Method for detecting local stress of fuel cell molded plate flow field area

Abstract

This invention discloses a method for detecting local stress in the flow field region of a fuel cell molded plate, comprising the following steps: (1) Sample size measurement: measuring the width and length of the flow channel of the molded plate sample; (2) Sample fracture peak test: placing the molded plate sample with completed size measurement on the stage of an electronic universal testing machine, applying pressure to the molded plate sample after startup until the electronic universal testing machine reaches a peak value, and recording the peak test force at this time; (3) Local stress calculation: calculating the local stress in the flow field region of the molded plate based on the peak test force recorded in step (2) and the flow channel width and length measured in step (1). This invention achieves for the first time the quantitative calculation of the local stress on the spine when a component with a flow channel structure fails, solving the technical problem of the traditional method of "only knowing the macroscopic strength, but not the cause of failure".

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to a method for detecting local stress in the flow field region of a fuel cell molded plate. Background Technology

[0002] Bipolar plates are a key component of proton exchange membrane fuel cells (PEMFCs), playing many important roles in fuel cells, such as supporting the membrane electrode structure, separating hydrogen and oxygen, collecting current, conducting heat, discharging water generated in the reaction, and preventing gas and coolant leakage.

[0003] Based on the different materials used, bipolar plates can be classified into metal bipolar plates, graphite bipolar plates, and composite material bipolar plates. Graphite bipolar plates are generally further classified according to their processing methods into machined graphite plates, injection-molded graphite plates, and compression-molded graphite plates. Compression-molded graphite plates (referred to as molded plates) are first prepared by mixing graphite powder and resin. Then, the mixture and mold are pre-treated. Using the polymer's melting temperature and a certain pressure, the powder flows through the mold and fills the entire cavity. After curing and demolding, the bipolar plate is obtained. For example, invention application CN119191877A discloses a flexible graphite bipolar plate for fuel cells and its preparation method.

[0004] Molded plates are widely used in fluid transportation, chemical reactions, energy supply, and other fields. Their flow field region, as the core area for fluid flow, directly affects the overall performance and service life of the molded plate. In actual working conditions, the flow field region must withstand multiple effects such as fluid pressure and media corrosion over long periods. Compressive strength is a key indicator for evaluating its structural stability and reliability.

[0005] The surface of the molded plate has flow channels, and the spaces between adjacent flow channels form flow channel ridges. For example, the utility model with authorization announcement number CN210182487U discloses a novel graphite bipolar plate structure for fuel cells. During the assembly and use of the molded plate, the flow channel ridges serve as stress-bearing areas.

[0006] Currently, the industry typically uses standard methods such as GB / T 13465.1 or ASTM C695 to test the compressive strength of channeled plates. In standard tests, the entire plate is placed between pressure plates and loaded until failure. The compressive strength is calculated by dividing the peak load by the nominal cross-sectional area of ​​the plate (total width × total thickness). This method yields the macroscopic strength of the overall structure. In actual testing, failure of channeled plates often begins with localized crushing or buckling of the channel ridge (peak load corresponds to ridge collapse). However, the standard method uses nominal area calculations, which masks the true stress state at the ridge and cannot distinguish whether the failure is caused by insufficient material strength or structural buckling.

[0007] Therefore, there is an urgent need for a method that can calculate local stress based on the actual contact area in order to accurately assess the load-bearing capacity and failure causes of components with flow channels. Summary of the Invention

[0008] The present invention aims to solve the technical problem that the actual local stress of the spine and the failure mode cannot be distinguished in the compression test of the component with flow channel structure in the prior art. It provides a method for determining local stress based on the actual contact area, which provides a reliable basis for structural optimization design, material selection and failure analysis.

[0009] A method for detecting local stress in the flow field region of a fuel cell molded plate includes the following steps: (1) Sample size measurement: Measure the width and length of the flow channel of the molded plate sample; (2) Peak fracture test of sample: Place the molded plate sample with completed dimensional measurement on the stage of the electronic universal testing machine. After starting, apply pressure to the molded plate sample until the electronic universal testing machine shows a peak value. Record the peak test force at this time. (3) Calculation of local stress: Based on the peak test force recorded in step (2) and the width and length of the flow channel measured in step (1), calculate the local stress in the flow field area of ​​the molded plate.

[0010] Preferably, in step (1), the width and length of the flow channel of the molded plate sample are measured using a 3D profilometer.

[0011] Preferably, in step (2), during the peak fracture test of the sample, after the electronic universal testing machine is started, pressure is applied to the molded plate sample at a loading rate of 1~5 mm / min.

