Micro-macro cross-scale temperature field simulation method for laser connection of metal and composite material

Abstract

The invention discloses a micro-macro cross-scale temperature field simulation method for laser connection of metal and a composite material. The micro-macro cross-scale temperature field simulation method comprises the following steps that a micro finite element model of the composite material is obtained; performing steady-state heat transfer calculation based on the mesoscopic finite element model of the composite material to obtain heat conductivity of different layers in the composite material; carrying out material attribute setting on the metal and composite material, and carrying out macroscale modeling to obtain a macroscopic model of the lapped metal and composite material; and performing simulated laser connection on the joint part of the macroscopic model, and performing instantaneous heat transfer calculation in the simulated laser connection process so as to generate transient temperature fields at different moments in real time. According to the method, the microscomic-macroscopic cross-scale temperature field simulation method from the CFRTP microscomic representative volume unit to the macroscopic three-dimensional model is established, the complexity of the microscomic and macroscopic models can be greatly reduced, and meanwhile, the accuracy of the temperature field simulation result in the laser connection process of the metal and the composite material is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of laser processing, and in particular is a fine-macro cross-scale temperature field simulation method for laser connection of metal and composite materials. Background Art

[0002] Laser connection has the advantages of non-contact processing, controllable energy, and high efficiency. It is an important direction for high-quality and efficient manufacturing of metal / CFRTP (Carbonfiber reinforced thermoplastics) components. When laser connecting CFRTP and metal, the laser energy is transferred to the lower CFRTP through the upper metal layer, melting the middle layer or thermoplastic substrate and solidifying it to achieve the connection between CFRTP and metal. However, due to the large difference in the physical and chemical properties of CFRTP and metal, the bonding mechanism between the two needs further in-depth research to more effectively improve the bonding strength. Therefore, simulation methods are usually used to reduce research and experimental costs.

[0003] However, the huge difference in physical and chemical properties between the two types of materials and the anisotropy of CFRTP itself have posed challenges to the computational cost and simulation accuracy of simulation. At present, metals are regarded as isotropic materials in simulation, and CFRTP uses an alternating resin-carbon fiber stacking method to reflect its anisotropy (where the resin layer and the carbon fiber layer are regarded as isotropic materials respectively). However, during the laser connection process, the laser energy is highly unevenly distributed, and the carbon fiber with excellent heat transfer performance in CFRTP will make the heat conduction process between metal and CFRTP more complicated, and the anisotropy caused by the carbon fiber distribution on the joint cannot be ignored.

[0004] Therefore, the current simulation method that regards CFRTP as an isotropic material cannot be applied to the temperature field simulation of laser joining of metal and CFRTP. Summary of the invention

[0005] To solve the above problems, the present invention proposes a fine-macro cross-scale temperature field simulation method for laser joining of metals and composite materials, which establishes a fine-macro cross-scale temperature field simulation method from the CFRTP micro-representative volume unit to the macroscopic three-dimensional model, which can greatly reduce the complexity of the micro- and macro-models, and at the same time improve the accuracy of the temperature field simulation results during the laser joining process of metals and composite materials.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for simulating fine-macro cross-scale temperature fields for laser joining of metal and composite materials, comprising the following steps:

[0008] Perform mesoscale modeling to obtain mesoscopic finite element models of composite materials;

[0009] Steady-state heat transfer calculations based on the mesoscopic finite element model of the composite material are performed to obtain the thermal conductivity of different layers in the composite material;

[0010] Setting material properties for metals and composite materials, and performing macro-scale modeling to obtain macro models of overlapped metals and composite materials, wherein the material properties of the composite materials include thermal conductivity of different layers in the composite materials;

[0011] The joint part of the macro model is simulated by laser connection, and transient heat transfer calculation is performed during the simulated laser connection process to generate transient temperature fields at different times in real time.

[0012] Preferably, the composite material comprises CFRTP.

[0013] Preferably, mesoscale modeling is performed to obtain a mesoscale finite element model of the composite material, comprising the following steps:

[0014] Obtain CFRTP cross-sectional characteristic information;

[0015] Determine a representative volume unit based on the CFRTP cross-sectional characteristic information and determine the key parameters of the representative volume unit to establish a mesoscopic RVE model of CFRTP;

[0016] Parameterize material properties;

[0017] The mesoscopic RVE model is meshed to obtain a mesoscopic finite element model.

