High-temperature creep deformation prediction method based on honeycomb structure characteristics

Abstract

The invention discloses a high-temperature creep deformation prediction method based on honeycomb structure characteristics, and the method comprises the following steps: S1, combining an initial honeycomb core high-temperature creep experiment and an initial constitutive model, and carrying out the fitting to obtain a high-temperature creep unified constitutive model; s2, measuring structural characteristic parameters of the initial honeycomb core, and calculating a stress conversion factor; s3, measuring structural characteristic parameters of the honeycomb core to be measured; s4, constructing a honeycomb core simulation model to be tested in simulation software; s5, applying a load to the honeycomb core simulation model to be tested, setting an analysis step, introducing a stress conversion factor, and embedding the high-temperature creep unified constitutive model; and S6, submitting operation, and predicting the high-temperature creep deformation of the honeycomb core to be tested. The method has the advantages that the accuracy is high, the experiment cost is reduced, the experiment risk is reduced, the manpower is saved, the simulation prediction mode is faster than the experiment mode, and the types of honeycomb cores which cannot be produced by the existing process can be predicted in advance.

Description

Technical Field

[0001] The invention belongs to the technical field of honeycomb composite materials, and in particular relates to a high temperature creep deformation prediction method based on honeycomb structure characteristics. Background Art

[0002] The honeycomb sandwich structure is mainly composed of a honeycomb core and upper and lower skins, which are bonded by adhesive film. According to its application form, the honeycomb sandwich structure is mainly divided into two application structures: honeycomb sandwich wall panel structure and full-height honeycomb sandwich structure. The full-height honeycomb sandwich structure is widely used in aircraft rudders and other structures due to its high stiffness and strength characteristics. In the full-height honeycomb sandwich structure, the upper and lower surfaces of the honeycomb core directly constitute the aerodynamic surface of the aircraft, that is, the aerodynamic shape accuracy of the aircraft directly determines the forming accuracy of the full-height honeycomb sandwich structure. According to the "Aerodynamic Outer Edge Tolerance of Civil Aircraft" (HB 7086-2023), for a class of aircraft with a cruising speed of ≥600km / h, it is stipulated that the concave and convex amount error of the control surface (rudder) is controlled within 0.5mm, and the type value error of the wing leading edge area is within 0.8mm. For domestic commonly used military aircraft, the basic tolerance of the type value is (-0.5, +1.0) mm, and the limit deviation is (-0.6, +1.2) mm. For high-precision satellites, the limit deviation of the honeycomb sandwich structure is even more demanding. If the dimensional accuracy of the sandwich structure parts does not meet the standard, it will not only affect the overall aerodynamic shape of the aircraft, but may also seriously affect the safety performance of the entire aircraft.

[0003] However, the honeycomb sandwich structure will undergo permanent shrinkage during the molding process, which will make it difficult for the molded honeycomb sandwich structure parts to meet the thickness tolerance. At the same time, according to the patent document CN119348280A, a molding method for a honeycomb sandwich structure based on margin compensation, it is known that among the irreversible deformations that occur during the molding process of the honeycomb sandwich structure, the creep deformation of the honeycomb core under high temperature and high pressure is the most difficult to measure, and the creep deformation is highly consistent with the irreversible deformation of the honeycomb core.

[0004] In current industrial production, due to the differences in the thickness of aramid paper, the dipping process and the honeycomb manufacturing process, the structural characteristics of the manufactured honeycomb core vary (wall thickness d, expansion angle θ, wall length h and l or different honeycomb cell types), which leads to different creep deformations of the honeycomb core during the molding process. If the high-temperature creep deformation of the honeycomb core under each set of different structural characteristics is measured, a lot of manpower and material resources will inevitably be wasted. In other words, the existing methods are difficult to meet the prediction and verification of high-temperature creep deformation of honeycomb cores with different structural characteristics.

[0005] Therefore, it is necessary to design a new high-temperature creep deformation prediction method based on honeycomb structure characteristics. Summary of the invention

[0006] The purpose of the present invention is to provide a high temperature creep deformation prediction method based on honeycomb structural characteristics to solve the problem that the existing method proposed in the background technology is difficult to meet the high temperature creep deformation prediction and verification problem of honeycomb cores with different structural characteristics.

