Method for analyzing fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structure

Abstract

The invention belongs to the field of marine composite material structures, and particularly relates to a method for analyzing fire-resistant heat transfer and fire-resistant bearing performance of a marine composite material structure, which comprises the following steps of: establishing a thermal response mathematical model of the marine composite material structure; the calculation model considers the influence caused by isotropic or anisotropic heat conduction of the material, heat convection of decomposition gas and heat absorption of material decomposition in the heating process; based on a heat transfer equation, a pyrolysis kinetic equation and a continuity equation, a UMATHT subprogram is adopted to establish a thermal response simulation method considering material pyrolysis, and the temperature, density, carbonization rate, carbonization rate and density change rate of the material are calculated and analyzed; a UMAT subprogram is adopted to realize fiber stretching and compression, matrix stretching and compression, stretching layering and compression layering failure behavior simulation of the fiber reinforced composite material; meanwhile, based on a Crushable foam model, the damage failure of the filling core material is calculated by using the constitutive relation of the filling core material at different temperatures.

Description

Technical Field

[0001] The invention belongs to the field of ship composite material structures, and in particular relates to a method for analyzing the fire-resistant heat transfer and fire-resistant bearing performance of ship composite material structures. Background Art

[0002] In recent years, the demand for new material structure application technology required by the lightweight design of superstructure structures has become increasingly prominent. In the 1950s, the United States first used composite materials in shipbuilding, and then countries around the world began to develop composite shipbuilding. Early small and medium-sized minehunters in Europe and the United States, such as the British "Sandown" class minehunters and the Norwegian "Oksoy" class minehunters, applied the non-magnetic properties of composite materials to improve the vitality of ships; subsequently, composite materials were applied to stealth ships, patrol boats and frigates, such as the French "Lafayette" frigate and the Swedish "Visby" series of frigates. At present, the US "San Antonio" class dock transport ship and even the latest generation of destroyers DDG1000; the new generation of Russian "Alexander Obukhov" minesweeper, which entered service in 2015, is the first minesweeper made of all composite materials. The ship has the world's largest composite ship hull. In addition, composite materials are also widely used in secondary load-bearing structures such as chimneys, bulkheads, decks, and rudders. Practice has shown that advanced composite materials can meet the development needs of future ships in terms of stealth, weight reduction, etc., especially the use of composite materials in superstructures, which can not only reduce weight, but also lower the center of gravity and effectively improve the stability of the ship. The application of composite materials in superstructure structures has become an important development trend in naval ships around the world.

[0003] Although composite materials have advantages that traditional metal materials cannot match, composite materials themselves also have certain disadvantages, such as fire characteristics, which is also an important factor limiting the large-scale use of their structures on ships. Although composite materials have good fire resistance and heat insulation properties, the molding resin matrix is ​​a potential flammable material. When the composite material structure is exposed to high temperature environment, it will lose strength and produce thermal decomposition. Therefore, when a fire occurs on a ship, the ship's composite material structure will quickly lose its bearing capacity in a high temperature fire environment, resulting in the collapse of the hull structure, which directly leads to the loss of combat effectiveness of the ship.

[0004] Therefore, the increasing demand for resin-based composite materials and the potential fire safety hazards caused by the use of composite materials on board ships are relatively prominent. Under the background that navies around the world have already started research on the fire resistance of composite materials structures, research on the fire resistance of marine composite materials structures is of great significance and value in promoting the large-scale engineering application of composite materials in marine structures, reducing the weight of ship structures, improving ship stealth, and increasing ship speed. Summary of the invention

[0005] The fire-resistant heat transfer and fire-resistant bearing performance analysis method of the ship composite structure provided by the present invention establishes a typical composite structure fire environment temperature field for the composite superstructure structure. First, taking the thermophysical performance parameters of typical composite materials (fiber-reinforced composite materials and filling core materials) as input, the heat transfer mechanism of typical ship composite structures under fire environment is studied through finite element simulation calculation method, and a fire-resistant heat insulation calculation method for typical ship composite structures is established; then, based on the fire environment temperature field, taking the high-temperature mechanical performance parameters of typical composite materials (fiber-reinforced composite materials and filling core materials) and the thermal expansion coefficient with temperature effect as input, the fire-resistant bearing characteristics of typical ship composite structures under fire environment are studied through finite element simulation calculation method, and a fire-resistant bearing characteristics calculation method for typical ship composite structures is established.

[0006] The method for analyzing the fire-resistant heat transfer and fire-resistant bearing performance of a marine composite material structure provided by the present invention comprises the following steps:

[0007] A1: Establish a mathematical model of thermal response of marine composite materials. The calculation model takes into account the effects of isotropic or anisotropic heat conduction of materials, heat convection of decomposed gases, and heat absorption caused by material decomposition during heating.

[0008] A2: Based on the heat transfer equation, pyrolysis kinetic equation and continuity equation, the UMATHT subroutine is used to establish a thermal response simulation method considering material pyrolysis, so as to calculate and analyze the material's temperature, density, carbonization rate, carbonization rate and density change rate;

[0009] A3: Based on step A2, the composite laminate theory, Hashin failure criterion, delamination failure criterion and material stiffness degradation model are used, and the UMAT subroutine is adopted to simulate the fiber tension and compression, matrix tension and compression, tension delamination and compression delamination failure behaviors of fiber reinforced composite materials. At the same time, based on the Crushable foam model, the constitutive relationship of the filling core material at different temperatures is used to calculate the damage failure of the filling core material.

