System and method for evaluating transverse compression performance of carbon fiber monofilament

Abstract

The invention discloses a carbon fiber monofilament transverse compression performance evaluation system and method, and relates to the field of material mechanical property detection. The system comprises a carbon fiber monofilament micro sample preparation unit, a loading and synchronous acquisition unit, a failure mode validity judgment unit and a data processing and analysis unit, according to the method, through accurate sample preparation, real-time loading observation, image feature extraction and data correction, compression full-process monitoring is achieved, a damage mode is accurately judged, and performance parameters are calculated. The method solves the problems of large measurement error, insufficient continuity and the like in the prior art, improves the test accuracy and data comparability, is compatible with the actual surface state of the fiber, is easy to industrialize, and can provide reliable support for carbon fiber process optimization and composite material design in the fields of aerospace and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material performance detection, and particularly relates to a carbon fiber single wire transverse compression performance evaluation system and method. BACKGROUND

[0002] Carbon fiber reinforced resin matrix composite has become a key material for the main load-bearing structure (such as wings, tail, fuselage) of an aircraft due to its high specific strength, high specific modulus and excellent fatigue resistance. The resistance ability of carbon fiber to low-energy impact damage in service is the core consideration of structural integrity design. In the low-speed impact event, the carbon fiber not only bears axial load, but also is subjected to transverse compression, which easily causes fiber buckling, fracture and interlaminar delamination. Therefore, accurately characterizing the transverse compression mechanical response of carbon fiber single wire is crucial for understanding the impact damage mechanism of composite materials, optimizing the fiber-matrix interface design and improving the structure crashworthiness.

[0003] The current carbon fiber performance evaluation system (in accordance with GB / T3362, GB / T30019, GB / T29761) mainly covers linear density, tensile strength, bulk density, surface sizing amount and other performances. The test of transverse compression performance still relies on the classic parallel plate method and self-built equipment test method, both of which have significant technical defects. Among them, the classic parallel plate method uses two parallel glass plates to clamp the carbon single wire, applies a transverse static load by a lever suspended weight, observes the interference fringes in the contact area by an optical microscope, and indirectly deduces the transverse compression modulus by combining the Poisson's ratio and the longitudinal elastic modulus. There are three limitations: 1. Insufficient measurement accuracy: the diameter of carbon fiber single wire is only 5-10 μm, and the contact width change caused by transverse compression is sub-micron to micron, which is lower than the diffraction limit resolution of conventional optical microscopic system; 2. Unable to capture continuous response: relying on static photography analysis of the microscope, it needs to pause at the loading gap, and cannot obtain the complete load-deformation continuous curve, which breaks the time continuity of the mechanical response; 3. Indirect calculation error transmission: the Poisson's ratio and the longitudinal tensile modulus are used as input parameters, and if there is an error in these parameters, it will directly lead to the decrease of the reliability and comparability of the calculation results of the transverse compression modulus.

[0004] The self-built equipment test method replaces the lower glass plane with a steel plane, uses an electromagnetic driver to accurately load, integrates a force sensor and a linear variable differential transformer (LVDT) to record data, and reduces human interference, but still has key defects: 1. Poor model adaptability: the actual engineering carbon fiber is covered with elastic sizing agent on the surface, which will cause nonlinear compression and transverse spreading during compression, thus destroying the geometric and mechanical boundary conditions relied on the traditional model; 2. Deformation measurement distortion: the displacement sensor reading is directly equivalent to the transverse deformation of the fiber, without considering the system flexibility of the indenter and the support platform, the local bending effect of the fiber and the constraint stiffness of the glued fixed end, which leads to the deviation of the measured value from the true deformation state.

[0005] In summary, the prior art has significant deficiencies in measurement accuracy, continuous deformation capture capability, indirect calculation error control and actual fiber state representation capability, and is difficult to provide direct, in-situ and full-process mechanical data support, and cannot meet the requirements of composite material mesoscopic damage evolution mechanism research and structure impact resistance optimization. SUMMARY

[0006] In view of the deficiencies in the prior art, the present application provides a carbon fiber single filament transverse compression performance evaluation system and method.

[0007] The present application discloses a carbon fiber single filament transverse compression performance evaluation system, comprising: A carbon fiber single filament micro sample preparation unit, comprising a carbon fiber shaft, an acetone tank, a dryer, an airflow filament separation device, a cutting device, a glue dropping device, an online damage identification system and a sample collection system connected in sequence; the acetone tank is used for carbon fiber tow desizing, the dryer is used for drying the desized carbon fiber tow, the airflow filament separation device is used for decomposing the carbon fiber tow into carbon fiber single filaments or multiple parallel carbon fiber single filaments, the cutting device is used for cutting the carbon fiber single filaments or multiple parallel carbon fiber single filaments into carbon fiber single filament segments of a fixed length, the glue dropping device is used for fixing the carbon fiber single filament segments or multiple parallel carbon fiber single filament segments on a transparent substrate to form a sample, the online damage identification system is used for screening defect-free samples, and the sample collection system is used for collecting qualified samples; A loading and synchronous acquisition unit, comprising a high-precision displacement sensor, a Z-direction driving module, a high-precision force sensor, a plane pressure head, an upper plane pressure disc, a control system, a lateral observation imaging system, a self-centering lower plane pressure disc, an X-Y direction driving module and an active vibration isolation system; the high-precision displacement sensor is used for measuring micro deformation, the Z-direction driving module is used for driving the axial movement of the plane pressure head, the high-precision force sensor is used for measuring compression force, the lateral observation imaging system is used for capturing lateral deformation, the X-Y direction driving module is used for adjusting the sample position, and the active vibration isolation system is used for suppressing environmental vibration; A failure mode effectiveness determination unit, comprising an ultra-deep three-dimensional imaging system and an image processing system; the ultra-deep three-dimensional imaging system acquires a three-dimensional image of the sample, the image processing system extracts and analyzes the features of the original image, and determines the failure mode in combination with the load data; A data processing and analysis unit, comprising a control system, for receiving the load and displacement data of the loading and synchronous acquisition unit, the failure mode determination result and image feature parameters of the failure mode effectiveness determination unit, and calculating the transverse compression performance parameters of the carbon fiber single filament segment according to a preset formula.

