Four-point bending test method
Through the four-point bending test method, the test environment and loading conditions are controlled and the test data is corrected, which solves the problem that the existing test methods cannot ensure the safe flight of the aircraft, and achieves higher-precision test results.
Patent Information
- Application Number
- CN202510712825.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-30
- Publication Date
- 2025-08-22
AI Technical Summary
The existing three-point bending test method cannot effectively ensure the safe flight of the DA40 NG aircraft. The simple four-point bending test method has data errors and cannot meet the aircraft's high-precision performance testing requirements.
The four-point bending test method is adopted to improve data accuracy by making the same test samples as the composite parts on the aircraft, controlling the test environment, accurately setting the fixtures and loading conditions, recording and correcting the test data, and using formulas to correct the load and deformation amount to improve data accuracy.
The test accuracy of aircraft housing components is improved, ensuring safe flight of the aircraft, reducing test errors through correction data, and meeting the testing standards for aircraft housing components of different types and specifications.
Smart Images
Figure CN120521995A_ABST
Abstract
Description
Technical field:
[0001] The present invention relates to the technical field of a four-point bending test method for composite materials, and more particularly to a four-point bending test method. Background technology:
[0002] Currently, the fuselage and wings (including the side and tail fins) of the DA40 NG aircraft are generally made of composite materials, primarily using multiple layers of fiber cloth, resin, and glue for curing. Before the DA40 NG is completed, it must meet certain performance requirements to ensure its safe flight. For example, the shells that make up the fuselage and wings must meet certain requirements. The current method for testing fiber material performance is the three-point bend test. The three-point bend test supports the specimen at both ends and applies a single concentrated load in the middle, forming a lateral bending force (existing shear force and bending moment). Because the maximum stress is concentrated near the loading point, local defects may be masked. The simple operation is only suitable for thin specimens or rapid testing in industrial production. The data from the three-point bend test cannot guarantee the safe flight of the DA40 NG aircraft, so a more precise performance test method is needed.
[0003] Therefore, some people have proposed the four-point bending test. In the four-point bending test, the specimen is supported at both ends, two load points are applied symmetrically, and the middle section forms pure bending (only bending moment, no shear force). The stress distribution is more uniform, which is suitable for thick specimens or scientific research sites that require higher precision. The current four-point bending test generally directly performs bending tests on a few simple specimens, and the test data is used to directly judge whether the composite performance requirements are met. However, for the DA40 NG aircraft (the DA40 NG aircraft is a small sports general aircraft), the four-point bending test of a few simple specimens and direct judgment based on test data (test data may have errors) still cannot fully and effectively guarantee flight safety. It is necessary to design a four-point bending test method with more complete test content and more accurate data judgment. Summary of the invention:
[0004] The purpose of the present invention is to address the shortcomings of the existing technology and provide a four-point bending test method, which has different test standards for aircraft shell components of different types and specifications. At the same time, it corrects the data based on the deviation of the test data set to improve the data accuracy and thus ensure the safe flight of the aircraft.
[0005] Four-point bending test method, the test steps are as follows:
[0006] Ⅰ. Spare parts: Test samples must be made of the same material as the composite parts on the aircraft and must be manufactured strictly in accordance with the design data requirements. Two of each test sample must be produced and marked "Sample A" and "Sample B" to distinguish them.
[0007] II. Status check before testing:
[0008] ① Vibration requirements: To avoid mechanical resonance of the testing machine, the test environment needs to control vibration, noise, collision and impact;
[0009] ② Electromagnetic requirements: The metal casing of the test machine controller, shielded wires, and related equipment must be connected to shielded protection grounding, and the high-frequency generator in the test environment must be shielded and protected;
[0010] ③. Temperature and humidity requirements: the temperature of the test environment is 10℃~35℃, and the relative humidity of the test environment is 20%~90%;
[0011] ④. Set the upper and lower fixtures of the testing machine to ensure that the upper and lower fixtures are in the same vertical plane, and that the two sets of pressure support points of the upper fixture and the two sets of support support points of the lower fixture are parallel. Then, install rulers on the upper and lower fixtures to determine the positions of the pressure support points and support support points respectively.
[0012] Ⅲ. Load the test sample and install it between the upper and lower fixtures of the testing machine. Different test samples use different support point spacings, and the spacing between the holding points remains unchanged.
