Bidirectional thermal coupling analysis method for orthogonal cutting process of aerospace composite material

Abstract

The invention provides a bidirectional thermal-mechanical coupling analysis method for an orthogonal cutting process of an aerospace composite material, which comprises the following steps of: performing quasi-static tensile test on a thermoplastic composite material at different test temperatures to obtain mechanical parameters of thermoplastic resin at different test temperatures; according to the method, the bidirectional thermal coupling simulation of the mesoscopic processing temperature rising process of the thermoplastic composite material is researched, a mesoscopic orthogonal cutting process temperature field model is constructed, a mesoscopic orthogonal cutting thermal coupling model is established according to a constitutive model considering the temperature influence, a VUMAT subprogram is written by applying a Fortran language, and the thermal coupling simulation of the mesoscopic processing temperature rising process of the thermoplastic composite material is established. And establishing a bidirectional thermal coupling orthogonal cutting model of the mesoscopic thermoplastic composite material by utilizing simulation software. According to the method, thermal and mechanical factors are considered, the thermal bidirectional coupling analysis method is achieved, and the method has important significance in understanding machining damage, improving machining quality, prolonging the service life of a tool and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and particularly to a method for bidirectional thermo-mechanical coupling analysis in the orthogonal cutting process of aerospace composite materials. Background Art

[0002] In the fields of aerospace, automotive, medical and health, etc., due to the increasing standards and requirements of the industry for lightweight, structural performance, material utilization rate, etc., higher standards and requirements for material performance have been put forward. Compared with traditional metals and thermosetting composite materials, thermoplastic composite materials (Fiber Reinforced Thermoplastic Plastic, FRTP) are lightweight, easy to process, recyclable, etc., and have become the focus of current research and engineering applications. The FRTP structure can significantly reduce the structural weight on the premise of ensuring that the structural strength meets the engineering requirements. Moreover, compared with FRSP, FRTP can achieve recyclable production, improve material utilization rate, save processing costs, and has great industrial and commercial application prospects.

[0003] During the material processing process, defects such as fiber peeling, fiber debonding, and fiber fracture will occur, affecting the surface quality of processing; due to the anisotropy and inhomogeneity of FRTP, especially the cutting performance differences caused by the mechanical property differences between carbon fibers, matrix, and interface phase, it is necessary to control processing parameters (such as cutting speed, cutting depth, feed, etc.) during processing to avoid delamination, tearing and other damages caused by excessive cutting force.

[0004] At present, the thermo-mechanical coupling research on composite materials is often limited to macroscopic cutting force and cutting heat, and for the mesoscopic material thermo-mechanical coupling problem, it leads to insufficient analysis of problems such as processing accuracy defects, material surface defects, and tool wear when processing thermoplastic composite materials.

[0005] Therefore, for the processing process of mesoscopic thermoplastic composite materials, developing a method that considers thermal and mechanical factors and realizes bidirectional thermo-mechanical coupling analysis is of great significance for understanding processing damage, improving processing quality, and extending tool service life, etc. Summary of the Invention

[0006] Aiming at the problems in the above-mentioned prior art, the present application proposes a method for bidirectional thermo-mechanical coupling analysis in the orthogonal cutting process of aerospace composite materials. Quasi-static tensile tests are carried out on thermoplastic composite materials at different test temperatures to obtain the mechanical parameters of thermoplastic composite materials at different test temperatures. For orthogonal cutting, constitutive models are established for the fibers, matrix, and interface phase of thermoplastic composite materials respectively, especially for Fiber and matrix Establish Thermomechanical coupling model, a VUMAT subroutine was written in Fortran language to establish a mesoscopic thermoplastic composite two-way thermo-mechanical coupled orthogonal cutting model, obtain the cutting force, material damage, cutting temperature and cutting quality at different initial temperatures, and compare the regional temperature and surface damage in the simulation results with those in the experimental results, verifying the accuracy and reliability of the two-way thermo-mechanical coupled constitutive model.

[0007] The orthogonal cutting temperature field model is as follows:

[0008]

[0009] In the formula, ρ is the material density, c is the specific heat of the material, T is the test temperature, t is the time, σ is the stress, is the equivalent plastic strain rate, η pl is the plastic factor in the energy consumption, μ(θ) is the friction coefficient between the tool and the material, which is related to the fiber angle, σ c is the normal stress of the tool cutting, α0 is the rake angle of the tool, γ0 is the clearance angle of the tool, R e is the edge angle of the tool, d is the contact thickness between the tool and the workpiece, k x 、k y 、k z 、k Tool are the thermal conductivities of the material in the x, y, z directions and the tool, is the relative slip between the tool and the Representative volume element (RVE).

