Finite element simulation method for pulsed laser ablation of carbon / carbon composites

Abstract

The application is a kind of finite element simulation method of pulsed laser ablation of carbon / carbon composite material, which belongs to the field of special processing of composite materials and relates to a kind of finite element simulation method of pulsed laser ablation of carbon / carbon composite material. The method is based on ANSYS APDL software to establish a three-dimensional heterogeneous geometric model of carbon / carbon composite material, define two kinds of material parameters and give them to the matrix and the fiber respectively, divide the model grid and set the solver and the boundary conditions. The laser heat flux density load is applied for transient thermal analysis solution, the matrix and fiber elements exceeding their respective sublimation temperature are removed respectively by using the birth and death element technology, the heat accumulation between adjacent pulses is considered, the laser loading on the exposed irregular surface is completed by combining the restart method and the APDL command stream. The timely removal of the material under the action of the laser is realized, and the ablation morphology and temperature distribution of the carbon / carbon composite material are obtained. The method effectively reduces the trial and error experiment and reduces the experimental cost, and has important reference significance for the laser precision manufacturing of carbon / carbon composite material grid.

Description

Technical Field

[0001] This invention belongs to the field of special processing of composite materials and relates to a finite element simulation method for pulsed laser ablation of carbon / carbon composite materials. Background Technology

[0002] Ion thrusters are core components enabling spacecraft to perform attitude control and orbital maneuvers in microgravity space. Their working principle involves using electrical energy to ionize the propellant, which is then extracted, focused, and accelerated by a grid assembly to generate thrust. They are characterized by low thrust, high specific impulse, and long lifespan. With increasingly stringent performance requirements for ion thrusters, the need for grid assemblies to possess better thermal stability and sputtering resistance under high beam density and high specific impulse is becoming increasingly urgent. Carbon / carbon composite materials possess excellent characteristics such as low density, high mechanical strength, low coefficient of thermal expansion, and low ion sputtering rate, making them an ideal grid material. However, carbon / carbon composite materials are characterized by high hardness, brittleness, and anisotropy, making them typical difficult-to-machine materials. Laser processing technology, due to its non-contact processing, applicability to various difficult-to-machine materials, and high flexibility, is an effective means of precision manufacturing for such carbon / carbon composite grids.

[0003] Carbon / carbon composite materials used in spacecraft applications are often of extremely high value. Using finite element method (FEM) simulations for laser processing can reduce trial-and-error experiments and save significant human and material resources. Furthermore, many unknown factors in the laser ablation mechanism of carbon / carbon composite materials remain unresolved. Relying solely on experimental and testing equipment cannot accurately grasp the morphological evolution and temperature changes within the material during laser processing. Therefore, finite element simulation of the thermophysical changes during processing is an effective means to solve this problem. Research on the laser processing mechanism of carbon / carbon composite materials using the finite element method is of significant value. Existing technical literature 1, Zhai Zhaoyang et al.'s patent publication number CN116108714A, "Simulation Modeling Method for Laser Ablation of Fiber-Reinforced Composite Materials," establishes a three-dimensional complex temperature field model based on the actual SiC / SiC dimensions. By changing the position of the laser spot, the changing law of the temperature field characteristics corresponding to laser ablation of SiC / SiC is obtained. However, it does not consider the timely removal of material during laser action, resulting in unclear morphology of the laser-ablated material. Technical document 2, "A numerical simulation method for pulsed laser paint removal and its application", by Zhou Jianzhong et al., patent publication number CN112149321A, utilizes a special curved surface mesh screening method to achieve load loading on arbitrary curved surfaces, ensuring that the laser energy distribution on the material surface conforms to reality. Combined with the birth and death element technology, it removes elements exceeding the threshold and intuitively presents the surface morphology after laser paint removal. However, it does not consider the heat accumulation between adjacent pulses. Summary of the Invention

[0004] The purpose of this invention is to develop a finite element simulation method for pulsed laser ablation of carbon / carbon composite materials. This method establishes a three-dimensional heterogeneous geometric model of the carbon / carbon composite material using ANSYS APDL software. Two material parameters are defined and assigned to the matrix and fibers respectively. The model is meshed, and solvers and boundary conditions are set. A laser heat flux load is applied for transient thermal analysis. The birth and death element technique is used to remove matrix and fiber elements exceeding their respective sublimation temperatures. Considering the heat accumulation between adjacent pulses, a restart method and APDL command flow are combined to load the laser onto the exposed irregular surface, achieving timely removal of material as the laser interacts, thus obtaining the ablation morphology and temperature distribution of the carbon / carbon composite material. This method can effectively reduce trial-and-error experiments and lower experimental costs, providing a basis for studying the mechanism of laser processing of carbon / carbon composite materials and optimizing the precision manufacturing process parameters of carbon / carbon composite gates.

