Design method of blended wing body mould based on temperature field and solidification field

Abstract

The application provides a design method of a blended wing body mould based on a temperature field and a curing field, and comprises the following steps: S1, establishing a 3D model of the blended wing body mould; S2, obtaining a convection heat transfer coefficient and establishing a temperature field; S3, curing a composite material structure model and establishing a curing field; S4, conducting heat conduction calculation and analysis; S5, conducting heat distribution compensation design; S6, conducting thermal strain compensation design, and confirming a final design scheme. The application effectively combines fluid simulation, a temperature field, a curing field and stress and strain simulation, makes up for the singleness of traditional methods in certain type analysis, considers the influence of actual factors to the maximum extent, proposes heat distribution compensation and thermal strain compensation according to simulation results, forms a complete design method of the blended wing body mould, improves design precision, reduces the dependence and blindness of traditional design which relies on experience design, and reduces test and production trial and error costs.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of aircraft mold design, and particularly provides a design method of a blended wing body mold based on a temperature field and a curing field. BACKGROUND

[0002] The unmanned aerial vehicle technology is booming worldwide, and a blended wing body unmanned aerial vehicle is a blended structure of a fuselage structure and a wing structure of a traditional aircraft layout, and has lighter structural quality and higher lift-drag ratio. In engineering, a forming process is usually adopted for an integrated wing body shape to improve the surface quality of a composite wing body, so that a forming mold has a crucial influence on the forming of the fuselage.

[0003] In the prior art, mold design is generally started from product structure design and a process scheme, and the mold is put into production after overall design, detailed design, review and drawing, the method is more dependent on the inherent experience of mold designers, and the rationality and optimizability of the structure cannot be judged more deeply, and the superiority of the mold is judged more blindly. In the process of mold design and manufacturing, a heat distribution method is adopted for a certain degree of guidance, but the heat stress of the mold itself is usually considered only, and still has certain limitations, so how to optimize the mold of the blended wing body becomes an important direction of mold design research. SUMMARY

[0004] To solve the above problems, the application provides a design method of a blended wing body mold based on a temperature field and a curing field, mainly performs calculation of a temperature field and a curing field on the basis of a traditional design method of a blended wing body aircraft mold, firstly performs simulation through a three-dimensional temperature fluid field to obtain the convective heat transfer coefficient of each node on the surface of the mold, then imports the convective heat transfer coefficient into a structure simulation software to perform heat conduction analysis of the temperature field and the curing field of the mold and the composite material structure, and then performs sequential thermal coupling based on the above results to analyze the stress and strain conditions. According to the results, it is judged whether heat distribution compensation and heat strain compensation are needed.

[0005] The design method of the blended wing body mold based on the temperature field and the curing field provided by the application comprises the following steps:

[0006] S1, a 3D model of a blended wing body mold is established;

[0007] S2, temperature fluid simulation is performed on the 3D model, a temperature field is established, and the convective heat transfer coefficient of each node on the surface of the 3D model is obtained;

[0008] S3, a composite material structure model is established on the surface of the 3D model; the 3D model and the composite material structure model are heated and cured, and a curing field is established;

[0009] S4, calculate the heat conduction of the 3D model and the composite structure model during the heating and curing process to obtain a temperature distribution map of the structure of the 3D model;

[0010] S5, determine whether to perform thermal distribution compensation design according to the temperature distribution map;

[0011] Based on the temperature distribution map, the regions with temperature difference exceeding 10% of the overall temperature rise value are corrected, and S2 is returned to be executed until the temperature difference of all regions does not exceed 10% of the overall temperature rise value.

[0012] S6, based on the calculation result of the heat conduction, stress and strain simulation is performed on the 3D model and the thermal strain generated by the composite structure model is solved; sequential thermal force coupling analysis is performed on the 3D model and it is determined whether to perform thermal strain compensation design; if the maximum deformation of the 3D model is not within the set tolerance range, the structure of the 3D model is modified, and S2 is returned to be executed until the maximum deformation of the 3D model is within the set tolerance range, and the final wing-body integrated mold model is confirmed.

