A method for evaluating limit bearing capacity and determining main load transmission path threshold based on virtual-real fusion across hierarchical structure

Abstract

This invention discloses a method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion. The method, through a cross-level organization of unit layer—connection layer—structural layer, achieves traceable assessment from local damage to overall bearing capacity under the constraints of a unified material and damage parameter package and failure labeling system. It employs a unified solution path combining direct analysis, substructure cohesion, and high-fidelity critical area analysis, synchronously updating global stiffness contribution and local nonlinear evolution in the same equilibrium iteration. A composite criterion of local failure triggering and global path index mutation is introduced at the structural layer, forming an interpretable and reproducible main force transmission path failure threshold. Finally, through cross-level failure information integration and failure mode competition mechanism analysis, a risk control strategy directly applicable to engineering practice is output, enabling the threshold determination results to be efficiently transformed into structural design optimization and service handling schemes.

Description

Technical Field

[0001] This invention belongs to the field of structural strength assessment and damage safety analysis technology, and relates to a method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion. Background Technology

[0002] In the design of complex assembly structures, the block-based method is typically used to verify the strength and failure modes of the "material-connection-structure" chain step by step. For structural systems containing multiple rows and columns of fasteners, if a uniform-scale, detailed model is applied to all fasteners across the entire structure and progressive damage analysis is performed, problems such as large computational scale, poor convergence stability, and difficulty in parameter calibration are often encountered.

[0003] The commonly used two-step method in engineering, "global first, local second," first extracts boundary displacements or loads from the global model and then applies them to the local model for analysis. This method suffers from issues such as secondary loading and coupling inconsistencies during boundary transfer, easily introducing error accumulation and resulting in insufficient consistency between load redistribution and local failure triggering. Furthermore, when local damage propagation causes connection stiffness degradation and conversely affects the global load path, the two-step method struggles to achieve stable and interpretable closed-loop updates.

[0004] Furthermore, in multi-row, multi-column fastener connection structures, engineering practice typically relies on experience to delineate the "main force transmission path," but there is a lack of quantifiable and reproducible threshold criteria for determining the main force transmission path. This results in a lack of unified basis for ultimate bearing capacity assessment, failure safety margin definition, and structural design improvements. Summary of the Invention

[0005] To address the aforementioned problems in the background technology, this invention provides a method for evaluating the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion includes the following steps:

[0008] Step S1: Construction of a unified modeling and solution system for the structural layer:

[0009] Based on the cross-level block organization method, a unified solution system is established in the structural layer: non-critical and approximately linear elastic wide-area regions adopt efficient elements and can be condensed into substructures to participate in the solution; contact and damage evolution are preserved in critical connection regions, so that the overall stiffness contribution and the nonlinearity of the key region are coupled and updated in the same equilibrium iteration, avoiding secondary boundary propagation error.

[0010] Step S2: Unit-level virtual-real fusion parameter calibration and failure mode labeling system establishment:

[0011] Based on unit layer test / simulation benchmarking data, an objective function is constructed, and a package of material and damage parameters is obtained through inversion optimization. A unified failure mode labeling system is established for sharing between the connection layer and the structural layer, so as to achieve consistent criteria across layers.

[0012] Step S3: Continuous failure analysis and threshold determination of the connection layer:

[0013] A multi-connection element analysis model for the connection layer is established. During the incremental loading process, a single-point sudden failure is simulated and loading continues to trigger load redistribution. The load increase ratio, bearing margin, connection layer threshold and dominant failure mode are calculated, and the allowable values ​​and trigger condition set of the connection layer are output.

[0014] Step S4: Assessment of the ultimate bearing capacity of the structural layer and determination of the threshold of the main force transmission path:

[0015] A single-point failure scenario is introduced into the structural layer and the load is increased incrementally; the redistribution law of the limiting load is extracted; the path participation degree and abrupt change criterion are constructed to obtain the failure threshold of the main force transmission path; the load is continued to the limit and the residual bearing capacity ratio is calculated, and the failure safety conclusion is output in combination with the specified load requirements.

