A method for determining the strength of amorphous carbon interface layers based on molecular dynamics

Abstract

This invention relates to a method for determining the strength of amorphous carbon interfacial layers based on molecular dynamics, belonging to the field of aerospace lightweight composite material design technology. This invention utilizes molecular dynamics to construct a method that satisfies the interlayer spacing and interlayer crosslinking segments of actual amorphous carbon interfacial layers, and calculates the tensile, compressive, and shear 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 interfacial layer preparation processes and the calculation of service strength in high-performance composite materials.

Description

Technical Field

[0001] This invention relates to a method for determining the strength of amorphous carbon interface layers 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 used molecular dynamics calculations 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 strength calculation of amorphous carbon interface layers on carbon fiber surfaces, Leyssale et al. constructed an atomic model of the interface layer that approximates the real state based on experimental image data, providing new ideas for research in this field. Wu Heng'an's research team conducted extensive molecular dynamics simulation studies on amorphous carbon interface layers. Based on the interlayer spacing obtained from measured high-resolution transmission electron microscopy images, they established an amorphous carbon interface layer model with interlayer crosslinking and various atomic structures of amorphous carbon, and studied the failure mechanisms of uniaxial tensile, compressive, and shear deformation. This method can only artificially create crosslinked segments with fixed atomic structures and does not consider random defects such as atomic vacancies inside the graphene layer. In-Chul Yeh et al. studied the effect of high-temperature annealing on the structural mechanical properties of amorphous carbon materials, obtaining carbon ring structure segments containing vacancy defects. Raphaëlle et al. established various atomic structures of amorphous carbon based on data such as microcrystalline interlayer spacing, length, and stacking thickness. The proposed concept of texture parameters provides guidance for research in this field; however, the interface layer structures obtained in this work are too short-range ordered, and their effectiveness in quantitatively studying the deformation and failure mechanisms of the interface layer warrants further discussion. Overall, there are still many problems in the molecular dynamics calculation methods of amorphous carbon interface layers and the study of fracture failure mechanisms under high-temperature service environments. Breakthroughs are needed in constructing atomic structure models that can accurately describe the distribution of interlayer crosslinking fragments.

[0004] Disadvantages of existing technology:

[0005] The interior of a conventional amorphous carbon interface layer is usually considered to be formed by stacking amorphous graphene layers composed of six-membered carbon rings. Wu Heng'an's research team [3-5] constructed amorphous carbon interface layers using interlayer crosslinking fragments with specific atomic structures. Although this can ensure that the interlayer spacing of the amorphous graphene layer is close to the measured interlayer spacing, it is difficult to artificially create crosslinking fragments with random atomic structures, and it does not take into account random defects such as atomic vacancies inside the graphene layer. Summary of the Invention

[0006] The technical problem solved by this invention is: based on the distribution of interlayer crosslinking fragments and interlayer spacing d002, as well as micro-nano indentation strength experimental data obtained from high-resolution transmission electron microscopy images and XRD patterns of the interface layer, this invention establishes the atomic structure of the amorphous carbon interface layer and conducts tensile, compressive and shear strength calculations under room temperature and high temperature environments.

[0007] The technical solution of this invention is:

[0008] A method for calculating the strength of amorphous carbon interface layers based on molecular dynamics, the method comprising the following steps:

[0009] Step 1: Obtain the interlayer spacing and the number of interlayer fringes from the transmission electron microscope image of the amorphous carbon interface sample. Then, obtain the average value L1 of the interlayer spacing and the average value N1 of the number of interlayer crosslinking layers based on the obtained interlayer spacing and the number of interlayer fringes.

[0010] Step 2: Create multilayer graphene, randomly fill the interlayers of graphene with cross-linked fragments with a set atomic structure, and delete 0.01-0.1% of carbon atoms in each graphene layer to obtain cross-linked regions with random atomic structures.

[0011] Step 3: Perform energy minimization, high-temperature relaxation and annealing calculations on the cross-linked regions obtained in Step 2 to form an atomic structure model of the amorphous carbon interface layer.

[0012] Step 4: Calculate the interlayer spacing L2 and the number of interlayer cross-linked segments N2 of the graphene fragments inside the atomic structure model obtained in Step 3, and calculate the relative error W1 between L2 and L1 and the relative error W2 between N2 and N1. When both W1 and W2 are less than 25%, the atomic structure model obtained in Step 3 is considered to conform to the amorphous carbon interface layer structure to be tested, and the atomic structure model obtained in Step 3 is used as the calculation model.

[0013] When either W1 or W2 is not less than 25%, the number of carbon atoms constructing interlayer cross-linking regions with a proportion of 0.1-0.01 is randomly deleted from the atomic structure model in step 3 to obtain the atomic structure model. Then, high-temperature relaxation and annealing calculations are performed on the obtained atomic structure model to finally form an amorphous interface layer atomic structure that is close to the experimental sample as the calculation model.

