A method and testing system for evaluating the transverse compressive properties of carbon fiber filaments

Abstract

The application discloses a kind of method and test system for evaluating carbon fiber monofilament transverse compression performance, including test sample preparation, test parameter and environment setting, sample positioning and size measurement, compression test and data acquisition and performance parameter analysis and evaluation, realize the accurate evaluation of carbon fiber monofilament transverse compression performance.The present application can improve the uniformity of sample preparation and test stability, cut off the error transmission of indirect parameters, solve the pain points of inaccurate measurement and large data dispersion of traditional methods, greatly improve the detection accuracy and efficiency, suitable for carbon fiber performance evaluation in the field of aerospace and other fields.

Description

Technical Field

[0001] This invention relates to the field of material performance testing technology, specifically to a method and testing system for evaluating the transverse compressive properties of carbon fiber monofilaments. Background Technology

[0002] Carbon fiber reinforced resin matrix composites have become the core material for high-end structural components in aerospace, transportation, energy, and construction due to their excellent properties such as high specific strength, high specific modulus, and fatigue resistance. For example, the application of composite materials in aircraft structures continues to increase, marking a new stage in the engineering application of low-cost composite material technology. Currently, all models of aircraft in my country use carbon fiber composite components to varying degrees.

[0003] With the expansion of composite material applications and the accumulation of experience, damage resistance under low-energy impact has become a key bottleneck issue in the design of aircraft composite material structures. In low-velocity impact damage events of composite materials, the fracture mode of carbon fibers directly determines the degree of structural damage. Among these, transverse and axial compressive failure is one of the main fracture forms of carbon fiber laminates under low-velocity impact damage. Therefore, accurately obtaining the transverse compressive properties of carbon fibers (including transverse compressive strength and modulus) is not only crucial data support for optimizing carbon fiber production processes and improving the overall performance of composite materials, but also plays an irreplaceable role in ensuring the design reliability and operational safety of composite material components.

[0004] However, due to the extremely small diameter of carbon fiber monofilaments (only 5μm~10μm) and the complex phenomena such as buckling instability and torsional failure that easily occur during transverse compression loading, the accurate evaluation of the transverse compression performance of carbon fibers is extremely challenging. Currently, the mainstream testing methods for the transverse compression performance of carbon fibers in the industry are mainly divided into two categories: the classic parallel plate method and the self-built equipment testing method, but both of these testing methods have certain limitations.

[0005] The core principle of the classic parallel plate method is to use two parallel glass plates to clamp a carbon fiber monofilament, apply a lateral compressive load by suspending a weight through a lever system, and observe the interference fringe pattern using an optical microscope. The contact width between the fiber and the glass under different loads is used as the lateral deformation, and the lateral compressive modulus is indirectly estimated by combining parameters such as Poisson's ratio and longitudinal tensile modulus of the carbon fiber. However, this method has significant technical drawbacks: 1. Limited measurement accuracy: The contact width of the carbon fiber monofilament is only on the micrometer scale, and the resolution of conventional optical microscopes cannot meet the requirements for accurate measurement, easily introducing micrometer-level measurement errors, which directly affect the performance calculation results; 2. Inability to capture continuous deformation: Loading needs to be paused to observe the interference fringes statically, making it impossible to record the continuous deformation and damage evolution of the fiber during compression in real time, making it difficult to reflect the performance response under actual load; 3. Indirect calculation error transmission: The solution for the lateral compressive modulus depends on input parameters such as Poisson's ratio and longitudinal tensile modulus. If these parameters themselves have testing errors, they will be directly transmitted to the lateral compressive performance results through the calculation process, leading to a significant decrease in the accuracy of the evaluation.

[0006] For the self-built equipment testing method, the core principle is to replace the lower clamping plane with a smooth steel plane, use an electromagnetic actuator to achieve precise loading of the upper indenter, integrate a force sensor to directly measure the compressive force, and record the indenter displacement through a linear differential transformer (LVDT), eliminating the need for real-time microscope observation to reduce human interference. During testing, the carbon fiber monofilament is placed on the steel plane, and a load is applied through the electromagnetic actuator, simultaneously collecting load-displacement data, and combining it with a theoretical model to calculate the transverse compressive modulus and strength. However, this method still does not solve the core technical pain points: 1. Amplified deviation in the contact area of ​​the elastic material: For carbon fiber monofilaments with polymer coatings, the contact area expands under load, resulting in a significant amplification of the deviation between the indenter displacement and the actual fiber deformation, which cannot accurately reflect the intrinsic transverse compressive performance of the fiber; 2. Theoretical model assumptions deviate from reality: Performance calculations rely on ideal assumptions such as "uniform contact" and "linear material response," while in actual compression, fibers are prone to non-uniform deformation and local plastic damage. The difference between the ideal model and actual working conditions will seriously affect the accuracy and stability of the test results.

[0007] In addition, existing technologies not only have the above-mentioned defects in the testing process, but also lack standardized procedures in the sample preparation process: the current preparation of carbon fiber monofilament transverse compression samples mostly relies on manual operation, and key parameters such as the fixed position of the adhesive and the straightness of the monofilament are difficult to control, which can easily introduce sample defects and sample preparation errors, further leading to large dispersion and low reliability of test results.

[0008] In summary, existing methods for testing the transverse compression performance of carbon fibers have significant shortcomings in terms of measurement accuracy, continuous deformation capture capability, indirect calculation error control, adaptability to elastic materials, and standardization of sample preparation. These methods cannot meet the needs of high-end fields such as aerospace for accurate and efficient evaluation of the transverse compression performance of carbon fibers. Therefore, there is an urgent need to propose an integrated technical solution that can achieve standardized sample preparation and accurate testing. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a method and testing system for evaluating the transverse compressive properties of carbon fiber monofilaments.

