Thermal-mechanical-chemical coupling simulation calculation method based on friction-induced energetic material ignition

Abstract

The invention discloses a thermal-mechanical-chemical coupling simulation calculation method for friction-induced energetic material ignition, which comprises the following steps: S1, establishing a three-dimensional finite element model of an energetic material, and performing mesh generation on the established three-dimensional finite element model; s2, embedding a model code of the friction-induced chemical thermal decomposition reaction of the energetic material into finite element analysis software; s3, in finite element analysis software embedded with model codes, performing thermal-mechanical-chemical coupling simulation on the three-dimensional finite element model after mesh division; and S4, performing visualization post-processing on a calculation result of the coupling simulation to obtain a corresponding model temperature field. The invention provides a heat-force-chemical coupling simulation calculation method for friction-induced energetic material ignition. The critical condition of friction-induced energetic material ignition can be researched. The thermal-mechanical-chemical coupling multi-aspect physical and chemical whole process monitoring of the energetic material in the friction process is realized, and the problem of friction induced ignition of different energetic materials can be simulated and researched.

Description

Technical Field

[0001] The present invention relates to the technical field of energetic material safety and friction heat and chemical coupling simulation analysis, and more specifically, to a thermal-mechanical-chemical coupling simulation calculation method based on friction-induced energetic material ignition. Background Art

[0002] As a source of power and strength for various weapons, missiles, and aerospace vehicles, the high-energy properties of energetic materials also make them face severe safety challenges during processing and service. The traditional theory of hot spots in explosives holds that energetic materials are heated unevenly, flash temperatures are formed on the surface of the energetic materials, and then hot spots are formed. These hot spots become potential ignition hot spot sources. Hot spots will trigger chemical reactions in the energetic materials themselves, causing their temperature, size, and pressure to rise rapidly in a short period of time. When enough heat accumulates on the surface of the energetic materials, ignition or even combustion and explosion will occur.

[0003] Due to the limitations of modern technology, the processing surface of energetic materials cannot be completely flat. Under the microstructure, there are many micro-protrusions on the surface of energetic materials. During the friction process, these micro-protrusions are the key reason for the generation of hot spots in energetic materials and even ignition and combustion. Since the hot spots of micro-protrusions on the friction interface have small spatial dimensions (only micrometers), short formation and duration (several μs to hundreds of μs), it is difficult to observe and understand the hot spot formation mechanism under the microstructure and the evolution mechanism of the hot spot's spatiotemporal characteristics by using high-speed infrared cameras and friction experiments. At present, most of the research on hot spot evolution is based on finite element simulation, and all of them take into account the mutual coupling of thermal, mechanical, and chemical properties of energetic materials (i.e., "thermal-mechanical-chemical" coupling). For example, Sun Baoping et al. (Numerical simulation of friction ignition evaluation experiment of explosives [J]. Journal of Beijing Institute of Technology, 2011, 31(06): 638-642) performed numerical simulation of ignition evaluation of PBX-C03 and PBX-C04 by assuming that the material contact surface is an ideal smooth plane and embedding the elastic-plastic model of thermal decomposition reaction, and obtained the critical load, speed and friction coefficient of friction ignition of PBX-C03. Xia Zhiquan et al. (The influence of PBX interface on hot spot formation and safety under impact loading [J]. Acta Ordnance, 2023, (04) 21: 1-14) established a two-dimensional PBX real microstructure model using image digital modeling technology, and obtained the critical hot spot density of PBX ignition as 0.68mm through the simulation experiment of flying piece impacting PBX explosives. -2. These studies have greatly promoted people's understanding of the friction ignition mechanism and critical safety boundary conditions of energetic materials. However, these research analyses have some shortcomings. They are all based on the assumption that the surface of the energetic material is a smooth ideal plane and a two-dimensional plane, and the friction work is completely converted into heat for the temperature rise of the energetic material. In real situations, the energetic material cannot be an ideal plane, an ideal rough surface, a two-dimensional random plane, and the friction heat cannot be completely converted into heat. These assumptions often ignore the uneven distribution of heat generated by friction on the surface of the energetic material due to the presence of micro-asperities, and the heat is often concentrated on the micro-asperities. These temperature distribution characteristics are the key factors that determine the formation, growth, and even transformation of hot spots. These micro-asperities will generate huge contact pressure during the contact process, resulting in a sharp increase in the temperature of the friction interface. Since the heat generated by the friction work cannot be transferred to the surrounding area in time, the heat accumulates on the top of the micro-asperities, thereby forming a hot spot on the micro-asperities. As the friction continues, the temperature, area, and pressure of the hot spot will continue to increase. When the temperature reaches the critical temperature of the chemical heat classification of the energetic material, the friction work and the chemical reaction are coupled to form a "thermal-mechanical-chemical" coupling. In the early stage of chemical thermal decomposition, friction work is needed to maintain the early thermal decomposition of the energetic material. In the later stage of "thermal-mechanical-chemical" coupling, the energy generated by the chemical reaction of the energetic material itself can maintain its own reaction, and the chemical reaction becomes the dominant factor leading to friction ignition. When the friction stops, the self-sustaining reaction of the energetic material will also lead to friction ignition of the energetic material.

