Finite element analysis-based pile cold-state stress characteristic analysis method

Abstract

The invention provides an electric pile cold state stress characteristic analysis method based on finite element analysis. The electric pile cold state stress characteristic analysis method comprises the following steps: S1, modeling and assembling according to a physical structure of a solid oxide electric pile to form a full-size electric pile model; s2, simulating a co-sintering process of a porous electrode and a thin-layer electrolyte in the full-size galvanic pile model through molecular dynamics, obtaining residual stress and a first stress parameter generated in the co-sintering process, and calculating first elastic stress and first inelastic stress; s3, acquiring assembly stress and a second stress parameter generated in the assembly process of each component part, and calculating a second elastic stress and a second non-elastic stress; and S4, taking the first elastic stress, the first non-elastic stress, the second elastic stress and the second non-elastic stress as characteristic analysis results of the cold-state stress of the galvanic pile. The method has the beneficial effects that the limitation in a complex stress coupling scene can be broken through, and meanwhile, accurate cold state stress characteristic analysis is carried out by combining multi-source stress and adapting to a large-scale galvanic pile.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cell reliability assessment, and in particular to a method for analyzing cold stress characteristics of a fuel cell based on finite element analysis. Background Art

[0002] As a key energy conversion device that can operate in both fuel cell (power generation) and electrolysis (hydrogen production) modes, the performance degradation and life loss of the solid oxide fuel cell stack during its service life are mainly regulated by multi-field coupled stress. This type of stress persists throughout the entire life cycle of the fuel cell stack. Cold stress, as the initial internal stress state of the solid oxide fuel cell stack after assembly at room temperature and before entering the high-temperature operation stage, has a fundamental impact on the stress evolution and structural stability under subsequent operating conditions. Cold stress mainly consists of two parts: one is the manufacturing residual stress, which originates from the non-uniform shrinkage and flattening treatment caused by the difference in thermal expansion coefficient (CTE) and elastic modulus (E) during the co-sintering process of the thin-layer electrolyte and porous electrode. The dynamic evolution of the material's thermophysical properties will exacerbate the complexity of its distribution. The other is the assembly stress, which is caused by the contact constraints between the components caused by the bolt preload. Its distribution characteristics are directly related to the geometric constraints and the magnitude of the preload.

[0003] Existing technologies have obvious limitations when evaluating cold stress: first, they often analyze residual stress or assembly stress in isolation, ignoring the coupling effect between the two, resulting in deviations in the assessment of fuel cell failure risk; second, for complex geometric models of fuel cell stacks with more than 30 units, since a single interconnect contains fine channels and fin structures, the calculation complexity is extremely high, making it difficult to balance accuracy and efficiency, limiting the quantitative study of multiple stress coupling mechanisms; third, they use small deformation theory to describe large deformations in the sintering process (such as the displacement gradient norm ‖∇u‖>0.1), ignoring geometric nonlinearity and dynamic changes in material properties, resulting in stress prediction errors exceeding 15%.

[0004] Therefore, it is urgent to establish a comprehensive evaluation method for cold stress characteristics that integrates multi-source stress and is suitable for large-scale fuel cell stacks, so as to break through the technical bottleneck in complex stress coupling scenarios and improve the evaluation accuracy and applicability. Summary of the Invention

[0005] The technical problem to be solved by the present invention is how to break through the limitations in complex stress coupling scenarios, perform precise cold stress characteristic analysis while taking into account the integration of multi-source stress and adaptation to large-scale fuel cell stacks, and improve the evaluation accuracy and applicability. In order to overcome the defects of the above-mentioned existing technologies (or related technologies), the present invention provides a fuel cell cold stress characteristic analysis method based on finite element analysis.