[0010] This invention discloses a method for evaluating the transverse compressive properties of carbon fiber monofilaments, comprising:

[0011] Step 1, Test sample preparation: The carbon fiber bundle is pretreated by desizing, drying, splitting and cutting into monofilament segments of fixed length. The monofilament segments are fixed to the transparent substrate by using adhesive droplets at a preset interval, and at least two test points are formed on the monofilament segments on a single transparent substrate.

[0012] Step 2, Test Parameters and Environment Settings: Fix the test platform below the variable zoom high magnification optical observation component, set the lateral compression loading rate, and activate the vibration suppression component to control environmental vibration;

[0013] Step 3, Sample positioning and size measurement: Place the sample prepared in step 1 on the test platform, adjust the test platform so that the test point of the single filament segment is located in the center of the field of view of the micro planar indenter and the outline is clear. Through the cooperation of the variable focal length high magnification optical observation component and the image acquisition component, measure the diameter of the single filament segment and the contact length between the single filament segment and the micro planar indenter at each test point.

[0014] Step 4, Compression Test and Data Acquisition: Start the loading mechanism and apply radial compression load to the monofilament segment at the test point according to the loading rate set in Step 2. Simultaneously acquire compression load data, monofilament compression displacement data and real-time image data of the test point during the loading process until the monofilament segment shows transverse compression failure and stop loading.

[0015] Step 5, Performance Parameter Analysis and Evaluation: Based on the dimensional data from Step 3 and the test data from Step 4, the basic mechanical parameters are obtained through preset calculation formulas. After the stress in the contact area of ​​the indenter and the monofilament segment is corrected, the transverse compression modulus is solved by using a reverse iterative optimization algorithm, combined with the relationship between the corrected mechanical parameters and strain. The transverse compression strength is determined based on the maximum load before the monofilament segment is crushed, thus completing the test and evaluation of the transverse compression performance of the carbon fiber monofilament.

[0016] As a further improvement of the present invention, it also includes a determination of the validity of the test, which specifically includes:

[0017] Based on the real-time image data acquired in step 4, if the sample slips, carbon fiber monofilaments bridge between fixed points, or the load reaches the set maximum value but the sample does not crush during the loading process, the test is deemed invalid and the corresponding test data is discarded; if transverse compression failure or shear failure occurs during the loading process, the test is deemed valid and the performance parameters of the test data are analyzed and evaluated in step 5.

[0018] As a further improvement of the present invention, step 1 specifically includes:

[0019] The carbon fiber bundle wound on the carbon fiber shaft is introduced into the acetone bath to remove the sizing agent;

[0020] The carbon fiber bundles, after the sizing agent has been removed, are drawn from the acetone bath and dried in a dryer. They are then separated into multiple continuous monofilaments by an airflow splitting device.

[0021] Multiple continuous monofilaments are cut into monofilament segments of fixed length 20mm±2mm by a cutting device;

[0022] The dispensing device fixes the monofilament segment onto a transparent substrate with adhesive droplets at a preset spacing of 5mm to 7mm. After curing, the monofilament segment sample is prepared. In the prepared monofilament segment sample, a test point is formed between two adjacent adhesive droplets.

[0023] As a further improvement of the present invention, in step 2, the variable focal length high magnification optical observation component includes a top-view optical head and a variable high magnification objective lens, which are used in conjunction with a light source controller to adjust the brightness of the observation field of view;

[0024] The vibration suppression component is a vibration damping table, which is used to suppress the amplitude of environmental vibration to 0.1. the following.

[0025] As a further improvement of the present invention, in step 3, the diameter of the micro planar indenter is 50 mm. The micro planar indenter is made of diamond, has a hardness Hv > 8000, and a surface roughness Ra < 0.01. .

[0026] As a further improvement of the present invention, in step 3, the image acquisition component is a high-resolution image sensor, which is used to capture in real time the contact state between the test point and the micro planar indenter and the deformation process of the carbon fiber monofilament; when the monofilament section sample is crushed, the high-resolution image sensor records the failure mode of the carbon fiber monofilament fracture site.

[0027] As a further improvement of the present invention, in step 5, the performance parameter analysis and evaluation process specifically includes:

[0028] Step 51, Calculation of basic mechanical parameters: Based on the diameter of the single filament segment measured in Step 3. Contact length between monofilament and miniature planar indenter and the compressive load data collected in step 4 Single-filament compression displacement data The transverse compressive force, transverse compressive strain and transverse compressive stress per unit length of carbon fiber monofilament are calculated using preset calculation formulas.

[0029] Step 52, Contact area stress correction: Based on the basic mechanical parameters calculated in Step 51, combined with the single filament radius R, the transverse compressive correction stress σ′ of the carbon fiber single filament considering the influence of the contact area is obtained through the contact section half-width calculation formula and the correction stress calculation formula.

[0030] Step 53, Iterative optimization solution and strength determination: The transverse compressive modulus of the single filament segment specimen is solved by iterative optimization, and the transverse compressive strength is determined based on the maximum load before the single filament segment specimen is crushed, thus completing the performance evaluation.

[0031] As a further improvement of the present invention, in step 51, the specific calculation process includes:

[0032] According to the formula: Calculate the transverse compressive force per unit length of carbon fiber monofilament In the formula, To compress load data, This represents the contact length between the monofilament and the miniature planar indenter;

[0033] According to the formula: Calculate the transverse compressive strain of a carbon fiber monofilament In the formula, This is data on the compression displacement of a single filament. The diameter of a single carbon fiber filament;

[0034] According to the formula: Calculate the transverse compressive stress of a carbon fiber monofilament ;

[0035] In step 52, the specific calculation process includes:

[0036] According to the formula: Calculate the half-width b of the contact section between the carbon fiber monofilament and the micro planar indenter. m), where E is the transverse compressive modulus of a single carbon fiber filament;

[0037] According to the formula: Calculation of transverse compressive stress of carbon fiber monofilament considering the influence of the contact area In the formula, Transverse compressive stress of carbon fiber monofilament R is the radius of the carbon fiber monofilament, and b is the half-width of the contact section between the carbon fiber monofilament and the micro planar indenter.

