively predict and analyze the mechanical behavior and damage problems of wood structures under load, providing a new approach for the study of anisotropic materials.

[0005] This invention is achieved through the following technical solution:

[0006] A near-field dynamic damage calculation method considering the anisotropy of timber structures includes the following steps:

[0007] Step 1: Discretize the solid model of the wooden structure to be simulated into a series of spatial material points. Each material point is located at the center of its discrete spatial domain. Calculate the spatial coordinates of each material point to simplify the model and facilitate calculation.

[0008] Step 2: Obtain the structural parameters, material property parameters, and external load parameters of the wood, and use them as inputs to the pre-built near-field dynamic damage prediction model to improve the accuracy and versatility of the model;

[0009] Step 3: Based on spatial coordinates, construct the constitutive relation of the wood anisotropy model, set the size of the near-field region, and determine the range of bond force action to improve the rationality of the model and the effectiveness of simulation and analysis.

[0010] Step 4: Determine the initial boundary conditions of the wooden structure model and apply external forces using a uniform loading method. Use a nonlocal short-range repulsive force method to describe the interactions between material points to prevent interpenetration between objects;

[0011] Step 5: Explicit iterative methods are used for dynamic calculations, updating the position, velocity, and acceleration of the material point in real time to calculate the net force acting on the material point. This allows for continuous iterative calculations, improving computational efficiency. Simultaneously, the critical elongation bond breakage criterion is used to describe the material's damage and cracking.

[0012] Step 6: Output the displacement and damage results at different times, and record the location and time of the damage and fracture to obtain the crack propagation path at different times, so as to predict the damage and mechanical behavior of the wood structure.

[0013] Furthermore, the spatial meshing method for the wooden structure entity model in step 1 is as follows: a certain material point in the material contains a series of related material points with certain physical information in its vicinity. In order to facilitate numerical calculation, the wooden structure entity model is discretized into a finite number of cubes with a spacing of Δx; each cube is of equal size, arranged uniformly, and occupies a certain volume.

[0014] Furthermore, in step 2, the physical parameters of the partitioned units are characterized by the geometric center of the small cube. After the model is discretized, the integral term is considered as a summation over a certain region in the numerical implementation. The governing equations are given as follows:

[0015] ,

[0016] Where f is x i and x j The point-to-point force function; ρ is the density of the material; b(x) i , t) represents the external force or body force density; u(x) i, t) is the displacement vector field of the material point; near-field region H δ Let be the set of all member points within the near field region, and have δ is the radius of the nonlocal near-field region of the matter point.

[0017] Furthermore, the constitutive relations of the wood anisotropy model and the bond breakage criteria in step 3 are as follows:

[0018] The simplified constitutive equation for wood is:

[0019] ,

[0020] Where ε1 and ε2 are the strains of wood under compression parallel and transverse to the grain, respectively; γ is the in-plane shear strain; E1 and E2 are the Young's moduli under compression parallel and transverse to the grain, respectively; and G is the strain of wood under compression parallel and transverse to the grain, respectively. 12 It is the in-plane shear modulus; ν 12 and ν 21 It is Poisson's ratio. The above material parameters can be determined through experimental measurement results, while σ1, σ2, and τ are the stress and shear strain of wood in the direction parallel to and across the grain, respectively.

[0021] Furthermore, step 3 abstracts the solid wood model into thin layers stacked along the fiber direction. Each layer is idealized as a discrete two-dimensional structure, and general bonds and reinforcing bonds are introduced to describe the macroscopic anisotropy of wood: the interaction of material points in the layer along the grain direction is strengthened by reinforcing bonds, resulting in higher strength; the interaction of material points in all other directions is controlled by general bonds. The micromodulus of the bonds in the model is set. for:

[0022] ,

[0023] In the formula, c g c r The micromodulometry of the general bond and the reinforcing bond are respectively derived from the principle of strain energy equivalence.