[0008] As a further improvement of the present application, the super-depth-of-field three-dimensional imaging system comprises a high-precision piezoelectric objective lens displacement system and a high-performance optical microscope main body, wherein the high-performance optical microscope main body comprises an overhead observation objective lens with a zoom range of 25 times to 1000 times for sample size measurement and surface state observation. The high-precision piezoelectric objective lens displacement system can drive the high-performance optical microscope main body and the overhead observation objective lens therein to move slightly along the axial direction, realize the collection and splicing of images at different depths, and meet the super-depth-of-field observation requirement.

[0009] As a further improvement of the present application, the sample collection system comprises a detachable collection substrate tray, a micro vacuum pump and a micro transparent sealing cover. The detachable collection substrate tray is located directly below the qualified sample screened by the online damage identification system and is used for directly receiving the sample; the micro vacuum pump is arranged below the side of the detachable collection substrate tray and is in communication with the detachable collection substrate tray through a flexible pipeline, and the micro vacuum pump is used for generating a weak negative pressure in the detachable collection substrate tray to assist the orderly settlement of the sample on the detachable collection substrate tray; the micro transparent sealing cover is arranged directly above the detachable collection substrate tray, and the micro transparent sealing cover is initially in an open state and can be closed to cover the detachable collection substrate tray after the negative pressure adsorption is completed.

[0010] The application discloses a carbon fiber monofilament transverse compression performance evaluation method, which is applied to the carbon fiber monofilament transverse compression performance evaluation system. Step S1, preparing a carbon fiber monofilament transverse compression micro sample: carbon fiber tows are sequentially subjected to desizing, drying, filament separation and cutting treatment to obtain carbon fiber monofilament segments or multiple parallel carbon fiber monofilament segments with a fixed length; the carbon fiber monofilament segments or multiple parallel carbon fiber monofilament segments are fixed on a transparent substrate at a preset interval by using a glue dropping device, and a micro sample comprising at least two test points is formed on each carbon fiber monofilament segment; the micro sample is subjected to online damage identification to screen out samples without initial defects for standby use. Step S2, setting test parameters and environment: fixing the test platform under the super-depth-of-field three-dimensional imaging system, setting a transverse compression loading rate, and starting the active shock elimination system to suppress the environmental vibration amplitude to below 0.1 μm. Step S3, sample positioning and size measurement: placing the sample screened in step S1 on a self-centering lower plane pressure disc, adjusting the X-Y direction driving module to make the sample test point located at the center of the plane pressure head visual area, and measuring the diameter of the carbon fiber monofilament segment at the test point and the contact length of the carbon fiber monofilament segment and the plane pressure head through the overhead observation objective lens of the super-depth-of-field three-dimensional imaging system. ​​Step S4, transverse compression loading and data synchronous acquisition: start the Z-direction driving module, apply a radial compression load to the test point through the plane pressure head, and synchronously acquire the load data and the single-fiber compression displacement data during the compression process; when the compression load reaches 20% of the pre-judged maximum load threshold, trigger the lateral observation imaging system to capture the lateral deformation state of the sample, and extract the contact half-width and the fiber surface wrinkle depth of the contact area ; continuously load until the sample is crushed, and record the maximum compression force and the load-displacement curve; Step S5, failure mode validity determination and performance parameter calculation: through the image processing system in the failure mode validity determination unit, feature extraction is performed on the dual-view original images of the super-depth-of-field three-dimensional imaging system and the lateral observation imaging system, and the load-displacement curve is used to determine whether the sample failure mode is an effective failure mode; for the sample with an effective failure mode, based on the size data measured in step S3, the test data acquired in step S4, and the image feature parameters extracted by the image processing system, the transverse compression force, the transverse compression strain, the transverse compression stress, the transverse compression strength, and the transverse compression modulus of the carbon fiber single-fiber segment are calculated according to the preset formula.

[0011] As a further improvement of the present application, in the step S1, the desizing treatment is realized by introducing the carbon fiber tows into a acetone tank, the drying treatment is realized by a dryer, the filamentation treatment is realized by a airflow filamentation device to decompose the carbon fiber tows into carbon fiber single-fiber segments or multiple parallel carbon fiber single-fiber segments, the cutting treatment is realized by a cutting device to cut the carbon fiber single-fiber segments or multiple parallel carbon fiber single-fiber segments into carbon fiber single-fiber segments or multiple parallel carbon fiber single-fiber segments with a length of 20mm±2mm; the preset interval is 5mm~7mm.

[0012] As a further improvement of the present application, in the step S1, the online damage identification includes identifying micro-cracks, residual sizing agent accumulation, fiber twisting and buckling defects of the carbon fiber single-fiber segment by an online damage identification system; the online damage identification system includes a high-resolution optical microscope and a full-electric zoom coding identification system, the resolution of the high-resolution optical microscope is 1μm, which is used to capture the micro features of the carbon fiber single-fiber segment to provide the basis for defect imaging; the zoom range of the full-electric zoom coding identification system is 25 times to 1000 times, which is used to adapt to the observation needs of different defects through automatic zoom.

[0013] As a further improvement of the present application, in the step S1, the screened sample without initial defects is collected by a sample collection system, the sample collection system includes a detachable collection base tray, a micro vacuum pump and a micro transparent sealing cover. The micro vacuum pump generates weak negative pressure to assist sample settlement, and the micro transparent sealing cover is closed after negative pressure adsorption to preserve the sample.

[0014] As a further improvement of the present application, in the step S4: The material of the flat indenter is diamond, the hardness HV>8000, and the roughness Ra<0.01 μm; so as to avoid the interference of deformation of the flat indenter itself on the measurement of compression displacement; The lateral observation imaging system comprises a high-speed CCD camera, the frame rate of the high-speed CCD camera is ≥1000 fps, and the high-speed CCD camera is used to capture the lateral deformation at the moment of compression failure; the high-speed CCD camera is configured with a light source part and a focusing part, the light source part is used to assist the high-speed CCD camera to clearly acquire the image of the contact area, and the focusing part is used to adjust the imaging focal length of the high-speed CCD camera.

