Search

CN-121384626-B - Method and test system for evaluating transverse compression performance of carbon fiber monofilaments

CN121384626BCN 121384626 BCN121384626 BCN 121384626BCN-121384626-B

Abstract

The invention discloses a method and a test system for evaluating the transverse compression performance of a carbon fiber monofilament, wherein the method comprises the steps of test sample preparation, test parameter and environment setting, sample positioning and size measurement, compression test and data acquisition, and performance parameter analysis and evaluation, so as to realize the accurate evaluation of the transverse compression performance of the carbon fiber monofilament. The invention can improve sample preparation uniformity and test stability, cut off indirect parameter error conduction, solve the problems of inaccurate measurement and large data discreteness of the traditional method, greatly improve detection precision and efficiency, and is suitable for carbon fiber performance evaluation in the fields of aerospace and the like.

Inventors

  • YAN JIN
  • MA HONGYI
  • DENG QIYU
  • CHEN LIJUAN
  • LI HONGYUN

Assignees

  • 中航复合材料有限责任公司

Dates

Publication Date
20260512
Application Date
20251225

Claims (10)

  1. 1. An evaluation method for evaluating transverse compression performance of carbon fiber monofilaments, comprising: Step 1, preparing a test sample, namely pretreating a carbon fiber tow into a monofilament section with a fixed length through desizing, drying, dividing and cutting, fixing the monofilament section on a transparent substrate by adopting glue solution drops according to a preset interval, and forming at least two test points on the monofilament section on a single transparent substrate; step 2, testing parameters and setting the environment, namely fixing a test platform below the variable-focus high-magnification optical observation assembly, setting a transverse compression loading rate, and starting the vibration suppression assembly to control the environment vibration; Step 3, positioning and measuring the size of the sample, namely placing the sample prepared in the step 1 on a test platform, adjusting the test platform to enable a test point of the monofilament section to be positioned at the center of a visual area of the miniature plane pressure head and to enable the outline to be clear, and measuring the diameter of the monofilament section at each test point and the contact length of the monofilament section and the miniature plane pressure head through matching of a variable-focus high-magnification optical observation assembly and an image acquisition assembly; Starting a loading mechanism, applying radial compression load to the single wire section at the test point according to the loading rate set in the step 2, and synchronously acquiring compression load data, single wire compression displacement data and real-time image data of the test point in the loading process until the single wire section is transversely compressed and damaged, and stopping loading; step 5, analyzing and evaluating performance parameters, namely obtaining basic mechanical parameters through a preset calculation formula based on the size data of the step 3 and the test data of the step 4, adopting a reverse iterative optimization algorithm after the stress of a contact area formed by the contact deformation of the miniature plane pressure head and the monofilament section is corrected, and solving transverse compression modulus by combining the corrected mechanical parameters and the relation of strain; wherein the contact area stress correction is performed by the formula: Calculating the transverse compressive correction stress of the carbon fiber monofilaments considering the influence of the contact area In which, in the process, The transverse compressive stress of the carbon fiber monofilaments is R, the radius of the carbon fiber monofilaments, and b, the half width of the contact section between the carbon fiber monofilaments and the miniature plane pressure head; The reverse iterative optimization algorithm specifically comprises the following steps: the transverse compression modulus E of the similar carbon fiber monofilaments is taken as an initial input and is based on a formula Calculation of the carbon fiber monofilament transverse compressive modulus Wherein Correcting stress for transverse compression of carbon fiber monofilaments Transverse compressive strain with carbon fiber monofilaments Is a slope of a curve linear segment of (a); will be calculated preliminarily As the E value of the new round, the half width b value of the contact section and the corresponding correction stress are recalculated A value; based on new corrected stresses Again calculate ; And repeating the iterative process until the ET variation amplitude obtained by two adjacent rounds of calculation meets a preset stability threshold, and the final ET value is not influenced by the initial E value, so as to obtain the final carbon fiber monofilament transverse compression modulus ET.
  2. 2. The assessment method according to claim 1, further comprising test effectiveness judgment, wherein the test effectiveness judgment specifically comprises judging that the test is effective according to the real-time image data acquired in the step 4, if the situation that the sample slips, the carbon fiber monofilaments bridge between fixed points and the load reaches the set maximum value but the sample is not crushed occurs in the loading process, judging that the test is ineffective and discarding the corresponding test data, and judging that the test data is effective and analyzing and assessing the performance parameters of the step 5 according to the test data if the transverse extrusion damage and the shearing damage occur in the loading process.
  3. 3. The assessment method according to claim 1, characterized in that in step 1, it specifically comprises: introducing carbon fiber tows wound on a carbon fiber shaft into an acetone tank to remove sizing agent; leading out the carbon fiber tows from the acetone tank, drying the carbon fiber tows by a dryer, and then decomposing the carbon fiber tows into a plurality of continuous monofilaments by entering an airflow filament dividing device; Cutting a plurality of continuous monofilaments into monofilament sections with fixed lengths of 20mm plus or minus 2mm by a cutting device; And the glue dropping device fixes the glue solution drops on the transparent substrate according to preset intervals of 5 mm-7 mm, and the preparation of the monofilament section sample is completed after solidification, wherein one test point is formed between two adjacent glue solution drops in the prepared monofilament section sample.
  4. 4. The method according to claim 1, wherein in the step 2, the variable-focus high-magnification optical observation assembly includes a top-view optical head and a variable high-magnification objective lens, and the brightness of the observation field of view is adjusted in cooperation with a light source controller; the vibration suppression component is a damping table for suppressing the amplitude of the environmental vibration to 0.1 The following is given.
