Method for analyzing durability of power battery

Abstract

The invention discloses a durability analysis method of a power battery, and relates to the technical field of power batteries. The method comprises the following steps: establishing a power battery geometric model, and processing the power battery geometric model to establish a welding seam unit at a part connecting part of the power battery; welding process parameters of the power battery are obtained; based on the life-death unit technology and the moving heat source subprogram, the welding heat process of the weld joint units is simulated one by one based on the welding process parameters according to the welding sequence, so that a welding whole-process temperature field is obtained; the temperature field of the whole welding process serves as a predefined temperature field to be imported into the structure model so as to calculate welding residual stress; the welding residual stress serves as an initial condition, and stress analysis results under different load working conditions are restarted and analyzed; obtaining a structural fatigue safety coefficient according to a stress analysis result; and evaluating the durability of the power battery according to the structural fatigue safety coefficient. Therefore, according to the method, the influence of the welding residual stress on the durability of the power battery is considered, and the durability evaluation accuracy is improved.

Description

Technical Field

[0001] This application relates to the field of power battery technology, and in particular to a method for analyzing the durability performance of power batteries. Background Technology

[0002] Durability analysis of power batteries is a key step in evaluating the battery's capacity decay and performance degradation patterns and influencing factors during long-term use or storage, in order to determine whether the battery's lifespan meets application requirements.

[0003] In related technologies, the durability performance of power batteries is determined by methods such as temperature shock treatment, vibration shock treatment, water immersion treatment, and physical analysis treatment. However, since there are many welds in the structure of power batteries, the above methods do not take into account the influence of welding residual stress, resulting in inaccurate evaluation of durability performance. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in related technologies. Therefore, the purpose of this application is to propose a method for analyzing the durability performance of a power battery. This method involves establishing a geometric model of the power battery to create weld seam units, simulating the welding thermal process of these units, obtaining the temperature field throughout the welding process, and importing this field into a structural model to calculate residual welding stress. Based on the stress analysis results, a structural fatigue safety factor is obtained to evaluate the durability performance of the power battery. This method considers the impact of residual welding stress on the durability performance of the power battery, thus improving the accuracy of the power battery durability performance evaluation.

[0005] To achieve the above objectives, embodiments of this application propose a method for analyzing the durability performance of a power battery. This method includes: establishing a geometric model of the power battery and processing the model to create weld seam units at the component connections; obtaining welding process parameters for the power battery; simulating the welding thermal process of each weld seam unit sequentially based on the welding process parameters and the birth-death unit technology and a moving heat source subroutine, according to the welding sequence, to obtain the temperature field throughout the welding process; importing the temperature field throughout the welding process as a predefined temperature field into the structural model to calculate welding residual stress; restarting the analysis of stress analysis results under different load conditions using the welding residual stress as an initial condition; obtaining the structural fatigue safety factor based on the stress analysis results; and evaluating the durability performance of the power battery based on the structural fatigue safety factor.

[0006] The durability performance analysis method for power batteries according to embodiments of this application establishes a geometric model of the power battery and processes the model to create weld seam units at the component connections. Welding process parameters are obtained, and based on the birth-death unit technology and a moving heat source subroutine, the welding thermal process of each weld seam unit is simulated sequentially according to the welding process parameters to obtain the temperature field throughout the welding process. This temperature field is then imported into the structural model as a predefined temperature field to calculate welding residual stress. Using this residual stress as an initial condition, the analysis is restarted to retrieve stress analysis results under different load conditions. The structural fatigue safety factor is obtained based on the stress analysis results, and the durability performance of the power battery is evaluated based on this factor. Therefore, this method improves the accuracy of power battery durability performance evaluation by establishing a geometric model of the power battery to create weld seam units, simulating the welding thermal process of these units, obtaining the temperature field throughout the welding process, importing it into the structural model to calculate welding residual stress, and obtaining the structural fatigue safety factor based on the stress analysis results.

[0007] In addition, the durability performance analysis method for power batteries according to the above embodiments of this application may also have the following additional technical features: According to one embodiment of this application, the durability performance of a power battery is evaluated based on a structural fatigue safety factor, including: determining that the durability performance of the power battery is unqualified when the structural fatigue safety factor is less than a preset threshold; and determining that the durability performance of the power battery is qualified when the structural fatigue safety factor is greater than or equal to the preset threshold.

[0008] According to one embodiment of this application, the stress analysis results under different load conditions are restarted using welding residual stress as the initial condition, including: determining the operating condition of the power battery; and importing the welding residual stress into the first inertial force condition and the second inertial force condition respectively through restarted analysis to obtain the stress analysis results of the structure under the action of the first inertial force and the second inertial force.

