CN115440325A - Simulation method for laser ablation full-weaving CFRP under tangential airflow - Google Patents

Simulation method for laser ablation full-weaving CFRP under tangential airflow Download PDF

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CN115440325A
CN115440325A CN202211058515.8A CN202211058515A CN115440325A CN 115440325 A CN115440325 A CN 115440325A CN 202211058515 A CN202211058515 A CN 202211058515A CN 115440325 A CN115440325 A CN 115440325A
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李泽文
周义青
唐杰
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Nanjing University of Science and Technology
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Abstract

The invention discloses a simulation method for laser ablation full-weaving CFRP under tangential airflow, which provides a compact structure mechanical ablation model of a full-weaving material under high-speed tangential airflow and high-power laser density, and simultaneously considers the influence of ablation pit vortex evolution on oxygen mass transfer and mechanical ablation; according to the method, through establishing a fluid-solid coupling model, the resin pyrolysis reaction, the oxidation and sublimation degradation of carbon fibers and residual carbon, the mechanical degradation caused by external tangential airflow and the mechanical degradation generated by internal pyrolysis gas of the CFRP in the laser ablation process are analyzed, and the contribution problem of different degradation of the CFRP in different stages of laser ablation is solved. The invention can reproduce the ablation process of any laser form on the CFRP within a certain flow velocity range, and provides theoretical and simulation basis for high-power laser damage composite material under high-flow velocity tangential airflow.

Description

Simulation method for laser ablation full-weaving CFRP under tangential airflow
Technical Field
The invention belongs to the field of laser processing and damage, and particularly relates to a simulation method of laser ablation full-weaving CFRP under tangential airflow.
Background
The carbon fiber reinforced resin matrix Composite (CFRP) is a layered composite material with carbon fibers as a reinforcing material and resin as a matrix. The CFRP has the characteristics of high specific strength, high specific modulus, high hardness, high temperature resistance, corrosion resistance, low expansibility, good fatigue resistance, small specific gravity, excellent mechanical property and the like. Fully woven CFRP is more widely used in aerospace and military weapons manufacturing, especially in the field of multi-purpose drones, due to its higher strength and superior mechanical properties compared to unidirectional and orthogonal CFRP. The existing missile has high interception cost and limited precision; the high-energy laser weapon has the advantages of continuous tracking and hitting, light speed damage, low cost and the like, so that the development of laser is of great importance for the research on the ablation characteristic of the full-braided CFRP under high-speed airflow.
Laser ablation CFRP is a very complex physicochemical process that includes pyrolysis of the resin, reaction and flow of the pyrolysis products, irreversible expansion and mechanical degradation phenomena caused by internal pressure, oxidation of the carbon residue and carbon fibers and changes in material strength caused by oxidation, shielding effect of the pyrolysis plume particles on the laser and obstruction to oxygen mass transfer; if gas flowing at a high speed exists on the surface of the material, the ablation process also comprises an external mechanical ablation effect, dynamic evolution of oxygen mass transfer, temperature evolution caused by convective heat transfer on the surface of the material and the like; when the temperature reaches the vaporization temperature of the carbon, sublimation of the material surface occurs. Thus, the disfigurement process that results in laser ablation of CFRP material under tangential airflow can be described as: pyrolysis, oxidation, internal mechanical degradation, external mechanical degradation and sublimation. The process of laser acting on the CFRP material is very violent, and it is very difficult to quantify various contributions in the ablation process through experimental research, so that numerical simulation becomes an increasingly important analysis means.
The existing numerical simulation mainly aims at the research of laser cutting CFRP under low power, the research of oxidation ablation under low flow rate, the research of external mechanical degradation under high flow rate and the like, the research of fully considering the contribution analysis of each physicochemical stage is fresh, and the research of laser ablation full weaving CFRP under tangential airflow is more limited. The special structure of the fully woven material is more complex than a unidirectional structure and an orthogonal structure in the ablation process, and thermophysical parameters are more difficult to quantitatively analyze. In the process of researching oxidative ablation and external mechanical ablation, the concentration of oxygen in a fluid region and the boundary flow rate are directly used as constant constants for calculation in many researches, and variable distribution generated along with the evolution of an ablation pit is not accurately considered. At present, temperature evolution is only considered for internal mechanical degradation of a CFRP material, and the staged characteristic of the internal mechanical degradation is not considered in combination with the actual consideration, namely, the internal mechanical degradation rate gradually approaches zero along with the completion of pyrolysis.
Therefore, a tangential airflow laser ablation full-weaving CFRP simulation method must be developed, and the staged contributions of pyrolysis, oxidation, sublimation, external mechanical ablation and internal mechanical ablation to the ablation process are qualitatively and quantitatively analyzed, so that the damage mechanism process of the laser to the high-speed target can be accurately realized, and the establishment of an efficient laser striking strategy is realized.
Disclosure of Invention
The invention aims to provide a simulation method for laser ablation full-weaving CFRP under tangential airflow.