[0010] The method for analyzing the fire-resistant heat transfer and fire-resistant bearing performance of a ship composite material structure according to claim 1 is characterized in that the ship composite material structure includes a composite laminate structure or a composite sandwich plate structure or a composite stiffened plate structure, and the ship composite material includes a fiber-reinforced composite material and a filling core material.

[0011] The method for analyzing fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structures according to claim 1 is characterized in that step A2 also considers internal gas convection after the material decomposes at high temperature and the thermal response of material decomposition and establishes a finite element model.

[0012] As a further optimization of the present invention, the simulation method established by the UMATHT subroutine in step A2 is:

[0013] In UMATHT, the internal heat energy per unit mass U and the partial derivative of the internal heat energy per unit mass with respect to temperature are defined as And the partial derivative of the thermal energy per unit mass with respect to the temperature gradient Define the heat flow vector f, the partial derivative of the heat flow vector f with respect to temperature and the partial derivative of the heat flux vector with respect to the temperature gradient

[0014] The method for analyzing the fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structures according to claim 1 is characterized in that a mathematical model of thermal response of fiber-reinforced composite materials and filling core materials is established in step A1, and the model takes into account the isotropic heat conduction of the filling core material and the anisotropic heat conduction of the fiber-reinforced composite material, the heat convection of the decomposed gas, the endothermic decomposition of the material, and the thermal equilibrium state between the solid material and the decomposed gas; the accumulation of gas generated by the decomposition of the material is not considered and all of it diffuses outward and overflows, and the thermochemical expansion generated by the decomposition of the material is not considered.

[0015] As a further optimization of the present invention, the heat transfer equation of the material under the action of thermal load is obtained as follows:

[0016]

[0017] In the formula, the first term represents the rate of change of the internal energy per unit volume of the material; the second term represents the heat flux of conduction inside the material; the third term represents the convection heat transfer of the decomposed gas inside the material; the fourth term represents the heat absorbed by the material analysis; T represents temperature, t represents time; ρ represents the density of the material; represents the gas mass flow rate; k1, k2, and k3 represent the thermal conductivity in three directions, respectively, where z is the thickness direction; Q is the decomposition heat, and if it is an endothermic reaction, Q is a negative value.

[0018] As a further optimization of the present invention, based on the calculation of the real-time temperature field of the structure by the UMATHT subroutine in step A2, step A3 establishes a damage failure simulation method for fiber reinforced composite materials and filled core materials.

[0019] The method for analyzing fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structures according to claim 7 is characterized in that the UMAT subroutine is used to simulate the damage and failure of fiber-reinforced composite materials, and the analysis method comprises the following steps:

[0020] B1: Assuming the temperature difference is ΔT(x,y,z), the expansion caused by the temperature difference is ε T The formula is as follows:

[0021] ε T =α·ΔT

[0022] Where: α is the thermal expansion coefficient. The constitutive equation of the laminate based on temperature influence is as follows:

[0023]

[0024] In the formula, There are 6 stress components and strain components It is expressed as follows:

[0025]

[0026] matrix The calculation formula is as follows:

[0027]

[0028] in:

[0029]

[0030] In the formula, They are the Poisson’s ratios of the corresponding materials at temperature T; They are the elastic modulus of the material corresponding to temperature T; They are the shear modulus of the material corresponding to temperature T;

[0031] B2: The Hashin criterion and the Yeh delamination failure criterion are combined to determine whether the material has failed. F1, F2 and F3 are used to describe the failure criteria of fiber, matrix and delamination respectively. Without considering shear nonlinearity, the strain-based damage failure state of the three-dimensional Hashin criterion and the delamination failure criterion is described as follows:

[0032]

[0033] In the formula, the upper and lower equations represent the fiber tensile and compressive fractures, respectively;

[0034]

[0035] In the formula, the upper and lower equations represent the tensile and compressive fracture of the matrix, respectively;

[0036]

[0037] In the formula, the upper and lower equations represent tensile stratification and compressive stratification respectively;

[0038] Where: ε ii (i=1,2,3) is the positive strain in the direction of the principal axis i of the material; or are the normal strains corresponding to the tensile or compressive strength in the direction of the principal axis i of the material at temperature T; They are the shear strains corresponding to the shear strength at temperature T in the 1-2, 1-3, and 2-3 planes:

[0039]

[0040] in: is the tensile strength and compressive strength in the X direction (or 1 direction) at temperature T; is the tensile strength and compressive strength in the Y direction (or 2 direction) at temperature T; It is the tensile strength and compressive strength at temperature T in three directions; They are the shear strengths of 1-2, 1-3, and 2-3 planes at temperature T;

[0041] B3: Construct a composite material stiffness degradation model. The stiffness degradation model is as follows:

[0042] When the material meets the damage criterion, the damage variable is expressed as follows:

[0043]

[0044] ft, fc, mt, mc, and ld represent fiber tensile damage, fiber compression damage, matrix tensile damage, and matrix compression damage, respectively; damage variables

[0045] The stress-strain matrix including damage is as follows:

[0046]

[0047] where ω i (i=1,2,3,4,5,6) is the damage variable, and the calculation expression is as follows:

[0048] ω1=max[0.0,max(0.0,d ft ,d fc )];ω2=max[0.0,max(0.0,d ft ,d fc ), max(0.0, d mt ,d mc )];

[0049] ω3=max[0.0,max(0.0,d ft ,d fc ), max(0.0, d mt ,d ld )]; ω4=ω2, ω5=ω6=ω3.