[0004] At present, safety accidents caused by friction occur frequently because of the unclear formation and evolution of hot spots at the interface of energetic materials under friction and even the friction ignition mechanism. Based on the real roughness characteristics of the surface of energetic materials, from the perspective of tribology and the coupling of "thermal-mechanical-chemical", a calculation method for the interface temperature rise of energetic materials at the microscopic level is established, and the evolution law and mechanism of temperature rise are revealed, which will not only help to strengthen the basic understanding of friction temperature rise of energetic materials, but also provide theoretical guidance for the safety boundary assessment of energetic materials. Summary of the invention

[0005] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0006] In order to achieve these purposes and other advantages of the present invention, a thermal-mechanical-chemical coupling simulation calculation method based on friction-induced ignition of energetic materials is provided, comprising:

[0007] S1. Establishing a three-dimensional finite element model of energetic materials, and meshing the established three-dimensional finite element model;

[0008] S2. Embedding the model code of friction-induced chemical thermal decomposition reaction of energetic materials in finite element analysis software;

[0009] S3. In the finite element analysis software embedded in the model code, a thermal-mechanical-chemical coupling simulation is performed on the meshed three-dimensional finite element model;

[0010] S4, performing visualization post-processing on the calculation results of the coupled simulation to obtain the corresponding model temperature field;

[0011] Among them, in the visualization post-processing, the hot spot area of ​​the friction interface is extracted through the embedded self-translation code, so as to determine whether the energetic material is ignited by obtaining the hot spot density in the hot spot area.

[0012] Preferably, in S1, the three-dimensional finite element model is established by determining different crystal planes and roughness of the energetic material based on the type of energetic material, and is obtained by scanning the three-dimensional morphology of the energetic crystal surface.

[0013] Preferably, the process of establishing the three-dimensional finite element model includes:

[0014] S10, measuring the crystal plane of the energetic material using a device to scan the three-dimensional morphology profile data of the energetic material using a three-dimensional morphology scanner;

[0015] S11, extracting a data matrix of microstructure based on the roughness of energetic materials in the three-dimensional topographic profile data;

[0016] S12, using the preset functions and codes in the programming software to extract the rough surface data from the data matrix, and obtaining the corresponding three-dimensional point coordinate data through digital processing;

[0017] S13, reconstructing and passivating the 3D shape contour data using internal commands of the 3D modeling software;

[0018] S14. Based on the solid modeling technology, a three-dimensional finite element model corresponding to the three-dimensional rough surface characteristics of energetic materials with different crystal planes is established.

[0019] Preferably, in S1, when meshing the three-dimensional finite element model, the quality of the entire mesh of the friction pair is set to be above 0.7 through Quality.

[0020] Preferably, in S2, the model code completes the three-dimensional "thermal-mechanical-chemical" coupled simulation calculation by executing the programmed thermal decomposition reaction code when the friction-induced temperature rise reaches the chemical thermal decomposition temperature condition of the energetic material, and the thermal decomposition reaction code is constructed as follows:

[0021] S20, extract the node temperature T' in the finite element model, and substitute T' into the following formula for thermal decomposition solution:

[0022]

[0023] In the above formula, Q is the heat released by thermal decomposition of the material, q m is the unit mass density of the material, A is the pre-exponential factor, E a is the activation energy of the material, R is the gas constant;

[0024] S21. The chemical thermal decomposition temperature ΔT of the energetic material is obtained by the following heat conversion formula:

[0025] ΔT=Q / c×M

[0026] In the above formula, c is the specific heat capacity of the material, and M is the mass of the material;

[0027] S22, real-time node temperature T is obtained by the following formula:

[0028] T=T′+ΔT.

[0029] Preferably, in S3, the thermal-mechanical-chemical coupling simulation is implemented based on finite element analysis software, and the parameter configuration of the finite element analysis software includes: material parameter setting, system parameter configuration, and contact pair construction;

[0030] Wherein, the material parameter configuration includes: density, elastic modulus, thermal expansion coefficient, specific heat capacity, thermal conductivity, Poisson's ratio;

[0031] The system parameter configuration includes: initial temperature field setting of energetic materials and boundary condition setting of finite element simulation;

[0032] The construction of the contact pair includes:

[0033] The solid surface with rough surface characteristics is selected as the contact surface, and the solid surface with smooth characteristics is selected as the target surface;

[0034] Setting of normal contact stiffness;

[0035] EYOPT(1) is defined as a structural thermal coupling problem; KEYOPT(2) uses the augmented Lagrangian algorithm; KEYOPT(4) is set to the Gaussian point calculation form, and the normal stiffness factor is selected to be greater than 2.

