Deformation prediction method for trepanning after composite material curing

Abstract

The invention discloses a deformation prediction method for trepanning after curing of a composite material, which comprises the following steps of: firstly, establishing a finite element model without trepanning by using three-dimensional modeling software, and performing grid division; a complete thermal coupling method is adopted, and the temperature, the curing rate, the curing degree and the stress result before demolding are obtained through calculation; the stress distribution result and the displacement deformation result of the finite element model after demolding are recalculated through a stress calculation method by converting boundary conditions of the finite element model, and the stress distribution result and the displacement deformation result after demolding are obtained; then marking an area needing to be perforated, performing rigidity reduction and stress release to realize simulation of perforated holes, and recalculating a stress distribution result and a displacement deformation result of the perforated finite element model through a stress calculation method; and exporting a back result of the component after trepanning and a result before curing, and performing high-precision fitting by means of Geomagi c Control software to obtain a final trepanning deformation result after curing.

Description

Technical Field

[0001] The present invention relates to the field of finite element simulation of composite materials, and particularly to a method for predicting deformation of a composite material after curing and then perforating. Background Art

[0002] A composite material is a material formed by optimally combining materials with different properties through an advanced material preparation technology. It is composed of two or more materials with different properties, and through physical or chemical methods, it forms a material with new properties macroscopically. In a composite material, usually one phase is a continuous phase, called the matrix; the other phase is a dispersed phase, called the reinforcing material. The dispersed phase is distributed in the entire continuous phase in an independent form, and there is a phase interface between the two phases.

[0003] Through curing deformation simulation, the deformation of composite materials under different process parameters (such as curing temperature, heating rate, pressure, etc.) can be predicted, so as to optimize the process parameters, reduce deformation, improve product quality. Conducting simulation before actual production can discover potential deformation problems in advance, avoid waste products and rework caused by unreasonable design or improper process, and reduce production costs. In the manufacturing of composite material components such as aircraft wings and fuselage structures, curing deformation simulation is widely used to optimize design and process to ensure the dimensional accuracy and performance reliability of components, reduce structural weight, and improve the fuel efficiency and flight performance of aircraft. For the structure of an aircraft fuselage, due to the existence of windows, an opening design is required during the manufacturing of the fuselage.

[0004] However, for perforating, whether to perforate first and then cure or cure first and then perforate, the prior art cannot accurately predict which method results in less deformation; in addition, since curing and then perforating will change the stress distribution and deformation amount of the material, it is impossible to achieve results similar to those of experiments through simulation prediction methods. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and propose a method for predicting deformation of a composite material after curing and then perforating. Based on a fully thermo-mechanical coupling method, it accurately grasps multiple actual situations such as the kinetic equation required for curing deformation, thermal strain and mechanical strain, the treatment of the demolding process, and the influence of the perforating sequence of perforating first and then perforating. For composite material components considering the perforated structure, the final manufacturing deformation is smaller, and it can effectively improve the accuracy of simulation prediction results.

[0006] To achieve the above purpose, the specific technical solution adopted by the present invention is as follows:

[0007] A method for predicting deformation of a composite material after curing and then perforating, comprising the following steps:

[0008] Step 1: Use 3D modeling software to establish a finite element model without holes, then perform mesh division through mesh processing software, and then import it into ABAQUS software to assign material parameters to the finite element model without holes, set the number of layers of the composite material, and set the corresponding material directions for each layer;

[0009] Step 2: Adopt a fully thermo-mechanical coupling method to set the temperature during the curing process of the composite material through curing process parameters, and calculate the temperature, curing rate, degree of cure, and stress results before demolding respectively;

[0010] Step 3: By converting the boundary conditions of the finite element model and using the stress calculation method, recalculate the stress distribution results and displacement deformation results of the finite element model after demolding to obtain the stress distribution results and displacement deformation results after demolding; then mark the area that needs to be drilled, and perform stiffness reduction to release stress to achieve the simulation of drilling. By using the stress calculation method, recalculate the stress distribution results and displacement deformation results of the finite element model after drilling;

[0011] Step 4: Export the results on the back of the component after drilling and the results before curing, and use Geomagic Control software for high-precision fitting to obtain the final deformation results of the drilled hole after curing.

[0012] Preferably, the mesh division method is: use ANSA software to perform geometric cleaning and mesh processing on the model, and then output an inp file that can be recognized by ABAQUS.

[0013] Preferably, in Step 2, the curing process parameters are: heating from room temperature to 70°C at a rate of 2°C / min, holding for 1 hour, then heating to 120°C at a rate of 2°C / min, holding for 1 hour, then heating to 180°C at a rate of 2°C / min, holding for 2 hours, and finally cooling to room temperature at a rate of 2°C / min.

