A method for calculating the mechanism of action of polymer composites at high strain rates

Abstract

The application discloses a kind of high strain rate under the calculation method of polymer composite action mechanism, comprising the following steps: determining the material of nanocomposite, thickness distribution, potential function;Using molecular dynamics modeling software constructs the target model of multilayer composite;By energy minimization and relaxation target model until the model reaches equilibrium state;Different piston impact velocity is applied to target model;The stress, density and temperature distribution of nanocomposite are output, Hugoniot relationship is calculated and energy dissipation is evaluated;Reveal the action mechanism of nanocomposite under strong dynamic load;Nanocomposite design strategy and optimization method are proposed.The application adopts the above-mentioned calculation method of polymer composite action mechanism under high strain rate, which uses molecular dynamics method to avoid the high cost of microscale impact test technology, reveals the micro-mechanism of polymer composite under extreme strain rate impact response, and provides reference for nanoscale design of protective materials.

Description

Technical Field

[0001] This invention belongs to the field of impact protection research based on molecular dynamics, specifically involving a calculation method for the action mechanism of polymer composite materials under high strain rates. Background Technology

[0002] Protective materials and structures are frequently subjected to various forms of impact and damage during daily use, facing extreme environments such as high temperature, high pressure, and high strain rate. Meanwhile, polymers and novel polymer-based composites are widely used in impact protection due to their high specific stiffness, high specific strength, and high toughness. Therefore, characterizing the impact response of polymer composites and understanding their dynamic behavior under relevant extreme conditions is crucial. Impact simulation of protective materials can be divided into macroscopic and microscopic scales. At the macroscopic scale, impact simulation of polymer composites is relatively mature, but its accuracy is limited by the material constitutive model and material parameters. At the microscopic scale, molecular dynamics methods can describe the microstructural evolution of materials during impact and reveal the microscopic mechanisms and dissipation mechanisms of polymer composites. Nanocomposites developed using this approach show great promise in advanced applications such as soft bulletproof vests and spacecraft protective shields.

[0003] Currently, microscale impact testing techniques (laser-induced projectile impact testing, LIPIT) are costly and time-consuming, and are mostly limited to the impact analysis of microscale impact specimens. Information on extreme velocity impact processes and dynamic deformation is scarce, and computational studies lack reports on stress wave propagation and failure mechanisms in nanoscale polymer composites. Therefore, it is urgent to investigate the microscopic mechanisms of the impact response of polymer composites under extreme strain rates, providing a new perspective and insights for designing superior protective materials. Summary of the Invention

[0004] The purpose of this invention is to provide a calculation method for the action mechanism of polymer composite materials under high strain rates. This method uses molecular dynamics to avoid the high cost of microscale impact testing techniques, reveals the microscopic mechanism of impact response of polymer composite materials under extreme strain rates, and provides a reference for the nanoscale design of protective materials.

[0005] To achieve the above objectives, this invention provides a method for calculating the action mechanism of polymer composite materials under high strain rates, comprising the following steps:

[0006] S1. Determine the material, thickness distribution, and potential function of the nanocomposite material based on the combination of materials in each layer of the polymer composite material.

[0007] S2. Construct a target model of a multilayer composite material using molecular dynamics modeling software;

[0008] S3. Minimize energy and relax the objective model until the model reaches equilibrium.

[0009] S4. Under the NVE ensemble, apply different piston impact velocities to the target model;

[0010] S5. Analyze the shock wave propagation process and the interface effects of different material combinations, output the stress, density and temperature distribution of the nanocomposite material along the impact direction, calculate the Hugoniot relationship and evaluate the energy dissipation ratio, and use visualization software to perform visual analysis of the trajectory file.

[0011] S6. Based on the indicators for measuring the propagation and dissipation performance of shock waves in step S5, discuss the influence of piston speed and interface factors, and reveal the mechanism of action of nanocomposite materials under strong dynamic loads.

[0012] S7. By comprehensively comparing the impact resistance of nanocomposites under different material combinations and thickness distributions, design strategies and optimization methods for nanocomposites are proposed.

[0013] Preferably, in step S1, the multilayer structure of the nanocomposite material is composed of alternating soft and hard phase layers, with the soft phase layer being a polymer and the hard phase layer being a metal or graphene; keeping the total thickness of the target model constant, the thickness of the multilayer structure is set by changing the thickness of the soft phase layer and the thickness of the hard phase layer.

[0014] Preferably, in step S1, if the hard phase layer is metal, without considering bond breaking, the full-atom model of the polymer adopts the potential functions of the non-reactive force fields PCFF, CVFF, and COMPASS, and the metal adopts the EAM potential function.