[0007] To achieve the above object, the present invention provides a high temperature creep deformation prediction method based on honeycomb structure characteristics, comprising the following steps: S1. Combining the initial honeycomb core high temperature creep experiment and the initial constitutive model suitable for creep, a unified constitutive model of high temperature creep of the honeycomb core is fitted; S2, measuring the structural characteristic parameters of the initial honeycomb core and calculating the stress conversion factor; S3, measuring the structural characteristic parameters of the honeycomb core to be tested; S4. constructing a simulation model of the honeycomb core to be tested according to the structural characteristic parameters of the honeycomb core to be tested in the simulation software; S5, applying load to the honeycomb core simulation model to be tested, setting analysis steps, introducing stress conversion factors, and embedding the fitted high-temperature creep unified constitutive model of the honeycomb core into the honeycomb core simulation model to be tested; S6. Submit the work to predict the high temperature creep deformation of the honeycomb core to be tested.

[0008] In a specific embodiment, the initial constitutive model suitable for creep is a Findley constitutive model.

[0009] In a specific implementation, in step S1, the nonlinear surface fitting method in Matlab is used for fitting.

[0010] In a specific implementation, during the fitting process, time and nominal stress of the honeycomb core are set as independent variables and do not participate in the fitting; time-creep deformation data is a dependent variable and does not need to be fitted; the variables to be fitted include initial creep deformation, creep parameters, stress dependence index and time index; the nominal stress = load / nominal area, and the nominal area is the overall area of ​​the honeycomb core; The initial constitutive model formula is input into the fitting software, and the time-creep deformation data of the initial honeycomb core at different temperatures and pressures in the initial honeycomb core high-temperature creep experiment are also input into the fitting software, and finally the variables to be fitted are fitted.

[0011] In a specific embodiment, the structural characteristic parameters include the straight wall length, inclined wall length, expansion angle, wall thickness of the honeycomb core cell, and the length, width and height of the overall size of the honeycomb core.

[0012] In a specific embodiment, the simulation software is Abaqus simulation software; in combination with FORTRAN and Visual Studio development environment, the fitted high-temperature creep unified constitutive model of the honeycomb core is embedded into the simulation software by combining the CREEP subroutine interface of the Abaqus simulation software's secondary development.

[0013] In a specific implementation, the stress conversion factor I=A1 / A2, A1 is the cross-sectional area of ​​the initial honeycomb core, and A2 is the nominal area of ​​the initial honeycomb core.

[0014] In a specific implementation, in step S1, the initial high-temperature creep experiment of the honeycomb core is performed using a creep machine with a planar compression creep assembly.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a high-temperature creep deformation prediction method based on honeycomb structure characteristics, which is not only highly accurate, but also reduces experimental costs, reduces experimental risks, saves manpower, and the simulation prediction method is faster than the experimental method. It can also predict in advance the types of honeycomb cores that cannot be produced by existing processes, which provides solid technical support for the performance prediction and optimization design of composite materials under extreme environmental conditions.

[0016] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention is further described in detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 It is a schematic diagram of a flow chart of an embodiment of the present invention; Figure 2 This is a fitting result diagram of an embodiment of the present invention at 120°C and 0.2-0.5MPa; Figure 3 This is a fitting result diagram of an embodiment of the present invention at 180°C and 0.2-0.5MPa; Figure 4 It is a diagram of the overall size and structural characteristic parameters of a honeycomb core of an embodiment of the present invention; Figure 5 It is a schematic diagram of a cross section of a hexagonal honeycomb core; Figure 6 It is a schematic diagram of a cross section of an over-expanded honeycomb core; Figure 7 This is a comparison diagram of simulated creep prediction deformation and experimental results of honeycomb cores with different structural characteristics according to an embodiment of the present invention; Figure 8 It is a schematic diagram of a honeycomb sandwich structure; wherein: 1. honeycomb core; 2. adhesive film; 3. upper skin; 4. lower skin. DETAILED DESCRIPTION

[0018] The embodiments of the present invention are described in detail below. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] Example 1 A high temperature creep deformation prediction method based on honeycomb structure characteristics of the present invention comprises the following steps: S1. Combining the initial honeycomb core high-temperature creep experiment and the initial constitutive model suitable for creep, a unified constitutive model of high-temperature creep of the honeycomb core is fitted.

[0020] The initial constitutive model suitable for creep is the Findley constitutive model, which is expressed as follows: , in, e (t) is the creep deformation when the creep time is t, e 0 is the initial creep strain, A is the creep parameter, which is affected by temperature and material properties. s is the applied stress, n is the stress dependence index, and m is the time index.

[0021] The initial honeycomb core in the high-temperature creep experiment of the initial honeycomb core is a hexagonal honeycomb core. The overall size of the hexagonal honeycomb core is: W×L×T=35mm×35mm×20mm, and the structural characteristic parameters of the honeycomb core cell are: h=1.99mm, l =2.02mm, d=0.05mm, θ=30°. Temperature conditions are: 120℃ and 180℃, nominal stress conditions are: 0.2MPa-0.5MPa, nominal stress = load / nominal area, nominal area = W×L, creep time is: 35h.