[0014] Preferably, in Step 2, given the curing process parameters and the curing kinetics equation, calculate the temperature, curing rate, and degree of cure through the curing kinetics method.

[0015] Preferably, in Step 2, determine the glass transition temperature through testing, obtain the known relevant parameters, and finally calculate the stress distribution results before demolding through the curing deformation mechanics model. The relevant parameters include the stiffness matrices in the rubber state and glass state, the effective strain vector, and the time at the glass transition point.

[0016] Preferably, in Step 3, use the UMAT subroutine to identify the drilled hole area by using the element number, and mark it with the state variable when it is judged that the element is in the hole area.

[0017] Preferably, in step 3, when it is determined that the stiffness reduction of the marking unit is performed, the glassy material parameters in the perforated area are reduced to a minimum value, allowing stress release, recalculating the stress distribution, and deleting it in the post-processing module by checking the marking status.

[0018] Preferably, in step 4, by extracting the displacement results of the unit on the back layer after perforation and the displacement results before curing from the ABAQUS calculation results, saving the results in the obj file format, and then importing them into the Geomagic Control software for high-precision fitting. Set the design model as the Reference object, set the simulation result as the Test object, and use the best-fit alignment algorithm to make the simulation result approach and fit the design model. Use the 3D comparison algorithm to generate the deformation result.

[0019] The present invention has the following characteristics and beneficial effects:

[0020] The present invention takes into account the complex process of composite material curing and forming, uses the actually measured curing kinetic equation, considers the thermal strain and curing shrinkage in different directions, considers the order of perforation before and after, realizes perforation treatment after demolding, accurately grasps the influencing factors of the deformation amount after perforation of the composite material after curing, provides an effective method for the manufacture of composite material components considering perforation, and reduces the deformation amount in the composite material manufacturing process. Brief Description of the Drawings

[0021] Figure 1 It is a flow chart of the curing-demolding-perforation relationship in a deformation prediction method for perforating a composite material after curing provided by the present invention.

[0022] Figure 2 It is a schematic diagram of the C-shaped component used in the embodiment of the present invention.

[0023] Figure 3 It is a flow chart of the relationship between the subroutine called by ABAQUS and perforation of the present invention.

[0024] Figure 4 It is a schematic diagram of the perforated area identification of the present invention.

[0025] Figure 5 It is a schematic diagram of the displacement prediction result of the present invention.

[0026] Figure 6 It is a schematic diagram of the high-precision fitting setting of the present invention.

[0027] Figure 7 It is a schematic diagram of the final deformation result of the present invention.

[0028] Figure 8 It is a schematic diagram of the material direction setting in the embodiment of the present invention.

[0029] Figure 9 Schematic diagram of the comparison points between the test and simulation results of the present invention. Specific embodiments

[0030] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0031] A method for predicting the deformation of a composite material after curing and then drilling holes, as Figure 1 shown, includes the following steps:

[0032] Step 1: Use 3D modeling software to establish a finite element model without holes, and then perform mesh division through mesh processing software. Specifically, use ANSA software to perform geometric cleaning and mesh processing on the model, and then output an inp file that ABAQUS can recognize.

[0033] Then import the inp file into ABAQUS software to assign material parameters to the finite element model without holes, set the number of layers of the composite material, and set the corresponding material directions for each layer;

[0034] It should be noted that the composite material is composed of fibers and resin, and the material direction refers to the orientation of the fibers; as Figure 8 shown, the red line in the figure is the fiber direction, 1 is the 0-degree direction, 2 is the 90-degree direction, and 3 is the thickness direction.

[0035] In this embodiment, taking the C-shaped component as an example, as shown in the appendix Figure 2 shown, use 3D modeling software to establish the required model, then import the model into ANSA software, perform geometric cleaning and mesh division, and then export the inp file; open this file through ABAQUS, set relevant material parameters such as density, user-defined material, user-defined field, etc.; perform ply division on the composite material, assign material properties to the model, and determine the material direction; adopt the fully thermo-mechanical coupling method, set the first analysis step as the temperature-displacement coupling analysis step, and the second and third analysis steps as the static-general analysis steps, set the output requests for fields such as temperature, displacement, stress, etc.; set the corresponding boundary conditions in the load module; assign the element type as the temperature-displacement coupling C3D8T element type in the mesh module.

[0036] Step 2: Adopt the fully thermo-mechanical coupling method to set the temperature during the curing process of the composite material through the curing process parameters, and calculate the temperature, curing rate, degree of cure, and stress results before demolding respectively.

