CN114239369B - Stress analysis method for honeycomb sandwich structure forming process - Google Patents
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Abstract
The invention discloses a stress analysis method for a honeycomb sandwich structure forming process, which comprises the steps of measuring basic data of mechanical properties of a composite material paper honeycomb core material through experiments, inputting the obtained basic data into ABAQUS simulation software for simulation, and finally forecasting the load condition of a typical part in the honeycomb sandwich structure forming process through a simulation result. When a finite element model is constructed, in an equivalent model, the skin adopts a shell unit, and the beam and the honeycomb core adopt a three-dimensional entity unit; and establishing a detail model at a key part with a higher stress level of the equivalent model, wherein in the detail model, the skin adopts a three-dimensional solid unit, the honeycomb core adopts a shell unit, and the adhesive layer adopts a complex unit. The method can forecast the stress in each direction in the forming process of the honeycomb sandwich structure in advance, is beneficial to analyzing the cause of some defects, is convenient for improving the production process in the later period, improves the product percent of pass, and has better practicability.
Description
Technical Field
The invention belongs to the technical field of honeycomb sandwich structure forming analysis, and particularly relates to a stress analysis method in a honeycomb sandwich structure forming process.
Background
The composite material paper honeycomb has the advantages of high specific stiffness, high specific strength, designable performance and the like, and is widely applied to various fields of aviation, aerospace, high-speed transportation means, modern structural engineering and the like. In the production and manufacturing process of the composite material honeycomb sandwich structure, under the combined action of factors such as pressure of a hot pressing tank, temperature change, water loss, incomplete gas internal pressure of local core grids and the like, because the tearing strength of certain batches of honeycomb paper is unstable, the honeycomb of the part with larger height of the structure is unstable to generate larger deformation, and even the cracking fault of the local core grids occurs. However, the problem of local cracking of the honeycomb is difficult to explain clearly from the perspective of simple theoretical analysis and engineering experience, and therefore, deep quantitative research is required to be carried out, and the main causative mechanism of the local cracking of the honeycomb is grasped by combining the theory and the engineering experience. The method is characterized in that a stress analysis model of the composite material honeycomb sandwich structure forming process is established and verified by means of modern calculation simulation means, so that the method is an important way for stress analysis and has a certain reference value for engineering application.
Disclosure of Invention
The invention aims to provide a stress analysis method for a honeycomb sandwich structure forming process, and aims to realize accurate stress analysis for the honeycomb sandwich structure forming process through a simulation method. The invention relates to a method for predicting mechanical properties of a composite material honeycomb sandwich structure in a forming process, which is characterized in that the modulus, the tear strength, the thermal expansion coefficient and the like of the honeycomb structure are tested through experiments, a simulation model of the composite material honeycomb sandwich structure with variable height and variable density under the action of heat-force coupling is established based on the real production process of the composite material honeycomb sandwich structure, and the internal stress distribution of the structure under various factors is analyzed, so that the mechanism of cracking cause of the honeycomb is revealed, and valuable theoretical reference is provided for engineering practice. The method is helpful for technologists to analyze the causes of defects, facilitates the technologists to improve the production process, and improves the product yield.
The invention is mainly realized by the following technical scheme:
a stress analysis method in a honeycomb sandwich structure forming process comprises the following steps:
step S100: basic data of mechanical properties of the honeycomb sandwich structure are tested in an experiment, and ABAQUS simulation software is input as material parameters for simulation modeling;
step S200: testing the peel strength or fracture toughness of the node adhesive bonding of the honeycomb sandwich structure, analyzing the damage mode of the aramid paper when the aramid paper is bonded and peeled through the node adhesive, and if the damage mode is the glue layer damage mode, selecting a cohesive unit of ABAQUS simulation software to simulate the glue layer during modeling;
step S300: testing the normal-temperature modulus, the high-temperature modulus and the thermal expansion coefficient of the aramid paper, and inputting ABAQUS simulation software as material parameters for simulation modeling;
step S400: constructing a finite element model of the honeycomb sandwich structure, and converting the three-dimensional geometric model into a three-dimensional mechanical finite element model; during modeling, the equivalent model comprises a skin, a beam and a honeycomb core, wherein in the equivalent model, the skin adopts a shell unit, and the beam and the honeycomb core adopt a three-dimensional entity unit; establishing a detail model of the honeycomb sandwich board at a key part with a higher stress level of the equivalent model, wherein the detail model comprises a panel, a honeycomb core and a glue layer, the skin adopts a three-dimensional solid unit, the honeycomb core adopts a shell unit, and the glue layer adopts a coherent unit;
step S500: applying uniformly distributed pressure loads to the finite element model constructed in the step S400 for simulation calculation, analyzing stress distribution and stress components of the key part, extracting W-direction stress in the stress cloud picture, comparing the W-direction stress with the peeling strength value in the step S200, if the W-direction stress is smaller than the peeling strength value, the key part is not damaged, otherwise, the key part is damaged;
step S600: the stress redistribution problem under thermal coupling is researched aiming at thermal shrinkage stress caused by pressure and temperature change in the honeycomb sandwich structure forming process, and the simulation result and the stress analysis result without thermal influence are compared and analyzed.
