A method for simulating the temperature field of laser bonding between composite materials and metals

Abstract

This invention provides a method for simulating the temperature field of laser bonding between composite materials and metals, belonging to the field of advanced laser manufacturing. For the laser bonding process of composite materials and metals, a finite element three-dimensional model of continuous fiber-reinforced resin matrix composite material and metal laser bonding is established. The composite material part is layered according to the actual sample, and the material physical properties are set to anisotropy based on the layup method and orientation of the fiber prepreg tape. This allows for accurate prediction of the temperature field distribution during the laser bonding process of the heterogeneous structure joint between composite materials and metals. This invention has high universality, accurately reflecting the influence of continuous fibers on the temperature field during the laser bonding process between composite materials and metals. By calculating the temperature field of the laser-bonded joint of continuous fiber-reinforced resin matrix composite material and metal, the laser bonding process window can be predicted, providing predictive and guiding functions for practical engineering and scientific research.

Description

Technical Field

[0001] This invention is a method for simulating the temperature field of laser bonding between continuous fiber-reinforced resin matrix composite materials and metal materials, belonging to the field of advanced laser manufacturing. Background Technology

[0002] Lightweight materials and structures are effective ways to achieve energy conservation, emission reduction, and improved energy efficiency. Among them, fiber-reinforced resin matrix composites and lightweight alloys, due to their excellent performance, have become important structural materials in modern equipment and have been applied in fields such as launch vehicles and aircraft. Most applications require the connection of composite materials with metal materials to form lightweight structures, and the quality of the joint connection determines the lifespan and performance of the structural components. Currently, the main methods for connecting composite materials and metals are mechanical connections (screws, riveting, etc.), adhesive bonding, and welding. Compared with these methods, laser bonding has advantages such as good accessibility, controllable energy, ease of shaping, and high efficiency. It is suitable for welding joints of various connection types and has many advantages in the heterogeneous structural connection of fiber-reinforced resin matrix composites and metals, gaining widespread attention in recent years. The principle of laser bonding is to directly irradiate the metal surface with a laser beam. Heat is conducted from the metal surface to the interface where it contacts the composite material, heating the resin on the surface of the composite material to melt it. Under the pressure applied by the fixture, the resin spreads, cools, and solidifies, bonding tightly with the metal material to achieve the connection.

[0003] With the development of computer science, numerical simulation has gradually become an important means of studying temperature changes in advanced laser manufacturing processes, and it also has wide applications in the engineering field. Numerical simulation can reduce experimental workload and decrease the blind spots in experiments. For laser joining of fiber-reinforced resin matrix composites and metal materials, finding suitable laser process parameters inevitably requires a large number of experiments, which consume a lot of time and materials. Establishing an appropriate finite element model to simulate and calculate the temperature field of the laser joining process can assist in the rational selection of parameters for process experiments, reducing the time and economic costs of experiments. Currently, many finite element simulations treat short fiber-reinforced resin matrix composites as isotropic homogeneous materials for calculation. However, in continuous fiber-reinforced resin matrix composites, a large number of single fibers are generally bundled into a prepreg tape and then bonded to the resin matrix in different laying methods. The fiber content is generally above 50%, and the thermal conductivity of the fiber material differs greatly between the radial and axial directions. Therefore, in the laser joining process based on heat conduction, the heat conduction behavior and temperature distribution in the joint between metal and continuous fiber-reinforced composite materials are significantly different from other materials, and the assumption of homogeneous materials is not applicable. A few studies have noted this difference, treating the continuous fiber layer and resin layer as separate layers, assuming that the fiber and resin layers have the same thickness and are both considered isotropic homogeneous materials. However, this assumption still contains some errors compared to reality, making it difficult to combine simulation results with actual experiments. Therefore, this study makes reasonable assumptions about the actual layup of continuous fiber reinforced resin matrix prepregs, establishes a three-dimensional model of the composite material and metal laser bonding, and performs finite element numerical simulation to predict the temperature field during the laser bonding process and explore the heat conduction mode in heterogeneous joints. This has important guiding significance for the selection of process parameters in actual laser bonding experiments. Summary of the Invention

[0004] This invention addresses the laser bonding process between continuous fiber reinforced resin matrix composites and metal materials. It establishes a finite element three-dimensional model for the laser bonding of continuous fiber reinforced resin matrix composites and metal materials. The composite material part is processed in layers according to the actual sample. The physical properties of the material are set to anisotropy according to the layup method and orientation of the fiber prepreg tape. This model can accurately predict the temperature field distribution during the laser bonding process of the heterogeneous structure joint between the composite material and the metal material.