[0012] Preferably, in step (2), the peak value of the electronic universal testing machine is the fracture load value corresponding to the failure or yielding of the molded plate sample.

[0013] Preferably, in step (3), the formula for calculating local stress is: σ=F / (n(L×W) ), Where σ is the local stress, F is the peak test force, n is the number of flow channels, L is the flow channel length, and W is the flow channel width.

[0014] More preferably, the unit of local stress σ is MPa, the unit of peak test force F is N, the unit of flow channel length L is mm, and the unit of flow channel width W is mm.

[0015] Preferably, the molded plate sample to be tested is a graphite molded monopolar plate.

[0016] Preferably, the local stress in the flow field region of the fuel cell molded plate is less than the intrinsic strength of the material of the molded plate sample.

[0017] Compared with the prior art, the present invention has the following advantages: Revealing the essence of failure: For the first time, quantitative calculation of local stress on the spine of a component with a flow channel structure has been achieved, solving the technical problem that traditional methods "only know the macroscopic strength, but not the cause of failure".

[0018] Distinguishing failure modes: By comparing with the intrinsic strength of the material, it is possible to clearly determine whether the failure is caused by material crushing or structural buckling, providing an objective basis for attributing the problem. Attached Figure Description

[0019] Figure 1 This is a 3D contour scan of the sample in Example 1.

[0020] Figure 2 This is a fracture peak diagram of the sample in Example 1.

[0021] Figure 3 The image shows the intrinsic fracture peak value of the sample in Example 1.

[0022] Figure 4 This is a 3D contour scan of the sample in Example 2.

[0023] Figure 5 This is a peak fracture curve of the sample in Example 2.

[0024] Figure 6 This is a peak value diagram of the intrinsic fracture of the material in Example 2.

[0025] Figure 7 This is a 3D contour scan of the sample in Example 3.

[0026] Figure 8 This is a fracture peak diagram of the sample in Example 3.

[0027] Figure 9 This is a peak value diagram of the intrinsic fracture of the material in Example 3.

[0028] Figure 10 This is a 3D contour scan of the sample in Example 4.

[0029] Figure 11 This is a fracture peak diagram of the sample in Example 4.

[0030] Figure 12 This is a peak value diagram of the intrinsic fracture of the material in Example 4.

[0031] Figure 13 This is a 3D contour scan of the sample in Example 5.

[0032] Figure 14 This is a fracture peak diagram of the sample in Example 5.

[0033] Figure 15 This is a peak value diagram of the intrinsic fracture of the material in Example 5.

[0034] Figure 16 This is a 3D contour scan of the sample in Example 6.

[0035] Figure 17 This is a fracture peak diagram of the sample in Example 6.

[0036] Figure 18 This is a peak value diagram of the intrinsic fracture of the material in Example 6. Detailed Implementation

[0037] 1. Sample Size Measurement: The width and length of the flow channel of the molded plate sample are accurately measured using a 3D profilometer. The specific operation is as follows: Fix the molded plate sample on the stage of the 3D profilometer, adjust the measurement parameters of the profilometer, start the profilometer to scan the sample flow channel, and measure the width and length of the flow channel based on the acquired three-dimensional profile data.

[0038] 2. Peak fracture test of sample: Place the sample with completed dimensional measurement on the stage of the electronic universal testing machine, ensuring that the sample is under the indenter of the electronic universal testing machine. Start the electronic universal testing machine and apply pressure to the sample at a loading rate of 3 mm / min until the test force displayed by the electronic universal testing machine reaches a peak (i.e., the sample flow field area shows obvious deformation or damage, and the test force begins to decrease). Record the peak test force at this time.

[0039] 3. Local Stress Calculation Steps: Based on the recorded peak test force and the measured flow channel width and length, calculate the local stress in the flow field region of the molding plate. The formula for calculating local stress is: σ = F / (n(L×W)), where σ is the local stress (i.e., compressive strength, unit: MPa), F is the peak test force (i.e., breaking load value, unit: N), n is the number of flow channels, L is the flow channel length (unit: mm), and W is the flow channel width (unit: mm). Substitute the relevant data into the above formula to calculate the local stress in the flow field region of the molding plate.

[0040] 4. Failure Mode Identification: Test the intrinsic compressive strength of the material of the same size plain plate sample (without flow channels). If the local stress of the sample is less than the intrinsic compressive strength of the material, it indicates that the failure is caused by structural buckling; if the local stress of the sample is approximately equal to the intrinsic compressive strength of the material, it indicates that the failure is caused by insufficient material strength.