[0015] As a further improvement of the present application, in the step S5, the effective failure mode includes elastic crushing, micro buckling phenomenon and shear failure; The elastic crushing is that the load-displacement curve is linear until sudden fracture, and the fracture surface is perpendicular to the fiber axis; the micro buckling phenomenon is that the sinusoidal / wave-shaped surface wrinkle appears in the later stage of loading, the fracture is located at the wrinkle valley, and the load-displacement curve slightly fluctuates before the peak value; The shear failure is that the high-modulus fiber appears local bending band with an inclination >30°, and the fibers in the band are broken in a zigzag shape.

[0016] As a further improvement of the present application, in the step S5, the transverse compression force, transverse compression strain, transverse compression stress and transverse compression modulus of the carbon fiber monofilament segment are calculated according to a preset formula, and the specific calculation process comprises: According to the formula: the transverse compression force per unit length of the carbon fiber monofilament segment is calculated , wherein, is the transverse compression force applied on the carbon fiber monofilament segment; is the contact length between the carbon fiber monofilament segment and the indenter; According to the formula: the transverse compression strain of the carbon fiber monofilament segment is calculated , wherein, is the transverse compression displacement of the carbon fiber monofilament segment; is the depth of the wrinkle depression on the fiber surface of the contact area; is the diameter of the carbon fiber monofilament segment; According to the formula: the transverse compression stress of the carbon fiber monofilament segment is calculated ; According to the formula: Transverse compressive strength of carbon fiber monofilament segment is calculated , wherein, is the maximum transverse compressive force of the carbon fiber monofilament segment; According to the formula: Transverse compressive modulus of the carbon fiber monofilament segment is calculated , wherein, is the actual contact half-width of the carbon fiber monofilament segment in transverse compression, is the radius of the carbon fiber monofilament segment.

[0017] Compared with the prior art, the beneficial effects of the present application are: The present application can efficiently meet the measurement needs of transverse compression performance of carbon fiber monofilaments of different brands and specifications by setting a carbon fiber monofilament micro sample preparation unit, a loading and synchronous acquisition unit, a failure mode effectiveness determination unit and a data processing and analysis unit, and the technical advantages are obvious. In the sample preparation and test implementation, the uniformity and effectiveness of the multiple test points are ensured by accurately controlling the titration distance of the glue solution, the curing time and the online damage identification, and single or multiple parallel sampling is supported to improve the efficiency and avoid human errors. A high-precision electromagnetic drive device and a plane pressure head are used in the loading link, and a lateral observation imaging system and an ultra-depth three-dimensional imaging system are matched to realize real-time monitoring of the whole compression process, accurately capture the complete mechanical response and measure key parameters such as contact half-width and wrinkle depth, and solve the pain points of large measurement error and insufficient continuous deformation capture in the prior art.

[0018] By fusing dynamic correction technology and contact area correction algorithm, the present application constructs a "measurement-correction" closed loop to compensate for errors such as deformation of sizing agent on the fiber surface and system flexibility, and improves the accuracy of performance parameter calculation. Relying on the failure mode effectiveness determination module to filter effective data ensures that the results are reliable and that the data of different batches and brands are comparable, providing accurate support for carbon fiber process optimization and composite material design. In addition, the present application is compatible with the actual surface state of the fiber and does not require special pretreatment. The core components are based on mature technology and are easy to industrialize, and can be widely applied in the fields of aerospace, transportation, etc. It has important significance for understanding the mesoscopic damage of composite materials and optimizing the interface bonding, and has innovation and practicality. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a structural composition diagram of the carbon fiber monofilament transverse compression performance evaluation system disclosed by the first embodiment of the present application; Figure 2 is a structural schematic diagram of the carbon fiber monofilament micro sample preparation unit of the carbon fiber monofilament transverse compression performance evaluation system disclosed by the first embodiment of the present application; Figure 3 is a carbon fiber monofilament transverse compression micro sample schematic diagram of the carbon fiber monofilament transverse compression performance evaluation system disclosed by the first embodiment of the present application; Figure 4 The structure composition diagram of the loading and synchronous acquisition unit, the damage mode effectiveness determination unit, and the data processing and analysis unit of the carbon fiber monofilament transverse compression performance evaluation system disclosed in the first embodiment of the present application is shown in the figure. Figure 5 The method flowchart of the carbon fiber monofilament transverse compression performance evaluation method disclosed in an embodiment of the present application is shown in the figure. Figure 6 The structure schematic diagram of the carbon fiber monofilament micro sample preparation unit of the carbon fiber monofilament transverse compression performance evaluation system disclosed in the second embodiment of the present application is shown in the figure. Figure 7 The carbon fiber monofilament transverse compression micro sample schematic diagram of the carbon fiber monofilament transverse compression performance evaluation system disclosed in the second embodiment of the present application is shown in the figure.

[0020] In the figure: 1, carbon fiber shaft; 2, acetone tank; 3, dryer; 4, air flow filament separation device; 5, cutting device; 6, glue dropping device; 7, online damage identification system; 8, sample collection system; 8-1, micro transparent sealing cover; 8-2, detachable collection base tray; 8-3, micro vacuum pump; 9, transparent base plate; 10, carbon fiber monofilament section; 11, glue liquid drop; 12, super-depth three-dimensional imaging system; 13, overhead observation objective lens; 14, high-precision displacement sensor; 15, Z-direction driving module; 16, high-precision force sensor; 17, plane pressure head; 18, upper plane pressure disc; 19, control system; 20, lateral observation imaging system; 21, self-centering lower plane pressure disc; 22, sample; 23, image processing system; 24, X-Y direction driving module; 25, active shock elimination system; 26, light source part. DETAILED DESCRIPTION

[0021] To make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0022] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" are only for the purpose of description and cannot be understood as indicating or implying relative importance.

