Fireproof simulation method for composite material structural member

Abstract

The invention provides a fireproof simulation method for a composite material structural member, and relates to the technical field of numerical simulation of aero-engine components. The fireproof simulation method of the composite material structural member comprises the following steps: constructing a first three-dimensional model with the composite material structural member, and importing the first three-dimensional model into simulation software; acquiring the relationship of the density of the composite material changing along with the temperature, the relationship of the thermal conductivity changing along with the temperature, the relationship of the specific heat capacity changing along with the temperature and pyrolytic reaction data, and editing the data into simulation software; initial conditions, boundary conditions, step length and time are set in simulation software; the simulation software is used for solving according to the energy control equation to obtain a simulation result so as to realize fireproof simulation of the composite material structural member, and meanwhile, in the fireproof simulation method, the thermophysical property heat transfer process and the thermal decomposition process in the fireproof process of the composite material structural member are simulated respectively; and the numerical simulation of the temperature distribution of the composite material structural member in the fireproof process can be accurately realized.

Description

Technical Field

[0001] The invention relates to the technical field of numerical simulation of aircraft engine components, and in particular to a fire prevention simulation method for composite material structural parts. Background Art

[0002] Fiber-reinforced composite materials have the advantages of high specific strength, high specific stiffness, strong designability, and good fatigue resistance. They are increasingly widely used in certain parts of civil aircraft engines, such as fan cases, nacelle covers, thrust reversers of nacelles, and fan blades. Some of these parts are in fire zones and need to meet the requirements of airworthiness fire protection clauses. According to the fire protection clauses of CCAR33.17, the materials used in the engine must minimize the possibility of fire and flame spread. Section 5 of the US FAA's advisory circular AC 33.17-1A[1] specifically explains the materials in the engine that may cause fire, including composite materials. The advisory circular recommends that when demonstrating compliance with 33.17(a), the applicant should conduct a material design assessment. In addition, for representative composite structural parts such as firewalls, according to AC 33.17-1A and AC 20-135, corresponding fire protection / fire resistance tests are required to demonstrate their compliance, that is, they can still maintain structural integrity after being subjected to standard flames for 15 / 5 minutes under specified working conditions. However, composite test pieces are complex to process and have a long test cycle. Fire resistance tests are destructive tests with high test costs. Developing composite simulation analysis technology is of great significance in establishing a composite fire resistance database, reducing test costs, shortening cycles, and improving the success rate of airworthiness compliance verification tests.

[0003] So far, the simulation research on composite materials in China has mainly focused on mechanics, and the numerical simulation methods for the fire resistance characteristics of composite materials are insufficient. The composite fire test process is a complex variable heat conduction process, and it is very difficult to accurately simulate the temperature field changes of composite materials during the impact of standard flames. Summary of the invention

[0004] The purpose of the present invention is to provide a fire protection simulation method for composite material structural parts, which can realize simulation research on fire protection of composite materials.

[0005] The embodiments of the present invention can be implemented in the following ways:

[0006] A fire prevention simulation method for a composite material structural member, comprising: constructing a first three-dimensional model having a composite material structural member, and importing the first three-dimensional model into simulation software;

[0007] Obtaining the density-temperature variation relationship, thermal conductivity-temperature variation relationship, specific heat capacity-temperature variation relationship and pyrolysis reaction data of the composite material, and editing them into the simulation software;

[0008] Setting initial conditions, boundary conditions, step length and time in the simulation software;

[0009] The simulation software simulates the process of standard flame impacting a composite material structure and solves the energy control equation to obtain the simulation result.

[0010] Optionally, the first three-dimensional model includes a solid domain formed by the composite material structural component and a fluid domain arranged at the back of the solid domain; the back of the solid domain is located within the range of the fluid domain.

[0011] Optionally, the energy control equation is:

[0012]

[0013] Where: ρ is the density at the current moment; C p is the specific heat capacity; T is the current temperature; t is the time; λ is the thermal conductivity; E is the activation energy of the pyrolysis reaction; R is the standard gas constant; A is the pre-exponential factor of the pyrolysis reaction; e is the natural constant; ρ f is the density of the carbonized layer of the composite material; ρ0 is the initial density of the composite material; x is the distance; h s is the latent heat of pyrolysis; h g is the enthalpy of pyrolysis gas; Q b Exchange heat for the airflow behind the composite material.

[0014] Optionally, the boundary condition includes a thermal boundary condition, and the fire protection simulation method for a composite material structural component further includes: acquiring the thermal boundary condition;

[0015] The step of obtaining the thermal boundary condition comprises:

[0016] Constructing a second three-dimensional model including a flame burner, a combustion area, and a composite material structure, wherein in the second three-dimensional model, the composite material structure is arranged in the combustion area;

[0017] The second three-dimensional model is processed by simulation software to simulate the process of standard flame impacting composite material structure;

[0018] The temperature field of the fire-exposed surface of the composite structural component after the standard flame impact is used as the thermal boundary condition.