[0038] As a further improvement of the present invention, in step 53, the transverse compressive modulus of the single filament segment sample is solved by an iterative optimization method. The specific calculation process includes:

[0039] Using the transverse compressive modulus E of the same type of carbon fiber monofilament in step 52 as the initial input, based on the formula Calculate the compressive modulus of carbon fiber monofilament In the formula, Correcting transverse compressive stress for carbon fiber monofilaments Transverse compressive strain of carbon fiber monofilament The slope of the linear segment of the curve;

[0040] Preliminary calculations As a new E value, the contact section plate width b value in step 52 is recalculated to obtain the contact section half-width b value and the corresponding corrected stress. value;

[0041] Based on the new corrected stress Solve again ;

[0042] Repeat the above iterative process until the results of two consecutive rounds of calculation are obtained. The magnitude of the change meets the preset stability threshold, and the final result is... The value is unaffected by changes in the initial transverse compressive modulus E of the same type of carbon fiber monofilament, thus obtaining the final transverse compressive modulus of the carbon fiber monofilament. value;

[0043] In step 53, the transverse compressive strength is determined based on the maximum load before the single-filament segment sample is crushed. The specific calculation process includes:

[0044] According to the formula: Calculate the transverse compressive strength of carbon fiber monofilament In the formula, This represents the maximum transverse compressive force of a single carbon fiber filament. This represents the contact length between the monofilament and the miniature planar indenter. It represents the diameter of a single carbon fiber filament.

[0045] This invention discloses a testing system for evaluating the transverse compressive properties of carbon fiber monofilaments, which is applied to the above-mentioned evaluation method and includes:

[0046] The sample preparation module includes a carbon fiber shaft, an acetone tank, a dryer, an airflow splitting device, a cutting device, and a dispensing device arranged in sequence. The acetone tank is used to remove the sizing from the carbon fiber bundle, the airflow splitting device is used to decompose the carbon fiber bundle into monofilaments, the cutting device is used to cut the monofilaments into monofilament segments of fixed length, and the dispensing device is used to fix the monofilament segments onto a transparent substrate at a preset interval, thus providing standardized samples for testing.

[0047] The test platform module includes a test platform, a vibration suppression component, and a sample positioning component. The vibration suppression component is used to control environmental vibration to ensure test stability. The sample positioning component is used to adjust the horizontal position and height of the test platform so that the test point of the single filament segment is accurately located in the center of the view area of ​​the micro planar indenter, providing a precise positioning basis for subsequent tests.

[0048] The synchronous optical imaging module includes a variable-focus high-magnification optical observation component and an image acquisition component. The variable-focus high-magnification optical observation component includes a top-view optical head and a variable high-magnification objective lens, used to clearly observe the sample and accurately measure the diameter of the single filament segment and the contact length between the single filament segment and the indenter. The image acquisition component is a high-resolution image sensor used to record the deformation process and failure mode image data of the single filament segment at the test point in real time.

[0049] An electromagnetic force-controlled micro-compression loading module includes a loading mechanism and a micro planar indenter. The loading mechanism applies a radial compressive load to a monofilament segment at a set loading rate. The micro planar indenter is used to directly contact the monofilament segment for loading, providing a loading basis for performance measurement.

[0050] The in-situ transverse compression performance measurement module includes a high-sensitivity force sensor and a high-precision displacement sensor. The two work together to collect load data and single-filament compression displacement data in situ during the compression process, so as to realize the real-time measurement of performance parameters.

[0051] The multi-performance data synchronous acquisition module is connected to the synchronous optical imaging module, the electromagnetic force-controlled micro-compression loading module, and the in-situ transverse compression performance measurement module respectively. It is used to synchronously summarize the acquired single filament segment size measurement data, real-time image data, load data, and displacement data to ensure the temporal consistency of multi-dimensional data.

[0052] The performance parameter reverse analysis module communicates with the multi-performance data synchronous acquisition module. It adopts a reverse iterative optimization algorithm, and solves the transverse compressive elastic modulus based on the synchronously acquired size data, load-displacement data and image data after contact area stress correction. It also determines the transverse compressive strength by combining the maximum load before the single filament segment is crushed.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0054] This invention constructs a closed-loop process of "sample preparation-positioning-loading-analysis," with each step closely linked and logically coherent, forming a standardized testing and evaluation system. It eliminates the need for complex auxiliary processes, enabling the complete operation from sample preparation to performance evaluation, thus improving testing efficiency and reducing operational complexity. Furthermore, it adapts to the testing needs of different specifications of carbon fiber monofilaments, accommodating both laboratory R&D and mass production testing scenarios, and possesses broad engineering applicability, solving the problems of fragmented and poorly adaptable testing processes in existing technologies.

[0055] This invention establishes a standardized sample preparation process, which involves desizing, drying, splitting, and cutting pre-treated monofilament segments. These segments are then fixed to a transparent substrate with adhesive droplets at preset intervals, forming at least two test points on each substrate. This design completely avoids the randomness of traditional manual sample preparation, ensuring the straightness and consistent positioning of the monofilaments. It reduces sample error from the source, providing a stable and standardized sample foundation for subsequent accurate testing, and solving the problem of large data dispersion caused by non-standard sample preparation in existing technologies.