[0014] Step 5: Use OVITO software to check the calculation model obtained in Step 4, delete the free discrete atoms, and use the compress yes command to reorder the atom numbers.

[0015] Step 6: Perform uniaxial compression and tensile deformation simulation on the calculation model obtained in Step 5 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 amorphous interface layer.

[0016] 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:

[0017] d 002 Interlayer spacing L1 = K·λ / B·cosθ

[0018] The number of interlayer cross-linked layers N1 = λ / 0.67sinθ.

[0019] 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).

[0020] In step 2, cylindrical, square, and other regions are constructed based on the geometric regions of the amorphous interface layer model. Then, n graphene layers are layered from bottom to top. The bottom height of the first graphene layer is L1, the top height is L2, and the bottom height of the nth graphene layer is L... n The height of the top surface is L n+1 Each layer is filled with graphene fragments;

[0021] In step 2, the filled graphene fragments are either armchair-shaped or serrated, and the graphene lattice constant 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).

[0022] In step 2, cross-linked fragments with predetermined atomic structures are randomly filled between graphene layers, with no less than 6 atomic structures; cross-linked regions with random atomic structures are constructed for each graphene layer using random, specified regions or groups of carbon atoms.

[0023] 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.

[0024] In step 6, the entire atomic structure is divided into a top region, a middle region, and a bottom region according to the height direction. The bottom region is fixed using the fix setforce command, the middle region is set with a target temperature, and the top region is set with a stretching, compression, or shearing rate. The rate of uniaxial compression, stretching, and shearing deformation does not exceed 0.001 Å / pf. The move command is used under the NVT (canonical ensemble, abbreviated as NVT, which means maintaining a definite number of particles N, volume V, and temperature T) system.

[0025] 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.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] This invention utilizes molecular dynamics to construct the interlayer spacing and interlayer crosslinking segments that satisfy practical amorphous carbon interfacial layers, and calculates the tensile, compressive, and shear 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 interfacial layer preparation processes and the calculation of service strength in high-performance composite materials.

[0028] This invention provides a method for establishing the atomic structure of the interface layer based on the measured interlayer spacing and the number of interlayer crosslinking fragments in a carbon / silicon carbide composite material sample. The atomic structure obtained by this method can more accurately characterize the stacking of graphene fragments and the distribution of interlayer crosslinking atoms within the real amorphous carbon interface layer. Tensile and shear strength calculations based on this atomic structure are closer to the measured data. Current technologies, primarily those developed by Leyssale et al. and Wu Heng'an's research team, construct near-realistic interface layer atomic models based on measured sample image data. These methods focus on comparing the graphene interlayer spacing with experimental results, but they cannot artificially control the shape and number distribution of interlayer crosslinking fragments and do not consider random defects such as atomic vacancies within the graphene layer, resulting in significant discrepancies with actual samples. Building upon these works, this patent proposes a method for actively controlling interlayer crosslinking fragments by actively deleting 0.01-0.2% of carbon atoms and introducing them into the interlayer crosslinking region. This significantly reduces the difference between the distribution of interlayer crosslinking fragments and the actual sample, providing a more realistic characterization of the interlayer atomic distribution of the interface layer than all previously reported methods. Attached Figure Description

[0029] Figure 1 The atomic structure of the amorphous carbon interface layer (blue represents carbon atoms, and red represents interlayer cross-linking fragments).

[0030] Figure 2 It has an amorphous carbon interface layer atomic structure;

[0031] Figure 3 Cross-sectional snapshots of interface layers with different numbers of interlayer crosslinking fragments ( Figure 3 (a) consists of 8 cross-linked segments. Figure 3 (b) consists of 4 crosslinked segments.

[0032] Figure 4 This is an axis view of the uniaxial stretching process;

[0033] Figure 5 This is the stress-strain curve during uniaxial tension. Detailed Implementation

[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 calculating the strength of amorphous carbon interface layers based on molecular dynamics is performed according to the following steps:

[0037] Step 1: Obtain the interlayer spacing and the number of interlayer fringes from the transmission electron microscope image of the amorphous carbon interface sample. Then, obtain the average value L1 of the interlayer spacing and the average value N1 of the number of interlayer crosslinking layers based on the obtained interlayer spacing and the number of interlayer fringes.

[0038] Step 2: Compile the input .in file for molecular dynamics calculations. Use metal units for the carbon atoms in the interface layer, and set the spatial dimension to three-dimensional with a periodic boundary. 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: Based on the desired geometric shape of the interface layer model, use the `region` command to create 20 layers from bottom to top, with dimensions of 85.216 Å, 83.64 Å, and 68 Å respectively. Each layer is filled with graphene fragments. The interlayer spaces are filled with 44 tilted hexagonal carbon rings. The `delete_atoms` command is used to randomly delete 1% of the carbon atoms within the cylindrical regions. Figure 1 The left image shows the initial carbon atom distribution, and the right image shows the atomic structure obtained after high-temperature relaxation. The red carbon atoms in the images are cross-linked segments, and the blue carbon atoms are carbon atoms within the layers.