[0019] Optionally, in the second three-dimensional model, a distance D between the composite material structure and an outlet of the flame burner is 100 mm ≤ D ≤ 104 mm.

[0020] Optionally, the step of obtaining the relationship between the thermal conductivity of the composite material and the temperature includes:

[0021] According to the test results of the thermal properties of the composite material, the variation of the thermal conductivity of the composite material with temperature is fitted to obtain the fitting equation of the variation of the thermal conductivity with temperature;

[0022] According to the test results of thermal properties of the composite material, an equation for the change of thermal conductivity of coke formed by the composite material after the fire test with temperature is obtained;

[0023] The thermal conductivity equation of the composite material during heating is obtained according to the fitting equation and the variation equation, and the thermal conductivity equation is used to characterize the relationship between the thermal conductivity of the composite material and the temperature.

[0024] Optionally, the thermal conductivity equation is:

[0025]

[0026] Among them, λ c is the fitted thermal conductivity obtained according to the fitting equation; λ m is the thermal conductivity of coke obtained according to the variation equation; ρ t is the density at the current moment; ρ f is the density of the carbonized layer of the composite material; ρ0 is the initial density of the composite material.

[0027] Optionally, the step of obtaining the relationship between the density of the composite material and the temperature includes:

[0028] Obtaining a discrete equation of density variation with temperature through the thermophysical property parameters of the composite material, so as to characterize the relationship between the density variation with temperature of the composite material through the discrete equation;

[0029] The discrete equation for the density variation with temperature is:

[0030]

[0031] Among them, ρ t is the density at the current moment; ρ t+1 is the density at the next moment; ρ f is the density of the carbonized layer of the composite material; A is the pre-exponential factor of the pyrolysis reaction; e is a natural constant; E is the activation energy of the pyrolysis reaction; R is the standard gas constant; T is the current temperature; and t is the time.

[0032] Optionally, the step of obtaining the relationship between the specific heat capacity of the composite material and the temperature includes:

[0033] According to the test results of the thermal properties of the composite material, the results of the change of specific heat capacity with temperature of the composite material are fitted to obtain a fitting equation for the change of specific heat capacity with temperature, so as to characterize the relationship between the change of specific heat capacity and temperature through the fitting equation for the change of specific heat capacity with temperature.

[0034] The beneficial effects of the fire protection simulation method for composite material structural parts provided by the embodiment of the present invention include:

[0035] The embodiment of the present invention provides a fire prevention simulation method for a composite material structure, the fire prevention simulation method comprises: constructing a first three-dimensional model of a composite material structure, and importing the first three-dimensional model into the simulation software; obtaining the density-temperature variation relationship, thermal conductivity-temperature variation relationship, specific heat capacity-temperature variation relationship and pyrolysis reaction data of the composite material, and editing them into the simulation software; setting the initial conditions, boundary conditions, step length and time in the simulation software; the simulation software obtains the simulation results according to the energy control equation, and then realizes the fire prevention simulation of the composite material structure, and at the same time, the fire prevention simulation method simulates the thermal physical property heat transfer and thermal decomposition process of the composite material structure in the fire prevention process respectively, and can accurately realize the numerical simulation of the temperature distribution of the composite material structure in the fire prevention process. It is thus helpful to improve the current technical problems of complex processing, long test cycle and high cost of composite material test pieces. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above features and advantages of the present invention can be better understood after reading the detailed description of the embodiments of the present disclosure in conjunction with the following drawings. In the drawings, the components are not necessarily drawn to scale, and components with similar related properties or features may have the same or similar reference numerals.

[0037] Figure 1 A flow chart showing a fire protection simulation method for a composite material structure provided according to one aspect of the present invention is shown;

[0038] Figure 2 A schematic diagram of the structure of a first three-dimensional model provided according to one aspect of the present invention is shown;

[0039] Figure 3 A schematic structural diagram of a first three-dimensional model provided in accordance with one aspect of the present invention at another viewing angle is shown;

[0040] Figure 4 A schematic diagram of the structure of a second three-dimensional model provided according to one aspect of the present invention is shown;

[0041] Figure 5 The simulation analysis results of the back-fired surface of the composite material structural component provided in Example 1 of the present invention are shown;

[0042] Figure 6The results of the experimental tests corresponding to Example 1 are shown;

[0043] Figure 7 The simulation analysis results of the back-fired surface of the composite material structural component provided in Example 2 of the present invention are shown;

[0044] Figure 8 The results of experimental tests corresponding to Example 2 are shown.