[0056] This invention constructs a testing system of "environmental control - precise measurement - dynamic monitoring" by setting the loading rate and activating the vibration suppression component, measuring key dimensions with a high-magnification optical observation component, and simultaneously acquiring load, displacement, and real-time images. This avoids interference from environmental vibrations on microscopic testing, achieves precise measurement of micrometer-level dimensions such as single-wire diameter and contact length, and fully captures the continuous deformation and damage evolution during compression. It addresses the core pain points of traditional methods, such as low measurement accuracy and inability to monitor in real time, significantly improving the reliability of test data.

[0057] This invention constructs an analytical system of "basic calculation + contact area correction", which directly solves the basic mechanical parameters through measured load, displacement and size data, without relying on indirect parameters such as Poisson's ratio, thus cutting off the error transmission at the source. By introducing a correction algorithm that takes into account the influence of the contact area, the accuracy of the test results is further improved. Attached Figure Description

[0058] Figure 1 This is a flowchart of a method for evaluating the transverse compressive properties of carbon fiber monofilaments, as disclosed in one embodiment of the present invention.

[0059] Figure 2 The image shows a modified stress-strain relationship curve for the transverse compression of carbon fiber monofilaments, as disclosed in an embodiment of the present invention, for evaluating the transverse compressive properties of carbon fiber monofilaments.

[0060] Figure 3 This is a structural diagram of a testing system for evaluating the transverse compressive properties of carbon fiber monofilaments, as disclosed in one embodiment of the present invention.

[0061] Figure 4This is a structural diagram of the sample preparation module of a test system for evaluating the transverse compressive properties of carbon fiber monofilaments, as disclosed in an embodiment of the present invention.

[0062] Figure 5 This is a top view of a single-filament segment specimen of a test system for evaluating the transverse compressive properties of carbon fiber monofilaments, as disclosed in an embodiment of the present invention.

[0063] Figure 6 This is a side view of the structure of a single filament segment sample of a test system for evaluating the transverse compressive properties of carbon fiber monofilaments, as disclosed in an embodiment of the present invention.

[0064] Figure 7 This is a schematic diagram of the carbon fiber monofilament transverse compression performance testing device, which is part of a testing system for evaluating the transverse compression performance of carbon fiber monofilaments according to an embodiment of the present invention.

[0065] In the picture:

[0066] 1. Electromagnetic force controlled micro-compression loading module; 2. In-situ lateral compression performance measurement module; 3. Synchronous optical imaging module; 4. Multi-performance data synchronous acquisition module; 5. Performance parameter reverse analysis module; 6. Carbon fiber shaft; 7. Acetone tank; 8. Dryer; 9. Airflow splitting device; 10. Cutting device; 11. Glue dispensing device; 11-1. Glue droplets; 12. Sample collection system; 13. Single filament segment sample; 14. Transparent substrate; 15. Vibration damping stage; 16. XY axis moving platform; 17. Z axis moving platform; 18. Lower compression platform; 19. Variable high magnification objective lens; 20. Top-view optical head; 21. Miniature planar indenter; 22. Loading mechanism; 23. High-sensitivity force sensor; 24. High-precision displacement sensor; 25. High-resolution image sensor; 26. Light source controller; 27. Control unit. Detailed Implementation

[0067] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0068] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0069] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0070] The present invention will now be described in further detail with reference to the accompanying drawings:

[0071] like Figure 1 As shown, the evaluation method for assessing the transverse compressive properties of carbon fiber monofilaments according to the present invention includes:

[0072] Step 1, Test sample preparation: The carbon fiber bundle is pretreated by desizing, drying, splitting and cutting into single filament segments of fixed length. The single filament segments are fixed to the transparent substrate 14 by using adhesive droplets at a preset interval. Each single filament segment on the transparent substrate 14 forms at least two test points.

[0073] In step 1, preferably, the following are specifically included:

[0074] The carbon fiber bundle wound on the carbon fiber shaft 6 is introduced into the acetone tank 7 to remove the sizing agent;

[0075] The carbon fiber bundles with the sizing agent removed are drawn out from the acetone tank 7 and dried in the dryer 8, and then enter the airflow splitting device 9 to be decomposed into multiple continuous monofilaments.

[0076] Multiple continuous monofilaments are cut into monofilament segments of fixed length 20mm±2mm by the cutting device 10;

[0077] The dispensing device 11 fixes the monofilament segment onto the transparent substrate 14 with adhesive droplets at a preset spacing of 5mm to 7mm. After curing, the monofilament segment sample 13 is prepared. In the prepared monofilament segment sample 13, a test point is formed between two adjacent adhesive droplets 11-1. In this embodiment, a liquid resin that cures rapidly at room temperature is selected as the fast-curing resin, and a curing time of 5min to 10min is recommended.

[0078] The prepared monofilament segment sample 13 is temporarily stored in the sample collection system 12.

[0079] Step 2, Test Parameters and Environment Settings: Fix the test platform below the variable zoom high magnification optical observation component, set the lateral compression loading rate, and activate the vibration suppression component to control environmental vibration;

[0080] In step 2, preferably, the variable-focus high-magnification optical observation assembly includes a top-view optical head 20 and a variable-magnification objective lens 19, which, in conjunction with a light source controller 26, adjust the brightness of the observation field of view; the vibration suppression assembly is a vibration damping table 15, which is used to suppress the amplitude of environmental vibrations to 0.1. the following.

[0081] In this step, preferably, the lateral compression loading rate is 7 mN / s.

[0082] Step 3, Sample positioning and size measurement: Place the sample prepared in step 1 on the test platform, adjust the test platform so that the test point of the single filament segment is located in the center of the field of view of the micro planar indenter 21 and the outline is clear. Through the cooperation of the variable focus high magnification optical observation component and the image acquisition component, measure the diameter of the single filament segment and the contact length between the single filament segment and the micro planar indenter 21 at each test point.