[0018] Preferably, in the macroscopic three-dimensional geometric model obtained by macro-scale modeling, the orientation of the carbon fibers at the joint lap interface is perpendicular to the laser connection direction, or the orientation of the carbon fibers at the joint lap surface is the same as the laser connection direction.

[0019] Preferably, a steady-state heat transfer calculation is performed based on a mesoscopic finite element model of the composite material to obtain the thermal conductivity of different layers in the composite material, comprising the following steps:

[0020] Under steady-state conditions, the temperature boundary conditions of the three paired surfaces, twelve edges and eight vertices of the microscopic finite element model all satisfy the periodic boundary conditions;

[0021] The temperature distribution in the microscopic finite element model is obtained through the temperature boundary condition, and the thermal conductivity of the microscopic finite element model in the x-axis, y-axis, and z-axis directions is obtained according to the following formulas:

[0022]

[0023] Among them, q i, k i and are heat flux, thermal conductivity and temperature gradient respectively, and ΔT is the average temperature difference of the corresponding nodes on the two surfaces perpendicular to the i direction in the microscopic finite element model; L i is the length of the microscopic finite element model in the i direction.

[0024] Preferably, when performing steady-state heat transfer calculations, the upper surface of the microscopic finite element model in the height direction is determined as the hot surface, the lower surface is determined as the cold surface, and the rest are determined as insulating surfaces.

[0025] Preferably, in the macroscopic three-dimensional geometric model obtained by macroscopic scale modeling, the overlapping parts of the metal and composite materials are divided into non-uniform grids, so that in the length direction, the grid changes from small to large along the direction away from the laser connection position, and in the height direction, the grid changes from small to large along the direction away from the overlapping surface.

[0026] Preferably, the joint part of the macro model is simulated by laser connection, and transient heat transfer calculation is performed during the simulated laser connection process to generate transient temperatures at different times in real time, including the following steps:

[0027] A double-cone composite heat source consisting of two three-dimensional cone heat sources is used as a simulated laser source;

[0028] Set the initial temperature and boundary conditions for transient heat transfer calculations in the macro model;

[0029] The simulated laser source is loaded so that the heat source model acts on the macro model of the joint and moves along the preset laser connection path. After the movement is completed, the effect of the simulated laser source on the joint part is released to simulate the cooling process after the laser connection is completed, so as to complete the entire process of simulated laser connection of the joint part. During the entire process of simulated laser connection, the transient temperature field at different times is generated in real time according to the initial temperature and boundary conditions calculated by the transient heat transfer of the macro model.

[0030] Preferably, the double cone composite heat source is described by the following formula:

[0031]

[0032] Where P is the laser power, η is the energy utilization rate, Q D is the effective laser heat input, α 1 , α 2 are the energy regulation factors of the upper cone heat source and the lower cone heat source respectively; t 、z i 、z b 、r t 、r i 、rb are the shape parameters of the double-cone composite heat source, which are the z coordinate of the upper surface of the upper cone heat source, the z coordinate of the lower surface of the upper cone heat source / the upper surface of the lower cone heat source, the z coordinate of the lower surface of the lower cone heat source, the upper surface radius of the upper cone heat source, the lower surface radius of the upper cone heat source / the upper surface radius of the lower cone heat source, and the lower surface radius of the lower cone heat source; q D1 ,q D2 are the heat flux densities of the upper cone heat source and the lower cone heat source respectively; q D is the total heat flux density of the double-cone composite heat source; Q D1 and Q D2 are the effective laser heat inputs of the upper cone heat source and the lower cone heat source, respectively;

[0033] And r 1 、r 2 Obtained by the following formula:

[0034]

[0035] Q D1 , Q D2 Obtained by the following formula:

[0036]

[0037]

[0038] Preferably, the boundary condition expression is as follows:

[0039]