[0005] The technical solution adopted in this invention is a finite element simulation method for pulsed laser ablation of carbon / carbon composite materials. This method establishes a three-dimensional heterogeneous geometric model of the carbon / carbon composite material based on ANSYS APDL software. Two material parameters are defined and assigned to the matrix and fibers respectively. The model is meshed, and solvers and boundary conditions are set. A laser heat flux density load is applied for transient thermal analysis. The birth and death element technique is used to remove matrix and fiber elements exceeding their respective sublimation temperatures. Considering the heat accumulation between adjacent pulses, the laser loading on the exposed irregular surface is completed by combining the restart method and APDL command flow, achieving timely removal of material as the laser acts, and obtaining the ablation morphology and temperature distribution of the carbon / carbon composite material. The specific steps of the method are as follows:

[0006] Step 1: Establish a three-dimensional heterogeneous geometric model of the matrix and fiber in the finite element software ANSYS APDL, and use APDL commands to achieve bonding of the two materials. The matrix is ​​isotropic while the fiber is anisotropic, and three different thermal conductivity coefficients K are introduced. x K y K z K x K y K represents the radial thermal conductivity. z Represents the axial thermal conductivity, and two material parameters are set for the matrix and fiber respectively.

[0007] Step 2: Mesh the model using hexahedral eight-node Solid70 heat transfer elements, apply a transient nonlinear heat conduction solver and configure restart settings, set the initial temperature of all nodes to room temperature, and define the non-laser-affected material surfaces as air convection boundaries. The convection heat transfer formula is as follows:

[0008] q c =-h(T0-T) (1)

[0009] In the formula, q c Let be the heat flux density between the material and the air, h be the convective heat transfer coefficient, T0 be the room temperature, and T be the temperature of a node in the material.

[0010] Step 3: Use a laser heat source with Gaussian distribution characteristics, the expression of which is:

[0011]

[0012] Where, q laser Let be the laser heat flux density, f be the material's absorptivity to the laser, P be the laser power, x0, y0, and z0 be the coordinates of the laser heat source center in the Cartesian coordinate system, and r0 be the laser spot radius. The laser heat source equation is exported as a heat source command stream using the function editor in APDL and loaded onto the material surface nodes in the form of heat flux density.

[0013] Enter the solver module to perform transient thermal analysis. The heat conduction process follows Fourier's law:

[0014]

[0015] In the formula, q i Where K is the heat flux density and K is the thermal conductivity of the material. Let be the temperature gradient along the outer normal direction of the boundary. Based on the law of conservation of energy and Fourier's law, we further construct the three-dimensional nonlinear transient heat transfer thermal balance equation for anisotropic materials during laser processing:

[0016]

[0017] In the formula, ρ is the material density, C is the specific heat capacity, and T is the temperature value of a point (x,y,z) in the model at time t. Laser processing also involves phase transitions, and ANSYS defines the latent heat of phase transition in the material enthalpy:

[0018]

[0019] In the formula, ΔH is the enthalpy of the material. The post-processing module obtains the element temperature information, and then the solution module uses the element birth and death technique to kill matrix and fiber elements that exceed their respective sublimation temperatures. The element birth and death technique involves changing the stiffness matrix of an element when its temperature exceeds its sublimation temperature, rendering the element inactive in the model, similar to a "killing" effect, thus achieving the effect of laser ablation to remove the material.

[0020] Step 4: To simulate the actual processing phenomenon of laser action on exposed irregular surfaces during the interaction between laser and material, it is necessary to repeatedly repeat the process from Step 3: entering the solution module for heat conduction calculation, entering the post-processing module to obtain unit temperature information, and then entering the solution module again to kill the unit. However, re-entering the solution module will cause the loss of residual temperature inside the material after laser action. Considering the residual temperature between adjacent solution modules, a restart method is used to realize the process of laser loading on irregular surfaces during material removal.

[0021] Specifically, the solution information of the last load substep of the previous loading is saved in a specific file, and the solution is specified as a restart analysis during the next loading. The solution information file saved from the previous loading is read, and a very short time step is solved to approximate the starting point of the restart analysis. At this time, the model can be regarded as the state after the last subload step of the previous loading has been solved, the element temperature inside the material has been preserved, and some elements that have exceeded the sublimation temperature have been killed.

