Cross-scale analysis method for wear behavior of solid lubrication gear pair

Abstract

The invention discloses a cross-scale analysis method for wear behaviors of a solid lubrication gear pair, and belongs to the technical field of cross-scale analysis. The method comprises the following steps: establishing a molecular dynamics model of the solid lubrication gear pair based on motion characteristics of the solid lubrication gear pair in a space environment; the molecular dynamics model comprises a pressure head and upper / lower base bodies located on the two sides of the pressure head, the pressure head is used for simulating a driven wheel of the gear pair, the upper / lower base bodies are used for simulating a driving wheel of the gear pair, and a model of a solid lubricating coating is established on the surfaces of the pressure head and the upper / lower base bodies; performing simulation motion based on the kinetic model; force is applied to a lower base body in the molecular dynamics model, so that the lower base body drives a pressure head to move, and the friction coefficient of the solid lubrication gear is obtained through simulation; and introducing the friction coefficient obtained by the molecular dynamics model into a finite element simulation model, and performing wear simulation of the finite element simulation model. The problem that the service life of the solid lubrication gear pair is difficult to predict in a space environment is effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of cross-scale analysis, and in particular relates to a cross-scale analysis method for wear behavior of a solid lubrication gear pair. Background Art

[0002] Gear transmission systems are widely used in the transmission joints of space manipulators and solar wing drive devices. They are the core components for the manipulators to complete the on-orbit assembly of spacecraft and for the solar wing to complete key actions such as orientation to the sun. Due to the harsh and complex space environment, traditional grease lubricants are difficult to perform space missions in the space environment. Molybdenum disulfide solid lubricants are widely used in various space mechanical structures due to their excellent friction and wear properties in the space environment. Existing studies have only qualitatively analyzed the role of solid lubricating coatings in gear transmission systems in space environments. However, due to the microscopic characteristics of solid lubricating coatings and the macroscopic characteristics of gears, it is difficult to link them for research. Aiming at the friction and wear problems of solid-lubricated gear pairs, the present invention adopts a cross-scale analysis method combining molecular dynamics simulation and finite element simulation to study the friction and wear characteristics of solid-lubricated gear pairs.

[0003] Since the commonly used friction and wear testing machines are difficult to simulate the rolling motion of gear pairs, the lubrication performance of solid lubricants in gear transmission systems has not been studied in depth; and in the ground environment, it is difficult to simulate the solid lubrication gear pair experimental model in the space environment, and the experimental data obtained have large errors. Summary of the invention

[0004] Technical issues to be solved:

[0005] In order to avoid the shortcomings of the prior art, the present invention provides a cross-scale analysis method for the wear behavior of a solid-lubricated gear pair. A molecular dynamics model of a gear pair covered with a solid lubricating coating is established in a simulation software. The motion state of the gear pair is simulated by the molecular dynamics model, and the friction coefficient of rolling and sliding motion is calculated. The calculated result of the friction coefficient is substituted into a finite element model to perform wear simulation, and the influence of the solid lubricating coating on the wear of the gear pair is analyzed, so as to effectively predict the life of the solid-lubricated gear pair.

[0006] The technical solution of the present invention is: a cross-scale analysis method for the wear behavior of a solid lubrication gear pair, and the specific steps are as follows:

[0007] Based on the motion characteristics of the solid lubricated gear pair in a space environment, the boundary conditions of the system are set in the simulation software, and a molecular dynamics model of the solid lubricated gear pair is established; the molecular dynamics model includes a pressure head and an upper / lower substrate located on both sides thereof, wherein the pressure head is used to simulate the driven wheel of the gear pair, and the upper / lower substrate is used to simulate the driving wheel of the gear pair, and a model of a solid lubricating coating is established on the surface of the pressure head and the upper / lower substrate;

[0008] Performing simulated motion based on the dynamic model; applying force to the lower matrix in the molecular dynamics model so that it drives the pressure head to move, and obtaining the friction coefficient of the solid lubrication gear through simulation;

[0009] The friction coefficient obtained from the molecular dynamics model is introduced into the finite element simulation model to perform wear simulation of the finite element simulation model.