[0013] IV. Test sample test, drive the upper fixture downward to load;
[0014] ① Preload setting: The preload is set to 1N~5N according to the surface flatness of the test sample, the preload speed is 5mm / min, and the preload time is within 60s. The surface flatness of some test samples can shorten the preload time.
[0015] ②. Sample measurement: Under preload, use a vernier caliper to measure the width and thickness of the test sample and record them;
[0016] ③. Loading setting: the upper fixture continues to move downward for loading, the loading and moving speed is 10mm / min, and the force attenuation threshold for terminating the test is set to 15%, the force threshold for fracture detection is set to 0.1%, the number of data acquisitions for fracture monitoring is set to 50, the force mutation is 5%, the negative strain gradient is 10%, and the positive strain gradient is 10%. The displacement interval of the data storage before fracture is 10um, the data storage time interval is 0.1s, and the data storage force interval is 1N. At the same time, the upper fixture of the test specimen is reset when it breaks;
[0017] When the test specimen breaks, record the results of the bending test, including elastic modulus, maximum force, deformation at maximum force, specimen thickness, specimen width, cross-sectional area, Fnom, Fcorr, Tnom, Bnom, and Ynom;
[0018] Ⅴ、Compare the test results, correct the load and deformation, take into account the deviation between the actual size and the nominal size, and make corrections to F nom The value of y nom The value of is corrected according to the following formula:
[0019]
[0020] Target value of load F tar and the target value y of deformation tar Calculated according to the following formula:
[0021] F tar =F corr ;
[0022]
[0023] The corrected load and corrected variable are then calculated and compared with the standard load and standard deformation of the corresponding standard sample.
[0024] Preferably, the types and sizes of the different test samples are as follows:
[0025]
[0026] The type and size of the standard sample are consistent with the type and size of the test sample respectively.
[0027] Preferably, when testing different test samples, the spacing between different support points is as follows:
[0028]
[0029]
[0030] The distance between the pressure support points is not 0.
[0031] Preferably, the upper and lower clamps on the testing machine are both provided with horizontal transverse groove rails, the holding fulcrum is located on the lower side of the groove rails on the upper clamp and is slidably connected to the groove rails; the supporting fulcrum is located on the upper side of the groove rails on the lower clamp and is slidably connected to the groove rails; the upper clamp is connected to a force sensor.
[0032] Preferably, the standard load, standard deformation and margin of the different standard samples are as follows;
[0033]
[0034] Numerical comparisons are performed between different types of standard samples and the corresponding test samples.
[0035] If the test machine is not in use for an extended period, it should be properly protected by a professional technician before use. The storage temperature range is -25°C to 55°C. Ensure that the storage environment is adequately ventilated and dehumidified. If stored for an extended period, the test machine should be sealed and packaged to ensure that no water accumulates in the packaging box in the presence of dripping water.
[0036] The beneficial effects of the present invention are:
[0037] This four-point bending test method has different test standards for aircraft shell components of different types and specifications. At the same time, it corrects the data based on the deviation of the test data set to improve the data accuracy and thus ensure the safe flight of the aircraft. Description of the drawings:
[0038] Figure 1 An Excel table that determines the corrected load based on the prepared formula;
[0039] Figure 2 An Excel table that determines the variables to be corrected based on the prepared formula;
[0040] Figure 3 It is a structural schematic diagram of the internal testing machine fixture of the present invention. Specific implementation method:
[0041] Example: Four-point bending test method, the test steps are as follows:
[0042] Ⅰ. Spare parts: Test samples must be made of the same material as the composite parts on the aircraft and must be manufactured strictly in accordance with the design data requirements. Two of each test sample must be produced and marked "Sample A" and "Sample B" to distinguish them.