[0010] The mesoscopic thermo-mechanical coupled orthogonal cutting model of thermoplastic composites is set as follows:

[0011] Establishment of the mesoscopic cutting model and mesh generation: Both the fiber and the matrix use C3D8T elements; Cohesive elements are used to simulate the matrix debonding behavior during the mesoscopic orthogonal cutting process of thermoplastic composites, and COH3D8 elements are used for mesh generation; the tool element type is selected as C3D8T, and the mesh in the machining area is refined; the analysis step selects a uniform time interval; the tangential behavior is set to "penalty", and the normal behavior is set to "hard contact"; the contact thermal conductivity is in tabular form; the feed speed is set at the tool reference point, the initial temperatures of the workpiece and the tool are set, the general contact is set as sub-contact, and the tool surface and the nodes of each part are surface-to-surface contact.

[0012] The above technical features can be combined in various suitable ways or replaced by equivalent technical features as long as the purpose of the present invention can be achieved.

[0013] A two-way thermo-mechanical coupled analysis method for the orthogonal cutting process of aerospace composite materials provided by the present invention has the following beneficial effects compared with the current technology:

[0014] A study was carried out on the two-way thermo-mechanical coupling simulation of the heating process in the mesoscopic machining of thermoplastic composites. A temperature field model for the mesoscopic orthogonal cutting process was constructed. Based on the constitutive model considering the influence of temperature, a mesoscopic orthogonal cutting thermo-mechanical coupling model was established. A VUMAT subroutine was written in Fortran language, and a two-way thermo-mechanical coupling orthogonal cutting model of mesoscopic thermoplastic composites was established using simulation software. The method of the present invention takes into account thermal and mechanical factors, realizes the method of two-way thermo-mechanical coupling analysis, and is of great significance for understanding machining damage, improving machining quality, and extending tool life, etc. Description of the Drawings

[0015] The present invention will be described in more detail hereinafter based on embodiments with reference to the drawings. Among them:

[0016] Figure 1 Shows a schematic diagram of a quasi-static tensile test shown in an exemplary embodiment of the present invention;

[0017] Figure 2 Shows a schematic diagram of the main heat sources in the dry machining of CFRTP shown in an exemplary embodiment of the present invention;

[0018] Figure 3 Shows the geometric relationships during the cutting process shown in an exemplary embodiment of the present invention;

[0019] Figure 4 Shows a flowchart of the subroutine update shown in an exemplary embodiment of the present invention.

[0020] Description of the Reference Numerals:

[0021] 1 - Material main shear plane, 2 - Chip-tool interface, 3 - Tool-workpiece interface. Detailed Description of the Embodiments

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention. It should be understood that the drawings are schematic, and the original components and elements are not necessarily drawn to scale.

[0023] The present invention provides a method for two-way thermo-mechanical coupling analysis in the orthogonal cutting process of aerospace composite materials. First, the mechanical properties of the composite materials are analyzed. Through quasi-static tensile tests at different test temperatures, the mechanical parameters of the thermoplastic resin at different test temperatures are obtained. Secondly, through the characterization relationship of the mechanical parameters of the composite materials, the mechanical parameters of the resin matrix material at different temperatures are obtained, and the characterization of the mechanical parameters considering the temperature effect is completed. Finally, the elastic response, damage criterion, and stiffness reduction of fibers, resin, and interface phase under mesoscopic conditions are analyzed, and a mesoscopic constitutive model of thermoplastic composite materials considering the temperature effect is established.

[0024] Obtain the mechanical property parameters of the resin to be tested at different test temperatures. As Figure 1 shown, a quasi-static tensile test is carried out on the thermoplastic resin to obtain the quasi-static tensile test data of the resin matrix material at different test temperatures and the stress-strain curve. The shear modulus G(T) of the thermoplastic resin is calculated through Equation 1.1(1.1).

[0025]

[0026] In the formula, T is the test temperature, E(T) is the elastic modulus of the material at different temperatures, and v(T) is the Poisson's ratio of the material at different temperatures.

[0027] This application establishes a mechanical constitutive model of thermoplastic composite materials at the mesoscopic scale. The damage of fiber bundles is defined using the generalized Hook's law and the Hashin damage criterion respectively. The tension and damage of the resin matrix are defined using Hook's law and the Johnson-Cook constitutive model, and the damage of the interface phase between the resin matrix and fibers is defined using the B-K criterion.