[0045] Reference numerals:

[0046] 100-first three-dimensional model; 111-solid domain; 112-fluid domain; 113-fired surface; 114-backfired surface; 200-second three-dimensional model; 211-flame burner; 212-combustion area; 213-composite material structure. DETAILED DESCRIPTION

[0047] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. Note that the aspects described below in conjunction with the accompanying drawings and specific embodiments are only exemplary and should not be construed as limiting the scope of protection of the present invention in any way.

[0048] At the same time, it should be noted that the terms "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0049] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified or limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, an integral connection, or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or the internal communication of two components, etc. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0050] Relevant terms in the description of the present invention:

[0051] Standard Flame: C20-135 defines a flame produced by a burner that meets the following conditions:

[0052] 1) Temperature is 2000±150℉(1093±83℃);

[0053] 2) The heat flux density is at least 9.3 Btu / ft2 / s (≥105.4 kW / m2), or the total heat flow measured by the copper tube water flow method is at least 4500 Btu / h (≥1320 W).

[0054] Fireproof: The ability of engine parts, accessories and components to withstand standard flames for at least 15 minutes and still perform their intended functions.

[0055] Fire Resistant: Engine parts, accessories and components are capable of withstanding standard flames for at least 5 minutes and still perform their intended functions.

[0056] Fire Zone: The area of ​​a flammable liquid spill containing a notional ignition source.

[0057] Designated Fire Zone: For turbine engines, the designated fire zone areas include:

[0058] 1) Compressor and accessories of turbine engines;

[0059] 2) The combustion chamber, turbine and tailpipe section of a turbine engine installation containing pipelines or components for conveying flammable liquids or gases.

[0060] CFD: Computational Fluid Dynamics.

[0061] Figure 1 This is a flow chart of the fire protection simulation method for composite material structural parts provided by the present invention. Figure 1 The present invention provides a fire prevention simulation method for a composite material structural member, and the fire prevention simulation method for a composite material structural member comprises the following steps:

[0062] S01: constructing a first three-dimensional model 100 having a composite material structure, and importing the first three-dimensional model 100 into simulation software.

[0063] Figure 2 1 shows a schematic structural diagram of a first three-dimensional model 100 provided in this embodiment. Figure 3 The schematic diagram of the structure of the first three-dimensional model 100 provided in this embodiment at another viewing angle is shown. Figure 2 and Figure 3 Step S01 includes constructing a three-dimensional model for fire prevention simulation, where the three-dimensional model is a first three-dimensional model 100 and has composite material structural parts, which constitute a solid domain 111 of the first three-dimensional model 100 .

[0064] Furthermore, the first three-dimensional model 100 also includes a fluid domain 112 disposed at the back of the solid domain 111. By disposing the fluid domain 112, numerical simulation is performed on the airflow at the back of the composite material structure, thereby considering the influence of the airflow on the fire resistance of the composite material under actual flight conditions. The wall surface on the side where the solid domain 111 and the fluid domain 112 are attached is the back-fire surface 114 of the solid domain 111, and the wall surface of the solid domain 111 on the side away from the fluid domain 112 along the thickness direction is the fire-receiving surface 113 of the solid domain 111. The back of the solid domain 111 is located within the range of the fluid domain 112. In other words, along the direction from the solid domain 111 to the fluid domain 112, the projection of the solid domain 111 at the fluid domain 112 is located within the fluid domain 112. Figure 2 The arrow in the middle is used to indicate the direction of the airflow in the fluid domain 112, that is, Figure 2 In the first three-dimensional model 100 shown, the air flow inlet is at the top of the fluid domain 112 , and the air flow outlet is at the bottom of the fluid domain 112 .

[0065] Alternatively, if Figure 3 As shown, the width of the solid domain 111 is consistent with that of the fluid domain 112, and the length of the solid domain 111 is smaller than that of the fluid domain 112. Specifically, the solid domain 111 can be set as a square plate-like member, and the fluid domain 112 can be set as a rectangular parallelepiped member attached to one side of the solid domain 111 in the thickness direction.

[0066] The constructed first three-dimensional model 100 is imported into the simulation software and meshed.

[0067] Specifically, the simulation software may adopt CFD simulation tools such as Fluent or PyroSim.

[0068] S02: Obtain the density-temperature variation relationship, thermal conductivity-temperature variation relationship, specific heat capacity-temperature variation relationship and pyrolysis reaction data of the composite material, and edit them into the simulation software.

[0069] By numerically simulating the heat transfer of thermal properties of composite structural parts during fire protection and the thermal decomposition process of composite materials respectively, it is helpful to accurately realize the numerical simulation of temperature distribution of composite structural parts during fire protection.