[0083] In step 3, preferably, the diameter of the miniature planar indenter 21 is 50 mm. The miniature planar indenter 21 is made of diamond, with a hardness Hv > 8000 and a roughness Ra < 0.01. The image acquisition component is a high-resolution image sensor 25, which is used to capture the contact state between the test point and the miniature planar indenter and the deformation process of the carbon fiber monofilament in real time. After the monofilament segment sample 13 is crushed, the high-resolution image sensor 25 records the failure mode of the carbon fiber monofilament fracture site. The failure mode includes effective failure mode and ineffective failure mode. The effective failure mode includes transverse compression failure and shear failure. The ineffective failure mode includes sample slippage during loading, bridging of the carbon fiber monofilament between the fixed adhesive joints (incomplete contact with the transparent substrate), and failure of the sample to crush when the load reaches the set maximum compressive force.

[0084] Step 4, Compression Test and Data Acquisition: Start the loading mechanism and apply radial compression load to the monofilament segment at the test point according to the loading rate set in Step 2. Simultaneously acquire compression load data, monofilament compression displacement data and real-time image data of the test point during the loading process until the carbon fiber monofilament shows transverse compression failure and stop loading.

[0085] Step 5, Performance Parameter Analysis and Evaluation: Based on the dimensional data from Step 3 and the test data from Step 4, the basic mechanical parameters are obtained through preset calculation formulas. After the stress in the contact area of ​​the indenter and the monofilament segment is corrected, the transverse compression modulus is solved by using a reverse iterative optimization algorithm, combined with the relationship between the corrected mechanical parameters and strain. The transverse compression strength is determined based on the maximum load before the monofilament segment is crushed, thus completing the test and evaluation of the transverse compression performance of the carbon fiber monofilament.

[0086] Step 5 specifically includes:

[0087] Step 51, Calculation of basic mechanical parameters: Based on the diameter of the single filament segment measured in Step 3. Contact length between monofilament and miniature planar indenter and the compressive load data collected in step 4 Single-filament compression displacement data The transverse compressive force, transverse compressive strain, and transverse compressive stress per unit length of carbon fiber monofilament are calculated using preset calculation formulas. The specific calculation process includes:

[0088] According to the formula: Calculate the transverse compressive force per unit length of carbon fiber monofilament In the formula, To compress load data, This represents the contact length between the monofilament and the miniature planar indenter;

[0089] According to the formula: Calculate the transverse compressive strain of a carbon fiber monofilament In the formula, This is data on the compression displacement of a single filament. The diameter of a single carbon fiber filament;

[0090] According to the formula: Calculate the transverse compressive stress of a carbon fiber monofilament ;

[0091] Step 52, Contact Zone Stress Correction: Based on the fundamental mechanical parameters calculated in Step 51, and combined with the single filament radius R, the transverse compressive stress σ′ of the carbon fiber single filament considering the influence of the contact zone is obtained using the formula for calculating the half-width of the contact section and the formula for calculating the corrected stress. The specific calculation process includes:

[0092] According to the formula: Calculate the half-width b of the contact section between the carbon fiber monofilament and the micro planar indenter. m), where E is the transverse compressive modulus of a single carbon fiber of the same type (for example, for 300 grade, 700 grade and 800 grade carbon fibers, the recommended initial value of E is given, and the recommended values ​​are 7.5GPa, 8.0GPa and 8.5GPa respectively).

[0093] According to the formula: Calculation of transverse compressive stress of carbon fiber monofilament considering the influence of the contact area In the formula, Transverse compressive stress of carbon fiber monofilament R is the radius of the carbon fiber monofilament, and b is the half-width of the contact section between the carbon fiber monofilament and the micro planar indenter.

[0094] Step 53: Iterative Optimization Solution and Strength Determination: The transverse compressive modulus of the monofilament segment specimen is solved using an iterative optimization method, and the transverse compressive strength is determined based on the maximum load before crushing of the monofilament segment specimen, thus completing the performance evaluation. Specifically, the calculation process for solving the transverse compressive modulus of the monofilament segment specimen using an iterative optimization method includes:

[0095] Using the transverse compressive modulus E of the same type of carbon fiber monofilament in step 52 as the initial input, based on the formula Calculate the compressive modulus of carbon fiber monofilament In the formula, Correcting transverse compressive stress for carbon fiber monofilaments Transverse compressive strain of carbon fiber monofilament The slope of the linear segment of the curve, The specific calculation method for the value is as follows: ;

[0096] Preferably, in this step, the transverse compressive strain is used. For the horizontal axis, the corrected stress for lateral compression. Using the vertical axis as the ordinate, the strain and corrected stress data points corresponding to different compression stages are fitted together to obtain the transverse compressive corrected stress of the carbon fiber monofilament. Transverse compressive strain of carbon fiber monofilament Relationship curve (e.g.) Figure 2 As shown), by observing the curve characteristics, the curve segment corresponding to strain 10% to 20% was selected as the linear segment, within which the transverse compressive corrected stress is measured. With transverse compressive strain It exhibits a linear response relationship, which can eliminate the interference of initial contact nonlinearity and subsequent plastic deformation, ensuring the accuracy of subsequent modulus calculations.

[0097] Preliminary calculations As a new E value, the half-width b value of the contact segment in step 52 is recalculated to obtain the half-width b value of the contact segment and the corresponding corrected stress. value;

[0098] Based on the new corrected stress Solve again ;

[0099] Repeat the above iterative process until the results of two consecutive rounds of calculation are obtained. The magnitude of the change meets the preset stability threshold, and the final result is... The value is unaffected by changes in the initial transverse compressive modulus E of the same type of carbon fiber monofilament, thus obtaining the final transverse compressive modulus of the carbon fiber monofilament. value.