[0036] Preferably, in S3, during the thermal-mechanical-chemical coupling simulation, constraints need to be imposed on the finite element friction model of the energetic material;

[0037] The constraints include:

[0038] Load constraints applied to the upper surface of the friction pair;

[0039] Apply x-direction displacement constraint to the friction pair as a whole;

[0040] Frictionless supports are provided on both sides of the friction pair;

[0041] Set a fixed constraint on the bottom surface of the friction base.

[0042] Preferably, in S3, the thermal-mechanical-chemical coupling simulation process further includes establishing two analysis steps of a load application process and a sliding process for the solution task;

[0043] In the analysis step I, the normal load is applied, the load increases linearly, and the friction pair and the base are in a static state;

[0044] In analysis step II, the normal load applied in analysis step I is maintained, and a fixed constraint is applied to the base and a displacement constraint is applied to the friction pair so that the friction pair slides in the positive x direction.

[0045] Preferably, in S3, the finite element analysis software performs heat transfer calculation analysis based on the following heat transfer differential equation:

[0046]

[0047] In the above formula, ρ is the density of the material, V is the unit volume of the material, c is the specific heat capacity of the material, T is the real-time temperature of the node, t represents the sliding time, k is the thermal conductivity of the material, x, y, z are the three-dimensional point coordinate data, q m is the unit mass density of the material, A is the pre-exponential factor, E a is the activation energy of the material, R is the gas constant, α is the friction power conversion coefficient, μ is the friction coefficient, P i is the node contact pressure, v i is the sliding speed of the node, and i is the point node.

[0048] Preferably, in S4, the content of the self-translation code includes: extracting the node temperature greater than 780K in the friction contact surface to obtain the input value for hot spot area calculation.

[0049] The present invention includes at least the following beneficial effects: compared with the traditional hot spot theory, the calculation method proposed in the present invention is closer to the formation and evolution of friction hot spots at the interface of energetic materials. Specifically, the present invention combines the real rough surface characteristics of the surface of energetic materials and the "thermal-mechanical-chemical" coupling effect of energetic materials for analysis, and the calculation results will be consistent with the actual situation, which lays a technical foundation for subsequent basic research.

[0050] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1It is a schematic flow chart of the "thermal-mechanical-chemical" coupling simulation calculation method for friction-induced ignition of energetic materials of the present invention;

[0052] Figure 2 Schematic diagram of a finite element model of an HMX crystal in an embodiment of the present invention;

[0053] Figure 3 Schematic diagram of the sliding process of the HMX crystal in an embodiment of the present invention;

[0054] Figure 4 This is a schematic diagram of the friction temperature rise of the HMX crystal with different pressure conditions as the friction sliding time changes in the embodiment of the present invention;

[0055] Figure 5 This is a schematic diagram of the friction temperature rise of HMX crystals with different speeds as the friction sliding time changes in an embodiment of the present invention;

[0056] Figure 6 This is a schematic diagram of the friction temperature rise of HMX crystals with different friction coefficients as the friction sliding time changes in an embodiment of the present invention;

[0057] Figure 7 This is a schematic diagram of the hot spot area of ​​the HHMX crystal under different pressure conditions in an embodiment of the present invention;

[0058] Figure 8 Schematic diagram of hot spot area of ​​HMX crystal with different speeds in an embodiment of the present invention;

[0059] Fig. 9 Schematic diagram of hot spot area of ​​HMX crystals with different friction coefficients in an embodiment of the present invention;

[0060] Fig.10 The distribution cloud diagram of HMX rough surface temperature under different normal pressure conditions. DETAILED DESCRIPTION

[0061] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0062] Existing friction temperature rise calculation models usually only consider the thermal-mechanical coupling effect. When the surface temperature of the energetic material reaches the self-sustaining chemical thermal decomposition temperature, the chemical exothermic effect will become an important energy source for the interface temperature rise. Therefore, the calculation results of the interface friction temperature rise under the "thermal-mechanical-chemical" coupling effect will be closer to the actual situation. Under actual working conditions, the surface of the energetic material cannot be an ideal smooth surface, an ideal rough surface or a two-dimensional random surface. Therefore, simulation and calculation based on the real roughness characteristics of the surface of the energetic material will produce results closer to the actual situation. Based on this, the present invention provides a "thermal-mechanical-chemical" coupling simulation calculation method and process for friction-induced ignition of energetic materials, which solves the problem that it is difficult to observe the entire process from hot spot formation to combustion and explosion during friction experiments, avoids safety accidents caused by accidents, and enables the calculation results to provide an effective reference for the improvement of the processing technology of energetic materials and the friction ignition sensitivity and safety assessment of energetic materials.