[0013] Preferably, S1 further comprises: setting the thickness and support form of the wing-body integrated mold.

[0014] Preferably, the temperature fluid simulation of the 3D model in S2 specifically comprises: simulating the temperature change of the wing-body integrated mold during the autoclave molding process, establishing a fluid calculation region according to the autoclave, calculating the fluid Reynolds number according to the air flow rate, density, viscosity and pipe diameter in the autoclave, and performing convective heat transfer calculation, and extracting the convective heat transfer coefficient of each node on the surface of the 3D model.

[0015] Preferably, the establishment of the composite structure model in S3 further comprises: meshing the composite structure model and the 3D model, wherein the mesh size of the composite structure model is set to 1% to 3% of the overall size, and the thickness direction is divided into not less than 3 layers of mesh.

[0016] Preferably, resin is added as a curing agent during the heating and curing process of the composite structure model.

[0017] Preferably, the calculation formula of the required amount for establishing the curing field in S3 is as follows:

[0018] The heat generation rate Q of the composite structure model and the resin during the heating and curing is solved as follows:

[0019]

[0020] Where, p r represents the base density of the resin, v f represents the fiber volume fraction, H r represents the total heat value generated during the complete curing of the resin, represents the curing rate, and a represents the degree of curing, a = 0 when uncured, and a = 1 when cured.

[0021] The curing kinetics equation is as follows:

[0022]

[0023] wherein K(T) represents the curing reaction constant of the resin, and w(a) represents the curing reaction mechanism function of the resin;

[0024] The expression of the curing degree of the resin is as follows:

[0025]

[0026] wherein At represents the incremental time step.

[0027] Preferably, the analysis and calculation of heat conduction in S4 are as follows:

[0028] The input calculation conditions are: density p, specific heat capacity C, thermal conductivity k, and convective heat transfer coefficient h;

[0029] The boundary conditions of the 3D model and the composite structure model are as follows: the heat conduction mode between the composite structure model and the environment in the autoclave is convection heat transfer; and the heat conduction mode between the composite structure model and the bonding surface of the 3D model is thermal conduction.

[0030] In combination with the curing field, the curing exothermicity of the composite structure model is taken as an internal heat source to obtain the three-dimensional transient heat conduction control equation as follows:

[0031]

[0032] wherein T represents the transient temperature, t represents the time used for curing, and x, y, and z represent the corresponding values of the X-axis, Y-axis, and Z-axis of the coordinate system.

[0033] Preferably, the correction mode in S5 is as follows: reducing the thickness of the region where the temperature difference value exceeds 10% of the overall temperature rise value or modifying the structural morphology of the region.

[0034] Preferably, the process of solving the thermal strain generated by the composite structure model in S6 is as follows: the temperature field and the curing field are introduced into the stress-strain simulation in the form of predefined fields, and the start and end time of heat conduction and the incremental time step are set after the temperature field is introduced; through sequential thermal-mechanical coupling analysis, the deformation prediction of the composite structure model is performed, and the strain e generated by the composite structure model in the process of heat conduction is solved as follows:

[0035] e = e e + e T ;

[0036] eT = η * ΔT

[0037] Wherein, ε e represents elastic strain, ε T represents thermal strain, η is thermal expansion rate, and ΔT is total temperature change.

[0038] Preferably, the thermal strain compensation design in S6 is specifically as follows: according to the displacement of each node in the calculation result of the sequential thermal coupling, that is, the displacement change value of each node on the composite material structure model, the displacement is compensated in reverse, that is, the original coordinates of each node are subtracted by the deformation displacement, to obtain the compensated coordinates, and the 3D model is compensated according to the compensated coordinates.