[0016] Step S5: Cross-level information integration and risk control output:

[0017] The method establishes mapping relationships between unit layer parameter packages and label systems, connection layer thresholds and allowable values, and structural layer path thresholds and residual bearing capacity; it analyzes failure mode competition mechanisms and outputs a risk control strategy library to achieve method closed loop.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] This invention, through a cross-level organization of "unit layer—connection layer—structural layer," and under the constraints of a unified material and damage parameter package and failure labeling system, achieves traceable assessment from local damage to overall load-bearing capacity, effectively avoiding threshold drift caused by inconsistent criteria in different level models. Employing a unified solution path of "direct analysis + substructure cohesion + high-fidelity critical area," it synchronously updates global stiffness contribution and local nonlinear evolution in the same equilibrium iteration, significantly reducing boundary propagation errors in the traditional two-step method and drastically reducing computational scale. Introducing a composite criterion of "local failure triggering + global path index mutation" at the structural layer forms an interpretable and reproducible main force transmission path failure threshold, thereby achieving a quantitative correlation between force transmission path migration and ultimate load-bearing capacity attenuation. Finally, through cross-level failure information integration and failure mode competition mechanism analysis, it outputs risk control strategies that can be directly applied to engineering practice, enabling the threshold determination results to be efficiently transformed into structural design optimization and service handling schemes. Attached Figure Description

[0020] Figure 1 This is a technical framework diagram of a method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion.

[0021] Figure 2 This is a schematic diagram of the organization method for cross-level block building analysis. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0023] This invention provides a method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion, such as... Figure 1 As shown, the method includes the following steps:

[0024] Step S1: Construction of a unified modeling and solution system for the structural layer:

[0025] in accordance with Figure 2 The cross-level block organization method shown establishes a unified solution system at the structural level: non-critical and approximately linearly elastic wide-area regions employ efficient elements and can be aggregated into substructures to participate in the solution; critical connection regions retain contact and damage evolution, allowing the overall stiffness contribution and the nonlinearity of the critical region to be coupled and updated in the same equilibrium iteration, avoiding secondary boundary propagation errors. The specific steps are as follows:

[0026] Step S101: Define the research object and the set of damage scenarios:

[0027] Obtain information on the geometric topology, material properties, connection types, fastener arrangement, and assembly clearances of complex assembly structures; define a set of failure scenarios. ,in It includes at least scenarios such as "single connection unit failure" or "typical unit failure". The set of failure scenarios is used to apply equivalent conditions for single-point failure or typical unit failure in subsequent steps S303 and S402, and serves as a scenario identifier for the output threshold and residual bearing capacity results.

[0028] Step S102, Cross-level partitioning and block organization:

[0029] The model hierarchy is organized as follows: "Unit layer - Connection layer - Structural layer": The unit layer is used for parameter calibration and failure mode labeling system establishment; the connection layer is used for load redistribution and successive failure mechanism analysis of multi-row and multi-column fastener connections; the structural layer is used to uniformly consider the global stiffness contribution and local nonlinearity of key connection areas within the same solution system, and output the ultimate bearing capacity and main force transmission path threshold.

[0030] Step S103: Construct a direct analysis model with a unified solution framework:

[0031] A global-local coupled model is established within the same finite element solution system, allowing the overall stiffness and nonlinearities such as contact / damage / plasticity in key connection areas to participate in the equilibrium solution simultaneously, avoiding the secondary boundary propagation error of "global first, local later". The specific steps are as follows:

[0032] Step S10301: Establish global equilibrium equations and parameterize loads:

[0033] External load is represented as an amplified version of the reference load vector:

[0034] (1)

[0035] Establish the equilibrium equations that include nonlinear internal variables:

[0036] (2)

[0037] In equations (1)-(2): The external load vector applied to the structural layer model; The reference load vector; This is the load amplification factor in the direct analysis of the structural / connection layers; This represents the overall balanced residual vector; This is the global displacement vector; It is a set of internal variables (including damage variables, contact state, plastic internal variables, etc.). This is the equivalent stiffness matrix;

[0038] Step S103012, through the... By progressively increasing the loading step and iteratively solving the equilibrium residual of equation (2), the displacement response, nonlinear evolution of the key connection area and load distribution results under different external load levels are obtained, providing a globally consistent mechanical basis for the subsequent determination of ultimate bearing capacity, load redistribution and force transmission path threshold.

[0039] The above solution process is completed within the same finite element solution system, enabling the global stiffness contribution and the local nonlinear response of the key connection area to be coupled and updated in the same equilibrium iteration process.

