Calculation method of crack growth in six-sided top press based on adaptive extended finite element

Abstract

Aiming at the crack propagation problem of the hinge beam structure of the diamond press, the present invention proposes an accurate calculation method based on adaptive extended finite element. First, the hinge beam structure model is discretized and the mesh is divided with the help of meshing software. Secondly, an extended finite element mathematical model of the hinge beam structure is constructed, and the crack tip strengthening function is introduced to describe the physical field properties of the crack tip. The integral equation is solved to obtain the displacement, strain and stress of the crack tip; thirdly, an adaptive mesh reconstruction technology is constructed to refine the mesh of the crack tip area through crack tip error estimation, thereby improving the calculation accuracy of the crack tip displacement, strain and stress. Finally, the crack tip stress intensity factor is calculated using the interaction integral, and the path direction of the crack propagation is determined by the maximum circumferential tensile stress criterion.

Description

Technical Field

[0001] The invention relates to the field of fracture mechanics, and in particular to a method for accurately calculating crack extension of a hinge beam structure of a diamond press. Background Art

[0002] The hinged beam structure is a key pressure-bearing component of the six-sided top press. It is subjected to large sudden loads during service, which leads to internal structural defects and crack initiation over time. Crack propagation can damage the hinged beam structure, causing major safety accidents and severe economic losses. Therefore, revealing the initiation and propagation patterns of internal cracks in the hinged beam structure and predicting its expansion trend through numerical simulation of the crack propagation process provides theoretical support for the service life of the hinged beam structure of the six-sided top press, which is conducive to ensuring the safe operation of the equipment.

[0003] In order to achieve accurate simulation of crack propagation, many new calculation methods are constantly emerging. At present, the main numerical methods for simulating crack propagation inside hinged beam structures are finite element method, meshless method, boundary element method, etc. The crack propagation problem of hinged beam structure is a typical discontinuous problem. The traditional finite element method is overly dependent on the grid, which makes the pre-processing process of the crack propagation problem too complicated. As the crack propagates, the grid needs to be re-divided for each extension, which increases the additional calculation amount. In addition, since conventional finite elements cannot reflect the properties of the crack tip, a large number of grids need to be divided in order to obtain a fairly accurate displacement and stress field. The meshless method can completely or partially eliminate the grid, and does not require grid division and reconstruction. However, the meshless method has difficulty in handling the convergence of discrete functions and requires a large amount of calculation, resulting in low computational efficiency. Its convergence, consistency and error analysis lack a solid theoretical basis and mathematical proof. The boundary element method (BEM) can encounter singular and near-singular integrals, requiring regional integrals to handle nonlinear terms, and cannot track crack propagation. The extended finite element method (EFM) uses extended shape functions based on discontinuities to describe discontinuities within a region, including cracks, pores, inclusions, and material interfaces. The description of discontinuities is completely independent of the computational mesh, offering significant advantages in addressing crack problems. By introducing a reinforcement function to capture crack tip discontinuities and employing the level set method to describe cracks, the capture of crack characteristics is independent of the EFM mesh, eliminating the need for re-meshing when simulating crack propagation. This improves computational efficiency while maintaining accuracy. However, for practical engineering structures, especially those with complex fractures, the EFM suffers from insufficient computational accuracy, making the simulation results of limited relevance. Introducing adaptive mesh technology and refining the crack tip region through error analysis can effectively improve computational accuracy.

[0004] Adaptive extended finite element (AFE) adaptively improves the extended finite element solution process, using error analysis to determine whether the current results meet the computational requirements. Based on these results, the mesh in areas of low computational accuracy is reconstructed to improve accuracy. First, an initial mesh is created based on the geometric characteristics and boundary conditions of the hinged beam model, and then an AFE calculation is performed. Error analysis is performed on the calculated results to determine whether the accuracy meets the specified requirements. If the accuracy is insufficient, the mesh is refined and the calculation continues. If the accuracy meets the requirements, the calculation proceeds to the next step. This improves computational accuracy without excessively increasing the computational burden.