[0006] The present invention provides a method for analyzing cold stress characteristics of a fuel cell stack based on finite element analysis, comprising: Step S1, performing three-dimensional modeling based on the physical structure of the solid oxide fuel cell stack to obtain multiple components of the solid oxide fuel cell stack, and assembling the components to form a full-size fuel cell stack model; Step S2, simulating the co-sintering process of the porous electrode and the thin-layer electrolyte in the full-scale stack model by molecular dynamics to obtain the residual stress and the first stress parameter generated in the co-sintering process, and obtaining the first elastic stress and the first inelastic stress of the full-scale stack model according to the residual stress and the first stress parameter based on the finite deformation theory and the second Piola-Kirchhoff stress tensor; Step S3, obtaining the assembly stress and second stress parameters generated by each component during the assembly process, and obtaining the second elastic stress and second inelastic stress of the full-scale stack model according to the assembly stress and the second stress parameters based on the small deformation theory and the linear elastic constitutive relationship; Step S4: taking the first elastic stress, the first inelastic stress, the second elastic stress, and the second inelastic stress as a result of cold stress characteristic analysis of the fuel cell stack.

[0007] Compared with the prior art, the cold stress characteristic analysis method of a fuel cell stack based on finite element analysis has the following advantages: In the present invention, a full-size stack model is constructed through step S1, the first elastic stress and the first inelastic stress split under residual stress are calculated through step S2, the second elastic stress and the second inelastic stress split under assembly stress are calculated through step S3, and the cold stress characteristic analysis results of the stack are generated by integration through step S4. In the above steps, a full-process coupling model of residual stress and assembly stress, namely a full-size stack model, is established to provide a basic model for co-sintering and assembly processes, breaking through the limitations in complex stress coupling scenarios and adapting to large-scale stacks to improve applicability. Through the segmented application of finite deformation theory and small deformation theory, the stress evolution process of the solid oxide stack from manufacturing to assembly is accurately described, and the multi-source stresses of the first elastic stress, the first inelastic stress, the second elastic stress and the second inelastic stress are integrated to perform precise cold stress characteristic analysis, thereby improving evaluation accuracy.

[0008] In one possible embodiment, in step S2, the instantaneous temperature during the co-sintering process, the real-time thermal expansion coefficient corresponding to different instantaneous temperatures, the reference temperature under stress-free conditions, the unit tensor, the intrinsic strain, the initial strain, the displacement gradient, the first elastic matrix and the deformation gradient matrix are obtained and included in the first stress parameter.

[0009] In a possible embodiment, in step S2, a thermal deformation gradient is obtained according to the real-time thermal expansion coefficient, the instantaneous temperature, the reference temperature, and the unit tensor; an intrinsic deformation gradient is obtained according to the intrinsic strain and the unit tensor; an initial deformation gradient is obtained according to the initial strain and the unit tensor; and then the first elastic stress and the first inelastic stress are obtained according to the residual stress, the displacement gradient, the thermal deformation gradient, the intrinsic deformation gradient, the initial deformation gradient, the first elastic matrix, and the deformation gradient matrix.

[0010] In a possible implementation, in step S2, the first elastic stress is obtained based on the displacement gradient, the thermal deformation gradient, the intrinsic deformation gradient, the initial deformation gradient, the first elastic matrix, and the deformation gradient matrix, and the first inelastic stress is obtained by subtracting the residual stress from the first elastic stress.

[0011] In a possible implementation, in step S2, the thermal deformation gradient is obtained by the following calculation formula: ; ; in, represents the thermal deformation gradient; represents the unit tensor; represents thermal strain; represents the real-time thermal expansion coefficient; Expressed as the instantaneous temperature during the sintering process; represents the reference temperature.

[0012] In a possible implementation, in step S2, the intrinsic deformation gradient and the initial deformation gradient are obtained by the following calculation formula: ; ; in, represents the intrinsic deformation gradient; represents the unit tensor; represents the intrinsic strain; represents the initial deformation gradient; represents the initial strain.