[0040] Step S104: Aggregate the substructure regions and participate in the same solution:

[0041] Non-critical regions that can be approximated as linearly elastic are defined as substructure regions. Within the same solution system, its degrees of freedom are condensed into equivalent stiffness contributions (superelement / condensation matrix) without secondary boundary loading. The specific steps are as follows:

[0042] Step S10401: Divide the degrees of freedom of the substructure into partitions:

[0043] (3)

[0044] Step S10402, Elimination The equivalent relationship after condensation is obtained:

[0045] , (4)

[0046] In equations (3)-(4): To preserve the displacement vectors of the degrees of freedom (main model / interface degrees of freedom); The displacement vector of the condensed degrees of freedom (degrees of freedom within the substructure); To preserve the external load vector corresponding to the degrees of freedom; The external load vector corresponding to the condensed degrees of freedom; , , , These are the stiffness submatrices after being divided into blocks according to degrees of freedom, where the subscripts represent the retained degrees of freedom and the condensed degrees of freedom, respectively; This is the equivalent stiffness matrix mapped onto the retained degrees of freedom after the substructure is condensed; The equivalent load vector after condensation; the equivalent stiffness matrix With equivalent load vector This method is used to incorporate the stiffness contribution of a substructure region into the direct analysis and solution system of the structural layer without secondary boundary transfer, thereby reducing the degrees of freedom and improving computational efficiency, while maintaining the consistency of load path and stiffness coupling. In each loading step, the substructure region determines its equivalent tangential stiffness based on the current damage state, and forms the corresponding equivalent stiffness contribution through static condensation. The equivalent stiffness contribution progresses with the loading step and is updated synchronously with the structural layer equilibrium iteration process.

[0047] Step S105, Shell-Solid Hybridization and Interface Coupling:

[0048] Shell elements are used extensively in the structure to ensure computational efficiency; solid elements are used in critical connection areas to preserve the bearing capacity, contact and damage evolution capabilities of the bore area; and coupling constraints that ensure displacement coordination and force transmission consistency are applied at the shell-solid interface, namely: interface displacement consistency constraints.

[0049] For interface nodes Set application:

[0050] (5)

[0051] In equation (5): For the displacement of the solid side interface, This represents the displacement of the shell-side interface. The transformation matrix is ​​determined by the geometry and degree-of-freedom mapping.

[0052] Step S2: Unit-level virtual-real fusion parameter calibration and failure mode labeling system establishment:

[0053] An objective function is constructed based on unit-level experimental / simulation benchmarking data. Material and damage parameter packages are obtained through inversion optimization, and a unified failure mode labeling system is established for sharing between the connection layer and the structural layer, achieving consistent criteria across layers. The specific steps are as follows:

[0054] Step S201: Develop a unit-level test / simulation benchmarking plan:

[0055] Tests and simulations were conducted on typical ply and connection elements under tensile, compressive, shear, and representative connection loading conditions to obtain a dataset of basic mechanical properties and failure characterization. ,in, For test / simulation conditions, input or feature vectors, This corresponds to the observed response characteristic quantity.

[0056] Step S202: Establish the material constitutive and damage evolution parameter package:

[0057] Define the set of damage variables Where 0 represents no damage and 1 represents failure, the damage variable is used to characterize the degree of damage accumulation of materials or connecting units under different load levels, and adopts the equivalent stiffness degradation form:

[0058] (6)

[0059] In equation (6): This is the initial stiffness matrix; To and Identity matrices of the same order; A degeneracy operator constructed from damage variables; Damaged state The equivalent constitutive stiffness matrix is ​​used to update the element stiffness in the simulation of the connection layer and the structural layer, so as to realize the characterization of load degradation caused by damage initiation and evolution.

[0060] Step S203, Virtual-Real Fusion Inversion Calibration:

[0061] Virtual-real fusion refers to a fusion method that uses experimental data to invert and calibrate the parameters of a simulation model, and then integrates the calibration results into the evaluation of the connection layer and the structural layer.

[0062] The objective function is constructed by combining the experimental response (force-displacement curve, ultimate load, failure location / mode, etc.) with the simulation response, and the parameters are obtained through inversion optimization. These data will ultimately be used for inversion calibration and will be integrated into steps S3 and S4:

[0063] (7)

[0064] In equation (7): The optimal parameters obtained through optimization are used as the final values ​​of the material and damage parameter package, so that subsequent connection layers and structural layers can be used for failure triggering, threshold determination and margin assessment under the same criterion system. The parameter vector to be calibrated (such as constitutive parameters, damage evolution parameters, contact / friction parameters, etc.). The number of sample data points; This represents the parameter values ​​that minimize the objective function; For the first The experimental observation response of each sample (e.g., force-displacement curve characteristics, ultimate load, failure location / mode index, etc.). To use parameters The obtained simulation prediction response; These are the regularization weight coefficients; This is the prior parameter vector (initial values ​​based on engineering experience).