[0043] II. Status check before testing:
[0044] ① Vibration requirements: To avoid mechanical resonance of the test machine, the test environment needs to control vibration, noise, collision and impact; shock absorbers should be installed in areas with large vibrations;
[0045] ② Electromagnetic requirements: The metal casing of the test machine controller, shielded wires, and related equipment must be connected to shielded protection grounding, and the high-frequency generator in the test environment must be shielded and protected;
[0046] ③. Temperature and humidity requirements: The test environment temperature is 10℃~35℃, and the suitable temperature range is 23℃±5℃; the relative humidity of the test environment is 20%~90%. It is recommended to install dehumidification equipment in areas with high humidity;
[0047] ④. Set the upper and lower fixtures of the testing machine to ensure that the upper fixture 1 and the lower fixture 2 of the testing machine are in the same vertical plane, and that the two sets of pressure support points 11 of the upper fixture 1 and the two sets of support support points 21 of the lower fixture are parallel. Then, respectively, install rulers on the upper fixture 1 and the lower fixture 2 to determine the positions of the pressure support points 11 and the support support points 21. The testing machine is provided with a frame, and a beam that is electrically driven to move up and down is provided in the frame. The lower fixture 2 is fixed to the bottom of the frame, and the upper fixture 1 is installed in the middle of the beam. A hard limit is provided during the movement of the beam. The hard limit limits the movement range of the beam in the testing machine frame. The setting of the hard limit must ensure that it includes and is greater than the movement range of the beam required for the test.
[0048] III. Load the test sample and install it between the upper and lower fixtures of the testing machine. Different test samples use different spacing between the support points 21, and the spacing between the holding support points 11 remains unchanged;
[0049] IV. Test sample test, drive the upper fixture downward to load;
[0050] ① Preload setting: The preload is set to 1N~5N according to the surface flatness of the test sample, the preload speed is 5mm / min, and the preload time is within 60s. The surface flatness of some test samples can shorten the preload time.
[0051] ②. Sample measurement: Under preload, use a vernier caliper to measure the width and thickness of the test sample and record them;
[0052] ③. Loading setting: the upper fixture continues to move downward for loading, the loading and moving speed is 10mm / min, and the force attenuation threshold for terminating the test is set to 15%, the force threshold for fracture detection is set to 0.1%, the number of data acquisitions for fracture monitoring is set to 50, the force mutation is 5%, the negative strain gradient is 10%, and the positive strain gradient is 10%. The displacement interval of the data storage before fracture is 10um, the data storage time interval is 0.1s, and the data storage force interval is 1N. At the same time, the upper fixture of the test specimen is reset when it breaks;
[0053] When the test specimen breaks, record the results of the bending test, including elastic modulus, maximum force, deformation at maximum force, specimen thickness, specimen width, cross-sectional area, Fnom (nominal load), Fcorr (corrected load), Tnom (nominal thickness of the L-layer component), Bnom (nominal width of the specimen), and Ynom (nominal deformation);
[0054] Ⅴ、Compare the test results, correct the load and deformation, take into account the deviation between the actual size and the nominal size, and make corrections to F nom The value of y nom The value of is corrected according to the following formula: tmeas is the actual thickness, b meas is the actual width;
[0055]
[0056] Target value of load F tar And the target value y of deformation tar Calculate according to the following formula: F tar =F corr , F tar is the target value of the load;
[0057] marginy / 100 is the deformation margin;
[0058] Then the corrected loads and corrected variables will be calculated, which can also be calculated based on Figure 1 and Figure 2 The Excel table with the formula shown is confirmed;
[0059] Compare the corrected load and variable with the standard load and standard deformation of the corresponding standard specimen. meas Greater than or equal to the reference value F tar (target value of load), F meas ≥F tar ; Corrected load F corr The deformation at (expressed in y meas F corr indicates) is less than or equal to the reference value y tar (target value of deformation), i.e. y meas F corr ≤y tar , that is, the composite performance requirements of the test sample;
[0060] And when y corr <y meas F corr ≤y tar When this occurs, the underlying cause needs to be investigated.
[0061] The types and sizes of the different test specimens are as follows:
[0062]
[0063] The type and size of the standard sample are consistent with the type and size of the test sample respectively.
[0064] When testing different test samples, the spacing between different support points 21 is as follows:
[0065] Type <![CDATA[Test fulcrum spacing l v (mm)]]> I 190 II 190 III 150 IV 110 V 110 VI 110
[0066] The distance between the pressing support points 11 is not zero.
[0067] like Figure 3 As shown, the upper clamp 1 and the lower clamp 2 on the testing machine are both provided with horizontal transverse groove rails, the holding fulcrum 11 is located on the lower side of the groove rail on the upper clamp 1 and is slidably connected to the groove rail; the supporting fulcrum 21 is located on the upper side of the groove rail on the lower clamp 2 and is slidably connected to the groove rail; the upper clamp 1 is connected to a force sensor.
[0068] The standard load, standard deformation and allowance of the different standard samples are as follows;
[0069]
[0070]
[0071] Numerical comparisons are performed between different types of standard samples and the corresponding test samples.