The technical solution for realizing the purpose of the invention is as follows: a tangential airflow laser ablation full-weaving CFRP simulation method comprises the following steps:
the first step is as follows: homogenizing the density, constant pressure heat capacity and heat conductivity of the material by a volume averaging method;
the second step is that: establishing a basic control equation of a fluid domain and a porous medium domain, based on a momentum conservation theorem, a mass conservation theorem and an energy conservation theorem, and tracking an interface retreating and ablating process by adopting a moving grid method;
the third step: constructing a compact structure physical model, tracking the change of the fluid speed of the surface of the material in the ablation pit, mapping the change to the surface of the material through a boundary similarity principle, and correcting the change by replacing a flow rate term of an original equation;
the fourth step: deducing and setting the anisotropic thermal conductivity of the material by taking the compact structure as a theoretical basis;
the fifth step: the pressure change of the pyrolysis gas is considered to do work and viscous dissipation, and the pressure change is added to a porous medium energy conservation equation for correction;
and a sixth step: tracking the evolution of the temperature and the pressure of the fluid on the surface of the material in the ablation pit, calculating the distribution of the oxygen concentration by combining an ideal gas equation, and correcting by replacing a constant concentration item of the original equation;
the seventh step: tracking Darcy velocity field evolution of the material surface, and correcting an internal mechanical degradation equation;
the eighth step: setting boundary conditions and initial values;
the ninth step: and setting grid moving conditions and moving rates by combining the rate equations derived and calculated, and analyzing the evolution of each ablation contribution in the ablation process through finite element iterative calculation.
A computer device comprises a memory, a processor and a computer program which is stored on the memory and can run on the processor, wherein the processor executes the computer program to realize the steps of the tangential airflow laser ablation full weaving CFRP simulation method.
Compared with the prior art, the invention has the remarkable advantages that: the invention provides a compact structure external mechanical ablation model for weaving a CFRP material under high-speed tangential airflow and high-power laser density, and the anisotropic thermal conductivity of the fully-woven CFRP material is deduced on the basis of the model. Meanwhile, the influence of ablation pit eddy current evolution on oxygen mass transfer and external mechanical degradation is considered, the internal mechanical degradation effect is corrected by combining the evolution of the Darcy velocity field on the surface of the material, the pressure change of pyrolysis gas is considered to do work and viscous dissipation, and the internal energy conservation equation of the material is further corrected. The simulation method simultaneously analyzes the problems of resin pyrolysis reaction, oxidation and sublimation degradation of carbon fibers and residual carbon, mechanical degradation caused by external tangential airflow and mechanical degradation generated by internal pyrolysis gas of the carbon fiber reinforced epoxy resin composite material in the laser ablation process by establishing the fluid-solid coupling model, and solves the problem of contribution analysis of different degradation of the carbon fiber reinforced epoxy resin composite material in different stages of laser ablation. The numerical simulation can reproduce the CFRP ablation process of any laser in a certain flow velocity range, and provides theoretical and simulation basis for high-power laser damage of the composite material under high-flow-velocity tangential airflow.
Drawings
FIG. 1 is a schematic diagram of two-dimensional modeling of a simulation method for laser ablation of a fully woven CFRP material under tangential airflow.
FIG. 2 is a physical model of a dense structure.
Figure 3 is a schematic illustration of the irregular eddy current temperature and velocity profile within an ablation pit.
FIG. 4 is a Darcy velocity evolution plot for a center point of a material.
Fig. 5 is a mesh division diagram.
Fig. 6 is a graph of the evolution of the contribution of different denudations.
Detailed Description
In order to make the technical solutions of the present invention more clear and definite for those skilled in the art, the present invention is further described in detail below with reference to the following examples and the accompanying drawings, but the embodiments of the present invention are not limited thereto.
The invention provides a simulation method for weaving a CFRP material by laser ablation under tangential airflow, which introduces an external mechanical ablation model of a compact structure for weaving the CFRP material under high-speed tangential airflow and high-power laser density in the process of establishing a numerical model, and deduces the anisotropic thermal conductivity of the fully woven CFRP material on the basis of the model. The influence of ablation pit eddy current evolution on oxygen mass transfer and external mechanical erosion is fully considered, the internal mechanical erosion effect is corrected by combining the evolution of the Darcy velocity field on the surface of the material, the pyrolysis gas pressure change is considered to do work and viscous dissipation, and the internal energy conservation equation of the material is further corrected, so that the calculation accuracy of the fluid-solid coupling model is improved.
A schematic diagram of a two-dimensional numerical model of the present invention is shown in fig. 1. On the basis of ensuring the reliability of the numerical calculation result, the following assumptions and simplifications are made for the model:
(1) The gas components in the fluid domain are not influenced by pyrolysis, oxidation and sublimation;
(2) Neglecting complex chemical reactions between pyrolysis gases and with materials;
(3) Neglecting the thermal expansion and contraction effects of the material;
(4) Neglecting the redistribution of the flow field caused by the irregular ablation and extraction of the material;
the method comprises the following specific steps:
the first step is as follows: the density, constant pressure heat capacity and heat conductivity of the material are homogenized by a volume averaging method.