[0041] Example 1 Cut a 0.8mm thick molded plate (graphite molded monopolar plate) into 10mm × 10mm dimensions (ensuring the ridges of the flow channels are intact and exist in whole numbers during cutting). Place the sample on the stage of a 3D profilometer and measure the width and length of the flow channels. Place the sample between two smooth flat plate clamps, positioning it at the center of the working surface of the electronic universal testing machine. Start the electronic universal testing machine and apply a load continuously and uniformly at a displacement control speed of 1mm / min until the sample fails or yields, and read the corresponding fracture load value.

[0042] A 0.8mm thick, smooth plate of the same material (without flow channels) is cut into 10mm × 10mm dimensions. An electronic universal testing machine is started, and a load is continuously and uniformly applied at a displacement control speed of 1mm / min until the specimen fails or yields. The corresponding fracture load value is then recorded. The failure mode is determined based on the fracture load value.

[0043] Example 2 Cut a 0.8mm thick molded plate (graphite molded monopolar plate) into 10mm × 10mm dimensions (ensuring the spine of the flow channel is intact and exists in whole numbers during cutting). Place it on the stage of a 3D profilometer and measure the width and length of the sample flow channel. Place the sample between two smooth flat plate clamps, positioning it at the center of the working surface of the electronic universal testing machine. Start the electronic universal testing machine and continuously and uniformly apply the load at a displacement control speed of 3mm / min until the sample fails or yields, and read the corresponding fracture load value.

[0044] A 0.8mm thick, smooth plate of the same material (without flow channels) is cut into 10mm × 10mm dimensions. An electronic universal testing machine is started, and a load is continuously and uniformly applied at a displacement control speed of 3mm / min until the specimen fails or yields. The corresponding fracture load value is then recorded. The failure mode is determined based on the fracture load value.

[0045] Example 3 Cut a 0.8mm thick molded plate (graphite molded monopolar plate) into 10mm × 10mm dimensions (ensuring the spine of the flow channel is intact and exists in whole numbers during cutting). Place it on the stage of a 3D profilometer and measure the width and length of the sample flow channel. Place the sample between two smooth flat plate clamps, positioning it at the center of the working surface of the electronic universal testing machine. Start the electronic universal testing machine and apply a load continuously and uniformly at a displacement control speed of 5mm / min until the sample fails or yields, and read the corresponding fracture load value.

[0046] A 0.8mm thick, smooth plate of the same material (without flow channels) is cut into 10mm × 10mm dimensions. An electronic universal testing machine is started, and a load is continuously and uniformly applied at a displacement control speed of 1mm / min until the specimen fails or yields. The corresponding fracture load value is then recorded. The failure mode is determined based on the fracture load value.

[0047] Example 4 Cut the 0.86mm thick molded plate (graphite molded monopolar plate) into 10mm × 10mm dimensions (ensuring the ridges of the flow channels are intact and exist in whole numbers during cutting). Place the sample on the stage of a 3D profilometer and measure the width and length of the flow channels. Place the sample between two smooth flat plate clamps, positioning it at the center of the working surface of the electronic universal testing machine. Start the electronic universal testing machine and continuously and uniformly apply the load at a displacement control speed of 1mm / min until the sample fails or yields, and read the corresponding fracture load value.

[0048] A 0.86mm thick, smooth plate of the same material (without flow channels) is cut into 10mm × 10mm dimensions. The electronic universal testing machine is started, and a load is continuously and uniformly applied at a displacement control speed of 1mm / min until the specimen fails or yields. The corresponding fracture load value is then read. The failure mode is determined based on the fracture load value.

[0049] Example 5 Cut the 0.86mm thick molded plate (graphite molded monopolar plate) into 10mm × 10mm dimensions (ensuring the spine of the flow channel is intact and exists in whole numbers during cutting). Place it on the stage of a 3D profilometer and measure the width and length of the sample flow channel. Place the sample between two smooth flat plate clamps, positioning it at the center of the working surface of the electronic universal testing machine. Start the electronic universal testing machine and apply the load continuously and uniformly at a displacement control speed of 3mm / min until the sample fails or yields, and read the corresponding fracture load value.

[0050] A 0.86mm thick, smooth plate of the same material (without flow channels) is cut into 10mm × 10mm dimensions. An electronic universal testing machine is started, and a load is continuously and uniformly applied at a displacement control speed of 3mm / min until the specimen fails or yields. The corresponding fracture load value is then recorded. The failure mode is determined based on the fracture load value.