[0039] Compared with the prior art, the application can achieve the following beneficial effects:

[0040] The application effectively combines fluid simulation, temperature field, curing field and stress strain simulation, makes up for the singleness of traditional methods for certain type of analysis, considers the influence of actual factors to the greatest extent, proposes thermal distribution compensation and thermal strain compensation according to the simulation result, forms a complete design method of wing-body fusion aircraft mold, improves the design precision, reduces the dependence and blindness of experience design in traditional design, and reduces the test and production trial and error cost. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a flow chart of a design method of a wing-body fusion mold based on a temperature field and a curing field according to an embodiment of the application;

[0042] Figure 2 is a temperature change curve of an autoclave process according to an embodiment of the application;

[0043] Figure 3 is a simulation schematic diagram of a 3D model and a composite material structure model according to an embodiment of the application;

[0044] Figure 4 is a temperature distribution diagram of a temperature rise to a temperature holding process of a heat conduction process according to an embodiment of the application.

[0045] The reference signs in the drawings include:

[0046] 3D model 1, composite material structure model 2, rigid surface 3. DETAILED DESCRIPTION

[0047] Hereinafter, embodiments of the application will be described with reference to the accompanying drawings. In the following description, the same modules are denoted by the same reference signs. In the case of the same reference signs, their names and functions are also the same. Therefore, the detailed description thereof will not be repeated.

[0048] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not constitute a limitation on the present application.

[0049] This embodiment is specifically described in combination with an aircraft upper cover mold. A 3D model of the aircraft upper cover mold is established by using a traditional design method, and a mold surface is directly designed by extracting a component shape. After curing and demolding, the traditional method often has a certain error with a theory. The main reason for the error is that the temperature change of the composite material structure and the mold material is not uniform due to different thermal conductivities, and a curing gradient may be generated in the curing process, so that internal stress is generated in the composite material structure, the stress is released and deformation occurs when demolding, and a difference in different degrees is caused between the final surface and the theoretical surface. Therefore, based on this, the present application analyzes the 3D model by simulation and performs compensation design.

[0050] Figure 1 A flowchart of a design method of a blended wing body mold based on a temperature field and a curing field is shown.

[0051] As shown in Figure 1 The design method of the blended wing body mold based on the temperature field and the curing field includes the following steps:

[0052] S1, according to the input of the technical conditions of the aircraft upper cover mold, the mold shape is extracted, the thickness and support form of the mold are set, and a 3D model is established.

[0053] S2, a fluid simulation model of the 3D model is established by using FLUENT software, temperature fluid simulation is performed, the temperature change of the mold in the autoclave molding process is simulated, a fluid calculation region is established according to the autoclave, the diameter of the fluid domain is set to 3m, the fluid Reynolds number is calculated according to the air flow rate, density, viscosity and pipe diameter in the autoclave, the fluid flow state is determined to be turbulent flow according to the Reynolds number, the k-e turbulent flow model is selected, and the convection heat transfer calculation is performed, and the convection heat transfer coefficient of each node on the surface of the 3D model is extracted.

[0054] In the heat exchange process of the autoclave molding process, the surface of the mold is a convection boundary, the mold exchanges heat with the surrounding environment through the convection boundary surface, the convection heat transfer coefficient of each node on the surface of the mold is input into the 3D model, and the convection boundary condition in the fluid calculation software is mapped to the structural simulation calculation software Abaqus used in subsequent calculation.

[0055] Figure 2 A temperature change curve of the autoclave process is shown.

[0056] AsFigure 2 The temperature change of the convection boundary of the mold in the actual process is shown: the process of temperature rise - holding - temperature drop.

[0057] Figure 3 The simulation structure of the 3D model and the composite structure model provided by the embodiment of the application is shown.

[0058] As Figure 3 shown, S3, the composite structure model 2 is established on the surface of the 3D model 1, and the composite structure model 2 and the 3D model 1 are meshed, wherein the mesh size of the composite structure model is set to 1% to 3% of the overall size, and the thickness direction is divided into not less than 3 layers of meshes. In the heating and curing process of the composite structure model 2, resin is added as a curing agent, and the 3D model 1 and the composite structure model 2 are heated and cured. In the heating and curing process of the 3D model 1 and the composite structure model 2, complex heat exchange and chemical reactions occur, and a temperature gradient is formed inside, which causes the curing degree of the composite structure model 2 to be non-uniform. Therefore, a curing kinetics reaction equation needs to be introduced, and a curing field needs to be established.