[0037] Specifically, the flow chart of the ABAQUS calling subroutine and the hole-opening relationship is as shown in the appendixFigure 3 As shown. The curing process parameters are as follows: heating from room temperature to 70 °C at a rate of 2 °C / min, holding for 1 hour, then heating to 120 °C at a rate of 2 °C / min, holding for 1 hour, then heating to 180 °C at a rate of 2 °C / min, holding for 2 hours, and finally cooling to room temperature at a cooling rate of 2 °C / min. Write it into the DISP subroutine.

[0038] In this embodiment, the degree of cure field variable is defined by the USDFLD subroutine; the heat inside the material is defined by the HETVAL subroutine, the degree of cure and the curing rate are calculated, and the degree of cure is updated. The curing rate is as follows:

[0039]

[0040] where α is the degree of cure and T is the temperature, is the curing rate;

[0041] Furthermore, the glass transition temperature is determined through testing, and known relevant parameters are obtained. Finally, the stress distribution result before demolding is calculated through the curing deformation mechanical model. The relevant parameters include the stiffness matrices in the rubber state and the glass state, the effective strain vector, and the time at the glass transition point.

[0042] Among them, the expression of the curing deformation mechanical model is as follows:

[0043]

[0044] In the formula, are the stiffness matrices in the rubber state and the glass state respectively, σ i is the stress distribution result before demolding, is the effective strain vector, t vit is the time at the glass transition point, T g (α) is the glass transition temperature; among them, the glass transition temperature measured through experiments is:

[0045]

[0046] The thermal strain and the curing shrinkage strain are calculated through the UEXPAN subroutine. According to the change in temperature ΔT in the incremental step, the thermal strain increment of the composite material can be calculated. It can be understood that the thermal strain increment is that the temperature will cause the material to thermally expand, thereby causing the strain to change; the change in strain will cause the stress to change, affecting the final stress result; the strain in the curing deformation mechanical model in step 2 is the total strain, which includes the thermal strain, that is

[0047]

[0048] where α iis the coefficient of thermal expansion; the coefficient of thermal expansion of the material measured by a thermomechanical analyzer (TMA) is as follows:

[0049]

[0050] The coefficient of thermal expansion in the fiber direction is 0; the curing shrinkage strain is measured by experiment, and the result in the direction perpendicular to the fiber is 0.45%.

[0051] The curing temperature curve is defined by the DISP subroutine, the heat inside the material is defined by the HETVAL subroutine, the degree of cure and the curing rate are calculated, the degree of cure is updated, the degree-of-cure field variable is defined by the USDFLD subroutine, data is transferred through the state variable STATEV and the user subroutine HETVAL, the thermal strain and the curing shrinkage strain are calculated by the UEXPAN subroutine, and the temperature-dependent material parameters, stiffness matrix, mechanical strain, and calculation of total stress strain are defined by the UMAT subroutine.

[0052] It should be noted that the results before demolding are calculated by the curing deformation mechanical model. After demolding, part of the stress is released to obtain the curing residual stress. After opening the holes, the stress is further released to obtain the final curing residual stress.

[0053] Step 3: By converting the boundary conditions of the finite element model and using the stress calculation method, recalculate the stress distribution results and displacement deformation results of the finite element model after demolding to obtain the stress distribution results and displacement deformation results after demolding; then mark the area where holes need to be opened, and perform stiffness reduction to release stress to simulate the opening of holes. By using the stress calculation method, recalculate the stress distribution results and displacement deformation results of the finite element model after opening the holes;

[0054] It is necessary to explain that when considering the opening of holes, instead of first opening the holes in the finite element model and then performing simulation calculations, an unopened finite element model is used. After the curing deformation simulation is completed, the demolding process is considered, and then the holes are opened after demolding. This method has a smaller curing deformation amount compared with opening the holes first.

[0055] In this embodiment, through the UMAT subroutine, the element number is used to identify the area where holes are opened. When it is determined that the element is in the hole area, the state variable is used to mark it, and stiffness reduction treatment is performed to recalculate the stress. The marking results are as shown in the appendix Figure 4 shown; the simulation method of opening holes draws on the element degradation and deletion technology used in the failure analysis of composite materials. Then, when it is determined that it is in the third analysis step, the stiffness of the marked elements is reduced, and the glassy material parameters in the hole area are reduced to a very small value. In this embodiment, the very small value is set to 0.001 to allow stress release, recalculate the stress distribution, delete the marked elements, and view the marked status to perform deletion in the post-processing module. The displacement results are as shown in the appendixFigure 5 as shown

[0056] Step 4: Export the results of the back side of the component after hole opening and the results before curing, and use Geomagic Control software for high-precision fitting to obtain the final deformation results after curing and hole opening.

