A method for determining carbon fiber strength based on molecular dynamics
By constructing a carbon fiber model with both crystalline and amorphous states using molecular dynamics methods, the problem of discrepancies between existing models and measured data was solved, enabling more accurate calculation of carbon fiber strength.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BEIJING INST OF TECH
- Filing Date
- 2025-10-16
- Publication Date
- 2026-07-07
AI Technical Summary
Existing technologies make it difficult to accurately construct carbon fiber models that include both crystalline and amorphous states, resulting in a significant gap between calculated strength and measured values. Furthermore, the distribution of interlayer crosslinking segments in graphene is difficult to control artificially.
By using molecular dynamics-based methods and high-resolution transmission electron microscopy images to obtain lattice spacing and interlayer fringes, we established oriented graphene fragments, performed high-temperature relaxation and annealing calculations, and formed a carbon fiber atomic structure in which crystalline and amorphous states coexist. We then adjusted the number of carbon atoms in the interlayer crosslinking regions to match the measured data.
This study enabled a more accurate characterization of the stacking of graphene fragments and the distribution of interlayer crosslinks within carbon fibers. The calculated results showed a high degree of agreement with the measured data, providing a theoretical basis for the preparation process of high-performance carbon fibers.
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Figure CN121483400B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for determining carbon fiber strength based on molecular dynamics, belonging to the field of aerospace lightweight composite material design technology. Background Technology
[0002] Carbon fiber reinforced silicon carbide matrix composites possess a comprehensive range of excellent properties, including lightweight, high modulus, high strength, corrosion resistance, high temperature resistance, and good electrical and thermal conductivity, and have been widely used in high-end equipment in aerospace and aviation fields. The properties of carbon fiber reinforced silicon carbide matrix composites are the result of the combined effects of microscopic interfaces, mesoscopic, and macroscopic structures. Due to the randomness of samples and the constraints of multiple scale levels, it is difficult to directly use traditional experimental methods such as optical, mechanical, magnetic, and acoustic methods to study the influence laws and mechanisms of specific factors. Therefore, many researchers at home and abroad have adopted molecular dynamics methods to study the enhancement mechanism of the mechanical properties of composite materials, with simulations ranging from the atomic scale to the nanoscale. From a microscopic perspective, carbon fiber reinforced silicon carbide matrix composites include carbon fibers, an amorphous carbon interface layer on the surface of the carbon fibers, and the silicon carbide matrix material.
[0003] In the study of carbon fiber strength, fibrous polymer carbon, formed by high-temperature carbonization of organic fibers in an inert atmosphere, belongs to inorganic non-metallic materials with a carbon content exceeding 90%. Conventional carbon fibers are fibrous materials composed of two-dimensional random-layer graphite microcrystals. They can generally be considered as microcrystals with a certain orientation along the fiber axis, formed by stacked graphite-like sheets composed of six-membered carbon rings, including crystalline and amorphous regions; the interlayer contains a certain amount of amorphous carbon as well as defects such as pores and dislocations. Desai et al. established a molecular dynamics calculation model for carbon fibers that includes microscopic defects, while Shi et al. used the Monte Carlo method to establish a model of completely amorphous carbon fibers in the transverse section, focusing on the high-temperature oxidation process and products. These modeling methods are relatively complex and difficult to obtain carbon fiber models with coexisting crystalline and amorphous states. Furthermore, the distribution of cross-linked segments between graphene layers differs significantly from reality, leading to a significant discrepancy between the calculated strength and the measured values. Overall, there are still many problems in the molecular dynamics calculation methods of carbon fiber materials and the study of fracture failure mechanisms under high-temperature service environments. Breakthroughs are needed in constructing a modeling method for carbon fiber materials that includes atomic distributions of both crystalline and amorphous regions.