[0005] The present invention proposes a precise calculation method for crack propagation in a six-sided top press based on adaptive extended finite elements. Relying on the advantages of the extended finite element method and adaptive technology in crack analysis, the accuracy of crack propagation simulation in hinged beam structures is improved, and accurate simulation of crack propagation paths in hinged beam structures is achieved. Summary of the Invention

[0006] To address the impact of crack defects on the operation and stability of the hinged beam structure of a diamond press, this paper proposes a crack propagation path prediction method based on a combination of extended finite element (FEM) and adaptive techniques. A physical model of the hinged beam structure of a diamond press was established, and meshing software was used to discretize the model. Adaptive meshing technology was introduced to adaptively improve the extended finite element solution process. Error analysis was used to determine whether the current results met the computational requirements. Based on the analysis results, the mesh in areas of low computational accuracy was reconstructed to improve computational accuracy. This method accurately simulated the crack propagation path of the hinged beam structure.

[0007] The technical solution of the present invention is achieved as follows: a method for calculating crack propagation of a six-sided top press based on an adaptive extended finite element, the method comprising the following steps:

[0008] S1: Establish a physical model of the hinge beam structure based on modeling software, including the characteristic dimensions of the structure, the location and size of the cracks;

[0009] S2: Perform meshing of the hinge beam structure and input the position of the crack tip;

[0010] Determine the starting point and tip of the crack; mesh the hinge beam structure model using finite element software or meshing software, creating a finer mesh near the crack and a uniform mesh in other areas. Extract mesh elements and nodes, and highly match the mesh density of the two areas to ensure mesh rationality.

[0011] S3: Solve the finite element integral equation of the hinged beam structure based on the extended finite element method;

[0012] S4: Solving the stress intensity factor of cracks in hinged beam structures by interaction integration method;

[0013] S5: Improvement of the extended finite element method based on adaptive technology;

[0014] S6: Determine the crack propagation path in the hinged beam structure model;

[0015] Furthermore, step S3 is specifically as follows:

[0016] S3.1: Introducing reinforcement function:

[0017] Introduce a step function node to simulate the strong discontinuity of the crack body:

[0018]

[0019] Crack tip strengthening function F of the element near the crack tip l (x) is usually a linear combination of the following four basis functions:

[0020]

[0021] where r and θ are parameters defining the crack tip in polar coordinates.

[0022] According to the two strengthening functions of formula (1) and (2), the displacement approximate expression of the two-dimensional composite crack problem is:

[0023]

[0024] Where the unit decomposition function N i (x), N j (x), N k (x) is the standard finite element shape function; is the node displacement; is the additional degree of freedom of the element penetrated by the crack, It is the additional degree of freedom of the unit near the crack tip, and the two have no clear physical meaning; I is the node set of the solution domain; J is the reinforcement node set of the unit through the unit; K is the reinforcement node set of the unit near the crack tip;

[0025] S:3.2: Establish the governing equations:

[0026]

[0027] Describe it in tensor form:

[0028]

[0029] The elastic boundary conditions are:

[0030] In Γ t Previous (6)

[0031] In Γ u Previous (7)

[0032] In Γ f Previous (8)

[0033] in, represents the differential operator; σ is the stress tensor; f b is the body force; t is the boundary stress vector; u is the boundary displacement vector; n is the interface normal vector.

[0034] Introducing the arbitrary displacement φ of the hinge beam structure at the equilibrium position T =(φ x ,φ y ), we get the finite element integral equation:

[0035]

[0036] S3.3: Introduce the principle of virtual work to derive the weak form of the finite element integral equation for the hinged beam structure and solve the finite element integral equation for the hinged beam structure;

[0037] According to the principle of virtual work, the weak form of the integral equation is obtained:

[0038] -∫ Ω σ T ε(φ)tdA+∫ A φ T ftdA+∫ L [(n x σ x +n y τ xy )φ x +(n x τ xy +n y σ y )φ y ]dL=0 (10)

[0039] Substituting equation (3) into (9), we obtain the discretized numerical equation of the extended finite element:

[0040] KU h =F (11)

[0041] Where U is the overall nodal displacement freedom vector, including conventional degrees of freedom and enhanced degrees of freedom, F is the overall load vector, which is composed of the load vector f of each element. e It is composed of groups according to the degree of freedom number; K is the overall stiffness matrix, which is composed of the stiffness matrix K of each unit e It is grouped according to the number of degrees of freedom in the total rigidity;

[0042] K e , f e The expressions are:

[0043]

[0044]

[0045] Where i and j are the unit node numbers. For a four-node linear unit, i and j = 1, 2, 3, 4.