[0059] The reaction process in the heating and curing process: in the actual processing process, the autoclave transmits heat to the mold through heating air and heat convection. After the surface of the mold is heated, heat conduction starts to transmit heat to the mold and the composite structure. The resin in the composite structure will undergo chemical reactions when heated, and will also release heat again during the curing process. For the simulation of the actual processing process, the chemical reactions of the resin are brought into the calculation as the curing field. Since there is secondary heat release during the curing process, the temperature field and the curing field are carried out at the same time, and the curing degree is 1 when the curing is completed.

[0060] In the process of establishing the curing field, the curing reaction state needs to be judged through the curing field subroutine in the Abaqus software. If curing has occurred, the current temperature is transmitted to the temperature control subroutine to solve the curing rate and the curing degree in the new state. According to the curing rate, the current heat is calculated, and the current heat data is transmitted to the heat conduction analysis for temperature calculation until the calculation time step is completed.

[0061] The calculation required when establishing the curing field is as follows:

[0062] The heat generation rate Q of the resin in the heating and curing is solved as follows:

[0063]

[0064] Wherein, ρ r represents the base density of the resin, v f represents the fiber volume fraction, and H rrepresents the total heat value generated during the complete curing process of the resin, represents the curing rate, and a represents the degree of curing, a = 0 when uncured; a = 1 when cured.

[0065] The curing kinetics equation is as follows:

[0066]

[0067] wherein K(T) represents the curing reaction constant of the resin, and w(a) represents the curing reaction mechanism function of the resin;

[0068] The expression of the degree of curing of the resin is as follows:

[0069]

[0070] wherein At represents the incremental time step.

[0071] S4, in the simulation software, input the calculation conditions: density p, specific heat capacity C, thermal conductivity k, and convective heat transfer coefficient h; apply the boundary conditions of 3D model 1 and composite material structure model 2: the heat conduction mode between the composite material structure model 2 and the environment in the autoclave is: convective heat transfer; the heat conduction mode between the lower surface of the composite material structure model 2 and the bonding surface of 3D model 1 is: heat conduction. Combine the curing field to take the curing exothermic heat as an internal heat source, and the three-dimensional transient heat conduction control equation is as follows:

[0072]

[0073] wherein T represents the transient temperature, t represents the time used for curing, and x, y and z represent the corresponding values of the X-axis, Y-axis and Z-axis of the coordinate system. According to the above conditions, the heat conduction during the heating and curing process of 3D model 1 and composite material structure model 2 is calculated, the convective heat transfer coefficient h is introduced into Abaqus, the curing field subroutine and the temperature field change process are set, the analysis unit of heat conduction is selected, and the heat conduction analysis is performed, so that the temperature distribution diagram of the structure of 3D model 1 can be obtained.

[0074] Figure 4 The temperature distribution of the heating to the holding process of the heat conduction process provided by the embodiment of the present application is shown.

[0075] As Figure 4 shown, S5, whether to perform heat distribution compensation design is judged according to the temperature distribution diagram;

[0076] Based on the temperature distribution map, the area where the temperature difference value exceeds 10% of the overall temperature rise value is corrected, and the thickness is reduced or the structure of the area is modified, and S2 is executed again until the temperature difference value of all areas does not exceed 10% of the overall temperature rise value. After multiple iterations, the maximum temperature difference of the temperature distribution map is 5.6% of the total temperature change, which is less than 10%, and no thermal distribution compensation is required. S6 is executed.

