Fatigue life frequency prediction method and method for manufacturing battery pack

Abstract

To provide a fatigue life frequency prediction method in a predetermined stress ratio of a material both in a low cycle fatigue region and in a high cycle fatigue region.SOLUTION: A fatigue life frequency prediction method includes: a first step of using CAE analysis for an F-N diagram obtained from an experiment result of a tensile test for a material to rewrite the F-N diagram into an S-N diagram; a second step of rewriting the S-N diagram into a Goodman diagram; a third step of writing a fatigue limit diagram of the material on the Goodman diagram; a fourth step of writing a predetermined stress ratio diagram desired to predict a fatigue life frequency on the Goodman diagram; a fifth step of moving in parallel a line of the fatigue limit diagram of the material to a predetermined first intersection point on the stress ratio diagram desired to predict the fatigue life frequency; a sixth step of determining stress amplitude of a stress ratio desired to predict the fatigue life frequency from a second intersection point as an intersection between the fatigue limit diagram moved in parallel and the fatigue limit diagram of the material; and a seventh step of determining the fatigue life frequency of the predetermined stress ratio desired to predict corresponding to the stress amplitude from the S-N diagram of the material.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present technology relates to a fatigue life cycle prediction method and a battery pack manufacturing method. [Background technology]

[0002] In the battery assembly manufacturing process, it is necessary to evaluate the strength of the materials used in the battery assembly when selecting them. In particular, it is important to predict the fatigue life cycle at a given stress ratio for materials used in spot welds and laser welds.

[0003] JP 2022-013082 A (Patent Document 1) discloses an invention relating to a damage diagnosis system and method for a rotating electric machine, which includes a strain range prediction unit that calculates the elastic strain and elastic stress in an evaluation portion of the rotating electric machine as a quadratic function of the rotation speed of the rotating electric machine detected by a sensor, counts the frequency of the elastic strain range and elastic stress range in the evaluation portion, and converts it into a total strain range of the elastic strain range and elastic stress range; a fatigue damage rate prediction unit that predicts the fatigue damage rate in the evaluation portion of the rotating electric machine from the converted total strain range; and an accumulator unit that accumulates the fatigue damage rates to predict a cumulative fatigue damage rate.

[0004] Japanese Patent Laid-Open Publication No. 05-001506 (Patent Document 2) discloses an invention relating to a material strength evaluation device, in which a stress evaluation calculation unit performs fatigue evaluation of materials using a diagram in which a so-called Goodman diagram is programmed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-013082 [Patent Document 2] Japanese Patent Application Publication No. 05-001506 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the above-mentioned prediction of the fatigue life cycle at a predetermined stress ratio of a material, the "strain" of the material is used in the low-cycle fatigue region, and the "stress" of the material is used in the high-cycle fatigue region, thereby predicting the fatigue life cycle at a predetermined stress ratio of the material. In other words, different indicators must be used to predict the fatigue life cycle at a predetermined stress ratio of a material in the low-cycle fatigue region and the high-cycle fatigue region.

[0007] The purpose of this technology is to solve the above-mentioned problems and to provide a fatigue life cycle prediction method and a battery assembly manufacturing method that can easily predict the fatigue life cycle at a specified stress ratio of a material in both the low-cycle fatigue region and the high-cycle fatigue region. [Means for solving the problem]

[0008] The present technology provides the following fatigue life cycle prediction method and battery pack manufacturing method.

[0009] [1] A method for predicting the number of fatigue cycles of a material at a predetermined stress ratio, comprising: a first step of converting an FN diagram obtained from the experimental results of a tensile test of the material into an SN diagram using CAE analysis; a second step of converting the SN diagram into a Goodman diagram; a third step of entering a fatigue limit diagram of the material on the Goodman diagram; a fourth step of entering a predetermined stress ratio diagram for which the number of fatigue cycles is to be predicted on the Goodman diagram; a fifth step of translating a line of the fatigue limit diagram of the material to a predetermined first intersection on the stress ratio diagram for which the number of fatigue cycles is to be predicted; a sixth step of determining the stress amplitude for the stress ratio for which the number of fatigue cycles is to be predicted from the second intersection where the translated fatigue limit diagram intersects with the fatigue limit diagram of the material; and a seventh step of determining the number of fatigue cycles of the material at the predetermined stress ratio for which the number of fatigue cycles is to be predicted, which corresponds to the stress amplitude, from the SN diagram of the material.

[0010] [2] The fatigue life cycle prediction method according to [1], further comprising an eighth step of selecting a plurality of second intersections at which the fatigue limit diagram intersects with the sixth step, determining the fatigue life cycles corresponding to the plurality of stress amplitudes obtained by the plurality of selections in the seventh step, and, based on the results, determining an SN diagram at the stress ratio for which the fatigue life cycle is desired to be predicted.