[0046] The submatrix is:

[0047]

[0048] Where D is the elasticity matrix, is the derivative matrix of the shape function

[0049]

[0050]

[0051]

[0052]

[0053] Among them, the derivative of the Heaviside enhancement function is:

[0054]

[0055] The derivative of the crack tip enhancement function is:

[0056]

[0057] According to the chain rule:

[0058]

[0059] In the above formula, (x, y) represents the local Cartesian coordinate system of the crack tip. therefore:

[0060]

[0061]

[0062] Convert to the global Cartesian coordinate system (X, Y) using the following formulas:

[0063]

[0064] We can get:

[0065]

[0066] The expressions of the components of the load vector in formula (12) are as follows:

[0067]

[0068]

[0069]

[0070] Among them, Equations 26-28 are the solutions of the finite element integral equations of the hinge beam structure.

[0071] Furthermore, step S4 is specifically as follows:

[0072] S4.1 Based on the mesh element data, crack surface, and crack tip location of the hinged beam structure, the mesh elements of the hinged beam structure are divided into cracked elements caused by crack penetration, elements in the crack tip area, and ordinary elements;

[0073] S4.2: Introduction to the basis of interaction integrals: J-integrals;

[0074] The expression is:

[0075]

[0076] Where Ω is the integration path, λ = (λ1, λ2) is the force per unit length of the integration path, and u = (u1, u2) is the displacement vector;

[0077] Strain energy density:

[0078]

[0079] where σ ij , ε ij are the stress and strain components on the integration path.

[0080] Introducing function δ 1j :

[0081]

[0082] Write equation (28) as

[0083]

[0084] where q is an arbitrary smooth function that is 1 on the inner path and 0 on the outer path.

[0085] When the J-integral for a composite crack is no longer applicable, the interaction integral is used to calculate the stress intensity factor. The stress and strain of the auxiliary state are selected to satisfy the equilibrium equation and the traction boundary conditions on the regional crack surface.

[0086]

[0087] in, are the variables of the true stress-strain field, is a variable of the auxiliary stress-strain field. It is defined as the sum of two states:

[0088] J=J (1) +J (2) +M (34)

[0089] Where M is the interaction integral between the two states:

[0090]

[0091] When the path Ω is close to the crack tip, the interaction integral and the stress intensity factors of the true deformation field and the additional deformation field have the following relationship:

[0092]

[0093] Where, E * is the combination of the material constants E (Young's modulus) and ν (Poisson's ratio):

[0094]

[0095] If the auxiliary field satisfies The I-type stress intensity factor of the true stress-strain field can be directly obtained by mutual integration Similarly, satisfaction The type II stress intensity factor of the true stress-strain field can be obtained

[0096]

[0097] Furthermore, step S5 is specifically as follows:

[0098] S5.1: Error Estimation

[0099] Based on the crack tip stress solution obtained by the extended finite element, the improved stress solution σ is constructed by stress recovery. * , change σ * Approximate the exact solution and use it for error estimation; compute the difference between the improved result and the numerical solution:

[0100]

[0101] The error in the entire domain is calculated using formula (38):

[0102]

[0103] S5.2: Error Criteria

[0104] For the calculation error, a target error is set as the criterion for whether to proceed to the next step of the calculation. The target error is not fixed according to different situations. For hinged beam structures subjected to large loads, a target error of 5%-15% is generally selected. If the error result is greater than the target error, that is, the accuracy is insufficient, the mesh in the crack tip area is reconstructed to continue the calculation. The new mesh density is created as follows:

[0105]

[0106] in, is the calculation error, ||e σ || i is the given target error.

[0107] S5.3: Reconstructing the Mesh

[0108] The hinge beam structure model is meshed and reconstructed based on the mesh density obtained by error estimation. In order to obtain an accurate numerical solution, the mesh reconstruction in the crack tip area requires more attention.

[0109] S5.4: Import mesh data and re-enter the loop

[0110] The number of mesh elements and nodes will increase after the update, and the mesh node numbers will be rearranged and selected. It is necessary to update the data, re-import it, and repeat the cycle to calculate the accuracy of the reconstructed mesh.

