A research method for regulating friction resonance of commensurate and incommensurate contact interfaces

Abstract

The present invention relates to a research method for regulating the friction resonance of commensurate and incommensurate contact interfaces. Taking double-layer graphene as the research object, a molecular dynamics model is established. By studying the change of friction force with speed under different contact states, the influence of speed and contact state on the friction force of graphene is determined, and the resonance theory is used to explain the local peak phenomenon of friction force in combination with the Fourier transform method. In addition, the present invention further determines the influence of the phonon spectrum matching degree of the graphene probe and the substrate on the energy dissipation during the friction process. Finally, a theoretical model for calculating the number of interface phonons is derived, and the difference in the frequency distribution range of the excited phonon number is compared to quantitatively explain the distinct internal mechanism of friction force under two contact states. The present invention provides an effective research method for determining the internal mechanism of the speed dependence of the friction force of graphene under different contact states, which can provide a theoretical reference for designing friction pairs considering the resonance frequency.

Description

Technical Field

[0001] The present invention relates to the field of molecular dynamics technology, and in particular to a research method for regulating friction resonance of commensurate and incommensurate contact interfaces. Background Art

[0002] Friction is a common physical phenomenon existing in mechanical systems. In most cases, the friction process is closely related to energy dissipation. In order to effectively control the dissipated energy during the friction process and reduce the energy loss caused by friction, it is urgent to study the factors affecting friction. From ancient times to the present, people have never stopped exploring the friction phenomenon. At the macroscopic scale, people found that the friction force is proportional to the normal load, but has nothing to do with the contact area and sliding speed. With the advancement of science and technology, through the study of atomic-scale friction phenomena, people found that the macroscopic friction law is no longer applicable to atomic-scale friction phenomena. The friction force at the atomic scale can be affected by factors such as temperature, speed, and the commensurability of the contact interface. Based on experimental and numerical analysis studies in recent years, among the above-mentioned influencing factors, the intrinsic mechanism of the influence of speed on atomic-scale friction is still controversial.

[0003] Some scholars have found that atomic-scale friction changes monotonically with increasing speed. Gnecco et al. slid a silicon probe along the surface of sodium chloride (100) at room temperature and found that when the relative sliding speed was less than 1 μm / s, the friction and barrier height were linearly related to the logarithm of the sliding speed, but when the speed exceeded 1 μm / s, this linear relationship failed. Later, Sang et al. and Dong et al. believed that the change in barrier height varied exponentially with the friction, and then obtained that the logarithm of the friction and sliding speed also showed an exponential relationship, which made the model applicable to a wider range of speeds.

[0004] At the same time, some researchers have found that friction shows a non-monotonic trend with speed. Riedo et al. and Li et al. used friction microscopy and molecular dynamics to study the effect of speed on friction. The results showed that when the speed is low, the friction changes linearly with the logarithm of the speed, and when the speed is higher than a certain critical value, the friction no longer changes with the increase of speed. The authors believe that when the speed is low, the thermal excitation effect is strong and the friction changes significantly with the speed. When the speed is high, the thermal excitation duration is so short that the thermal effect can be ignored, resulting in a weakened dependence of friction on speed.

[0005] In addition to the above-mentioned influence of velocity on atomic-scale friction, the influence of the commensurate and incommensurate states of the contact interface on friction has also become a research hotspot. Chen et al. found that the relationship between the size of the contact area and the friction is different for commensurate and incommensurate contact surfaces. In addition, many scholars have achieved ultra-low friction by changing the mismatch angle of the contact surface. During the friction process, the energy dissipation process of the two non-metallic surfaces is mainly completed in the form of phonons. Therefore, the influence of phonon dissipation of different contact surfaces on friction has also been widely studied. Torres et al. proposed that the key factor in determining friction energy dissipation is whether new dissipation channels are excited. Due to the elastic deformation of the commensurate interface, new phonon dissipation channels are generated in the non-harmonic mode, resulting in higher friction.