[0051] Example 6 Cut the 0.86mm thick molded plate (graphite molded monopolar plate) into 10mm × 10mm dimensions (ensuring the ridges of the flow channels are intact and exist in whole numbers during cutting). Place the sample on the stage of a 3D profilometer and measure the width and length of the flow channels. Place the sample between two smooth flat plate clamps, positioning it at the center of the working surface of the electronic universal testing machine. Start the electronic universal testing machine and apply the load continuously and uniformly at a displacement control speed of 5mm / min until the sample fails or yields, and read the corresponding fracture load value.

[0052] A 0.86mm thick, smooth plate of the same material (without flow channels) is cut into 10mm × 10mm dimensions. An electronic universal testing machine is started, and a load is continuously and uniformly applied at a displacement control speed of 5mm / min until the specimen fails or yields. The corresponding fracture load value is then recorded. The failure mode is determined based on the fracture load value.

[0053] The detection data for each embodiment are shown in Tables 1 and 2 below. The detection results for each embodiment are illustrated in the figures below. Figures 1-18 As shown, where, Figures 1-3 The images shown are the 3D contour scan, fracture peak image, and intrinsic fracture peak image of the sample in Example 1, respectively. Figures 4-6 The images shown are the 3D contour scan, fracture peak image, and intrinsic fracture peak image of the sample in Example 2, respectively. Figures 7-9 These are the 3D contour scan image, fracture peak image, and intrinsic fracture peak image of the sample in Example 3, respectively. Figures 10-12 These are the 3D contour scan image, fracture peak image, and intrinsic fracture peak image of the sample in Example 4, respectively. Figures 13-15 The images shown are the 3D contour scan, fracture peak image, and intrinsic fracture peak image of the sample in Example 5, respectively. Figures 16-18 These are the 3D contour scan, fracture peak image, and intrinsic fracture peak image of the sample in Example 6, respectively.

[0054] Table 1. Local stress data of the samples Table 2. Intrinsic Strength Data of Materials Based on the above test data, it can be seen that the local stress is less than the intrinsic compressive strength of the material, and the failure mode is structural buckling.

Claims

1. A method for detecting local stress in a flow field region of a fuel cell molded plate, characterized by, Includes the following steps: (1) Sample size measurement: Measure the width and length of the flow channel of the molded plate sample; (2) Peak fracture test of sample: Place the molded plate sample with completed dimensional measurement on the stage of the electronic universal testing machine. After starting, apply pressure to the molded plate sample until the electronic universal testing machine shows a peak value. Record the peak test force at this time. (3) Local stress calculation: Based on the peak test force recorded in step (2) and the width and length of the flow channel measured in step (1), calculate the local stress in the flow field area of ​​the molded plate.

2. The method of claim 1, wherein the step of detecting the local stress of the flow field region of the fuel cell pressboard is characterized by: In step (1), the width and length of the flow channel of the molded plate sample are measured using a 3D profilometer.

3. The method of claim 1, wherein the step of detecting the local stress of the flow field region of the fuel cell pressboard is characterized by: In step (2), during the peak fracture test of the sample, after the electronic universal testing machine is started, pressure is applied to the molded plate sample at a loading rate of 1~5 mm / min.

4. The method of claim 1, wherein the step of detecting the local stress of the flow field region of the fuel cell pressboard is characterized by: In step (2), the peak value that appears in the electronic universal testing machine is the fracture load value corresponding to the failure or yielding of the molded plate sample.

5. The method of claim 1, wherein the step of detecting the local stress of the flow field region of the fuel cell pressboard is characterized by: In step (3), the formula for calculating local stress is: σ=F / (n(L×W) ), Where σ is the local stress, F is the peak test force, n is the number of flow channels, L is the flow channel length, and W is the flow channel width.

6. The method of claim 5, wherein the step of detecting the local stress of the flow field region of the fuel cell pressboard is characterized by: The unit of local stress σ is MPa, the unit of peak test force F is N, the unit of flow channel length L is mm, and the unit of flow channel width W is mm.

7. The method of claim 1, wherein the step of detecting the local stress of the flow field region of the fuel cell pressboard is characterized by: The molded plate sample to be tested is a graphite molded monopolar plate.

8. The method of claim 1, wherein the step of detecting the local stress of the flow field region of the fuel cell pressboard is characterized by: The local stress in the flow field region of the fuel cell molded plate is less than the intrinsic compressive strength of the material of the molded plate sample.

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