[0013] In a possible implementation, in step S2, the first elastic stress and the first inelastic stress are obtained by the following calculation formula: ; ; ; ; in, represents the residual stress; represents the first elastic stress; represents the first inelastic stress; represents the determinant of the deformation gradient matrix; Indicates that the matrix is ​​first inverted; Indicates that the matrix is ​​first inverted and then transposed; represents the first elastic matrix; represents elastic strain; represents the displacement deformation gradient; represents the unit tensor; represents the displacement gradient; represents the elastic deformation gradient; represents the inelastic deformation gradient; represents the thermal deformation gradient; represents the intrinsic deformation gradient; represents the initial deformation gradient; represents elastic strain.

[0014] In one possible embodiment, the second stress parameter includes the elastic modulus, Poisson's ratio, initial strain and stack displacement of the material of each component in the assembly process at room temperature. In step S3, a second elastic matrix is ​​obtained according to the elastic modulus and the Poisson's ratio, the total strain of the stack is obtained according to the stack displacement, the inelastic strain of the stack is obtained according to the initial strain, the elastic strain of the stack is obtained according to the total strain of the stack and the inelastic strain of the stack, the second elastic stress is obtained according to the elastic strain of the stack and the second elastic matrix, and the second inelastic stress is obtained by subtracting the assembly stress from the second elastic stress.

[0015] In a possible implementation, in step S3, the second elasticity matrix is ​​obtained by the following calculation formula: ; in, represents the second elastic matrix; represents the elastic modulus; represents the Poisson's ratio.

[0016] In a possible implementation, in step S3, the second elastic stress and the second inelastic stress are obtained by the following calculation formula: ; ; ; ; ; in, represents the assembly stress; represents the second elastic stress; represents the second inelastic stress; represents the total strain of the stack; represents the displacement of the battery stack; Indicates that the matrix is ​​first inverted and then transposed; represents the inelastic strain of the battery stack; represents the initial strain; represents the elastic strain of the battery stack; represents the second elastic matrix. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a flow chart of the steps of the present invention; Figure 2 Schematic diagram of the assembly process of the solid oxide fuel cell stack of the present invention; Figure 3 Schematic diagram of the geometry of the solid oxide stack of the present invention; Figure 4 Schematic diagram of the grid division of the solid oxide fuel cell stack of the present invention. DETAILED DESCRIPTION

[0018] First, those skilled in the art should understand that these embodiments are merely for explaining the technical principles of the embodiments of the present invention and are not intended to limit the scope of protection of the embodiments of the present invention. Those skilled in the art may make adjustments as needed to adapt to specific application scenarios.

[0019] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] See also Figure 1 The embodiment of the present invention discloses a method for analyzing cold stress characteristics of a fuel cell stack based on finite element analysis, comprising: Step S1, performing three-dimensional modeling based on the physical structure of the solid oxide fuel cell stack to obtain multiple components of the solid oxide fuel cell stack, and assembling the components to form a full-size fuel cell stack model; Step S2, simulating the co-sintering process of the porous electrode and the thin-layer electrolyte in the full-scale stack model by molecular dynamics to obtain the residual stress and first stress parameters generated during the co-sintering process, and obtaining the first elastic stress and first inelastic stress of the full-scale stack model based on the residual stress and the first stress parameters based on the finite deformation theory and the second Piola-Kirchhoff stress tensor; Step S3, obtaining the assembly stress and second stress parameters generated by each component during the assembly process, and obtaining the second elastic stress and second inelastic stress of the full-scale stack model based on the assembly stress and second stress parameters based on the small deformation theory and the linear elastic constitutive relationship; Step S4: taking the first elastic stress, the first inelastic stress, the second elastic stress, and the second inelastic stress as the cold stress characteristic analysis results of the fuel cell stack.

[0021] In an embodiment of the present invention, in step S2, the co-sintering process of the porous electrode and the thin layer electrolyte in the battery cell in the solid oxide battery stack is simulated by molecular dynamics to obtain the dynamic evolution law of the thermal expansion coefficient and elastic modulus and the microscopic shrinkage rate in the length direction, which are introduced as input into the battery cell sintering finite element simulation, and the shrinkage rate is correlated with the intrinsic strain, and the residual stress is obtained by combining the geometric nonlinear theory analysis.