[0100] In step 53, the transverse compressive strength is determined based on the maximum load before the single-filament segment specimen is crushed. The specific calculation process includes:

[0101] According to the formula: Calculate the transverse compressive strength of carbon fiber monofilament In the formula, This represents the maximum transverse compressive force of a single carbon fiber filament. This represents the contact length between the monofilament and the miniature planar indenter. It represents the diameter of a single carbon fiber filament.

[0102] In the above embodiments, preferably, the test validity determination is also included, which specifically includes: based on the real-time image data collected in step 4, if the sample slips, carbon fiber monofilaments bridge between fixed points, or the load reaches the set maximum value but the sample does not crush during the loading process, the test is determined to be invalid and the corresponding test data is discarded; if transverse compression failure or shear failure occurs during the loading process, the test is determined to be valid and the test data is analyzed and evaluated for performance parameters in step 5.

[0103] In the above embodiments, preferably, the number of tests in each group is not less than 25.

[0104] like Figure 3-7 As shown, another test system for evaluating the transverse compressive properties of carbon fiber monofilaments according to the present invention, applied to the above-mentioned evaluation method, includes:

[0105] The sample preparation module includes a carbon fiber shaft 6, an acetone tank 7, a dryer 8, an airflow splitting device 9, a cutting device 10, and a dispensing device 11 arranged in sequence. The acetone tank 7 is used to desizing the carbon fiber bundle, the airflow splitting device 9 is used to decompose the carbon fiber bundle into monofilaments, the cutting device 10 is used to cut the monofilaments into monofilament segments of fixed length, and the dispensing device 11 is used to fix the monofilament segments onto the transparent substrate 14 at a preset interval, so as to provide standardized monofilament segment samples 13 for testing.

[0106] The test platform module includes a test platform, a vibration suppression component, and a sample positioning component. The vibration suppression component includes a damping table 15, which controls environmental vibration to ensure test stability. The sample positioning component adjusts the horizontal position and height of the test platform, ensuring the test point of the single filament segment is precisely located at the center of the micro-plane indenter's field of view, providing a precise positioning basis for subsequent testing. The sample positioning component includes a Z-axis moving platform 17 mounted on the test platform, an XY-axis moving platform 16 mounted on the Z-axis moving platform 17, and a lower compression platform 18 mounted on the XY-axis moving platform 16. The lower compression platform 18 forms a fixing part for placing and fixing the single filament segment sample 13. The lower compression platform 18 can be adjusted horizontally (forward / backward, left / right) and vertically (up / down) via the XY-axis moving platform 16 and the Z-axis moving platform 17 to meet the high-precision positioning and focusing requirements of the single filament segment sample 13. In this embodiment, the stiffness of the lower compression platform 18 is much greater than the stiffness of the tested carbon fiber single filament to ensure that the compression displacement data truly reflects the sample deformation, rather than system deformation.

[0107] The synchronous optical imaging module 3 includes a variable-focus high-magnification optical observation component and an image acquisition component mounted on the test platform. The variable-focus high-magnification optical observation component includes a top-view optical head 20 and a variable high-magnification objective lens 19, which are used to clearly observe the sample and accurately measure the diameter of the single filament segment and the contact length between the single filament segment and the indenter. The image acquisition component is a high-resolution image sensor 25, which is used to record the deformation process and failure mode image data of the single filament segment at the test point in real time.

[0108] The electromagnetic force-controlled micro-compression loading module 1 includes a loading mechanism 22 and a micro-plane indenter 21. The loading mechanism 22 applies a radial compressive load to the test point of the monofilament segment sample 13 located on the lower compression platform 18 at a set loading rate. The micro-plane indenter 21 is used to directly contact the monofilament segment sample 13 for loading, providing a loading basis for performance measurement.

[0109] The in-situ transverse compression performance measurement module 2 includes a high-sensitivity force sensor 23 and a high-precision displacement sensor 24. The two work together to collect load data and single-filament compression displacement data in the in-situ compression process, so as to realize the real-time measurement of performance parameters.

[0110] The multi-performance data synchronous acquisition module 4 includes a control unit 27, which is connected to the synchronous optical imaging module 3, the electromagnetic force-controlled micro-compression loading module 1, and the in-situ transverse compression performance measurement module 2 respectively. It is used to synchronously summarize the acquired single filament segment size measurement data, real-time image data, load data, and displacement data to ensure the time consistency of multi-dimensional data.

[0111] The performance parameter reverse analysis module 5 communicates with the multi-performance data synchronous acquisition module 4. It adopts a reverse iterative optimization algorithm, and solves the transverse compressive elastic modulus based on the synchronously acquired size data, load-displacement data and image data after contact area stress correction. It also determines the transverse compressive strength by combining the maximum load before the single filament segment is crushed.

[0112] Example

[0113] As shown in Table 1, this embodiment conducted transverse compression performance tests on carbon fiber monofilaments of different grades / specifications, namely 300 grade (3K), 700 grade (3K), and 800 grade (12K), using the aforementioned evaluation method and testing system. The results showed that the compression strength and compression modulus dispersion coefficients of each grade of carbon fiber monofilament were at a low level (≤6.8%). This demonstrates that the testing system and evaluation method provided by this invention have stable and reliable test results for different batches and grades.

[0114] Table 1. Test data on transverse compression properties of carbon fiber monofilaments

[0115]

[0116] The advantages of this invention are:

[0117] This invention constructs a closed-loop process of "sample preparation-positioning-loading-analysis," with each step closely linked and logically coherent, forming a standardized testing and evaluation system. It eliminates the need for complex auxiliary processes, enabling the complete operation from sample preparation to performance evaluation, thus improving testing efficiency and reducing operational complexity. Furthermore, it adapts to the testing needs of different specifications of carbon fiber monofilaments, accommodating both laboratory R&D and mass production testing scenarios, and possesses broad engineering applicability, solving the problems of fragmented and poorly adaptable testing processes in existing technologies.

