Method for simulating plastic deformation evolution process of UHMWPE (Ultra High Molecular Weight Polyethylene) under friction action based on molecular dynamics

Abstract

The invention provides a method for simulating a plastic deformation evolution process of UHMWPE (Ultra High Molecular Weight Polyethylene) under a friction effect based on molecular dynamics. The method comprises the following steps: constructing geometric models of amorphous UHMWPE and a mating part Fe plate in a simulation box; setting a simulation system and boundary conditions based on molecular dynamics, and simulating interaction among molecules by using a PCFF force field; carrying out friction simulation on the geometric models of the amorphous state UHMWPE and the crystalline state Fe plate; the microstructure change and the movement track in the friction simulation process are observed, and the simulation result is visualized; and carrying out data analysis on the motion trail, and respectively calculating distribution conditions, crystallinity and entanglement angles of the particles in different speed ranges to realize simulation of the plastic deformation evolution process. According to the invention, the dynamic characteristics and key functions of the high-molecular polymer in the plastic deformation process under the friction effect can be deeply explored.

Description

Technical Field

[0001] The present invention relates to the field of materials science and technology, and particularly to a method for simulating the plastic deformation evolution process of UHMWPE under friction based on molecular dynamics. Background Art

[0002] In recent years, with the increasingly strict requirements for marine environmental protection and the promotion of relevant regulations, the tail bearing lubrication technology using water as a lubricating and cooling medium has gradually made breakthroughs and has been widely applied to ship propulsion systems. Due to their unique performance advantages, rubber and plastic polymer bearings are widely used in ship systems. Compared with traditional metal bearings, rubber and plastic polymer bearings have lower friction coefficients, better self-lubricating properties, and higher corrosion resistance, and are particularly suitable for environments where ships frequently come into contact with water during navigation.

[0003] However, under water lubrication conditions, due to the low viscosity of water itself, the friction pair is prone to be in the boundary lubrication or dry friction state. At this time, the rubber and plastic polymer bearings are prone to friction with other components, resulting in surface wear. It is still challenging to directly observe material wear and analyze the formation mechanism of material wear. Only the characteristics of the worn surface can be indirectly analyzed offline or the wear process can be inferred by analyzing the grinding debris. During the wear process of UHMWPE materials, repeated pressure and friction will cause plastic deformation in the worn area on the surface of the bearing material. This shear deformation at the microscale is considered to be a precursor to material surface wear. When its plastic strain continuously accumulates and reaches its strain limit, the material undergoes fatigue fracture and forms submicron wear particles, which further exacerbate the friction with other components.

[0004] Since the plastic deformation on the surface of the worn area evolves at the micro-nano scale, there is a lack of corresponding in-situ characterization techniques for analyzing it during the experiment. The friction simulation based on the molecular dynamics method can be used to characterize the friction process occurring at the nanoscale on the material surface layer, and to analyze the complex dynamic behavior of polymer molecular chains in the worn area on the surface of the bearing material, helping to understand the wear and plastic deformation processes, and ultimately providing necessary theoretical support for optimizing the wear resistance of materials and extending their service life. Therefore, when studying the wear mechanism, it is necessary to provide a research method for friction simulation and material plastic deformation evolution process based on molecular dynamics. Summary of the Invention

[0005] According to the above-mentioned technical problems, a method for simulating the plastic deformation evolution process of UHMWPE under friction based on molecular dynamics is provided. The present invention deeply studies the specific method of the plastic deformation evolution process in the surface wear area of ultra-high molecular weight polyethylene (UHMWPE) under friction. The present invention can not only reveal the complex dynamic behavior of molecular chains in the surface wear area of UHMWPE during the friction process at the nanoscale, but also provide strong support for understanding its wear mechanism in practical applications.