[0009] According to one embodiment of this application, obtaining the structural fatigue safety factor based on stress analysis results includes: importing the stress analysis results into fatigue analysis software, cycling the welding residual stress under a first inertial load and a second inertial load a preset number of times to obtain the superimposed stress amplitude, thereby determining the structural fatigue safety factor.

[0010] According to one embodiment of this application, based on the birth-death element technique and the moving heat source subroutine, the welding thermal process of each weld seam unit is simulated sequentially according to the welding process parameters to obtain the temperature field of the entire welding process. This includes: determining the welding sequence based on the actual welding process and defining welding process parameters in the moving heat source subroutine; using the birth-death element technique to set the current weld seam unit to an inactive state while keeping the remaining weld seam units active; using the Goldak double ellipsoidal heat source model to calculate the welding thermal process sequentially according to the weld seam sequence, obtaining the temperature field file for the welding process of each weld seam unit; and determining the temperature field of the entire welding process based on the temperature field file for the welding process of each weld seam unit.

[0011] According to one embodiment of this application, the heat flux density distribution function of the Goldak double ellipsoidal heat source model is: First half of the ellipsoidal heat flux density distribution function: The heat flux density distribution function of the ellipsoid in the second half: ,in, Indicates heat source efficiency. and This represents the coefficient for heat distribution. , , , , These are the shape parameters of the heat source.

[0012] According to one embodiment of this application, the temperature field of the entire welding process is imported into the structural model as a predefined temperature field to calculate the welding residual stress, including: using a thermal-structural coupling analysis method, taking the temperature field of the entire welding process as the initial condition, calculating the stress distribution of the structure during the cooling process as the welding residual stress.

[0013] According to one embodiment of this application, processing a power battery geometric model to establish weld seam units at the component connections of the power battery includes: dividing the power battery geometric model into a mesh; assembling the components of the power battery according to the mesh, wherein the components are connected by a tie; and establishing weld seam units at the component connections.

[0014] According to one embodiment of this application, the durability performance analysis method of the power battery further includes: before welding the weld unit, applying boundary constraint conditions based on the actual vehicle installation state of the power battery, wherein the boundary constraint conditions include: applying a fixing constraint at the battery pack hoisting bolt hole, applying a natural convection heat transfer boundary condition on the outer surface of the battery pack, and applying a corresponding heat conduction boundary condition inside the battery pack.

[0015] According to one embodiment of this application, the durability performance analysis method for the power battery further includes: determining the properties of the metal material used in the power battery. Attached Figure Description

[0016] Figure 1 This is a flowchart of a method for analyzing the durability performance of a power battery according to some embodiments of this application; Figure 2 This is a schematic diagram of the geometric model of a power battery according to a specific embodiment of this application; Figure 3 This is a schematic diagram of the weld at the intersection of the horizontal and vertical beams of the power battery box according to a specific embodiment of this application; Figure 4 This is a flowchart of a method for analyzing the durability performance of a power battery according to a specific embodiment of this application. Detailed Implementation

[0017] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0018] The durability performance analysis method of the power battery according to the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0019] Reference Figure 1 The durability performance analysis method for power batteries according to embodiments of this application includes the following steps: S1. Establish the geometric model of the power battery and process the battery geometric model to create weld seam units at the component connection points of the power battery.

[0020] Specifically, a power battery geometric model is a model that digitally abstracts and mathematically represents the physical structure of a power battery. Its core function is to accurately describe the spatial shape, dimensional relationships, and arrangement of the battery's key components, providing a foundation for battery performance simulation, structural design optimization, and manufacturing process adaptation. The geometric model of a power battery must strictly correspond to its actual physical structure. Figure 2 This is a schematic diagram of the geometric model of a power battery, including a battery module composed of multiple battery cells, a housing providing structural support and protection, electrical system components, cooling / heat dissipation system components, and the fixing and supporting structures. The geometric model of a power battery is not merely a structural drawing, but rather the foundation for subsequent performance analysis.

[0021] The components of a power battery have welds at their joints, which are critical areas for structural strength, heat conduction, and current conduction. The purpose of establishing weld elements is to transform the actual welded structure into a computable model unit, allowing subsequent power battery durability performance analysis to accurately simulate the weld performance and avoid analysis errors caused by neglecting weld details.