[0022] Next, delete the previously applied heat source load and apply the next heat source load to the exposed irregular surface inside the model. Use the selection set command "EXT" to obtain all outer surface nodes of the currently surviving elements, and exclude nodes on surfaces with air convection to obtain the node set of the laser irradiated area. Apply laser heat flux density to achieve load application on the irregular surface as material is removed. Repeat step three to obtain element temperature information and kill elements until the solution time step reaches the pulse width of a single pulse.

[0023] Step 5: Solving for multi-pulse restart

[0024] Pulsed laser in one emission cycle t period Within, the pulse duration is t on The pulse interval time is t off Consider solving for t using a single pulse. on After t off The transfer of internal heat is similarly addressed using the restart method, continuing the solution for a period of time t after the laser load is removed. off Complete one light emission cycle t period The ablation process is solved by repeating the solution for multiple pulse output cycles until the number of pulses reaches the preset requirement, thereby realizing the finite element simulation of multi-pulse laser ablation of carbon / carbon composite materials and obtaining the ablation morphology and temperature distribution of carbon / carbon composite materials.

[0025] The significant effects and benefits of this invention are that it utilizes a laser loading method on irregular surfaces to achieve real-time material removal via laser ablation. Furthermore, it considers the heat accumulation between adjacent pulses in multi-pulse processing, combining a restart method and APDL command streams to complete the laser loading on exposed irregular surfaces, thus achieving timely material removal during laser action. This method is highly versatile, computationally simple, effectively reduces trial-and-error experiments, lowers experimental costs, and can simulate the temperature distribution and ablation morphology during laser processing of carbon / carbon composite materials. It provides a basis for studying the mechanism of laser processing of carbon / carbon composite materials and has important reference value for the laser precision manufacturing of carbon / carbon composite material gates. Attached Figure Description

[0026] Figure 1 This is a flowchart of a finite element simulation method for pulsed laser ablation of carbon / carbon composite materials.

[0027] Figure 2 a) is a three-dimensional geometric model of carbon / carbon composite materials. Figure 2 b) is a mesh generation model, using hexahedral mesh elements.

[0028] Figure 3 This is a laser heat source model with Gaussian distribution characteristics. The X and Y axes represent the position of the pulse spot, respectively, and the Z axis represents the pulsed laser heat flux density. The peak laser heat flux density is 2.538 × 10⁻⁶. 11 W / m 2 .

[0029] Figure 4 The image shows the residual temperature results after restarting the model. Residual temperatures exist on the ablated surface, reaching a maximum of 3000.9K.

[0030] Figure 5 a) The image shows the irregular surface exposed as the material is removed. Figure 5 b) The figure shows the simulated ablation profile of the cross section when a laser load is applied to an irregular surface.

[0031] Figure 6 This is a schematic diagram of multi-pulse laser output, t period For the light output period, t on t is the pulse duration. off This is the pulse interval time.

[0032] Figure 7 Figure a) shows the overall view of the ablation morphology and temperature distribution of the carbon / carbon composite material; Figure b) shows the simulated ablation cross-section profile under laser load; Figure c) shows the experimental ablation cross-section profile. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0034] Appendix Figure 1 This is a flowchart of a finite element simulation method for pulsed laser ablation of carbon / carbon composite materials. The method establishes a three-dimensional heterogeneous geometric model of the carbon / carbon composite material using ANSYS APDL software. Two material parameters are defined and assigned to the matrix and fibers respectively. The model is meshed, and solvers and boundary conditions are set. A laser heat flux load is applied for transient thermal analysis. The birth and death element technique is used to remove matrix and fiber elements exceeding their respective sublimation temperatures. Considering the heat accumulation between adjacent pulses, a restart method and APDL command flow are combined to load the laser onto the exposed irregular surface, achieving timely removal of material as the laser interacts, thus obtaining the ablation morphology and temperature distribution of the carbon / carbon composite material.

[0035] Taking the millisecond pulsed laser ablation of carbon / carbon composite materials with a spot radius of 36.8 μm and a peak laser power of 150 W as an example, the simulation process of this method is explained in detail. The specific steps of the method are as follows:

[0036] Step 1: Establish a geometric model of the carbon / carbon composite material, adding parameters for both the matrix and fiber materials.