Figure BDA0003825958580000041
V i ＝m i /ρ i i＝f,p,ch,g
Figure BDA0003825958580000042
Figure BDA0003825958580000043
Figure BDA0003825958580000044
Figure BDA0003825958580000045
Figure BDA0003825958580000046
The density of each component in the above formula is assumed to be constant, f, p, ch and g correspond to carbon fiber, resin, residual carbon and pyrolysis gas in turn,
Figure BDA0003825958580000047
representing the volume fraction, p, of each component i Denotes the constant density of the components, c pi The constant pressure heat capacity of each component is shown, and xi is the mass fraction of pyrolysis gas.
The second step: and establishing a control equation, based on the momentum conservation theorem, the mass conservation theorem and the energy conservation theorem, and tracking the interface retreating and ablating process by adopting a moving grid method.
The fluid domain calculation adopts a compressible fluid-conservation form NaviStokes equation:
Figure BDA0003825958580000051
Figure BDA0003825958580000052
Figure BDA0003825958580000053
Figure BDA0003825958580000054
Figure BDA0003825958580000055
Figure BDA0003825958580000056
in the above formula, ρ air In order to be the density of the air,
Figure BDA0003825958580000057
is the air velocity vector, p air Is the air pressure, μ air Is the kinematic viscosity of air, F is the force source term, c P,air Is constant pressure heat capacity of air, lambda air For air thermal conductivity, I is the unit matrix tensor, Q vd For viscous dissipation terms, Q p In order to obtain the work term of the pressure,
Figure BDA0003825958580000058
is a hamiltonian.
The basic control equation of the porous medium domain combines a modified Fourier equation, a single-step Arrenus equation, a single-phase Darcy's law equation and a Connier-Karman permeability model theory, and is specifically described as follows:
Figure BDA0003825958580000059
Figure BDA00038259585800000510
Figure BDA00038259585800000511
Figure BDA00038259585800000512
Figure BDA00038259585800000513
in the above formula rho eff Is the overall equivalent density of the material, c p,eff Is the integral equivalent specific heat capacity of the material,
Figure BDA00038259585800000514
as Hamiltonian, L P For the latent heat of pyrolysis, ρ g 、ρ p The densities of the pyrolysis gas and the resin respectively,
Figure BDA00038259585800000515
respectively, porosity and resin volume fraction,
Figure BDA0003825958580000061
for the pyrolysis gas darcy velocity vector,
Figure BDA0003825958580000062
for the pyrolytic reaction, the pre-factor, E p In order to activate the energy of the pyrolysis reaction,
Figure BDA0003825958580000063
is the volume fraction of the resin at the end of the reaction,
Figure BDA0003825958580000064
is the initial resin volume fraction, κ is the permeability, p g Darcy pressure, mu, caused by pyrolysis of gases g For pyrolysis of the gas dynamic viscosity, d particle The particle size of the porous medium, R is a constant of the universal gas, T is the temperature of the matrix, T is the calculation time, xi is the mass fraction of the pyrolysis gas, and n is the reaction order.
The third step: and constructing an external mechanical ablation compact structure physical model as shown in FIG. 2, tracking the fluid velocity change of the material surface in the ablation pit, mapping the fluid velocity change to the material surface through a boundary similarity principle, and replacing the flow rate term of the original equation for modification.
Under the action of high-power laser irradiation and high-speed tangential airflow, the mechanical degradation of the carbon fiber is more severe, on one hand, the strength of the carbon fiber is rapidly reduced at high temperature, and on the other hand, the dense structure of the material can be better maintained by the rapid pyrolysis of the resin and the slow pyrolysis at lower power, so that based on the facts, the invention constructs a physical model of the external mechanical degradation dense structure.
In the fluid-solid coupling model, a velocity fluid domain exists on the surface of the material, so that the flow velocity should be 0 in theory close to the surface of the material. However, this is not the case, and the irregular ablation topography on the material surface will destroy the ideal velocity fluid domain, so to characterize the mechanical ablation effect of the tangential airflow on the material, by tracking the fluid velocity a certain distance above the material surface, the changing velocity field can be accurately tracked in the irregular ablation pits by the boundary similarity mapping principle, and the mechanical ablation rate is corrected in turn, thereby calculating the contribution of the mechanical ablation more accurately.