[0022] In the step S1, the initial honeycomb core high temperature creep experiment uses a creep machine with a planar compression creep assembly to conduct high temperature creep of the honeycomb core under multiple sets of commonly used experimental conditions, laying a foundation for the subsequent establishment of a unified constitutive model.

[0023] The plane compression creep assembly includes a tensile conduction compression mold, an upper plane compression mold and a lower plane compression mold; the tensile conduction compression mold includes a first compression block and a second compression block, and a spacing for installing a sample is maintained between the first compression block and the second compression block along the tensile direction of the creep machine, and the spacing value can be adjusted. When the spacing becomes smaller, it is used to provide a creep compression loading operation for the sample, and when the spacing becomes larger, it is used to remove the sample; a first threaded hole is provided on the second compression block, and the axis of the first threaded hole is the same as the tensile direction of the creep machine, and a first through hole coaxial with the first threaded hole is provided on the first compression block; the upper plane compression mold includes an upper cylindrical rod, an externally threaded end and an upper circular plate, and one end of the upper cylindrical rod is fixed to the externally threaded end The upper circular plate is connected, one side plate surface of the upper circular plate is fixedly connected to the other end of the upper cylindrical rod, and the external threaded end and the upper circular plate are coaxially arranged with the upper cylindrical rod; the external threaded end is matched and arranged on the first threaded hole; the lower plane compression mold includes a lower cylindrical rod, a cylindrical base, a column pin and a lower circular plate, the cylindrical base is plate-shaped, one end of the column pin is fixedly connected to one side of the cylindrical base, the other side of the cylindrical base is fixedly connected to one end of the lower cylindrical rod, the lower circular plate is fixedly arranged at the other end of the lower cylindrical rod, the column pin and the lower circular plate are coaxially arranged with the lower cylindrical rod, the surface of the cylindrical base close to the column pin is perpendicular to the axis of the lower cylindrical rod, and the surface of the lower circular plate away from the column pin is parallel to the surface of the cylindrical base close to the column pin; the column pin is matched and arranged on the first through hole. The preferred planar compression creep assembly is the same as the structure disclosed in patent document CN202410785728.3.

[0024] In the step S1, the nonlinear surface fitting method in Matlab is used for fitting.

[0025] During the fitting process, the creep time t and the nominal stress of the honeycomb core s Set as an independent variable, not involved in fitting, creep time t as an independent variable, nominal stress on the honeycomb core s is an environmental variable, which changes with the change of the load applied in the experiment; time-creep deformation data e (t) is the dependent variable and does not need to be fitted; the variables to be fitted include the initial creep deformation e 0, creep parameter A, stress dependence index n and time index m; the nominal stress = load / nominal area, the nominal area is the overall area of ​​the honeycomb core; The initial constitutive model formula is input into the fitting software, and the time-creep deformation data of the initial honeycomb core at different temperatures and pressures in the initial honeycomb core high-temperature creep experiment are also input into the fitting software, and finally the variables to be fitted are fitted.

[0026] S2. Measure the structural characteristic parameters of the initial honeycomb core and calculate the stress conversion factor.

[0027] Under the same experimental conditions (temperature and load), when the structural characteristics of the honeycomb core change (cell wall thickness, cell size, wall length or cell type), the equivalent stress inside the honeycomb core will inevitably change (equivalent stress is the stress on each tiny unit in the honeycomb core, which is different from the nominal stress. The nominal stress refers to the pressure on the honeycomb core as a whole, which is often equal to the experimental pressure). Once the equivalent stress inside the honeycomb core changes, the equivalent stress is converted into the nominal stress in the unified constitutive model through the stress conversion factor, and finally the creep deformation prediction simulation of the honeycomb core under different structural characteristics is realized.

[0028] The stress conversion factor is a constant, which is mainly used to convert the equivalent stress of the honeycomb core used in the experiment into the nominal stress required in the unified creep constitutive model. s This factor is determined by the ratio of the cross-sectional area of ​​the initial honeycomb core to the nominal area.

[0029] Determination of stress conversion factor: First, the structural characteristic parameters of the initial honeycomb core are measured, wherein the structural characteristic parameters include the straight wall length, inclined wall length, expansion angle, wall thickness of the honeycomb core cell, and the length, width and height of the overall size of the honeycomb core.