[0022] In the embodiment of the present invention, the coordinated quantification of residual stress and assembly stress is achieved through multi-physics field coupling modeling. The main technical solutions adopted include: Full-scale stack modeling: Build a 3D model based on the actual stack geometry, including repeating units, seals, and bolt connection details; Multi-stress coupling analysis: Integrating manufacturing residual stress (intrinsic strain obtained through molecular dynamics simulation) and assembly stress (bolt preload), the finite deformation theory and linear elastic constitutive relationship are used to calculate the cold stress characteristic analysis results of the fuel cell stack, including the first elastic stress, the first inelastic stress, the second elastic stress, and the second inelastic stress.

[0023] In the embodiment of the present invention, the assembly process of the solid oxide fuel cell stack is one of the important processes, including assembly alignment and bolt tightening, such as Figure 2 As shown, it is worth noting that since the battery will have a bulge in the middle after sintering during the manufacturing process, it needs to be flattened with a 2 kg pressing block before assembling the solid oxide stack. The flattened battery (air electrode facing up) is placed on the lower pole connector of the solid oxide stack so that it is aligned with the reference position. Then, the lower sealant, metal frame, upper sealant and upper pole connector are placed in sequence. Finally, the assembled solid oxide stack is bolted. The tightening force of a single bolt used in this embodiment is 5844 Newtons.

[0024] In the embodiment of the present invention, a full-scale three-dimensional stack model is developed, such as Figure 3 As shown, the battery is embedded in the internal square cavity of the metal frame, and the pole connectors and sealants are installed on both sides of the battery to form a repeating unit of the solid oxide stack. It should be noted that the battery is surrounded by the metal frame to provide edge support so that the pressure of other components does not act directly on the battery. These repeating units are assembled in series to form the solid oxide stack, and then clamped between the top and bottom end plates by eight bolts to achieve a tight seal.

[0025] In the embodiment of the present invention, the terminal connector of the solid oxide fuel cell stack is made of Crofer 22 APU, the end plate and the frame are made of SUS 310 material, the sealing material is the flexible sealing material Flexitallic 866, and the core component cell of the solid oxide fuel cell stack includes porous fuel electrode Ni-8YSZ, air electrode La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3–δ –Gd 0.1 Ce 0.9 O 1.95 (LSCF–GDC) and a dense electrolyte layer 8YSZ.

[0026] In the embodiment of the present invention, Figure 4 As shown in the figure, different discretization schemes are implemented according to the geometric characteristics of the various components of the solid oxide fuel cell stack. For the full-scale fuel cell stack model, a structured hexahedral mesh is generated by using a parameter sweep algorithm in orthogonal geometric regions (such as the air electrode and the pole connector). An unstructured triangular mesh method is applied to the four fillet transition regions of the fuel electrode and the electrolyte layer. An adaptive tetrahedral mesh refinement technique is used for complex geometric shapes including metal frames and fasteners.

[0027] In an embodiment of the present invention, the manufacturing process of the battery cells in the solid oxide fuel cell stack mainly involves high-temperature sintering and subsequent flattening at room temperature. Specifically, the air electrode composite material is deposited on the electrolyte surface of the sintered half-cell by screen printing technology (i.e., the first sintering step), and then sintered to form a complete full-cell structure (i.e., the second sintering step).

[0028] During the manufacturing process of battery cells in solid oxide fuel cell stacks, although the absolute deformation occurs on the millimeter scale, the relative deformation becomes quite large due to the total thickness of the battery cell of 630 microns. For example, the deformation displacement caused by sintering can reach 8.04 mm, which is about 12.76 times the total thickness of the battery cell. Under such conditions, the Frobenius norm of the displacement gradient tensor (‖∇u‖) may exceed the threshold applicable to the small deformation theory (i.e., ‖∇u‖≪1).