[0011] [3] A method for manufacturing a battery pack having various components, wherein the fatigue life cycle prediction method described in [1] or [2] is used to predict the number of fatigue life cycles at a predetermined stress ratio of the materials constituting the components. [Effects of the Invention]

[0012] According to the present technology, a fatigue life cycle prediction method and a battery assembly manufacturing method are provided that employ a simple method for predicting the fatigue life cycle at a specified stress ratio for a material in both the low-cycle fatigue region and the high-cycle fatigue region. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a flow chart of a method for predicting the number of cycles of fatigue life at a predetermined stress ratio of a material according to an embodiment. [Figure 2] This is an FN diagram obtained from experimental results for the material. [Figure 3] This is a diagram in which the FN diagram shown in Figure 2 has been redrawn as an SN diagram. [Figure 4] This is a diagram in which the SN diagram shown in Figure 3 has been redrawn as a Goodman diagram. [Figure 5] This is a diagram in which a stress ratio diagram for predicting the fatigue life cycle of a material is added to Figure 4. [Figure 6] FIG. 1 is a diagram showing a method for predicting the number of cycles of fatigue life at a predetermined stress ratio of a material. [Figure 7] FIG. 7 is a flow diagram illustrating the prediction method shown in FIG. 6. [Figure 8] This is an SN diagram created based on data obtained using a method for predicting the number of cycles of fatigue life at a specified stress ratio for a material. [Figure 9] This is an SN diagram of a material at a predetermined stress ratio obtained from an experiment. [Figure 10] FIG. 10 is a graph comparing predicted fatigue life cycles with experimental results at a predetermined stress ratio for a material. [Figure 11] FIG. 1 is a first diagram showing an overview of an evaluation method for predicting the number of cycles of fatigue life at a predetermined stress ratio of a material according to an embodiment. [Figure 12] FIG. 2 is a second diagram showing an overview of an evaluation method for predicting the number of cycles of fatigue life at a predetermined stress ratio of a material according to an embodiment. [Figure 13] FIG. 2 is a perspective view showing the configuration of a battery pack. [Figure 14] 1 is a diagram illustrating a configuration of a fatigue life cycle prediction device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present technology will be described. Note that the same or corresponding parts are denoted by the same reference characters, and description thereof may not be repeated.

[0015] In the embodiments described below, when numbers, amounts, etc. are mentioned, the scope of the present technology is not necessarily limited to those numbers, amounts, etc., unless otherwise specified. Furthermore, in the following embodiments, each component is not necessarily essential to the present technology, unless otherwise specified. Furthermore, the present technology is not necessarily limited to those that achieve all of the effects mentioned in the present embodiments.

[0016] In this specification, the words "comprise," "include," and "have" are open-ended, meaning that when a certain feature is included, other features may or may not be included.

[0017] In this specification, the term "battery assembly" is not limited to lithium-ion battery assembly, but may include other battery assembly such as nickel-metal hydride batteries and sodium-ion batteries. In this specification, the term "electrode" may collectively refer to a positive electrode and a negative electrode.

[0018] In the battery assembly manufacturing process, when selecting the various materials to be used in the battery assembly, it is important to know the fatigue life of the materials to be used in advance. The fatigue life of a material can be obtained through experiments, but conducting experiments on all components requires a huge amount of work. On the other hand, if the fatigue life of a material can be accurately predicted, it will be possible to improve the manufacturing efficiency of battery assembly. The term "material" is used in a broad sense to include base materials and test specimens.

[0019] In particular, it is important to predict the fatigue life cycle for various stress ratios of the materials of spot welds and laser welds used in the manufacturing process of a battery pack. Hereinafter, a method for predicting the fatigue life cycle for a material at a predetermined stress ratio in an embodiment will be described with reference to the drawings.

[0020] The flow of a method for predicting the number of cycles of fatigue life of a material at a predetermined stress ratio will be described with reference to Figures 1 to 8. Figure 1 is a flow diagram of the method for predicting the number of cycles of fatigue life of a material at a predetermined stress ratio, Figure 2 is an FN diagram obtained from experimental results for the material, Figure 3 is an SN diagram obtained by redrawing the FN diagram shown in Figure 2, Figure 4 is a Goodman diagram obtained by redrawing the SN diagram shown in Figure 3, Figure 5 is a diagram obtained by adding a stress ratio diagram for predicting the number of cycles of fatigue life of a material to Figure 4, Figure 6 is a diagram showing the method for predicting the number of cycles of fatigue life of a material at a predetermined stress ratio, Figure 7 is a flow diagram showing the prediction method shown in Figure 6, and Figure 8 is an SN diagram created based on data obtained by the method for predicting the number of cycles of fatigue life of a material at a predetermined stress ratio.