[0024] Furthermore, in step 3, the bond elongation of the point bonds in the near-field dynamics is:

[0025] ,

[0026] in, For bond elongation, η = u j -u i ξ represents the relative displacement of two material points in a reference configuration. j -x iThis represents the relative positions of two material points in the reference configuration. ||ξ|| and ||η+ξ|| are the bond lengths before and after deformation, respectively. When s is greater than the critical elongation s0, it indicates that the point-to-point force disappears. The point-to-point force function is as follows:

[0027] .

[0028] Furthermore, in step 5, for bonds along the grain direction, if the bond elongation exceeds the critical elongation of both the reinforcing bond and the general bond, breakage occurs; for all bonds in other directions, if the bond elongation exceeds the critical elongation of the general bond, breakage occurs. The scalar function μ(η,ξ) is a discontinuous function characterizing whether a bond breaks.

[0029] ,

[0030] In the formula, s r and s g These represent the elongation of reinforcing bonds and ordinary bonds, respectively. rt0 s rc0 s gt0 s gc0 These represent the critical elongation rates for stretching and compression of reinforcing and ordinary bonds, respectively.

[0031] Furthermore, the bond damage factor describes the bond breakage situation at any local material point x in the material. i Damage at a point is defined at the level of material point pairs using the local damage function φ(x). i The expression , t) indicates that the local damage function represents a local damage range of 0 to 1. When the local damage is 1, all interactions related to that point are eliminated, while when the local damage is 0, all interactions are intact.

[0032] .

[0033] Furthermore, in step 4, the nonlocal short-range repulsive force method is used to describe the interactions between undamaged material points, between individual detached material points, and between an individual detached material point and the original continuum material points. Its expression is:

[0034] ,

[0035] In the formula, x i x j L is the position vector of the material points in the current configuration; α is the repulsive force constant, determined by the micromodulus c; L r It is a matter point x i and x jThe critical distance at which short-range repulsive forces act between the wood and the rigid body. Wood and rigid bodies are considered to be composed of many material points, and the interaction that occurs when wood and rigid bodies come into contact employs this repulsive force.

[0036] Furthermore, in step 5, during explicit dynamic calculations, acceleration and velocity are approximated using finite difference forms of displacement; by using the finite difference approximation of the second derivative of the material point k with respect to the displacement and velocity at a given initial moment, the velocity and displacement at the next time step are obtained:

[0037] ,

[0038] ,

[0039] Where Δt is the time step and n is the number of computation steps; , The velocities of the material point at time t+Δt and time t are respectively. , These are the displacements of the material point at time t+Δt and t, respectively;

[0040] In step 5, to ensure accuracy during explicit dynamic calculations, volume correction coefficients and surface correction terms are applied to particles in the near-field region, but not all of them, as well as to material points of the particles at the solid boundary, to reduce numerical errors.

[0041] The technical principle of this invention, a near-field dynamic damage calculation method considering the anisotropy of timber structures, is as follows: Using computer simulation technology, the solid model of the timber structure to be simulated is discretized into a series of spatial material points, and the spatial coordinates of each material point are calculated. By acquiring the structural parameters, material property parameters, and external load parameters of the timber as input, the constitutive relation of the anisotropic timber model is constructed, the near-field domain size is set, and the bond force range is determined. After determining the initial boundary conditions of the timber structure model, an explicit iterative method is used for dynamic calculations, updating the position, velocity, acceleration, and other physical and mechanical information of the material points in real time, and using the critical elongation bond breakage criterion to describe the material's damage and cracking. Finally, the displacement and damage results at different times are output, and the location and time of fracture are recorded to obtain the crack propagation path at different times.

[0042] Compared with the prior art, the present invention has the following obvious substantive features and advantages:

[0043] 1. This invention provides a specific implementation of a wood anisotropy model based on peridynamics, which expands the peridynamics model and numerical solution system, and introduces peridynamics into a wider range of engineering applications.

[0044] 2. This invention adopts the constitutive relation of the wood anisotropic model and the bond fracture criterion, inherits the property of natural description of structural damage by near-field dynamics and direct penetration of crack propagation, and effectively improves the calculation accuracy of structural deformation by adding volume correction coefficients and surface correction terms.