[0050] As a further optimization of the present invention, the damage failure model of the filling core material adopts the Abauqs software embedded module: constructing the crushable foam model.

[0051] The present invention provides a method for calculating and analyzing the fire-resistant heat transfer and fire-resistant bearing performance of a ship composite material structure considering the thermal decomposition of the material, establishes a mathematical model of the thermal response of the ship composite material structure and derives the UMATHT variable expression. The calculation model considers the influence of isotropic or anisotropic heat conduction of the material, thermal convection of the decomposed gas and endothermic decomposition of the material during the heating process. Based on the heat transfer equation, the thermal decomposition kinetic equation and the continuity equation, a composite material thermal response simulation method considering the thermal decomposition of the material is established through the UMATHT subroutine. The method can realize the calculation and analysis of the temperature, density, carbonization rate, carbonization rate and density change rate of the composite material, and can further clarify the thermal decomposition process of the composite material under a fire environment.

[0052] At the same time, based on the temperature field established by the UMATHT subroutine, the composite laminate theory, Hashin failure criterion, delamination failure criterion and material stiffness degradation model are used, and the UMAT subroutine is adopted to realize the simulation of fiber tension and compression, matrix tension and compression, tension delamination and compression delamination failure behaviors of fiber reinforced composites; at the same time, based on the Crushablefoam model, the constitutive relationship of the filling core material at different temperatures is used to calculate the damage failure of the filling core material, and finally a system considering different damage failure forms of marine composite structures is established. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a schematic diagram of a flat plate model of Example 1;

[0054] Figure 2 yes Figure 1 Schematic diagram of the model's thermal load state;

[0055] Figure 3 yes Figure 1 Schematic diagram of the model laminate before decomposition;

[0056] Figure 4 yes Figure 3 Schematic diagram after decomposition;

[0057] Figure 5 yes Figure 1 Schematic diagram of thermal decomposition of two layers of the model;

[0058] Figure 6 yes Figure 1 The temperature variation over time at different distances from the center of the model to the fire surface;

[0059] Figure 7 a-7d are Figure 1 Stress cloud diagrams of the model when heated for 20s, 50s, 100s, and 250s respectively;

[0060] Figure 8 a-8d correspond to Figure 7 a-7b temperature field distribution cloud diagram analysis;

[0061] Fig. 9 yes Figure 1 The density variation trend of the model center area at different distances from the fire surface with heating time;

[0062] Fig.10 yes Fig. 9 Trend of carbonization rate over time;

[0063] Fig.11 This is a schematic diagram of heat load of the model in Example 2;

[0064] Fig.12 Schematic diagram of the overall temperature field (left) and carbonization rate of the surface composite material (right) of Example 2;

[0065] Fig.13 Schematic diagram of carbonization rate of the surface composite material (left) and density change of the surface composite material (right) in Example 2;

[0066] Fig.14 Schematic diagram of the density change rate of the surface composite material (left) and the carbonization rate of the middle filling core material (right) in Example 2;

[0067] Fig.15 Schematic diagram of the carbonization rate of the middle filling core material (left) and the density change of the middle filling core material (right) in Example 2;

[0068] Fig.16 is a schematic diagram of the density change rate of the intermediate filling core material in Example 2;

[0069] Fig.17 This is a schematic diagram of heat load of the model in Example 3;

[0070] Fig.18 Schematic diagram of Mises stress cloud diagram (left) and displacement (right) of Example 3;

[0071] Fig.19 Schematic diagram of the carbonization rate (left) and pyrolysis carbonization rate (right) of the material in Example 3;

[0072] Fig. 20 Schematic diagram of fiber tensile damage (left) and fiber compression damage (right) in Example 3;

[0073] Fig.21 This is a schematic diagram of heat load of the model of Example 4;

[0074] Fig. 22 Schematic diagram of Mises stress cloud diagram (left) and displacement (right) of the upper laminate of Example 4;

[0075] Fig.23 Schematic diagram of Mises stress cloud diagram (left) and displacement (right) of the lower laminate of Example 4;

[0076] Fig.24 Schematic diagram of the Mises stress cloud diagram (left) and displacement (right) of Example 4.

[0077] Embodiment 1:

[0078] The ship composite material structure includes a composite laminate structure, a composite sandwich plate structure or a composite stiffened plate structure. The ship composite material includes a fiber reinforced composite material and a filling core material.

[0079] The marine composite material structure considering material decomposition used in this embodiment adopts a composite material laminate structure, and a heat transfer characteristic analysis method is provided based on the composite material laminate structure.