[0070] The density, thermal conductivity and specific heat capacity of the composite materials were tested through the thermal physical properties test of the composite materials, and their changes with temperature and time were summarized. The change process of material density, thermal conductivity and specific heat capacity was digitized, and the corresponding mathematical model was established. It was then edited into the CFD analysis software through UDF.

[0071] S21: Obtain the relationship between density and temperature of the composite material.

[0072] Through the thermophysical parameters of the composite material, a discrete equation of density variation with temperature is obtained, so as to characterize the relationship between density variation with temperature of the composite material through the discrete equation;

[0073] The discrete equation for the change of density with temperature is:

[0074]

[0075] Among them, ρ t is the density at the current moment; ρ t+1 is the density at the next moment; ρ f is the density of the carbonized layer of the composite material; A is the pre-exponential factor of the pyrolysis reaction; e is a natural constant, whose value is approximately 2.718281828; E is the activation energy of the pyrolysis reaction; R is the standard gas constant, whose value is 8.314 J / (K·mol); T is the current temperature; and t is the time.

[0076] S22: Obtain the relationship between the thermal conductivity of the composite material and temperature.

[0077] According to the test results of the thermal properties of composite materials, the relationship between the thermal conductivity of the composite materials and the temperature is fitted, and the fitting equation of the thermal conductivity changing with temperature is obtained.

[0078] According to the test results of thermal properties of composite materials, the equation of the change of thermal conductivity of char formed by the composite material after the fire test with temperature is obtained.

[0079] The thermal conductivity equation of the composite material during the heating process is obtained according to the fitting equation and the change equation, so as to characterize the law of the density change of the composite material with temperature through the thermal conductivity equation during the heating process.

[0080] Specifically, the formula for obtaining the thermal conductivity equation of the composite material during heating is as follows according to the fitting equation and the change equation:

[0081]

[0082] Among them, λ c is the fitted thermal conductivity obtained according to the fitting equation; λ m is the thermal conductivity of coke obtained according to the variation equation; ρ t is the density at the current moment; ρ f is the density of the carbonized layer of the composite material; ρ0 is the initial density of the composite material.

[0083] S23: Obtain the relationship between the specific heat capacity of the composite material and the temperature.

[0084] According to the test results of the thermal properties of the composite material, the temperature variation structure of the specific heat capacity of the composite material is fitted to obtain a fitting equation for the temperature variation of the specific heat capacity, so as to characterize the relationship between the specific heat capacity and the temperature through the fitting equation for the temperature variation of the specific heat capacity.

[0085] The pyrolysis reaction data includes the heat absorbed by the composite material when it is thermally decomposed. s :

[0086]

[0087] Where A is the pre-exponential factor of the pyrolysis reaction, ρ t is the density at the current moment; ρ f is the density of the carbonized layer of the composite material; e is a natural constant; E is the activation energy of the pyrolysis reaction; R is the standard gas constant; T is the current temperature; h s It is the latent heat of pyrolysis, and its value can be obtained through DSC test.

[0088] Specifically, the pre-exponential factor, activation energy and pyrolysis latent heat of the composite material can be obtained through the composite material combustion performance test to analyze the ablation mechanism of the composite material and reflect the composite material pyrolysis reaction data in the form of energy in the simulation software.

[0089] The pyrolysis reaction data also includes the heat S taken away by the decomposition gas when the composite material is heated. g :

[0090]

[0091] Where A is the pre-exponential factor of the pyrolysis reaction, ρ t is the density at the current moment; ρ f is the density of the carbonized layer of the composite material; e is a natural constant; E is the activation energy of the pyrolysis reaction; R is the standard gas constant; T is the current temperature; h g is the enthalpy of the pyrolysis gas.

[0092] S03: Set the initial conditions, boundary conditions, step size and time in the simulation software.

[0093] In this embodiment, the initial condition includes the initial density of the composite material. The boundary condition includes a thermal boundary condition, so accordingly, the fire protection simulation method for a composite material structure provided in this embodiment also includes a step of obtaining a thermal boundary condition.

[0094] The steps to obtain thermal boundary conditions include:

[0095] S31 : constructing a second three-dimensional model 200 including a flame burner 211 , a combustion region 212 , and a composite material structure 213 , wherein in the second three-dimensional model 200 , the composite material structure is arranged in the combustion region 212 .

[0096] Figure 4 The schematic diagram of the structure of the second three-dimensional model 200 provided in this embodiment is shown. Figure 4 The second three-dimensional model 200 includes a flame burner 211, a combustion area 212 and a composite material structure 213. The second three-dimensional model 200 simplifies the structure that has no effect on the flame, and the structure is relatively simple, which is convenient for subsequent simulation processes.