Figure BDA0003825958580000065
Figure BDA0003825958580000066
Figure BDA0003825958580000067
Figure BDA0003825958580000068
Figure BDA0003825958580000069
Figure BDA0003825958580000071
Figure BDA0003825958580000072
Figure BDA0003825958580000073
Figure BDA0003825958580000074
Figure BDA0003825958580000075
In the above formula v out For external mechanical equivalent ablation rate, D p Is the external mechanical ablation isovelocity of the resin matrix, D u For the mechanical degradation rate of the outer radial carbon fibres, D f Delta is the mechanical degradation rate of the axial carbon fiber, delta is the fiber layer and the resin layerRatio of thickness, p f 、ρ p Is a constant density of the carbon fiber and the resin,
Figure BDA0003825958580000076
a leading factor for the gasification reaction of carbon fibers and resins, E Af 、E Ap Activation energy, lambda, for the gasification reaction of carbon fibers and resin f 、λ p Is the thermal conductivity of the carbon fibers and the resin, c f 、c p Is the constant pressure heat capacity of the carbon fiber resin,
Figure BDA0003825958580000077
initial strength of the carbon fiber in the axial and radial directions and initial strength of the matrix of the resin, σ f 、σ f⊥ 、σ pT Axial, radial and resin matrix real-time strengths,
Figure BDA0003825958580000078
respectively are the strength change factors of the carbon fiber and the resin matrix,
Figure BDA0003825958580000079
to correct for the temperature-dependent variation of the intensity factor,
Figure BDA00038259585800000710
are real-time volume fractions of carbon fibers, resin and residual carbon respectively,
Figure BDA00038259585800000711
is the initial volume fraction of the resin, T w Is the real-time temperature, T, of the surface of the material 0 The initial temperature of the surface of the material, t is the action time of the laser, R is the constant of the universal gas, and P ∑ Is the material surface pressure head.
The change in fluid velocity at the material surface within the ablation pit is tracked, as shown in fig. 1, and instead of the flow term of the original equation, a correction is made in which the material surface head is described by a material surface flow correction:
P ∑ ＝ρ air (u airsurface (t)·cos(θ)) 2
where ρ is air Is the density of air, u airsurface (t) is the air flow speed of the material surface evolving along with the ablation pit, and theta is the included angle between the normal speed and the horizontal plane.
The fourth step: the anisotropic thermal conductivity of the material is deduced and set by taking the compact structure as a theoretical basis, and is described as follows:
Figure BDA0003825958580000081
Figure BDA0003825958580000082
Figure BDA0003825958580000083
Figure BDA0003825958580000084
Figure BDA0003825958580000085
Figure BDA0003825958580000086
Figure BDA0003825958580000087
Figure BDA0003825958580000088
in the above formula solid Is the solid equivalent thermal conductivity, λ 1 ,λ 2 Is the material surface direction thermal conductivity, lambda 3 The material thickness direction thermal conductivity; lambda [ alpha ] ch 、λ p 、λ f Constant thermal conductivity of the residual carbon, the resin and the carbon fiber respectively;
Figure BDA0003825958580000089
respectively the real-time volume fractions of carbon fiber, residual carbon and resin,
Figure BDA00038259585800000810
is the initial volume fraction of carbon fibers, A * 、N 1 、N 2 、b * 、s b 、s p η is the ratio of the residual carbon thermal conductivity to the matrix thermal conductivity, which is an intermediate variable.
The fifth step: and (4) performing work and viscous dissipation by considering the pressure change of the pyrolysis gas, and adding the work and the viscous dissipation into an energy conservation equation of the porous medium for correction.
The generation of pyrolysis gas can lead to the change of the internal pressure of the material, meanwhile, due to the pressure gradient between the interior and the boundary, the pyrolysis gas can continuously overflow to the boundary, the pressure is continuously changed in the escape process of the pyrolysis gas, and the viscosity exists between the pyrolysis gas and the pores, so that the evolution rule of the internal temperature of the material can be calculated more accurately by considering the pressure change work and the viscosity dissipation.
Figure BDA0003825958580000091
Figure BDA0003825958580000092
Figure BDA0003825958580000093
Figure BDA0003825958580000094
In the above formula rho eff To describe the equivalent density of the porous media, c p,eff Is equivalent constant pressure heat capacity, lambda eff Is an equivalent thermal conductivity matrix, ρ p The density of the resin is constant, and the resin,
Figure BDA0003825958580000095
is the real-time volume fraction of the resin, L P As latent heat of pyrolysis of the resin, c pg Constant pressure heat capacity, rho, for pyrolysis gases g In order to obtain the density of the pyrolysis gas,
Figure BDA0003825958580000096
is the pyrolysis gas Darcy velocity vector, p g For pyrolysis gas pressure, Q vd ' viscous dissipation, Q, generated by pyrolysis gas flow p ' is a work term for the change of the internal pyrolysis gas pressure, T is the material temperature, T represents the calculation time,
Figure BDA0003825958580000097
is a hamiltonian.
And a sixth step: and tracking the temperature and pressure evolution of the fluid close to the material surface in the ablation pit, and calculating the distribution of the oxygen concentration by combining an ideal gas equation so as to replace a constant concentration term of the original equation for correction.