[0010] A further technical solution of the present invention is: in the simulation area of ​​the molecular dynamics model, the XY plane is set to be parallel to the upper / lower substrate surface, the X-axis direction is the movement direction, the Y-axis direction is parallel to the axial direction of the pressure head, and the Z-axis direction is perpendicular to the upper / lower substrate surface; the X-axis and Y-axis directions of the simulation area are set as periodic boundary conditions, and the Z-axis direction is set as a fixed boundary condition.

[0011] A further technical solution of the present invention is: the method for establishing a molecular dynamics model of a solid lubrication gear pair is:

[0012] Construct models of the indenter and upper / lower substrate in the molecular dynamics model;

[0013] A solid lubricating coating is established on the surface of a cylindrical indenter by adopting a curling modeling method; the upper / lower substrate is composed of three atomic layers: a fixed layer, a constant temperature layer, and a Newtonian layer, wherein a solid lubricating coating is established on the surface of the Newtonian layer; and the indenter is set as a rigid body, and the upper / lower substrates are both elastic bodies, thus obtaining a solid lubricating gear pair dynamic model covered with a solid lubricating coating;

[0014] After initializing the atomic velocities and positions, the system is relaxed under the canonical ensemble NVT. After the relaxation is completed, the Newton layer is changed to the microcanonical ensemble NVE and relaxed again so that the dynamic model reaches a thermal equilibrium stable state.

[0015] A further technical solution of the present invention is: the material of the solid lubricating coating is molybdenum disulfide, and the solid lubricating coating is simulated by a layered two-dimensional material.

[0016] A further technical solution of the present invention is: the dimensions of the molecular dynamics model in the X, Y and Z directions are 100p, 40p and 110p respectively, containing 339162 atoms; the radius of the cylindrical indenter r=22p, containing 40178 Fe atoms; the dimensions of the upper / lower substrates are both 100p×40p×15p, containing a total of 244000 Fe atoms; the molybdenum disulfide coating uses a double layer of molybdenum disulfide, the dimensions in the X and Y directions are smaller than the upper / lower substrate surface, containing a total of 36656 S atoms and 18328 Mo atoms.

[0017] A further technical solution of the present invention is: the process of simulating motion of the dynamic model is as follows:

[0018] Apply a positive Z-axis velocity V to the lower substrate fixed layer. z =10m / s, the lower substrate is lifted up by a distance of d1, so that the pressure head contacts the upper / lower substrate. The calculation formula of d1 is:

[0019] d1=d d -d f

[0020] Where, d1>0; d d is the distance between the indenter and the substrate surface; d f is the thickness of the multi-layer MoS2 coating;

[0021] After the pressure head is lifted, the system relaxes to equilibrium under the NVE ensemble;

[0022] Apply a positive velocity V in the X-axis direction to the lower substrate fixed layer. x =100m / s, driving the pressure head to move.

[0023] A further technical solution of the present invention is that the materials of the pressure head and the upper / lower substrate are all iron, the lattice structure is a body-centered cubic structure, and the lattice constant p is 0.2863nm.

[0024] A further technical solution of the present invention is: the specific steps of the finite element simulation model for wear simulation are:

[0025] Some meshing teeth pairs of solid lubrication gear pairs were cut for research;

[0026] Define the material and cross-section properties for the solid lubrication gear pair model;

[0027] The contact setting is performed on the meshing surface, and the friction coefficient of the solid lubrication gear is set and simulated;

[0028] Densify and verify the partial mesh of the meshing area;

[0029] Boundary condition setting and load analysis step setting; pre-contact the solid lubrication gear pair, limit the freedom of the driven wheel, give the driving wheel an angular displacement around the Z axis, so that the gear pair can contact correctly; release the freedom of the driven wheel to rotate around the Z axis, preload, and give the driven wheel a resistance torque in the opposite direction; finally, perform rotational loading, apply a certain torque and speed to the driving wheel, simulate the meshing state of the gear pair under actual working conditions, and control the operating state of the gear pair by changing the analysis step length and angular velocity.