[0029] In this case, geometric nonlinearity needs to be considered when ‖∇u‖>0.1, which makes the Cauchy stress tensor σ The linear constitutive model cannot fully describe the nonlinear deformation behavior. Therefore, a finite deformation framework is adopted in this embodiment: the initial undeformed state is defined as the reference configuration, the kinematics are controlled by the total Lagrangian formulation, and the constitutive equations integrate the second Piola-Kirchhoff stress tensor.

[0030] In an embodiment of the present invention, in step S2, the instantaneous temperature during the co-sintering process, the real-time thermal expansion coefficient corresponding to different instantaneous temperatures, the reference temperature under stress-free conditions, the unit tensor, the intrinsic strain, the initial strain, the displacement gradient, the first elastic matrix, and the deformation gradient matrix are obtained and included in the first stress parameter. In step S2, the thermal deformation gradient is obtained according to the real-time thermal expansion coefficient, the instantaneous temperature, the reference temperature, and the unit tensor, the intrinsic deformation gradient is obtained according to the intrinsic strain and the unit tensor, and the initial deformation gradient is obtained according to the initial strain and the unit tensor. Subsequently, the first elastic stress and the first inelastic stress are obtained according to the residual stress, the displacement gradient, the thermal deformation gradient, the intrinsic deformation gradient, the initial deformation gradient, the first elastic matrix, and the deformation gradient matrix.

[0031] In the embodiment of the present invention, the residual stress can be directly calculated by COMSOL finite element software based on the loading conditions (such as temperature change), the material constitutive relationship (such as elastic modulus), and the deformation gradient. The assembly stress is obtained in the same way as the residual stress and is not subsequently expanded. The expression of the residual stress is as follows: ; in, represents the residual stress; represents the first elastic stress; represents the first inelastic stress; The first elastic stress is calculated by the following formula: ; ; ; in, represents the determinant of the deformation gradient matrix; Indicates that the matrix is ​​first inverted; Indicates that the matrix is ​​first inverted and then transposed; represents the first elastic matrix; represents elastic strain; represents the displacement deformation gradient; represents the unit tensor; represents the displacement gradient; represents the elastic deformation gradient; represents the inelastic deformation gradient; represents the thermal deformation gradient; represents the intrinsic deformation gradient; represents the initial deformation gradient; represents elastic strain; The intrinsic deformation gradient and initial deformation gradient are calculated using the following formula: ; ; in, represents the intrinsic deformation gradient; represents the unit tensor; represents the intrinsic strain; represents the initial deformation gradient; Represents the initial strain; when evaluating the entire stack sintering process, the initial strain used is the residual strain inside the half-cell after the first sintering is completed, while when simulating the entire stack assembly process, the initial strain is the residual strain inside the entire cell after the second sintering stage is completed. In addition, it should be noted that represents the small deformation strain that describes the volume change, and its non-zero component appears only on the diagonal line. During the sintering process of the battery stack, particle aggregation and neck formation will cause the planar shrinkage of the sintered battery stack. The molecular dynamics (MD) method is used to emphasize and quantitatively evaluate the shrinkage rate along the x-axis (i.e., the horizontal length direction) to evaluate the shrinkage effect of particle clusters, which is further correlated with the intrinsic strain. The thermal deformation gradient is calculated using the following formula: ; ; in, represents the thermal deformation gradient; represents the unit tensor; represents thermal strain; represents the real-time thermal expansion coefficient; Expressed as the instantaneous temperature during the sintering process; Represents the reference temperature; the sintering process of the battery cell includes multiple stages of heating, heat preservation and cooling. The inherent temperature gradient formed in each stage will drive the sintered structure to undergo cooperative deformation under the corresponding thermal environment.