[0045] 3. This invention proposes the idea of ​​simplifying the anisotropy of wood, which can efficiently solve the problems of deformation and cracking damage in wood structures. Attached Figure Description

[0046] Figure 1 This is a diagram of the near-field dynamics model of the present invention;

[0047] Figure 2 This is a schematic diagram illustrating the realization of wood anisotropy in this invention;

[0048] Figure 3 The constitutive relations of the near-field dynamics model of wood used in this invention (including) Figure 3 a, 3b);

[0049] Figure 4 This is a schematic diagram of the near-field dynamics modeling and solution process of the present invention;

[0050] Figure 5 This is a simplified and discretized schematic diagram of the wooden structure solid model provided in an embodiment of the present invention;

[0051] Figure 6 A schematic diagram of the damage cracking process provided in the embodiments of the present invention (including...) Figure 6 a, 6b);

[0052] Figure 7 A schematic diagram comparing the load-displacement curves of the calculation results with the experimental results provided for embodiments of the present invention (including...) Figure 7 a, 7b). Detailed Implementation

[0053] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0055] A near-field dynamic damage calculation method considering the anisotropy of timber structures includes the following steps:

[0056] Step 1: Discretize the solid model of the wooden structure to be simulated into a series of spatial material points. Each material point is located at the center of its discrete spatial domain. Calculate the spatial coordinates of each material point.

[0057] Step 2: Obtain the structural parameters, material property parameters, and external load parameters of the wood, and use them as inputs to the pre-built near-field dynamic damage prediction model;

[0058] Step 3: Based on spatial coordinates, construct the constitutive relation of the wood anisotropic model, set the size of the near-field region, and determine the range of bond force action;

[0059] Step 4: Determine the initial boundary conditions of the timber structure model and apply external forces using a uniform loading method;

[0060] Step 5: Perform dynamic calculations using an explicit iterative method, updating physical and mechanical information such as the position, velocity, and acceleration of material points in real time, while using the critical elongation bond breaking criterion to describe the damage and cracking of the material.

[0061] Step 6: Output the displacement and damage results at different times, and record the location and time of the damage fracture to obtain the crack propagation path at different times.

[0062] Furthermore, the spatial mesh generation method for the wooden structure solid model in step one is as follows:

[0063] like Figure 1 As shown, a certain material point in the material contains a series of related material points with certain physical information within its surrounding region. For the convenience of numerical calculation, these points are discretized into a finite number of cubes with a spacing of Δx. Each cube is of equal size, uniformly arranged, and occupies a certain volume. The physical parameters of the dividing unit are represented by the geometric center of the small cube. After discretization, the integral term in the numerical implementation is considered as a summation over a certain region. The governing equations are given below:

[0064] ,

[0065] Where f is x i and x j The point-to-point force function; ρ is the density of the material; b(x) i , t) represents the external force or body force density; u(x) i , t) is the displacement vector field of the material point; near-field region H δ Let be the set of all member points within the near field region, and have δ is the radius of the nonlocal near-field region of the matter point.

[0066] The constitutive relations and bond breakage criteria of the wood anisotropic model in step three are as follows:

[0067] The simplified constitutive equation for wood is:

[0068] ,

[0069] Where ε1 and ε2 are the strains of wood under compression parallel and cross-grain, respectively; γ is the in-plane shear strain; and E1 and E2 are the Young's moduli under compression parallel and cross-grain, respectively. 12 It is the in-plane shear modulus; ν 12 and ν 21 It is Poisson's ratio. The above material parameters can be determined through experimental measurement results, while σ1, σ2, and τ are the stress and shear strain of wood in the direction parallel to and across the grain, respectively.

[0070] like Figure 2 As shown, the solid wood model is abstracted as thin layers stacked along the fiber direction, each idealized as a discrete two-dimensional structure. General bonds and reinforcing bonds are introduced to describe the macroscopic anisotropy of wood: the interaction of material points in the grain direction within the thin layer is strengthened by reinforcing bonds, resulting in higher strength; the interaction of material points in all other directions is controlled by general bonds. The micromodulus of the bonds in the model is then defined. for:

[0071] ,

[0072] In the formula, c g c r The micromodulometry of the general bond and the reinforcing bond are respectively derived from the principle of strain energy equivalence.