[0111] Furthermore, step S6 is specifically as follows:

[0112] After each error calculation, if the calculation accuracy meets the requirements, the crack propagation direction is determined by the maximum hoop tensile stress criterion;

[0113] In the local coordinate system of the crack tip, let the shear stress be zero to obtain the crack extension angle θ c The formula is:

[0114] K I sin(θ c )+K II (3cos(θ c )-1)=0 (42)

[0115] From formula (41), we can get:

[0116]

[0117] In order to prevent the crack from bending and extending in the opposite direction, it is necessary to ensure |θ c |less than Then formula (42) only takes the negative sign:

[0118]

[0119] Among them, θ c The sign of K II The positive and negative K II When θ is positive, c is a negative value; K II When θ is negative, c is a positive value. Based on the obtained angle, the next crack expansion direction can be obtained. If the crack expansion step is fixed, the crack tip position after the first expansion can be obtained. The calculation is repeated until the crack expansion stops or the structure is damaged.

[0120] Compared with the existing technology, the present invention has the following beneficial effects: using the combination of extended finite element method and adaptive technology in crack analysis, using the extended finite element method to efficiently calculate crack propagation, obtaining main parameters such as stress intensity factor and stress, combining with the adaptive finite element method to reconstruct the grid, improving the accuracy of crack propagation simulation in the hinge beam structure, and realizing accurate simulation of the crack propagation path in the hinge beam structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0121] Figure 1 A flowchart of this application;

[0122] Figure 2 It is the physical model of the hinged beam structure. DETAILED DESCRIPTION

[0123] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0124] A method for calculating crack growth of a six-sided top press based on adaptive extended finite element, such as Figure 1 As shown, the method includes the following steps:

[0125] S1: Based on the modeling software, a physical model of the hinge beam structure is established, including the characteristic dimensions of the structure, the location and size of the cracks, etc. Figure 2 As shown;

[0126] S2: Perform meshing of the hinge beam structure and input the position of the crack tip;

[0127] Determine the starting point and tip of the crack; mesh the hinge beam structure model using finite element software or meshing software, creating a finer mesh near the crack and a uniform mesh in other areas. Extract mesh elements and nodes, and highly match the mesh density of the two areas to ensure mesh rationality.

[0128] S3: Solve the finite element integral equation of the hinged beam structure based on the extended finite element method;

[0129] S3.1: Introducing reinforcement function:

[0130] Introduce a step function node to simulate the strong discontinuity of the crack body:

[0131]

[0132] Crack tip strengthening function F of the element near the crack tip l (x) is usually a linear combination of the following four basis functions:

[0133]

[0134] where r and θ are parameters defining the crack tip in polar coordinates.

[0135] According to the two strengthening functions of formula (1) and (2), the displacement approximate expression of the two-dimensional composite crack problem is:

[0136]

[0137] Where the unit decomposition function N i (x), N j (x), N k (x) is the standard finite element shape function; is the node displacement; is the additional degree of freedom of the element penetrated by the crack, It is the additional degree of freedom of the unit near the crack tip, and the two have no clear physical meaning; I is the node set of the solution domain; J is the reinforcement node set of the unit through the unit; K is the reinforcement node set of the unit near the crack tip;

[0138] S:3.2: Establish the governing equations:

[0139]

[0140] Describe it in tensor form:

[0141]

[0142] The elastic boundary conditions are:

[0143] In Γt Previous (6)

[0144] In Γ u Previous (7)

[0145] In Γ f Previous (8)

[0146] in, represents the differential operator; σ is the stress tensor; f b is the body force; t is the boundary stress vector; u is the boundary displacement vector; n is the interface normal vector.

[0147] Introducing the arbitrary displacement φ of the hinge beam structure at the equilibrium position T =(φ x ,φ y ), we get the finite element integral equation:

[0148]

[0149] S3.3: Introduce the principle of virtual work to derive the weak form of the finite element integral equation for the hinged beam structure and solve the finite element integral equation for the hinged beam structure;

[0150] According to the principle of virtual work, the weak form of the integral equation is obtained:

[0151] -∫ Ω σ T ε(φ)tdA+∫ A φ T ftdA+∫ L [(n x σ x +n y τ xy )φ x +(n x τ xy +n y σ y )φ y ]dL=0 (10)

[0152] Substituting equation (3) into (9), we obtain the discretized numerical equation of the extended finite element:

[0153] KU h =F (11)

[0154] Where U is the overall nodal displacement freedom vector, including conventional degrees of freedom and enhanced degrees of freedom, F is the overall load vector, which is composed of the load vector f of each element. e It is composed of groups according to the degree of freedom number; K is the overall stiffness matrix, which is composed of the stiffness matrix K of each unite It is grouped according to the number of degrees of freedom in the total rigidity;

[0155] K e , f e The expressions are:

[0156]

[0157] f i e ={f i u ,f i a ,f i b1 ,f i b2 ,f i b3 ,f i b4} T (13)

[0158] Where i and j are the unit node numbers. For a four-node linear unit, i and j = 1, 2, 3, 4.