[0006] The technical means adopted by the present invention are as follows:

[0007] A method for simulating the plastic deformation evolution process of UHMWPE under friction based on molecular dynamics, including:

[0008] Construct a geometric model of amorphous UHMWPE and a counterpart Fe plate in a simulation box;

[0009] Based on molecular dynamics, set the simulation system and boundary conditions, and use the PCFF force field to simulate the intermolecular interactions;

[0010] Conduct a friction simulation on the geometric models of amorphous UHMWPE and crystalline Fe plate;

[0011] Observe the microscopic structure changes and movement trajectories during the friction simulation, and visualize the simulation results;

[0012] Conduct data analysis on the movement trajectories, calculate the distribution of particles in different velocity ranges, crystallinity, and entanglement angles respectively, and realize the simulation of the plastic deformation evolution process.

[0013] Further, the construction of the geometric model of amorphous UHMWPE and the counterpart Fe plate in the simulation box includes:

[0014] When constructing the amorphous UHMWPE model, select multiple polyethylene molecular chains and randomly distribute them in the simulation box. The interweaving and interaction between molecular chains conform to the structural characteristics of amorphous polymers;

[0015] The counterpart Fe plate model uses a face-centered cubic structure as the friction surface, and based on the crystal structure of face-centered iron, constructs a single crystal cell of face-centered iron structure, and constructs the counterpart Fe plate model by performing periodic expansion on the single crystal cell.

[0016] Further, the setting of the simulation system and boundary conditions based on molecular dynamics and the use of the PCFF force field to simulate the intermolecular interactions include:

[0017] Set the simulation parameters, set the boundary condition as the periodic boundary condition, so that the simulation box can perform periodic boundary processing in three directions; select the PCFF force field, use the Lennard-Jones 9-6 potential function to describe the intermolecular interaction, and use the Coulomb long-range interaction to handle the interaction between charges.

[0018] Further, the friction simulation of the geometric models of the amorphous UHMWPE and the crystalline Fe plate includes:

[0019] After minimizing the energy of the initial coordinate structure of the friction model, perform the friction simulation. During the simulation in the equilibrium stage, control the system temperature using the constant pressure and constant temperature system and the constant volume and constant temperature system respectively, and set a certain relaxation time;

[0020] In the friction simulation stage, use the constant energy system and combine the heat bath method to maintain the temperature of the system, and output the trajectory coordinate file of the friction system regularly during the friction simulation.

[0021] Further, the observation of the microscopic structure changes and motion trajectories during the friction simulation and the visualization of the simulation results include:

[0022] Perform de-periodization processing on the trajectory coordinate file output during the friction simulation. Through visualization processing, obtain the friction conformation diagram during the friction simulation, observe the continuous multi-frame friction conformation diagrams, and depict the plastic flow process occurring under the friction action.

[0023] Further, calculate the distribution of particles in different velocity ranges, the crystallinity, and the entanglement angle, specifically including:

[0024] The distribution of particles in different velocity ranges is used to generate a velocity distribution diagram. Obtain the coordinates of particles in each frame image through the trajectory coordinate file, calculate the velocity of particles within a preset time step, and classify them into the corresponding height layers and velocity intervals according to their velocity and height. Count the number of particles of all particles in different height layers and velocity intervals to obtain the distribution of particles in different velocity ranges, and summarize the particle data in each frame to generate a three-dimensional velocity distribution diagram;

[0025] The crystallinity is used to describe the degree of order in the material structure. Read the carbon atom coordinates in each frame through the trajectory coordinate file, form an atom string with each carbon atom and its adjacent atoms before and after, calculate the spatial vector according to the spatial positions of the atoms in the atom string, calculate the dot product of every two spatial vectors, and count the calculation results of the dot products to solve the average value of the dot products; calculate the bond order parameter of each carbon atom according to the following formula:

[0026]