[0006] In summary, speed and contact surface state have a significant effect on friction at the atomic scale. Friction is an irreversible energy dissipation process caused by the interaction of atoms at the contact interface, and involves a very complex non-equilibrium thermodynamic process. Many scholars have made a lot of research for this. However, under different contact states, there is no reasonable study on the phonon mechanism of the velocity dependence of friction. Therefore, the present invention establishes a graphene friction pair under commensurate and incommensurate contact states, studies the dependence of its friction on speed, and combines phonons to explain the intrinsic mechanism of its friction energy dissipation. The friction curve obtained by the research of the present invention has some friction peaks under commensurate and incommensurate contact states. Through the fast Fourier transform of instantaneous friction, the present invention confirms that these local friction peaks are caused by phonon resonance. The present invention further uses phonon spectrum and phonon number to study the dissipation mechanism of friction energy under different contact states. By studying the phonon mechanism of the velocity dependence of friction of graphene under commensurate and incommensurate contact states, the present invention can provide a reference for regulating the behavior of interface friction resonance. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a research method for regulating the friction resonance of commensurate and incommensurate contact interfaces. It takes graphene as the research object, provides an effective research method for determining the intrinsic mechanism of the velocity dependence of the friction force of graphene under different contact states, and further provides a theoretical reference for designing friction pairs considering the resonance frequency.

[0008] In order to solve the above problems, the present invention provides a research method for regulating friction resonance of commensurate and incommensurate contact interfaces, the research method comprising:

[0009] (1) Establishment of molecular dynamics model

[0010] The model includes a substrate supported by a rigid body and a probe graphene arranged on the substrate, wherein the substrate is a double-layer graphene; each atom of the probe graphene is provided with springs in three directions, namely, x, y and z; the spring in the x direction is connected to a slider that moves at a constant speed in a directional manner; the spring in the y direction is used to prevent the probe graphene from rotating around the z axis and translating along the y axis during sliding; and the spring in the z direction is used to apply a normal load; the stiffness of the spring in the x direction is 570 n / m, and the total stiffness of the springs in the y and z directions is 320 n / m; periodic boundary conditions are applied in the x and y directions, and free boundary conditions are set in the z direction; the atoms on both sides of the fixed boundary of the upper graphene layer of the substrate are set as temperature regulation areas by using the Brandsen temperature regulation method;

[0011] (2) Determine the effect of speed on the friction of graphene in commensurate / incommensurate contact states and its mechanism

[0012] In the case where the probe graphene and the substrate are in commensurate / incommensurate contact, the slider is given different speeds from 5m / s to 250m / s, the model is run respectively, and the friction between the probe graphene and the substrate at different speeds during the friction process is calculated; the potential barrier height of the model during the friction process under the commensurate / incommensurate contact state is calculated to explain the difference in friction under the commensurate / incommensurate contact state;

[0013] (3) Determine the internal mechanism of the peak value of friction force with increasing speed in the commensurate / non-commensurate state

[0014] The potential energy topography of the probe of the model during the friction process in the two contact states of commensurate / incommensurate is calculated to analyze the difference in vibration frequency presented by the periodic excitation of the probe atoms by the potential energy; the frequency distribution of the vibration amplitude obtained by fast Fourier transform of the friction force is combined to explain the friction peak phenomenon caused by resonance, thereby providing a theoretical reference for designing friction pairs considering the resonance frequency; and the vibration amplitude is used to explain the phenomenon that the friction force in the commensurate / incommensurate state changes with speed from the perspective of energy dissipation.