[0073] The bond elongation of point bonds in near-field dynamics is:

[0074] ,

[0075] in, For bond elongation, η = u j -u i ξ represents the relative displacement of two material points in a reference configuration. j -x i This represents the relative positions of two material points in the reference configuration. ||ξ|| and ||η+ξ|| are the bond lengths before and after deformation, respectively. When s is greater than the critical elongation s0, it indicates that the point-to-point force disappears. The point-to-point force function is as follows:

[0076] ,

[0077] For bonds along the grain direction, breakage occurs if the bond elongation exceeds the critical elongation of both reinforcing and ordinary bonds; for all bonds in other directions, breakage occurs if the bond elongation exceeds the critical elongation of ordinary bonds. The scalar function μ(η,ξ) is a discontinuous function characterizing whether point bonds in a substance break.

[0078] ,

[0079] In the formula, s r and s g These represent the elongation of reinforcing bonds and ordinary bonds, respectively. rt0 s rc0 s gt0 s gc0 These represent the critical elongation at stretching and compression of reinforcing and ordinary bonds, respectively. Figure 3 .in Figure 3 'a' is a schematic diagram of the elongation of a general bond. Figure 3 b is a schematic diagram of the bond elongation. The horizontal axis represents the bond elongation, the negative horizontal axis represents the compressive elongation, and the positive horizontal axis represents the tensile elongation; the vertical axis represents the constitutive force, and the model fails when the constitutive force is 0.

[0080] Therefore, the bond damage factor describes the fracture of material point pairs. The damage at any local material point x in the material is defined at the level of material point pairs by the local damage function φ(x). i The local damage function (t) represents the local damage range from 0 to 1. When the local damage is 1, all interactions associated with that point are eliminated, while when the local damage is 0, all interactions are intact.

[0081] ,

[0082] In step five, during explicit dynamic calculations, acceleration and velocity are approximated using finite difference forms of displacement; by using the finite difference approximation of the second derivative of the material point k with respect to the displacement and velocity at a given initial moment, the velocity and displacement at the next time step are obtained.

[0083]

[0084]

[0085] Where Δt is the time step and n is the number of computation steps; , The velocities of the material point at time t+Δt and time t are respectively. , These are the displacements of the material point at time t+Δt and time t, respectively.

[0086] In actual simulations, in order to ensure accuracy requirements, this invention adopts volume correction coefficients and surface correction terms for particles that are in the near field but not entirely in the near field, as well as for material points of the particles at the solid boundary, to reduce numerical errors. Specific Implementation

[0087] like Figure 4 As shown, this embodiment uses the dynamic deformation and embedment damage of glued laminated timber in a dowel bearing test as an example to perform near-field dynamic modeling and analysis using the method of this invention. In the parallel-grain loading test, the glued laminated timber dimensions are L×W×H: 100 mm × 50 mm × 100 mm; in the transverse-grain loading test, the dimensions are L×W×H: 300 mm × 50 mm × 75 mm; the opening diameter is d0 = 22 mm in both cases; the dowel diameter is d = 20 mm; and the glued laminated timber density is ρ = 399 kg / m³. 3 The elastic modulus parallel to the grain is E1 = 14269 MPa, the elastic modulus transversely is E2 = 246 MPa, and the Poisson's ratio is v. 12 = 0.41、v 21 = 0.02, the loading speed of the pin in the experiment was 1 mm / min. The pin was treated as a rigid body, and a velocity boundary of v = 1 mm / s was applied to the upper part of the glued laminated timber, and a displacement boundary of y = 0 mm was applied to the bottom. The specific implementation includes the following steps:

[0088] S1: As Figure 5 As shown, the solid model of the wooden structure to be simulated is discretized into a series of spatial material points, each of which is located at the center of its discretized spatial domain. The spatial coordinates of each material point are calculated. In this embodiment, solid models of the wooden structure under parallel and transverse loading are established respectively. The dimensions of the parallel loading model are L×W×H: 100 mm×50 mm×100 mm, and the dimensions of the transverse loading model are L×W×H: 300 mm×50 mm×75 mm. The opening diameter of both is d0 = 22 mm. The same material parameters are assigned to the wood. The dimensions of the material points meet the calculation accuracy requirements, and Δx is taken as 1 mm and 1.5 mm respectively. Specifically, the solid model of the wooden structure is uniformly divided into meshless particles. The parallel loading model is discretized into 10044 material points, and the transverse loading model is discretized into 10034 material points.

[0089] S2: Obtain the structural parameters, material property parameters, and external load parameters of the wood, and use them as inputs to a pre-built near-field dynamic damage prediction model. Based on the initial position coordinates of the material point and the near-field radius, determine the governing equations for point association as follows:

[0090] ,

[0091] Where f is x i and x j The point-to-point force function; ρ is the density of the material; b(x) i , t) represents the external force or body force density; u(x) i , t) is the displacement vector field of the material point; near-field region H δ Let be the set of all member points within the near field region, and have δ is the radius of the nonlocal near-field region of the matter point.

[0092] Then, all the geometric parameters and attribute parameters from the previous steps are input into the wood near-field dynamics model as input items.

[0093] S3: Based on spatial coordinates, construct the constitutive relation of the anisotropic wood model, set the near-field region size, and determine the bond force range. The constitutive relation of the wood model is as follows:

[0094] ,

[0095] in, This represents the microscopic modulus of elasticity, in the direction parallel to the grain of the wood. Other directions . c g c r , respectively, represent the micromodulus of the general bond and the enhanced bond; μ is the local damage function; Let η be the bond elongation rate. For bonds along the grain direction, if the bond elongation rate exceeds the critical elongation rate of both reinforcing and general bonds, breakage occurs. For all bonds in other directions, if the bond elongation exceeds the critical elongation rate of general bonds, breakage occurs. μ(η,ξ) is the local damage function; η = u j -u i ξ = x represents the relative displacement of two material points in a reference configuration. j -x i This represents the relative position of two material points in the reference configuration, the vector η+ξ represents the deformed bond, and ||η+ξ|| is the length of the deformed bond.

[0096] Based on the material point size and the characteristic scale of the wood structure model, the near-field ranges of point association and bond association are generated. Specifically, based on the material point size Δx and the characteristic scale of the wood structure model, the radius of the near-field range is determined to be δ = 3.015Δx.

[0097] S4: Determine the initial boundary conditions for the timber structure model and apply external forces using a uniform loading method. In this embodiment, the initial conditions are set as follows: the initial displacement and initial velocity of all material points are 0; a uniform velocity boundary and loading method that varies with time are used, with a velocity boundary of v = 1 mm / s applied to the upper part of the glued laminated timber and a displacement boundary of y = 0 mm applied to the bottom. The application time is the first 50,000 time steps.

[0098] S5: An explicit iterative method is used for dynamic calculations, updating the physical and mechanical information such as the position, velocity, and acceleration of material points in real time. Simultaneously, the critical elongation bond-breaking criterion is used to describe the material's damage and cracking. Specifically, for the dynamic deformation and embedded damage problem in this embodiment, a differential algorithm using an explicit Verlet velocity scheme is employed to achieve time stepping, obtaining the velocity and displacement at time t+Δt, i.e.:

[0099] ,

[0100] .

[0101] Where Δt is the time step and n is the number of computation steps; , The velocities of the material point at time t+Δt and time t are respectively. , These are the displacements of the material point at time t+Δt and time t, respectively.