[0027] crystalline = 3 / 2 * <(e i ·e j ) 2 > - 1 / 2

[0028] where r i represents the position vector of the i-th particle on a molecular chain, e i represents the unit vector parallel to the stress direction, <(e i ·e j ) 2 > represents the average value of the dot product, crystalline represents the bond order parameter, ei represents the unit vector parallel to the stress direction, and the bond order parameter is used to characterize the degree of crystallinity;

[0029] The entanglement angle is used to describe the degree of interweaving and entanglement of the molecular chains of UHMWPE in three-dimensional space. By reading the conformational coordinates of each frame from the trajectory coordinate file, the molecular chains are divided, multiple atoms are used as a statistical unit, the spatial vectors of carbon atoms in each statistical unit are calculated, and the vector angle Q between adjacent statistical units is calculated i :

[0030]

[0031] where r i-n 、r i 、r i+n represent the position coordinates of the i - n, i, and i + n particles on the same molecular chain respectively, represents the average value of the vector angle;

[0032] Calculate the average value of the vector angles of all statistical units and the average value of the vector angles of all statistical units on each molecular chain to evaluate the entanglement degree of the UHMWPE molecular chains.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] The method provided by the present invention for simulating the plastic deformation evolution process of UHMWPE under friction based on molecular dynamics constructs a geometric model of amorphous UHMWPE and the counter - part Fe plate in a simulation box; sets the simulation system and boundary conditions based on molecular dynamics, and simulates the intermolecular interaction using the PCFF force field; conducts friction simulation on the geometric models of amorphous UHMWPE and crystalline Fe plate; observes the microscopic structure changes and movement trajectories during the friction simulation, and visualizes the simulation results; conducts data analysis on the movement trajectories, calculates the distribution of particles in different velocity ranges, crystallinity, and entanglement angle respectively, and realizes the simulation of the plastic deformation evolution process.

[0035] The present invention can be used to analyze the process of plastic flow occurring on the surface layer of polymer materials under frictional shear. Under frictional shear, the surface of the polymer is affected by shear forces, leading to plastic flow of the surface molecular chains. By analyzing this process, it is possible to understand how polymers deform and wear under different frictional conditions.

[0036] The present invention can be used to characterize the influence of factors such as the entanglement state of molecular chains on the material surface and the proportion of the crystalline phase on the plastic flow process of the material surface. The entanglement angle and the proportion of the crystalline phase of the polymer have an important influence on its surface plastic flow process. A higher entanglement angle makes the molecular chains more compact, thus inhibiting plastic flow, while a lower entanglement angle increases fluidity. Similarly, polymers with a higher degree of crystallinity exhibit stronger plasticity under friction and are less likely to undergo plastic deformation. By adjusting the entanglement angle and the degree of crystallinity, the plastic fluidity of the polymer can be better controlled, thereby improving its performance in different applications.

[0037] The present invention can be used to study the influence law of the presence of lubricating media or pollutants and their diffusion into the material matrix on the plastic flow of polymer bearing materials. In polymer bearing materials, the presence of lubricating media or pollutants affects the plastic flow process. Lubricating media can reduce friction, lower the degree of surface plastic flow, and extend the service life of the material. However, if the lubricating medium fails or pollutants enter the matrix, it may lead to an increase in friction, thereby promoting excessive plastic flow on the polymer surface. Therefore, studying the influence of lubricating media and pollutants helps to optimize the performance of bearing materials and improve their stability and durability in complex environments.

[0038] For the above reasons, the present invention can be widely promoted in the fields of materials science and technology, etc. Description of the Drawings

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0040] Figure 1 It is a flowchart of the method for the plastic deformation evolution process of UHMWPE under friction based on molecular dynamics simulation of the present invention.

[0041] Figure 2 It is a schematic diagram of the initial friction conformation of UHMWPE and the counter-part Fe plate in the embodiment of the present invention.

[0042] Figure 3This is a snapshot of the plastic deformation of UHMWPE and the counterpart Fe plate in the embodiments of the present invention.

[0043] Figure 4 This is the calculated distribution diagram of the plastic deformation rate of UHMWPE in the embodiments of the present invention.