[0037] A three-dimensional heterogeneous geometric model was created in the finite element software ANSYS APDL, comprising a matrix phase of carbon and a reinforcing phase of carbon fibers. The overall model dimensions are 120 μm × 115.4 μm × 144 μm (length × width × height), and it contains a total of 320 fibers. Each carbon fiber has a diameter of 7 μm, with a center-to-center spacing of 7.2 μm. The fibers are evenly distributed within the model, and the remaining portion is filled with a carbon matrix. Figure 2 As shown in a), heat conduction occurs between the matrix and the fiber during processing. The APDL command is used to bond the two materials together to achieve load transfer between the different materials. Figure 2 b) is the mesh generation model, with hexahedral mesh elements of 2μm×2μm×2μm in size, containing a total of 338,340 mesh elements.

[0038] In carbon / carbon composites, the carbon matrix is ​​isotropic while the carbon fibers are anisotropic. For laser ablation analysis, this is specifically reflected in the fact that the axial thermal conductivity of the carbon fibers is greater than their radial thermal conductivity. We introduce thermal conductivity K in three different directions. x K y K z K x K y The radial thermal conductivity is represented by 0.96 W / (m·K), K. zThis represents the axial thermal conductivity, taken as 9.6 W / (m·K).

[0039] Other material parameters of carbon matrix and carbon fiber include density, specific heat, and sublimation temperature, as shown in Table 1.

[0040] Table 1. Thermophysical parameters of carbon fiber and carbon matrix

[0041]

[0042] Step 2: Mesh the entire model and set the solver and boundary conditions.

[0043] Solid70 elements were selected for mesh generation. This type of element is a hexahedral eight-node heat transfer element, with each node possessing one degree of temperature freedom, suitable for three-dimensional transient thermal analysis. To ensure the accuracy of the simulation results, the mesh element size was set to 2μm × 2μm × 2μm. The meshed model is shown below. Figure 2 As shown in b), the model contains a total of 338,340 grid cells.

[0044] Laser ablation is a transient nonlinear heat conduction process involving phase transition. A preconditioned conjugate gradient method solver was selected, and the complete Newton-Raphson method was used to solve the nonlinear equations. Automatic time stepping was enabled to obtain efficient solutions with fewer resources. The transient integration constant was set to 1 to employ the backward Euler difference method. Linear search was enabled to accelerate the solution of the phase transition problem, and the load step was specified as a step loading mode. The initial temperature condition for all nodes was set to room temperature (293 K). The non-laser-affected material surface was set as an air convection boundary, and the convection heat transfer coefficient h was set to 10 W / (m²). 2 ·K), from equation (1), the heat flux density of convective heat transfer can be obtained as:

[0045] q c = -10 × (293 - T)

[0046] Step 3: Apply Gaussian laser heat flux density load and solve.

[0047] The material's absorptivity f to laser light is set to 0.8, the peak laser power P is set to 150W, and the laser spot radius r0 is set to 36.8μm. A laser heat source with Gaussian distribution characteristics is used, such as... Figure 3 As shown, the X and Y axes represent the positions of the pulsed laser spot, respectively, and the Z axis represents the pulsed laser heat flux density. The peak laser heat flux density is 2.538 × 10⁻⁶. 11 W / m 2 From equation (2), the expression for the laser heat source can be obtained as follows:

[0048]

[0049] The laser heat source expression is defined through the function editor, saved, and then read and exported as an APDL command stream. This stream is then applied to the material surface nodes in the form of heat flux density to complete the loading of the laser heat source.

[0050] Entering the solution module, the laser processing of the carbon / carbon composite material is simulated, and its heat conduction process follows Fourier's law:

[0051]

[0052] Based on the law of conservation of energy and Fourier's law, a three-dimensional nonlinear transient heat transfer thermal balance equation for anisotropic materials during laser processing is further constructed:

[0053]

[0054] Laser processing of carbon / carbon composites primarily involves sublimation removal, which raises the issue of phase transitions. Phase transition analysis must consider latent heat. ANSYS defines the latent heat of phase transition within the material's enthalpy, i.e.:

[0055]

[0056] Upon entering the post-processing module, the unit temperature information is acquired. Information on carbon matrix units with temperatures exceeding the matrix phase sublimation temperature of 3373 K and carbon fiber units with temperatures exceeding the fiber phase sublimation temperature of 4273 K are stored in arrays to prevent information loss when re-entering the solution module. Upon re-entering the solution module, the previously stored units with temperatures exceeding the sublimation temperature are eliminated using the dead / birth element technique, achieving material removal through laser ablation.