[0072] The embodiments are intended to illustrate the present invention and are not intended to limit the present invention. Any person skilled in the art may modify the embodiments without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be as set forth in the claims of the present invention.
Claims
1. Four-point bending test method, characterized by: The test steps are as follows: Ⅰ. Spare parts: Test samples must be made of the same material as the composite parts on the aircraft and must be manufactured strictly in accordance with the design data requirements. Two of each test sample must be produced and marked "Sample A" and "Sample B" to distinguish them. II. Status check before testing: ① Vibration requirements: To avoid mechanical resonance of the testing machine, the test environment needs to control vibration, noise, collision and impact; ② Electromagnetic requirements: The metal casing of the test machine controller, shielded wires, and related equipment must be connected to shielded protection grounding, and the high-frequency generator in the test environment must be shielded and protected; ③. Temperature and humidity requirements: the temperature of the test environment is 10℃~35℃, and the relative humidity of the test environment is 20%~90%; ④. Set the upper and lower fixtures of the testing machine to ensure that the upper fixture (1) and the lower fixture (2) of the testing machine are in the same vertical plane, and ensure that the two sets of pressure support points (11) of the upper fixture (1) and the two sets of support support points (21) of the lower fixture are parallel. Then, respectively install rulers on the upper fixture (1) and the lower fixture (2) to determine the positions of the pressure support points (11) and the support support points (21); III. Load the test sample and install the test sample between the upper and lower clamps of the testing machine. Different test samples use different spacings between the support points (21), and the spacing between the pressure support points (11) remains unchanged; IV. Test sample test, drive the upper fixture downward to load; ① Preload setting: The preload is set to 1N~5N according to the surface flatness of the test sample, the preload speed is 5mm / min, and the preload time is within 60s. The surface flatness of some test samples can shorten the preload time. ②. Sample measurement: Under preload, use a vernier caliper to measure the width and thickness of the test sample and record them; ③. Loading setting: the upper fixture continues to move downward for loading, the loading and moving speed is 10mm / min, and the force attenuation threshold for terminating the test is set to 15%, the force threshold for fracture detection is set to 0.1%, the number of data acquisitions for fracture monitoring is set to 50, the force mutation is 5%, the negative strain gradient is 10%, and the positive strain gradient is 10%. The displacement interval of the data storage before fracture is 10um, the data storage time interval is 0.1s, and the data storage force interval is 1N. At the same time, the upper fixture of the test specimen is reset when it breaks; When the test specimen breaks, record the results of the bending test, including elastic modulus, maximum force, deformation at maximum force, specimen thickness, specimen width, cross-sectional area, Fnom, Fcorr, Tnom, Bnom, and Ynom; Ⅴ、Compare the test results, correct the load and deformation, take into account the deviation between the actual size and the nominal size, and make corrections to F nom The value of y nom The value of is corrected according to the following formula: Target value of load F tar And the target value y of deformation tar Calculated according to the following formula: F tar =F corr ; The corrected load and corrected variable are then calculated and compared with the standard load and standard deformation of the corresponding standard sample.
2. The four-point bending test method according to claim 1, wherein: The types and sizes of the different test specimens are as follows: The type and size of the standard sample are consistent with the type and size of the test sample respectively.
3. The four-point bending test method according to claim 1, wherein: When testing different test samples, the spacing between different support points (21) is as follows: The distance between the pressing support points (11) is not zero.
4. The four-point bending test method according to claim 1, wherein: The upper fixture (1) and the lower fixture (2) on the testing machine are both provided with horizontal transverse groove rails, the holding fulcrum (11) is located at the lower side of the groove rail on the upper fixture (1) and is slidably connected to the groove rail; the supporting fulcrum (21) is located at the upper side of the groove rail on the lower fixture (2) and is slidably connected to the groove rail; the upper fixture (1) is connected to a force sensor.
5. The four-point bending test method according to claim 1, wherein: The standard load, standard deformation and allowance of the different standard samples are as follows; Numerical comparisons are performed between different types of standard samples and the corresponding test samples.
6. The four-point bending test method according to claim 1, wherein: If the test machine is not in use for an extended period, it should be properly protected by a professional technician before use. The storage temperature range is -25°C to 55°C. Ensure that the storage environment is adequately ventilated and dehumidified. If stored for an extended period, the test machine should be sealed and the packaging box should be protected from water accumulation in a dripping environment.