[0015] Preferably, in step S1, if the hard phase layer is graphene, both the polymer and graphene adopt a coarse-grained model, and a potential function suitable for the coarse-grained model is selected.

[0016] The Lennard-Jones potential function describing the nonbonded interaction between coarse polymer particles and coarse graphene particles is:

[0017]

[0018] In the formula, r is the distance between coarse grains, r c By varying the cutoff radius, the interatomic spacing where the σ potential energy is zero, and the ε potential well depth, the influence of interfacial interactions on the dynamic impact response of layered nanocomposite films was investigated.

[0019] Preferably, in step S2, the specific method for constructing the target model of the multilayer composite material using molecular dynamics modeling software is as follows:

[0020] S21. Use molecular modeling software or code to generate the initial configuration of soft phase layer cubic cells;

[0021] S22. The soft phase layer cubic cell compression simulation was carried out using a reflective wall to generate soft phase layers of different thicknesses. After compression, the surface of the soft phase layer became denser and smoother.

[0022] S23. Use LAMMPS to perform a complete annealing process on the soft phase layer to eliminate polymer inhomogeneity;

[0023] S24. The hard phase layer is modeled using the LAMMPS internal modeling method, and then the soft and hard phase layers are combined to form an alternating structure target model.

[0024] Preferably, in step S4, applying different piston impact velocities to the target model specifically involves dividing the left hard phase layer of the target model into pistons, applying a constant impact velocity to the pistons for a period of time, then canceling the impact velocity applied to the pistons, and continuing the simulation process after impact unloading.

[0025] Preferably, the target model uses periodic boundary conditions in the X and Y directions and aperiodic boundary conditions in the Z direction to represent a target model with finite thickness, and a vacuum layer is added on both sides of the model.

[0026] Preferably, in step S5, the target model is divided into N layers of equal thickness along the Z-axis, and the atoms in each layer are averaged to obtain local state variables. The stress, density and temperature distribution of the nanocomposite material along the impact direction are output as cloud maps to analyze the shock wave propagation process and spalling behavior of the composite material.

[0027] To calculate the local temperature distribution along the impact direction, the influence of the center-of-mass velocity needs to be removed, and the local temperature T bin The calculation formula is as follows:

[0028]

[0029] In the formula, m i Given the mass of atom i in a given sheet, u i,z U is the velocity of the atom in the Z direction. Z Given the centroid velocities of all atoms in the sheet, N bin Given the total number of atoms in the lamella, K B Boltzmann constant.

[0030] Preferably, in step S5, the impact Hugoniot relation is determined by the average particle velocity U. p Shock wave velocity U s Impact pressure P shock Temperature T and volume V are thermodynamic state variables that characterize the propagation of shock waves in materials.

[0031] Hugoniot relations are determined by U s -U p The relationship is represented as follows:

[0032] U s =c0+kU p

[0033] In the formula, c0 is the overall sound velocity, k is the material constant, and U is the sound velocity. s Shock wave velocity, U p Piston speed.

[0034] Preferably, in step S5, the dissipation ratio, which measures the impact dissipation energy index, is defined as the ratio of dissipated energy to input energy; the input energy of piston impact is defined as the difference between the initial total energy and the final total energy; and the dissipated energy is represented by the final increment of potential energy.

[0035] The beneficial effects of this invention are:

[0036] 1. This invention provides a calculation method for polymer composites under high strain rates, revealing the microscopic mechanism of impact response of polymer composites under extreme strain rates;

[0037] 2. The soft and hard phases of the composite material target model of the present invention can be replaced with other polymer materials and metals for material design, and provide a reference for the nanoscale design of protective materials through molecular dynamics methods.

[0038] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0039] Figure 1 This is a flowchart illustrating an embodiment of a calculation method for the action mechanism of polymer composite materials under high strain rates according to the present invention.

[0040] Figure 2 This invention provides a calculation method for the interaction mechanism of polymer composite materials under high strain rates, and serves as the target model for nanocomposite materials in an embodiment of this invention.

[0041] Figure 3 Example 1: Normal stress cloud diagram at a piston impact velocity of 1 km / s, which is a calculation method for the action mechanism of polymer composite materials under high strain rate according to the present invention.

[0042] Figure 4 Example of a calculation method for the action mechanism of polymer composite materials under high strain rate according to the present invention: density cloud map at a piston impact velocity of 1 km / s;

[0043] Figure 5This is a schematic diagram of the shock wave input energy and dissipated energy, representing an embodiment of the calculation method for the action mechanism of polymer composite materials under high strain rate according to the present invention.