[0040] Where T is the initial temperature, h c is the equivalent heat transfer coefficient.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention establishes a fine-macro cross-scale temperature field simulation method from a CFRTP meso-representative volume unit to a macroscopic three-dimensional model. The method predicts and calculates the material properties of the macroscopic three-dimensional model scale through a meso-scale RVE model, connects the fine-macro model into a whole, and during the simulation calculation, only the material properties of the meso-scale need to be set, so that the anisotropic characteristics caused by the distribution of fibers and resins in CFRTP can be considered in the macroscopic simulation, thereby greatly reducing the complexity of the meso- and macroscopic models, and expressing the anisotropy of CFRTP at the meso-scale in the macroscopic simulation, thereby improving the accuracy of the temperature field simulation results during the laser connection of metals and composite materials, especially improving the temperature simulation accuracy at the overlapping interface that has the greatest impact on the connection performance of different types of joints. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a flow chart of the steps of the micro-macro cross-scale temperature field simulation method of the present invention;

[0044] Figure 2 Schematic diagram of the model of CFRTP material at different scales;

[0045] Figure 3 It is a schematic diagram of the constant heat surface, cold surface and adiabatic surface of the RVE model when performing steady-state heat transfer calculation in the present invention;

[0046] Figure 4 is the temperature distribution in the RVE model of the present invention;

[0047] Figure 5 It is a schematic diagram of components when solving ΔT in the temperature gradient equation in the present invention;

[0048] Figure 6 It is a macroscopic model of the overlapped metal and composite materials in the present invention;

[0049] Figure 7 It is a cross-section and grid schematic diagram of a macro model of overlapped metal and composite materials in the present invention;

[0050] Figure 8 Schematic diagram of the double cone composite heat source in the present invention;

[0051] Fig. 9 In the present invention, when simulating laser connection, the transient temperature field at 0.1s, 1s, 2s, and 15000s;

[0052] Fig.10 The weld morphology obtained after the real laser connection of joint A and joint B ((a) joint A, (b) joint B) and the temperature field at the weld after the temperature field simulation of joint A and joint B in this application ((c) joint A, (d) joint B);

[0053] Fig.11 The morphology of the overlapping interface obtained after the actual laser connection of joint A and joint B ((a) joint A, (b) joint B) and the temperature field at the overlapping interface after the temperature field simulation of joint A and joint B in this application ((c) joint A, (d) joint B). DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solution and advantages of the technical solution more clear, the technical solution is further described in detail below in conjunction with specific implementation methods. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the technical solution.

[0055] Embodiment 1:

[0056] This embodiment provides a method for simulating fine-macro cross-scale temperature fields of laser joining metal and composite materials, such as Figure 1 As shown, it includes the following steps:

[0057] S1. Perform mesoscale modeling to obtain a mesoscale finite element model of the composite material, such as Figure 2 As shown in part (a) of FIG. 1 , in this embodiment, the composite material includes CFRTP (Carbon fiber reinforced thermoplastics), and by weight, the CFRTP includes 56.13% resin (such as polyphenylene sulfide (PPS)) and 43.87% continuous carbon fiber (such as T700 carbon fiber, with a diameter of 7 microns), and Figure 2 As shown in parts (b) and (c), the carbon fiber is a 0° and 90° laminated structure, and each layer of carbon fiber and resin is evenly distributed, without obvious fiber accumulation and local carbon fiber loss;

[0058] Specifically, step S1 includes the following steps:

[0059] A scanning electron microscope is used to obtain CFRTP cross-sectional characteristic information. In this embodiment, the CFRTP cross-sectional characteristic information includes the fiber cross-sectional diameter, the distribution of the fiber and the resin (such as whether the distribution is uniform), etc.