[0004] Disadvantages of existing technology:
[0005] Conventional carbon fibers are typically composed of stacked graphite-like sheets of six-membered carbon rings, forming microcrystals with a certain orientation along the fiber axis, including both crystalline and amorphous regions. Shi et al. used the Monte Carlo method to establish a completely amorphous carbon fiber model in the transverse section. This method uses short graphite fragments to obtain long, stacked graphite-like structures under high-temperature relaxation. This modeling process relies entirely on the high-temperature relaxation process, making it difficult to artificially control the distribution of graphite fragments. Consequently, the resulting carbon fiber structure is too disordered and fails to achieve an atomic structure where crystalline and amorphous states coexist. Summary of the Invention
[0006] The technical problem solved by this invention is to overcome the shortcomings of existing technologies and propose a method for determining the strength of carbon fibers based on molecular dynamics. This invention obtains the d-value of microcrystals in experimental testing of carbon fibers. 002 Based on the test data of interlayer spacing and uniaxial tensile strength, a carbon fiber atomic structure with crystalline and amorphous states was obtained by conducting high-temperature relaxation on oriented graphene fragments.
[0007] The technical solution of this invention is:
[0008] A method for determining carbon fiber strength based on molecular dynamics, the method comprising the following steps:
[0009] Step 1: Obtain the lattice spacing and the number of interlayer fringes from the high-resolution transmission electron microscope image of the carbon fiber to be tested. Then, obtain the d-value of the graphene fragment based on the obtained lattice spacing and the number of interlayer fringes. 002 Interlayer spacing L1, number of interlayer cross-linking layers N1;
[0010] Step 2: Randomly fill the inside of the cylinder with discontinuous graphene fragments to obtain the initial carbon fiber atomic structure;
[0011] Step 3: Calculate the initial carbon fiber atomic structure obtained in Step 2 by performing energy minimization, high-temperature relaxation and annealing calculations to obtain a carbon fiber atomic structure in which crystalline and amorphous states coexist.
[0012] Step 4: Examine the d-values of the graphene fragments within the carbon fiber atomic structure obtained in Step 3, where crystalline and amorphous states coexist. 002 The interlayer spacing L2 and the number of interlayer cross-linking layers N2 are calculated, and the relative errors W1 between L2 and L1 and W2 between N2 and N1 are calculated. When both W1 and W2 are less than 30%, the carbon fiber atomic structure with crystalline and amorphous coexistence obtained in step 3 is considered to conform to the microstructure of the carbon fiber to be tested, and the carbon fiber atomic structure with crystalline and amorphous coexistence obtained in step 3 is used as the calculation model.
[0013] When either W1 or W2 is not less than 30%, randomly delete 0.1-0.01% of the carbon atom interlayer crosslinking region from the initial carbon fiber atomic structure in step 2 or the carbon fiber atomic structure in step 3 where crystalline and amorphous states coexist, to obtain a carbon atom structure model. Then, perform high-temperature relaxation and annealing calculations on the obtained carbon atom structure model to finally form a carbon fiber atomic structure containing crystalline and amorphous states as a calculation model.
[0014] Step 5: Perform uniaxial compression and tensile deformation simulation on the calculation model obtained in Step 4 at temperatures ranging from 300K to 2000K to obtain stress-strain results. Then, based on the stress-strain results, obtain the compressive strength and tensile strength values of the carbon fiber to be tested.
[0015] In step 1, the d of the graphene fragment is obtained based on the acquired lattice spacing and the number of interlayer fringes. 002 The formulas for interlayer spacing L1 and the number of interlayer cross-linking layers N1 are:
[0016] d 002 Interlayer spacing L1=K·λ / B·cosθ
[0017] The number of interlayer cross-linking layers N1 = λ / 0.67sinθ.
[0018] In the formula, λ is the X-ray diffraction wavelength, θ is the diffraction angle of the crystal plane diffraction peak, and B is the full width at half maximum (FWHM).