[0159] The submatrix is:

[0160]

[0161] Where D is the elasticity matrix, is the derivative matrix of the shape function

[0162]

[0163]

[0164]

[0165]

[0166] Among them, the derivative of the Heaviside enhancement function is:

[0167]

[0168] The derivative of the crack tip enhancement function is:

[0169]

[0170] According to the chain rule:

[0171]

[0172] In the above formula, (x, y) represents the local Cartesian coordinate system of the crack tip. therefore:

[0173]

[0174]

[0175] Convert to the global Cartesian coordinate system (X, Y) using the following formulas:

[0176]

[0177] We can get:

[0178]

[0179] The expressions of the components of the load vector in formula (12) are as follows:

[0180]

[0181]

[0182]

[0183] Among them, Equations 26-28 are the solutions of the finite element integral equations of the hinge beam structure.

[0184] S4: Solving the stress intensity factor of cracks in hinged beam structures by interaction integration method;

[0185] S4.1 Based on the mesh element data, crack surface, and crack tip location of the hinged beam structure, the mesh elements of the hinged beam structure are divided into cracked elements caused by crack penetration, elements in the crack tip area, and ordinary elements;

[0186] S4.2: Introduction to the basis of interaction integrals: J-integrals;

[0187] The expression is:

[0188]

[0189] Where Ω is the integration path, λ = (λ1, λ2) is the force per unit length of the integration path, and u = (u1, u2) is the displacement vector;

[0190] Strain energy density:

[0191]

[0192] where σ ij , ε ij are the stress and strain components on the integration path.

[0193] Introducing function δ1j :

[0194]

[0195] Write equation (28) as

[0196]

[0197] where q is an arbitrary smooth function that is 1 on the inner path and 0 on the outer path.

[0198] When the J-integral for a composite crack is no longer applicable, the interaction integral is used to calculate the stress intensity factor. The stress and strain of the auxiliary state are selected to satisfy the equilibrium equation and the traction boundary conditions on the regional crack surface.

[0199]

[0200] in, are the variables of the true stress-strain field, is a variable of the auxiliary stress-strain field. It is defined as the sum of two states:

[0201] J=J (1) +J (2) +M (34)

[0202] Where M is the interaction integral between the two states:

[0203]

[0204] When the path Ω is close to the crack tip, the interaction integral and the stress intensity factors of the true deformation field and the additional deformation field have the following relationship:

[0205]

[0206] Where, E * is the combination of the material constants E (Young's modulus) and ν (Poisson's ratio):

[0207]

[0208] If the auxiliary field satisfies The I-type stress intensity factor of the true stress-strain field can be directly obtained by mutual integration Similarly, satisfaction The type II stress intensity factor of the true stress-strain field can be obtained

[0209]

[0210] S5: Improvement of the extended finite element method based on adaptive technology;

[0211] For hinged beam structures, the numerical solution obtained by the extended finite element method has a certain error compared to the exact solution. The adaptive algorithm uses a reliable error estimation method to evaluate the current mesh quality, improve the calculation accuracy and make the calculation result closer to the exact solution.

[0212] S5.1: Error Estimation

[0213] Based on the crack tip stress solution obtained by the extended finite element, the improved stress solution σ is constructed by stress recovery. * , change σ * Approximate the exact solution and use it for error estimation; compute the difference between the improved result and the numerical solution:

[0214]

[0215] The error in the entire domain is calculated using formula (38):

[0216]

[0217] S5.2: Error Criteria

[0218] For the calculation error, a target error is set as the criterion for whether to proceed to the next step of the calculation. The target error is not fixed according to different situations. For hinged beam structures subjected to large loads, a target error of 5%-15% is generally selected. If the error result is greater than the target error, that is, the accuracy is insufficient, the mesh in the crack tip area is reconstructed to continue the calculation. The new mesh density is created as follows:

[0219]

[0220] in, is the calculation error, ||e σ || i is the given target error.

[0221] S5.3: Reconstructing the Mesh

[0222] The hinge beam structure model is meshed and reconstructed based on the mesh density obtained by error estimation. In order to obtain an accurate numerical solution, the mesh reconstruction in the crack tip area requires more attention.