In the fluid-solid coupling model, as the ablation pit deepens, heat flow from downwind to upwind region is formed in the ablation pit, and as the inflow speed increases, the vortex heat flow becomes more unstable and develops in a disordered direction, as shown in fig. 3. Therefore, in the air flow area with violent temperature disturbance in the ablation pit, the air flow temperature greatly and irregularly evolves to cause the oxygen concentration distribution in the ablation pit to generate difference, the evolution distribution of the oxygen concentration in the ablation pit can be calculated based on an ideal gas equation by combining the pressure of the change and the development in the ablation pit, and the oxidation ablation rate equation is corrected so as to ensure that the calculation result is more accurate.
Figure BDA0003825958580000098
Figure BDA0003825958580000099
In the above formula v oxi For the rate of the oxidation reaction, A oxi Indicating a pro-factor for the oxidation reaction, E oxi Activation energy for oxidation reaction, M i The average molar mass of the surface material participating in the oxidation reaction,
Figure BDA00038259585800000910
to take part in the oxidation reaction, the equivalent surface density, p air,surface Is the partial pressure of oxygen on the surface of the material near the ablation pit, T air,surface Is the surface gas temperature, T, of the material near the ablation pit surface Zeta is the correction coefficient, and R is the universal gas constant.
The seventh step: tracking Darcy velocity field evolution of the surface of the material, and correcting an internal mechanical degradation equation according to distribution characteristics of the Darcy velocity field of the surface of the material.
In the process of laser ablation of materials, resin is subjected to pyrolysis reaction at a low temperature, and due to the fact that the temperature rise rate is high, pyrolysis gas is accumulated in a large amount in a short time, and the pressure inside the material close to the surface is increased rapidly. At this stage, according to the results observed experimentally, the internal mechanical degradation effect was found to be the most severe, whereas with the completion of the resin pyrolysis, no more pyrolysis gas was collected and escaped from the surface, and therefore the internal mechanical degradation effect gradually decreased and stabilized, as shown in fig. 4. Based on the facts, the invention tracks the evolution of Darcy velocity field on the surface of the material and corrects the internal mechanical degradation rate by the evolution, and the expression is as follows:
Figure BDA0003825958580000101
Figure BDA0003825958580000102
in the above formula v int For the rate of internal mechanical degradation,
Figure BDA0003825958580000103
is a pre-exponential factor, lambda, of the resin pyrolysis reaction p Is the resin thermal conductivity, ρ p Is the resin density, c p Is the constant pressure heat capacity of the resin, K is the permeability,. L 0 Is the pore size, σ pT As resin strength, E P Is activation energy of resin pyrolysis reaction, R is universal gas constant, T surface Is the surface temperature, σ, of the material compsite,T Is the strength of the composite material, phi is a correction term, chi is a correction coefficient, u is the Darcy speed of the surface of the material, u is the surface of the material max Is the Darcy velocity peak constant of the material surface, and omega is a constant.
Eighth step: and calculating the gasification rate of the material surface according to a Hertz-Langmuir gasification equation and a Clausius-Capulon saturated vapor pressure equation.
Figure BDA0003825958580000111
Figure BDA0003825958580000112
Figure BDA0003825958580000113
ΔH sub ＝M c L sub
In the above formula, v sub As sublimation rate, m sub For the mass flow density of the carbon dissipation,
Figure BDA0003825958580000114
the equivalent density, P, of the material surface participating in gasification th Is the saturated vapor pressure, beta is the inverse diffusion coefficient, Δ H sub Is the enthalpy of gasification of carbon, M c Is the molar mass of carbon, L sub Is the latent heat of vaporization of carbon, T sub Is the gasification temperature, T, of carbon surface Is the surface temperature of the material, P 0 Is standard atmospheric pressure, R is a universal gasA constant value.
The ninth step: boundary conditions and initial conditions are set.
Conservation of energy at the fluid-solid boundary:
Figure BDA0003825958580000115
in the above formula eff The equivalent thermal conductivity of the whole material is obtained,
Figure BDA0003825958580000116
alpha is the absorption coefficient of the material to laser, I Lase Is a power density distribution,. Epsilon.is an emissivity coefficient,. Sigma.is a Stefan-Boltzmann constant, T surface Is the surface temperature, T, of the material e Is at the temperature of the surroundings and is,
Figure BDA0003825958580000117
is the equivalent density of the material surface participating in oxidation and sublimation, L oxi For latent heat of oxidation, L sub To the latent heat of sublimation, v oxi To the rate of oxidation, v sub Is the sublimation rate.
Fluid-solid heat transfer boundary conditions and initial conditions:
upper boundary of fluid field:
Figure BDA0003825958580000118
fluid field inlet:
Figure BDA0003825958580000119
fluid domain outlet:
Figure BDA00038259585800001110
on the solid lowering boundary:
Figure BDA00038259585800001111
initial conditions: t is a unit of priamry ＝273.15[Kl
In the above formula
Figure BDA00038259585800001112
Is a normal vector perpendicular to the boundary, λ air In order to achieve the thermal conductivity of air,
Figure BDA00038259585800001113
is a temperature gradient, ρ air Is the density of the air, and is,
Figure BDA0003825958580000121
is the inlet enthalpy difference, h aL Is a natural convective heat transfer coefficient, T enviroment Is the ambient temperature and T is the material temperature.