[0065] Step S204: Establish a failure mode labeling system:

[0066] A set of failure modes was summarized for each type of sample in the unit layer. This forms a "mode-criteria-trigger threshold" mapping table: when the corresponding failure criterion is met, it is recorded as an occurrence mode. And record the corresponding load amplification factor. The failure mode labeling system provides a unified label for the connection layer and the structural layer, based on the damage evolution path. This failure mode labeling system is used to identify the dominant failure mode and triggering conditions in the connection layer step S305, and to associate "local failure triggering" with "global force transmission path mutation" in the structural layer step S5, thereby enabling interpretable output of the force transmission path failure threshold and risk control strategy.

[0067] Step S3: Continuous failure analysis and threshold determination of the connection layer:

[0068] A multi-connection element analysis model for the connection layer is established. During the incremental loading process, a single-point sudden failure is simulated and loading continues to trigger load redistribution. The load increase ratio, bearing margin, connection layer threshold, and dominant failure mode are calculated using equations (8)-(11), and the allowable values ​​and trigger condition set of the connection layer are output. The specific steps are as follows:

[0069] Step S301: Establish a multi-connector element connection analysis model for the connection layer:

[0070] In the connection layer, a multi-connector connection analysis model is established by selecting representative multi-connector connection regions in complex assembly structures. High-fidelity 3D solid models are used for critical connectors and their adjacent local areas, preserving contact, friction, and damage evolution. Non-critical connectors or edge regions are simplified using equivalent connectors (beams / springs, etc.) to control the degree of freedom. The model's material parameters, contact parameters, and damage evolution parameters are uniformly provided by the material and damage parameter package obtained in step S2.

[0071] Step S302: Construct typical unit / single connection element failure scenarios and perform incremental load analysis:

[0072] Apply progressively increasing external loads (corresponding to the scaling factor of the structural layer design load) to the multi-connector connection analysis model obtained in step S301. During the loading process, monitor the load sharing, bearing / shear response, and damage variable evolution of each connection element. When a typical unit or a connection element first reaches the failure criterion described in step S204, record its failure time, failure mode label, and external load level. In subsequent steps S303 to S305, perform "removal or de-rating" processing on the unit / connector to simulate a single-point sudden failure scenario. Then continue loading to obtain the load redistribution and potential chain failure trend of the remaining connection elements.

[0073] Step S303: Define the load redistribution index and margin index for the connection layer:

[0074] To quantitatively characterize the load increment and risk concentration of adjacent connected elements after a single-point failure, a connected element is defined. The load increase ratio in adjacent loading steps With load margin :

[0075] (8)

[0076] (9)

[0077] In equations (8)-(9): For the first Each loading step external load scaling factor; This is the external load scaling factor for the previous loading step; For connection element exist The equivalent working load is as follows; For connection element Maximum allowed capacity; This represents the relative load increase; For the remaining bearing capacity margin, when The system determines when the connection element has reached or exceeded the allowed capacity.

[0078] Step S304: Determining and giving the threshold value for the connection layer:

[0079] Define the connection layer failure threshold The minimum external load scaling factor required to first satisfy the condition that "other connected elements show signs of impending failure or chain failure" under a single-point failure scenario:

[0080] (10)

[0081] In formula (10): This is the threshold for connection layer failure. For sudden load increases; This indicates that at least one connection element has exhausted its capacity margin; This indicates a precursor to an abnormally sudden increase in load redistribution; further based on Provide recommendations for allowed values ​​for the connection layer. ,satisfy Less than And it can be determined in conjunction with a safety factor.

[0082] Step S305: Identification of Dominant Failure Mode and Triggering Conditions:

[0083] Based on the failure mode labeling system in step S204, the frequency of each failure mode label is counted in the simulation results of the connection layer under multiple operating conditions and multiple parameter combinations, and failure modes are defined. dominance :

[0084] (11)

[0085] In equation (11): Number the failure mode label; For pattern Trigger count; output the mode with high dominance (its dominance ranks in the preset number among all failure modes, such as the top 1 to 2) and its corresponding trigger condition set, which are used for the determination of the main force transmission path threshold and the interpretation of risk control in the structural layer.