[0019] In step 2, the cylindrical region is determined based on the diameter of the carbon fiber atomic structure. Starting from the center of the cylindrical region, n cylinders are sequentially arranged outwards. The inner diameter of the first cylinder is R1, and its outer diameter is R2, and so on, with the inner diameter of the nth cylinder being R... n The outer diameter is R n+1 Each cylinder is filled with graphene fragments;
[0020] In step 2, the graphene fragments filling the cylindrical region are armchair-shaped or sawtooth-shaped, and the lattice constant of the graphene is 1.414, a1(1.732, 0, 0), a2(0, 0, 3), a3(0, 0, 3), basis1(0, 0, 0), basis2(0, 0.333, 0), basis3(0.5, 0.5, 0), basis4(0.5, 0.833, 0);
[0021] In step 3, the conjugate gradient method is used during high-temperature relaxation to adjust atoms that are too close together. The NPT (constant-pressure, constant-temperature, abbreviated as NPT, means maintaining a definite number of particles N, pressure T) ensemble relaxation is applied for 10 ps, 100 ps, and 10 ps respectively under the conditions of 300 K and 0.1 MPa, 1200 K and 0.1 MPa, and 300 K and 0.1 MPa, so that the energy of the system reaches a stable state.
[0022] In step 5, the rate of uniaxial compression and tensile deformation does not exceed 0.001 angstroms / pf.
[0023] The present invention also provides an electronic device, including a processor and a memory, the memory storing program code that, when executed by the processor, causes the processor to perform the steps of the method.
[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0025] This invention utilizes molecular dynamics to construct a method that satisfies the interlayer spacing and interlayer crosslinking segments required for actual carbon fibers, and calculates the tensile and compressive strengths at room temperature (300K) to high temperature (2000K). Furthermore, the experimental and simulation results show extremely high agreement, providing a strong theoretical basis for the development of high-performance carbon fiber manufacturing processes and the calculation of service strength.
[0026] This invention provides a method for establishing the atomic structure of carbon fibers based on the measured interlayer spacing and the number of interlayer crosslinking segments. The atomic structure obtained by this method can more accurately characterize the stacking of graphene segments and the distribution of interlayer crosslinking atoms inside the real carbon fibers. The tensile and compressive strength calculation results based on the atomic structure obtained by this method are closer to the measured data.
[0027] Current technologies primarily rely on the Monte Carlo method employed by Shi et al. to establish a completely amorphous carbon fiber model within the transverse cross-section. This modeling method is complex and struggles to produce a carbon fiber model where crystalline and amorphous states coexist. Furthermore, the distribution of crosslinking segments between graphene layers cannot be artificially controlled, resulting in a significant discrepancy between the calculated and measured strengths. This patent proposes a method that actively introduces crosslinking into the interlayer crosslinking region by actively deleting 0.01-0.2% of carbon atoms. This method effectively controls the distribution of crosslinking segments and significantly reduces the difference between the distribution of crosslinking segments and the actual sample. Consequently, it more realistically depicts the internal microscopic atomic distribution of carbon fibers compared to all previously published literature. Attached Figure Description
[0028] Figure 1The atomic structures of single-layer and multi-layer carbon fibers were established (the left figure shows the initial structure, and the right figure shows the final structure obtained after relaxation).
[0029] Figure 2 The distribution of stacked and interlayer crosslinked segments within the carbon fiber cross-section;
[0030] Figure 3 This is an axial view of the carbon fiber uniaxial stretching process.
[0031] Figure 4 This is an axial view of the carbon fiber uniaxial compression process.
[0032] Figure 5 This is the stress-strain curve during the uniaxial tensile process of carbon fiber. Detailed Implementation
[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments.
[0034] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any reasonable combination of the specific embodiments.
[0035] Example
[0036] A method for determining the tensile and compressive strength of carbon fibers based on molecular dynamics, the method comprising the following steps:
[0037] Step 1: High-resolution transmission electron microscopy images of the carbon fiber sample are used to obtain the interlayer spacing and the number of interlayer stripes. The average values of the interlayer spacing and the number of interlayer crosslinking layers of the graphene fragments are calculated.