[0044] Figure 6 This is a schematic diagram illustrating the change in dissipation ratio under different piston impact velocities in an embodiment of the calculation method for the action mechanism of polymer composite materials under high strain rates according to the present invention. Detailed Implementation

[0045] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0046] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0047] Example

[0048] like Figure 1 As shown, a calculation method for the action mechanism of polymer composites under high strain rates includes the following steps:

[0049] S1. Determine the nanocomposite material, thickness distribution, and potential function based on the combination of each layer of the polymer composite material.

[0050] like Figure 2 As shown, the multilayer structure of the nanocomposite material consists of alternating soft and hard phase layers. The soft phase layers absorb energy and provide toughening, while the hard phase layers offer high stiffness and strength. The shock wave coupling effect generated by the interlayer impedance difference in the alternating soft and hard phase structure enhances energy dissipation. Soft phase materials are often made of polymers such as polyethylene, polyurea, polyurethane, and polymethyl methacrylate (PMMA), while hard phase materials are often made of common metals (copper, aluminum, iron) or graphene.

[0051] Under certain conditions, the composite material is composed of a replica array of repeating units (a single soft phase layer and a single hard phase layer forming repeating units), and does not belong to a gradient structure. First, the total thickness of the target model is kept at 80 nm. Then, the ratio factor between the thickness of the soft phase layer and the thickness of the hard phase layer is determined to be 4, and the number of repeating units is set to 4, 6, 8, and 10, thereby determining the thickness distribution of the composite material.

[0052] If the hard phase layer is metal, without considering bond breaking, the all-atom model of polymer materials can use the potential functions of the non-reactive force fields PCFF, CVFF, and COMPASS, while the EAM potential function is used for metals. If the hard phase layer is graphene, both polymers and graphene can use coarse-grained models, selecting potential functions suitable for the coarse-grained model.

[0053] The Lennard-Jones potential function describing the nonbonded interactions between coarse polymer particles and coarse graphene particles is:

[0054]

[0055] In the formula, r is the distance between coarse grains, r c The cutoff radius, the interatomic spacing where the σ potential energy is zero, and the ε potential well depth can be used to study the influence of interfacial interactions on the dynamic impact response of layered nanocomposite films by changing ε.

[0056] Taking the composite material composed of aluminum / polymethyl methacrylate as an example, aluminum uses the EAM potential function, the all-atom model of polymethyl methacrylate uses the PCFF potential function, and the interfacial force field of the two is corrected using the IFF potential function.

[0057] S2. Use molecular dynamics modeling software to construct a target model of multilayer composite materials.

[0058] S21. The initial configuration of polymethyl methacrylate (PMMA) cubic cells was generated using EMC software.

[0059] S22. A reflection wall was used to simulate the compression of polymethyl methacrylate cubic cells (PMMA) to generate soft phase layers of different thicknesses. After compression, the surface of the soft phase layers became denser and smoother.

[0060] S23. Use LAMMPS to perform a complete annealing process on the soft phase layer of the polymer layer to eliminate polymer inhomogeneity.

[0061] S24. The hard phase layer is modeled using the LAMMPS internal modeling method, and then the soft and hard phase layers are combined to form an alternating structure target model.

[0062] S3. The target model is relaxed for 200 picoseconds each under the conditions of NPT and NVT ensembles and temperature of 300K, through energy minimization and relaxation until the model reaches equilibrium.

[0063] S4. Under the NVE ensemble, apply different piston impact velocities to the target model.

[0064] Since the shock wave is an instantaneous process (adiabatic / isentropic), the NVE ensemble is used to capture the complete dynamic evolution of thermodynamic state variables during the shock wave loading process.

[0065] The target model is represented by periodic boundary conditions in the X and Y directions and aperiodic boundary conditions in the Z direction, indicating a finite-thickness target model. A 100nm vacuum layer is added on both sides of the model. The hard phase layer at the left end of the target model is designated as a piston with a thickness of 2nm.

[0066] The left piston impacts at speeds U of 0.125 km / s, 0.25 km / s, 0.5 km / s, 1 km / s, 1.5 km / s, and 2 km / s respectively. p The target model is propelled to generate a shock wave. The piston impacts at a constant speed for 10 picoseconds, then the impact speed applied to the piston is removed, and the simulation of the post-impact unloading process continues for 50 picoseconds.

[0067] S5. Analyze the shock wave propagation process and the interface effects of different material combinations, output cloud maps of stress, density and temperature distribution of nanocomposite materials along the impact direction, calculate Hugoniot relations and evaluate the energy dissipation ratio and other indicators to assess the shock resistance performance of nanocomposite materials, and use OVITO software to visualize the shock wave propagation process of the trajectory file.