[0023] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0024] The present application will be further described in detail below in conjunction with the drawings: Example 1 As Figures 1-4As shown, the carbon fiber monofilament transverse compression performance evaluation system provided by the application comprises a carbon fiber monofilament micro sample preparation unit, a loading and synchronous acquisition unit, a failure mode validity determination unit, and a data processing and analysis unit. The carbon fiber monofilament micro sample preparation unit comprises, in sequence, a carbon fiber shaft 1, an acetone tank 2, a dryer 3, an airflow filament separation device 4, a cutting device 5, a glue dropping device 6, an online damage identification system 7, and a sample collection system 8. The acetone tank 2 is used for carbon fiber tow desizing, the dryer 3 is used for drying the desized carbon fiber tow, the airflow filament separation device 4 is used for decomposing the carbon fiber tow into carbon fiber monofilament segments 10, the cutting device 5 is used for cutting the carbon fiber monofilament or multiple parallel carbon fiber monofilaments into carbon fiber monofilament segments 10 of a fixed length, the glue dropping device 6 is used for fixing the carbon fiber monofilament segments 10 to a transparent substrate to form a sample 22, the online damage identification system 7 is used for screening defect-free samples 22, and the sample collection system 8 is used for collecting qualified samples 22. The loading and synchronous acquisition unit comprises a high-precision displacement sensor 14, a Z-direction driving module 15, a high-precision force sensor 16, a plane compression head 17, an upper plane compression disc 18, a control system 19, a lateral observation imaging system 20, a self-centering lower plane compression disc 21, an X-Y direction driving module 24, and an active shock isolation system 25. The high-precision displacement sensor 14 is used for measuring micro deformation, the Z-direction driving module is used for driving the axial movement of the plane compression head, the high-precision force sensor 16 is used for measuring compression force, the lateral observation imaging system 20 is used for capturing lateral deformation, the X-Y direction driving module 24 is used for adjusting the position of the sample 22, and the active shock isolation system 25 is used for suppressing environmental vibration. The failure mode validity determination unit comprises an ultra-deep three-dimensional imaging system 12 and an image processing system 23. The ultra-deep three-dimensional imaging system 12 acquires a three-dimensional image of the sample, the image processing system 23 extracts and analyzes the features of the original image, and determines the failure mode in combination with the load data. The data processing and analysis unit comprises the control system 19, which is used for receiving the load and displacement data of the loading and synchronous acquisition unit, the failure mode determination result and image feature parameters of the failure mode validity determination unit, and calculating the transverse compression performance parameters of the carbon fiber monofilament segment 10 according to a preset formula.

[0025] Specifically: As Figures 2-3 shown in the above embodiment, preferably, the ultra-deep three-dimensional imaging system 12 comprises a high-precision piezoelectric objective lens displacement system and a high-performance optical microscope main body. The high-performance optical microscope main body comprises an overhead observation objective lens, and the zoom range of the overhead observation objective lens is 25 times to 1000 times, so as to accurately measure the size and observe the surface state of the sample 22, and provide high-precision data guarantee for accurate measurement of compression displacement. The high-precision piezoelectric objective lens displacement system can drive the high-performance optical microscope main body and the overhead observation objective lens therein to move slightly along the axial direction, realize the acquisition and splicing of images at different depths, and meet the ultra-deep observation requirement.

[0026] In the above embodiment, preferably, the sample collection system 8 comprises a detachable collection substrate tray 8-2, a micro vacuum pump 8-3 and a micro transparent sealing cover 8-1; the detachable collection substrate tray 8-2 is located directly below the qualified sample 22 screened by the online damage identification system, and is used to directly receive the sample 22; the micro vacuum pump 8-3 is arranged below the side of the detachable collection substrate tray 8-2 and communicates with the detachable collection substrate tray 8-2 through a flexible pipeline, and the micro vacuum pump 8-3 is used to generate a weak negative pressure in the detachable collection substrate tray 8-2 to assist the sample 22 to orderly settle on the detachable collection substrate tray 8-2; the micro transparent sealing cover 8-1 is arranged above the detachable collection substrate tray 8-2, and the micro transparent sealing cover 8-1 is initially in an open state, and after the negative pressure adsorption is completed, the micro transparent sealing cover 8-1 can be closed to cover the detachable collection substrate tray 8-2.

[0027] As shown in Figure 3 In the above embodiment, preferably, the sample 22 is composed of a transparent substrate 9, a carbon fiber monofilament segment 10 and glue droplets 11, wherein the carbon fiber monofilament segment 10 is fixed on one transparent substrate 9 by using three glue droplets 11 through the glue dropping device 6, the length of the carbon fiber monofilament segment 10 is 20 mm±2 mm, the distance between adjacent two glue droplets 11 is controlled to be 5 mm~7 mm, and a test point is formed between adjacent two glue droplets 11, that is, there are two test points on the carbon fiber monofilament segment 10. In this embodiment, the fast-curing resin is selected to be a liquid resin which can be cured at room temperature, and the recommended curing time is 5 min~10 min. Figure 3 Fig. a is a plan view of the sample 22, and Fig. b is a side view of the sample 22.

[0028] As shown in Figure 4 In the above embodiment, preferably, the loading and synchronous acquisition unit, the damage mode effectiveness determination unit and the data processing and analysis unit jointly constitute the in-situ test device for the transverse compression performance of carbon fiber monofilament. The number of high-precision displacement sensors 14 is 2, and the two high-precision displacement sensors 14 are symmetrically distributed on the two sides of the upper plane pressure disc 18, so that the accurate measurement of micro deformation at the sub-micron precision level can be realized; the Z-direction driving module 15 can realize the accurate movement of the measurement system in the axial direction, the maximum measurement range of the high-precision force sensor 16 is 2000 mN, and the electromagnetic driving principle is adopted, so that the accurate measurement of micro force value can be realized.

[0029] In the above embodiment, preferably, the material of the plane pressure head 17 is diamond, the hardness , and the roughness , and the plane pressure head 17 has high parallelism, so as to ensure the reliability and stability of the compression system. The upper plane pressure disc 18 is directly connected with the plane pressure head 17, so as to ensure the uniformity and stability of the transverse compression force applied to the carbon fiber monofilament segment 10.