[0063] The processing flow of the "thermal-mechanical-chemical" coupled simulation calculation method for friction-induced ignition of energetic materials is as follows: Figure 1 However, in actual implementation, Figure 1 Expanded to include the following steps:

[0064] (1) Use professional analytical equipment to measure and analyze the crystal planes of specific energetic materials (for energetic materials with different crystal planes) to determine the crystal planes and crystal forms of energetic materials. Then, the energetic material samples are inlaid with epoxy resin materials, and the sample surfaces are polished and polished with a polishing machine to make their roughness meet the requirements of the friction test. After the energetic material is polished, the sample is placed on the clamping platform of the friction and wear tester, and a 3D profile scanner is used to perform roughness detection and 3D profile scanning on the polished sample to obtain the sample roughness, 3D profile, and structural data matrix of the 3D profile.

[0065] (2) Compile the code using the command of the code software to digitize the microstructure data matrix and draw the microstructure of the surface of the energetic material. Then use the function to perform noise reduction on the microstructure of the energetic material. Finally, output and save the microstructure data of the surface of the energetic material in the form of point coordinates. The point coordinates of the microstructure of the energetic material are marked as (x, y, z), where x and y are the horizontal and vertical coordinate values ​​of the morphological structure, and z is the height of the point.

[0066] (3) The microstructure data of the energetic material surface is imported into the software through the "polygon" function in the 3D modeling software and the boundary parameters of the 3D morphology profile are determined. Then, the point data is fitted into a 3D rough surface with a microstructure using the "parametric surface" function. Then, the reconstructed energetic material surface microstructure is passivated. The reconstructed 3D morphology profile is solidified using the solidification modeling function of the software as shown in the attached figure. Figure 2As shown, a model with zero roughness and a smooth plane is then created. Finally, the two models are assembled into a friction pair, and it is assumed that the model with rough surface characteristics is the friction pair, and the model with smooth surface characteristics is the substrate.

[0067] (4) Import the energetic material finite element model into professional meshing software for meshing. Select regular tetrahedral mesh for the model part with rough surface characteristics, select regular hexahedral mesh for the model with smooth surface characteristics, select denser mesh for the rough surface, and use sparser mesh away from the rough surface. Refine the mesh of the rough surface, and then select Quality to set the overall mesh quality of the friction pair to be greater than 0.7.

[0068] (6) Import the three-dimensional finite element model with mesh into the finite element analysis software, and use the Engineering data (engineering material database) to import the relevant physical parameters of the energetic material, such as hardness, elastic modulus, density, Poisson's ratio, specific heat capacity, thermal expansion coefficient, thermal conductivity and other parameters.

[0069] (7) Perform contact settings on the contact surfaces of the friction pair, including the selection of contact type and the setting of keyword options.

[0070] (7.1) Set the three-dimensional surface with micro-convex bodies, dense mesh and surface characteristics as the contact surface, set the smooth solid surface with rough mesh and smooth surface as the target surface, and set the contact unit type.

[0071] (7.2) Set the normal contact stiffness. The normal contact stiffness can be specified by a proportional factor or an absolute value. The normal contact stiffness varies depending on the material properties of the energetic material.

[0072] (7.3)KEYOPT(1) is defined as the structural thermal coupling solution problem; KEYOPT(2) uses the augmented Lagrangian algorithm; KEYOPT(4) is set to the Gaussian point calculation form.

[0073] (8) Set the boundary conditions of the finite element simulation in the Coupled Field Transient, including the initial temperature of the environment and energetic material model, and the heat dissipation method during the friction process, which includes heat convection and heat conduction.

[0074] (9) Constraints are imposed on the finite element friction model of energetic materials. Specifically, the constraints imposed are: displacement constraints, loads, and fixed constraints. The compiled chemical thermal decomposition reaction model code of energetic materials is imported. The thermal decomposition reaction code includes: adding thermal decomposition code during the ANSYS solution process, adding the chemical thermal decomposition code with the unique properties of energetic materials on the basis of the original "thermal-mechanical" coupling solution, extracting the node temperature in the finite element model (i.e., the "thermal-mechanical" coupling temperature T′), and then bringing the node temperature into the code for thermal decomposition. Calculation is then performed, and the thermal decomposition temperature ΔT of the energetic material is calculated through the heat conversion formula (ΔT=Q / c×M). The calculated thermal decomposition temperature is superimposed on the node: real-time node temperature T=“thermal-mechanical” coupling temperature+chemical thermal decomposition temperature (ie, T=T′+ΔT). The temperature solution in this method takes into account both the thermal effect and heat conduction factors generated by the chemical thermal decomposition of the energetic material.

[0075] (10) Establish the analysis steps. The entire solution process is divided into two analysis steps.

[0076] (10.1) In analysis step 1, the applied load is set, and the friction pair and the base are in a stationary state.

[0077] (10.2) In analysis step 2, the load applied in analysis step 1 is maintained, the base is in a stationary state, and a displacement constraint is applied to the friction pair to cause the friction pair to displace.