In step S400, since the equivalent model is completely consistent with the actual part structure size, the model is large, and therefore, the calculation efficiency can be improved by using a shell unit for the skin; the detail model is relatively small because only the region with higher stress level in the equivalent model is intercepted, and the application of boundary conditions is facilitated by adopting the solid units, so that the skin is adopted to be modeled by adopting the solid units. In addition, in order to further improve the calculation accuracy, the equivalent model is consistent with the size of a prototype, the exposed part of the skin and the core on one side is completely fixed and supported, the size of the honeycomb cell element of the detail model is consistent with the actual structure, the surface of the skin on one side is fixed and supported, the constraint condition is consistent with the constraint condition in the forming process of the honeycomb sandwich structure, the accuracy of later-stage stress analysis is guaranteed, and the method has better practicability.
In order to better implement the present invention, the basic data in step S100 further includes elastic modulus, tensile strength and thermal expansion coefficient of the honeycomb sandwich structure at normal temperature and high temperature in each direction. Wherein, the various moduli and strengths are obtained by converting a load-displacement curve into a stress-strain curve, and the thermal expansion coefficient is taken as a test value.
In order to better implement the present invention, in step S200, the fracture toughness of the joint dispensing adhesive of the honeycomb sandwich structure is the tensile strength of the honeycomb sandwich structure in the W direction.
In order to better implement the present invention, further, in step S200, if the paper destruction mode is adopted, the destruction interface is fibrous, and the interface is rough; if the glue is in a failure mode, the failure interface is smoother.
In order to better implement the present invention, further, in step S400, uniform compressive stress is applied to the equivalent model, simulation calculation is performed, and all calculation results are stored in the odb file; and (3) calling a stress cloud picture in the simulation result, accurately positioning the structural performance change part according to the color distribution of the cloud picture, determining the part with high stress as a key part, and establishing a detail model for the key part.
In order to better implement the present invention, further, in step S600, in the simulation result, an SDEG cloud chart of the glue layer unit is extracted, if the value of SDEG is greater than 0, the glue layer is considered to start to enter into damage, and if the value of SDEG is greater than or equal to 0.99, the glue layer is considered to be completely damaged; and finally determining the damage initial position and the final damage form of the adhesive layer by observing the SDEG values of different adhesive layer units.
The invention has the beneficial effects that:
(1) the invention firstly obtains basic data of the mechanical property of the composite material paper honeycomb core material through experiment measurement, then inputs the obtained basic data into ABAQUS simulation software for simulation calculation, and finally forecasts the load condition of a typical part in the forming process of the material honeycomb sandwich structure according with the simulation result. The invention can forecast the stress of materials such as honeycomb and the like in all directions in the forming of the composite material honeycomb sandwich structure in advance, is beneficial to analyzing the cause of defects, is convenient for technologists to improve the production process, improves the product percent of pass and has better practicability;
(2) in the equivalent model, the model is huge because the structural size of the equivalent model is completely consistent with that of an actual part, so that the calculation efficiency can be improved by adopting a shell unit for the skin; the detail model is relatively small because only the region with higher stress level in the equivalent model is intercepted, and the application of boundary conditions is facilitated by adopting the solid units, so that the skin is adopted to be modeled by adopting the solid units. In addition, in order to further improve the calculation accuracy, the equivalent model is consistent with the size of a prototype, the exposed part of the skin and the core on one side is completely fixed and supported, the size of the honeycomb cell element of the detail model is consistent with the actual structure, the surface of the skin on one side is fixed and supported, the constraint condition is consistent with the constraint condition in the forming process of the honeycomb sandwich structure, the accuracy of later-stage stress analysis is guaranteed, and the method has better practicability.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is an effect diagram of the composite material honeycomb sandwich structure equivalent model of the invention;
FIG. 3 is a stress cloud of the honeycomb sandwich structure equivalent model of the invention;
FIG. 4 is a W-axis stress cloud diagram of the honeycomb sandwich structure equivalent model of the invention;
FIG. 5 is an effect diagram of a detail model of the honeycomb sandwich structure of the present invention;
FIG. 6 is a cloud diagram of the adhesive layer SDEG of the honeycomb sandwich structure detail model of the invention.