[0060] Assuming that the fibers and resin in CFRTP are in full contact, and both the fibers and the resin are regarded as isotropic materials, the representative volume element (RVE) is determined based on the CFRTP cross-sectional characteristic information obtained by scanning electron microscopy and the material specification provided by the CFRTP manufacturer using tools such as the Mechanical APDL Product Launcher 19.1 module of the ANSYS software, and the key parameters of the representative volume element (the key parameters specifically include the diameter and arrangement spacing of the carbon fiber filaments, and the length u, width v, and height w of the RVE) are determined to establish a mesoscopic finite element model of CFRTP to display the fiber arrangement mode, fiber arrangement direction, and CFRTP cross-sectional characteristics in CFRTP; in this embodiment, the mesoscopic finite element model is a hexahedral structure, such as a cube with a length × width × height of 9.06 × 9.06 × 9.06 microns, and the length, width, and height directions correspond to the x-axis, y-axis, and z-axis directions, respectively, and the yz plane displays 4 1 / 4 carbon fibers and the resin filled between the carbon fibers (i.e. Figure 2 In the “RVE” shown in part (a), both the carbon fiber and the resin are constructed using eight-node hexahedral thermal elements Solid 70;

[0061] Using tools such as ANSYS APDL command statements, the material properties of carbon fiber and resin are parameterized based on experimental data and existing scientific research materials (for example, at 25°C, the carbon fiber density is 1.76g / cm 3 The corresponding APDL command is MPTEMP,,,,,,,,MPTEMP,1,25MPDATA,DENS,3,,1760), where the material properties include the density, thermal conductivity and specific heat of the carbon fiber, and the density, thermal conductivity and specific heat of the resin;

[0062] The mesoscopic RVE model is further meshed to obtain a mesoscopic finite element model. In this embodiment, the total number of meshes used to divide the mesoscopic RVE model is 89608, and the total number of nodes is 96021 (i.e. Figure 2 The “grid” shown in part (a) of the figure);

[0063] S2. Steady-state heat transfer calculations are performed based on the microscopic finite element model of the composite material to obtain the thermal conductivity of different layers in the composite material under the interaction between carbon fiber and resin, which specifically includes the following contents:

[0064] Under steady-state conditions (i.e., heat flux density remains unchanged), a steady-state heat transfer finite element calculation is performed on the mesoscopic finite element model to obtain the thermal conductivity of the mesoscopic finite element model; Figure 3 As shown, the micro-finite element model (i.e. Figure 2 The upper surface of the “RVE model” in the figure is determined as the hot surface (set to a constant heat flux of 1500 W / m 2 ), the lower surface is determined as a cold surface (set to a constant temperature of 25°C), and the rest are determined as adiabatic surfaces (set symmetric boundary conditions); in this calculation process, the heat loss caused by convection and radiation is not considered, and the specific calculation process is as follows:

[0065] In this example, under steady-state heat transfer conditions, the inflow and outflow of heat energy reach a balance, so that the energy of the system remains constant. The conduction of heat energy satisfies Fourier's law, and its control equation can be described according to formula (1):

[0066]

[0067] Where T is the temperature, are the temperature gradients in the x-axis, y-axis and z-axis directions respectively; kxx, kyy and kzz are the thermal conductivities in the x-axis, y-axis and z-axis directions respectively;

[0068] Considering the periodic distribution characteristics of the mesoscopic finite element model, the temperature boundary conditions of the three paired surfaces (i.e., three sets of opposite and parallel planes), twelve edges, and eight vertices of the mesoscopic finite element model must all satisfy the periodic boundary conditions. Therefore,

[0069] The temperature boundary conditions of the three matching surfaces are as follows:

[0070]

[0071]

[0072] The temperature boundary conditions of the twelve edges are as follows:

[0073]

[0074] Among them, T1, T2, ...T12 correspond to the temperatures of the twelve edges of the mesoscopic finite element model;

[0075] The temperature boundary conditions of the eight vertices are as shown in formula (4):

[0076]

[0077] Among them, T I , T II ,...T VIII They correspond to the temperatures of the eight vertices of the mesoscopic finite element model;

[0078] Based on the above heat conduction control equation and temperature boundary condition settings, the temperature distribution in the RVE model can be obtained with the help of ANSYS APDL command statements (such as Figure 4 As shown), further, the thermal conductivity of the RVE model in the x-axis, y-axis, and z-axis directions can be obtained according to formula (5):

[0079]