[0078] (11) Submit the solution task and perform the "thermal-mechanical-chemical" coupled transient solution. The analysis steps are activated gradually during the solution process;

[0079] Finite element software performs heat transfer calculation and analysis based on heat transfer differential equations:

[0080]

[0081] In formula (1), ρ is the density of the material, c is the specific heat capacity of the material, k is the thermal conductivity of the material, T is the temperature of the material, and q m is the unit mass density of the material, V i is the unit volume of the material, A is the pre-exponential factor, E a is the activation energy of the material, R is the conventional gas constant, μ is the friction coefficient, α is the friction power conversion coefficient (obtained from friction experiments), P i is the node contact pressure, v i is the sliding speed of the node, i is the point node, and t is the sliding time.

[0082] (12) Solve the temperature field;

[0083] (12.1) Enter the post-processor to obtain the overall temperature field distribution of the finite element model. By compiling the subroutine, extract the unit nodes where the contact surface temperature of the friction pair is greater than the hot spot temperature of the energetic material, and calculate the total area of ​​the target surface and the contact surface where the temperature is greater than the thermal decomposition temperature of the energetic material.

[0084] Example:

[0085] 1. Taking the representative energetic material HMX as an example, the crystal plane of HMX is determined by Raman measurement and analysis. In order to ensure that the surface roughness of HMX single crystal meets the standard of engineering application, resin material is used for inlay treatment and polishing. Then, a three-dimensional profile white light interferometer is used to measure the roughness of the polished HMX crystal and scan the surface microstructure to obtain the surface roughness, three-dimensional morphology profile and microstructure data matrix of HMX crystal.

[0086] 2. Use the "Surf" command of MATLAB software to compile the code to digitize the microstructure data matrix and draw the microstructure of the HMX crystal. Then use the "Adapthisteq" function to denoise the microstructure of the HMX crystal. Finally, output and save the microstructure data of the HMX crystal in the form of point coordinates. The microstructure point coordinates of the HMX crystal are marked as (x, y, z), where x and y are the horizontal and vertical coordinate values ​​of the morphological structure, and z is the height of the point.

[0087] 3. Use the "polygon" function in COMSOL software to import the microstructure data of HMX crystal into COMSOL software and determine the boundary parameters of the three-dimensional morphology profile, then use the "parametric surface" function to fit the point data into a three-dimensional rough surface with a microstructure, and then passivate the reconstructed HMX crystal microstructure. Since the real surface of energetic materials has micro-convex bodies of various shapes and sizes, and is not smooth, this may make it difficult for subsequent simulation calculations to converge. Therefore, in order to increase the convergence of the simulation, it is necessary to passivate the reconstructed three-dimensional morphology profile to make it smoother.

[0088] 4. Import the reconstructed HMX crystal surface morphology into SOLIDWORKS software, and then use the solid modeling technology to solidify the reconstructed microstructure, as shown in the attached figure. Figure 2As shown, a model with zero roughness and a smooth plane is then created, and finally the two models are assembled into a friction pair, and the three-dimensional solid model with rough surface characteristics is assumed to be the friction pair, and the solid model with smooth surface is assumed to be the substrate. Since the three-dimensional solid model with real rough surface characteristics is only applicable to the micro-nano scale, and the microscopic protrusions in the real rough surface will occupy a lot of computing resources, if a solid model with a 1:1 real rough surface feature size is established, it will increase the difficulty of meshing in subsequent simulation calculations, and will also consume a lot of computing resources, causing unnecessary waste, and the contact behavior of the friction pair interface can reflect the real contact behavior between HMX crystals.

[0089] 5. Import the three-dimensional finite element model of energetic materials into the Hypermesh software for meshing. Select regular tetrahedral meshes for models with rough surface characteristics, select regular hexahedral meshes for solid models with smooth surfaces, select denser meshes for the rough surface and its vicinity, and use sparser meshes away from the rough surface. Use the sweeping method to mesh the friction pair, use "refinement" to select the rough surface for mesh optimization, and then select Quality to adjust the overall mesh quality of the finite element model.

[0090] 6. Import the three-dimensional finite element model of energetic materials with mesh into the finite element analysis software ANSYS Workbench, and use Engineering data to define the physical performance parameters of HMX crystal, including hardness, elastic modulus, density, Poisson's ratio, specific heat, thermal expansion coefficient, thermal conductivity coefficient and other parameters, and assign material properties to corresponding structural parts. The physical parameter properties of HMX crystal are shown in Table 1:

[0091]

[0092] 7. The construction of contact pairs mainly includes the selection of contact type and the setting of keyword options.

[0093] 7.1. Set the three-dimensional surface with micro-convex bodies, dense mesh and surface characteristics as the contact surface, and set the smooth solid surface with rough mesh and smooth surface as the target surface, and set the contact unit to Contact 174 and the target unit to Target 170.

[0094] 7.2. Set the normal contact stiffness.

[0095] 7.3. KEYOPT(1) is defined as the structural thermal coupling solution problem; KEYOPT(2) uses the augmented Lagrangian algorithm; KEYOPT(4) is set to the Gaussian point calculation form.

[0096] 8. Set the boundary conditions of the finite element simulation in Coupled Field Transient, including the initial temperature of the environment and energetic material model, and the heat dissipation method during the friction process, which includes heat convection and heat conduction.