[0038] Step 2: Compile the input .in file for molecular dynamics calculations. The model atoms use metal units, and the spatial dimension is set to three-dimensional with periodic boundaries. Define the crystal structure of the graphene fragment with a lattice constant of 1.414: a1(1.732, 0, 0), a2(0, 0, 3), a3(0, 0, 3), basis1(0, 0, 0), basis2(0, 0.333, 0), basis3(0.5, 0.5, 0), basis4(0.5, 0.833, 0).
[0039] Step 3: Create cylindrical regions based on the desired carbon fiber model diameter. Use the region command to sequentially set cylindrical regions (R1, R2), ..., (R...) from the center of the cylinder outwards. n R n+1 Each cylindrical region is filled with graphene fragments. The interlayer spacing between adjacent cylindrical regions is R. n+1 -R n =10 angstroms, the cylindrical region R at the very center of the carbon fiber cylinder n+1The cylinder is completely filled with graphene fragments, with all regions having the same height. The delete_atoms command is used to randomly delete 1% of the carbon atoms within each cylindrical region. Figure 1 The left-middle column shows the initial carbon atom distribution, the first row shows the atomic structure with only one layer, and the second row shows the atomic structure with six rows.
[0040] Step 4: The potential function was Airebo, and the initial velocity of the entire system was set to 300K. High-temperature relaxation was performed on the NPT system at 0.1MPa, with five temperature ranges applied sequentially: 300K isothermal, 300K to 1200K, 1200K isothermal, 1200K to 300K, and 300K isothermal again. Each temperature relaxation lasted 100 ps. The atomic trajectory calculation results were output using the dump command; the in file was run using the LAMMPS open-source software.
[0041] Step 5: Open the dump output using OVITO software and count the interlayer spacing and the number of interlayer crosslinking fragments. Figure 2 The results of the interlayer carbon atom distribution obtained after high-temperature relaxation show that the interlayer spacing is 3.4 Å and the average number of interlayer crosslinking segments is 6.
[0042] Step 6: Compare the interlayer spacing of the initial atomic structure (3.4 Å) with the measured value. Based on the comparison between the number of interlayer crosslinking segments in the initial atomic structure and the measured value, the number of interlayer crosslinking regions is adjusted by deleting 1% of carbon atoms.
[0043] Step 7: Compare the interlayer spacing of the initial atomic structure with the measured value. If the error between the interlayer crosslinking segments of the carbon fiber atomic structure and the measured value exceeds 30%, then iterate through steps 3 to 6 again.
[0044] Step 8: Perform uniaxial tensile and compressive deformation calculations in the Z-axis on the relaxed carbon fiber atomic structure, with a tensile rate of 0.001 Å / pf. Set the initial velocity of all atoms to 300 K, and set the ambient pressure in the x and y directions to 0. Use the dump command to output the atomic trajectories and the stress-strain calculation results for the Z-axis tension. Figure 3 Snapshots of deformation at 0.2 and 0.4 uniaxial tensile strains. Figure 4 This is a snapshot of deformation at 0.2 and 0.3 for uniaxial tensile strain.
[0045] Step 9: Compare the trend of the simulation results with the experimental results to verify the effectiveness of the simulation results. Figure 5 The stress-strain curve obtained from the uniaxial tensile simulation was used to find the highest point of the curve on the vertical axis, which is the carbon fiber strength value at that temperature, which is 6.09 GPa. The error between this value and the manufacturer's stated value of 5.50 GPa is 7.2%.
[0046] Step 10: Adjust the initial velocities of all atoms from 500K, 1000K, and 2000K, and submit the LAMMPS calculation. Repeat steps 8 and 9 above to obtain the tensile and compressive strengths at the three high temperatures mentioned above.