[0080] Among them, q i , k i and are heat flux, thermal conductivity and temperature gradient respectively, and ΔT is the average temperature difference of the corresponding nodes on the two surfaces perpendicular to the i direction in the microscopic finite element model, for example Figure 5 As shown, when i=z, Pm and Pm' are corresponding nodes on two surfaces perpendicular to the z direction (i.e., two parallel xy planes), m=1, 2, ....n, and m is a positive integer; L i is the length of the finite element model in the i direction, that is, when i is x, y, and z respectively, L i Lu=u, Lv=v, Lw=w respectively;

[0081] Furthermore, the positions of the hot surface and the cold surface of the mesoscopic finite element model are changed, and the above-mentioned process of performing steady-state heat transfer finite element calculation on the mesoscopic finite element model is repeated to obtain the thermal conductivity of different layers in the CFRTP in different directions (i.e., the x-axis, y-axis, and z-axis directions), as shown in Table 1:

[0082] Table 1 Thermal conductivity of 0° / 90° layers in different directions in RVE model and CFRTP

[0083]

[0084] Note: The 0° and 90° layer direction identification in CFRTP can be found in Figure 2 part (b) of

[0085] S3. Perform macro-scale modeling to obtain the macro-model of the overlapped metal and composite materials, which specifically includes the following contents:

[0086] like Figure 6 As shown, the macroscopic three-dimensional geometric model of the overlapped metal and composite material is established by using tools such as the Mechanical APDL Product Launcher 19.1 module of the ANSYS software; in this embodiment, the metal is Ti-6Al-4V (i.e., TC4), the metal and the composite material have the same size, length × width × height are all 50 × 30 × 2 mm, and the overlap length is 30 mm;

[0087] The metal is regarded as an isotropic material and the composite material is regarded as an anisotropic material, and different material properties are set respectively. The material properties of the composite material include the material properties of the 0° layer and the material properties of the 90° layer. The setting can be achieved by changing the orientation of the carbon fiber (that is, the main direction of the microscopic finite element model), so as to investigate the influence of CFRTP anisotropy on the connection performance of the TC4 / CFRTP joint;

[0088] Specifically, the material properties of the composite material (CFRTP) include: thermal conductivity of different layers in different directions (as shown in Table 1), density and specific heat capacity; the material properties of the metal part (TC4) include: density, thermal conductivity and specific heat capacity at different temperatures (as shown in Table 2); at the same time, the setting of the material properties can also be completed using tools such as ANSYA's APDL command statements;

[0089] Table 2 Density, thermal conductivity and specific heat capacity of TC4

[0090]

[0091] In the macroscopic three-dimensional geometric model, the overlapping parts of metal and composite materials are divided into non-uniform grids. Specifically, Figure 7As shown, in the length direction (i.e., the x-axis direction), the grid increases from small to large along the direction away from the connection position, and in the height direction (i.e., the z-axis direction), the grid increases from small to large along the direction away from the overlap surface. Based on the highly nonlinear characteristics of heat transfer during the laser connection process, this embodiment uses non-uniform grids to divide the overlap part model, which can reduce the calculation time;

[0092] S4, simulating laser connection of the joint part of the macro model, and performing transient heat transfer calculation during the simulated laser connection process to generate transient temperature fields at different times in real time, which includes the following contents:

[0093] According to the laser power, energy distribution and cross-sectional morphology of the overlapped part of the laser used in the real laser connection, a suitable heat source model is selected as the load for temperature field calculation; in this embodiment, a double-cone composite heat source composed of two three-dimensional cone heat sources is used as the simulated laser source, that is, the heat source model, such as Figure 8 As shown, the heat source model is suitable for forming a full penetration weld or a partial penetration weld;

[0094] Specifically, the double cone composite heat source can be described by the following formula:

[0095]

[0096] Where P is the laser power, η is the energy utilization rate, Q D is the effective laser heat input, α 1 , α 2 are the energy regulation factors of the upper cone heat source and the lower cone heat source respectively; t 、z i 、z b 、r t 、r i 、r b are the shape parameters of the double-cone composite heat source, which are the z coordinate of the upper surface of the upper cone heat source, the z coordinate of the lower surface of the upper cone heat source / the upper surface of the lower cone heat source, the z coordinate of the lower surface of the lower cone heat source, the upper surface radius of the upper cone heat source, the lower surface radius of the upper cone heat source / the upper surface radius of the lower cone heat source, and the lower surface radius of the lower cone heat source, which can be set according to actual needs; q D1 ,q D2 are the heat flux densities of the upper cone heat source and the lower cone heat source respectively; q D is the total heat flux density of the double-cone composite heat source; Q D1 and Q D2 are the effective laser heat inputs of the upper cone heat source and the lower cone heat source, respectively;