  5. 5. The method of claim 1, wherein in step 3, the diameter of the micro planar indenter is 50 The micro plane pressure head is made of diamond, the hardness Hv of the micro plane pressure head is more than 8000, and the pressure head roughness Ra of the micro plane pressure head is less than 0.01 。
  6. 6. The method according to claim 1, wherein in the step 3, the image acquisition component is a high-resolution image sensor, and the image acquisition component is used for capturing the contact state of the point to be tested and the micro plane pressure head and the deformation process of the carbon fiber monofilament in real time, and after the monofilament section sample is crushed, the high-resolution image sensor is used for recording the damage mode of the broken part of the monofilament section sample.
  7. 7. The method according to claim 1, wherein in the step 5, the performance parameter analyzing and evaluating process specifically includes: step 51, calculating basic mechanical parameters, namely measuring the diameter of the monofilament section based on the step 3 Contact length of monofilament with miniature planar indenter And the compression load data collected in the step 4 Data of single filament compression displacement Respectively calculating the transverse compressive force, the transverse compressive strain and the transverse compressive stress of the carbon fiber monofilaments in unit length through a preset calculation formula; Step 52, correcting the stress of the contact area, namely, based on the basic mechanical parameters calculated in the step 51, combining the filament radius R, and obtaining a carbon fiber filament transverse compression correction stress sigma' considering the influence of the contact area through a contact section half-width calculation formula and a correction stress calculation formula; And 53, carrying out iterative optimization solving and strength determination, namely adopting an iterative optimization mode to solve the transverse compression modulus of the single-wire section sample, and determining the transverse compression strength according to the maximum load before crushing of the single-wire section sample to finish performance evaluation.
  8. 8. The assessment method according to claim 7, wherein in said step 51, the specific calculation procedure comprises: According to the formula: Calculating transverse compressive force of carbon fiber monofilaments per unit length In which, in the process, In order to compress the load data, The contact length of the monofilament and the miniature plane pressure head is; According to the formula: Calculation of carbon fiber monofilament transverse compressive Strain In which, in the process, For the monofilament compression displacement data, Is the diameter of the carbon fiber monofilament; According to the formula: Calculating the transverse compressive stress of the carbon fiber monofilaments ; In the step 52, the specific calculation process includes: According to the formula: And calculating the half width b of the contact section between the carbon fiber monofilament and the miniature plane pressure head, wherein E is the transverse compression modulus of the carbon fiber monofilament of the same type.
  9. 9. The method of evaluating according to claim 7, wherein in said step 53, the transverse compressive strength is determined based on the maximum load of the monofilament segment sample before crushing, and wherein the calculating comprises: According to the formula: Calculation of carbon fiber monofilament transverse compressive Strength In which, in the process, Is the transverse maximum compression force of the carbon fiber monofilaments, For the contact length of the monofilament with the miniature plane pressure head, Is the diameter of the carbon fiber monofilament.
  10. 10. A test system for evaluating the transverse compressive properties of carbon fiber monofilaments for use in the evaluation method according to any one of claims 1 to 9, comprising: the sample preparation module comprises a carbon fiber shaft, an acetone groove, a dryer, an airflow wire dividing device, a cutting device and a glue dripping device which are sequentially arranged, wherein the acetone groove is used for desizing carbon fiber tows, the airflow wire dividing device is used for dividing the carbon fiber tows into monofilaments, the cutting device is used for cutting the monofilaments into monofilament sections with fixed lengths, and the glue dripping device is used for fixing the monofilament sections on a transparent substrate according to preset intervals to provide standardized samples for testing; The test platform module comprises a test platform, a vibration suppression assembly and a sample positioning assembly, wherein the vibration suppression assembly is used for controlling environmental vibration so as to ensure test stability, and the sample positioning assembly is used for adjusting the horizontal position and the height of the test platform, so that a point to be tested of a single wire section is accurately positioned at the center of a visual area of the miniature plane pressure head, and a precise positioning basis is provided for subsequent testing; the synchronous optical imaging module comprises a variable-focus high-magnification optical observation assembly and an image acquisition assembly, wherein the variable-focus high-magnification optical observation assembly comprises a overlook optical head and a variable-magnification objective lens and is used for clearly observing a sample and accurately measuring the diameter of a monofilament section and the contact length of the monofilament section and the pressure head; The electromagnetic force control micro-compression loading module comprises a loading mechanism and a micro plane pressure head, wherein the loading mechanism applies radial compression load to the monofilament section according to a set loading rate; The in-situ transverse compression performance measurement module comprises a high-sensitivity force sensor and a high-precision displacement sensor, and the high-sensitivity force sensor and the high-precision displacement sensor are matched to acquire load data and monofilament compression displacement data in the compression process in situ, so that real-time measurement of performance parameters is realized; The multi-performance data synchronous acquisition module is respectively connected with the synchronous optical imaging module, the electromagnetic force control micro-compression loading module and the in-situ transverse compression performance measurement module in a data manner and is used for synchronously summarizing the acquired single-wire section size measurement data, real-time image data, load data and displacement data, so that the time consistency of multi-dimensional data is ensured; And the performance parameter reverse analysis module is in data intercommunication with the multi-performance data synchronous acquisition module, adopts a reverse iteration optimization algorithm, solves the transverse compression elastic modulus after the stress correction of the contact area based on the size data, the load-displacement data and the image data which are synchronously acquired, and combines the maximum load before the single wire section is crushed to determine the transverse compression strength.