[0015] Preferably, after step (3), the method further comprises:

[0016] (4) Determine the phonon mechanism of friction force changing with velocity under commensurate / incommensurate conditions

[0017] The phonon state density of carbon atoms in the selected area of ​​the model is calculated, and the phonon spectra of the probe graphene and the substrate during the friction process under different contact states are obtained, and the difference in the phonon spectra under the commensurate / incommensurate states is used to explain the difference in friction under the two states; a theoretical model of the phonon number is derived, and the frequency distribution of the phonon number at different speeds under the commensurate / incommensurate states is calculated, and the difference in the phonon number distribution is used to intuitively explain the difference in friction under two different contact states.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. In the present invention, a molecular dynamics model is first established, and then the model is run respectively under different contact states and different sliding speeds, and the interlayer friction force, phonon spectrum and other data in the friction process are calculated and analyzed and processed, which provides an effective research method for determining the influence of speed on the friction force of commensurate / incommensurate graphene and its internal mechanism, and further provides a theoretical reference for designing friction pairs considering the resonant frequency.

[0020] 2. The present invention uses fast Fourier transform to analyze the instantaneous friction force. It is finally found that the resonance phenomenon is the cause of the local peak value of the friction force, and the vibration amplitude of the probe graphene mass center atom obtained after Fourier transform can be used to further explain the change of friction force.

[0021] 3. The present invention uses the phonon spectrum matching degree of the probe graphene and the substrate in the commensurate and incommensurate contact states to reveal the difference in friction energy consumption. In the commensurate state, the phonon spectrum of the probe and the substrate matches, while in the incommensurate state, the phonon spectrum presents a mismatch state, making the friction force in the commensurate state much higher than the friction force in the incommensurate state.

[0022] 4. The present invention derives a theoretical model of the number of phonons and counts the number of phonons in two contact states to quantitatively explain the difference in friction energy consumption. When the number of phonons is large, the friction energy consumption is high, resulting in a large friction force.

[0023] In summary, the study of friction force under different states based on phonon spectrum matching and phonon number in the present invention can provide a theoretical reference for designing friction pairs considering the resonant frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0025] Figure 1 A molecular dynamics model provided by an embodiment of the present invention.

[0026] Figure 2 The embodiment of the present invention provides the dependence of the friction force between graphene layers and the speed under the commensurate / incommensurate state.

[0027] Figure 3 The potential barrier heights at different speeds under commensurate / incommensurate conditions provided by the embodiment of the present invention.

[0028] Figure 4 The potential energy topography of the probe under commensurate / incommensurate conditions provided by the embodiment of the present invention.

[0029] Figure 5The fast Fourier transform of instantaneous friction force at different speeds in commensurate / incommensurate states provided by the embodiment of the present invention.

[0030] Figure 6 The phonon spectrum at the same speed in the commensurate / incommensurate state provided by the embodiment of the present invention.

[0031] Figure 7 The frequency distribution of the number of phonons at different speeds in the commensurate / incommensurate state provided by the embodiment of the present invention. DETAILED DESCRIPTION

[0032] The present invention takes graphene as the research object, explores the dependence of friction force between graphene layers and speed under different contact states and the friction force peak phenomenon caused by resonance, and studies the phonon mechanism of friction energy dissipation. The present invention provides a research method for regulating friction resonance of commensurate and incommensurate contact interfaces, which specifically includes the following contents:

[0033] (1) Establishment of molecular dynamics model

[0034] The present invention uses a molecular dynamics simulation method based on LAMMPS to implement the simulation process. Figure 1 The schematic diagram of the molecular dynamics model under the established commensurate state. In the present invention, the molecular dynamics model includes a square graphene sheet for simulating an atomic force microscope probe and a substrate composed of two layers of graphene. The graphene atoms at the bottom of the substrate and the graphene atoms at both ends of the y direction of the top layer of the substrate are set to be fixed without vibration. In order to prevent the probe from rotating along the z axis or moving along the y axis, all atoms of the probe are set to be connected to a spring with a stiffness of 320n / m in the y direction and the z direction. In order to keep the distance between the probe and the substrate constant and unchanged during the sliding process, a normal load of 0.25nN is applied to the z direction of the probe atom. In the x direction, each atom of the probe is connected to a slider moving along the x direction with a certain speed through a spring with a stiffness of 570n / m, so that the graphene probe can slide along the x direction at the same speed. The contact state between the graphene probe and the substrate is regulated by the mismatch angle between the two, and the mismatch angle of the non-commensurate contact state is 30°. The mismatch angle is defined as the angle at which two identical surfaces rotate relative to each other along the lattice arrangement direction.