[0097] The combustion area 212 is established above the expansion cone outlet of the flame burner 211. The combustion area 212 model can be established in a cubic shape. Preferably, the size of the combustion area 212 model is 800mm*800mm*800mm.

[0098] Preferably, the composite material structure 213 is configured as a flat plate structure having the same size and material as the solid domain 111 in the first three-dimensional model 100. The flat plate-shaped composite material structure 213 is disposed inside the combustion area 212, and the distance between the composite material structure 213 and the outlet of the flame burner 211 is D, 100mm≤D≤104mm.

[0099] S32: Processing the second three-dimensional model 200 through simulation software and simulating a process of a standard flame impacting the composite material structure 213 .

[0100] The second three-dimensional model 200 is imported into the simulation software, and the entire combustion area 212 is divided into structured grids.

[0101] Based on the combustion model, simulation software is used to simulate the process of a standard flame impacting the composite material structure 213. It should be noted that the specific type of the combustion model is selected according to the type of simulation software.

[0102] S33: The temperature field of the fire-exposed surface 113 of the composite structural component after the standard flame impact is used as a thermal boundary condition.

[0103] The temperature field of the fire-exposed surface 113 of the composite structural component after the standard flame impact is extracted to form a file, and the file is imported into the simulation software as the thermal boundary condition of the fire protection simulation of the first three-dimensional model 100 .

[0104] It is understandable that the thermal boundary condition needs to be imported into the simulation software before simulating the first three-dimensional model 100, but the timing of obtaining the thermal boundary condition can be adjusted according to demand, for example, it can be performed before executing step S01.

[0105] In the first three-dimensional model 100, the interface between the fluid domain 112 and the solid domain 111 is a coupling surface, and the setting of boundary conditions also includes setting the inlet velocity and setting the turbulence model. Optionally, the inlet velocity can be set to a value between 0 and 90 m / s according to the actual back airflow velocity.

[0106] The step length and the number of integral steps are set, and the number of integral steps is set according to the actual required time, that is, after the step length and the number of integral steps are set, the preset time is determined. Optionally, the step length can be set to a value within the range of 0.0005s to 0.005s; the preset time can be set to 15 minutes.

[0107] S04: The simulation software simulates the process of standard flame impacting composite structural parts and solves the energy control equation to obtain the simulation results.

[0108] After executing step S01, step S02 and step S03, the simulation software implements fire protection simulation of the composite material structure according to the solution of the energy control equation and obtains corresponding simulation results.

[0109] Specifically, the energy control equation is:

[0110]

[0111] Where ρ is the density at the current moment; C p is the specific heat capacity; T is the current temperature; t is the time; λ is the thermal conductivity; E is the activation energy of the pyrolysis reaction; R is the standard gas constant; A is the pre-exponential factor of the pyrolysis reaction; e is the natural constant; ρ f is the density of the carbonized layer of the composite material; ρ0 is the initial density of the composite material; x is the distance; h s is the latent heat of pyrolysis; h g is the enthalpy of pyrolysis gas; Q b Exchange heat for the airflow behind the composite material.

[0112] The specific heat capacity C in the above energy control equation p Obtained based on the fitting equation of the change of specific heat capacity with temperature.

[0113] At the same time, according to the energy control equation, the three terms on the right side of the equation are related to heat conduction, thermal decomposition of composite materials and back airflow heat transfer. Specifically, The term represents heat conduction, where λ is the thermal conductivity calculated by formula (2); The term represents the thermal decomposition process of the composite material, which is basically consistent with the sum of the above formula (3) and formula (4); Q b The term represents the back airflow heat transfer, and its value is directly obtained by the simulation software according to the airflow velocity during the simulation process.

[0114] The simulation software simulates the process of composite material structure being impacted by standard flame, and solves the energy control equation according to the various relational expressions edited into the simulation software in step S03, so as to obtain the temperature field distribution at different distances, and save the calculation results at different times, until the simulation time reaches the preset time. If the time does not reach the preset time, the energy control equation is solved again after the parameter update. Specifically, the "parameter update" here refers to the density ρ, specific heat capacity C p , thermal conductivity λ and enthalpy h of pyrolysis gas g And other parameters.

[0115] The fire prevention simulation method of composite structural parts numerically simulates the fire prevention process of composite structural parts, including the heat transfer of thermophysical properties and the thermal decomposition process of composite materials. At the same time, the pre-exponential factor, activation energy and pyrolysis latent heat of composite materials are obtained through the composite combustion performance test, the ablation mechanism of composite materials is analyzed, and the pyrolysis reaction process of composite materials is reflected in the simulation software in the form of energy source. The airflow on the back of the structural parts is numerically simulated to consider the influence of airflow on the fire prevention performance of composite materials under actual flight conditions. By changing different inlet flow rates and turbulence intensities, the influence of actual airflow on the back heat exchange can be simulated, and the thermal response law of composite materials can be accurately predicted, which provides technical support for the design and verification of composite fire prevention airworthiness compliance.