[0022] The geometric model of the power battery is established using professional 3D computer-aided design or computer-aided engineering software. Since the initial model may not include weld details, it needs to be processed in a targeted manner. For example, small features unrelated to the weld are removed to avoid the model being too complex and affecting the calculation efficiency. Alternatively, the outline of the weld can be clearly defined at the component connection according to the actual welding process. Geometric cleaning can also be performed to correct the small gaps and overlaps on the component connection surfaces to ensure that the weld unit fits the connection part and conforms to the actual assembly logic.

[0023] S2, obtain the welding process parameters of the power battery.

[0024] Specifically, welding process parameters are determined based on the actual power battery box welding process, including welding current, welding voltage, welding thermal efficiency, welding speed, welding heat source power, and welding heat source size.

[0025] S3, based on the birth and death unit technology and the moving heat source subroutine, simulates the welding thermal process of each weld unit according to the welding sequence and welding process parameters to obtain the temperature field of the entire welding process.

[0026] Specifically, the cell birth and death technique is an analytical technique that simulates the gradual generation or disappearance of structures by activating or eliminating specific cells in a model. It does not actually delete or create cells, but rather adjusts the key properties of cells to achieve their effective participation or invalidation in computation.

[0027] The moving heat source subroutine is used to simulate the dynamic characteristics of the welding heat source, such as its shape, power density, and moving speed, ensuring that the energy input method of the welding heat source is consistent with that of actual welding. Welding must follow a specific sequence, such as welding from left to right or in segments. This sequence must be strictly matched, and the welding thermal process is simulated line by line for each weld unit according to the actual welding process parameters. Each step calculates the temperature change in that area, such as the high temperature at the center of the heat source and the cooling down of areas away from the heat source. After all steps are connected, the temperature field of the entire welding process can be obtained. Subsequently, key indicators such as welding residual stress and deformation can be analyzed based on this temperature field.

[0028] S4 imports the temperature field of the entire welding process as a predefined temperature field into the structural model to calculate the welding residual stress.

[0029] Specifically, welding is a typical thermo-mechanical coupling process. Temperature changes cause thermal expansion and contraction of materials, resulting in stress. Conversely, stress concentration may slightly affect local heat conduction. However, direct, fully coupled analysis requires extremely high computational power and is prone to instability due to parameter coupling. Therefore, after completing the temperature field of the entire welding process, this temperature field is imported into the structural mechanics model as a known load. The model focuses solely on calculating the stress caused by temperature changes, achieving thermo-mechanical decoupling and balancing computational efficiency and accuracy. After the temperature field is imported, the structural model calculates the free thermal expansion / contraction that should occur at each location based on the material's thermal expansion coefficient, elastic modulus, yield strength, and other mechanical parameters, according to the temperature changes at each location. It then solves for the internal stress generated by deformation constraints using mechanical equilibrium equations, ultimately obtaining the residual welding stress after cooling.

[0030] S5, using welding residual stress as the initial condition, restarts the analysis of stress analysis results under different load conditions.

[0031] Specifically, the restart analysis does not start from scratch. Instead, it uses existing welding residual stress analysis results as initial conditions and then superimposes subsequent different load conditions, such as random vibration, fixed frequency, frequency sweep, and inertial forces in various directions, to avoid neglecting the influence of initial welding residual stress on the final stress. By comprehensively considering the superposition effect of initial welding residual stress and external load stress, the final stress analysis results of each part of the power battery are output. This more realistically simulates the stress state of the power battery under actual operating conditions, providing an accurate basis for structural optimization and performance evaluation.

[0032] S6. Obtain the structural fatigue safety factor based on the stress analysis results.

[0033] Specifically, the structural fatigue safety factor is an indicator that measures the safety of a structure against fatigue failure under repeated stress. Its core function is to mitigate the risk of failure due to long-term fatigue accumulation, such as the propagation of metal cracks leading to fracture, by using the ratio of the theoretical load-bearing capacity to the actual working load. The ratio is calculated as follows: using the fatigue limit of the structure or material (the maximum stress that will not cause failure under long-term repeated stress) as the numerator, and the maximum alternating stress that the structure withstands in actual working conditions as the denominator. A larger ratio indicates higher safety; a smaller ratio means that the actual stress is closer to the fatigue limit, and the structure is at risk of fatigue failure. The structural fatigue safety factor is determined by extracting stress amplitudes from stress analysis results using specialized software.

[0034] S7 evaluates the durability of power batteries based on the structural fatigue safety factor.

[0035] Specifically, by setting appropriate conditions, if the structural fatigue safety factor meets the requirements, the durability performance of the power battery is determined to be qualified; if the structural fatigue safety factor does not meet the requirements, the durability performance of the power battery is determined to be unqualified. For unqualified cases, the specific welding structure locations need to be identified, the structure optimized, and then re-analyzed until the qualified conditions are met.