[0118] This invention establishes a standardized sample preparation process, which involves desizing, drying, splitting, and cutting pre-treated monofilament segments. These segments are then fixed to a transparent substrate 14 with adhesive droplets at preset intervals, forming at least two test points on each substrate. This design completely avoids the randomness of traditional manual sample preparation, ensuring the straightness of the monofilaments and the consistency of their fixed positions. This reduces sample error from the source, providing a stable and standardized sample foundation for subsequent accurate testing and solving the problem of large data dispersion caused by non-standard sample preparation in existing technologies.

[0119] This invention constructs a testing system of "environmental control - precise measurement - dynamic monitoring" by setting the loading rate and activating the vibration suppression component, measuring key dimensions with a high-magnification optical observation component, and simultaneously acquiring load, displacement, and real-time images. This avoids interference from environmental vibrations on microscopic testing, achieves precise measurement of micrometer-level dimensions such as single-wire diameter and contact length, and fully captures the continuous deformation and damage evolution during compression. It addresses the core pain points of traditional methods, such as low measurement accuracy and inability to monitor in real time, significantly improving the reliability of test data.

[0120] This invention constructs an analytical system of "basic calculation + contact area correction", which directly solves the basic mechanical parameters through measured load, displacement and size data, without relying on indirect parameters such as Poisson's ratio, thus cutting off the error transmission at the source. By introducing a correction algorithm that takes into account the influence of the contact area, the accuracy of the test results is further improved.

[0121] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for evaluating the transverse compressive properties of carbon fiber monofilaments, characterized in that, include: Step 1, Test sample preparation: The carbon fiber bundle is pretreated by desizing, drying, splitting and cutting into monofilament segments of fixed length. The monofilament segments are fixed to the transparent substrate by using adhesive droplets at a preset interval, and at least two test points are formed on the monofilament segments on a single transparent substrate. Step 2, Test Parameters and Environment Settings: Fix the test platform below the variable zoom high magnification optical observation component, set the lateral compression loading rate, and activate the vibration suppression component to control environmental vibration; Step 3, Sample positioning and size measurement: Place the sample prepared in step 1 on the test platform, adjust the test platform so that the test point of the single filament segment is located in the center of the field of view of the micro planar indenter and the outline is clear. Through the cooperation of the variable focal length high magnification optical observation component and the image acquisition component, measure the diameter of the single filament segment and the contact length between the single filament segment and the micro planar indenter at each test point. Step 4, Compression Test and Data Acquisition: Start the loading mechanism and apply radial compression load to the monofilament segment at the test point according to the loading rate set in Step 2. Simultaneously acquire compression load data, monofilament compression displacement data and real-time image data of the test point during the loading process until the monofilament segment shows transverse compression failure and then stop loading. Step 5, Performance Parameter Analysis and Evaluation: Based on the dimensional data from Step 3 and the test data from Step 4, the basic mechanical parameters are obtained through preset calculation formulas; After the stress in the contact area of ​​the micro planar indenter and the single filament segment is corrected, the transverse compressive modulus is solved by using a reverse iterative optimization algorithm and combining the relationship between the corrected mechanical parameters and strain. The transverse compressive strength was determined based on the maximum load before the single filament segment was crushed, and the transverse compressive performance of the carbon fiber single filament was tested and evaluated. The stress correction in the contact area is achieved using the following formula: Calculation of transverse compressive stress of carbon fiber monofilament considering the influence of the contact area In the formula, R is the transverse compressive stress of the carbon fiber monofilament, R is the radius of the carbon fiber monofilament, and b is the half-width of the contact section between the carbon fiber monofilament and the micro planar indenter. The inverse iterative optimization algorithm specifically includes the following steps: Using the transverse compressive modulus E of a similar carbon fiber monofilament as the initial input, based on the formula Calculate the transverse compressive modulus of carbon fiber monofilament ,in Correcting transverse compressive stress for carbon fiber monofilaments Transverse compressive strain of carbon fiber monofilament The slope of the linear segment of the curve; Preliminary calculations As a new E value, the half-width b value of the contact section and the corresponding corrected stress are recalculated. value; Based on the new corrected stress Calculate again ; Repeat the above iterative process until the change in ET calculated in two adjacent rounds meets the preset stability threshold, and the final ET value is not affected by the initial E value, thus obtaining the final transverse compressive modulus ET of the carbon fiber monofilament.

2. The evaluation method according to claim 1, characterized in that, It also includes determining the validity of the test, which specifically includes: based on the real-time image data collected in step 4, if the sample slips, carbon fiber monofilaments bridge between fixed points, or the load reaches the set maximum value but the sample does not crush during the loading process, it is determined to be an invalid test and the corresponding test data is discarded; if transverse compression failure or shear failure occurs during the loading process, it is determined to be a valid test and the test data is analyzed and evaluated for performance parameters in step 5.

3. The evaluation method according to claim 1, characterized in that, Step 1 specifically includes: The carbon fiber bundle wound on the carbon fiber shaft is introduced into the acetone bath to remove the sizing agent; The carbon fiber bundles with the sizing agent removed are drawn out from the acetone tank and dried in a dryer, and then enter the airflow splitting device to decompose them into multiple continuous monofilaments. Multiple continuous monofilaments are cut into monofilament segments of fixed length 20mm±2mm by a cutting device; The dispensing device fixes the monofilament segment onto a transparent substrate with adhesive droplets at a preset spacing of 5mm to 7mm. After curing, the monofilament segment sample is prepared. In the prepared monofilament segment sample, a test point is formed between two adjacent adhesive droplets.