[0044] Figure 5 This is a schematic diagram of the carbon atom bond order parameter in the present invention.

[0045] Figure 6 This is a schematic diagram showing the change of the crystallinity of the plastic deformation of UHMWPE with time in the embodiments of the present invention.

[0046] Figure 7 This is a three-dimensional schematic diagram of the entanglement angle of the plastic deformation of UHMWPE in the embodiments of the present invention. Detailed implementation manners

[0047] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way restricts the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0049] It should be noted that the terms used herein are only for describing the specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of the features, steps, operations, devices, components, and / or their combinations.

[0050] Unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn in accordance with actual proportional relationships. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the said technologies, methods, and devices should be regarded as part of the authorization specification. In all the examples shown and discussed here, any specific values should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that: Similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0051] As Figure 1 shown, the present invention provides a method for simulating the plastic deformation evolution process of UHMWPE under friction based on molecular dynamics, including:

[0052] Constructing a geometric model of amorphous UHMWPE and a counterpart Fe plate in a simulation box, as Figure 2 shown;

[0053] Specifically in implementation, as a preferred implementation manner of the present invention, the constructing of the geometric model of amorphous UHMWPE and the counterpart Fe plate in the simulation box includes:

[0054] When constructing the amorphous UHMWPE model, 14 polyethylene molecular chains were selected and randomly placed in a cuboid-shaped simulation box, and the size of the box was set to Inside this simulation box, the distribution of polyethylene molecular chains is random to ensure that the interweaving and interaction between molecular chains conform to the structural characteristics of actual amorphous polymers. The spatial arrangement inside the simulation box takes into account the interaction between molecular chains and their contact with the box walls, and strives to reflect the real physical state during the simulation.

[0055] In the Materials Studio molecular modeling software, the counterpart Fe plate model uses a face-centered cubic structure as the friction surface, and based on the crystal structure of face-centered iron, its lattice size is set to And the lattice angles are α = β = γ = 90°, constructing a single crystal cell of face-centered iron structure, and performing periodic expansion on the single crystal cell through the Supercell function in the Materials Studio software to construct the Fe plate structure required for friction simulation, and the size of the box is This model has a total of 9520 atoms.

[0056] During implementation, the amorphous polyethylene (UHMWPE) geometric model was constructed using the Amorphous Cell module of Materials Studio software. Each polyethylene single chain consists of 1000 carbon atoms (Carbon, C) and 2002 hydrogen atoms (Hydrogen, H). The specific structure includes 998 methylene groups (-CH2-) and methyl groups (-CH3-) at both ends of the molecular chain. Therefore, the total number of atoms in each polyethylene molecular chain is 3002.

[0057] In the Materials Studio modeling software, the car file was exported, and the msi2lmp instruction msi2lmppolyethylene-class II-frc pcff-i>data.polyethylene was used to generate a data file containing information such as initial atomic coordinates, bonds, and angles.

[0058] Based on molecular dynamics, the simulation system and boundary conditions were set, and the PCFF force field was used to simulate the intermolecular interactions;

[0059] The molecular dynamics simulation software LAMMPS was used to conduct a simulation study on UHMWPE molecules. During specific implementation, as a preferred implementation mode of the present invention, setting the simulation system and boundary conditions based on molecular dynamics and using the PCFF force field to simulate the intermolecular interactions includes:

[0060] Set the simulation parameters, set the boundary condition as the periodic boundary condition, so that the simulation box can perform periodic boundary processing in three directions; select the PCFF force field, use the Lennard-Jones 9-6 potential function to describe the intermolecular interactions, and use the Coulomb long-range interaction to handle the interactions between charges. The cutoff distance is set to When dealing with the long-range electric potential, the (Particle-Particle Particle-Mesh, PPPM) method was used, and the grid accuracy was set to 0.0001.