[0030] A further technical solution of the present invention is: when the meshing surfaces are contacted, surface-to-surface contact is selected, the contact surface of the driven wheel is selected as the main surface, and the contact surface of the driving wheel is selected as the slave surface; the normal force is hard contact, the tangential force is friction contact, and the friction coefficient is set to 0.015.

[0031] A further technical solution of the present invention is that the mesh size at the meshing portion is 0.05 mm, and a C3D8R unit, ie a three-dimensional eight-node hexahedral unit, is used.

[0032] Beneficial Effects

[0033] The beneficial effects of the present invention are as follows: the present invention proposes a cross-scale analysis method that combines molecular dynamics research methods with finite element simulation, which effectively solves the problem that the life of solid lubrication gear pairs in space environments is difficult to predict. Based on the motion characteristics of space mechanisms, a molecular dynamics model of solid lubrication gear pairs in space environments was established, and the friction performance of molybdenum disulfide coatings in rolling contact was explored. Compared with the case without coating, the molybdenum disulfide coating isolates the direct contact between the pressure head and the substrate, effectively reducing the atomic stacking; the interlayer force causes interlayer slippage between the coatings, and the friction force is reduced by about 80%, which can obtain a more ideal rolling friction coefficient. Based on the friction coefficient calculated by molecular dynamics, finite element simulation was performed on the solid lubrication gear pair, the contact stress and corresponding relative slip distance required for wear calculation were extracted, the wear amount of the gear pair after a certain period of operation was calculated, and the influence of the solid lubrication coating on the wear of the solid lubrication gear pair was analyzed. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the meshing of gear pairs;

[0035] Figure 2 The molecular dynamics model of the solid lubricated gear pair covered with molybdenum disulfide coating proposed by the present invention;

[0036] Figure 3 A simulation flow chart of the solid lubrication gear pair proposed by the present invention;

[0037] Figure 4 The friction force comparison between solid lubricating coating and no coating;

[0038] Figure 5 The finite element wear simulation flow chart proposed by the present invention;

[0039] Figure 6 Schematic diagram of mesh division of finite element model;

[0040] Figure 7 It is a schematic diagram of the solid lubricating coating in the finite element simulation;

[0041] Figure 8 Comparison of the wear of gear pairs with coating lubrication and without coating.

[0042] Explanation of the reference numerals: 1. upper substrate (Fe), 2. indenter, 3. lower substrate (Fe). DETAILED DESCRIPTION

[0043] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0044] Based on the fact that the currently commonly used friction and wear testing machine is difficult to simulate the rolling motion of the gear pair, the lubrication performance of the solid lubricant in the gear transmission system has not been studied in depth; and in the ground environment, it is difficult to simulate the solid lubrication gear pair experimental model in the space environment, and the experimental data obtained have large errors, etc., the present invention provides a cross-scale analysis method for the wear behavior of the solid lubrication gear pair, and the specific steps are as follows:

[0045] Step 1: Based on the motion characteristics of the solid-lubricated gear pair in a space environment, the boundary conditions of the system are set in the simulation software, and a molecular dynamics model of the solid-lubricated gear pair is established; the molecular dynamics model includes a pressure head and an upper / lower substrate located at both ends thereof, wherein the pressure head is used to simulate the driven wheel of the gear pair, and the upper / lower substrate is used to simulate the driving wheel of the gear pair, and a model of a solid lubricating coating is established on the surface of the pressure head and the upper / lower substrate;

[0046] Step 2: simulate the motion based on the dynamic model; apply force to the lower matrix in the molecular dynamics model to drive the pressure head to move, and obtain the friction coefficient of the solid lubrication gear through simulation;

[0047] Step 3: Introduce the friction coefficient obtained from the molecular dynamics model into the finite element model for wear simulation.