[0035] Periodic boundary conditions were applied in the x and y directions to ensure that the atomic vibrations of the contact surface were continuously excited during the friction process, while free boundary conditions were used in the z direction. In the upper graphene layer of the substrate, the atoms close to the fixed boundaries on both sides of the y direction were set as temperature regulation areas using the Brandsen thermostat method. Before the probe and the substrate slid relative to each other, the system took 0.05ns to relax to the thermal equilibrium state. In order to eliminate the influence of phonons caused by the background temperature during the simulation, the temperature of the thermostat layer was always kept stable at 0K during the simulation. The LJ potential was used to characterize the weak interactions between the interlayer atoms. The parameters of the LJ potential include the potential well depth ε = 3.73meV and the equilibrium constant σ = 0.34nm. In addition, the cutoff radius of the LJ potential was 0.884nm. The strong covalent bonding between the same layer of graphene was calculated using the optimized Tersoff potential. The time step was set to 0.5fs during the simulation.

[0036] (2) Determine the effect of speed on commensurate / incommensurate graphene friction and its underlying mechanism

[0037] (21) Determine the effect of speed on commensurate / incommensurate graphene friction

[0038] The above models were run under the conditions of commensurate / incommensurate contact between the probe graphene and the substrate, respectively. Figure 2 are the friction images calculated by the above model under the commensurate and incommensurate contact states, respectively. Figure 2 As shown in (a), under the normal state, the friction force increases with the increase of speed. When the sliding speed reaches a fixed value, the friction force decreases with the speed. The trend of the friction force calculated by the present invention with the speed is the same as that of previous scholars. Figure 2 As shown in (b), the friction force in the non-commensurate state is two orders of magnitude lower than the friction force in the commensurate state. The huge difference between the commensurate and non-commensurate states obtained by the present invention is consistent with the previous studies of scholars.

[0039] (22) Study the intrinsic mechanism of velocity dependence of friction force under commensurate / incommensurate contact conditions

[0040] (221) Using the potential barrier height to explain the difference in friction between commensurate and incommensurate contact states

[0041] The huge difference in friction between commensurate and incommensurate contact states can be attributed to the difference in interfacial barrier height. The barrier height is the net change between the instantaneous maximum and minimum values ​​of the interfacial van der Waals potential energy. Figure 3As shown, the present invention counts the potential barrier heights under commensurate and non-commensurate conditions. Under commensurate conditions, the potential barrier is higher, which means that the substrate needs a larger spring force to cross the potential barrier during the friction process, resulting in a correspondingly higher friction force. On the contrary, under non-commensurate conditions, a lower potential barrier height results in a lower friction force. The present invention further reveals that under commensurate conditions, the barrier height increases significantly with speed, resulting in an increase in friction force.

[0042] (222) The potential energy topography is used to explain the vibrational frequencies of the graphene probe and substrate atoms.