[0086] Step S4: Assessment of the ultimate bearing capacity of the structural layer and determination of the threshold of the main force transmission path:

[0087] A single-point failure scenario is introduced into the structural layer and the load is increased incrementally; Equation (12) is used to extract the load redistribution law; Equations (13)-(15) are further used to construct the path participation degree and abrupt change criterion to obtain the failure threshold of the main force transmission path; the load is continued to the limit and the residual bearing capacity ratio is calculated using Equation (16), and the failure safety conclusion is output in combination with the specified load requirements. The specific steps are as follows:

[0088] Step S401: Establish a direct analysis model of the structural layer and embed nonlinearity in key connection regions:

[0089] Within the same finite element solution system, a structural layer model of a complex assembly structure is established: efficient elements are used in a large area that can be approximated as linear elastic, and can further participate in the solution in the form of substructure condensation; contact and damage evolution are preserved in the key connection area, so as to simultaneously reflect the overall stiffness contribution and the local nonlinear response of the key connection area in a single solution process.

[0090] Step S402: Set up structural layer failure scenarios and incrementally increase load:

[0091] In the structural layer model, the scenario of "single connection unit / single connection group / typical unit failure" is introduced: equivalent failure conditions (such as stiffness reduction, strength reduction or unit removal) are applied to the assumed failure site, and then the design load is gradually increased to obtain the stress, deformation and damage evolution of the remaining connection units under different external load levels.

[0092] Step S403: Extraction of the redistribution law of the constraint load:

[0093] Extract equivalent working loads from each key connection unit of the structural layer. And calculate the load distribution ratio :

[0094] (12)

[0095] In equation (12): The set of key connection units being monitored; for Equivalent working load of the lower connecting unit; This represents the load-sharing ratio of the connection unit within the critical connection set.

[0096] Step S404: Construction of main force transmission path index and definition of mutation criterion:

[0097] Several candidate force transmission paths are predefined for the structural layer. Calculate path participation :

[0098] (13)

[0099] Define path mutation index:

[0100] (14)

[0101] When the conditions of "local failure tag trigger + global path index mutation" are met, the main force transmission path failure is determined, and the corresponding external load proportional factor is defined as the main force transmission path failure threshold. :

[0102] (15)

[0103] In equations (13)-(14): Number the path; For the first The set of components / units contained in each candidate path; For statistical force flow, it is the complete set of components / elements; For components / units exist Force flow characterization quantities (axial force / shear force / bending moment / equivalent internal force or combinations thereof); For path participation; This represents the magnitude of the change in path participation between adjacent loading steps; The threshold for path mutation; "local failure tag triggering" refers to any critical failure mode in the tagging system of step S204 being determined to be triggered in a critical area of ​​the structural layer.

[0104] The above candidate path construction rules are as follows: It can be constructed from a sequence of connected elements from the load input boundary to the reaction force boundary in the structural topology diagram; preferably, a directed graph is constructed with key connection elements / key components as nodes and force flow connectivity as edges, using... The candidate set is obtained by finding the shortest path / maximum flow path. The number of candidate force transmission paths. A preset positive integer (e.g., 3–10) is used to control the size of the candidate set.

[0105] Selection rules: When the structure is mainly driven by axial force, take axial force; when it is mainly driven by shear, take shear force; when it is mainly driven by bending, take bending moment.

[0106] Define the rules: It can be taken as the average of the increments under the same operating conditions in the perfect scenario plus... 10 ... This is the sensitivity coefficient. ∈[1,3], can be selected according to the engineering conservatism requirements. ); or take the case where the change in adjacent steps exceeds a certain fixed percentage threshold (such as 0.1~0.3).

[0107] Step S405, Determination of Residual Bearing Capacity and Failure Safety Compliance:

[0108] Define the residual bearing capacity ratio :

[0109] (16)

[0110] In equation (16): The ultimate load of the structure under damage scenarios. The ultimate load of the structure in its intact state; when the following conditions are met simultaneously: ; ; If the load level is not less than the required load level of the structural layer, it is determined that the failure safety requirements are met; otherwise, proceed to step S5 to output the risk control strategy.

[0111] Step S5: Cross-level failure information integration and risk control output:

[0112] A mapping relationship is established between the unit layer parameter package and the label system, the connection layer threshold and the allowable value, and the structural layer path threshold and the residual bearing capacity; the failure mode competition mechanism is analyzed and a risk control strategy library is output to achieve method closed loop. The specific steps are as follows:

[0113] Step S501, Cross-level information mapping:

[0114] Summarize the unit layer parameter package and label system (step S2), the connection layer threshold and allowable value (step S3), the main force transmission path threshold and residual bearing capacity of the structural layer (step S4), and establish a mapping relationship of "local failure mode - connection layer threshold - structural layer path threshold / bearing capacity" to explain the source of threshold and bearing capacity changes.