[0036] This embodiment establishes a geometric model of the power battery to create weld seam units, simulates the welding thermal process of the weld seam units, obtains the temperature field of the entire welding process, and imports it into the structural model to calculate welding residual stress. Based on the stress analysis results, the structural fatigue safety factor is obtained to evaluate the durability performance of the power battery. This method considers the impact of welding residual stress on the durability performance of the power battery, improves the accuracy of the durability performance evaluation of the power battery, and can accurately optimize the structure for welded structural locations with unqualified durability performance, thereby improving the reliability of the power battery.

[0037] In some embodiments of this application, the durability performance of the power battery is evaluated based on the structural fatigue safety factor, including: determining that the durability performance of the power battery is unqualified when the structural fatigue safety factor is less than a preset threshold; and determining that the durability performance of the power battery is qualified when the structural fatigue safety factor is greater than or equal to the preset threshold.

[0038] Specifically, a higher structural fatigue safety factor indicates higher safety, while a lower factor indicates a greater risk of fatigue failure. The preset threshold can be set according to this principle. For example, a threshold of 1.3 means that if the structural fatigue safety factor is less than 1.3, the battery's durability performance is considered unqualified; if the factor is greater than or equal to 1.3, the battery's durability performance is considered qualified. For cases of unqualified durability performance, the specific welded structural locations need to be identified and the structure optimized. This includes optimizing the weld type and layout, adjusting the structural geometry, and optimizing the stress state of the welded joints. The optimized structure needs to undergo secondary analysis to re-determine the structural fatigue safety factor until the battery's durability performance is deemed qualified.

[0039] This embodiment judges the structural fatigue safety factor by setting a preset threshold to evaluate the durability performance of the power battery. The preset threshold provides a clear judgment standard for the structural fatigue safety factor, which can accurately identify whether the durability performance of the power battery is qualified, identify potential risks, and optimize the structure to extend the actual service life of the power battery.

[0040] In some embodiments of this application, the stress analysis results under different load conditions are restarted using welding residual stress as the initial condition, including: determining the operating condition of the power battery; and importing the welding residual stress into the first inertial force condition and the second inertial force condition respectively through restarted analysis to obtain the stress analysis results of the structure under the action of the first inertial force and the second inertial force.

[0041] Specifically, typical operating conditions for power batteries include random vibration, fixed frequency, frequency sweep, and inertial forces in various directions. Taking the vertical inertial force condition as an example, the first inertial force condition can be set as a vertical -5g inertial force condition, and the second inertial force condition can be set as a vertical +3g inertial force condition. Using the welding residual stress results as the initial condition for restart analysis, the vertical -5g inertial force condition and the vertical +3g inertial force condition are superimposed respectively to obtain the superimposed stress of the structure under the action of -5g and +3g inertial forces, which is used to determine whether the structure meets the strength requirements.

[0042] This embodiment uses welding residual stress as the initial condition to restart the analysis of superimposed stress of the power battery under different load conditions, making the stress calculation closer to the actual working state of the power battery, accurately identifying high stress areas under superimposed effects, discovering structural weak points in advance, providing data support for power battery structure optimization, ensuring structural reliability and safety, and ultimately improving the service life of the power battery.

[0043] In some embodiments of this application, obtaining the structural fatigue safety factor based on the stress analysis results includes: importing the stress analysis results into fatigue analysis software, cycling the welding residual stress under the action of a first inertial load and a second inertial load a preset number of times to obtain the superimposed stress amplitude, so as to determine the structural fatigue safety factor.

[0044] Specifically, fatigue analysis software is a specialized tool used to simulate and evaluate the gradual damage and eventual fatigue failure of power battery structures under cyclic loading. The stress analysis results are imported into the fatigue analysis software, and the cyclic load data is set, such as setting the first inertial load to a vertical -5g inertial load, the second inertial load to a vertical +3g inertial load, and the preset number of cycles to 10. 9 The structure was calculated to undergo 10 cycles under vertical inertial loads of -5g and +3g. 9 The stresses are calculated by first obtaining the stresses, and then the superimposed stress amplitude is obtained. The ratio of the superimposed stress amplitude to the fatigue limit stress of the structure is the fatigue safety factor of the structure.

[0045] This embodiment imports the stress analysis results into fatigue analysis software, cycles the load under the first inertial load and the second inertial load a preset number of times, and obtains the superimposed stress amplitude to determine the structural fatigue safety factor. This is more in line with the actual stress scenario of the structure, and the calculation of the fatigue safety factor is more practically meaningful. It can effectively identify potential fatigue failure risk points. Based on the accurate structural fatigue safety factor, it can provide a key basis for structural optimization and improve the reliability of power batteries.