[0043] exist Figure 2 In the experiment, the curves of friction force changing with speed in the commensurate and non-commensurate states are not smooth. Some local peaks of friction force appear before the highest friction force. These friction peaks in the commensurate state are the same as the experimental results described in previous literature, but they are often regarded as experimental errors. The friction process is an inelastic collision between the graphene probe and the substrate. When the probe slides on the substrate, the relative motion between the graphene probe and the substrate will stimulate the atoms on the contact surface to move at the washboard frequency f. t =v s / L vibrates, where L is the potential energy period. During the sliding process, when the excitation frequency is equal to the natural frequency of the probe, resonance occurs, resulting in friction force peaks in two states. Therefore, the present invention further studies the frequency distribution of the probe graphene under commensurate and incommensurate contact states during the friction process. In order to determine the potential energy period length of different contact states, the probe and substrate are set as rigid bodies. At this time, the model is different from Figure 1 Then the graphene probe is slid back and forth on the substrate, and the following Figure 4 The potential energy topography of the probe shown. Figure 4 As shown in (a), the potential energy period of the probe and the substrate under the commensurate state is a is the length of the carbon-carbon bond in the graphene structure; Figure 4 As shown in (b), in the incommensurate state, the potential energy period of the probe becomes 3a, while the potential energy period length of the substrate in the incommensurate state is still 3a because there is no rotation. Therefore, the washboard frequencies of the base atoms in the commensurate state and the incommensurate state can be expressed as and f = v s / 3a. Although the probe and the substrate are set as rigid bodies, the potential energy difference in the commensurate state is much greater than that in the incommensurate state. The obvious difference in the potential energy topography is consistent with Figure 3 The difference in the potential barrier height is consistent.

[0044] (223) Fast Fourier transform of the instantaneous friction force of the probe atom is used to explain the intrinsic mechanism of the velocity dependence of the friction force in the commensurate / incommensurate state, and resonance is used to explain the peak value of the friction force.

[0045] In order to further study the effect of vibration frequency on friction energy dissipation, the instantaneous friction force on the probe graphene is subjected to fast Fourier transform. inst The calculation formula is F inst =K(v s tx), x is the moving distance of the probe, and t is the sliding time of the probe during the friction process. The Fourier transform spectrum can reflect the probe frequency and amplitude of the sliding probe. The Fourier transform spectrum drawn by the present invention is as follows Figure 5 shown.

[0046] like Figure 5 As shown in (a), under the condition of commensurate degree, when the sliding speed is small (v s =13m / s), the interface constraint between the substrate and the probe is strong, so the vibration amplitude of the probe atoms is distributed above the washboard frequency and its multiples. At this time, the lower amplitude leads to less energy dissipation in the friction process. Figure 5 (c) and Figure 5 As shown in (e), with the increase of speed, the potential energy constraint effect gradually weakens, and the amplitude is mainly distributed at the probe's washboard frequency f t And the natural frequency In the above, m is the mass of the probe. In addition, higher amplitudes cause greater friction. Figure 5 As shown in (g), when the speed increases to 106.2 m / s, the washboard frequency f t It coincides with the natural frequency f. At this time, the amplitude reaches its maximum value and the peak of friction occurs at Figure 2 In (a), the speed corresponding to the washboard frequency f is expressed as like Figure 5 (c), when the speed is 53.1 m / s, the corresponding washboard frequency is half of the natural frequency of the graphene probe. At this time, the amplitude is relatively high, and a friction peak also appears. Figure 2 (a) is marked as v f / 2. In addition, when the sliding speed is equal to v f / n (n=3,4,5,…), the corresponding washboard frequency is close to f / n, and more friction peaks appear. In short, when the washboard frequency is close to the natural frequency and its fractional frequency, resonance will cause friction peaks. Figure 5 (c) with Figure 5 (i) When the washboard frequency is offset from the natural frequency and its fractional frequency, resonance does not occur and the amplitude is low, resulting in lower friction.

[0047] like Figure 5As shown in (b), when the probe graphene and the substrate are in non-commensurate contact and the friction process speed is low, the amplitude of the probe atoms is mainly distributed above the washboard frequency and the natural frequency due to the weak constraint between the contact interfaces. And as the speed increases, the potential energy constraint becomes weaker, so the amplitude will be concentrated above the natural frequency. Figure 5 (d) with Figure 5 (h), consistent with the commensurate state, when the sliding speed of the probe is close to v f / 2 and v f = 3af, the higher amplitude caused by resonance causes the peak of friction force. In addition, when the sliding speed approaches v f / n (n=3,4,5,…), the corresponding washboard frequency is close to other fractional frequencies of the natural frequency f / n, and the corresponding sliding speed is close to v f / n, such as Figure 2 As shown in (b), a friction peak will also appear. Figure 5 (f) Figure 5 (j) When the washboard frequency moves away from the natural frequency and its fractions, the reduction in amplitude results in lower friction.