[0080] like Figure 1 As shown, this embodiment establishes a flat plate model of a composite laminate. Specifically, a carbon fiber epoxy resin-based composite material is used. The model has a length and width of 150 mm*150 mm, a thickness of 4 mm, and an effective heating area of ​​100 mm*100 mm in the central area. A heat flux of 116 kW / m2 is applied to one side of the composite laminate. Figure 2 As shown, the predefined temperature field model temperature is 25°C.

[0081] In this embodiment, the effects of anisotropic heat conduction of the composite laminate, thermal convection of the decomposed gas, and endothermic decomposition of the material are taken into account, and it is assumed that the solid material and the decomposed gas are in thermal equilibrium. However, the accumulation of gas produced by the decomposition inside the material and its outward diffusion and overflow are not considered, and the thermochemical expansion produced by the decomposition of the material is not considered, that is, the heat loss caused by the work done by the expansion of the material is not considered.

[0082] Based on the above considerations and non-considerations, according to the law of conservation of energy, a physical heat transfer model of composite materials under heat flow load is established as follows Figure 3 , 4 As shown, the heat transfer equation of the composite material under the action of heat flux load is:

[0083]

[0084] In the formula, the first term represents the rate of change of the internal energy per unit volume of the material; the second term represents the heat flux of conduction inside the material; the third term represents the convection heat transfer of the decomposed gas inside the material; the fourth term represents the heat absorbed by the material analysis; T represents temperature, t represents time; ρ represents the density of the material; Represents the gas mass flow rate (mass flow through the cross section per unit time); and Represent the enthalpy change of solid material and gas material (Δh=C P ΔT, CP and C Pg are the specific heat capacity of solid materials and gas respectively, T0 represents the initial temperature, and the above formula can only be satisfied under constant pressure);

[0085] k1, k2, and k3 represent thermal conductivity in three directions, respectively, where z is the thickness direction; Q is the decomposition heat, and if it is an endothermic reaction, Q is a negative value.

[0086] The material pyrolysis equation is determined by the pyrolysis kinetic model:

[0087]

[0088] The above formula is transformed from the thermolysis kinetic equation, namely the Arrhenius equation get.

[0089] Where: v is the raw material density, ρ c is the density of the material after carbonization, A, E, and n are reaction rate constants, that is, the three factors of thermal analysis kinetics, which are pre-exponential factor, ignition energy, and reaction order, respectively, and R is the ideal gas constant.

[0090] Based on the assumption that the decomposed gas accumulates continuously inside the material, the continuity equation can be expressed as:

[0091]

[0092] The thermal parameters of materials mainly include density ρ, thermal conductivity k and specific heat capacity C p ,Thermogravimetric curves show that the composite material mainly undergoes a single-stage thermal decomposition reaction at high temperature, such as Figure 5 As shown, the composite material decomposes from its intact state into fiber carbon and volatile gases. Therefore, at a certain temperature, the density of the composite material can be regarded as a combination of the densities of the undecomposed and decomposed materials.

[0093] According to the law of mixture, the material density ρ of the composite material after decomposition is obtained p for:

[0094] ρ p =(1-α p )ρ v +α p ρ c (4)

[0095] In the formula, α p is the degree of thermal decomposition; ρ v is the density of the composite material before decomposition, which is 1810kg / m 3 ρ cis the material density after the composite material is completely decomposed; since the mass fraction of the composite material after thermal decomposition is about 65%, the material density after decomposition is obtained as c =1810*65%=1158kg / m 3 Obviously, according to formula (4), as the thermal decomposition of the composite material continues, the density continues to decrease.

[0096] Determining the thermal parameters of materials is one of the key factors in thermal response analysis of composite materials. Under unilateral heating conditions, the thermal physical parameters of materials are functions of temperature and decomposition degree. During the material decomposition process, the decomposition degree of the material can be expressed by the residual mass fraction of the original material. The expression for the retention rate of the residual mass fraction of the original material is as follows:

[0097]

[0098] Therefore, according to the law of mixtures, the anisotropic thermal conductivity of the material can be expressed as:

[0099] k i =Fk v +(1-F)k c ,i=1,2,3 (6)

[0100] Where kv is the thermal conductivity of the original material, and kc is the thermal conductivity of the completely carbonized material.

[0101] The specific heat capacity of solid materials also uses the law of mixtures, and the specific expression is:

[0102] C p =FC pv +(1-F)C pc (7)

[0103] In the formula, C pv is the specific heat capacity of the original material, C pc is the specific heat capacity of completely carbonized material.

[0104] To simulate the thermal response of composite materials under unilateral heating, the corresponding initial conditions and boundary conditions need to be defined. At the initial moment, no decomposition gas is generated:

[0105] t=0,T=T0,ρ=ρ v , ρ c =0 (8)

[0106] Fire-facing surface boundary conditions (third type of boundary conditions):

[0107] q f =(q rad -εσT 4 )+h f (T ∞ -Ts ) (9)

[0108] In the formula, the heat flux of the heated surface = radiation heat flux (external radiation heat flux - radiation heat of the material on the fire-facing surface) + gas convection heat flux (gas convection heat transfer on the fire-facing surface).