[0032] In the embodiment of the present invention, during the assembly process, the flattened cell is tightly sealed with other components of the solid oxide stack (such as the frame and sealant) by a bolt pre-tightening device. Due to the rigid constraint imposed by the bolt pre-tightening force, the deformation of each component is limited to a small deformation range. Assuming that the mechanical behavior of all components in the solid oxide stack conforms to the small deformation theory assumption, in this case, the Cauchy stress tensor σ Effectively utilize the true stress distribution in current solid oxide stack configurations to describe the linearized Cauchy strain tensor ε The linear elastic constitutive relations can reasonably describe the local stress response caused by the preload of the solid oxide fuel cell stack assembly.

[0033] In an embodiment of the present invention, the second stress parameter includes the elastic modulus, Poisson's ratio, initial strain and stack displacement of the materials of each component during the assembly process at room temperature. In step S3, the second elastic matrix is ​​obtained according to the elastic modulus and Poisson's ratio, the total strain of the stack is obtained according to the stack displacement, the inelastic strain of the stack is obtained according to the initial strain, the elastic strain of the stack is obtained according to the total strain of the stack and the inelastic strain of the stack, and the second elastic stress and the second inelastic stress are obtained according to the elastic strain of the stack and the second elastic matrix.

[0034] In the embodiment of the present invention, the second elastic stress and the second inelastic stress are calculated using the following formula: ; ; ; ; ; in, represents the assembly stress; represents the second elastic stress; represents the second inelastic stress; represents the total strain of the stack; represents the displacement of the battery stack; Indicates that the matrix is ​​first inverted and then transposed; represents the inelastic strain of the battery stack; represents the initial strain; represents the elastic strain of the battery stack; represents the second elastic matrix; at room temperature without the supply of reactant gas, the stack maintains a thermal equilibrium state due to the lack of electrochemical reaction, so the thermal expansion effect can be ignored; The second elastic matrix is ​​calculated by the following formula: ; in, represents the second elastic matrix; represents the elastic modulus; represents the Poisson's ratio; wherein the material properties of the components in the solid oxide fuel cell stack are shown in Table 1 below: Table 1 Material properties of components in the solid oxide fuel cell stack ; The second elastic matrix can be obtained by substituting the values ​​corresponding to the elastic modulus and Poisson's ratio in Table 1.

[0035] In the description of the present invention, the reference terms "one embodiment", "some embodiments", "in the present embodiment", "specific examples", or "some examples" mean that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0036] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for analyzing cold stress characteristics of a fuel cell stack based on finite element analysis, characterized in that: The following steps are involved: Step S1, performing three-dimensional modeling based on the physical structure of the solid oxide fuel cell stack to obtain multiple components of the solid oxide fuel cell stack, and assembling the components to form a full-size fuel cell stack model; Step S2, simulating the co-sintering process of the porous electrode and the thin-layer electrolyte in the full-scale stack model by molecular dynamics to obtain the residual stress and the first stress parameter generated in the co-sintering process, and obtaining the first elastic stress and the first inelastic stress of the full-scale stack model according to the residual stress and the first stress parameter based on the finite deformation theory and the second Piola-Kirchhoff stress tensor; Step S3, obtaining the assembly stress and second stress parameters generated by each component during the assembly process, and obtaining the second elastic stress and second inelastic stress of the full-scale stack model according to the assembly stress and the second stress parameters based on the small deformation theory and the linear elastic constitutive relationship; Step S4: taking the first elastic stress, the first inelastic stress, the second elastic stress, and the second inelastic stress as a result of cold stress characteristic analysis of the fuel cell stack.

2. The method for analyzing cold stress characteristics of a fuel cell stack based on finite element analysis according to claim 1, characterized in that: In step S2, the instantaneous temperature during the co-sintering process, the real-time thermal expansion coefficient corresponding to different instantaneous temperatures, the reference temperature under stress-free conditions, the unit tensor, the intrinsic strain, the initial strain, the displacement gradient, the first elastic matrix, and the deformation gradient matrix are obtained and included in the first stress parameter.