[0048] (224) Phonon spectrum explains friction energy dissipation channel

[0049] The present invention shows that at higher speeds, the amplitudes of the graphene probe and substrate in the non-commensurate state are mostly higher than the amplitudes in the commensurate state (except when the speed is 13m / s). Figure 2 The friction force in the commensurate state is much higher than that in the incommensurate state. This proves that compared with the commensurate state, only a small part of the energy generated by the higher amplitude in the incommensurate state is dissipated. Since the ability to dissipate energy during friction depends on the amount of kinetic energy absorbed by the substrate from the probe, in order to clarify the different forms of friction energy dissipation in the commensurate and incommensurate states, the present invention statistically analyzed the phonon state density during friction in the commensurate and incommensurate states. The results are as follows: Figure 6 As shown in Figure 2. Under the two different contact states, the excited phonon modes are distributed above the washboard frequency and its double frequencies, and the atoms on the contact surface are affected by the potential energy of the relative surface. Figure 4 As shown in (a), in the contact state, the potential energy period of the probe and the substrate is Therefore, if Figure 6 As shown in (a), the probe's rubboard frequency and the substrate's rubboard frequency are both equal to In this case, a smooth energy dissipation channel can be formed, and the vibration energy during the friction process can be effectively transferred from the probe to the substrate and absorbed by the isothermal layer in the model. Therefore, more energy is dissipated during sliding, resulting in higher friction; on the contrary, in the non-commensurate state, the potential energy period of the probe becomes 3a, so the washboard frequency of the substrate is equal to v s / 3a, while the probe's washboard frequency is still like Figure 6 As shown in (b), due to the mismatch of phonon frequency distribution between contact interfaces, the energy generated by the friction process is difficult to transfer from the probe to the substrate. Therefore, even if the vibration amplitude of the probe in the non-commensurate state is higher than that in the commensurate state, less energy is dissipated, resulting in extremely low friction. In short, more energy generated by higher amplitude can be dissipated under the same contact state, but the amount of dissipated energy based on the negative value of vibration cannot be compared under different contact states, because different contact states represent different dissipation channels between the probe and the substrate.

[0050] (225) The phonon number theory model was derived to quantitatively explain the energy change during friction.

[0051] The friction process will generate additional phonons, and the number of phonons can reflect the magnitude of the friction energy dissipation of the system. In order to quantitatively study the obvious difference in friction force under commensurate and incommensurate contact states, the present invention derives a theoretical model for calculating the number of phonons.

[0052] Based on theories of solid state physics, lattice dynamics, and quantum mechanics, the total energy of the system is

[0053]

[0054] In the formula

[0055] T——system temperature (K);

[0056] ——Reduced Planck constant;

[0057] K B ——Boltzmann constant;

[0058] ω——angular frequency;

[0059] g(ω)——theoretical state density.

[0060] In molecular dynamics, the power spectral density can be expressed as

[0061]

[0062] In the formula

[0063] <v(t)·v(0)>——Velocity autocorrelation function

[0064] The velocity autocorrelation function can also be obtained by the inverse fast Fourier transform of the power spectrum density:

[0065]

[0066] The average kinetic energy per unit volume in the equilibrium state can be calculated as

[0067]

[0068] In the formula

[0069] N——the number of atoms in the unit group;

[0070] m – the mass of a single atom (Kg).