[0057] Specifically, by extracting the displacement results of the back layer elements after hole opening and the displacement results before curing from the ABAQUS calculation results, saving the results in the obj file format, then importing them into Geomagic Control software for high-precision fitting, setting the design model as the Reference object, setting the simulation results as the Test object, using the best-fit alignment algorithm to make the simulation results approach and fit the design model, and using the 3D comparison algorithm to generate the deformation results, as shown in the appendix Figure 7 as shown

[0058] To further clarify the error between the simulation and the test, taking the appendix Figure 9 model as an example, according to the structural characteristics of the model, 8 characteristic points are selected in the 1 / 4 area on the back side for comparison of deformation data.

[0059] Table 1 shows the comparison results between the simulation and the test as follows:

[0060]

[0061] It can be seen from Table 1 that the error between the simulation and the test is very small, and the difference does not exceed 0.2 mm. Therefore, predicting deformation problems in advance through simulation can reduce the number of trial and error and material waste, and shorten the product development cycle. Accurate deformation prediction helps to improve product reliability and meet the stringent requirements for the performance of composite materials in high-end fields. It has clear application value in high-end fields such as aerospace and automotive manufacturing, and can significantly improve the manufacturing accuracy and efficiency of composite components. Although there are certain technical thresholds and data dependence problems, its core advantage of optimizing the process and reducing costs through simulation makes it have broad prospects in industrial production. With the continuous expansion of the application of composite materials, this method is expected to become one of the standard technologies in the industry.

[0062] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art of this industry should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only the preferred examples of the present invention, and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for predicting deformation of composite materials after curing and then opening holes, characterized in that: The steps include: Step 1: Use 3D modeling software to establish a finite element model without openings, then use mesh processing software to perform meshing, and then import ABAQUS software to assign material parameters to the finite element model without openings, set the number of layers of the composite material, and set the corresponding material direction of each layer; Step 2: Using a fully thermomechanical coupling method, the temperature during the curing process of the composite material is set by the curing process parameters, and the curing rate, curing degree, and stress results before demolding are obtained by calculation; Step 3, by converting the boundary conditions of the finite element model and using the stress calculation method, recalculate the stress distribution result and displacement deformation result of the finite element model after demoulding, and obtain the stress distribution result and displacement deformation result after demoulding; Then, the area where the hole needs to be opened is marked, and the stiffness is reduced to release the stress to simulate the opening. The stress distribution results and displacement deformation results of the finite element model after the hole is opened are recalculated through the stress calculation method. Step 4: Export the back side results of the component after opening and the results before curing, and use Geomagic Control software for high-precision fitting to obtain the final deformation results of the opening after curing.

2. The method for predicting deformation of composite materials after curing and then opening holes according to claim 1, characterized in that: The meshing method is: geometrically clean the model and process the mesh using ANSA software, and then output an inp file that can be recognized by ABAQUS.

3. The method for predicting deformation of composite materials after curing and then opening holes according to claim 1, characterized in that: In step 2, the curing process parameters are: heating from room temperature to 70°C at 2°C / min, keeping warm for 1 hour, then heating to 120°C at 2°C / min, keeping warm for 1 hour, then heating to 180°C at 2°C / min, keeping warm for 2 hours, and finally cooling to room temperature at a cooling rate of 2°C / min.

4. The method for predicting deformation of composite materials after curing and then opening holes according to claim 1, characterized in that: In step 2, the curing process parameters and curing kinetics equation are known, and the curing rate and curing degree are calculated by the curing kinetics method.

5. The method for predicting deformation of composite materials after curing and then opening holes according to claim 1, characterized in that: In step 2, the glass transition temperature is determined by testing, and known related parameters are obtained. Finally, the stress distribution result before demolding is calculated by the curing deformation mechanics model. The related parameters include the stiffness matrix of the rubber state and the glass state, the effective strain vector and the time of the glass transition point.

6. The method for predicting deformation of composite materials after curing and then opening holes according to claim 1, characterized in that: In step 3, the unit number is used to identify the hole area through the UMAT subroutine, and when the unit is judged to be in the hole area, it is marked using the state variable.

7. The method for predicting deformation of composite materials after curing and then opening holes according to claim 6, characterized in that: In step 3, when it is determined that the marked unit is to be subjected to stiffness reduction, the glass material parameter in the opening area is reduced to a minimum value, stress release is allowed, the stress distribution is recalculated, and then the marking status is checked and deleted in the post-processing module.

8. The method for predicting deformation of composite materials after curing and then opening holes according to claim 1, characterized in that: In step 4, the displacement results of the back layer unit after the hole is opened and the displacement results before curing are extracted from the ABAQUS calculation results, the results are saved in obj file format, and then imported into Geomagic Control software for high-precision fitting, the design model is set as the Reference object, the simulation result is set as the Test object, the best fit alignment algorithm is used to fit the simulation result to the design model, and the deformation result is generated by the 3D comparison algorithm.

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