4. The evaluation method according to claim 1, characterized in that, In step 2, the variable focal length high magnification optical observation assembly includes a top-view optical head and a variable high magnification objective lens, which, together with a light source controller, adjust the brightness of the observation field of view. The vibration suppression component is a vibration damping table, which is used to suppress the amplitude of environmental vibration to 0.

1. the following.

5. The evaluation method according to claim 1, characterized in that, In step 3, the diameter of the miniature planar indenter is 50 mm. The micro planar indenter is made of diamond, has a hardness Hv > 8000, and a surface roughness Ra < 0.

01. .

6. The evaluation method according to claim 1, characterized in that, In step 3, the image acquisition component is a high-resolution image sensor, which is used to capture in real time the contact state between the test point and the micro planar indenter and the deformation process of the carbon fiber monofilament; when the monofilament segment sample is crushed, the high-resolution image sensor records the failure mode of the fracture site of the monofilament segment sample.

7. The evaluation method according to claim 1, characterized in that, In step 5, the performance parameter analysis and evaluation process specifically includes: Step 51, Calculation of basic mechanical parameters: Based on the diameter of the single filament segment measured in Step 3. Contact length between monofilament and miniature planar indenter and the compressive load data collected in step 4 Single-filament compression displacement data The transverse compressive force, transverse compressive strain and transverse compressive stress per unit length of carbon fiber monofilament are calculated using preset calculation formulas. Step 52, Contact area stress correction: Based on the basic mechanical parameters calculated in Step 51, combined with the single filament radius R, the transverse compressive correction stress σ′ of the carbon fiber single filament considering the influence of the contact area is obtained through the contact section half-width calculation formula and the correction stress calculation formula. Step 53, Iterative optimization solution and strength determination: The transverse compressive modulus of the single filament segment specimen is solved by iterative optimization, and the transverse compressive strength is determined based on the maximum load before the single filament segment specimen is crushed, thus completing the performance evaluation.

8. The evaluation method according to claim 7, characterized in that, In step 51, the specific calculation process includes: According to the formula: Calculate the transverse compressive force per unit length of carbon fiber monofilament In the formula, To compress load data, This represents the contact length between the monofilament and the miniature planar indenter; According to the formula: Calculate the transverse compressive strain of a carbon fiber monofilament In the formula, This is data on the compression displacement of a single filament. The diameter of a single carbon fiber filament; According to the formula: Calculate the transverse compressive stress of a carbon fiber monofilament ; In step 52, the specific calculation process includes: According to the formula: Calculate the half-width b of the contact section between the carbon fiber monofilament and the micro planar indenter, where E is the transverse compressive modulus of the same type of carbon fiber monofilament.

9. The evaluation method according to claim 7, characterized in that, In step 53, the transverse compressive strength is determined based on the maximum load before the single-filament segment sample is crushed. The specific calculation process includes: According to the formula: Calculate the transverse compressive strength of carbon fiber monofilament In the formula, This represents the maximum transverse compressive force of a single carbon fiber filament. This represents the contact length between the monofilament and the miniature planar indenter. It represents the diameter of a single carbon fiber filament.

10. A test system for evaluating the transverse compressive properties of carbon fiber monofilaments, applied to the evaluation method described in any one of claims 1-9, characterized in that, include: The sample preparation module includes a carbon fiber shaft, an acetone tank, a dryer, an airflow splitting device, a cutting device, and a dispensing device arranged in sequence. The acetone tank is used to remove the sizing from the carbon fiber bundle, the airflow splitting device is used to decompose the carbon fiber bundle into monofilaments, the cutting device is used to cut the monofilaments into monofilament segments of fixed length, and the dispensing device is used to fix the monofilament segments onto a transparent substrate at a preset interval, thus providing standardized samples for testing. The test platform module includes a test platform, a vibration suppression component, and a sample positioning component. The vibration suppression component is used to control environmental vibration to ensure test stability. The sample positioning component is used to adjust the horizontal position and height of the test platform so that the test point of the single filament segment is accurately located in the center of the view area of ​​the micro planar indenter, providing a precise positioning basis for subsequent tests. The synchronous optical imaging module includes a variable-focus high-magnification optical observation component and an image acquisition component. The variable-focus high-magnification optical observation component includes a top-view optical head and a variable high-magnification objective lens, used to clearly observe the sample and accurately measure the diameter of the single filament segment and the contact length between the single filament segment and the indenter. The image acquisition component is a high-resolution image sensor used to record the deformation process and failure mode image data of the single filament segment at the test point in real time. An electromagnetic force-controlled micro-compression loading module includes a loading mechanism and a micro planar indenter. The loading mechanism applies a radial compressive load to a monofilament segment at a set loading rate. The micro planar indenter is used to directly contact the monofilament segment for loading, providing a loading basis for performance measurement. The in-situ transverse compression performance measurement module includes a high-sensitivity force sensor and a high-precision displacement sensor. The two work together to collect load data and single-filament compression displacement data in situ during the compression process, so as to realize the real-time measurement of performance parameters. The multi-performance data synchronous acquisition module is connected to the synchronous optical imaging module, the electromagnetic force-controlled micro-compression loading module, and the in-situ transverse compression performance measurement module respectively. It is used to synchronously summarize the acquired single filament segment size measurement data, real-time image data, load data, and displacement data to ensure the temporal consistency of multi-dimensional data. The performance parameter reverse analysis module communicates with the multi-performance data synchronous acquisition module. It adopts a reverse iterative optimization algorithm, and solves the transverse compressive elastic modulus based on the synchronously acquired size data, load-displacement data and image data after contact area stress correction. It also determines the transverse compressive strength by combining the maximum load before the single filament segment is crushed.

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