[0097] Thermal convection heat dissipation boundary conditions are set on the entire surface of the friction pair and the substrate.

[0098] 9. Apply constraints to the finite element friction model of energetic materials. The specific constraints imposed are: displacement constraints, loads, and fixed constraints.

[0099] As attached Figure 3 As shown in the figure, a load (F) constraint is applied to the upper surface of the friction pair (solid A); a sliding velocity (V) in the positive x direction is applied to the friction pair as a whole, so that the friction pair can slide frictionally; frictionless supports are set on both sides of the friction pair to limit the large deformation of the friction pair in the y direction; a fixed constraint is set on the bottom surface of the base (solid B) to limit the overall movement of the base.

[0100] 10. Establish the "thermal-mechanical-chemical" coupling model and solution task of the friction sliding process of HMX crystal.

[0101] 11. Establish analysis steps. Two analysis steps are set for the HMX crystal sliding process, namely the load application process and the sliding process.

[0102] 11.1. In analysis step 1, a normal load is applied, and the load increases linearly. The friction pair and the base are at rest.

[0103] 11.2. In analysis step 2, the applied normal load is maintained and a fixed constraint is imposed on the base. In order to ensure that the base is in a stationary state, a displacement constraint is imposed on the friction pair so that the friction pair slides in the positive x direction.

[0104] 12. Submit the solution task.

[0105] Submit the solution task and perform transient solution of "thermal-mechanical-chemical" coupling. The analysis steps are activated gradually during the solution process. ANSYS Workbench finite element software performs heat transfer calculation and analysis based on the heat transfer differential equation. The heat transfer differential equation is:

[0106]

[0107] 13. Solve the temperature field.

[0108] Enter the visualization post-processing module to obtain the overall temperature field distribution of the HMX rough surface model under the "thermal-mechanical-chemical" coupling effect. By compiling the subroutine (i.e., self-translated code), extract the unit nodes whose contact surface temperature of the friction pair model is greater than the hot spot temperature of the HMX crystal (780K), and calculate the total area of ​​the target surface and the contact surface temperature greater than 780K respectively. Extract the maximum temperature of the HMX rough surface and obtain the time when the HMX crystal reaches the thermal runaway temperature (780K). The time of HMX thermal runaway is the time when the HMX crystal undergoes local ignition. When the hot spot density of the HMX rough surface model is greater than 0.68μm -2 When the ignition temperature is high, the energetic material will undergo an ignition reaction based on the theory of ignition of energetic materials based on the hot spot density.

[0109] The contents of the compilation subroutine include:

[0110] print("Concentration ofmodel:",soly[0])

[0111] print("Time:",sol.t)

[0112] print("Surface area(T>780(K)"):,sum(Surface areas))

[0113] According to the left side of the heat conduction differential equation (1), the friction parameters (normal pressure P, sliding speed v, friction coefficient μ) are the key parameters that determine the friction heat generation at the HMX / HMX interface. In order to fully measure the effect of the friction parameters on the temperature rise of the HMX / HMX friction interface, it is necessary to study the effect of each friction parameter on the HMX / HMX friction temperature rise. The normal contact pressure is applied in the range of 10MPa to 100MPa; the sliding speed is applied in the range of 0.05m / s to 5m / s; and the friction coefficient is applied in the range of 0.06 to 0.3.

[0114] As attached Figure 4 As shown in the figure, under the conditions of sliding speed of 5m / s and friction coefficient of 0.3, when the normal pressure increases from 10MPa to 100MPa, the time for local friction ignition at the HMX interface increases from 0.167μs to 0.061μs, the normal pressure increases by 9 times, and the friction ignition time decreases by 1.73 times. Figure 5As shown in the figure, when the friction coefficient is 0.3 and the normal contact pressure is 100MPa, when the sliding speed increases from 0.05m / s to 5m / s, the sliding speed increases by 99 times, and the time for local friction ignition at the HMX interface decreases from 2.95μs to 0.061μs, and the friction ignition time decreases by 47.36 times. When the sliding speed is less than 0.1m / s, the maximum friction temperature is 347K. It is worth noting that the critical temperature of HMX thermal decomposition reaction is about 500K. Therefore, when the friction coefficient is 0.3, the contact pressure is 100MPa, and the sliding speed is less than 0.1m / s, HMX is in an absolutely safe state during the sliding process. As shown in the attached figure Figure 6 As shown in the figure, under the conditions of normal pressure of 100MPa and sliding speed of 5m / s, when the friction coefficient increases from 0.06 to 0.3, the time for local friction ignition of the HMX interface increases from 0.19μs to 0.061μs, the friction coefficient increases by 4 times, and the friction ignition time decreases by 2.2 times. It is worth noting that when the friction coefficient of HMX is 0.06, although the friction temperature reaches the critical condition for the thermal decomposition of HMX, and the temperature generated by the "thermal-mechanical-chemical" coupling is about 595K, the heat generated by the work done by friction is too low to maintain the thermal decomposition of HMX to generate enough heat to maintain the ignition reaction of HMX.