[0115] Step S502, Failure Mode Competition Mechanism and Key Factor Screening:

[0116] Under multiple load conditions and parameter disturbances, statistical analysis is performed on the initiation sequence, dominance changes, and critical transition conditions of possible failure modes. The set of key influencing factors leading to the switching of dominant modes and path mutations is output to guide the prioritization of risk control.

[0117] Step S503, Risk control strategy output:

[0118] Based on steps S501-S502, a risk control strategy library is output, including early warning indicators, design optimization suggestions, and service disposal suggestions.

Claims

1. A method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion, characterized in that... The method includes the following steps: Step S1: Construction of a unified modeling and solution system for the structural layer: Based on the cross-level block organization method, a unified solution system is established in the structural layer: non-critical and approximately linearly elastic wide-area regions adopt efficient elements and can be condensed into substructures to participate in the solution; The key connection area retains the contact and damage evolution, so that the overall stiffness contribution and the nonlinearity of the key area are coupled and updated in the same equilibrium iteration, avoiding the secondary boundary propagation error. Step S2: Unit-level virtual-real fusion parameter calibration and failure mode labeling system establishment: Based on unit layer test / simulation benchmarking data, an objective function is constructed, and a package of material and damage parameters is obtained through inversion optimization. A unified failure mode labeling system is established for sharing between the connection layer and the structural layer, so as to achieve consistent criteria across layers. Step S3: Continuous failure analysis and threshold determination of the connection layer: A multi-connection element analysis model for the connection layer is established to simulate single-point sudden failure during incremental loading and continue loading to trigger load redistribution; Calculate the load increase ratio, load margin, connection layer threshold and dominant failure mode, and output the allowable value of the connection layer and the set of triggering conditions. Step S4: Assessment of the ultimate bearing capacity of the structural layer and determination of the threshold of the main force transmission path: A single-point failure scenario is introduced into the structural layer and the load is incrementally increased. Extract the redistribution pattern of the confined load; By constructing the path participation degree and abrupt change criterion, the failure threshold of the main force transmission path is obtained; the load is continued to the limit and the residual bearing capacity ratio is calculated, and the failure safety conclusion is output in combination with the specified load requirements. Step S5: Cross-level information integration and risk control output: Establish mapping relationships between unit layer parameter packages and label systems, connection layer thresholds and allowable values, and structural layer path thresholds and residual bearing capacity; Analyze the failure mode competition mechanism and output a risk control strategy library to achieve a closed-loop methodology.

2. The method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion as described in claim 1, characterized in that... The specific steps of step S1 are as follows: Step S101: Define the research object and the set of damage scenarios: Obtain information on the geometric topology, material properties, connection types, fastener arrangement, and assembly clearances of complex assembly structures; define a set of failure scenarios. ,in It should include at least the scenario of "single connection unit failure / typical unit failure"; Step S102, Cross-level partitioning and block organization: The model hierarchy is organized as "unit layer - connection layer - structural layer": the unit layer is used for parameter calibration and failure mode labeling system establishment; the connection layer is used for load redistribution and successive failure mechanism analysis of multi-row and multi-column fastener connections; the structural layer is used to uniformly consider the global stiffness contribution and local nonlinearity of key connection areas within the same solution system, and output the ultimate bearing capacity and main force transmission path threshold. Step S103: Construct a direct analysis model with a unified solution framework: A global-local coupled model is established within the same finite element solution system, so that the overall stiffness and the contact / damage / plastic nonlinearity of the key connection area participate in the equilibrium solution at the same time. Step S104: Aggregate the substructure regions and participate in the same solution: Non-critical regions that can be approximated as linearly elastic are defined as substructure regions. Within the same solution system, its degrees of freedom are condensed into equivalent stiffness contributions, without secondary boundary loading; Step S105, Shell-Solid Hybridization and Interface Coupling: Shell elements are used extensively in the structure to ensure computational efficiency; solid elements are used in critical connection areas to preserve the bearing capacity, contact, and damage evolution capabilities of the bore areas; and coupling constraints that ensure displacement coordination and force transmission are applied at the shell-solid interface. (5) In the formula: For interface nodes, For the displacement of the solid side interface, This represents the displacement of the shell-side interface. The transformation matrix is ​​determined by the geometry and degree-of-freedom mapping.