[0097] Furthermore, r in formula (6) 1 、r 2 Obtained by the following formula:

[0098]

[0099] Q in formula (6) D1 , Q D2 Obtained by the following formula:

[0100]

[0101] The initial temperature and boundary conditions for the transient heat transfer calculation of the macro model are set, wherein the initial temperature is 25°C. Considering the heat radiation loss and heat convection loss, this embodiment uses equivalent heat exchange as the boundary condition, and the boundary condition expression is as follows:

[0102]

[0103] Where, T is the initial temperature (25°C), h c is the equivalent heat transfer coefficient;

[0104] like Fig. 9 As shown, the heat source model is loaded so that the heat source model acts on the macro model of the joint and moves along the preset laser connection path. After the movement is completed, the effect of the heat source model on the joint part is released to simulate the cooling process after the laser connection is completed, thereby completing the entire process of simulating the laser connection of the joint part. During the entire process of simulating the laser connection, the transient temperature field at different times is generated in real time according to the initial temperature and boundary conditions calculated by the transient heat transfer of the macro model.

[0105] In addition, to verify the effectiveness of this simulation method, Figure 6 As shown in (b) and (c), the joint part in this embodiment includes two types of joints: in joint A, the orientation of the carbon fiber at the overlapping interface is perpendicular to the laser connection direction; in joint B, the orientation of the carbon fiber at the overlapping surface is the same as the laser connection direction.

[0106] On this basis, the fine-macro cross-scale simulation method in this application is used to simulate laser welding of two types of joints, joint A and joint B. Fig.10 As shown in (c) and (d) in the figure, the temperature field at the joint can be formed. At the same time, the same laser connection parameters (laser power of 500W, connection speed of 15mm / s, defocus distance of 0mm, swing radius of 0.25mm, swing frequency of 200Hz) are used to perform real laser connection on joint A and joint B respectively. Fig.10 It can be seen that there is almost no difference in the weld morphology dimensions (i.e., the penetration depth and width) of the TC4 side between the two types of joints (e.g. Fig.10However, there are obvious differences in the interface morphology and size at the lap joint interface, which is mainly due to the difference in carbon fiber orientation, which affects the temperature distribution at the lap joint interface, thereby affecting the ultimate shear resistance of the two types of joints: the ultimate shear resistance of joint A and joint B are 1463.1N and 857.2N, respectively.

[0107] It can be seen that how to accurately simulate the temperature distribution at the joint lap interface is crucial to accurately evaluate the joint connection strength and optimize the laser connection parameters.

[0108] Based on this, the temperature distribution of the laser connection process of two types of joints, joint A and joint B, was simulated by using the micro-macro cross-scale simulation method in this application. Fig.11 It can be seen that the present application can obtain the temperature fields at the lap interfaces of the two joints respectively. According to the morphological characteristics of the tensile shear section of the CFRTP side, it can be divided into a pyrolysis zone (PPS is mainly pyrolysis reaction), a melting zone (PPS is mainly melting reaction) and a softening zone (PPS is mainly crystallinity change). Among them, the softening zone is the farthest from the connection position, but due to the clamping pressure and the extrusion of the pyrolysis gas generated in the center area of ​​the connection, the molten PPS may flow and eventually solidify in the softening zone. Furthermore, from Fig.11 It can be seen that even under the same laser energy, the difference in simulated temperature fields at the lap interface of joint A and joint B is still obvious, indicating that the present application can effectively consider the influence of the carbon fiber orientation at the joint interface on the energy conduction of laser-connected TC4 / CFRTP.