[0030] Then, the cross-sectional area A1 of the initial honeycomb core is calculated according to the structural characteristic parameters. The cross-sectional area is the area directly supported by the honeycomb core, not the area hollowed out in the middle of the hexagon of the honeycomb core, or the area occupied by the solid material.

[0031] The external experimental pressure conditions are s 1 as an example, assuming that the nominal area of ​​the honeycomb core = A2, the force F applied to the surface of the honeycomb core can be calculated according to the pressure formula = s 1×A2 (Note: the cross-sectional area of ​​the honeycomb core is not the same as the nominal area).

[0032] In the simulation, the experimental conditions are applied to obtain the stress of the internal unit of the honeycomb core, assuming that s 2=F / A1. The stress in the unified constitutive s is equal to s 1, so it is necessary to introduce a stress conversion factor I to convert the stress output by the simulation model s 2. Stress converted to the constitutive model s 1. Because s 2=F / A1, F= s 1×A2 roll out: s 2*A1 / A2= s 1 Therefore, A1 / A2 is defined as a new constant I, i.e., stress conversion factor, to convert the creep stress output in the simulation model to the nominal stress in the constitutive model. The creep stress output in the simulation model is the equivalent stress, i.e., the stress on the internal unit of the honeycomb core during the creep process.

[0033] Then calculate the nominal area of ​​the initial honeycomb core, the nominal area A2 = W × L, the nominal area is the entire area of ​​the honeycomb core, that is Figure 4 W×L in.

[0034] Finally, the stress conversion factor I=A1 / A2 is calculated, where A1 is the cross-sectional area of ​​the initial honeycomb core and A2 is the nominal area of ​​the initial honeycomb core. The stress conversion factor is used to convert the creep stress output in the simulation model to the nominal stress in the constitutive model. s .

[0035] S3. Measure the structural characteristic parameters of the honeycomb core to be tested.

[0036] S4. Construct a simulation model of the honeycomb core to be tested in the simulation software according to the structural characteristic parameters of the honeycomb core to be tested. The modeling in the simulation software adopts a single-layer orthotropic method, and the aramid paper and the phenolic resin are equivalent to a unified entity unit.

[0037] S5, applying load to the honeycomb core simulation model to be tested, setting analysis steps, introducing stress conversion factors, and embedding the fitted high-temperature creep unified constitutive model of the honeycomb core into the honeycomb core simulation model to be tested; Apply load F, load = experimental pressure condition (nominal stress) × W × L.

[0038] The simulation software is Abaqus2023 simulation software; combined with FORTRAN 2020 and Visual Studio 2019 development environment, the constitutive model is compiled and embedded, and the high-temperature creep unified constitutive model of the honeycomb core obtained by fitting is embedded into the simulation software by combining the CREEP subroutine interface of the Abaqus simulation software's secondary development to realize the high-temperature creep simulation of the honeycomb core.

[0039] During the compilation process, the stress conversion factor I is introduced to realize the creep deformation prediction of honeycomb cores with different structural characteristics.

[0040] During the compilation process, the Findley model is divided into two analysis steps to embed the model step by step.

[0041] Findley constitutive model: .

[0042] In the creep simulation of the honeycomb core, two viscous analysis steps are set. The Findley constitutive model is separated separately, that is, the embedding of the first viscous analysis step e 0, the second sticky analysis step to embed . Because in the second analysis step The function is a continuous function, so the normal calculation can be performed. e 0 is a step function, and because e 0 is a fixed constant, so a linear increment method is used to e 0 is calculated by multiple fixed increments, the purpose is to e 0 step function, converted to a linear continuous function to achieve the purpose of computational convergence. Example: Using n fixed increments to smooth e 0, deformation in each fixed increment e 0 / n, where n is determined through multiple simulation trials until the calculation converges.

[0043] S6. Submit the work to predict the high temperature creep deformation of the honeycomb core to be tested.

[0044] Experimental verification: Verification 1. Comparison of creep deformation prediction and experimental results under different pressures for the same honeycomb core.

[0045] Experimental materials: Hexagonal honeycomb core with the same structural characteristics (structural characteristics: h=1.99mm, l =2.02mm, d=0.05mm, θ=30°), which is the same as the initial honeycomb core, with an overall size of W×L×T=35mm×35mm×20mm.

[0046] Experimental conditions: 180℃, 0.6MPa, 35h (the unified constitutive model was established at 0.2-0.5MPa, so the applicability of the model under different pressure conditions was verified).

[0047] Experimental equipment: The same creep machine with a planar compression creep assembly.