[0048] The following examples and drawings further illustrate the above technical solution:

[0049] This embodiment proposes a cross-scale analysis method for the wear behavior of a solid-lubricated gear pair, which is mainly divided into two parts: molecular dynamics simulation and finite element simulation. Among them, the molecular dynamics simulation model includes a pressure head and an upper / lower substrate. The pressure head is a cylindrical structure, which is used to simulate the driven wheel of the gear pair. The upper / lower substrates are both rectangular structures, which are used to simulate the driving wheel of the gear pair. The surface of the pressure head and the substrate are covered with a solid lubricating coating. The finite element simulation model includes a pair of partially meshing teeth of a meshing gear pair, and the surface of the gear teeth is covered with a solid lubricating coating. The coating is defined by a skin unit and includes the following steps:

[0050] Step 1: Based on Figure 1The kinematic characteristics of the gear pair are analyzed, the actual model is simplified to a certain extent, and the dynamic model of the solid lubrication gear pair covered with MoS2 coating is further established.

[0051] In this embodiment, the XY plane is set to be parallel to the upper / lower substrate surface, the X-axis direction is the movement direction, the Y-axis direction is parallel to the axial direction of the indenter, and the Z-axis direction is perpendicular to the upper / lower substrate surface; the X-axis and Y-axis directions are set to periodic boundary conditions, and the Z-axis direction is set to a fixed boundary condition; the interatomic interaction potential function is determined to be the LJ potential, the EAM potential, and the REBO potential function; the time step is set to 0.001ps; the initial temperature of the system is set to T=300K; and a molecular dynamics simulation model of the indenter and the substrate is established;

[0052] The specific operations are as follows:

[0053] Step 1.1: Construct the models of the indenter and upper / lower substrate in the molecular dynamics model; respectively establish the indenter and substrate models in the LAMMPS software, such as Figure 2 As shown, the materials of the indenter and the substrate are both metal Fe, which is a body-centered cubic lattice with a lattice constant of p = 0.2863nm. The dimensions of the model in the X, Y, and Z directions are 100p, 40p, and 110p respectively. The indenter is a cylinder with a radius of r = 22p, and the dimensions of the upper and lower substrates are both 100p × 40p × 15p;

[0054] A solid lubricating coating is established on the surface of the cylindrical indenter using the curling modeling method; the surface of the indenter is covered with a molybdenum disulfide coating as a solid lubricating coating, and the molybdenum disulfide coating uses a double layer of molybdenum disulfide, and the dimensions in the X and Y directions are slightly smaller than the surface of the substrate. The entire dynamic model contains a total of 339,162 atoms, of which the upper and lower substrates contain a total of 244,000 Fe atoms, the indenter contains 40,178 Fe atoms, and the molybdenum disulfide coating contains a total of 36,656 S atoms and 18,328 Mo atoms. The upper (lower) substrate atoms are divided into three layers: the top (bottom) three atomic layers are set as fixed layers, the two layers of atoms below (above) the fixed layer atoms are set as constant temperature layers, and the remaining atoms are set as Newtonian layers;

[0055] Step 1.2: Relax the Newtonian layer and isothermal layer atoms in the canonical ensemble NVT to allow the model to reach equilibrium. After the relaxation is completed, change the Newtonian layer atoms to the microcanonical ensemble NVE and relax again.

[0056] Step 2: Use the kinetic model established in step 1 to perform simulation;

[0057] Step 2.1: Apply a positive Z-axis velocity to the lower substrate fixed layer to lift the lower substrate up by a distance of d1 so that the pressure head contacts the upper and lower substrates. The calculation method of d1 is:

[0058] d1=d d -df

[0059] Where, d1>0; d d is the distance between the indenter and the substrate surface; d f is the thickness of the MoS2 coating;

[0060] Step 2.2: After the lifting is completed, relax the model again under the microcanonical ensemble NVE to completely stop the movement of the indenter;

[0061] Step 2.3: Apply a velocity along the positive direction of the X-axis to the lower substrate fixed layer to drive the indenter to move and perform friction simulation, such as Figure 3 As shown;

[0062] Step 2.4: Get the friction force and friction coefficient during the motion, the magnitude is as follows Figure 4 as shown.