[0005] The technical solution of the present invention is as follows.

[0006] A method for simulating the temperature field of laser bonding between composite materials and metals includes the following steps:

[0007] Step S1: Treat the metal as an isotropic homogeneous material and establish a finite element three-dimensional model;

[0008] Step S2: Treat the resin layer as an isotropic homogeneous material and perform a layering process on the resin layer and fiber layer in the composite material.

[0009] Step S3: Set parameters for the fiber layer based on the orientation and layup method of the prepreg, and perform numerical simulation.

[0010] Preferably, the composite material and the metal are in the form of plates;

[0011] The metal is selected from titanium alloys, aluminum alloys, magnesium alloys, and stainless steel; the thickness of the metal plate is 1-3 mm;

[0012] The fibers in the composite material include carbon fiber, glass fiber and aramid fiber, and the resin layer includes PPS, PA, PET and PEEK; the thickness of the composite material is 1-4 mm.

[0013] Preferably, the physical properties of the composite material and the metal change with temperature.

[0014] Preferably, the joint between the composite material and the metal includes a laser irradiation zone, a transition zone, and a base material.

[0015] Preferably, the grid dimensions of the laser irradiation zone of the metal are 1 / 8 to 1 / 4 of the metal plate thickness; the grid dimensions of the transition zone on the metal side are 1 / 4 to 1 / 2 of the metal plate thickness; and the grid dimensions of the base material region on the metal side are 1 / 4 to 1 / 2 of the metal plate thickness.

[0016] Preferably, the thickness of the fiber layer and the resin layer is set to be consistent with their actual thickness during the layering process.

[0017] Preferably, the ratio of the grid height dimension of the fiber layer or resin layer in the composite material to the thickness of the fiber layer or resin layer is 1 / 2-1.

[0018] Preferably, the length and width dimensions of the grid in the laser irradiation area on the composite material side are 1 / 8 to 1 / 4 of the thickness of the composite material plate; the length and width dimensions of the grid in the transition area on the composite material side are 1 / 4 to 1 / 2 of the thickness of the composite material plate; and the length and width dimensions of the grid in the parent material area on the composite material side are 1 / 4 to 1 / 2 of the thickness of the composite material plate.

[0019] Preferably, step S3, which sets the material properties according to the placement direction and layup method of the fiber prepreg in the composite material, further includes:

[0020] For unidirectional 0° or unidirectional 90° placement methods, the axial and radial physical properties of the fiber layer material are set respectively;

[0021] For the 0° / 90° alternating layup method, each layer of fiber material is configured with axial and radial physical properties corresponding to the layup direction.

[0022] For the 0° / 90° weaving placement method, the fiber layer is regarded as an orthogonal material, and the horizontal direction is set as the axial physical property of the fiber material, and the vertical direction is set as the radial physical property of the fiber material.

[0023] Through the above technical solutions, this invention establishes a realistic finite element three-dimensional model for laser bonding of continuous fiber-reinforced resin matrix composites and metal materials, and conducts numerical simulation studies on the joint temperature field. Since the thickness and direction of the fiber layup differ between fiber and resin layers in actual situations, this invention further improves calculation accuracy by layering the composite material according to the actual sample. The resin and fiber layers are alternately distributed, with the resin layer being isotropic and the fiber layer being anisotropic when unidirectional and orthotropic when woven, depending on the prepreg tape layup method. Furthermore, the changes in the material's physical properties with temperature and different boundary conditions are considered.

[0024] This invention offers the following advantages: It utilizes finite element simulation software to establish a three-dimensional model closely resembling the actual working conditions of laser bonding between continuous fiber-reinforced resin matrix composites and metal materials. This model simulates and calculates the temperature field distribution in the heterogeneous joint. By understanding only the relevant physical properties of the materials, the absorptivity to the corresponding wavelength of laser light, the heat source expression function, and the layup pattern of the continuous fibers in the composite material, finite element calculations can be performed on the temperature field of laser bonding between different metal materials and different continuous fiber-reinforced resin matrix composites. Based on the characteristic temperatures of the resin matrix, such as melting point, thermal decomposition temperature, and glass transition temperature, the process window for laser bonding of heterogeneous joints can be predicted. Experimental results demonstrate that this method has high accuracy and can provide guidance for process testing in laser bonding of continuous fiber-reinforced resin matrix composites and metals. Attached Figure Description

[0025] Figure 1 Finite element simulation mesh generation: (a) 3D model; (b) TC4 mesh generation; (c) CFPEEK mesh generation

[0026] Figure 2 Schematic diagram of CFPEEK composite material: (a) morphology and schematic diagram of carbon fiber weaving; (b) cross-sectional morphology and schematic diagram of delamination;

[0027] Figure 3 Schematic diagram of laser connection to CFPEEK / TC4 test

[0028] Figure 4Comparison of actual and simulated melt depths of samples (3500W): (a) TC4; (b) CFPEEK

[0029] Figure 5 Comparison of actual and simulated weld widths of CFPEEK composite materials at different speeds (P = 3500W):

[0030] Figure 6 Test and calculated values ​​of CFPEEK surface resin melt width. Detailed Implementation

[0031] The present invention will be further described below with reference to the embodiments, but is not limited to the following embodiments.