[0102] S6: Outputs displacement and damage results at different times, and records the location and time of fracture to obtain the crack propagation path at different times. After obtaining the explicit dynamic calculation results, the critical elongation fracture criterion is used to describe the damage and cracking, outputting load-displacement results and damage contour plots at different times, such as... Figure 6 , 7 .in Figure 6 a represents the damage contour maps of the glued laminated timber model along the grain at time steps 13500, 14500, and 15500. Figure 6 b represents the damage cloud maps of the glued laminated wood crossgrain model at 15000, 25000, and 35000 time steps, respectively. The legend is the damage index, which represents the ratio of the number of the largest broken bonds to the number of the original interacting bonds in the near field. Figure 7 To compare the load-displacement curves from PD simulation and experimental results, the labels on the curves indicate error analysis. Figure 7 'a' represents the load-displacement curve of the specimen with parallel grain. The maximum error between the PD simulation and experimental results is 3.22%. Figure 7 b represents the load-displacement curve of the striation specimen. The maximum error between the PD simulation and the experimental results is 8.63%.

[0103] The accuracy of this method was demonstrated by experiments. In actual experiments, the Pearson correlation coefficient between the experimental curve and the simulated curve for parallel loading was 97.80%, and the Pearson correlation coefficient for the cross-grain loading curve was 95.97%, which is close to the experimental results. Based on this, the wood damage prediction analysis was carried out.

[0104] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made based on the spirit and principle of the technical solution of the present invention shall be equivalent substitutions. As long as they meet the purpose of the invention and do not deviate from the technical principle and inventive concept of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A near-field dynamic damage calculation method considering the anisotropy of wooden structures, characterized in that, Includes the following steps: Step 1: Discretize the solid model of the wooden structure to be simulated into a series of spatial material points. Each material point is located at the center of its discrete spatial domain. Calculate the spatial coordinates of each material point to simplify the model and facilitate calculation. Step 2: Obtain the structural parameters, material property parameters, and external load parameters of the wood, and use them as inputs to the pre-built near-field dynamic damage prediction model to improve the accuracy and versatility of the model; Step 3: Based on spatial coordinates, construct the constitutive relation of the wood anisotropy model, set the size of the near-field region, and determine the range of bond force action to improve the rationality of the model and the effectiveness of simulation and analysis. Step 4: Determine the initial boundary conditions of the wooden structure model, apply external forces using uniform loading, and use the nonlocal short-range repulsive force method to describe the interaction between material points to prevent mutual penetration between objects; Step 5: Perform dynamic calculations using an explicit iterative method, updating the position, velocity, and acceleration of the material point in real time, and calculating the net force on the material point, thereby achieving continuous iterative calculations and improving calculation efficiency. At the same time, the critical elongation bond breaking criterion is used to describe the damage and cracking of the material. Step 6: Output the displacement and damage results at different times, and record the location and time of damage and fracture to obtain the crack propagation path at different times, so as to predict the damage and mechanical behavior of the wood structure. Step 3 abstracts the solid wood model into thin layers stacked along the fiber direction. Each layer is idealized as a discrete two-dimensional structure, and general bonds and reinforcing bonds are introduced to describe the macroscopic anisotropy of wood: the interaction of material points in the layer along the grain direction is strengthened by reinforcing bonds, resulting in higher strength; the interaction of material points in all other directions is controlled by general bonds. The micromodulus of the bonds in the model is set. for: ， In the formula, c g c r The micromodulometry of the general bond and the reinforcing bond are respectively derived from the strain energy equivalence principle; In step 5, for bonds along the grain direction, if the bond elongation exceeds the critical elongation of both the reinforcing bond and the general bond, then breakage occurs; for all bonds in other directions, if the bond elongation exceeds the critical elongation of the general bond, then breakage occurs. The scalar function μ(η,ξ) is a discontinuity function characterizing whether a bond breaks, where η represents the relative displacement of two material points in the reference configuration, and ξ represents the relative position of two material points in the reference configuration.

2. The near-field dynamic damage calculation method considering the anisotropy of wooden structures according to claim 1, characterized in that, The spatial meshing method for the wooden structure solid model in step 1 is as follows: a certain material point in the material contains a series of related material points with certain physical information in its vicinity. In order to facilitate numerical calculation, the wooden structure solid model is discretized into a finite number of cubes with a spacing of Δx. Each cube is of equal size, arranged uniformly, and occupies a certain volume.