[0048] Verification 2: Comparison of creep deformation prediction and experimental results of honeycomb cores with different structural characteristics.

[0049] Experimental materials: Overexpanded honeycomb core with different structural characteristics (structural parameters: h = 1.77 mm, l =3.85mm, d=0.085mm, θ=11°), overall size: W×L×T=35mm×35mm×20mm.

[0050] Experimental conditions: 180℃, 0.6MPa, 35h.

[0051] Experimental equipment: The same creep machine with a planar compression creep assembly.

[0052] Verification results: Under the same experimental conditions, in terms of the prediction of the final creep deformation, the simulation prediction accuracy of the hexagonal honeycomb core is 98%, and for the over-expanded honeycomb cores with different structural characteristics, the simulation prediction accuracy is as high as 97.1%, indicating that the simulation prediction method provided by the present invention can realize the prediction of the out-of-plane compression creep deformation of honeycomb cores with different nominal stresses and different structural characteristics, and has high prediction accuracy, proving the feasibility of the method. This provides a solid technical support for the performance prediction and optimization design of honeycomb composite materials under extreme environmental conditions.

[0053] The present invention provides a high-temperature creep deformation prediction method based on honeycomb structure characteristics, which can be used to predict the creep deformation of honeycomb cores with different structural characteristics in advance, and then add a honeycomb core margin while milling the honeycomb core to compensate for the shrinkage deformation of the honeycomb sandwich structure during the molding process, ultimately achieving the purpose of precise molding of the honeycomb sandwich structure.

[0054] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A high temperature creep deformation prediction method based on honeycomb structure characteristics, characterized in that: The steps include: S1. Combining the initial honeycomb core high temperature creep experiment and the initial constitutive model suitable for creep, a unified constitutive model of high temperature creep of the honeycomb core is fitted; S2, measuring the structural characteristic parameters of the initial honeycomb core and calculating the stress conversion factor; S3, measuring the structural characteristic parameters of the honeycomb core to be tested; S4. constructing a simulation model of the honeycomb core to be tested according to the structural characteristic parameters of the honeycomb core to be tested in the simulation software; S5, applying load to the honeycomb core simulation model to be tested, setting analysis steps, introducing stress conversion factors, and embedding the fitted high-temperature creep unified constitutive model of the honeycomb core into the honeycomb core simulation model to be tested; S6. Submit the work to predict the high temperature creep deformation of the honeycomb core to be tested.

2. The high temperature creep deformation prediction method based on honeycomb structure characteristics according to claim 1, characterized in that: The initial constitutive model suitable for creep is the Findley constitutive model.

3. The high temperature creep deformation prediction method based on honeycomb structure characteristics according to claim 1, characterized in that: In the step S1, the nonlinear surface fitting method in Matlab is used for fitting.

4. The high temperature creep deformation prediction method based on honeycomb structure characteristics according to claim 3 is characterized in that: During the fitting process, time and nominal stress of the honeycomb core are set as independent variables and do not participate in the fitting; time-creep deformation data is the dependent variable and does not need to be fitted; the variables to be fitted include initial creep deformation, creep parameters, stress dependence index and time index; the nominal stress = load / nominal area, and the nominal area is the overall area of ​​the honeycomb core; The initial constitutive model formula is input into the fitting software, and the time-creep deformation data of the initial honeycomb core at different temperatures and pressures in the initial honeycomb core high-temperature creep experiment are also input into the fitting software, and finally the variables to be fitted are fitted.

5. The high temperature creep deformation prediction method based on honeycomb structure characteristics according to claim 1, characterized in that: The structural characteristic parameters include the straight wall length, inclined wall length, expansion angle, wall thickness of the honeycomb core cell, and the length, width and height of the overall size of the honeycomb core.

6. The high temperature creep deformation prediction method based on honeycomb structure characteristics according to claim 1, characterized in that: The simulation software is Abaqus simulation software; combining FORTRAN and Visual Studio development environment, the high-temperature creep unified constitutive model of the honeycomb core obtained by fitting is embedded into the simulation software by combining the CREEP subroutine interface of the Abaqus simulation software with secondary development.

7. The high temperature creep deformation prediction method based on honeycomb structure characteristics according to claim 1, characterized in that: The stress conversion factor I=A1 / A2, A1 is the cross-sectional area of ​​the initial honeycomb core, and A2 is the nominal area of ​​the initial honeycomb core.

8. The high temperature creep deformation prediction method based on honeycomb structure characteristics according to claim 1, characterized in that: In the step S1, the initial high temperature creep experiment of the honeycomb core is performed using a creep machine with a planar compression creep assembly.

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