[0109] At the same time, since the simulation method in this application is a heat-solid simulation, the flow behavior of the fluid is not considered. For this reason, this application only selects the experimental results of the pyrolysis zone and the melting zone for comparison with the simulation results obtained by the simulation method of this application, wherein the experimental results refer to the actual temperature and weld morphology at the lap interface obtained when the joint is actually welded. As shown in Table 3, the simulation results obtained by the simulation method of this application are analyzed for errors, and the obtained interface simulation errors (i.e., the error between the simulation results and the experimental results = (simulation results-experimental results) / experimental results) are all less than 5%, indicating that this application can achieve the simulation accuracy of temperature distribution at different joint interfaces.

[0110] Table 3 Simulation errors of two types of joints using the micro-macro cross-scale simulation method

[0111]

[0112]

[0113] It should be noted that after the temperature field is obtained by the simulation method of the present invention, the simulated weld morphology can be obtained according to the temperature field, for example Fig.10 In parts (c) and (d), the gray part P (i.e., the part above the melting point of the material) in the temperature field in the upper right part can be considered as a simulated weld, and its outline is the simulated weld morphology. By comparing it with the weld obtained after real welding, the above-mentioned cross-section simulation error and interface simulation error can be obtained.

[0114] It can be seen from Table 3 that after adopting the simulation method of the present invention, the cross-sectional simulation error and interface simulation error of the two joints are less than 5%, indicating that the simulation results of the simulation method of the present invention are reliable and can effectively simulate the influence of CFRTP anisotropy. If the anisotropy of the CFRTP part is not taken into account during the simulation, the simulation results of the two types of joints with the same laser connection parameters will be the same, and the difference in temperature distribution during the laser connection of the two types of joints cannot be simulated. The fine-macro cross-scale simulation method of the present invention not only has significant advantages in the morphological simulation accuracy of the joint cross section and interface, but also can effectively capture the influence of CFRTP anisotropy on temperature distribution (i.e., simulating the difference in temperature distribution during the laser connection of the two types of joints, especially the temperature distribution at the interface that has the greatest influence on the connection strength).

[0115] In summary, the present invention establishes a fine-macro cross-scale temperature field simulation method from the micro-representative volume unit of CFRTP to the macroscopic three-dimensional model. It predicts and calculates the material properties of the macroscopic three-dimensional model scale through the meso-scale RVE model, connects the fine-macro model into a whole, and in the simulation calculation, only the material properties of the meso-scale need to be set, so that the anisotropic characteristics caused by the distribution of fibers and resins in CFRTP can be considered in the macroscopic simulation, thereby greatly reducing the complexity of the meso- and macro-models, and expressing the anisotropy of CFRTP at the meso-scale in the macroscopic simulation, thereby improving the accuracy of the temperature field simulation results during the laser connection of metals and composite materials, especially improving the temperature simulation accuracy at the lap interface that has the greatest impact on the connection performance of different types of joints, thereby effectively supporting more accurate strength analysis and mechanism research of metal and composite connections, and promoting the industrial application of laser connection technology in the field of metal and composite connection.

[0116] The above contents are only preferred embodiments of the present invention. For ordinary technicians in this field, many changes can be made in the specific implementation methods and application scopes based on the ideas of the present technical content. As long as these changes do not deviate from the concept of the present invention, they all fall within the scope of protection of this patent.

Claims

1. A method for simulating fine-macroscopic cross-scale temperature fields for laser joining of metal and composite materials, characterized in that: The steps include: Perform mesoscale modeling to obtain mesoscopic finite element models of composite materials; Steady-state heat transfer calculations based on the mesoscopic finite element model of the composite material are performed to obtain the thermal conductivity of different layers in the composite material; Setting material properties for metals and composite materials, and performing macro-scale modeling to obtain macro models of overlapped metals and composite materials, wherein the material properties of the composite materials include thermal conductivity of different layers in the composite materials; The joint part of the macro model is simulated by laser connection, and transient heat transfer calculation is performed during the simulated laser connection process to generate transient temperature fields at different times in real time.

2. The temperature field simulation method according to claim 1, characterized in that: The composite material includes CFRTP.

3. The temperature field simulation method according to claim 1, characterized in that: Performing mesoscale modeling to obtain a mesoscopic finite element model of the composite material includes the following steps: Obtain CFRTP cross-sectional characteristic information; Determine a representative volume unit based on the CFRTP cross-sectional characteristic information and determine the key parameters of the representative volume unit to establish a mesoscopic RVE model of CFRTP; Parameterize material properties; The mesoscopic RVE model is meshed to obtain a mesoscopic finite element model.