[0109] Back-fire boundary conditions (third type boundary conditions):

[0110] q b =εσ(T b 4 -T ∞ 4 )+h b (T b -T s ) (10)

[0111] Wherein, the surface heat flux of the back-fire surface = radiation heat flux (heat radiated from the back-fire surface to the atmosphere) + gas convection heat flux (gas convection heat transfer on the back-fire surface).

[0112] In the above formula, q f is the net heat flux on the heated surface, q rad is the externally applied radiation heat flux, σ is the Boltzmann constant, Ts, T b are the surface and back temperatures of the material, T∞ is the ambient temperature, h f and h b are the convective heat transfer coefficients on the surface and back of the material, respectively, and ε is the emissivity of the material.

[0113] Based on the above theory, the secondary development of the UMATHT subroutine established a composite material thermal response finite element model that takes into account the internal gas convection and matrix decomposition after the composite material decomposes at high temperature. In order to solve the three-dimensional heat conduction model and continuity equation of the composite material, it is necessary to define the unit mass internal heat energy U and the unit mass internal heat energy partial derivative with respect to temperature in UMATHT. And the partial derivative of the thermal energy per unit mass with respect to the temperature gradient In addition, it is necessary to define the heat flow vector f and the partial derivative of the heat flow vector f with respect to temperature and the partial derivative of the heat flux vector with respect to the temperature gradient These variables need to be calculated in every increment.

[0114] By transforming formula (1) and substituting it into the continuity equation (3) and the specific heat capacity expression, the final form of the heat transfer equation for finite element implementation can be obtained:

[0115]

[0116] The basic energy balance equation for heat transfer in the model is:

[0117]

[0118] in, is the rate of change of thermal energy in the material with temperature, q is the heat flux per unit area flowing into the control body, and r is the heat supplied to the control body per unit volume.

[0119] Combining the above equations (11) and (12), we can calculate U and Equivariable expressions;

[0120] The calculation expression of U at the end of the incremental step is:

[0121] U(t+Δt)=U(t)+ΔU (13)

[0122] In one incremental step, the internal heat energy increment ΔU is calculated as:

[0123]

[0124] Then, in the above formula (13), The expression is:

[0125]

[0126] The expression is:

[0127]

[0128] The expression of heat flow vector f is:

[0129]

[0130] The calculation expression is:

[0131]

[0132] The calculation formula is:

[0133]

[0134] By defining the above variables and updating the state variables through the UMATHT subroutine, the thermal response analysis and calculation of the composite material considering the decomposition gas convection heat transfer and material decomposition can be carried out. Specifically, along the thickness direction of the laminate, the temperature of the center area at 0mm, 1mm, 2mm, 3mm and 4mm away from the fire surface changes with time, such as Figure 6 shown.

[0135] Depend on Figure 6It can be seen that in the initial stage of heating, the temperature at different depths gradually increases with the increase of heating time. This is mainly because the thickness of the material is only 4mm. Under the action of the larger external flame heat flux, more heat is transferred to the back of the material in a short time, resulting in a significant temperature rise at each depth in the initial stage of heating. As the heating time increases, the temperature rise rate at each depth decreases. This is mainly because the increase in the temperature of the heated surface leads to an enhanced radiation heat dissipation capacity, and the material reaches the pyrolysis temperature to undergo a pyrolysis reaction, absorbing part of the heat, and the pyrolysis gas diffuses to the surface of the material to take away part of the heat. In the later stage of heating, the temperature rise rate at 1mm and 2mm continued to decrease, and the temperature rose slowly; the temperature at 3mm and 4mm was close to a stable state, which was mainly because the heat exchange between the back of the material and the environment reached a dynamic balance. The stress cloud diagram is shown as follows Figure 7 shown.

[0136] Depend on Figure 7 As shown in a-7b and 8a-8d, with the increase of heating time, the temperature of the heated surface gradually increases. When heated to 100s, the temperature of most heated surfaces has reached the pyrolysis temperature of epoxy resin. Due to the heat transfer of the material in the plane direction, the heat is gradually transferred from the heated surface to the insulation area. The temperature in the same plane tends to gradually decrease from the center to the edge. The area where the material temperature reaches the pyrolysis temperature of epoxy resin is gradually increasing, and the material temperature in some insulation areas has reached the pyrolysis temperature, and pyrolysis reaction occurs. In the thickness direction, heat is gradually transferred from the heated surface of the material to the back. With the increase of heating time, the maximum material temperature appears at the center of the heated surface. The temperature of the area close to the back of the material gradually increases and no longer changes significantly. The temperature in the thickness direction shows a gradient distribution. When heated to 300s, the maximum material temperature is 1107K.

[0137] like Fig. 9 As shown in the figure, Y-0 represents the fire-facing surface, and Y-4 represents the back-facing surface. As the material thickness increases, the longer it takes for the material to reach the critical pyrolysis temperature, the later the pyrolysis reaction occurs. For the fire-facing surface, under the action of high temperature, it is rapidly carbonized after heating to 45 seconds, and gradually moves toward the back-facing surface. As the thickness increases, the material pyrolysis reaction time increases. Due to the thin model, the back-facing surface material is also quickly and completely carbonized.