[0032] Example

[0033] The example uses continuously woven carbon fiber reinforced polyetheretherketone (CFPEEK) composite material and TC4 titanium alloy, with dimensions of 60mm×25mm×2mm and 60mm×30mm×2mm respectively. The rough surface is achieved through grinding. Based on the above principles and the actual experimental conditions, the following assumptions are made in the finite element model:

[0034] (1) The initial temperature and ambient temperature of TC4 titanium alloy and CFPEEK composite material were both 25℃.

[0035] (2) The resin layer and fiber layer in CFPEEK composite material have the same thickness. The resin layer is an isotropic homogeneous material and the fiber layer is an orthogonal material.

[0036] (3) A rectangular light spot acts on the surface of TC4 titanium alloy;

[0037] (4) The TC4 titanium alloy and CFPEEK are tightly fitted together, and there is no assembly gap.

[0038] For isotropic continuous media, the thermal conductivity of the material as a function of temperature in the model is given by the material properties and can be regarded as a constant. Furthermore, there is no internal heat source, and the partial differential equation for heat conduction can be simplified to equation (1). In the equation, α is the thermal conductivity coefficient, λ is the thermal conductivity of the material, ρ is the density of the material, c is the specific heat capacity of the material, t is the temperature, and τ is the time.

[0039]

[0040] Considering the heat conduction between the fixture and the TC4 titanium alloy, between CFPEEK and the metal substrate, and convective heat transfer between other parts and the surrounding air in actual laser connection experiments, the model adopts a third type of boundary condition as shown in equation (2), which gives the temperature of the fluid exchanging heat with the object surface and the surface heat transfer coefficient. In the equation, λ is the thermal conductivity. Let h be the temperature gradient, h be the surface heat transfer coefficient, and t be the temperature gradient. f For ambient temperature, t w The temperature is on the boundary surface.

[0041]

[0042] The laser heat source uses a moving rectangular spot shaped by an integrating mirror, and the heat flux density function Q is shown in equation (3). In the equation, P is the laser power, l and w are the length and width of the spot, respectively, and A is the absorption rate of TC4 titanium alloy to the laser, which is determined to be 40% by spectrophotometer testing.

[0043]

[0044] like Figure 1 As shown, a 3D model of the CFPEEK / TC4 lap laser connection was created based on the actual material dimensions. Figure 2 The diagram shows the carbon fiber layup and layering method. To improve the accuracy of the simulation results while maintaining computational efficiency, a gradient mesh size was used. In the TC4 module, the mesh size for the irradiated area is 0.25mm × 0.25mm × 0.25mm, the mesh size for the overlapping areas on both sides of the heat source loading area is 0.5mm × 0.5mm × 0.5mm, and the mesh size for the remaining areas is 1mm × 0.5mm × 0.5mm. Based on a PEEK layer thickness of 0.1mm and a carbon fiber layer thickness of 0.2mm, the CFPEEK module was meshed. The mesh size for the irradiated area is 0.25mm × 0.25mm × 0.1 / 0.2mm, the mesh size for the overlapping areas on both sides is 0.5mm × 0.5mm × 0.1 / 0.2mm, and the mesh size for the remaining areas is 1mm × 0.5mm × 0.1 / 0.2mm. In CFPEEK, the material orientation of the carbon fiber layer is defined to be consistent with the model coordinate system, that is, the X and Z directions are horizontal (axial) and the Y direction is vertical (radial). The thermal conductivity of the carbon fiber layer is set accordingly. The material parameters used in the numerical simulation are shown in Table 1.

[0045] Table 1 Material parameters in finite element simulation

[0046]

[0047] A laser lap joint experiment was conducted using a laser power of 3500W and a welding speed of 10-25 mm / s (Figure 3). The actual joint results were compared with the simulation results under the corresponding parameters to verify the accuracy of the model. In the contour plot, the melt pool depth of TC4 can be obtained by setting the upper limit of the contour plot display temperature according to the melting point of TC4 (1690℃). The simulation results are compared with the melt depth of TC4 in the actual sample. Figure 4As shown in (a), the depth of the molten pool on one side of the TC4 titanium alloy is close to the TC4 melting depth calculated by simulation.