[0046] In some embodiments of this application, based on the birth-death element technique and the moving heat source subroutine, the welding thermal process of each weld seam unit is simulated sequentially according to the welding process parameters to obtain the temperature field of the entire welding process. This includes: determining the welding sequence based on the actual welding process and defining the welding process parameters in the moving heat source subroutine; using the birth-death element technique to set the current weld seam unit to an inactive state while keeping the remaining weld seam units active; using the Goldak double ellipsoidal heat source model to calculate the welding thermal process sequentially according to the weld seam sequence to obtain the temperature field file of the welding process of each weld seam unit; and determining the temperature field of the entire welding process based on the temperature field file of the welding process of each weld seam unit.

[0047] Specifically, Figure 3 This diagram illustrates the weld seams at the intersection of the horizontal and vertical beams of the power battery box. Weld seams 1, 2, 3, and 4 form a group. In the actual welding process, welding is performed in the order of weld seam 1-weld seam 2-weld seam 3-weld seam 4. Welding process parameters are defined in the moving heat source subroutine, including welding heat source power, shape, welding dimensions, welding speed, and welding current and voltage. The welding heat source used is a Goldak double ellipsoidal heat source. Using the dead / born element technique, weld seams 1, 2, 3, and 4 are set to an inactive state in step 0, and then the elements of weld seam 1 are activated sequentially in steps 1-10. The duration of each analysis step is... ( For welding speed, For the first (The length of the weld seam), Step 11 is the cooling step, lasting 3000s. Then, the heat flux is set, the effective area is selected as the element near the weld seam, and the distribution method is defined using the flux distribution subroutine. The initial temperature is set to 20℃ through a predefined field. Finally, the flux distribution subroutine is written, a restart is set, and the calculation is submitted. Through the above process, the temperature field file of weld seam 1 is obtained. When analyzing the welding temperature field of weld seam 2, the temperature field file of weld seam 1 needs to be imported. The temperature field analysis process of weld seam 2 is the same as that of weld seam 1. Similarly, the temperature field analysis of weld seams 3 and 4 is performed, finally obtaining the temperature field results of the entire welding process for this group of weld seams.

[0048] This embodiment uses the birth and death unit technology and the moving heat source subroutine to simulate the welding thermal process of each weld unit according to the welding sequence and welding process parameters, so as to obtain the temperature field of the entire welding process, accurately restore the welding thermal process, improve the consistency between the temperature field and the actual working conditions, provide core data support for welding stress calculation, and reduce the deviation caused by inaccurate thermal field data.

[0049] In some embodiments of this application, the heat flux density distribution function of the Goldak double ellipsoidal heat source model is: First half of the ellipsoidal heat flux density distribution function: The heat flux density distribution function of the ellipsoid in the second half: ,in, Indicates heat source efficiency. and This represents the coefficient for heat distribution. , , , , These are the shape parameters of the heat source.

[0050] Specifically, the Goldak double-ellipsoidal heat source model is a three-dimensional moving heat source model. It accurately describes the energy distribution characteristics of heat sources such as electric arcs or lasers in the weld region through the combination of two semi-ellipsoids. In actual welding, the heat source energy is not uniformly distributed; when the heat source acts on the workpiece surface, the heat flux density is more concentrated forward and more dispersed backward. Therefore, the Goldak model uses two symmetrical semi-ellipsoids to simulate the energy distribution in the front and rear halves of the weld region, respectively. and This represents the heat distribution ratio coefficient, which can be adjusted according to the welding method, for example... Set to 1.4, Set to 0.6. This can be adjusted... , , , The heat source shape parameters are adapted to different welding methods and workpiece materials, such as arc welding, laser welding, and electron beam welding. The first half of the ellipsoid has a short axis and small volume along the welding direction, corresponding to concentrated heat flow, while the second half of the ellipsoid has a long axis and large volume against the welding direction, corresponding to dispersed heat flow. The two ellipsoids share a symmetry plane and cover the molten pool area of ​​the weld as a whole.

[0051] This embodiment determines the welding heat source model as the Goldak double ellipsoidal heat source model, which can accurately reproduce the energy gradient changes of the heat source in different regions of the weld during welding, avoid temperature distribution distortion caused by the simplification of the heat source model, and improve the reliability of welding residual stress calculation.

[0052] In some embodiments of this application, the temperature field of the entire welding process is imported into the structural model as a predefined temperature field to calculate the welding residual stress, including: using a thermal-structural coupling analysis method, taking the temperature field of the entire welding process as the initial condition, calculating the stress distribution of the structure during the cooling process as the welding residual stress.