[0071] According to the law of equipartition of energy, the kinetic energy and potential energy of the system are equal, so the total energy of the system can be expressed as

[0072]

[0073] Since the total energy generated in the friction process calculated by the theoretical model and the molecular dynamics simulation is equal, combining formulas (1) and (5), we can obtain the following equilibrium relationship:

[0074]

[0075] Since g(ω) is the theoretical state density, is the number of phonons at frequency ω. The distribution of the number of phonons per unit volume on the frequency axis is

[0076]

[0077] Figure 7 is the distribution of the number of phonons per unit volume on the frequency axis calculated by formula (7). Figure 7 (a) with Figure 7 (c) shows the contact state of the commensurate degree, and Figure 7 (b) with Figure 7 In the non-common contact state shown in (d), the excited phonons are distributed on the washboard frequency of the probe and its multiple times. However, the frequency ranges of excited phonons in the two different contact states are different. In the common contact state, a large number of phonons can still be excited above seven times the washboard frequency, while in the non-common contact state, very few phonons are excited by three times the washboard frequency, and the magnitude of the phonon spectrum peak in the non-common state is consistent with that in the common state. In addition, the number of phonons excited in the two contact states will increase with the increase of sliding speed. The difference in the phonon number spectrum reveals that more phonons will be generated in the common state than in the non-common state. More phonons mean that more friction energy is dissipated, resulting in higher friction. The present invention quantitatively explains the phenomenon that friction varies with different contact states from the perspective of excited phonons.

[0078] The technical solution provided by the present invention is described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A research method for regulating friction resonance of commensurate and incommensurate contact interfaces, characterized in that: The research methods include: (1) Establishment of molecular dynamics model The model includes a substrate supported by a rigid body and a probe graphene arranged on the substrate, wherein the substrate is a double-layer graphene; each atom of the probe graphene is provided with springs in three directions, namely, x, y and z; the spring in the x direction is connected to a slider that moves at a constant speed in a directional manner; the spring in the y direction is used to prevent the probe graphene from rotating around the z axis and translating along the y axis during sliding; and the spring in the z direction is used to apply a normal load; the stiffness of the spring in the x direction is 570 n / m, and the total stiffness of the springs in the y and z directions is 320 n / m; periodic boundary conditions are applied in the x and y directions, and free boundary conditions are set in the z direction; the atoms on both sides of the fixed boundary of the upper graphene layer of the substrate are set as temperature regulation areas by using the Brandsen temperature regulation method; (2) Determine the effect of speed on the friction of graphene in commensurate / incommensurate contact states and its mechanism In the case where the probe graphene and the substrate are in commensurate / incommensurate contact, the slider is given different speeds from 5m / s to 250m / s, the model is run respectively, and the friction between the probe graphene and the substrate at different speeds during the friction process is calculated; the potential barrier height of the model during the friction process under the commensurate / incommensurate contact state is calculated to explain the difference in friction under the commensurate / incommensurate contact state; (3) Determine the internal mechanism of the peak value of friction force with increasing speed in the commensurate / non-commensurate state The potential energy topography of the probe of the model during the friction process in the two contact states of commensurate / incommensurate is calculated to analyze the difference in vibration frequency presented by the periodic excitation of the probe atoms by the potential energy; the frequency distribution of the vibration amplitude obtained by fast Fourier transform of the friction force is combined to explain the friction peak phenomenon caused by resonance, thereby providing a theoretical reference for designing friction pairs considering the resonance frequency; and the vibration amplitude is used to explain the phenomenon that the friction force in the commensurate / incommensurate state changes with speed from the perspective of energy dissipation.

2. The research method according to claim 1, characterized in that: After step (3), the method further includes: (4) Determine the phonon mechanism of friction force changing with velocity under commensurate / incommensurate conditions The phonon state density of carbon atoms in the selected area of ​​the model is calculated, and the phonon spectra of the probe graphene and the substrate during the friction process under different contact states are obtained, and the difference in the phonon spectra under the commensurate / incommensurate states is used to explain the difference in friction under the two states; a theoretical model of the phonon number is derived, and the frequency distribution of the phonon number at different speeds under the commensurate / incommensurate states is calculated, and the difference in the phonon number distribution is used to intuitively explain the difference in friction under two different contact states.

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