3. The method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion as described in claim 2, characterized in that... The specific steps of step S103 are as follows: Step S10301: Establish global equilibrium equations and parameterize loads: External load is represented as an amplified version of the reference load vector: (1) Establish the equilibrium equations that include nonlinear internal variables: (2) In the formula: The external load vector applied to the structural layer model; The reference load vector; This is the load amplification factor in the direct analysis of the structural / connection layers; This represents the overall balanced residual vector; This is the global displacement vector; For the set of internal variables, This is the equivalent stiffness matrix; Step S103012, through the... By progressively increasing the loading step and iteratively solving the equilibrium residual of equation (2), the displacement response, nonlinear evolution of the key connection area, and load distribution results under different external load levels are obtained.

4. The method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion as described in claim 2, characterized in that... The specific steps of step S104 are as follows: Step S10401: Divide the degrees of freedom of the substructure into partitions: (3) Step S10402, Elimination The equivalent relationship after condensation is obtained: ， (4) In the formula: To preserve the displacement vectors of the degrees of freedom; The displacement vector of the condensed degrees of freedom; To preserve the external load vector corresponding to the degrees of freedom; The external load vector corresponding to the condensed degrees of freedom; , , , These are the stiffness submatrices after being divided into blocks according to degrees of freedom, where the subscripts represent the retained degrees of freedom and the condensed degrees of freedom, respectively; This is the equivalent stiffness matrix mapped onto the retained degrees of freedom after the substructure is condensed; This is the equivalent load vector after condensation.

5. The method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion as described in claim 1, characterized in that... The specific steps of step S2 are as follows: Step S201: Develop a unit-level test / simulation benchmarking plan: Tests and simulations were conducted on typical ply and connection elements under tensile, compressive, shear, and representative connection loading conditions to obtain a dataset of basic mechanical properties and failure characterization. ,in, For test / simulation conditions, input or feature vectors, These are the corresponding observed response characteristic quantities; Step S202: Establish the material constitutive and damage evolution parameter package: Define the set of damage variables Where 0 represents no damage and 1 represents failure, the damage variable is used to characterize the degree of damage accumulation of materials or connecting units under different load levels, and adopts the equivalent stiffness degradation form: (6) In the formula: This is the initial stiffness matrix; To and Identity matrices of the same order; A degeneracy operator constructed from damage variables; Damaged state The equivalent constitutive stiffness matrix is ​​as follows; Step S203, Virtual-Real Fusion Inversion Calibration: The objective function is constructed using the experimental and simulated responses, and the parameters are obtained through inversion optimization. : (7) In the formula: The optimal parameters were obtained through optimization. The parameter vector to be calibrated; The number of sample data points; This represents the parameter values ​​that minimize the objective function; For the first The experimental observation response of each sample; To use parameters The obtained simulation prediction response; These are the regularization weight coefficients; For the prior parameter vector; Step S204: Establish a failure mode labeling system: A set of failure modes was summarized for each type of sample in the unit layer. This forms a "mode-criteria-trigger threshold" mapping table: when the corresponding failure criterion is met, it is recorded as an occurrence mode. And record the corresponding load amplification factor. Based on the damage evolution path, a unified label is provided for the connection layer and the structural layer.

6. The method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion as described in claim 5, characterized in that... The specific steps of step S3 are as follows: Step S301: Establish a multi-connector element connection analysis model for the connection layer: In the connection layer, a multi-connection element connection analysis model is established by selecting representative multi-connection element connection regions in complex assembly structures. High-fidelity 3D solid modeling is used for key connection elements and their adjacent local regions, and contact, friction and damage evolution are preserved. Non-key connection elements or edge regions are simplified by using equivalent connection elements to control the degree of freedom. Step S302: Construct typical unit / single connection element failure scenarios and perform incremental load analysis: An increasing external load is applied to the multi-connector connection analysis model of the connection layer obtained in step S301. During the loading process, the load sharing, bearing / shear response, and damage variable evolution of each connection element are monitored. When a typical unit or a connection element first reaches the failure criterion described in step S204, its failure time, failure mode label, and external load level are recorded. In subsequent steps S303 to S305, the unit / connector is subjected to "removal or derating" processing to simulate a single-point sudden failure scenario. Loading continues, and the load redistribution and potential chain failure trend of the remaining connection elements are obtained. Step S303: Define the load redistribution index and margin index for the connection layer: To quantitatively characterize the load increment and risk concentration of adjacent connected elements after a single-point failure, a connected element is defined. The load increase ratio in adjacent loading steps With load margin : (8) (9) In the formula: For the first Each loading step external load scaling factor; This is the external load scaling factor for the previous loading step; For connection element exist The equivalent working load is as follows; For connection element Maximum allowed capacity; This represents the relative load increase; For the remaining bearing capacity margin, when The connection element is determined to have reached or exceeded its allowable capacity at that time. Step S304: Determining and giving the threshold value for the connection layer: Define the connection layer failure threshold The minimum external load scaling factor required to first satisfy the condition that "other connected elements show signs of impending failure or chain failure" under a single-point failure scenario: (10) In the formula: This is the threshold for connection layer failure. For sudden load increases; This indicates that at least one connection element has exhausted its capacity margin; This indicates a precursor to an abnormally sudden increase in load redistribution; further based on Provide recommendations for allowed values ​​for the connection layer. ,satisfy Less than ; Step S305: Identification of Dominant Failure Mode and Triggering Conditions: Based on the failure mode labeling system in step S204, the frequency of each failure mode label is counted in the simulation results of the connection layer under multiple operating conditions and multiple parameter combinations, and failure modes are defined. dominance : (11) In the formula: Failure mode label number; For pattern Trigger count; Output the dominant patterns and their corresponding triggering condition sets for use in determining the threshold of the main force transmission path in the structural layer and interpreting risk control.