Boundary conditions and initial conditions of fluid flow:
normal flow is provided at the fluid field inlet: u. of in ＝u air
Fluid field outlet set static pressure: p out ＝1[atm]
The fluid domain upper boundary is arranged symmetrically:
Figure BDA0003825958580000122
the extended boundary below the fluid domain sets the slip condition (as shown in detail): u. of air ＝u in
The boundary below the solid is set with a non-slip condition: u. u air ＝0
In the above formula
Figure BDA0003825958580000123
Is a normal vector, u, perpendicular to the boundary air For the velocity of the incoming flow, P out Is the outlet pressure.
Darcy's law boundary conditions and initial conditions:
porous media boundary set outlet pressure: p is boundary ＝1[atm]
Initial conditions inside the porous medium: p priamry ＝1[atm]
In the above formula P boundary As boundary pressure, P priamry Is the initial pressure inside the porous medium.
Initial conditions of domain differential equation characterizing resin pyrolysis:
Figure BDA0003825958580000124
initial conditions of a domain differential equation characterizing carbon fiber ablation:
Figure BDA0003825958580000125
in the above formula
Figure BDA0003825958580000126
Is the initial volume fraction of the resin,
Figure BDA0003825958580000127
is the initial volume fraction of carbon fibers.
The tenth step: quadrilateral division is carried out on the grid as shown in fig. 5, grid moving conditions and rates are set, and evolution of each ablation contribution in the ablation process is analyzed through finite element iterative computation as shown in fig. 6.
v total ＝v out +v int +v oxi +v sub
Fig. 6 is an ablation rate evolution curve of a center point of a material, and it can be seen from the graph that in an initial ablation stage, the increasing trends of internal mechanical ablation and external mechanical ablation rates are obvious, which are consistent with the physical fact that the surface of the material is expanded by pyrolysis gas, and with the completion of the pyrolysis gas, the internal mechanical ablation does not substantially contribute to the ablation after 2.5s, while with the increase of the groove depth, the fluid velocity near the wall surface is gradually reduced, and does not substantially contribute to the ablation after 2.3 s. The oxidation rate of the material surface gradually increased to a stable value of about 0.2mm/s with increasing temperature, while in the case model no significant gasification denudation rate was shown in the figure because the temperature did not reach the gasification temperature of the carbon. During the whole ablation process, the overall ablation rate rapidly rises from 0 to 1.5s, reaches a peak value of 0.85mm/s around 1.5s, then decreases to around 2.3s and is basically maintained around 0.23mm/s, and the material enters a steady-state ablation stage.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A simulation method for laser ablation full-weaving CFRP under tangential airflow is characterized by comprising the following steps:
the first step is as follows: homogenizing the density, constant-pressure heat capacity and thermal conductivity of the material by adopting a volume averaging method;
the second step is that: establishing a basic control equation of a fluid domain and a porous medium domain, based on a momentum conservation theorem, a mass conservation theorem and an energy conservation theorem, and tracking an interface retreating and ablating process by adopting a moving grid method;
the third step: constructing a compact structure physical model, tracking the change of the fluid speed of the surface of the material in the ablation pit, mapping the change to the surface of the material through a boundary similarity principle, and correcting the change by replacing a flow rate term of an original equation;
the fourth step: deducing and setting the anisotropic thermal conductivity of the material by taking the compact structure as a theoretical basis;
the fifth step: the pressure change of the pyrolysis gas is considered to do work and viscous dissipation, and the pressure change is added to a porous medium energy conservation equation for correction;
and a sixth step: tracking the evolution of the temperature and the pressure of the fluid on the surface of the material in the ablation pit, calculating the distribution of the oxygen concentration by combining an ideal gas equation, and correcting by replacing a constant concentration item of the original equation;
the seventh step: tracking Darcy velocity field evolution of the material surface, and correcting an internal mechanical degradation equation;
eighth step: setting boundary conditions and initial values;
the ninth step: and setting grid moving conditions and moving rates by combining the rate equations derived and calculated, and analyzing the evolution of each ablation contribution in the ablation process through finite element iterative calculation.
2. The simulation method for laser ablation fully woven CFRP under tangential airflow according to claim 1, wherein in the second step, the fluid domain calculation adopts a compressible fluid-conservation form NaviStokes equation:
Figure FDA0003825958570000011
Figure FDA0003825958570000012
Figure FDA0003825958570000013
Figure FDA0003825958570000014
Figure FDA0003825958570000021
Figure FDA0003825958570000022
in the above formula, ρ air In order to be the density of the air,
Figure FDA0003825958570000023
is the air velocity vector, p air Is the air pressure, μ air Is the kinematic viscosity of air, F is the force source term, c P，air Is constant pressure heat capacity of air, lambda air Is emptyThermal conductivity of gas, I is the unit matrix tensor, Q vd For viscous dissipative terms, Q p In order to obtain the work term of the pressure,
Figure FDA0003825958570000024
is a hamiltonian.