[0057] Step 4: Solving for Single-Pulse Restart

[0058] To achieve real-time material ablation and the effect of laser action on the exposed irregular surface as the material is removed, it is necessary to repeatedly repeat step three: entering the solution module for heat conduction calculation, entering the post-processing module to obtain the unit temperature information, and then entering the solution module again to kill the unit. However, when re-entering the solution module, the calculation data from the previous solution is overwritten, resulting in the loss of residual temperature inside the material after laser action. Considering the residual temperature between adjacent solution modules, a restart method is used to realize the process of loading the laser onto the irregular surface as the material is removed.

[0059] After the previous load and solution were completed, the solution information for the last load step was saved in the restart file. The next load was specified as a restart analysis, the solution information file saved from the previous load was read, and a very short time step was solved to approximate the starting point of the restart analysis. In this example, the laser pulse width is in the millisecond range; therefore, a nanosecond time step was then restarted. At this point, the model can be considered to be in the state after the last load step of the previous load was solved, preserving the element temperature inside the material and eliminating some elements exceeding the sublimation temperature. Figure 4 As shown, residual temperatures exist on the ablated surface, reaching a maximum of 3000.9K.

[0060] The previously applied heat flux density load is deleted, and the next heat flux density load is applied to the exposed irregular surfaces inside the model. To obtain the nodes on these irregular surface elements, the selection set command "EXT" is used to obtain all outer surface nodes of the currently surviving elements, excluding nodes on air convection surfaces to obtain the node set of the laser irradiated area. Laser heat flux density is applied to the element nodes in the irradiated area, achieving load loading on the irregular surface as material is removed, ensuring that the laser energy distribution on the material surface matches the actual situation, such as... Figure 5 As shown, Figure 5 a) shows the irregular surface exposed as material is removed, and b) shows a schematic diagram of applying a laser load to the irregular surface. The initial laser load moves downward as material is removed, and the peak laser heat flux density is 2.538 × 10⁻⁶. 11 W / m 2 Repeat step three to obtain the unit temperature information and kill the unit, with a pulse width of 0.1ms, until the solution time step reaches the pulse width of a single pulse of 0.1ms, thus completing the solution of single-pulse laser ablation.

[0061] Step 5: Solving for multi-pulse restart

[0062] According to the principle of pulsed lasers, one light output period t period Within, the pulse duration is t on The pulse interval time is t off ,like Figure 6 As shown. The millisecond pulse laser emission period t used in this embodiment. period The pulse width is 1ms, which is the pulse duration t. on The pulse interval time is 0.1ms. off The time is 0.9ms. Consider solving for t using a single pulse. on =0.1ms later t off =The heat transfer within 0.9ms, and the resulting surface after a single pulse is also irregular, similarly using the restart method, we continue to solve for a pulse interval t after the laser load is removed.off =0.9ms, completing the laser ablation of carbon / carbon composite materials within one light output cycle. The preset pulse count is 3 pulses, and the solution is repeated for multiple pulse output cycles until the pulse count reaches 3, realizing the finite element simulation of multi-pulse laser ablation of carbon / carbon composite materials, obtaining the ablation morphology and temperature distribution of the carbon / carbon composite materials, such as... Figure 7 As shown. Figure 7 Figure a) shows the overall view of the ablation morphology and temperature distribution of the carbon / carbon composite material; figure b) shows the simulated ablation cross-section profile under laser load; and figure c) shows the experimental ablation cross-section profile. The measured cross-sectional morphology and the simulated and experimental ablation depths are 100.978 μm and 101.961 μm, respectively, showing a high degree of agreement between the simulated and experimental ablation morphologies.

[0063] This invention utilizes a laser load method on irregular surfaces to achieve real-time material removal via laser ablation, while also considering the heat accumulation between adjacent pulses in multi-pulse processing. This method is characterized by its versatility and simple calculation process, enabling the simulation of temperature distribution and ablation morphology during laser processing of carbon / carbon composite materials. It provides a basis for studying the mechanism of laser processing of carbon / carbon composite materials and has significant reference value for the laser precision manufacturing of carbon / carbon composite material gates.