7. The method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion as described in claim 1, characterized in that... The specific steps of step S4 are as follows: Step S401: Establish a direct analysis model of the structural layer and embed nonlinearity in key connection regions: Within the same finite element solution system, a structural layer model of a complex assembly structure is established: efficient elements are used in a large area that can be approximated as linear elastic, and further participate in the solution in the form of substructure condensation; contact and damage evolution are preserved in the key connection area, so as to simultaneously reflect the overall stiffness contribution and the local nonlinear response of the key connection area in a single solution process; Step S402: Set up structural layer failure scenarios and incrementally increase load: In the structural layer model, failure scenarios of single connection unit / single connection group / typical unit are introduced: equivalent failure conditions are applied to the assumed failure location, and then the overall design load is applied in a stepwise manner to obtain the stress, deformation and damage evolution of the remaining connection units under different external load levels. Step S403: Extraction of the redistribution law of the constraint load: Extract equivalent working loads from each key connection unit of the structural layer. And calculate the load distribution ratio : (12) In the formula: The set of key connection units being monitored; for Equivalent working load of the lower connecting unit; The load sharing ratio of the connection unit in the critical connection set; Step S404: Construction of main force transmission path index and definition of mutation criterion: Several candidate force transmission paths are predefined for the structural layer. Calculate path participation : (13) Define path mutation index: (14) A main power transmission path failure is determined when both a local failure tag trigger and a sudden change in global path indicators are met, and the corresponding external load proportional factor is defined as the main power transmission path failure threshold. : (15) In the formula: Number the path; For the first The set of components / units contained in each candidate path; For statistical force flow, it is the complete set of components / elements; For components / units exist The force flow characterization quantity under the following conditions; For path participation; This represents the magnitude of the change in path participation between adjacent loading steps; This is the threshold for path mutation. Step S405, Determination of Residual Bearing Capacity and Failure Safety Compliance: Define the residual bearing capacity ratio : (16) In the formula: The ultimate load of the structure under damage scenarios. The ultimate load of the structure in its intact state; when the following conditions are met simultaneously: ; ; If the load level is not less than the required load level of the structural layer, it is determined that the failure safety requirements are met; otherwise, proceed to step S5 to output the risk control strategy.

8. The method for assessing the ultimate bearing capacity of cross-level structures and determining the threshold of the main force transmission path based on virtual-real fusion as described in claim 7, characterized in that... The specific steps of step S5 are as follows: Step S501, Cross-level information mapping: The unit layer parameter package and label system, the connection layer threshold and allowable value, the main force transmission path threshold and residual bearing capacity of the structural layer are summarized. The mapping relationship between local failure mode, connection layer threshold and structural layer path threshold / bearing capacity is established to explain the source of the changes in threshold and bearing capacity. Step S502, Failure Mode Competition Mechanism and Key Factor Screening: Under multiple load conditions and parameter disturbances, statistical analysis is performed on the initiation sequence, dominance changes and critical transition conditions of possible failure modes, and the set of key influencing factors that lead to the switching of dominant modes and path changes is output to guide the priority ranking of risk control. Step S503, Risk control strategy output: Based on steps S501-S502, a risk control strategy library is output, including early warning indicators, design optimization suggestions, and service disposal suggestions.

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