[0077] S6, based on the calculation results of heat conduction, stress and strain simulation is performed on the 3D model to solve the thermal strain generated by the composite structure model. The specific thermal strain analysis and calculation are as follows:

[0078] A stress-strain simulation model is established, the temperature field and solidification field are imported into the stress-strain simulation in the form of predefined fields, and the start and end time and increment time step of heat conduction are set after the temperature field is imported. Through sequential thermal force coupling analysis, deformation prediction of the composite structure model is performed, and the strain ε generated by the composite structure model in the process of heat conduction is solved as follows:

[0079] ε = ε e + ε T ;

[0080] ε T = η · ΔT;

[0081] Wherein, ε e represents elastic strain, ε T represents thermal strain, η is thermal expansion rate, and ΔT is total temperature change.

[0082] As shown in Figure 3 , the stress-strain process is as follows: 3D model 1 and composite structure model 2 are placed on rigid surface 3, 3D model 1 and composite structure model 2 are in frictional contact with rigid surface 3, and composite structure model 2 is tightly attached above 3D model 1. Before demolding, the two are considered to be bound constraints, and after demolding, the composite structure model 2 releases the internal residual stress through deformation and releases the binding constraints with the 3D model 1. The deformation, i.e. the displacement of each node, is recorded in this process. 3D model 1 and composite structure model 2 are usually symmetrical structures, and symmetrical constraints can be selected on the symmetrical surface to prevent rigid body displacement.

[0083] If the maximum deformation of the 3D model is not within the set tolerance range, modify the structure of the 3D model and return to execute S2 until the maximum deformation of the 3D model is within the set tolerance range, and confirm the model of the final wing-body fusion mold.

[0084] The specific process of thermal strain compensation is as follows: the displacement of each node in the sequential thermal coupling calculation result is extracted, which is the displacement change amount of each node due to the release of internal residual stress, and then reverse compensation is performed to subtract the displacement from the original coordinates of each node to obtain the compensated coordinates, and the 3D model is compensated according to the compensated coordinates.

[0085] In this embodiment, the maximum deformation of the aircraft upper cover is 1.02 mm, which exceeds the set tolerance of 1 mm, and needs to be designed for thermal strain compensation. After multiple iterations, the maximum deformation of the upper cover is finally 0.32 mm, which meets the tolerance range. The final design scheme is confirmed.

[0086] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

[0087] The specific embodiments of the present application do not constitute a limitation on the scope of protection of the present application. Any various other corresponding changes and modifications made according to the technical concept of the present application shall be included in the scope of protection of the claims of the present application.

Claims

1. A method for designing a blended wing body mold based on temperature field and solidification field, characterized in that, The method comprises the following steps: S1, establishing a 3D model of a blended wing body mold; S2, performing temperature fluid simulation on the 3D model to establish a temperature field and obtain a convective heat transfer coefficient of each node on the surface of the 3D model; S3, establishing a composite material structure model on the surface of the 3D model; performing heating and solidification on the 3D model and the composite material structure model, and establishing a solidification field; S4, calculating heat conduction of the 3D model and the composite material structure model during the heating and solidification process to obtain a temperature distribution map of the structure of the 3D model; S5, judging whether to perform thermal distribution compensation design according to the temperature distribution map; Based on the temperature distribution map, the regions with a temperature difference exceeding 10% of the overall temperature rise value are modified, and the step S2 is performed until the temperature difference of all regions does not exceed 10% of the overall temperature rise value; S6, based on the calculation result of the heat conduction, performing stress and strain simulation on the 3D model and solving thermal strain generated by the composite material structure model; performing sequential thermal coupling analysis on the 3D model and judging whether to perform thermal strain compensation design; if the maximum deformation of the 3D model is not within the set tolerance range, modifying the structure of the 3D model, and performing the step S2 until the maximum deformation of the 3D model is within the set tolerance range, and confirming the model of the final blended wing body mold.

2. The method of designing a blended wing body tool based on temperature field and solidification field according to claim 1, wherein, In the step S1, the thickness and support form of the blended wing body mold are set.