[0223] S5.4: Import mesh data and re-enter the loop

[0224] The number of mesh elements and nodes will increase after the update, and the mesh node numbers will be rearranged and selected. You will need to update the data, re-import it, and repeat the cycle to calculate the accuracy of the reconstructed mesh.

[0225] S6: Determine the crack propagation path in the hinged beam structure model;

[0226] After each error calculation, if the calculation accuracy meets the requirements, the crack propagation direction is determined by the maximum hoop tensile stress criterion;

[0227] In the local coordinate system of the crack tip, let the shear stress be zero to obtain the crack extension angle θ c The formula is:

[0228] K I sin(θ c )+K II (3cos(θ c )-1)=0 (42)

[0229] From formula (41), we can get:

[0230]

[0231] In order to prevent the crack from bending and extending in the opposite direction, it is necessary to ensure |θ c |less than Then formula (42) only takes the negative sign:

[0232]

[0233] Among them, θ c The sign of K II The positive and negative K II When θ is positive, c is a negative value; K II When θ is negative, c is a positive value. Based on the obtained angle, the next crack expansion direction can be obtained. If the crack expansion step is fixed, the crack tip position after the first expansion can be obtained. The calculation is repeated until the crack expansion stops or the structure is damaged.

[0234] The method provided by the present invention is described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only intended to help understand the method of the present invention and its core concept. It should be noted that, for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications may be made to the present invention, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for calculating crack propagation of a six-sided top press based on adaptive extended finite element, characterized in that: The method comprises the following steps: S1: Establish a physical model of the hinge beam structure based on modeling software, including the characteristic dimensions of the structure, the location and size of the cracks; S2: Perform meshing of the hinge beam structure and input the position of the crack tip; Determine the starting point and tip of the crack; mesh the hinge beam structure model using finite element software or meshing software, creating a finer mesh near the crack and a uniform mesh in other areas. Extract mesh elements and nodes, and highly match the mesh density of the two areas to ensure mesh rationality. S3: Solve the finite element integral equation of the hinged beam structure based on the extended finite element method; S4: Solving the stress intensity factor of cracks in hinged beam structures by interaction integration method; S5: Improvement of the extended finite element method based on adaptive technology; S6: Determine the crack propagation path in a hinged beam structural model.

2. The method for calculating crack propagation of a six-sided top press based on adaptive extended finite element according to claim 1, characterized in that: Step S3 is specifically as follows: S3.1: Introducing reinforcement function; S3.2: Establish the governing equations; S3.3: Introduce the principle of virtual work to derive the weak form of the finite element integral equation for the hinge beam structure, and solve the finite element integral equation for the hinge beam structure.

3. The method for calculating crack propagation of a six-sided top press based on adaptive extended finite element according to claim 1, characterized in that: Step S4 is specifically as follows: S4.1 Based on the mesh element data, crack surface, and crack tip location of the hinged beam structure, the mesh elements of the hinged beam structure are divided into cracked elements caused by crack penetration, elements in the crack tip area, and ordinary elements; S4.2: Introducing the basis of interaction integrals: J-integrals.

4. The method for calculating crack propagation of a six-sided top press based on adaptive extended finite element according to claim 1, characterized in that: Step S5 is specifically as follows: S5.1: Error estimation; S5.2: Error criteria; S5.3: Reconstruct the grid; S5.4: Import the mesh data and re-enter the loop.

5. The method for calculating crack propagation of a six-sided top press based on adaptive extended finite element according to claim 1, characterized in that: Step S6 is specifically as follows: After each error calculation, if the calculation accuracy meets the requirements, the crack propagation direction is determined by the maximum hoop tensile stress criterion; In the local coordinate system of the crack tip, let the shear stress be zero to obtain the crack extension angle θ c The formula is: K Ι sin(θ c )+K ΙΙ (3cos(θ) c )-1)=0 Then we get: In order to prevent the crack from bending and extending in the opposite direction, it is necessary to ensure |θ c |less than Then the formula only takes the negative sign: Among them, θ c The sign of K ΙΙ The positive and negative of K ΙΙ When θ is positive, c is a negative value; K ΙΙ When θ is negative, c is a positive value; based on the obtained angle, the next crack expansion direction can be obtained. If the crack expansion step is fixed, the crack tip position after the first expansion can be obtained, and the calculation is repeated until the crack expansion stops or the structure is damaged.

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