3. The method for simulating laser ablation fully woven CFRP under tangential airflow according to claim 2, wherein in the second step, the basic control equation of the porous medium domain combines a modified Fourier equation, a single-step Arrenus equation, a single-phase Darcy's law equation and a Connier-Karman permeability model theory, and is specifically described as follows:
Figure FDA0003825958570000025
Figure FDA0003825958570000026
Figure FDA0003825958570000027
Figure FDA0003825958570000028
Figure FDA0003825958570000029
in the above formula rho eff Is the overall equivalent density of the material, c p，eff Is the overall equivalent specific heat capacity of the material, L P For the latent heat of pyrolysis, ρ g 、ρ p The densities of the pyrolysis gas and the resin respectively,
Figure FDA00038259585700000210
respectively, porosity and resin volume fraction,
Figure FDA00038259585700000211
for the pyrolysis gas darcy velocity vector,
Figure FDA00038259585700000212
for the pyrolytic reaction, the pre-factor, E p In order to activate the energy of the pyrolysis reaction,
Figure FDA00038259585700000213
is the volume fraction of the resin at the end of the reaction,
Figure FDA00038259585700000214
is the initial resin volume fraction, κ is the permeability, p g Darcy pressure, mu, caused by pyrolysis of gases g For pyrolysis of the gas dynamic viscosity, d particle The particle size of the porous medium, R is a constant of the universal gas, T is the temperature of the matrix, T is the calculation time, xi is the mass fraction of the pyrolysis gas, and n is the reaction order.
4. The method for simulating the laser ablation fully woven CFRP under the tangential air flow according to claim 3, wherein in the third step, a mechanical ablation model of a dense structure is constructed, which is described as:
Figure FDA0003825958570000031
Figure FDA0003825958570000032
Figure FDA0003825958570000033
Figure FDA0003825958570000034
Figure FDA0003825958570000035
Figure FDA0003825958570000036
Figure FDA0003825958570000037
Figure FDA0003825958570000038
Figure FDA0003825958570000039
Figure FDA00038259585700000310
in the above formula, v out For external mechanical equivalent ablation rate, D p Is the external mechanical ablation equal rate of the resin matrix, D u For the mechanical degradation rate of the outer radial carbon fibres, D f The mechanical degradation rate of the axial carbon fiber, delta is the ratio of the thickness of the fiber layer to the thickness of the resin layer, rho f 、ρ p Is a constant density of the carbon fiber and the resin,
Figure FDA00038259585700000311
is a pre-exponential factor of the gasification reaction of carbon fibers and resins, E Af 、E Ap Is the activation energy of the gasification reaction of the carbon fibers and the resin,λ f 、λ p is the thermal conductivity of the carbon fibers and the resin, c f 、c p Is the constant pressure heat capacity of the carbon fiber resin,
Figure FDA00038259585700000312
initial strength of the carbon fiber in the axial and radial directions and initial strength of the matrix of the resin, σ f 、σ f⊥ 、σ pT Axial, radial and resin matrix real-time strengths,
Figure FDA0003825958570000041
respectively are the strength change factors of the carbon fiber and the resin matrix,
Figure FDA0003825958570000042
to correct for the temperature-dependent variation of the intensity factor,
Figure FDA0003825958570000043
are real-time volume fractions of carbon fibers, resin and residual carbon respectively,
Figure FDA0003825958570000044
is the initial volume fraction of the resin, T w Is the real-time temperature, T, of the surface of the material 0 Is the initial temperature of the surface of the material, t is the laser action time, P ∑ Pressing head on the surface of the material;
taking into account the change in fluid velocity at the surface of the material within the ablation pit and modifying in place of the flow term of the original equation, wherein the material surface head is described by a material surface flow modification as:
P ∑ ＝ρ air (u airsurface (t)·cos(θ)) 2
wherein u is airsurface (t) is the air flow speed of the material surface evolving along with the ablation pit, and theta is the included angle between the normal speed and the horizontal plane.
5. The simulation method for laser ablation fully woven CFRP under tangential airflow according to claim 4, wherein in the fourth step, the anisotropic thermal conductivity of the solid phase of the fully woven composite material is deduced based on the compact structure, and is described as:
Figure FDA0003825958570000045
Figure FDA0003825958570000046
Figure FDA0003825958570000047
Figure FDA0003825958570000048
Figure FDA0003825958570000049
Figure FDA00038259585700000410
Figure FDA00038259585700000411
Figure FDA0003825958570000051
in the above formula, λ solid Is the solid equivalent thermal conductivity, λ 1 ，λ 2 Is the material surface direction thermal conductivity, lambda 3 The material thickness direction thermal conductivity; lambda [ alpha ] ch Constant thermal conductivity for carbon residue;
Figure FDA0003825958570000052
is the real-time volume fraction of carbon residue,
Figure FDA0003825958570000053
is the initial volume fraction of carbon fibers, A * 、N 1 、N 2 、b * 、s b 、s p η is the ratio of the residual carbon thermal conductivity to the matrix thermal conductivity, which is an intermediate variable.