[0115] Attached Fig.10 The temperature distribution cloud diagram of the HMX rough surface under different normal pressure conditions is shown. It can be seen that the temperature of the HMX rough surface is all concentrated on the micro-convex bodies. This is because the micro-convex bodies on the HMX rough surface are in contact with the plane of the HMX substrate in the real contact state during the friction process. During the friction process, the heat conductivity coefficient of HMX is very low and the friction time is very short, resulting in the heat being concentrated on the micro-convex bodies and unable to be transferred to the surroundings in time. This is also the reason for the uneven heat distribution on the HMX rough surface. Fig.10 Item (a) is a "thermal-mechanical-chemical" coupled calculation of the HMX chemical thermal decomposition code under pressure conditions of 30MPa, 50MPa, and 100MPa. Fig.10 Item (b) is a “thermal-mechanical” coupled calculation without embedding the HMX chemical thermal decomposition code under pressure conditions of 30MPa, 50MPa, and 100MPa. Fig.10From the two items (a) and (b), it can be found that the high temperature area of ​​the temperature cloud map with the chemical thermal decomposition code simulation calculation embedded is significantly higher than the temperature cloud map without the chemical thermal decomposition code simulation calculation embedded. According to the hot spot theory of explosives, the hot spot area is one of the important conditions for determining the safety of explosives. This is because if the surface temperature remains constant in a certain area for a long time, the energetic material may also be at risk of ignition or even combustion and explosion. Therefore, it is very necessary to determine whether HMX undergoes friction ignition reaction by counting the hot spot area and hot spot density of HMX (the hot spot density is the hot spot area divided by the apparent area of ​​HMX).

[0116] Specifically, as attached Figure 7 As shown in Figure 2, under the conditions of sliding velocity of 5 m / s and friction coefficient of 0.3, when the normal pressure increases from 10 MPa to 100 MPa, the hot spot density of the HMX substrate increases from 0.62 μm -2 Increased to 2.89 μm -2 The hot spot density of HMX friction pair is from 0.43μm -2 Increased to 1.92 μm -2 . As attached Figure 8 As shown in Figure 2, under the conditions of a friction coefficient of 0.3 and a normal contact pressure of 100 MPa, when the sliding speed increases from 0.05 m / s to 5 m / s, the hot spot density of the HMX substrate increases from 0.56 μm -2 Increased to 2.89 μm -2 The hot spot density of HMX friction pair is from 0.33μm -2 Increased to 1.92 μm -2 . As attached Fig. 9 As shown in Figure 2, under the conditions of normal pressure of 100 MPa and sliding speed of 5 m / s, when the friction coefficient increases from 0.06 to 0.30, the hot spot density of the HMX substrate increases from 0.34 μm -2 Increased to 2.89 μm -2 The hot spot density of HMX friction pair is from 0.12μm -2 Increased to 1.92 μm -2 It is worth noting that when the hot spot density of HMX reaches 0.68μm -2 Therefore, the critical conditions for friction ignition of HMX are that the load is greater than 10MPa, the friction coefficient is greater than 0.1, and the sliding speed is greater than 0.5m / s.

[0117] The above solution is only an illustration of a preferred embodiment, but is not limited thereto. When implementing the present invention, appropriate replacement and / or modification can be performed according to user needs.

[0118] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and the embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily realized. Therefore, without departing from the general concept defined by the claims and equivalent scope, the present invention is not limited to the specific details and the illustrations shown and described here.

Claims

1. A thermal-mechanical-chemical coupling simulation calculation method based on friction-induced ignition of energetic materials, characterized in that: include: S1. Establishing a three-dimensional finite element model of energetic materials, and meshing the established three-dimensional finite element model; S2. Embedding the model code of friction-induced chemical thermal decomposition reaction of energetic materials in finite element analysis software; S3. In the finite element analysis software embedded in the model code, a thermal-mechanical-chemical coupling simulation is performed on the meshed three-dimensional finite element model; S4, performing visualization post-processing on the calculation results of the coupled simulation to obtain the corresponding model temperature field; Among them, in the visualization post-processing, the hot spot area of ​​the friction interface is extracted through the embedded self-translation code, so as to determine whether the energetic material is ignited by obtaining the hot spot density in the hot spot area.

2. The thermal-mechanical-chemical coupling simulation calculation method based on friction-induced ignition of energetic materials according to claim 1, characterized in that: In S1, the three-dimensional finite element model is established by determining different crystal planes and roughness of the energetic material based on the type of energetic material, and is obtained by scanning the three-dimensional morphology of the energetic crystal surface.