3. The near-field dynamic damage calculation method considering the anisotropy of wooden structures according to claim 2, characterized in that, In step 2, the physical parameters of the dividing unit are characterized by the geometric center of the small cube. After the model is discretized, the integral term is considered as a summation over a certain region in the numerical implementation. The governing equations are given as follows: ， Where f is x i and x j The point-to-point force function; ρ is the density of the material; b(x) i , t) represents the external force or body force density; u(x) i ,t) is the displacement vector field of the material point; near-field region H δ Let be the set of all member points within the near field region, and have δ is the radius of the nonlocal near-field region of the matter point.

4. The near-field dynamic damage calculation method considering the anisotropy of wooden structures according to claim 1, characterized in that, The constitutive relations and bond breakage criteria of the wood anisotropic model in step 3 are as follows: The simplified constitutive equation for wood is: ， Where ε1 and ε2 are the strains of wood under compression parallel and transverse to the grain, respectively; γ is the in-plane shear strain; E1 and E2 are the Young's moduli under compression parallel and transverse to the grain, respectively; and G is the strain of wood under compression parallel and transverse to the grain, respectively. 12 It is the in-plane shear modulus; ν 12 and ν 21 It is Poisson's ratio. The above material parameters can be determined through experimental measurement results, while σ1, σ2, and τ are the stress and shear strain of wood in the direction parallel to and across the grain, respectively.

5. The near-field dynamic damage calculation method considering the anisotropy of wooden structures according to claim 1, characterized in that, In step 3, the bond elongation of the point bonds in the near-field dynamics is: ， in, For bond elongation, η = u j -u i ξ = x represents the relative displacement of two material points in a reference configuration. j -x i Let |ξ|| and |η+ξ|| represent the relative positions of two material points in the reference configuration, respectively. |ξ|| and |η+ξ|| represent the bond lengths before and after deformation. When s is greater than the critical elongation s0, it indicates that the point-to-point force disappears. The point-to-point force function is as follows: 。 6. The near-field dynamic damage calculation method considering the anisotropy of wooden structures according to claim 1, characterized in that, The bond damage factor describes the bond breakage situation at any local material point x in the material. i Damage at a point is defined at the level of material point pairs using the local damage function φ(x). i The expression , t) indicates that the local damage function represents a local damage range of 0 to 1. When the local damage is 1, all interactions related to that point are eliminated, while when the local damage is 0, all interactions are intact. ， Near field H δ It is the set of all member points within the near field.

7. The near-field dynamic damage calculation method considering the anisotropy of wooden structures according to claim 1, characterized in that, In step 4, the nonlocal short-range repulsive force method is used to describe the interactions between undamaged material points, between individual detached material points, and between an individual detached material point and the original continuum material points. Its expression is: ， In the formula, x i x j L is the position vector of the material points in the current configuration; α is the repulsive force constant, determined by the micromodulus c; L r It is a matter point x i and x j The critical distance between the short-range repulsive forces between the wood and the rigid body is considered as being composed of many material points. The interaction that occurs when the wood and the rigid body come into contact employs this repulsive force.

8. The near-field dynamic damage calculation method considering the anisotropy of wooden structures according to claim 1, characterized in that, In step 5, during explicit dynamic calculations, acceleration and velocity are approximated using finite difference forms of displacement; by using the finite difference approximation of the second derivative of the material point k with respect to the displacement and velocity at a given initial moment, the velocity and displacement at the next time step are obtained. ， ， Where Δt is the time step and n is the number of computation steps; , The velocities of the material point at time t+Δt and time t are respectively. , These are the displacements of the material point at time t+Δt and t, respectively; In step 5, to ensure accuracy during explicit dynamic calculations, volume correction coefficients and surface correction terms are applied to particles in the near-field region, but not all of them, as well as to material points of the particles at the solid boundary, to reduce numerical errors.

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