[0021] <Step 10 (S10)> Step 10 (S10) will be explained with reference to Figures 1 and 2. A tensile test (experiment) is conducted on the material. A tensile shear test of the material is conducted using a four-point spot test piece. Based on the results of this experiment, an FN diagram (line L1) for the material is created as shown in Figure 2. The horizontal axis represents the number of repetitions (cycles), and the vertical axis represents the maximum load (kN). The stress ratio is constant at 0.1.

[0022] <Step 20 (S20)> Next, step 20 (S20) will be described with reference to Figures 1 and 3. The FN diagram (line L1) of the material shown in Figure 2 is redrawn into an SN diagram (line L2) as shown in Figure 3 using CAE (Computer Aided Engineering) analysis (specifically, the von Mises stress generated in a linear analysis of statically pulling the material in the longitudinal direction of the material). The horizontal axis represents the "number of repetitions [cycles]" and the vertical axis represents the "stress amplitude [MPa]."

[0023] <Step 30 (S30)> Step 30 (S30) will be described with reference to Figures 1 and 4. Figure 4 shows the SN diagram of the material shown in Figure 3 redrawn as a Goodman diagram, which is the fatigue limit diagram of the material (line L3). The horizontal axis represents "mean stress (MPa)" and the vertical axis represents "stress amplitude (MPa)." In line L3, the intersection point (P1) with the vertical axis indicates the "maximum material fatigue limit," and the intersection point (P2) with the horizontal axis indicates the "maximum material tensile strength." In Figure 4, line L4, which is a stress ratio diagram (fatigue test result) for a material with a known fatigue life, is entered.

[0024] <Step 40 (S40)> Step 40 (S40) will be described with reference to Figures 1 and 5. Figure 5 shows a diagram of the stress ratio for which the fatigue life cycle is to be predicted, plotted on the above-mentioned Figure 4. In the diagram, line L11 is a diagram of the stress ratio for σmin / σmax=0.5, and line L12 is a diagram of the stress ratio for σmin / σmax=0.

[0025] <Step 50 (S50)> Step 50 (S50) will be described with reference to Figures 1, 6, and 7. Based on the diagram obtained in Figure 5, Steps A to D shown in Figure 7 are executed to predict the number of fatigue life cycles of the material at the desired stress ratio.

[0026] [Step A] 6 and 7, the fatigue limit diagram L3 is maintained at its original slope and translated to the predetermined first intersection point A where the fatigue life cycle is to be predicted. In FIG. 6, the fatigue limit diagram after translation is shown as line L3p. Here, this is done under the assumption that the slope of line L3p is the same in the low-cycle fatigue region and the high-cycle fatigue region. Whether this assumption is correct or not is verified by comparing it with the experimental results of an actual fatigue test.

[0027] [Step B] Next, a second intersection B where line L3p of the translated fatigue limit diagram intersects with line L4 of the stress ratio diagram with a known fatigue life is calculated, and P12, which is the stress amplitude (MPa) at this time, is found.

[0028] [Step C] Using the SN diagram (line L2) shown in FIG. 3, P13, which is the number of fatigue life cycles, is calculated from the stress amplitude (MPa) of P12.

[0029] [Step D] Next, the above-mentioned procedures from [Step A] to [Step C] are performed for the specified plot points of the first sample (line L11) where σmin / σmax = 0 and the specified plot points of the second sample (line L12) where σmin / σmax = 0.5. This is redrawn on the SN diagram shown in Figure 8. Line L21 is the SN diagram for the stress ratio of σmin / σmax = 0.5, and line L22 is the SN diagram for the stress ratio of σmin / σmax = 0 (7th and 8th steps).

[0030] In FIG. 9, line L31 is an SN diagram obtained from actual experimental results at a stress ratio of σmin / σmax=0.5, and line L32 is an SN diagram obtained from actual experimental results at a stress ratio of σmin / σmax=0.

[0031] 10 shows the fatigue life cycles (cycles) in the prediction results of the present disclosure and the fatigue life cycles (cycles) in the experimental results at various stress ratios. As a result of the comparison, it was confirmed that the prediction results of the present disclosure could be predicted with approximately 1.5 times the accuracy.

[0032] (Outline of the evaluation method of the present disclosure) Here, the gist of the evaluation method of the present disclosure will be described with reference to Figures 11 and 12. This fatigue life cycle prediction method includes the following steps.