[0030] In the above embodiment, preferably, the control system 19 implements multi-performance data synchronous acquisition and performance parameter reverse analysis. The lateral observation imaging system 20 includes a high-speed CCD camera with a frame rate of ≥1000 fps, which is used to capture the lateral deformation at the moment of compression failure, and is configured with a light source part 26 for assisting the high-speed CCD camera to clearly obtain the contact area image and a focusing part for adjusting the imaging focal length of the high-speed CCD camera. That is, in the present embodiment, the lateral observation imaging system 20 can realize real-time monitoring of the compression process of the carbon fiber single filament section 10, can capture the compression deformation and damage evolution process in situ and in real time, avoids disturbing the sample during disassembly, realizes double-view imaging of the lateral compression process of the carbon fiber single filament section 10, facilitates verification of the failure mode and reconstruction of the three-dimensional features, avoids single-view blind area, and improves data reliability. Through the high-speed CCD camera, the compression failure moment can be captured; the pictures and videos of the compression failure process can be accurately captured, and the load and image information can be recorded synchronously, which facilitates analysis of the damage evolution process.

[0031] In the above embodiment, preferably, the lower surface of the self-centering lower plane pressure disc 21 is a spherical base, which can achieve the best balance between rigidity and self-centering, and ensure uniform stress on the sample 22. The rigidity of the upper plane pressure disc 18 and the self-centering lower plane pressure disc 21 is much greater than that of the measured carbon fiber single filament section 10, so as to ensure that the compression displacement data truly reflects the deformation of the sample rather than the deformation of the system. The image processing system 23 can synchronously perform optical imaging, display the actual surface state of the sample in real time, display the loading condition in real time, display the corresponding compression force and displacement curve in real time, and display the corresponding typical failure mode, so as to realize the judgment of the effectiveness of the failure mode.

[0032] In the above embodiment, preferably, the active anti-vibration system 25 is a vibration table, which can suppress the vibration amplitude to below 0.1 μm, ensuring the authenticity of the micro-compression displacement data.

[0033] As shown in Figure 5 According to the carbon fiber single filament lateral compression performance evaluation method provided by the present application, which is applied to the above-mentioned carbon fiber single filament lateral compression performance evaluation system, comprising: Step S1, preparing a carbon fiber single filament lateral compression micro sample: the carbon fiber tows are sequentially subjected to desizing, drying, filament separation and cutting treatment to obtain carbon fiber single filament sections 10 with a fixed length; the carbon fiber single filament sections 10 are fixed on a transparent substrate at a predetermined interval by using a glue dropping device, and a micro sample containing at least two test points is formed on each carbon fiber single filament section 10; the micro sample is subjected to online damage identification, and the sample without initial defects is selected for standby use; In step S1, the desizing process is achieved by introducing the carbon fiber bundle into the acetone tank 2, the drying process is achieved by the dryer 3, the fiber splitting process is achieved by the airflow fiber splitting device 4 to decompose the carbon fiber bundle into carbon fiber monofilament segments 10, and the cutting process is achieved by the cutting device 5 to cut the carbon fiber monofilament segments 10 into carbon fiber monofilament segments 10 with a length of 20mm±2mm; the preset spacing is 5mm~7mm.

[0034] In step S1, online damage identification includes identifying microcracks, residual sizing agent buildup, fiber torsion, and buckling defects in the carbon fiber monofilament segment 10 through an online damage identification system. The online damage identification system 7 includes a high-resolution optical microscope and a fully electric zoom coding identification system. The high-resolution optical microscope has a resolution of 1 μm and is used to capture the microscopic features of carbon fiber monofilament segments 10 to provide a basis for defect imaging. The fully electric zoom coding identification system has a zoom range of 25x to 1000x and is used to adapt to the observation needs of different defects through automatic zoom.

[0035] In step S1, the screened samples without initial defects are collected by the sample collection system 8, which includes a detachable collection base tray 8-2, a micro vacuum pump 8-3, and a micro transparent sealing cover 8-1. The micro vacuum pump 8-3 generates a weak negative pressure to assist the sample settling, and the micro transparent sealing cover 8-1 closes after the negative pressure adsorption ends to preserve the sample.

[0036] Step S2: Set test parameters and environment: Fix the test platform under the ultra-depth-of-field 3D imaging system 12, set the lateral compression loading rate, and start the active vibration damping system 25 to suppress the ambient vibration amplitude to below 0.1μm; Step S3, Sample Positioning and Size Measurement: Place the sample 22 selected in step S1 on the self-centering lower plane pressure plate 21, and adjust the X-Y drive module 24 so that the test point of the sample 22 is located at the center of the viewing area of ​​the plane pressure head 17; measure the diameter of the carbon fiber monofilament segment 10 at the test point through the top-view observation objective lens 13 of the ultra-depth-of-field three-dimensional imaging system 12. and the contact length between the carbon fiber monofilament segment 10 and the flat pressure head 17 ; Step S4, Lateral Compression Loading and Synchronous Data Acquisition: The Z-axis drive module 15 is activated, and a radial compression load is applied to the test point through the planar indenter 17. Load data and single-wire compression displacement data are acquired synchronously during the compression process. When the compression load reaches 20% of the predicted maximum load threshold, the lateral observation imaging system 20 is triggered to capture the lateral deformation state of the sample 22 and extract the contact half-width. and the depth of wrinkles and depressions on the fiber surface in the contact area Continue loading until specimen 22 is crushed, and record the maximum compressive force. and load-displacement curves; In step S4: The flat indenter 17 is made of diamond with a hardness HV>8000 and a roughness Ra<0.01μm to avoid interference from the deformation of the flat indenter 17 itself on the compression displacement measurement. The lateral observation imaging system 20 includes a long-focal-length microscope objective, a high-speed CCD camera with a frame rate of ≥1000fps, a precision optical path adapter component, and a mechanical positioning and anti-vibration module. The high-speed CCD camera is used to capture the lateral deformation at the moment of compression failure, the precision optical path adapter component is used to coordinate the brightness of the light source and the camera exposure to clearly obtain the image of the contact area, and the mechanical positioning and anti-vibration module is used to fix the field of view. The active vibration damping system 25 suppresses environmental vibrations through a real-time monitoring-feedback control system, and the vibration amplitude is suppressed to below 0.1μm, ensuring the authenticity of microscopic compression displacement data.