[0116] Example 1

[0117] In this embodiment, the composite material is a carbon fiber reinforced epoxy resin composite material, and the PyroSim software is used to simulate the process of a standard flame impacting the fire surface of a composite structural component, and the Fluent software is used to calculate the complex variable property heat conduction process of the composite material under the impact of the flame and the back airflow, that is, the following step S014 is performed. The process of executing the fire prevention simulation method of the composite structural component in this embodiment is described below:

[0118] S011: A composite material structure with a plane size of 600mm×600mm and a thickness of 1mm is established as the solid domain 111 of the first three-dimensional model 100. The composite material structure is in the shape of a square plate. A fluid domain 112 is formed by the airflow of the component behind the solid domain 111. The length, width and thickness of the fluid domain 112 are 3000mm, 600mm and 100mm respectively. The three-dimensional model is imported into Fluent software and meshed.

[0119] S012: Input the thermal physical property parameters of carbon fiber reinforced epoxy resin composite material through UDF compilation, and the density discrete equation of its pyrolysis process is the above formula (1). And the initial density of the carbon fiber reinforced epoxy resin composite material ρ0=1500Kg / m3; the carbonization layer density ρ f=1150Kg / m3. At the same time, according to the thermogravimetric test, the pyrolysis process is divided into three steps, and the activation energy E of the pyrolysis reaction is 150kJ / mol, 90kJ / mol and 110kJ / mol respectively; the pre-exponential factor A of the pyrolysis reaction is 315000s-1 after experimental testing.

[0120] According to the test results of thermal properties of composite materials, the fitting relationship between the specific heat capacity of the carbon fiber reinforced epoxy resin composite material and the temperature is: p =-1290+11.38T-0.0122T 2 ; Wherein, T is temperature;

[0121] The fitting relationship between thermal conductivity and temperature is: c =-0.4376+0.0048T-5*10 -6 T 2 ; Wherein, T is temperature;

[0122] The relationship between the thermal conductivity and temperature of the coke formed after the composite material fire test is: m =0.1314+0.00013T-7×10 -6 T 2 ; Wherein, T is temperature;

[0123] The thermal conductivity of the composite material during heating can be expressed as:

[0124]

[0125] The heat absorbed by the composite material when it is decomposed by heat is as shown in the above formula (3). At the same time, the latent heat of pyrolysis h in formula (3) is s The value of is obtained according to DSC test, which is 110KJ / Kg.

[0126] The heat carried by the volatilization of the gas in the composite material is as shown in the above formula (4), and the enthalpy of the pyrolysis gas in formula (4) is: Where T is temperature.

[0127] S013: Set the initial density ρ0=1500Kg / m3.

[0128] The process of obtaining thermal boundary conditions includes:

[0129] A simulation three-dimensional model was generated by UG NX, which included a flame burner 211, a combustion area 212 and a composite material structure 213. The combustion area 212 model was located above the expansion cone outlet of the flame burner 211, and the composite material structure 213 model was located in the combustion area 212, and the composite material structure 213 was placed 102±2 mm from the flame burner 211 outlet. The constructed three-dimensional model was then exported in .stl format.

[0130] The exported .stl format file is imported into the PyroSim software to perform structured mesh division on the entire combustion area 212, and a preferred number of meshes is 1.1 million.

[0131] Based on the LES unsteady combustion model, PyroSim software was used to simulate the process of standard flame impacting composite structural parts, and the temperature field of the composite plate fire surface 113 after the standard flame impact was extracted to form a prof file.

[0132] When setting the boundary conditions, the above-mentioned prof file is imported as the thermal boundary condition in the fire protection simulation process of the composite material structure. The interface between the fluid domain 112 and the solid domain 111 in the three-dimensional model constructed in step S011 is a coupling surface, and the inlet velocity is set to 30m / s according to the actual back airflow velocity, and the turbulence model is SST k-ω. It can be understood that the inlet velocity can also be set to other values ​​within the range of 0 to 90m / s according to the test requirements.

[0133] Set the non-steady-state time step (0.0005s-0.005s) and integration steps. The integration steps are set according to the actual required time. The initialization setting method is hyb initialization.

[0134] S014: Fluent software solves and calculates the temperature distribution field at different times and distances according to the energy control equation (i.e., the above formula (5)), and saves the calculation results at different times. After being impacted by the flame for 15 minutes (i.e., reaching the fire test duration), the simulation analysis results of the back-fire surface 114 of the composite material structural component are as follows: Figure 5 As shown in the figure, the test results of the same composite material structure are shown in the figure Figure 6 As shown, Figure 6 The horizontal axis is time and the vertical axis is temperature. Figure 5 and Figure 6 ,The experiment shows that after reaching steady state, the average temperature of 9 thermocouples in the back fire surface 114 is about 287 ℃, and the simulation result is about 319 ℃. The error between the simulation and ,experimental is 11.1%, which accurately predicts the back temperature.