[0061] Friction simulation was performed on the geometric models of amorphous UHMWPE and crystalline Fe plates;

[0062] During specific implementation, as a preferred implementation mode of the present invention, the friction simulation of the geometric models of amorphous UHMWPE and crystalline Fe plates includes:

[0063] Friction simulation is carried out after minimizing the energy of the initial coordinate structure of the friction model to avoid the influence of high-energy states caused by unreasonable initial structures on the simulation results. During the simulation in the equilibrium stage, constant-pressure constant-temperature and constant-volume constant-temperature systems are respectively adopted, and the Nosé-Hoover heat bath method is combined to control the system temperature at 298K. In this stage, the relaxation times are set to 100ps and 20ps respectively to ensure that the system can reach the equilibrium state within an appropriate time scale.

[0064] In the friction simulation stage, a constant-energy system is adopted, the simulation time is 1ns, the temperature is 298K, and the Langevin heat bath method is introduced to maintain the system temperature stable at 298.15K (25°C). During the friction simulation, the trajectory coordinate file of the friction system is output regularly.

[0065] During implementation, when the simulation runs, the trajectory coordinate file of the friction system is output every 1000 steps, as Figure 3 shown, which is convenient for subsequent visualization analysis.

[0066] Observe the microscopic structure changes and movement trajectories during the friction simulation process, and visualize the simulation results;

[0067] Specifically in implementation, as a preferred implementation mode of the present invention, the observing the microscopic structure changes and movement trajectories during the friction simulation process and visualizing the simulation results include:

[0068] Use VMD software to perform de-periodic processing on the trajectory coordinate file output during the friction simulation process. Import the car file exported by Materials Studio into VMD software, and load the trajectory coordinate file of the simulation process on this conformation basis. Secondly, in the tkConsole command window, input the display model box instruction and the de-periodic instruction, such as pbcset{99.8 60.6 128.5}–all and pbc unwrap de-periodic instruction. At this time, the coordinate file is de-periodically processed in the VMD visualization software. It can effectively display the movement trajectories of atoms changing with time during the simulation process. Through the dynamic change behaviors of different atoms, deeply understand the overall movement characteristics of UHMWPE under friction and its interaction process with the iron plate surface.

[0069] Through visualization processing, obtain the friction conformation diagram during the friction simulation process, observe the continuous multi-frame friction conformation diagrams, depict the plastic flow process occurring under friction, and judge the interaction between the material surface and the iron plate.

[0070] Export the trajectory coordinate file (in xyz format) of all carbon atoms after the solution period. Based on this file, physical properties such as the plastic deformation, crystallinity change, and chain entanglement angle of UHMWPE materials under friction can be further analyzed, helping to study the evolution of its microstructure and the relationship with surface friction behavior. Through these analyses, the evolution law of plastic deformation of UHMWPE during the friction process and the response characteristics of the material surface under different friction conditions can be comprehensively revealed.

[0071] Perform data analysis on the said trajectory, calculate the distribution of particles in different velocity ranges, crystallinity, and entanglement angle respectively, and realize the simulation of the plastic deformation evolution process.

[0072] When specifically implemented, as a preferred implementation manner of the present invention, the calculation of the distribution of particles in different velocity ranges, crystallinity, and entanglement angle specifically includes:

[0073] During implementation, use Matlab software to read each frame of xyz data file. For the C atoms (carbon atoms) in the friction model, the program will screen them according to the height (assumed to be the Z coordinate). For each qualified carbon atom, the program will record its position P0 at the initial moment (t = 0), and after a time interval of 1 femtosecond (fs) (that is, in the next frame or the preset time step), record the final position P1 of this carbon atom. Use the formula v = (P1 - P0) / Δt to calculate the velocity of each C atom within this time interval. This velocity value will reflect the movement of the carbon atoms.