[0063] Step 3: Based on molecular dynamics, finite element simulation analysis of solid lubricated gear pairs is performed from a macroscopic perspective to explore the effect of solid lubricant coating on wear. The process is as follows: Figure 5 As shown, the specific steps are as follows:

[0064] Step 3.1: Cut out some meshing tooth pairs of the gear pair for study;

[0065] Step 3.2: Define the material and section properties of the model, select the gear pair material as CF170 alloy steel, select the solid lubricant coating material as molybdenum disulfide, select the membrane element (Membrane) to simulate the solid lubricant coating, and set the thickness to 0.005mm. Figure 6 As shown;

[0066] Step 3.3: Set the contact of the meshing surface, select surface-to-surface contact, the driven wheel contact surface as the master surface, and the driving wheel contact surface as the slave surface. The normal force is hard contact, the tangential force is friction contact, and the friction coefficient is set to 0.015;

[0067] Step 3.4: Densify the mesh at the meshing part, and select a mesh size of 0.05 mm. The difference between the calculated result and the mesh size of 0.1 mm is less than 5%. The C3D8R unit, that is, a three-dimensional eight-node hexahedral unit, is used. The results are as follows: Figure 7 As shown;

[0068] Step 3.5: Boundary condition setting and load analysis step setting. Pre-contact the gear pair, limit the freedom of the driven wheel, and apply an angular displacement around the Z axis to the driving wheel so that the gear pair can contact correctly. Release the freedom of the driven wheel to rotate around the Z axis, and apply a small torque for preloading. Finally, perform rotational loading, apply a certain torque and speed to the driving wheel, simulate the meshing state of the gear pair under actual working conditions, and control the operating state of the gear pair by changing the analysis step length and angular velocity;

[0069] Step 3.6: Extract the contact stress and sliding distance data during the simulation process, and use the Archard wear formula to calculate the wear depth of the gear pair. The output results are as follows: Figure 8 shown.

[0070] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A cross-scale analysis method for wear behavior of solid lubrication gear pairs, characterized by The specific steps are as follows: Based on the motion characteristics of the solid lubricated gear pair in a space environment, the boundary conditions of the system are set in the simulation software, and a molecular dynamics model of the solid lubricated gear pair is established; the molecular dynamics model includes a pressure head and an upper / lower substrate located on both sides thereof, wherein the pressure head is used to simulate the driven wheel of the gear pair, and the upper / lower substrate is used to simulate the driving wheel of the gear pair, and a model of a solid lubricating coating is established on the surface of the pressure head and the upper / lower substrate; Performing simulated motion based on the dynamic model; applying force to the lower matrix in the molecular dynamics model so that it drives the pressure head to move, and obtaining the friction coefficient of the solid lubrication gear through simulation; The friction coefficient obtained from the molecular dynamics model is introduced into the finite element simulation model to perform wear simulation of the finite element simulation model.

2. The cross-scale analysis method for wear behavior of a solid lubrication gear pair according to claim 1, characterized in that: In the simulation area of ​​the molecular dynamics model, the XY plane is set to be parallel to the upper / lower substrate surface, the X-axis direction is the movement direction, the Y-axis direction is parallel to the axis of the indenter, and the Z-axis direction is perpendicular to the upper / lower substrate surface; the X-axis and Y-axis directions of the simulation area are set as periodic boundary conditions, and the Z-axis direction is set as a fixed boundary condition.