[0028] The main reason for the anisotropy shown by thermoplastic composite materials is the directionality of fiber layup. Generally, the fibers are assumed to be perfectly elastic bodies, and the fiber constitutive relationship can be expressed as.

[0029] σ ij =C ijkl ε kl (0.2)

[0030] In the formula (i, j, k, l ∈ {1, 2, 3}), C ijkl is the stiffness matrix. Direction 1 is along the fiber axial direction, and directions 2 and 3 are defined as perpendicular to the fiber axis direction. According to the stress components to represent the strain components, (1.2) can be rewritten as:

[0031] ε kl =S ijkl σ ij (0.3)

[0032] In the formula, S ijklis the flexibility matrix, which can be expressed as:

[0033]

[0034] In the formula, E i (i ∈ {1, 2, 3}) represents the elastic modulus in each direction, G ij (i, j ∈ {1, 2, 3}, i ≠ j) represents the shear modulus in each coordinate plane, ν ij (i, j ∈ {1, 2, 3}, i ≠ j) represents the Poisson's ratio in the coordinate plane. The relationship between the elastic modulus and the Poisson's ratio is as follows:

[0035]

[0036] Since C ijkl and S ijkl are inverse matrices of each other, the coefficients of the stiffness matrix can be obtained as follows:

[0037]

[0038] The tension and compression of the fiber can be divided into the tension and compression failures along the fiber direction. The tensile damage criterion along the fiber can be expressed as (σ 11 > 0):

[0039]

[0040] The compression along the fiber direction (σ 11 < 0) damage criterion can be expressed as:

[0041]

[0042] The tensile damage criterion in the direction perpendicular to the fiber (σ 22 + σ 33 > 0) is:

[0043]

[0044] The compression damage criterion in the direction perpendicular to the fiber (σ 22 + σ 33 < 0) is:

[0045]

[0046] In the formula, X t , X c , Y t , Y c represent the axial tensile strength, axial compressive strength, radial tensile strength, and radial compressive strength respectively, S ij(i,j∈{1,2,3},i≠j) represents the shear strength in all directions in three-dimensional space. The corresponding F k (k = ft, fc, mt, mc) represents the load on the fiber.

[0047] After the damage of the fiber is determined, its stiffness will decrease along with the damage evolution and crack propagation. Currently, the exponential decay model is commonly used to simulate fiber failure. The Linde model is a matrix model expressing exponential stiffness reduction, which can be expressed as:

[0048]

[0049] where C f is the damage matrix, and its expression form is:

[0050]

[0051] d f 、d m are damage variables, and their calculation formulas are:

[0052]

[0053] f k represents the failure criterion. When the fiber material fails and breaks.

[0054]

[0055] The resin matrix is generally considered to be an isotropic material during the processing. The softening effect of the resin matrix during temperature change is the main reason for the temperature-mechanical property change of thermoplastic composites. In the elastic stage, the stiffness matrix of the isotropic material considering the temperature effect can be expressed as:

[0056] K σ =∫ V [B] T [D T [B]dV(0.15)

[0057] In the formula, [B] is the shape function matrix, and [D T is the structural stress matrix considering the temperature effect. [D T can be expressed as:

[0058]

[0059] The Johnson-Cook model is commonly used to characterize the mechanical properties of isotropic materials in the yield stage, and its expression can be written as:

[0060]

[0061] In the formula, σ is the equivalent stress, ε is the equivalent strain, A is the yield stress constant under standard conditions, B is the strain hardening variable, C is the strain rate strengthening coefficient, n is the strain strengthening factor, and m is the thermal softening coefficient. From left to right, this equation represents the strain hardening effect, the strain rate strengthening effect, and the thermal softening effect respectively. The stress-strain equation in the yield stage is obtained under the combined action of these three effects.

[0062]

[0063] In the formula is the reference strain rate, which is given by experiments; T ref is the reference temperature. Generally, room temperature of 25 °C is used as the reference temperature, and T melt is the melting temperature of the resin matrix.