[0068] Based on the stress, density, and temperature distribution cloud maps, the shock wave propagation process and spalling behavior of the composite material are analyzed.

[0069] The target model is divided into N layers of equal thickness along the Z-axis, and the local state variables (such as stress, density, and temperature) are obtained by averaging the atoms in each layer.

[0070] like Figure 3 As shown, the normal stress cloud diagram reveals that delamination occurs when the positive unloading wave intersects with the rarefied wave reflected from the free surface. The stress wave also generates a series of reflected waves when it encounters the hard phase layer interface within the polymer composite material, resulting in complex shock wave coupling and a complex stress state within the material. Combined with... Figure 3 Normal stress cloud diagram and Figure 4 Density cloud map analysis reveals that during the tensile stage, the convergence of unloading waves and reflected waves causes a continuous decrease in the density of the surrounding tensile region. The low-density region expands in the tensile region at a certain angle over time, indicating that pores / cracks inside the material continue to grow, the damaged area expands significantly, and eventually delamination failure occurs.

[0071] Temperature contour maps can be used to reveal the intrinsic relationship between damage evolution and temperature rise during composite material delamination. Calculating the local temperature distribution along the impact direction under impact loading requires considering the influence of the center-of-mass velocity and subtracting the contribution of this kinetic energy.

[0072] Local temperature T bin The calculation formula is:

[0073]

[0074] In the formula, m i Given the mass of atom i in a given sheet, u i,z U is the velocity of the atom in the Z direction. Z Given the centroid velocities of all atoms in the sheet, Nbin Given the total number of atoms in the lamella, K B Boltzmann constant.

[0075] The Hugoniot relation and dissipation ratio were calculated to evaluate the impact resistance of nanocomposites. The impact Hugoniot relation was expressed through the average particle velocity U. p Shock wave velocity U s Impact pressure P shock Thermodynamic state variables such as temperature T and volume V characterize the propagation of shock waves in materials.

[0076] Hugoniot relations can be derived from U s -U p The relationship is represented as:

[0077] U s =c0+kU p

[0078] In the formula, c0 is the overall sound velocity, k is the material constant, and U is the sound velocity. s Shock wave velocity, U p Piston speed.

[0079] The dissipation ratio, a measure of impact energy dissipation, is defined as the ratio of dissipated energy to input energy. Figure 5 As shown, the input energy of piston impact is defined as the difference between the initial total energy and the final total energy. Dissipated energy is represented by the final increment of potential energy, mainly reflecting the energy dissipated during irreversible (plastic) deformation and at the interface, while ignoring the effect of temperature rise caused by energy dissipation. Figure 6 It reflects the dissipation ratio of the target model at different piston impact velocities, where point d indicates the optimal dissipation performance at that piston impact velocity.

[0080] S6. Based on the cloud map of the shock wave propagation monitored in step S5 and the index for measuring dissipation performance, discuss the influence of piston speed and interface factors, and reveal the mechanism of action of nanocomposite materials under strong dynamic loads.

[0081] S7. By comprehensively comparing the impact resistance of nanocomposites under different material combinations and thickness distributions, design strategies and optimization methods for nanocomposites are proposed.

[0082] Therefore, this invention employs the above-mentioned calculation method for the action mechanism of polymer composite materials under high strain rates. This method uses molecular dynamics to avoid the high cost of microscale impact testing techniques, revealing the microscopic mechanism of impact response of polymer composite materials under extreme strain rates, and providing a reference for the nanoscale design of protective materials.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A calculation method for the action mechanism of polymer composite materials under high strain rates, characterized in that, Includes the following steps: S1. Determine the material, thickness distribution, and potential function of the nanocomposite material based on the combination of materials in each layer of the polymer composite material. S2. Construct a target model of a multilayer composite material using molecular dynamics modeling software; S3. Minimize energy and relax the objective model until the model reaches equilibrium. S4. Under the NVE ensemble, apply different piston impact velocities to the target model; S5. Analyze the shock wave propagation process and the interface effects of different material combinations, output the stress, density and temperature distribution of the nanocomposite material along the impact direction, calculate the Hugoniot relationship and evaluate the energy dissipation ratio, and use visualization software to perform visual analysis of the trajectory file. S6. Based on the indicators for measuring the propagation and dissipation performance of shock waves in step S5, discuss the influence of piston speed and interface factors, and reveal the mechanism of action of nanocomposite materials under strong dynamic loads. S7. By comprehensively comparing the impact resistance of nanocomposites under different material combinations and thickness distributions, design strategies and optimization methods for nanocomposites are proposed.