3. The thermal-mechanical-chemical coupling simulation calculation method based on friction-induced ignition of energetic materials according to claim 2, characterized in that: The process of establishing the three-dimensional finite element model includes: S10, measuring the crystal plane of the energetic material using a device to scan the three-dimensional morphology profile data of the energetic material using a three-dimensional morphology scanner; S11, extracting a data matrix of microstructure based on the roughness of energetic materials in the three-dimensional topographic profile data; S12, using the preset functions and codes in the programming software to extract the rough surface data from the data matrix, and obtaining the corresponding three-dimensional point coordinate data through digital processing; S13, reconstructing and passivating the 3D shape contour data using internal commands of the 3D modeling software; S14. Based on the solid modeling technology, a three-dimensional finite element model corresponding to the three-dimensional rough surface characteristics of energetic materials with different crystal planes is established.

4. The thermal-mechanical-chemical coupling simulation calculation method based on friction-induced ignition of energetic materials according to claim 1, characterized in that: In S1, when meshing the three-dimensional finite element model, the overall mesh quality of the friction pair is set to above 0.7 through Quality.

5. The thermal-mechanical-chemical coupling simulation calculation method based on friction-induced ignition of energetic materials according to claim 1, characterized in that: In S2, the model code completes the three-dimensional thermal-mechanical-chemical coupling simulation calculation by executing the programmed thermal decomposition reaction code when the friction-induced temperature rise reaches the chemical thermal decomposition temperature condition of the energetic material. The thermal decomposition reaction code is constructed as follows: S20, extract the node temperature T' in the finite element model, and substitute T' into the following formula for thermal decomposition solution: In the above formula, Q is the heat released by thermal decomposition of the material, q m is the unit mass density of the material, A is the pre-exponential factor, E a is the activation energy of the material, R is the gas constant; S21. The chemical thermal decomposition temperature ΔT of the energetic material is obtained by the following heat conversion formula: ΔT=Q / c×M In the above formula, c is the specific heat capacity of the material, and M is the mass of the material; S22, the node real-time temperature T is obtained by the following formula: T=T′+ΔT.

6. The thermal-mechanical-chemical coupling simulation calculation method based on friction-induced ignition of energetic materials according to claim 1, characterized in that: In S3, the thermal-mechanical-chemical coupling simulation is implemented based on finite element analysis software, and the parameter configuration of the finite element analysis software includes: material parameter setting, system parameter configuration, and contact pair construction; Wherein, the material parameter configuration includes: density, elastic modulus, thermal expansion coefficient, specific heat capacity, thermal conductivity, Poisson's ratio; The system parameter configuration includes: initial temperature field setting of energetic materials and boundary condition setting of finite element simulation; The construction of the contact pair includes: The solid surface with rough surface characteristics is selected as the contact surface, and the solid surface with smooth characteristics is selected as the target surface; Setting of normal contact stiffness; EYOPT(1) is defined as a structural thermal coupling problem; KEYOPT(2) uses the augmented Lagrangian algorithm; KEYOPT(4) is set to the Gaussian point calculation form, and the normal stiffness factor must be greater than 2.

7. The thermal-mechanical-chemical coupling simulation calculation method based on friction-induced ignition of energetic materials according to claim 6, characterized in that: In S3, during the thermal-mechanical-chemical coupling simulation, constraints need to be imposed on the finite element friction model of energetic materials; The constraints include: Load constraints applied to the upper surface of the friction pair; Apply x-direction displacement constraint to the entire friction pair; Frictionless supports are provided on both sides of the friction pair; Set a fixed constraint on the bottom surface of the friction base.

8. The thermal-mechanical-chemical coupling simulation calculation method based on friction-induced ignition of energetic materials according to claim 7, characterized in that: In S3, the thermal-mechanical-chemical coupling simulation process also includes establishing two analysis steps of load application process and sliding process for the solution task; In the analysis step I, the normal load is applied, the load increases linearly, and the friction pair and the base are in a static state; In analysis step II, the normal load applied in analysis step I is maintained, and a fixed constraint is applied to the base and a displacement constraint is applied to the friction pair so that the friction pair slides in the positive x direction.

9. The thermal-mechanical-chemical coupling simulation calculation method based on friction-induced ignition of energetic materials according to claim 8, characterized in that: In S3, the finite element analysis software performs heat transfer calculations based on the following heat transfer differential equations: In the above formula, ρ is the density of the material, V is the unit volume of the material, c is the specific heat capacity of the material, T is the real-time temperature of the node, t represents the sliding time, k is the thermal conductivity of the material, x, y, z are the three-dimensional point coordinate data, q m is the unit mass density of the material, A is the pre-exponential factor, E a is the activation energy of the material, R is the gas constant, α is the friction power conversion coefficient, μ is the friction coefficient, P i is the node contact pressure, v i is the sliding speed of the node, and i is the point node.

10. The thermal-mechanical-chemical coupling simulation calculation method based on friction-induced ignition of energetic materials according to claim 1, characterized in that: In S4, the content of the self-translated code includes: obtaining an input value for hot spot area calculation by extracting node temperatures greater than 780K in the friction contact surface.

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