3. The method of designing temperature field and solidification field based blended wing body die as claimed in claim 1 wherein, In the step S2, the temperature fluid simulation on the 3D model specifically comprises: simulating the temperature change of the blended wing body mold in the autoclave molding process, establishing a fluid calculation region according to the autoclave, calculating the fluid Reynolds number according to the air flow rate, density, viscosity and pipe diameter in the autoclave, and performing convective heat transfer calculation to extract the convective heat transfer coefficient of each node on the surface of the 3D model.

4. The method of designing a blended wing body tool based on temperature field and solidification field according to claim 1, wherein, In the step S3, the composite material structure model further comprises: meshing the composite material structure model and the 3D model, wherein the mesh size of the composite material structure model is set to 1% to 3% of the overall size, and the thickness direction is divided into not less than 3 layers of meshes.

5. The method of designing temperature field and solidification field based blended wing body die as claimed in claim 1 wherein, Resin is added as a curing agent during the heating and solidification process of the composite material structure model.

6. The method of designing a blended wing body mould based on temperature field and solidification field as claimed in claim 5 wherein, The calculation formula of the required amount for establishing the solidification field in the step S3 is as follows: The heat generation rate Q of the composite material structure model and the resin during the heating and solidification is solved as follows: wherein p r represents the base density of the resin, v f represents the fiber volume fraction, H r represents the total heat value generated during the complete curing of the resin, represents the curing rate, and a represents the degree of cure, with a = 0 when uncured and a = 1 when cured. The curing kinetics equation is as follows: Wherein, K(T) represents the curing reaction constant of the resin, and w(α) represents the curing reaction mechanism function of the resin; The resin curing degree expression is as follows: Wherein, Δt represents the incremental time step.

7. The method of designing a blended wing body tool based on temperature field and solidification field according to claim 3, wherein, The analysis and calculation of the heat conduction in the step S4 are as follows: The input calculation conditions are: density ρ, specific heat capacity C, thermal conductivity k, and the convective heat transfer coefficient h; The boundary conditions of the 3D model and the composite material structure model are: the heat conduction mode between the composite material structure model and the environment in the autoclave is convective heat transfer, and the heat conduction mode of the bonding surface between the composite material structure model and the 3D model is thermal conduction; In combination with the curing field, the curing exothermicity of the composite structure model is taken as an internal heat source to obtain a three-dimensional transient heat conduction control equation as follows: Wherein, T represents a transient temperature, t represents a curing time, x, y, and z represent corresponding numerical values of X-axis, Y-axis, and Z-axis of a coordinate system.

8. The method of designing temperature field and solidification field based blended wing body die as claimed in claim 1 wherein, The correction method in S5 is to reduce the thickness of a region where a temperature difference value exceeds 10% of a total temperature rise value or modify a structural form of the region.

9. The method of designing temperature field and solidification field based blended wing body die as claimed in claim 1 wherein, The process of solving the thermal strain of the composite structure model in S6 is as follows: the temperature field and the curing field are introduced into the stress-strain simulation in the form of predefined fields, and the start and end time and the increment time step of the heat conduction are set after the temperature field is introduced; through the sequential thermal-mechanical coupling analysis, the deformation prediction of the composite structure model is performed, and the strain ε generated by the composite structure model in the heat conduction process is solved as follows: ε = ε e + ε T ; ε T = η · ΔT; where ε e represents elastic strain, ε T represents thermal strain, η is the thermal expansion rate, and ΔT is the total temperature change.

10. The method of designing temperature field and solidification field based blended wing body die as claimed in claim 1 wherein, The specific process of the thermal strain compensation design in S6 is as follows: according to the displacement amount of each node in the calculation result of the sequential thermal-mechanical coupling, which is the displacement change value of each node of the composite structure model, the displacement amount is inversely compensated, that is, the original coordinates of each node are reduced by the deformation displacement amount to obtain the compensated coordinates, and the 3D model is compensated for thermal strain according to the compensated coordinates.

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