[0053] Specifically, welding is a process of localized high-temperature heating followed by rapid cooling. Temperature changes directly cause structural expansion / contraction, while structural constraints limit this deformation, leading to residual welding stress. Thermal-structural coupling considers the interaction of these two effects simultaneously. It uses temperature field data to calculate structural deformation and also uses structural deformation feedback to correct the temperature field, avoiding errors from analyzing either thermally or structurally in isolation.

[0054] During welding, the high temperature of the electric arc causes a rapid increase in the temperature of the weld and surrounding area, forming a temperature gradient from the weld to the base material. During the cooling phase, the temperature gradient reverses. The generation of stress directly depends on how the temperature changes. The greater the temperature difference between different areas and the faster the cooling, the more significant the deformation difference, and the greater the subsequent stress. Therefore, the temperature field throughout the entire process is used as the initial condition.

[0055] The cooling stage is crucial for stress accumulation and eventual residual stress. During heating, the structure softens due to high temperatures, allowing for relatively free deformation. During cooling, the areas that cool first contract and harden, while the areas that cool later are hindered from free deformation by the hardened areas, thus generating constrained stress internally. By calculating the stress distribution during this stage through coupled analysis, the stress remaining after cooling to room temperature is identified as residual welding stress.

[0056] This embodiment uses the temperature field of the entire welding process as the initial condition and adopts a thermal-structural coupling analysis method to calculate the stress distribution of the structure during the cooling process, which is used as the welding residual stress. This method can accurately reproduce the initial impact of temperature changes on material stress during welding, avoid calculation deviations caused by ignoring key factors such as temperature gradient and thermal expansion and contraction differences, and thus accurately obtain the welding residual stress.

[0057] In some embodiments of this application, the geometric model of the power battery is processed to establish weld seam units at the component connections of the power battery, including: dividing the geometric model of the power battery into a mesh; assembling the components of the power battery according to the mesh, wherein the components are connected by a tie; and establishing weld seam units at the component connections.

[0058] Specifically, the geometric model of a power battery often includes non-core structures such as bolt holes, chamfers, small protrusions, and cable grooves, which have minimal impact on thermal field and stress analysis. These minor features need to be removed first to avoid over-refinement of the mesh or inability to generate a continuous mesh due to excessive detail. The geometric model may also contain geometric defects, such as gaps between surfaces, overlapping surfaces, and free edges. These need to be repaired, such as filling gaps, deleting overlapping surfaces, and merging free edges, to ensure that each geometric region forms a complete boundary, providing a clear topological structure for mesh generation. The overall power battery geometric model can be divided into regular mesh sub-regions according to structural function or geometric shape. For example, according to structural function, the cell array region, cooling pipe region, and outer casing region can be separated, resulting in a more unified structure within each sub-region.

[0059] After meshing, the components of the power battery are assembled into a whole according to the divided mesh sub-regions. The components are connected using Tie connections, a common binding connection method in engineering simulation and physical assembly. In power battery assembly, it primarily serves the dual purpose of structural fixation and heat transfer. Power batteries experience vibration and temperature changes during operation. Loose connections between components could lead to risks such as cell short circuits and cooling failures. Tie connections can offset the effects of vibration through rigid bonding, while also assisting in heat transfer. Weld elements are created at the connection points of each component, such as... Figure 3 Welds 1, 2, 3, and 4 in the model are transformed into calculable weld elements, providing basic data support for subsequent simulation of the entire welding process to obtain the temperature field.

[0060] This embodiment divides the geometric model of the power battery into a mesh, assembles the components according to the mesh, and establishes weld seam units at the connection points to provide data support for the subsequent simulation of the entire actual welding process. This makes the simulation results of temperature field and stress distribution in the subsequent welding process more consistent with the actual production scenario, thereby improving the realism and accuracy of the simulation.

[0061] In some embodiments of this application, the durability performance analysis method of the power battery further includes: before welding the weld unit, applying boundary constraint conditions based on the actual vehicle installation state of the power battery, wherein the boundary constraint conditions include: applying fixing constraints at the battery pack hoisting bolt holes, applying natural convection heat transfer boundary conditions on the outer surface of the battery pack, and applying corresponding heat conduction boundary conditions inside the battery pack.