[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 show the interlayer carbon atom distribution after high-temperature relaxation. 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, and adjust the NPT pressure setting value according to the interlayer spacing. Compare the number of interlayer crosslinking segments in the initial atomic structure with the measured value, and adjust the number of interlayer crosslinking regions by deleting 1.5% 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 interface layer atomic structure and the measured value exceeds 20%, then iterate through steps 3 to 6 again. Figure 2 This is the final atomic structure model of the interface layer. Figure 3 This is a cross-sectional view of the interface layer model from multiple perspectives.

[0044] Step 8: Perform uniaxial tension and compression calculations in the Z-axis and shear deformation calculations in the XZ plane on the relaxed carbon fiber atomic structure. The deformation loading rate is 0.001 Å / pf. Set the initial velocity of all atoms at 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 stress-strain calculation results. Figure 4 (a) is a snapshot of deformation at 0.2 and 0.4 uniaxial tensile strains. Figure 4 (b) is the overall deformation and XZ plane section view with a shear strain of 0.15.

[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 shear deformation simulation was used to find the highest point on the vertical axis, which is the maximum strength value of 0.72 GPa at that temperature. After the maximum strength, the stress value gradually tends to stabilize. The average value of this stage is 0.115 GPa and the maximum value is 0.26 GPa. The error between this stage and the value of 0.13 GPa obtained by the micro-nano indentation test is 15.5%.

[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, compressive, and shear 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 calculating the strength of amorphous carbon interface layers based on molecular dynamics, characterized in that... The steps of this method include: Step 1: Obtain the interlayer spacing and the number of interlayer fringes from the transmission electron microscope image of the amorphous carbon interface sample. Then, obtain the average value L1 of the interlayer spacing and the average value N1 of the number of interlayer crosslinking layers based on the obtained interlayer spacing and the number of interlayer fringes. Step 2: Establish multilayer graphene, randomly fill cross-linked fragments with a set atomic structure between graphene layers, and delete 1% to 10% of carbon atoms in each graphene layer to obtain cross-linked regions with random atomic structures. Step 3: Perform energy minimization, high-temperature relaxation and annealing calculations on the cross-linked regions obtained in Step 2 to form an atomic structure model of the amorphous carbon interface layer. Step 4: Calculate the interlayer spacing L2 and the number of interlayer cross-linked segments N2 of the graphene fragments inside the atomic structure model obtained in Step 3, and calculate the relative error W1 between L2 and L1 and the relative error W2 between N2 and N1. When both W1 and W2 are less than 25%, the atomic structure model obtained in Step 3 is used as the calculation model. When either W1 or W2 is not less than 25%, 1% to 10% of the carbon atoms in the atomic structure model in step 3 are randomly deleted to construct the interlayer crosslinking region, thus obtaining the atomic structure model. Then, the obtained atomic structure model is subjected to high-temperature relaxation and annealing calculations to obtain the 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 amorphous interface layer.

2. The method for calculating the strength of amorphous carbon interface layers 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 calculating the strength of amorphous carbon interface layers based on molecular dynamics according to claim 1, characterized in that: In step 2, a cylindrical or square region is constructed based on the geometric region of the amorphous interface layer model, and n graphene layers are set from bottom to top. The bottom height of the first graphene layer is L1, the top height is L2, and the bottom height of the nth graphene layer is L... n The height of the top surface is L n+1 Each layer is filled with graphene fragments.

4. The method for calculating the strength of amorphous carbon interface layers based on molecular dynamics according to claim 3, characterized in that: In step 2, the filled graphene fragments are either armchair-shaped or serrated, and the graphene lattice constant 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 calculating the strength of amorphous carbon interface layers based on molecular dynamics according to claim 1, characterized in that: In step 2, cross-linked fragments with predetermined atomic structures are randomly filled between graphene layers, with no less than 6 atomic structures; cross-linked regions with random atomic structures are constructed for each graphene layer using random, specified regions or groups of carbon atoms.

6. The method for calculating the strength of amorphous carbon interface layers 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.

7. The method for calculating the strength of amorphous carbon interface layers based on molecular dynamics according to claim 1, characterized in that: In step 6, the entire atomic structure is divided into a top region, a middle region, and a bottom region according to the height direction. The bottom region is fixed using the fix setforce command, the middle region is set with a target temperature, and the top region is set with a stretching, compression, or shearing rate. The rate of uniaxial compression, stretching, or shearing deformation does not exceed 0.001 angstroms / pf, and is implemented using the move command under the NVT system.

8. 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 1-7.

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