6. The simulation method for laser ablation fully woven CFRP under tangential airflow according to claim 5, characterized in that in the fifth step, work is done considering the viscous dissipation and pressure variation of the pyrolysis gas, and is added to the energy conservation equation of the solid porous medium for correction, and the description is as follows:
Figure FDA0003825958570000054
Figure FDA0003825958570000055
Figure FDA0003825958570000056
Figure FDA0003825958570000057
in the above formula, λ eff Is an equivalent thermal conductivity matrix, c pg For constant pressure heat capacity, Q, of pyrolysis gas vd ' viscous dissipation, Q, generated by pyrolysis gas flow p ' is the internal pyrolysis gas pressure change doing term, T is the material temperature, and T represents the calculation time.
7. The simulation method for laser ablation fully woven CFRP under tangential airflow according to claim 6, characterized in that, in the sixth step, the evolution of the temperature and pressure of the surface fluid of the material in the ablation pit is considered, the surface chemical reaction of the material is simplified, and the oxidation reaction of carbon is only considered if the oxygen is sufficient; calculating the real-time distribution of the oxygen concentration by combining an ideal gas equation, and correcting by replacing the concentration term of the original equation, wherein the description is as follows:
Figure FDA0003825958570000058
Figure FDA0003825958570000061
in the above formula v oxi For the rate of the oxidation reaction, A oxi Indicating a pro-factor for the oxidation reaction, E oxi Activation energy for oxidation reaction, M i The average molar mass of the surface material participating in the oxidation reaction,
Figure FDA0003825958570000062
to an equivalent surface density participating in the oxidation reaction, p air，surface Is the partial pressure of oxygen on the surface of the material near the ablation pit, T air，surface Is the surface gas temperature, T, of the material near the ablation pit surface Zeta is the correction factor for the material surface temperature.
8. The method for simulating the laser ablation fully woven CFRP under the tangential airflow according to claim 7, wherein in the seventh step, the internal mechanical ablation equation is modified by considering the Darcy velocity field evolution of the material surface, and the modification is described as follows:
Figure FDA0003825958570000063
Figure FDA0003825958570000064
in the above formula v int For the rate of internal mechanical degradation,
Figure FDA0003825958570000065
is a pre-factor of the resin pyrolysis reaction, c p Is the constant pressure heat capacity of the resin, K is the permeability,. L 0 Is the pore size, σ pT As resin strength, E P Activation energy for resin pyrolysis reaction, T surface Is the surface temperature, σ, of the material compsite，T Is the strength of the composite material, phi is a correction term, chi is a correction coefficient, u is the Darcy speed of the surface of the material, and u is max Is the Darcy velocity peak constant of the material surface, and omega is a constant.
9. The simulation method of the laser ablation fully woven carbon fiber reinforced epoxy resin composite material under the tangential airflow according to claim 8, wherein in the eighth step, the conservation of energy of the fluid-solid interface is described as:
Figure FDA0003825958570000066
in the above formula, λ eff The equivalent thermal conductivity of the whole material is obtained,
Figure FDA0003825958570000067
alpha is the absorption coefficient of the material to laser, I Laser Is a power density distribution,. Epsilon.is an emissivity coefficient,. Sigma.is a Stefan-Boltzmann constant, T surface Is the surface temperature, T, of the material e Is at the temperature of the surroundings and is,
Figure FDA0003825958570000071
is the equivalent density of the material surface participating in oxidation and sublimation, L oxi For latent heat of oxidation, L sub To the latent heat of sublimation, v oxi To the rate of oxidation, v sub Is the sublimation rate.
10. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the steps of the method according to any of claims 1 to 9 are implemented by the processor when executing the computer program.
CN202211058515.8A 2022-08-31 2022-08-31 Simulation method for laser ablation full-weaving CFRP under tangential airflow Pending CN115440325A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116305765A (en) * 2022-12-29 2023-06-23 中国航天三江集团有限公司 Simulation method and system for high-energy laser irradiation resin-based fiber reinforced composite material
CN117148900A (en) * 2023-10-27 2023-12-01 济南泰格电子技术有限公司 Environment safety management method and device for archive

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116305765A (en) * 2022-12-29 2023-06-23 中国航天三江集团有限公司 Simulation method and system for high-energy laser irradiation resin-based fiber reinforced composite material
CN117148900A (en) * 2023-10-27 2023-12-01 济南泰格电子技术有限公司 Environment safety management method and device for archive
CN117148900B (en) * 2023-10-27 2024-02-02 济南泰格电子技术有限公司 Environment safety management method and device for archive

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