[0033] (I) The method includes a step of converting an FN diagram obtained from the experimental results of a tensile test of the material into an SN diagram using CAE analysis. (II) The method includes a step of converting the SN diagram into a Goodman diagram. (III) The method includes a step of plotting the fatigue limit diagram of the material (line L4) on the Goodman diagram. (IV) The method includes a step of plotting a predetermined stress ratio diagram (line L11, line L12) for which the fatigue life cycle is to be predicted on the Goodman diagram. (V) The method includes a step of translating the fatigue limit diagram of the material (line L3) to a predetermined point (A) on the stress ratio diagram (line L11, line L12) for which the fatigue life cycle is to be predicted. (VI) The method includes a step of determining the stress amplitude (P12) from the intersection point B where the translated fatigue limit diagram (line L3p) intersects with the fatigue limit diagram of the material (line L4). (VII) The method includes a step of determining the fatigue life cycle (P13) for the stress ratio for which the fatigue life cycle corresponding to the stress amplitude (P12) is to be predicted from the SN diagram of the material.

[0034] By the above-described method for predicting the number of fatigue life cycles, the number of fatigue life cycles at a predetermined stress ratio of a material can be obtained.

[0035] By using this method for predicting the number of cycles of fatigue life at a specified stress ratio for a material, it is possible to easily predict the number of cycles of fatigue life at a specified stress ratio for a material in both the low-cycle fatigue region and the high-cycle fatigue region.

[0036] The above-mentioned method for predicting the number of fatigue life cycles is preferably performed by a computer. For example, as shown in Fig. 14, a fatigue life recovery prediction device 1 using a computer may include a data input unit 2 for inputting various data, a calculation unit 3 for executing the above steps (I) to (VII), a result output unit 4 for outputting the calculation results, and a data recording unit 5 for storing various data.

[0037] (Application to manufacturing method of battery pack 1000) 13 is a diagram showing an example of the configuration of a battery pack 1000. This battery pack 1000 has components such as a plurality of battery cell units 10, bus bars 300, end plates 400, and restraining members 500.

[0038] In predicting the fatigue life cycles of these components, the above-mentioned fatigue life cycle prediction method can be used to accurately evaluate materials. Furthermore, the fatigue life cycles of complex actual products can be accurately predicted from the prediction results using simple materials.

[0039] In particular, for materials used in spot welds and laser welds, it is possible to accurately grasp the fatigue life limits of components and design them to an appropriate size. As a result, it is possible to design lighter and smaller mechanical components and realize battery packs using those components. This allows more energy to be stored in a smaller area, which is expected to result in higher energy density battery packs.

[0040] Although the embodiments of the present technology have been described above, the embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present technology is defined by the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0041] 1 fatigue life recovery prediction device, 2 data input unit, 3 calculation unit, 4 result output unit, 5 data recording unit, 10 battery cell unit, 300 bus bar, 400 end plate, 500 restraint member, 600 wiring member, 700 duct, 800 connection terminal, 1000 battery pack.

Claims

1. A method for predicting the number of fatigue life cycles of a material at a predetermined stress ratio, comprising: A first step of converting an F-N diagram obtained from the experimental results of a tensile test of the material into an S-N diagram using CAE analysis; A second step of rewriting the SN diagram into a Goodman diagram; a third step of plotting a fatigue limit diagram of the material onto the Goodman diagram; a fourth step of inputting a predetermined stress ratio diagram for predicting the number of fatigue life cycles into the Goodman diagram; a fifth step of translating the line of the fatigue limit diagram of the material to a predetermined first intersection point on the stress ratio diagram for which the fatigue life cycle is to be predicted; a sixth step of determining a stress amplitude of the stress ratio for which the number of fatigue life cycles is to be predicted from a second intersection point where the translated fatigue limit diagram intersects with the fatigue limit diagram of the material; a seventh step of determining the number of fatigue life cycles at a predetermined stress ratio to be predicted corresponding to the stress amplitude from the S-N diagram of the material; A fatigue life cycle prediction method comprising:

2. In the sixth step, a plurality of second intersections are selected at which the fatigue limit diagram intersects with the second intersections; In the seventh step, the fatigue life times corresponding to the plurality of stress amplitudes obtained by selecting a plurality of stress amplitudes are calculated, An eighth step of determining an S-N diagram at the stress ratio for which the fatigue life cycle is to be predicted based on the results of the calculation. The fatigue life cycle prediction method according to claim 1 .

3. A method for manufacturing a battery pack having various components, comprising: The fatigue life cycle prediction method according to claim 1 or 2 is used to predict the fatigue life cycle at a predetermined stress ratio of the material constituting the component. A method for manufacturing a battery pack.

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