[0074] The distribution of the said particles in different velocity ranges is used to generate a velocity distribution map. Obtain the coordinates of the particles in each frame image through the trajectory coordinate file, calculate the velocity of the particles within the preset time step, and classify them into the corresponding height layers and velocity intervals according to their velocity and height. Count the number of particles of all particles in different height layers and velocity intervals to obtain the distribution of the particles in different velocity ranges, and summarize the particle data in each frame to generate a three-dimensional velocity distribution map;

[0075] The velocity distribution map is a graph drawn through molecular dynamics simulation or experimental data, used to represent the distribution of particles (such as molecules, atoms, or ions) in the system in different velocity ranges. By using Matlab software to draw the image, the movement characteristics of the particles in the system under specific conditions can be intuitively understood. Since there are 500 frames of data in total, the program will summarize the atomic statistical data in all frames and finally generate a three-dimensional image, as Figure 4 shown, showing the number of atoms in each height layer and each velocity interval within 500 frames, as well as the corresponding velocity magnitudes.

[0076] The crystallinity is used to describe the degree of order in the material structure. By reading the carbon atom coordinates in each frame from the trajectory coordinate file, an atom string is formed by taking each carbon atom and the 3 atoms before and after it (a total of 7 atoms). The spatial vectors are calculated based on the spatial positions of the atoms in the atom string. After sorting according to the atom numbers, the spatial vector between two such atoms is calculated, and this vector reflects the relative positional relationship of the atom with its surrounding atoms in space.

[0077] Calculate the dot product of every two spatial vectors, count the calculation results of the dot products, and solve for the average value of the dot products. The average value can be used to describe the degree of order of the atomic arrangement. A larger average dot product value indicates a more ordered atomic arrangement, while a smaller dot product value indicates a more disordered atomic arrangement. Calculate the bond order parameter for each carbon atom according to the following formula:

[0078]

[0079] crystaline=3 / 2*<(e i ·e j ) 2 >-1 / 2

[0080] where, r i represents the position vector of the i-th particle on a molecular chain, e i represents the unit vector parallel to the stress direction, <(e i ·e j ) 2 > represents the average value of the dot product, crystaline represents the bond order parameter, ei represents the unit vector parallel to the stress direction, and the crystallinity size is characterized by the bond order parameter;

[0081] Through this method, the degree of crystallization of the polymer within different frames can be effectively measured, and then the orderliness of the polymer can be inferred. The higher the crystallinity, the more ordered the atomic arrangement of this layer, which is usually related to the crystalline region of the polymer; while a lower crystallinity indicates that the atoms in this layer are in an amorphous state. Through this process, researchers can further understand the structural characteristics of the polymer chain and the possible performance changes it may bring.

[0082] The entanglement angle is used to describe the degree of interweaving and entanglement of the molecular chains of UHMWPE in three-dimensional space. As Figure 7 shown, it reflects the structural morphology of the polymer chains and their entanglement in space. This program characterizes the entanglement of polyethylene chains by calculating the vector angles of C atoms from the polymer chain dynamic trajectory file. By reading the conformational coordinates of each frame from the trajectory coordinate file, the molecular chains are divided, with twenty atoms as a statistical unit. Calculate the spatial vectors of the carbon atoms in each statistical unit, and calculate the vector angle Q i :

[0083]

[0084] wherein, r i-n 、r i 、r i+n respectively represent the position coordinates of the (i - n)-th, i-th, and (i + n)-th particles on the same molecular chain, represents the average value of the vector angles;

[0085] First, calculate the average vector angle of the atomic coordinates of each small segment, and obtain the vector angle of this segment through the singular value decomposition (SVD, svd command in Matlab) method. Calculate the average value of the vector angles of all statistical units and the average value of the vector angles of all statistical units on each molecular chain to evaluate the entanglement degree of the UHMWPE molecular chain. A smaller average angle usually indicates a tight entanglement between the chains, while a larger average angle indicates a higher degree of chain looseness.