[0047] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. 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 determining carbon fiber strength based on molecular dynamics, characterized in that... The steps of this method include: Step 1: Obtain the lattice spacing and the number of interlayer fringes from the high-resolution transmission electron microscope image of the carbon fiber to be tested. Then, obtain the d-value of the graphene fragment based on the obtained lattice spacing and the number of interlayer fringes. 002 Interlayer spacing L1, number of interlayer cross-linking layers N1; Step 2: Randomly fill the inside of the cylinder with discontinuous graphene fragments to obtain the initial carbon fiber atomic structure; Step 3: Calculate the initial carbon fiber atomic structure obtained in Step 2 by performing energy minimization, high-temperature relaxation and annealing calculations to obtain a carbon fiber atomic structure in which crystalline and amorphous states coexist. Step 4: Examine the d-values of the graphene fragments within the carbon fiber atomic structure obtained in Step 3, where crystalline and amorphous states coexist. 002 The interlayer spacing L2 and the number of interlayer cross-linking layers N2 are calculated, and the relative errors W1 between L2 and L1 and W2 between N2 and N1 are calculated. When both W1 and W2 are less than 30%, the carbon fiber atomic structure with crystalline and amorphous states coexisting obtained in step 3 is used as the calculation model. When either W1 or W2 is not less than 30%, 1% to 10% of the carbon atom interlayer crosslinking regions are randomly deleted from the initial carbon atom structure in step 2 or the carbon atom structure in step 3 where crystalline and amorphous states coexist, to obtain a carbon atom structure model. Then, high-temperature relaxation and annealing calculations are performed on the obtained carbon atom structure model to finally form a calculation model. Step 5: Perform uniaxial compression and tensile deformation simulation on the calculation model obtained in Step 4 at temperatures ranging from 300K to 2000K to obtain stress-strain results. Then, based on the stress-strain results, obtain the compressive strength and tensile strength values of the carbon fiber to be tested.
2. The method for determining carbon fiber strength based on molecular dynamics according to claim 1, characterized in that: In step 1, the d of the graphene fragment is obtained based on the acquired lattice spacing and the number of interlayer fringes. 002 The formulas for interlayer spacing L1 and the number of interlayer cross-linking layers N1 are: d 002 Interlayer spacing L1=K·λ / B·cosθ The number of interlayer cross-linking layers, N1 = λ / 0.67sinθ; In the formula, λ is the X-ray diffraction wavelength, θ is the diffraction angle of the crystal plane diffraction peak, and B is the full width at half maximum (FWHM).
3. The method for determining carbon fiber strength based on molecular dynamics according to claim 1, characterized in that: In step 2, the cylindrical region is determined based on the diameter of the carbon fiber atomic structure. Starting from the center of the cylindrical region, n cylinders are sequentially arranged outwards. The inner diameter of the first cylinder is R1, and its outer diameter is R2, and so on, with the inner diameter of the nth cylinder being R... n The outer diameter is R n+1 Each cylinder is filled with graphene fragments.
4. The method for determining carbon fiber strength based on molecular dynamics according to claim 1, characterized in that: In step 2, the graphene fragments filling the cylindrical region are armchair-shaped or serrated, and the lattice constant of the graphene is 1.414, a1(1.732, 0, 0), a2(0, 0, 3), a3(0, 0, 3), basis1(0, 0, 0), basis2(0, 0.333, 0), basis3(0.5, 0.5, 0), basis4(0.5, 0.833, 0).
5. The method for determining carbon fiber strength based on molecular dynamics according to claim 1, characterized in that: In step 3, the conjugate gradient method is used during high-temperature relaxation to adjust atoms that are too close together. NPT ensemble relaxation is applied for 10 ps, 100 ps, and 10 ps respectively under the conditions of 300 K and 0.1 MPa, 1200 K and 0.1 MPa, and 300 K and 0.1 MPa to bring the energy of the system to a stable state.
6. The method for determining carbon fiber strength based on molecular dynamics according to claim 1, characterized in that: In step 5, the rate of uniaxial compression and tensile deformation does not exceed 0.001 angstroms / pf.
7. An electronic device, characterized in that... It includes a processor and a memory, the memory storing program code that, when executed by the processor, causes the processor to perform the steps of the method according to any one of claims 1-6.