[0135] Example 2

[0136] In this embodiment, the composite material is PEEK, and the simulation software used is Fluent software. The process of executing the fire prevention simulation method of the composite material structure in this embodiment is described below:

[0137] S021: A composite material structure with a plane size of 600 mm × 600 mm and a thickness of 1.24 mm is established as the solid domain 111 of the first three-dimensional model 100. The composite material structure is in the shape of a square plate. A fluid domain 112 is formed by the airflow of the component at the back of the solid domain 111. The length, width and thickness of the fluid domain 112 are 3000 mm, 600 mm and 100 mm respectively. The three-dimensional model is imported into Fluent software and meshed.

[0138] S022: Input the thermal properties of PEEK through UDF compilation, and the density discrete equation of the pyrolysis process is the above formula (1). The initial density of PEEK is ρ0=1630Kg / m3; the density of the carbonized layer is ρ f =1350Kg / m3.

[0139] According to the test results of the thermal properties of the composite material, the activation energy of the pyrolysis reaction of PEEK is E+245KJ / mol, and the pre-exponential factor of the pyrolysis reaction is A=3.15×1014s-1.

[0140] The fitting relationship between specific heat capacity and temperature is: p =-0.0008T 2 +3.6965T-119.33; where T is temperature;

[0141] The fitting relationship between thermal conductivity and temperature is: c =0.1724+0.0017T-10 -6 T 2 ; Wherein, T is temperature;

[0142] The relationship between the thermal conductivity and temperature of the coke formed after the composite material fire test is: m =0.1314+0.00013T-7×10 -6 T 2 ; Wherein, T is temperature;

[0143] The thermal conductivity of the composite material during heating can be expressed as:

[0144]

[0145] The heat absorbed by the composite material when it is decomposed by heat is as shown in the above formula (3). At the same time, the latent heat of pyrolysis h in formula (3) is s The value of is obtained according to DSC test, which is 236KJ / Kg.

[0146] The heat carried by the volatilization of the gas in the composite material is as shown in the above formula (4), and the enthalpy of the pyrolysis gas in formula (4) is: Where T is temperature.

[0147] S023: Set the initial density ρ0=1630Kg / m3.

[0148] The process of obtaining thermal boundary conditions includes:

[0149] A simulation three-dimensional model is generated by UG NX, which includes a flame burner 211, a combustion area 212 and a composite material structure 213. The combustion area 212 model is located above the expansion cone outlet of the flame burner 211, and the composite material structure 213 model is located in the combustion area 212, and the composite material structure 213 is placed 102±2mm from the outlet of the flame burner 211. Then the constructed three-dimensional model is exported in .x_t format.

[0150] Import the exported .x_t format file into ICEM for meshing. The number of meshes is about 4 million, and export the .msh file.

[0151] The .msh file is imported into Fluent, and based on the non-premixed combustion model, the Fluent software is used to simulate the process of standard flame impacting the composite structural component, and the temperature field of the fire-receiving surface 113 of the composite plate after the standard flame impact is extracted to form a prof file.

[0152] When setting the boundary conditions, the above-mentioned prof file is imported as the thermal boundary condition in the fire protection simulation process of composite structural parts. The interface between the fluid domain 112 and the solid domain 111 in the three-dimensional model constructed in step S021 is a coupling surface, the inlet velocity is set to 45m / s according to the actual back airflow velocity, the turbulence model is SST k-ω, and the remaining outer wall surfaces are adiabatic no-slip walls. It can be understood that the inlet velocity can also be set to other values ​​within the range of 0 to 90m / s according to the test requirements.

[0153] Set the non-steady-state time step (0.0005s-0.005s) and integration steps. The integration steps are set according to the actual required time. The initialization setting method is hyb initialization.

[0154] S024: The simulation software calculates and solves the energy control equation (i.e., the above formula (5)) to obtain the temperature distribution field at different times and distances, and saves the calculation results at different times. After being impacted by the flame for 15 minutes (i.e., reaching the fire test duration), the simulation analysis results of the back-fire surface 114 of the composite material structural component are as follows: Figure 7 As shown in the figure, the test results of the same composite material structure are shown in the figure Figure 8 As shown, Figure 8 The horizontal axis is time and the vertical axis is temperature. Figure 7 and Figure 8,The experiment shows that after reaching steady state, the average temperature of 9 thermocouples in the back fire surface 114 is about 135 ℃, and the simulation result is about 149 ℃. The error between the simulation and ,experiment is 10.4%, which predicts the back temperature more accurately.