[0037] Step S5, Failure Mode Validity Determination and Performance Parameter Calculation: The image processing system in the failure mode validity determination unit extracts features from the dual-view original images of the ultra-depth-of-field 3D imaging system 12 and the lateral observation imaging system 20, and determines whether the failure mode of the specimen is an effective failure mode by combining the load-displacement curve; for specimens with effective failure modes, based on the dimensional data measured in step S3, the test data collected in step S4, and the image feature parameters extracted by the image processing system, the transverse compressive force, transverse compressive strain, transverse compressive stress, transverse compressive strength, and transverse compressive modulus of the carbon fiber monofilament segment 10 are calculated according to the preset formula.

[0038] In step S5, the effective failure modes include elastic crushing, microbuckling, and shear failure; Elastic crushing is characterized by a linear load-displacement curve until sudden fracture, with the cross-section perpendicular to the fiber axis. Specifically, the load-displacement curve is perfectly linear until sudden fracture, with the cross-section being a neat, flat section perpendicular to the fiber axis. The micro-buckling phenomenon is characterized by sinusoidal / wavy surface wrinkles appearing in the middle and late stages of loading, with the fracture located at the trough of the wrinkle, and slight fluctuations before the peak of the load-displacement curve. Shear failure manifests as localized bending bands with an inclination of >30° in high-modulus fibers (>500GPa), with the fibers within the band exhibiting serrated fractures.

[0039] In step S5, the transverse compressive force, transverse compressive strain, transverse compressive stress, and transverse compressive modulus of the carbon fiber monofilament segment 10 are calculated according to a preset formula. The specific calculation process includes: According to the formula: Calculate the transverse compressive force per unit length of a carbon fiber monofilament segment. In the formula, This refers to the transverse compressive force applied to the carbon fiber monofilament segment; This is the contact length between the carbon fiber monofilament segment and the indenter; According to the formula: Calculate the transverse compressive strain of a single carbon fiber filament segment In the formula, This represents the lateral compressive displacement of a single carbon fiber filament segment. The depth of the wrinkles and depressions on the fiber surface in the contact area; The diameter of a single carbon fiber filament segment; According to the formula: Calculate the transverse compressive stress of a carbon fiber monofilament segment. ; According to the formula: Calculate the transverse compressive strength of a carbon fiber monofilament segment In the formula, This represents the maximum transverse compressive force of a single carbon fiber filament segment. According to the formula: Calculate the transverse compressive modulus of a carbon fiber monofilament segment. In the formula, This represents the actual half-width of the transverse compression contact of a single carbon fiber filament segment. R is the radius of the carbon fiber monofilament segment.

[0040] In the above embodiments, preferably, the number of tests in each group is not less than 25.

[0041] In the above embodiments, preferably, as shown in Table 1, this embodiment conducted transverse compression performance tests on carbon fiber monofilaments of different grades / specifications (300 grade (3K), 700 grade (3K), and 800 grade (12K)) using the above evaluation method and testing system. The results showed that the transverse compression performance test results of carbon fiber monofilaments of different grades (specifications) and different batches were stable and reliable. It can be seen that the carbon fiber monofilament transverse compression performance evaluation system and evaluation method provided by the present invention can significantly improve the uniformity and consistency of sample preparation for carbon fiber monofilament transverse compression performance evaluation, ensure the stability of the test loading process and the accuracy and reliability of the test results, and improve the detection precision and detection efficiency.

[0042] Table 1. Test data on transverse compression properties of carbon fiber monofilaments

[0043] Example 2 like Figures 6-7 The second embodiment of the present invention is shown, which differs from Embodiment 1 only in the carbon fiber monofilament micro-sample preparation unit; the rest is the same as Embodiment 1 and will not be described in detail here. The sample 22 prepared by the carbon fiber monofilament micro-sample preparation unit in this embodiment may contain multiple carbon fiber monofilament segments 10.

[0044] likeFigure 6 As shown, in the above embodiment, preferably, the carbon fiber monofilament micro sample preparation unit includes a carbon fiber shaft 1, an acetone tank 2, a dryer 3, an airflow splitting device 4, a cutting device 5, a dispensing device 6, an online damage identification system 7, and a sample collection system 8 connected in sequence; the acetone tank 2 is used to desizing the carbon fiber bundle, the dryer 3 is used to dry the desizing carbon fiber bundle, the airflow splitting device 4 is used to decompose the carbon fiber bundle into multiple parallel carbon fiber monofilament segments 10, the cutting device is used to cut multiple parallel carbon fiber monofilament segments 10 to a fixed length, the dispensing device is used to fix multiple parallel carbon fiber monofilament segments 10 onto a transparent substrate 9 to form a sample 22, the online damage identification system 7 is used to screen for defect-free samples 22, and the sample collection system 8 is used to collect qualified samples 22.

[0045] like Figure 7 As shown, in the above embodiment, preferably, the sample 22 consists of a transparent substrate 9, multiple parallel carbon fiber monofilament segments 10, and adhesive droplets 11. The multiple parallel carbon fiber monofilament segments 10 are fixed to a transparent substrate 9 using three adhesive droplets 11 via an adhesive dispensing device 6. The length of the multiple parallel carbon fiber monofilament segments 10 is 20mm ± 2mm, and the spacing between two adjacent adhesive droplets 11 is controlled at 5mm to 7mm. A test point is formed between two adjacent adhesive droplets 11, meaning there are two test points on a single carbon fiber monofilament segment 10. The number of test points on the multiple parallel carbon fiber monofilament segments 10 is 2N (N is the number of carbon fiber monofilament segments 10). In this embodiment, the preferred number of parallel carbon fiber monofilament segments 10 is three. Figure 7 In the diagram, a is a plan view of sample 22, and b is a side view of sample 22.