4. The temperature field simulation method according to claim 3, characterized in that: In the macroscopic three-dimensional geometric model obtained by macro-scale modeling, the orientation of the carbon fibers at the joint lap interface is perpendicular to the laser connection direction, or the orientation of the carbon fibers at the joint lap surface is the same as the laser connection direction.

5. The temperature field simulation method according to claim 1, characterized in that: Steady-state heat transfer calculations based on the microscopic finite element model of the composite material are performed to obtain the thermal conductivity of different layers in the composite material, including the following steps: Under steady-state conditions, the temperature boundary conditions of the three paired surfaces, twelve edges and eight vertices of the microscopic finite element model all satisfy the periodic boundary conditions; The temperature distribution in the microscopic finite element model is obtained through the temperature boundary condition, and the thermal conductivity of the microscopic finite element model in the x-axis, y-axis, and z-axis directions is obtained according to the following formulas: Among them, q i , k i and are heat flux, thermal conductivity and temperature gradient respectively, and ΔT is the average temperature difference of the corresponding nodes on the two surfaces perpendicular to the i direction in the microscopic finite element model; L i is the length of the microscopic finite element model in the i direction.

6. The temperature field simulation method according to claim 5, characterized in that: When performing steady-state heat transfer calculations, the upper surface of the microscopic finite element model in the height direction is determined as the hot surface, the lower surface is determined as the cold surface, and the rest are determined as insulation surfaces.

7. The temperature field simulation method according to claim 1, characterized in that: In the macroscopic three-dimensional geometric model obtained by macro-scale modeling, the overlapping parts of metal and composite materials are divided into non-uniform grids, so that in the length direction, the grid increases from small to large along the direction away from the laser connection position, and in the height direction, the grid increases from small to large along the direction away from the overlapping surface.

8. The temperature field simulation method according to claim 1, characterized in that: The joint part of the macro model is simulated by laser connection, and transient heat transfer calculation is performed during the simulated laser connection process to generate transient temperatures at different times in real time, including the following steps: A double-cone composite heat source consisting of two three-dimensional cone heat sources is used as a simulated laser source; Set the initial temperature and boundary conditions for transient heat transfer calculations in the macro model; The simulated laser source is loaded so that the heat source model acts on the macro model of the joint and moves along the preset laser connection path. After the movement is completed, the effect of the simulated laser source on the joint part is released to simulate the cooling process after the laser connection is completed, so as to complete the entire process of simulated laser connection of the joint part. During the entire process of simulated laser connection, the transient temperature field at different times is generated in real time according to the initial temperature and boundary conditions calculated by the transient heat transfer of the macro model.

9. The temperature field simulation method according to claim 8, characterized in that: The double cone composite heat source is described by the following formula: Where P is the laser power, η is the energy utilization rate, Q D is the effective laser heat input, α1 and α2 are the energy adjustment factors of the upper cone heat source and the lower cone heat source respectively; z t 、z i 、z b 、r t 、r i 、r b are the shape parameters of the double-cone composite heat source, which are the z coordinate of the upper surface of the upper cone heat source, the z coordinate of the lower surface of the upper cone heat source / the upper surface of the lower cone heat source, the z coordinate of the lower surface of the lower cone heat source, the upper surface radius of the upper cone heat source, the lower surface radius of the upper cone heat source / the upper surface radius of the lower cone heat source, and the lower surface radius of the lower cone heat source; q D1 ,q D2 are the heat flux densities of the upper cone heat source and the lower cone heat source respectively; q D is the total heat flux density of the double-cone composite heat source; Q D1 and Q D2 are the effective laser heat inputs of the upper cone heat source and the lower cone heat source, respectively; And r1 and r2 are obtained by the following formula: Q D1 , Q D2 Obtained by the following formula:

10. The temperature field simulation method according to claim 8, characterized in that: The boundary condition expression is as follows: Where T is the initial temperature, h c is the equivalent heat transfer coefficient.

Images