[0138] Depend on Fig.10 It can be seen that at 45 seconds, the fire-facing area began to thermally decompose, but did not completely enter the carbonization stage. As the heating time increased, at 50 seconds, the fire-facing area underwent complete thermal decomposition. At 120 seconds, the back-fired area of ​​the laminate structure completely thermally decomposed and entered the carbonization stage.

[0139] Furthermore, by utilizing composite laminate theory, Hashin failure criterion, delamination failure criterion and material stiffness degradation model, the UMAT subroutine is adopted to simulate the failure behaviors of fiber tension and compression, matrix tension and compression, tension delamination and compression delamination of fiber reinforced composites.

[0140] It should be noted that since this embodiment only calculates the model temperature field and assumes that no thermochemical expansion occurs during expansion, its thermal expansion deformation cannot be calculated. However, the expansion deformation or displacement can be obtained by the refractory bearing characteristic calculation method (working thermal-mechanical coupling method), of course, provided that the applied mechanical load is small enough not to affect the thermal expansion deformation.

[0141] This embodiment establishes a method for simulating damage and failure of fiber-reinforced composite materials and filled core materials based on the calculation of the real-time temperature field of the structure by the UMATHT subroutine. Specifically, the UMAT subroutine is used to simulate the damage and failure of the fiber-reinforced composite materials. The analysis method includes the following steps:

[0142] Composite laminate theory. Assuming the temperature difference is ΔT(x,y,z), the expansion caused by the temperature difference is ε T It can be calculated by the following formula:

[0143] ε T =α·ΔT (20)

[0144] Where: α is the thermal expansion coefficient. The constitutive equation of the laminate based on temperature influence is as follows:

[0145]

[0146] In the formula, There are 6 stress components and strain components It can be expressed by the following formula:

[0147]

[0148] matrix The calculation formula is as follows:

[0149]

[0150] in:

[0151]

[0152] In the formula, They are the Poisson’s ratios of the corresponding materials at temperature T; They are the elastic modulus of the material corresponding to temperature T; They are the shear modulus of the material corresponding to temperature T;

[0153] B2: Composite laminate theory: Failure criteria for composite materials. A combination of the Hashin criterion and the Yeh delamination failure criterion is used to determine whether the material has failed. F1, F2 and F3 are used to describe the failure criteria of the fiber, matrix and delamination respectively. When damage failure occurs inside a composite laminate, the stress distribution in the local damaged area is complex and changes dramatically, while the strain distribution is relatively continuous and smooth before and after the damage. Therefore, the strain-based failure criterion is more suitable for describing the progressive damage evolution of composite materials. In this embodiment, without considering shear nonlinearity, the strain-based damage failure state of the three-dimensional Hashin criterion and the delamination failure criterion is described as follows:

[0154]

[0155] In the formula, the upper and lower equations represent the fiber tensile and compressive fractures, respectively;

[0156]

[0157] In the formula, the upper and lower equations represent the tensile and compressive fracture of the matrix, respectively;

[0158]

[0159] In the formula, the upper and lower equations represent tensile stratification and compressive stratification respectively;

[0160] Where: ε ii (i=1,2,3) is the positive strain in the direction of the principal axis i of the material; or (i=1, 2, 3) are the normal strains corresponding to the tensile or compressive strength in the direction of the principal axis i of the material at temperature T; They are the shear strains corresponding to the shear strength at temperature T in the 1-2, 1-3, and 2-3 planes:

[0161]

[0162] in: (j=t,c) is the tensile strength and compressive strength in the X direction (or 1 direction) at temperature T; (j=t,c) is the tensile strength and compressive strength in the Y direction (or 2 direction) at temperature T; (j=t,c) is the tensile strength and compressive strength at temperature T in three directions; They are the shear strengths of 1-2, 1-3, and 2-3 planes at temperature T;

[0163] B3: Construct a composite material stiffness degradation model. According to the failure criteria of fiber-reinforced composite materials, as the axial load on the laminate gradually increases, when the stress of a unit in the material reaches one or more failure equation conditions, its internal unit is damaged. It is necessary to embed a stiffness degradation model to improve the basic material parameters so as to calculate the stress and damage evolution of the laminate. The stiffness degradation model is as follows:

[0164] When the material meets the damage criterion, the damage variable is expressed as follows:

[0165]

[0166] ft, fc, mt, mc, and ld represent fiber tensile damage, fiber compression damage, matrix tensile damage, and matrix compression damage, respectively; damage variable:

[0167]

[0168] The stress-strain matrix including damage is as follows:

[0169]

[0170] where ω i (i=1,2,3,4,5,6) is the damage variable, and the calculation expression is as follows:

[0171] ω1=max[0.0,max(0.0,d ft ,d fc )];ω2=max[0.0,max(0.0,d ft ,d fc ), max(0.0, d mt ,d mc )];

[0172] ω3=max[0.0,max(0.0,d ft ,d fc ), max(0.0, d mt ,d ld )]; ω4=ω2, ω5=ω6=ω3 (32)

[0173] Then, based on the crushable foam model, the damage failure of the filling core material is calculated by using the constitutive relationship of the filling core material at different temperatures. Specifically, the damage failure model of the filling core material adopts the Abauqs software embedded module: the crushable foam model is constructed, that is, by inputting the true stress-strain constitutive relationship, yield stress ratio and plastic Poisson's ratio of the filling core material at different temperatures.