[0046] Advantages of this invention: This invention, by setting up a carbon fiber monofilament micro-sample preparation unit, a loading and synchronous acquisition unit, a failure mode validity determination unit, and a data processing and analysis unit, can efficiently meet the measurement needs of transverse compression performance of carbon fiber monofilaments of different grades and specifications, demonstrating significant technical advantages. In sample preparation and testing, by precisely controlling the adhesive titration interval, curing time, and online damage identification, the uniformity and effectiveness of multi-test-point samples are ensured, supporting single or multiple parallel sample preparation to improve efficiency and avoid human error. The loading process employs a high-precision electromagnetic drive device and a planar indenter, combined with a lateral observation imaging system 20 and a super-depth-of-field three-dimensional imaging system 12, to achieve real-time monitoring of the entire compression process, accurately capture the complete mechanical response, and measure key parameters such as contact half-width and wrinkle indentation depth, solving the pain points of large measurement errors and insufficient continuous deformation capture in existing technologies.

[0047] This invention integrates dynamic correction technology and contact zone correction algorithms to construct a "measurement-correction" closed loop, compensating for errors such as sizing agent deformation and system flexibility on the fiber surface, thereby improving the accuracy of performance parameter calculations. It utilizes a failure mode effectiveness determination module to screen valid data, ensuring reliable results and comparability across different batches and grades, providing precise support for carbon fiber process optimization and composite material design. Furthermore, this invention is compatible with actual fiber surface conditions, requires no special pretreatment, and its core components are based on mature technologies that are easily industrialized. It can be widely applied in aerospace, transportation, and other fields, and is of great significance for understanding microscopic damage in composite materials and optimizing interfacial bonding, combining innovation and practicality.

[0048] 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 system for evaluating the transverse compressive performance of carbon fiber monofilaments, characterized in that, include: A carbon fiber monofilament micro-sample preparation unit includes a carbon fiber shaft, an acetone tank, a dryer, an airflow splitting device, a cutting device, a dispensing device, an online damage identification system, and a sample collection system connected in sequence. The acetone tank is used to desizing the carbon fiber bundle; the dryer is used to dry the desizing carbon fiber bundle; the airflow splitting device is used to decompose the carbon fiber bundle into carbon fiber monofilaments or multiple parallel carbon fiber monofilaments; the cutting device is used to cut the carbon fiber monofilaments or multiple parallel carbon fiber monofilaments into carbon fiber monofilament segments of fixed length; the dispensing device is used to fix the carbon fiber monofilament segments or multiple parallel carbon fiber monofilament segments onto a transparent substrate to form a sample; the online damage identification system is used to screen for defect-free samples; and the sample collection system is used to collect qualified samples. The loading and synchronous acquisition unit includes a high-precision displacement sensor, a Z-axis drive module, a high-precision force sensor, a planar indenter, an upper planar pressure plate, a control system, a lateral observation imaging system, a self-centering lower planar pressure plate, an XY-axis drive module, and an active vibration damping system. The high-precision displacement sensor is used to measure minute deformations, the Z-axis drive module is used to drive the planar indenter to move axially, the high-precision force sensor is used to measure compressive force, the lateral observation imaging system is used to capture lateral deformation, the XY-axis drive module is used to adjust the sample position, and the active vibration damping system is used to suppress environmental vibrations. The failure mode validity determination unit includes a super depth-of-field three-dimensional imaging system and an image processing system; the super depth-of-field three-dimensional imaging system acquires three-dimensional images of the sample, and the image processing system extracts and analyzes features from the original images and determines the failure mode in combination with load data. The data processing and analysis unit includes a control system, which receives load and displacement data from the loading and synchronous acquisition unit, as well as failure mode determination results and image feature parameters from the failure mode effectiveness determination unit, and calculates the transverse compression performance parameters of the carbon fiber monofilament segment according to a preset formula.

2. The carbon fiber monofilament transverse compression performance evaluation system according to claim 1, characterized in that, The ultra-depth-of-field three-dimensional imaging system includes a high-precision piezoelectric objective lens displacement system and a high-performance optical microscope body. The high-performance optical microscope body includes a top-view objective lens with a zoom range of 25x to 1000x, which is used for sample size measurement and surface condition observation. The high-precision piezoelectric objective lens displacement system can drive the main body of the high-performance optical microscope and the top-view objective lens therein to move slightly along the axis, so as to realize the acquisition and stitching of images at different depths to meet the needs of ultra-depth of field observation.

3. The carbon fiber monofilament transverse compression performance evaluation system according to claim 1, characterized in that, The sample collection system includes a detachable collection substrate tray, a miniature vacuum pump, and a miniature transparent sealing cover; The detachable collection base tray is located directly below the qualified samples screened by the online damage identification system, and is used to directly receive the samples. The micro vacuum pump is located below the detachable collection base tray and is connected to the detachable collection base tray through a flexible pipeline. The micro vacuum pump is used to generate a weak negative pressure inside the detachable collection base tray to assist the samples in orderly settling onto the detachable collection base tray. The micro transparent sealing cover is located directly above the detachable collection base tray. The micro transparent sealing cover is initially in an open state, and can be closed to cover the detachable collection base tray after the negative pressure adsorption ends.