[0064] The Johnson-Cook constitutive model believes that the fracture strain of materials usually depends on the stress triaxiality, temperature, and strain rate. The JC damage model can be expressed as:

[0065]

[0066] In the formula, D is the damage variable, △ε p is the plastic strain increment, and ε f is the failure plastic strain. When the damage variable D reaches 1, the material fails, and the failure process can be expressed as:

[0067]

[0068] In the formula, d1 to d5 are the failure model parameters, is the stress triaxiality, which is the ratio of the mean stress σ m to the equivalent stress σ eq

[0069] The composite material interface phase refers to the transition region between the fiber reinforcement phase and the matrix phase of the composite material. In the FEM simulation process, a thin layer of Cohesive element layer is often used to simulate the mechanical property characteristics of the composite material interface phase. CFRP usually adopts the Benzeggagh-Kenane model (B-K model) to simulate the failure form of the interface phase, and it can be expressed by the formula:

[0070]

[0071] In the formula, G c represents the critical energy release rate under the mixed mode, G I represents the I-type fracture energy release rate, G II is the II-type fracture energy release rate, and η is the material parameter determined by experiments.​

[0072] The main heat sources in the dry machining of CFRTP mainly consist of three parts: (1) heat generated by plastic deformation on the main shear plane of the material. In this area, the composite material undergoes severe deformation and the local temperature rises rapidly; (2) heat generated by friction at the tool-chip interface. The main cutting heat generated in this area comes from cutting deformation and the work done to overcome the sliding friction between the cutting and the rake face of the tool; (3) heat generated by friction at the tool-workpiece interface. Heat is generated by the friction work between the flank face and the workpiece in this area. For the specific areas, refer to Figure 2 .

[0073] During the cutting process, the cutting heat is affected by cutting speed, depth of cut, tool geometry, etc. The heat sources in cutting are mainly divided into two types. The first is the plastic power consumption caused by cutting force. The plastic work of the material includes energy storage. Since fibers are often regarded as elastic bodies, it is mainly reflected in the deformation of the resin matrix, and the accumulation of plastic strain will gradually increase. The heat flux can be expressed by Equation (1.22).

[0074]

[0075] In the formula, η pl is the plastic factor in energy consumption, σ is the stress, is the equivalent plastic strain rate, and it satisfies:

[0076] The other is the heat generated by friction between the tool and the chip, and the workpiece, which can be expressed as:

[0077]

[0078] In the formula, μ(θ) is the friction coefficient between the tool and the material, which is related to the fiber angle, σ c is the normal stress of the tool cutting, η s is the heat energy ratio conducted to the tool, the workpiece, and the cutting, is the relative slip between the tool and the representative volume element (RVE).

[0079] The total heat energy obtained by the unit can be expressed as the total heat energy generated by plastic work and friction work. It can be expressed as the temperature rise in the area and the part of the heat lost due to heat conduction of the material. Its heat flow balance equation can be expressed as:

[0080]

[0081] In the formula, c is the specific heat of the material, ρ is the density of the material, k is the thermal conductivity of the material, is the temperature gradient operator, and it can be expressed as

[0082]

[0083] k x 、k y 、k z are the thermal conductivities of the material in the x, y, and z directions, and q(x, y, z) is the heat flux density of the heat source. According to the geometric relationships in the cutting process (such as Figure 3 ), the contact area between the tool and the workpiece can be obtained as:

[0084]

[0085] In the formula, α0 is the rake angle of the tool, γ0 is the clearance angle of the tool, R e is the edge angle of the tool, d is the contact thickness between the tool and the workpiece, and the thermal energy ratio of the tool can be calculated by the following formula.

[0086]

[0087] Therefore, the temperature fields of the workpiece and the chip in the mesoscopic simulation can be expressed as:

[0088]

[0089] VUMAT algorithm:

[0090] State variable setting: In this paper, 17 state variables are used, as shown in Table 1.

[0091] Table 1 Definition of state variables

[0092]

[0093] The calculation statements for the carbon fiber stiffness matrix parameters are shown in Table 2.

[0094] Table 2 Algorithm expression of the stiffness matrix coefficients

[0095]

[0096]

[0097] Hashin damage criterion determination: The carbon fiber in CFRP is the main reason for the anisotropy shown by CFRP during processing. In this paper, according to the Hashin criterion, it is compiled into Fortran statements as shown in Table 3:

[0098] Table 3 Algorithm expression of the Hashin damage criterion

[0099]

[0100] Stiffness degradation: In this paper, the stiffness degradation of carbon fiber is analyzed according to the Linde model, and the coefficients of the stiffness degradation matrix are expressed in Fortran language with reference to Table 4.

[0101] Table 4 Algorithm expression of the coefficients of the stiffness degradation matrix

[0102]

[0103] The flowchart of the subroutine update is as Figure 4 shown.

[0104] The above disclosure is only the preferred embodiment of the present invention, but the present invention is not limited thereto. Any non-creative changes that can be thought of by those skilled in the art, as well as several improvements and refinements made without departing from the principle of the present invention, should be within the protection scope of the present invention.