[0086] Example

[0087] As Figure 1 shown, the present invention provides a method for simulating the plastic deformation evolution process of UHMWPE under friction based on molecular dynamics. To analyze the plastic deformation evolution process of the material in the surface wear area of UHMWPE under friction, it is first necessary to establish a geometric model that can truly reflect the behavior of the friction interface. The present invention constructs a composite model composed of a high molecular polymer and iron atoms, aiming to simulate the interaction between the metal and the polymer during the friction process, and selects the PCFF (Polymer Consistent Force Field) force field to perform molecular dynamics simulation on this model. Through relaxation optimization, the energy of the model is minimized. This process is very crucial because only in the optimized low-energy state model can accurate motion trajectory data be obtained, laying a foundation for the analysis of plastic deformation and friction wear.

[0088] After constructing a reasonable molecular model and completing energy minimization, the next step is to conduct simulation experiments on the friction process. This experiment is carried out under friction speeds and temperature conditions that match the actual environment, restoring the real environment faced by UHMWPE during artificial joint replacement. The design of the friction experiment takes into account factors such as speed, load, and contact area, which directly affect the change in frictional force and the resulting plastic deformation of the material during movement. Through molecular dynamics simulation, a detailed trajectory file of the movement of each atom during the friction process can be obtained, and the kinetic characteristics and key roles of the plastic deformation process of the high molecular polymer under friction can be explored in depth. The relevant calculation files provide more detailed mechanical parameters and kinetic data, such as crystallinity, entanglement angle, velocity distribution map, and the changes in interaction forces and energies.

[0089] By deeply analyzing the trajectory file and relevant calculation files, the kinetic characteristics of the plastic deformation of UHMWPE under friction can be revealed. Plastic deformation is very crucial in the process of friction and wear because it directly determines the wear resistance and service life of the material. Through simulation, microscopic phenomena such as the slip movement, structural rearrangement, and plastic flow of the molecular chains of the material under friction can be observed, further clarifying its deformation mechanism during the friction process. Understanding these processes helps to reveal how polymer molecules respond to external mechanical loads, especially the influence on the contact surface area, and how it macroscopically manifests as wear and material damage.

[0090] The simulation experiment of the present invention provides a new perspective for revealing the mechanism of UHMWPE during the friction and wear process. Through molecular dynamics simulation, the local frictional force, deformation, and the generation process of wear particles of the material can be observed at the atomic scale. Therefore, mastering the influence of the microscopic wear mechanism of the material on the ship's tail shaft not only helps to deeply understand the wear, plastic deformation, and fatigue phenomena that occur during the long-term use of the marine tail shaft, but also provides important guidance for the optimization of the tail shaft material.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for simulating the plastic deformation evolution of UHMWPE under friction based on molecular dynamics, characterized in that: include: Construct the geometric models of amorphous UHMWPE and the counterpart Fe plate in the simulation box; The simulation system and boundary conditions are set based on molecular dynamics, and the PCFF force field is used to simulate the interaction between molecules; The friction simulation is carried out on the geometric model of amorphous UHMWPE and crystalline Fe plate; Observe the microstructure changes and motion trajectories during the friction simulation and visualize the simulation results; Data analysis is performed on the motion trajectory to calculate the distribution of particles in different speed ranges, crystallinity and entanglement angles, so as to simulate the plastic deformation evolution process.

2. The method for simulating the plastic deformation evolution of UHMWPE under friction based on molecular dynamics according to claim 1, characterized in that: The geometric model of the amorphous UHMWPE and the counterpart Fe plate is constructed in the simulation box, including: When constructing the amorphous UHMWPE model, multiple polyethylene molecular chains are selected and randomly distributed in the simulation box. The interweaving and interaction between the molecular chains conform to the structural characteristics of the amorphous polymer. The dual-part Fe plate model uses a face-centered cubic structure as a friction surface, and based on the crystal structure of face-centered iron, constructs a single crystal cell of the face-centered iron structure, and constructs the dual-part Fe plate model by periodically expanding the single crystal cell.