[0155] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technology in the field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A fire prevention simulation method for composite material structural parts, characterized in that: The fire protection simulation method of the composite material structural member comprises: Constructing a first three-dimensional model of a composite material structure, and importing the first three-dimensional model into simulation software; Obtaining the density-temperature variation relationship, thermal conductivity-temperature variation relationship, specific heat capacity-temperature variation relationship and pyrolysis reaction data of the composite material, and editing them into the simulation software; Setting initial conditions, boundary conditions, step length and time in the simulation software; The simulation software simulates the process of standard flame impacting a composite material structure and solves the energy control equation to obtain the simulation result.

2. The fire prevention simulation method for composite material structural parts according to claim 1, characterized in that: The first three-dimensional model includes a solid domain formed by the composite material structural component and a fluid domain arranged at the back of the solid domain; the back of the solid domain is located within the range of the fluid domain.

3. The fire prevention simulation method for composite material structural parts according to claim 1, characterized in that: The energy control equation is: Where: ρ is the density at the current moment; C p is the specific heat capacity; T is the current temperature; t is the time; λ is the thermal conductivity; E is the activation energy of the pyrolysis reaction; R is the standard gas constant; A is the pre-exponential factor of the pyrolysis reaction; e is the natural constant; ρ f is the density of the carbonized layer of the composite material; ρ0 is the initial density of the composite material; x is the distance; h s is the latent heat of pyrolysis; h g is the enthalpy of pyrolysis gas; Q b Exchange heat for the airflow behind the composite material.

4. The fire prevention simulation method for composite material structural parts according to claim 1, characterized in that: The boundary conditions include thermal boundary conditions, and the fire protection simulation method for composite material structural parts further includes: obtaining the thermal boundary conditions; The step of obtaining the thermal boundary condition comprises: Constructing a second three-dimensional model including a flame burner, a combustion area, and a composite material structure, wherein in the second three-dimensional model, the composite material structure is arranged in the combustion area; The second three-dimensional model is processed by simulation software to simulate the process of standard flame impacting composite material structure; The temperature field of the fire-exposed surface of the composite structural component after the standard flame impact is used as the thermal boundary condition.

5. The fire prevention simulation method for composite material structural parts according to claim 4, characterized in that: In the second three-dimensional model, the distance between the composite material structure and the outlet of the flame burner is D, 100 mm≤D≤104 mm.

6. The fire prevention simulation method for composite material structural parts according to claim 1, characterized in that: The step of obtaining the relationship between the thermal conductivity of the composite material and the temperature includes: According to the test results of the thermal properties of the composite material, the variation of the thermal conductivity of the composite material with temperature is fitted to obtain the fitting equation of the variation of the thermal conductivity with temperature; According to the test results of thermal properties of the composite material, an equation for the change of thermal conductivity of coke formed by the composite material after the fire test with temperature is obtained; The thermal conductivity equation of the composite material during heating is obtained according to the fitting equation and the variation equation, and the thermal conductivity equation is used to characterize the relationship between the thermal conductivity of the composite material and the temperature.

7. The fire prevention simulation method for composite material structural parts according to claim 6, characterized in that: The thermal conductivity equation is: Among them, λ c is the fitted thermal conductivity obtained according to the fitting equation; λ m is the thermal conductivity of coke obtained according to the variation equation; ρ t is the density at the current moment; ρ f is the density of the carbonized layer of the composite material; ρ0 is the initial density of the composite material.

8. The fire prevention simulation method for composite material structural parts according to claim 1, characterized in that: The step of obtaining the relationship between the density of the composite material and the temperature includes: Obtaining a discrete equation of density variation with temperature through the thermophysical property parameters of the composite material, so as to characterize the relationship between the density variation with temperature of the composite material through the discrete equation; The discrete equation for the density variation with temperature is: Among them, ρ t is the density at the current moment; ρ t+1 is the density at the next moment; ρ f is the density of the carbonized layer of the composite material; A is the pre-exponential factor of the pyrolysis reaction; e is a natural constant; E is the activation energy of the pyrolysis reaction; R is the standard gas constant; T is the current temperature; and t is the time.

9. The fire prevention simulation method for composite material structural parts according to claim 1, characterized in that: The step of obtaining the relationship between the specific heat capacity of the composite material and the temperature includes: According to the test results of the thermal properties of the composite material, the results of the change of specific heat capacity with temperature of the composite material are fitted to obtain a fitting equation for the change of specific heat capacity with temperature, so as to characterize the relationship between the change of specific heat capacity and temperature through the fitting equation for the change of specific heat capacity with temperature.

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