3. The method for analyzing cold stress characteristics of a fuel cell stack based on finite element analysis according to claim 2, characterized in that: In step S2, a thermal deformation gradient is obtained according to the real-time thermal expansion coefficient, the instantaneous temperature, the reference temperature, and the unit tensor; an intrinsic deformation gradient is obtained according to the intrinsic strain and the unit tensor; an initial deformation gradient is obtained according to the initial strain and the unit tensor; and then the first elastic stress and the first inelastic stress are obtained according to the residual stress, the displacement gradient, the thermal deformation gradient, the intrinsic deformation gradient, the initial deformation gradient, the first elastic matrix, and the deformation gradient matrix.

4. The method for analyzing cold stress characteristics of a fuel cell stack based on finite element analysis according to claim 3, characterized in that: In step S2, the first elastic stress is obtained according to the displacement gradient, the thermal deformation gradient, the intrinsic deformation gradient, the initial deformation gradient, the first elastic matrix, and the deformation gradient matrix, and the first inelastic stress is obtained by subtracting the first elastic stress from the residual stress.

5. The method for analyzing cold stress characteristics of a fuel cell stack based on finite element analysis according to claim 3, characterized in that: In step S2, the thermal deformation gradient is obtained by the following calculation formula: ； ； in, represents the thermal deformation gradient; represents the unit tensor; represents thermal strain; represents the real-time thermal expansion coefficient; Expressed as the instantaneous temperature during the sintering process; represents the reference temperature.

6. The method for analyzing cold stress characteristics of a fuel cell stack based on finite element analysis according to claim 3, characterized in that: In step S2, the intrinsic deformation gradient and the initial deformation gradient are obtained by the following calculation formula: ； ； in, represents the intrinsic deformation gradient; represents the unit tensor; represents the intrinsic strain; represents the initial deformation gradient; represents the initial strain.

7. The method for analyzing cold stress characteristics of a fuel cell stack based on finite element analysis according to claim 4, characterized in that: In step S2, the first elastic stress and the first inelastic stress are obtained by the following calculation formula: ； ； ； ； in, represents the residual stress; represents the first elastic stress; represents the first inelastic stress; represents the determinant of the deformation gradient matrix; Indicates that the matrix is ​​first inverted; Indicates that the matrix is ​​first inverted and then transposed; represents the first elastic matrix; represents elastic strain; represents the displacement deformation gradient; represents the unit tensor; represents the displacement gradient; represents the elastic deformation gradient; represents the inelastic deformation gradient; represents the thermal deformation gradient; represents the intrinsic deformation gradient; represents the initial deformation gradient; represents elastic strain.

8. The method for analyzing cold stress characteristics of a fuel cell stack based on finite element analysis according to claim 1, characterized in that: The second stress parameters include the elastic modulus, Poisson's ratio, initial strain and stack displacement of the materials of each component during the assembly process at room temperature. In step S3, a second elastic matrix is ​​obtained based on the elastic modulus and Poisson's ratio, the total strain of the stack is obtained based on the stack displacement, the inelastic strain of the stack is obtained based on the initial strain, the elastic strain of the stack is obtained based on the total strain of the stack and the inelastic strain of the stack, the second elastic stress is obtained based on the elastic strain of the stack and the second elastic matrix, and the second inelastic stress is obtained by subtracting the assembly stress from the second elastic stress.

9. The method for analyzing cold stress characteristics of a fuel cell stack based on finite element analysis according to claim 8, characterized in that: In step S3, the second elastic matrix is ​​obtained by the following calculation formula: ； in, represents the second elastic matrix; represents the elastic modulus; represents the Poisson's ratio.

10. The method for analyzing cold stress characteristics of a fuel cell stack based on finite element analysis according to claim 8, characterized in that: In step S3, the second elastic stress and the second inelastic stress are obtained by the following calculation formula: ； ； ； ； ； in, represents the assembly stress; represents the second elastic stress; represents the second inelastic stress; represents the total strain of the stack; represents the displacement of the battery stack; Indicates that the matrix is ​​first inverted and then transposed; represents the inelastic strain of the battery stack; represents the initial strain; represents the elastic strain of the battery stack; represents the second elastic matrix.

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