[0174] The analysis method of this embodiment is applied to a three-dimensional thermal model. In other embodiments, the dimensions in this embodiment are adaptively adjusted and can also be applied to heat transfer calculations and fire resistance bearing performance analysis of one-dimensional and two-dimensional thermal models.

[0175] Example 2

[0176] The marine composite material structure considering material decomposition used in this embodiment adopts a composite material sandwich plate structure, and a calculation and analysis method for structural heat transfer characteristics is provided based on the composite material sandwich plate structure.

[0177] This embodiment is basically the same as Embodiment 1, except that this embodiment adopts a composite sandwich structure with a length and width of 800*800mm and a thickness of 28mm; the upper and lower surface material systems are both SW220430LV with a thickness of 4mm; the middle filling core material is PMI foam with a thickness of 20mm.

[0178] like Fig.11 As shown in the figure, fixed support constraints are applied to the surrounding overlap plate area as boundary conditions. Temperature load condition: The fire-facing surface of the composite sandwich panel is heated by high temperature. The analysis results are shown in Figure 12-16 .

[0179] Example 3

[0180] The ship-use composite material structure considering material decomposition used in this embodiment adopts a composite material laminate structure, and a fire-resistant bearing property calculation and analysis method is provided based on the composite material laminate structure.

[0181] This embodiment is basically the same as the embodiment 1, except that this embodiment uses a composite material laminate structure with a size of 800*800mm and a thickness of 2mm; the overlapping plate area around is 100mm*100mm.

[0182] like Fig.17 As shown, fixed support constraints are applied to the surrounding overlap plate areas as boundary conditions. Temperature load conditions: The fire-facing surface of the composite laminate is heated at high temperature. Mechanical load conditions: The model first applies a uniform load of 0.1MPa to the 100mm*100mm area in the center of the back-fire panel grid. The load application order: First, a 0.1MPa uniform load is applied to the back-fire surface of the model, and a temperature load is applied to the fire-facing surface of the model (complete thermal-mechanical coupling).

[0183] The mechanical response of the composite laminate after a 0.1 MPa uniform load is applied to the model at room temperature (300K) is shown in Fig.18 ; Under the complete thermal-mechanical coupling after 873.15K temperature and 0.1MPa uniform load, the temperature field changes, see Fig.19; Fully thermal-mechanical coupling at 873.15K temperature and 0.1MPa uniform load, mechanical response of composite laminate, see Fig. 20 .

[0184] Example 4

[0185] The marine composite material structure considering material decomposition used in this embodiment adopts a composite sandwich plate structure, and a fire-resistant bearing property calculation and analysis method is provided based on the composite sandwich plate structure.

[0186] This embodiment is basically the same as Embodiment 1, except that this embodiment adopts a composite sandwich structure with a length and width of 800*800mm and a thickness of 28mm; the upper and lower surface material systems are both SW220430LV with a thickness of 4mm; the middle filling core material is PMI foam with a thickness of 20mm.

[0187] like Fig.21 As shown in the figure, fixed support constraints are applied to the lap plate area around the edges as boundary conditions. Temperature load conditions: The fire-facing surface of the composite sandwich panel is heated at high temperature.

[0188] Mechanical load conditions: The model first applies a uniform load of 10KPa to the 600mm*600mm area in the center of the back-fire panel grid. The load size is 10KPa. Load application order: First, apply a 10KPa uniform load to the back-fire surface of the model, and apply a temperature load to the front-fire surface of the model (complete thermal-mechanical coupling). After applying a 10KPa uniform load to the model at room temperature (300K), the mechanical response of the surface composite laminate is shown in Figure 1. Figure 21-23 .

[0189] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for analyzing the fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structures, characterized in that: The following steps are involved: A1: Establish a mathematical model of thermal response of marine composite materials. The calculation model takes into account the effects of isotropic or anisotropic heat conduction of materials, heat convection of decomposed gases, and heat absorption caused by material decomposition during heating. A2: Based on the heat transfer equation, pyrolysis kinetic equation and continuity equation, the UMATHT subroutine is used to establish a thermal response simulation method considering material pyrolysis, so as to calculate and analyze the material's temperature, density, carbonization rate, carbonization rate and density change rate; A3: Based on step A2, the composite laminate theory, Hashin failure criterion, delamination failure criterion and material stiffness degradation model are used, and the UMAT subroutine is adopted to simulate the fiber tension and compression, matrix tension and compression, tension delamination and compression delamination failure behaviors of fiber reinforced composite materials. At the same time, based on the Crushable foam model, the constitutive relationship of the filling core material at different temperatures is used to calculate the damage failure of the filling core material.

2. The method for analyzing fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structures according to claim 1, characterized in that: The marine composite material structure includes a composite laminate structure, a composite sandwich plate structure or a composite stiffened plate structure; the marine composite material includes a fiber reinforced composite material and a filling core material.