[0105] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed, as long as they do not depart from the spirit and scope of the present invention as defined by the appended claims. It should be understood that different dependent claims and the features described herein can be combined in a manner different from that described in the original claims. It should also be understood that the features described in connection with a single embodiment can be used in other described embodiments.

Claims

1. A bidirectional thermal-mechanical coupling analysis method for orthogonal cutting of aerospace composite materials, characterized in that: The following steps are included: S1. Performing quasi-static tensile tests on thermoplastic composite materials at different test temperatures to obtain mechanical parameters of thermoplastic resins at different test temperatures; S2. Obtain the mechanical parameters of the resin matrix material at different temperatures through the mechanical parameter characterization relationship of the thermoplastic composite material, and complete the mechanical parameter characterization considering the temperature effect; S3. For orthogonal cutting, the elastic response, damage criterion and stiffness reduction of fiber, resin and interface phase under mesoscopic conditions are analyzed, and a constitutive model of mesoscopic thermoplastic composite materials considering the influence of temperature is established.

2. The bidirectional thermal-mechanical coupling analysis method for orthogonal cutting of aerospace composite materials according to claim 1, characterized in that: Step S3 includes establishing a thermomechanical coupling model for the fiber and the matrix, establishing a bidirectional thermomechanical coupling orthogonal cutting model for the mesoscopic thermoplastic composite material, and obtaining the cutting force, material damage, cutting temperature and cutting quality at different initial temperatures.

3. The bidirectional thermal-mechanical coupling analysis method for orthogonal cutting of aerospace composite materials according to claim 1, characterized in that: The orthogonal cutting temperature field model of step S3 is: In the formula, ρ is the material density, c is the material specific heat, T is the test temperature, t is the time, σ is the stress, is the equivalent plastic strain rate, η pl is the plasticity factor in energy consumption, μ(θ) is the friction coefficient between the tool and the material, which is related to the fiber angle, and σ c is the normal stress of tool cutting, α0 is the tool rake angle, γ0 is the tool back angle, R e is the tool edge angle, d is the contact thickness between the tool and the workpiece, k x , k y , k z , k Tool is the thermal conductivity of the material in the x, y, z directions and the tool, is the relative slip between the tool and the representative volume element (RVE).

4. The bidirectional thermal-mechanical coupling analysis method for orthogonal cutting of aerospace composite materials according to claim 1, characterized in that: The setting of the bidirectional thermal-mechanical coupling orthogonal cutting model of thermoplastic composite materials in step S3 is as follows: Cutting model establishment and meshing: C3D8T units are used for both fiber and matrix; Cohesive units are used to simulate the matrix debonding behavior of thermoplastic composites during mesoscopic orthogonal cutting, and COH3D8 units are used to mesh; C3D8T is selected as the tool unit type, and the mesh in the processing area is refined; uniform time interval is selected for the analysis step; the tangential behavior is set to "penalty", and the normal behavior is set to "hard contact"; The contact heat conductivity is in table form; the feed rate is set at the tool reference point, the initial temperature of the workpiece and the tool is set, the general contact is set to sub-contact, and the tool surface and each part of the node are surface-to-surface contact.

5. The bidirectional thermal-mechanical coupling analysis method for orthogonal cutting of aerospace composite materials according to claim 1, characterized in that: According to the geometric relationship during cutting, the contact area between tool and workpiece can be obtained. for: Where α0 is the tool rake angle, γ0 is the tool back angle, R e is the tool edge angle, and d is the contact thickness between the tool and the workpiece.

6. The bidirectional thermal-mechanical coupling analysis method for orthogonal cutting of aerospace composite materials according to claim 1, characterized in that: The thermal energy ratio of the tool can be calculated by the following formula: Where α0 is the tool rake angle, γ0 is the tool back angle, R e is the tool edge angle, d is the contact thickness between the tool and the workpiece, is the temperature gradient operator, k Tool is the thermal conductivity of the tool, μ(θ) is the friction coefficient between the tool and the material, which is related to the fiber angle, and σ c is the normal stress of tool cutting, is the relative slip between the tool and the representative volume element (RVE).

7. The bidirectional thermal-mechanical coupling analysis method for orthogonal cutting of aerospace composite materials according to claim 6, characterized in that: The temperature field of the workpiece and chips in the mesoscopic simulation can be expressed as: In the formula, ρ is the material density, c is the material specific heat, k is the thermal conductivity of the material, and k x , k y , k z is the thermal conductivity of the material in the x, y, and z directions, η pl is the plasticity factor in energy consumption, σ is the stress, is the equivalent plastic strain rate.

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