Description

Method and test system for evaluating transverse compression performance of carbon fiber monofilaments Technical Field The invention relates to the technical field of material performance detection, in particular to a method and a test system for evaluating transverse compression performance of carbon fiber monofilaments. Background The carbon fiber reinforced resin matrix composite has become a core material of high-end structural members in the fields of aerospace, traffic, energy, construction and the like due to excellent performances such as high specific strength, high specific modulus, fatigue resistance and the like, for example, in an aircraft structure, the application ratio of the composite is continuously improved, the low-cost composite technology is marked to enter a new engineering application stage, and at present, all types of aircraft in China adopt carbon fiber composite members to different degrees. Along with the expansion of the application scene of the composite material and the accumulation of application experience, the damage resistance under low energy impact becomes a key bottleneck problem of the structural design of the composite material of the aircraft. In the event of low-speed impact damage to the composite material, the fracture mode of the carbon fibers directly determines the degree of structural damage, wherein the transverse and axial compressive failure of the fibers is one of the main fracture modes of low-speed impact damage to the carbon fiber laminate. Therefore, the carbon fiber transverse compression performance (comprising transverse compression strength and modulus) is accurately obtained, the carbon fiber production process is optimized, the core data support of the overall performance of the composite material is improved, and the irreplaceable effects on the design reliability and the use safety of the composite material component are ensured. However, since the carbon fiber monofilaments have extremely small diameters (only 5-10 μm), and complicated phenomena such as buckling instability, torsion damage and the like are easily accompanied in the transverse compression loading process, accurate assessment of the transverse compression performance of the carbon fibers is very challenging. At present, the mainstream carbon fiber transverse compression performance test methods in the industry are mainly divided into two types, namely a classical parallel plate method and a self-built equipment test method, but the two types of test methods have certain limitations. For a classical parallel plate method, the core principle of the method is that two parallel glass plates are adopted to clamp carbon fiber monofilaments, a lever system is used for suspending a weight to apply transverse compression load, an interference fringe spectrum is observed by means of an optical microscope, the contact width of the fiber and glass under different loads is used as transverse deformation, and parameters such as poisson ratio, longitudinal tensile modulus and the like of the carbon fiber are combined to indirectly estimate the transverse compression modulus. The method has the obvious technical defects that 1, the measurement accuracy is limited, the contact width of a carbon fiber monofilament is only in a micron level, the resolution of a conventional optical microscope cannot meet the requirement of accurate measurement, micron-level measurement errors are easy to introduce, performance calculation results are directly influenced, 2, continuous deformation cannot be captured, namely, loading is needed to be suspended to statically observe interference fringes, continuous deformation and damage evolution of the fiber in the compression process cannot be recorded in real time, performance response under real load is difficult to reflect, 3, indirect calculation error conduction, namely, the solution of transverse compression modulus depends on input parameters such as poisson ratio, longitudinal tensile modulus and the like, if test errors exist in the parameters, the parameters are directly transmitted to the transverse compression performance results through the calculation process, and the evaluation accuracy is greatly reduced. For the self-building equipment testing method, the core principle of the method is that a lower clamping plane is replaced by a smooth steel plane, an upper pressure head is accurately loaded by adopting an electromagnetic driver, an integrated force sensor directly measures compression force, displacement of the pressure head is recorded by a linear differential transformer (LVDT), real-time observation by a microscope is not needed to reduce artificial interference, a carbon fiber monofilament is placed on the steel plane during testing, load is applied by the electromagnetic driver, load-displacement data are synchronously acquired, and the transverse compression modulus and strength are calculated by combining a theoretical model. The method