[0062] Specifically, based on the actual installed state of the power battery, boundary constraints are applied to simulate the real operating conditions of the power battery after installation, making the subsequent analysis of welding residual stress more realistic and avoiding a disconnect between theoretical analysis and actual performance after installation. Specifically, applying fixed constraints at the battery pack mounting bolt holes simulates the spatial positioning of the power battery after installation, preventing false displacements of the battery pack during analysis and ensuring that the stress and deformation directions of the weld unit are consistent with actual installation. Applying natural convection heat transfer boundary conditions to the outer surface of the battery pack restores the external heat exchange pattern of the battery pack during welding, avoiding temperature calculation deviations caused by assuming the outer surface is adiabatic or irregular heat exchange. Applying corresponding heat conduction boundary conditions inside the battery pack simulates the actual heat transfer path of welding heat within the battery pack. For example, welding heat does not diffuse indiscriminately inside, but varies in speed depending on the material of the components, more accurately reflecting the heat-affected zone around the weld.

[0063] This embodiment is based on the actual vehicle installation state of the power battery. Before welding the weld unit, boundary constraints are applied to simulate the real working conditions after the power battery is actually installed in the vehicle. This avoids positional shifts and unreasonable heat transfer caused by lack of constraints or simulation deviations, thereby improving welding accuracy and adaptability.

[0064] In some embodiments of this application, the durability performance analysis method for the power battery further includes: determining the properties of the metallic material used in the power battery.

[0065] Specifically, experiments are conducted to obtain the material properties of metals, including the temperature-dependent curves of parameters such as density, elastic modulus, Poisson's ratio, yield strength, and specific heat capacity, as well as thermal parameters such as coefficient of thermal expansion, thermal conductivity, surface emissivity, and heat transfer coefficient. The properties of metallic materials directly determine the suitability of welding processes. Different metallic materials can be matched with different process parameters such as welding current, welding voltage, welding thermal efficiency, welding speed, and welding heat source size to ensure that the welding effect better matches actual production conditions.

[0066] This embodiment determines the properties of the metal materials used in the power battery and matches different welding processes based on these properties, so that the welding simulation is more in line with actual production conditions, thereby improving the accuracy and realism of the welding simulation.

[0067] As a specific embodiment of this application, such as Figure 4 As shown, the durability performance analysis method for this power battery may include the following steps: S101, Establish the geometric model of the power battery and mesh the model.

[0068] S102, assemble the various components of the power battery according to the divided grid, and establish weld seam units at the connection of the components.

[0069] S103: Obtain the welding process parameters and metal material properties of the power battery, and apply boundary constraints.

[0070] S104, determine the welding sequence according to the actual welding process, and define the welding process parameters in the moving heat source subroutine.

[0071] S105, using the birth and death element technique, sets the current weld element to an inactive state, while keeping the other weld elements active.

[0072] S106, calculate the welding thermal process sequentially according to the weld sequence to obtain the temperature field file of the welding process of each weld unit.

[0073] S107. Determine whether the welding heat calculation for all welds has been completed. If yes, proceed to step S109; otherwise, proceed to step S108.

[0074] S108, import the welding process temperature field file of the previous weld into the welding process temperature field analysis of the next weld by restarting the analysis.

[0075] S109, determine the temperature field throughout the welding process.

[0076] S110 uses the temperature field throughout the welding process as the initial condition to calculate the stress distribution of the structure during the cooling process, which is then used as the welding residual stress.

[0077] S111, using welding residual stress as the initial condition, restart the analysis of stress analysis results under different load conditions.

[0078] S112. Import the stress analysis results into the fatigue analysis software to determine the structural fatigue safety factor.

[0079] S113: If the structural fatigue safety factor is less than the preset threshold, the durability performance of the power battery is determined to be unqualified; otherwise, the durability performance is qualified.

[0080] S114. For non-compliant cases, structural optimization is performed, followed by secondary analysis until the durability performance meets the requirements.

[0081] In summary, the durability performance analysis method for power batteries according to the embodiments of this application establishes a geometric model of the power battery and processes the model to create weld seam units at the component connections of the power battery. It obtains the welding process parameters of the power battery and, based on the birth and death unit technology and the moving heat source subroutine, simulates the welding thermal process of each weld seam unit according to the welding sequence and welding process parameters to obtain the temperature field throughout the welding process. This temperature field is then imported into the structural model as a predefined temperature field to calculate welding residual stress. Using the welding residual stress as an initial condition, the analysis is restarted to analyze the stress analysis results under different load conditions. The structural fatigue safety factor is obtained based on the stress analysis results, and the durability performance of the power battery is evaluated based on the structural fatigue safety factor. Therefore, this method improves the accuracy of power battery durability performance evaluation by establishing a geometric model of the power battery to create weld seam units, simulating the welding thermal process of the weld seam units, obtaining the temperature field throughout the welding process, importing it into the structural model to calculate welding residual stress, and obtaining the structural fatigue safety factor based on the stress analysis results to evaluate the durability performance of the power battery.