3. The method for analyzing fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structures according to claim 1, characterized in that: Step A2 also considers the internal gas convection after the material decomposes at high temperature and the thermal response of the material decomposition and establishes a finite element model.

4. The method for analyzing fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structures according to claim 1, characterized in that: The simulation method established by the UMATHT subroutine in step A2 is: In UMATHT, the internal heat energy per unit mass U and the partial derivative of the internal heat energy per unit mass with respect to temperature are defined as And the partial derivative of the thermal energy per unit mass with respect to the temperature gradient Define the heat flow vector f, the partial derivative of the heat flow vector f with respect to temperature and the partial derivative of the heat flux vector with respect to the temperature gradient 5. The method for analyzing fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structures according to claim 1, characterized in that: In step A1, a mathematical model of thermal response of fiber reinforced composite materials and filling core materials is established. The model takes into account the isotropic heat conduction of the filling core material and the anisotropic heat conduction of the fiber reinforced composite material, the heat convection of the decomposition gas, the endothermic decomposition of the material, and the thermal equilibrium between the solid material and the decomposition gas. The accumulation of gas generated by the decomposition inside the material and its diffusion and overflow are not considered, and the thermochemical expansion caused by the decomposition of the material is not considered.

6. The method for analyzing fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structures according to claim 5, characterized in that: The heat transfer equation of the material under the action of thermal load is obtained as follows: In the formula, the first term represents the rate of change of the internal energy per unit volume of the material; the second term represents the conduction heat flux inside the material; the third term represents the convection heat transfer of the decomposed gas inside the material; the fourth term represents the heat absorbed by the material analysis; T represents temperature, and t represents time; ρ represents the material density; represents the gas mass flow rate; k1, k2, and k3 represent the thermal conductivity in three directions, respectively, where z is the thickness direction; Q is the heat of decomposition. If it is an endothermic reaction, Q is a negative value.

7. The method for analyzing fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structures according to claim 1, characterized in that: Based on the calculation of the real-time temperature field of the structure by the UMATHT subroutine in step A2, step A3 establishes a damage failure simulation method for fiber reinforced composite materials and filled core materials.

8. The method for analyzing fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structures according to claim 7, characterized in that The UMAT subroutine is used to simulate the damage failure of fiber reinforced composite materials. The analysis method includes the following steps: B1: Assuming the temperature difference is ΔT(x,y,z), the expansion caused by the temperature difference is ε T The formula is as follows: e T =α·ΔT Where: α is the thermal expansion coefficient. The constitutive equation of the laminate based on temperature influence is as follows: In the formula, There are 6 stress components and strain components It is expressed as follows: matrix The calculation formula is as follows: in: In the formula, They are the Poisson’s ratios of the corresponding materials at temperature T; They are the elastic modulus of the material corresponding to temperature T; They are the shear modulus of the material corresponding to temperature T; B2: The Hashin criterion and the Yeh delamination failure criterion are combined to determine whether the material has failed. F1, F2 and F3 are used to describe the failure criteria of fiber, matrix and delamination respectively. Without considering shear nonlinearity, the strain-based damage failure state of the three-dimensional Hashin criterion and the delamination failure criterion is described as follows: In the formula, the upper and lower equations represent the fiber tensile and compressive fractures, respectively; In the formula, the upper and lower equations represent the tensile and compressive fracture of the matrix, respectively; In the formula, the upper and lower equations represent tensile stratification and compressive stratification respectively; Where: ε ii (i=1,2,3) is the positive strain in the direction of the principal axis i of the material; or are the normal strains corresponding to the tensile or compressive strength in the direction of the principal axis i of the material at temperature T; They are the shear strains corresponding to the shear strength at temperature T in the 1-2, 1-3, and 2-3 planes: in: is the tensile strength and compressive strength in the X direction (or 1 direction) at temperature T; is the tensile strength and compressive strength in the Y direction (or 2 direction) at temperature T; It is the tensile strength and compressive strength at temperature T in three directions; They are the shear strengths of 1-2, 1-3, and 2-3 planes at temperature T; B3: Construct a composite material stiffness degradation model. The stiffness degradation model is as follows: When the material meets the damage criterion, the damage variable is expressed as follows: f t 、f c 、m t 、m c , l d Respectively represent fiber tensile damage, fiber compression damage, matrix tensile damage, and matrix compression damage; damage variables The stress-strain matrix including damage is as follows: where ω i (i=1,2,3,4,5,6) is the damage variable, and the calculation expression is as follows: ω1=max[0.0,max(0.0,d ft ,d fc )];ω2=max[0.0,max(0.0,d ft ,d fc ),max(0.0,d mt ,d mc )]; ω3=max[0.0,max(0.0,d ft ,d fc ),max(0.0,d mt ,d ld )];ω4=ω2,ω5=ω6=ω3。 9. The method for analyzing fire-resistant heat transfer and fire-resistant bearing performance of marine composite material structures according to claim 7, characterized in that: The damage failure model of the filling core material adopts the Abauqs software embedded module: constructing the crushable foam model.

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