Claims

1. A finite element simulation method for pulsed laser ablation of carbon / carbon composite materials, characterized in that, This method establishes a three-dimensional heterogeneous geometric model of carbon / carbon composite material based on ANSYS APDL software. Two material parameters are defined and assigned to the matrix and fiber respectively. The model is meshed, and solvers and boundary conditions are set. A laser heat flux load is applied for transient thermal analysis. The birth and death element technique is used to remove matrix and fiber elements exceeding their respective sublimation temperatures. Considering the heat accumulation between adjacent pulses, a restart method and APDL command flow are combined to complete the laser loading on the exposed irregular surface, achieving timely material removal as the laser interacts. This yields the ablation morphology and temperature distribution of the carbon / carbon composite material. The specific steps of the method are as follows: Step 1: Establish a three-dimensional heterogeneous geometric model of the matrix and fiber in the finite element software ANSYS APDL, and use APDL commands to achieve the bonding of the two materials; the matrix is ​​isotropic while the fiber is anisotropic, and thermal conductivity K in three different directions is introduced. x K y K z K x K y K represents the radial thermal conductivity. z Representing the axial thermal conductivity, two material parameters are assigned to the matrix and fiber respectively; Step 2: Mesh the model using hexahedral eight-node Solid 70 heat transfer elements, apply a transient nonlinear heat conduction solver and configure restart settings, set the initial temperature of all nodes to room temperature, and define the non-laser-affected material surfaces as air convection boundaries. The convection heat transfer formula is as follows: q c =-h(T0-T) (1) In the formula, q c Let be the heat flux density exchanged between the material and the air, h be the convective heat transfer coefficient, T0 be the room temperature, and T be the temperature of a node in the material. Step 3: Use a laser heat source with Gaussian distribution characteristics, the expression of which is: Where, q laser Let f be the laser heat flux density, p be the material's absorption rate of the laser, y be the laser power, x0, y0, z0 be the coordinates of the laser heat source center in the Cartesian coordinate system, and r0 be the laser spot radius. The laser heat source equation is exported as a heat source command stream using the function editor in APDL and loaded onto the material surface nodes in the form of heat flux density. Enter the solver module to perform transient thermal analysis. The heat conduction process follows Fourier's law: In the formula, q i Where K is the heat flux density and K is the thermal conductivity of the material. The temperature gradient is defined along the direction of the outer normal to the boundary. Based on the law of conservation of energy and Fourier's law, a three-dimensional nonlinear transient heat transfer equilibrium equation for anisotropic materials during laser processing is further constructed: In the formula, ρ is the material density, C is the specific heat capacity, and T is the temperature value of a point (x,y,z) in the model at time t; laser processing also involves phase transition problems, and ANSYS defines the latent heat of phase transition in the material enthalpy: In the formula, ΔH is the enthalpy of the material; the post-processing module obtains the unit temperature information, and then the solution module uses the birth and death element technique to kill the matrix elements and fiber elements that exceed their respective sublimation temperatures. Step 4: To simulate the actual processing phenomenon of laser action on exposed irregular surfaces during the interaction between laser and material, it is necessary to repeatedly repeat the process in Step 3, which involves entering the solution module for heat conduction calculation, entering the post-processing module to obtain unit temperature information, and then entering the solution module to kill the unit. However, re-entering the solution module will cause the loss of residual temperature inside the material after laser action. Considering the residual temperature between adjacent solution modules, a restart method is used to realize the process of laser loading on irregular surfaces during material removal. The solution information of the last load substep of the previous loading is saved in a specific file. When loading again, the solution is specified as a restart analysis. The solution information file saved in the previous loading is read and a very short time step is solved to approximate the starting point of the restart analysis. At this time, the model can be regarded as the state after the last load substep of the previous loading is solved. The element temperature inside the material is preserved and some elements that exceed the sublimation temperature have been killed. Furthermore, the previously applied heat source load is deleted, and the next heat source load is applied to the irregular surface exposed inside the model; the selection set command "EXT" is used to obtain all the outer surface nodes of the currently surviving elements, and the nodes of the air convection surface are excluded to obtain the node set of the laser irradiation area. The laser heat flux density is applied to realize the load application on the irregular surface as the material is removed; the process of obtaining the element temperature information and killing the element in step three is repeated until the solution time step reaches the pulse width of a single pulse; Step 5: Solving for multi-pulse restart Pulsed laser in one emission cycle t period Within, the pulse duration is t on The pulse interval time is t off Consider solving for t using a single pulse. on After t off The transfer of internal heat is similarly addressed using the restart method, continuing the solution for a period of time t after the laser load is removed. off Complete one light emission cycle t period The ablation solution is obtained by repeating multiple pulse output cycles until the number of pulses reaches the preset requirement, thereby realizing the finite element simulation of laser multi-pulse ablation of carbon / carbon composite materials and obtaining the ablation morphology and temperature distribution of carbon / carbon composite materials.

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