3. The method for simulating the evolution of plastic deformation of UHMWPE under friction based on molecular dynamics according to claim 1, characterized in that: The method of setting the simulation system and boundary conditions based on molecular dynamics and simulating the interaction between molecules using the PCFF force field includes: Set the simulation parameters and set the boundary conditions to periodic boundary conditions so that the simulation box can perform periodic boundary treatment in three directions; select the PCFF force field, use the Lennard-Jones 9-6 potential function to describe the interaction between molecules, and use the Coulomb long-range interaction to deal with the interaction between charges.

4. The method for simulating the plastic deformation evolution of UHMWPE under friction based on molecular dynamics according to claim 1, characterized in that: The friction simulation of the geometric model of the amorphous UHMWPE and the crystalline Fe plate includes: After the initial coordinate structure of the friction model is subjected to energy minimization, the friction simulation is performed. During the simulation of the equilibrium stage, the system temperature is controlled by using a constant pressure, constant temperature and constant volume, constant temperature system, and a certain relaxation time is set. During the friction simulation stage, a constant energy system is used in combination with a heat bath method to maintain the system temperature, and the trajectory coordinate file of the friction system is output regularly during the friction simulation process.

5. The method for simulating the evolution of plastic deformation of UHMWPE under friction based on molecular dynamics according to claim 1, characterized in that: The observation of microstructure changes and motion trajectories during the friction simulation process and visualization of simulation results include: The trajectory coordinate file output during the friction simulation is de-periodicized, and the friction conformation diagram during the friction simulation is obtained through visualization. The friction conformation diagrams of multiple consecutive frames are observed to depict the plastic flow process under the action of friction.

6. The method for simulating the evolution of plastic deformation of UHMWPE under friction based on molecular dynamics according to claim 1, characterized in that: The calculation of the distribution, crystallinity and entanglement angle of particles in different speed ranges specifically includes: The distribution of particles in different speed ranges is used to generate a speed distribution map. The coordinates of the particles in each frame of the image are obtained through the trajectory coordinate file, the speed of the particles in a preset time step is calculated, and the particles are classified into corresponding height layers and speed intervals according to their speed and height. The number of particles in different height layers and speed intervals is counted to obtain the distribution of particles in different speed ranges, and the particle data in each frame are summarized to generate a three-dimensional speed distribution map; The crystallinity is used to describe the degree of order in the material structure. The coordinates of the carbon atoms in each frame are read through the trajectory coordinate file. Each carbon atom and the atoms before and after it form an atomic string. The space vector is calculated according to the spatial position of the atoms in the atomic string. The dot product of each two space vectors is calculated. The calculation results of the dot product are counted, and the average value of the dot product is solved. The bond order parameter of each carbon atom is calculated according to the following formula: Among them, r i represents the position vector of the i-th particle on a molecular chain, e i represents the unit vector parallel to the stress direction, <(e i ·e j ) 2 > represents the average value of the dot product, crystaline represents the bond order parameter, ei represents the unit vector parallel to the stress direction, and the bond order parameter is used to characterize the degree of crystallinity; The entanglement angle is used to describe the degree of interweaving and entanglement of the molecular chains of UHMWPE in three-dimensional space. The conformational coordinates of each frame are read through the trajectory coordinate file, the molecular chain is divided, multiple atoms are taken as a statistical unit, the spatial vector of the carbon atom in each statistical unit is calculated, and the vector angle Q between adjacent statistical units is calculated. i : Among them, r i-n 、r i 、r i+n They represent the position coordinates of the inth, ith, and i+nth particles on the same molecular chain, respectively. represents the average value of the vector angle; The average value of the vector angles of all statistical units and the average value of the vector angles of all statistical units on each molecular chain were calculated to evaluate the degree of entanglement of UHMWPE molecular chains.

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