3. The cross-scale analysis method for wear behavior of a solid lubrication gear pair according to claim 2, characterized in that: The method for establishing the molecular dynamics model of the solid lubrication gear pair is: Construct models of the indenter and upper / lower substrate in the molecular dynamics model; A solid lubricating coating is established on the surface of a cylindrical indenter by adopting a curling modeling method; the upper / lower substrate is composed of three atomic layers: a fixed layer, a constant temperature layer, and a Newtonian layer, wherein a solid lubricating coating is established on the surface of the Newtonian layer; and the indenter is set as a rigid body, and the upper / lower substrates are both elastic bodies, thus obtaining a solid lubricating gear pair dynamic model covered with a solid lubricating coating; After initializing the atomic velocities and positions, the system is relaxed under the canonical ensemble NVT. After the relaxation is completed, the Newton layer is changed to the microcanonical ensemble NVE and relaxed again so that the dynamic model reaches a thermal equilibrium stable state.

4. The cross-scale analysis method for wear behavior of a solid lubrication gear pair according to claim 3, characterized in that: The material of the solid lubricating coating is molybdenum disulfide, and the solid lubricating coating is simulated by a layered two-dimensional material.

5. A cross-scale analysis method for wear behavior of a solid lubrication gear pair according to claim 4, characterized in that: The sizes of the molecular dynamics model in the X, Y and Z directions are 100p, 40p and 110p respectively, containing 339162 atoms; the radius of the cylindrical indenter is r=22p, containing 40178 Fe atoms; the sizes of the upper and lower substrates are both 100p×40p×15p, containing a total of 244000 Fe atoms; the molybdenum disulfide coating uses a double layer of molybdenum disulfide, the sizes in the X and Y directions are smaller than the upper and lower substrate surfaces, containing a total of 36656 S atoms and 18328 Mo atoms.

6. A cross-scale analysis method for wear behavior of a solid lubrication gear pair according to claim 5, characterized in that: The process of simulating motion by the dynamic model is as follows: Apply a positive Z-axis velocity V to the lower substrate fixed layer. z =10m / s, the lower substrate is lifted up by a distance of d1, so that the pressure head contacts the upper / lower substrate. The calculation formula of d1 is: d1=d d -d f Where, d1>0; d d is the distance between the indenter and the substrate surface; d f is the thickness of the multi-layer MoS2 coating; After the pressure head is lifted, the system relaxes to equilibrium under the NVE ensemble; Apply a positive velocity V in the X-axis direction to the lower substrate fixed layer. x =100m / s, driving the pressure head to move.

7. A cross-scale analysis method for wear behavior of a solid lubrication gear pair according to claim 6, characterized in that: The material of the indenter and the upper / lower substrates are both iron, the lattice structure is a body-centered cubic structure, and the lattice constant p is 0.2863 nm.

8. The cross-scale analysis method for wear behavior of a solid lubrication gear pair according to claim 7, characterized in that: The specific steps of the finite element simulation model for wear simulation are: Some meshing teeth pairs of solid lubrication gear pairs were cut for research; Define the material and cross-section properties for the solid lubrication gear pair model; The contact setting is performed on the meshing surface, and the friction coefficient of the solid lubrication gear is set and simulated; Densify and verify the partial mesh of the meshing area; Boundary condition setting and load analysis step setting; pre-contact the solid lubrication gear pair, limit the freedom of the driven wheel, give the driving wheel an angular displacement around the Z axis, so that the gear pair can contact correctly; release the freedom of the driven wheel to rotate around the Z axis, preload, and give the driven wheel a resistance torque in the opposite direction; finally, perform rotational loading, apply a certain torque and speed to the driving wheel, simulate the meshing state of the gear pair under actual working conditions, and control the operating state of the gear pair by changing the analysis step length and angular velocity.

9. A cross-scale analysis method for wear behavior of a solid lubrication gear pair according to claim 8, characterized in that: When the meshing surfaces are contacted, surface-to-surface contact is selected, the driven wheel contact surface is selected as the master surface, and the driving wheel contact surface is selected as the slave surface; the normal force is hard contact, the tangential force is friction contact, and the friction coefficient is set to 0.

015.

10. The cross-scale analysis method for wear behavior of a solid lubrication gear pair according to claim 8, characterized in that: The mesh size at the meshing portion is 0.05 mm, and a C3D8R unit, ie, a three-dimensional eight-node hexahedral unit, is used.

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