[0048] Based on the melting temperature of PEEK resin (343℃), the upper limit of the cloud map display temperature is set to obtain the melting area of ​​the resin in the CFPEEK module. Figure 4 (b) A comparison of the actual CFPEEK melting depth with the calculated temperature field at different welding speeds shows that the molten resin changes from light to dark in the cross-section of the actual sample, and bubbles generated during solidification are present in the PEEK layer. Based on this, the actual CFPEEK melting depth is close to the calculated result. A comparison of the simulated melting width of the composite-surface resin with the actual sample, based on the upper limit of 343℃. Figure 3-3 As shown. Figure 5 (b, c, d) are the actual melting area and temperature field cloud diagrams of the CFPEEK composite material at welding speeds of 10, 15, and 20 mm / s, respectively. It can be seen that the actual resin melting area on the surface of the composite material is similar in width to the area above 343℃ on the surface of the composite material in the cloud diagram. Figure 6 The experimental and calculated values ​​of the resin melt width on the CFPEEK surface layer are presented. The results show that within the welding speed range (10-35 mm / s) that can form a joint with good appearance, the calculated and experimental values ​​of the resin melt width on the composite material surface are in good agreement. In summary, the temperature field distribution obtained from the simulation calculation is in good agreement with the experimental results, which can provide guidance for the process experiment of laser joining CFPEEK composite materials and TC4 titanium alloy.

[0049] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for simulating the temperature field of laser bonding between composite materials and metals, characterized in that, Includes the following steps: Step S1: Treat the metal as an isotropic homogeneous material and establish a finite element three-dimensional model; Step S2: The composite material is a continuous fiber reinforced resin matrix composite material. The resin layer is regarded as an isotropic homogeneous material. The resin layer and fiber layer in the composite material are separated into layers. The physical properties of the material are set to anisotropic according to the layup method and orientation of the fiber prepreg. The physical properties include thermal conductivity. Step S3 involves setting parameters for the fiber layer regarding the orientation and layup method of the prepreg, and then performing numerical simulation. Setting parameters for the placement orientation and layup method of the fiber prepreg in the composite material further includes: For unidirectional 0° or unidirectional 90° placement methods, the axial and radial physical properties of the fiber layer material are set respectively; For the 0° / 90° alternating layup method, each layer of fiber material is configured with axial and radial physical properties corresponding to the layup direction. For the 0° / 90° weaving placement method, the fiber layer is regarded as an orthogonal material, and the horizontal direction is set as the axial physical property of the fiber material, and the vertical direction is set as the radial physical property of the fiber material; The joint between the composite material and the metal includes a laser irradiation zone, a transition zone, and a base material, with the mesh size divided using a gradient. The length, width, and height of the grid in the laser irradiation zone of the metal are 1 / 8 to 1 / 4 of the thickness of the metal plate; the length, width, and height of the grid in the metal-side transition zone are 1 / 4 to 1 / 2 of the thickness of the metal plate; and the length, width, and height of the grid in the metal-side base material zone are 1 / 4 to 1 / 2 of the thickness of the metal plate. The ratio of the grid height of the fiber layer or resin layer in the composite material to the thickness of the fiber layer or resin layer is 1 / 2-1.

2. The method for simulating the temperature field of laser-connected composite materials and metals according to claim 1, characterized in that, The composite material and the metal are in plate form; The metal is selected from titanium alloys, aluminum alloys, magnesium alloys, and stainless steel; the thickness of the metal plate is 1-3 mm; The fibers in the composite material include carbon fiber, glass fiber and aramid fiber, and the resin layer includes PPS, PA, PET and PEEK; the thickness of the composite material is 1-4 mm.

3. The method for simulating the temperature field of laser-connected composite materials and metals according to claim 2, characterized in that: The physical properties of the composite material and the metal change with temperature.

4. The method for simulating the temperature field of laser-connected composite materials and metals according to claim 1, characterized in that: During the layered processing, the thickness settings of the fiber layer and the resin layer are consistent with their actual thicknesses.

5. The method for simulating the temperature field of laser-connected composite materials and metals according to claim 1, characterized in that: The length and width of the grid in the laser irradiation zone on the composite material side are 1 / 8 to 1 / 4 of the thickness of the composite material plate; the length and width of the grid in the transition zone on the composite material side are 1 / 4 to 1 / 2 of the thickness of the composite material plate; and the length and width of the grid in the parent material region on the composite material side are 1 / 4 to 1 / 2 of the thickness of the composite material plate.

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