2. The calculation method for the action mechanism of polymer composite materials under high strain rate according to claim 1, characterized in that: In step S1, the multilayer structure of the nanocomposite material is composed of alternating soft and hard phase layers. The soft phase layer is a polymer, and the hard phase layer is a metal or graphene. Keeping the total thickness of the target model constant, the thickness of the multilayer structure is set by changing the thickness of the soft phase layer and the thickness of the hard phase layer.

3. The calculation method for the action mechanism of polymer composite materials under high strain rate according to claim 2, characterized in that: In step S1, if the hard phase layer is metal, without considering bond breaking, the full-atom model of the polymer adopts the potential functions of the non-reactive force fields PCFF, CVFF, and COMPASS, while the metal adopts the EAM potential function.

4. The calculation method for the action mechanism of polymer composite materials under high strain rate according to claim 3, characterized in that: In step S1, if the hard phase layer is graphene, then both the polymer and graphene adopt the coarse-grained model, and a potential function suitable for the coarse-grained model is selected. The Lennard-Jones potential function describing the nonbonded interaction between coarse polymer particles and coarse graphene particles is: In the formula, r is the distance between coarse grains, r c By varying the cutoff radius, the interatomic spacing where the σ potential energy is zero, and the ε potential well depth, the influence of interfacial interactions on the dynamic impact response of layered nanocomposite films was investigated.

5. The calculation method for the action mechanism of polymer composite materials under high strain rate according to claim 4, characterized in that: In step S2, the specific method for constructing the target model of the multilayer composite material using molecular dynamics modeling software is as follows: S21. Use molecular modeling software or code to generate the initial configuration of soft phase layer cubic cells; S22. The soft phase layer cubic cell compression simulation was carried out using a reflective wall to generate soft phase layers of different thicknesses. After compression, the surface of the soft phase layer became denser and smoother. S23. Use LAMMPS to perform a complete annealing process on the soft phase layer to eliminate polymer inhomogeneity; S24. The hard phase layer is modeled using the LAMMPS internal modeling method, and then the soft and hard phase layers are combined to form an alternating structure target model.

6. The calculation method for the action mechanism of polymer composite materials under high strain rate according to claim 5, characterized in that: In step S4, applying different piston impact velocities to the target model specifically involves dividing the hard phase layer at the left end of the target model into pistons, applying a constant impact velocity to the pistons for a period of time, then canceling the impact velocity applied to the pistons, and continuing the simulation process after impact unloading.

7. The calculation method for the action mechanism of polymer composite materials under high strain rate according to claim 6, characterized in that: The target model uses periodic boundary conditions in the X and Y directions and non-periodic boundary conditions in the Z direction to represent a target model with finite thickness, and a vacuum layer is added on both sides of the model.

8. The calculation method for the action mechanism of polymer composite materials under high strain rate according to claim 7, characterized in that: In step S5, the target model is divided into N layers of equal thickness along the Z-axis. The atoms in each layer are averaged to obtain local state variables, and cloud maps of stress, density, and temperature distribution of the nanocomposite material along the impact direction are output to analyze the shock wave propagation process and spalling behavior of the composite material. To calculate the local temperature distribution along the impact direction, the influence of the center-of-mass velocity needs to be removed, and the local temperature T bin The calculation formula is as follows: In the formula, m i Given the mass of atom i in a given sheet, u i,z U is the velocity of the atom in the Z direction. Z Given the centroid velocities of all atoms in the sheet, N bin Given the total number of atoms in the lamella, K B Boltzmann constant.

9. The calculation method for the action mechanism of polymer composite materials under high strain rate according to claim 8, characterized in that: In step S5, the impact Hugoniot relation is determined by the average particle velocity U. p Shock wave velocity U s Impact pressure P shock Temperature T and volume V are thermodynamic state variables that characterize the propagation of shock waves in materials. Hugoniot relations are determined by U s -U p The relationship is represented as follows: You s =c0+kU p In the formula, c0 is the overall sound velocity, k is the material constant, and U is the sound velocity. s Shock wave velocity, U p Piston speed.

10. The calculation method for the action mechanism of polymer composite materials under high strain rate according to claim 9, characterized in that: In step S5, the dissipation ratio, which measures the impact energy dissipation index, is defined as the ratio of dissipated energy to input energy. The input energy of the piston impact is defined as the difference between the initial total energy and the final total energy; the dissipated energy is represented by the final increment of potential energy.

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