[0082] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0083] It should be understood that various parts of this application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0084] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0085] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0086] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0087] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for analyzing the durability performance of a power battery, characterized in that, The method includes: A geometric model of the power battery is established, and the battery geometric model is processed to create weld seam units at the component connections of the power battery. Obtain the welding process parameters of the power battery; Based on the birth and death unit technology and the mobile heat source subroutine, the welding thermal process of the weld unit is simulated one by one according to the welding process parameters in the welding sequence to obtain the temperature field of the entire welding process. The temperature field of the entire welding process is imported into the structural model as a predefined temperature field to calculate the welding residual stress. Using the aforementioned welding residual stress as the initial condition, the stress analysis results under different load conditions were restarted and analyzed. The structural fatigue safety factor is obtained based on the stress analysis results. The durability performance of the power battery is evaluated based on the structural fatigue safety factor.

2. The method for analyzing the durability performance of a power battery according to claim 1, characterized in that, The durability performance of the power battery is evaluated based on the structural fatigue safety factor, including: If the structural fatigue safety factor is less than a preset threshold, the durability performance of the power battery is determined to be unqualified. If the structural fatigue safety factor is greater than or equal to the preset threshold, the durability performance of the power battery is determined to be qualified.

3. The method for analyzing the durability performance of a power battery according to claim 1, characterized in that, Using the aforementioned welding residual stress as an initial condition, the stress analysis results under different load conditions are restarted and analyzed, including: Determine the operating conditions of the power battery; The welding residual stress was imported into the first inertial force condition and the second inertial force condition through restart analysis, respectively, to obtain the stress analysis results of the structure under the action of the first inertial force and the second inertial force.

4. The method for analyzing the durability performance of a power battery according to claim 3, characterized in that, The structural fatigue safety factor is obtained based on the stress analysis results, including: The stress analysis results are imported into fatigue analysis software. The welding residual stress is subjected to a preset number of cycles under the action of the first inertial load and the second inertial load to obtain the superimposed stress amplitude, so as to determine the fatigue safety factor of the structure.

5. The method for analyzing the durability performance of a power battery according to claim 1, characterized in that, Based on the birth-and-death unit technology and the moving heat source subroutine, the welding thermal process of each weld unit is simulated sequentially according to the welding process parameters to obtain the temperature field of the entire welding process, including: The welding sequence is determined according to the actual welding process, and the welding process parameters are defined in the moving heat source subroutine; The aforementioned dead / born unit technique is used to set the current weld unit to an inactive state, while keeping the other weld units in an active state; Using the Goldak double ellipsoidal heat source model, the welding thermal process was calculated sequentially according to the weld seam order, resulting in the temperature field file of the welding process for each weld seam unit. The temperature field of the entire welding process is determined based on the temperature field file of the welding process for each weld unit.

6. The method for analyzing the durability performance of a power battery according to claim 5, characterized in that, The heat flux density distribution function of the Goldak double ellipsoidal heat source model is: The heat flux density distribution function of the first half of the ellipsoid: ， The heat flux density distribution function of the ellipsoid in the second half: ， in, Indicates heat source efficiency. and This represents the coefficient for heat distribution. , , , , These are the shape parameters of the heat source.

7. The method for analyzing the durability performance of a power battery according to claim 1, characterized in that, The temperature field of the entire welding process is imported into the structural model as a predefined temperature field to calculate the welding residual stress, including: A thermo-structural coupling analysis method is used, taking the temperature field of the entire welding process as the initial condition, to calculate the stress distribution of the structure during the cooling process, which is then used as the welding residual stress.

8. The method for analyzing the durability performance of a power battery according to claim 1, characterized in that, Processing the geometric model of the power battery to establish weld seam units at the component connections of the power battery includes: The geometric model of the power battery is meshed; The components of the power battery are assembled according to a divided grid, wherein the components are connected by a tie. The weld unit is established at the connection of each component.

9. The method for analyzing the durability performance of a power battery according to claim 1, characterized in that, The method further includes: Before welding the weld unit, boundary constraints are applied based on the actual vehicle installation state of the power battery. The boundary constraints include: applying fixing constraints at the battery pack mounting bolt holes, applying natural convection heat transfer boundary conditions on the outer surface of the battery pack, and applying corresponding heat conduction boundary conditions inside the battery pack.

10. The method for analyzing the durability performance of a power battery according to claim 1, characterized in that, The method further includes: Determine the properties of the metallic materials used in the power battery.

Images