4. A method for evaluating the transverse compressive performance of carbon fiber monofilaments, applied to the carbon fiber monofilament transverse compressive performance evaluation system according to any one of claims 1-3, characterized in that, include: Step S1: Preparation of carbon fiber monofilament transverse compression micro-samples: The carbon fiber bundle is sequentially subjected to desizing, drying, splitting, and cutting processes to obtain carbon fiber monofilament segments of fixed length or multiple parallel carbon fiber monofilament segments; the carbon fiber monofilament segments or multiple parallel carbon fiber monofilament segments are fixed to a transparent substrate at a preset interval using a dispensing device, and a micro-sample containing at least two test points is formed on each carbon fiber monofilament segment; the micro-samples are subjected to online damage identification, and samples without initial defects are selected for use. Step S2: Set test parameters and environment: Fix the test platform below the ultra-depth-of-field 3D imaging system, set the lateral compression loading rate, and start the active vibration damping system to suppress the ambient vibration amplitude to below 0.1μm; Step S3, Sample Positioning and Size Measurement: Place the sample selected in Step S1 onto the self-centering lower plane pressure plate, adjust the XY drive module to position the sample test point at the center of the plane pressure head's field of view; measure the diameter of the carbon fiber monofilament segment at the test point through the top-view objective lens of the ultra-depth-of-field 3D imaging system. and the contact length between the carbon fiber monofilament segment and the flat indenter ; Step S4, Lateral Compression Loading and Synchronous Data Acquisition: The Z-axis drive module is activated, and a radial compression load is applied to the test point via the planar indenter. Load data and single-wire compression displacement data are acquired synchronously during the compression process. When the compression load reaches 20% of the predicted maximum load threshold, the lateral observation imaging system is triggered to capture the lateral deformation state of the sample and extract the contact half-width. and the depth of wrinkles and depressions on the fiber surface in the contact area Continue loading until the sample crushes, and record the maximum compressive force. and load-displacement curves; Step S5, Failure Mode Validity Determination and Performance Parameter Calculation: The image processing system in the failure mode validity determination unit extracts features from the dual-view original images of the ultra-depth-of-field 3D imaging system and the lateral observation imaging system, and determines whether the failure mode of the specimen is an effective failure mode by combining the load-displacement curve; for specimens with effective failure modes, based on the dimensional data measured in step S3, the test data collected in step S4, and the image feature parameters extracted by the image processing system, the transverse compressive force, transverse compressive strain, transverse compressive stress, transverse compressive strength, and transverse compressive modulus of the carbon fiber monofilament segment are calculated according to the preset formula.

5. The method for evaluating the transverse compressive performance of carbon fiber monofilaments according to claim 4, characterized in that, In step S1, the desizing process is achieved by introducing the carbon fiber bundle into an acetone bath, the drying process is achieved by a dryer, the fiber splitting process is achieved by using an airflow fiber splitting device to break down the carbon fiber bundle into single carbon fiber segments or multiple parallel carbon fiber segments, and the cutting process is achieved by using a cutting device to cut the single carbon fiber segments or multiple parallel carbon fiber segments into single carbon fiber segments or multiple parallel carbon fiber segments with a length of 20mm±2mm; the preset spacing is 5mm~7mm.

6. The method for evaluating the transverse compressive performance of carbon fiber monofilaments according to claim 4, characterized in that, In step S1, the online damage identification includes identifying microcracks, residual sizing agent buildup, fiber torsion, and buckling defects in carbon fiber monofilament segments through an online damage identification system. The online damage identification system includes a high-resolution optical microscope and a fully electric zoom coding identification system. The high-resolution optical microscope has a resolution of 1 μm and is used to capture the microscopic features of carbon fiber single filament segments to provide a basis for defect imaging. The fully electric zoom coding identification system has a zoom range of 25x to 1000x and is used to adapt to the observation needs of different defects through automatic zoom.

7. The method for evaluating the transverse compressive properties of carbon fiber monofilaments according to claim 4, characterized in that, In step S1, the screened samples without initial defects are collected by a sample collection system, which includes a detachable collection base tray, a micro vacuum pump, and a micro transparent sealing cover. The micro vacuum pump generates a weak negative pressure to assist sample settling, and the micro transparent sealing cover closes after the negative pressure adsorption is completed to preserve the sample.

8. The method for evaluating the transverse compressive properties of carbon fiber monofilaments according to claim 4, characterized in that, In step S4: The planar indenter is made of diamond with a hardness HV>8000 and a roughness Ra<0.01μm, in order to avoid interference from the deformation of the planar indenter itself on the compression displacement measurement. The lateral observation imaging system includes a high-speed CCD camera with a frame rate ≥1000fps. The high-speed CCD camera is used to capture lateral deformation at the moment of compression failure. The high-speed CCD camera is equipped with a light source and a focusing unit. The light source is used to assist the high-speed CCD camera in clearly acquiring images of the contact area, and the focusing unit is used to adjust the imaging focal length of the high-speed CCD camera.

9. The method for evaluating the transverse compressive properties of carbon fiber monofilaments according to claim 4, characterized in that, In step S5, the effective failure modes include elastic crushing, microbuckling, and shear failure. The elastic crushing is characterized by a linear load-displacement curve until sudden fracture, with the fracture surface perpendicular to the fiber axis; The micro-buckling phenomenon is characterized by sinusoidal / wavy surface wrinkles appearing in the middle and late stages of loading, with the fracture located at the trough of the wrinkle and slight fluctuations before the peak of the load-displacement curve. The shear failure is manifested as localized bending bands with an inclination >30° appearing in the high-modulus fibers, with the fibers within the bands exhibiting serrated fractures.

10. The method for evaluating the transverse compressive performance of carbon fiber monofilaments according to claim 4, characterized in that, In step S5, the transverse compressive force, transverse compressive strain, transverse compressive stress, and transverse compressive modulus of the carbon fiber monofilament segment are calculated according to a preset formula. The specific calculation process includes: According to the formula: Calculate the transverse compressive force per unit length of a carbon fiber monofilament segment. In the formula, This refers to the transverse compressive force applied to the carbon fiber monofilament segment; This is the contact length between the carbon fiber monofilament segment and the indenter; According to the formula: Calculate the transverse compressive strain of a single carbon fiber filament segment In the formula, This represents the lateral compressive displacement of a single carbon fiber filament segment. The depth of the wrinkles and depressions on the fiber surface in the contact area; The diameter of a single carbon fiber filament segment; According to the formula: Calculate the transverse compressive stress of a carbon fiber monofilament segment. ; According to the formula: Calculate the transverse compressive strength of a carbon fiber monofilament segment In the formula, This represents the maximum transverse compressive force of a single carbon fiber filament segment. According to the formula: Calculate the transverse compressive modulus of a carbon fiber monofilament segment. In the formula, This represents the actual half-width of the transverse compression of a single carbon fiber filament segment. R is the radius of the carbon fiber monofilament segment.

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