Detailed Description
Example 1:
a stress analysis method in a honeycomb sandwich structure forming process comprises the following steps:
step S100: basic data of mechanical properties of the honeycomb sandwich structure are tested in an experiment, and ABAQUS simulation software is input as material parameters for simulation modeling;
step S200: testing the peel strength or fracture toughness of the node adhesive bonding of the honeycomb sandwich structure, analyzing the damage mode of the aramid paper when the aramid paper is bonded and peeled through the node adhesive, and if the damage mode is the glue layer damage mode, selecting a cohesive unit of ABAQUS simulation software to simulate the glue layer during modeling;
step S300: testing the normal temperature modulus, the high temperature modulus and the thermal expansion coefficient of the aramid paper, and inputting ABAQUS simulation software as material parameters to carry out simulation modeling;
step S400: constructing a finite element model of the honeycomb sandwich structure, and converting the three-dimensional geometric model into a three-dimensional mechanical finite element model; during modeling, the equivalent model comprises a skin, a beam and a honeycomb core, wherein in the equivalent model, the skin adopts a shell unit, and the beam and the honeycomb core adopt a three-dimensional entity unit; establishing a detail model of the honeycomb sandwich board at a key part with a higher stress level of the equivalent model, wherein the detail model comprises a panel, a honeycomb core and a glue layer, the skin adopts a three-dimensional solid unit, the honeycomb core adopts a shell unit, and the glue layer adopts a cohesive unit;
step S500: applying uniformly distributed pressure loads to the finite element model constructed in the step S400 for simulation calculation, analyzing stress distribution and stress components of the key part, extracting W-direction stress in the stress cloud picture, comparing the W-direction stress with the peeling strength value in the step S200, if the W-direction stress is smaller than the peeling strength value, the key part is not damaged, otherwise, the key part is damaged;
step S600: the stress redistribution problem under thermal coupling is researched aiming at thermal shrinkage stress caused by pressure and temperature changes in the honeycomb sandwich structure forming process, and comparative analysis is carried out on a simulation result and a stress analysis result without thermal influence.
Further, the basic data in step S100 includes the elastic modulus, the tensile strength, and the thermal expansion coefficient of the honeycomb sandwich structure at normal temperature and high temperature in each direction.
Further, in the step S200, the fracture toughness of the joint dispensing adhesive bonding of the honeycomb sandwich structure is the tensile strength of the honeycomb sandwich structure in the W direction.
Further, in the step S200, if the paper destruction mode is adopted, the destruction interface is fibrous, and the interface is rough; if the glue is in a failure mode, the failure interface is smoother.
In step S400, since the equivalent model is completely consistent with the actual part structure size, the model is large, and therefore, the calculation efficiency can be improved by using a shell unit for the skin; the detail model is relatively small because only the region with higher stress level in the equivalent model is intercepted, and the application of boundary conditions is facilitated by adopting the solid units, so that the skin is adopted to be modeled by adopting the solid units. In addition, in order to further improve the calculation accuracy, the equivalent model is consistent with the size of a prototype, the exposed part of the skin and the core on one side is completely fixed and supported, the size of the honeycomb cell element of the detail model is consistent with the actual structure, the surface of the skin on one side is fixed and supported, the constraint condition is consistent with the constraint condition in the forming process of the honeycomb sandwich structure, the accuracy of later-stage stress analysis is guaranteed, and the method has better practicability.
The invention relates to a method for predicting mechanical properties of a composite material honeycomb sandwich structure in a forming process, which is characterized in that the modulus, the tear strength, the thermal expansion coefficient and the like of a honeycomb structure are tested through experiments, a simulation model of the composite material honeycomb sandwich structure with variable height and variable density under the action of heat-force coupling is established based on the real production process of the composite material honeycomb sandwich structure, and the internal stress distribution of the structure under all factors is analyzed, so that the honeycomb cracking cause mechanism is revealed, and valuable theoretical reference is provided for engineering practice. The method is beneficial to analyzing the causes of defects by technologists, facilitates the technologists to improve the production process, and improves the product yield.
Example 2:
in this embodiment, optimization is performed on the basis of embodiment 1, in step S400, uniform compressive stress is applied to the equivalent model, simulation calculation is performed, and all calculation results are stored in the odb file; and (3) calling a stress cloud picture in the simulation result, accurately positioning the structural performance change part according to the color distribution of the cloud picture, determining the part with larger stress as a key part, and establishing a detail model for the key part.
In the equivalent model, because the structural size of the equivalent model is completely consistent with that of an actual part, the model is large, and therefore, the calculation efficiency can be improved by adopting shell units for covering; because only the region with higher stress level in the equivalent model is intercepted in the detail model, the model is relatively small, and the application of boundary conditions is facilitated by adopting the solid units, the skin is adopted for modeling by adopting the solid units. In addition, in order to further improve the calculation accuracy, the equivalent model is consistent with the size of a prototype, the exposed part of the skin and the core on one side is completely fixed and supported, the size of the honeycomb cell element of the detail model is consistent with the actual structure, the surface of the skin on one side is fixed and supported, the constraint condition is consistent with the constraint condition in the forming process of the honeycomb sandwich structure, the accuracy of later-stage stress analysis is guaranteed, and the method has better practicability.
Other parts of this embodiment are the same as embodiment 1, and thus are not described again.
Example 3:
in the present embodiment, optimization is performed on the basis of embodiment 1 or 2, in the step S600, in the simulation result, an SDEG cloud chart of the adhesive layer unit is extracted, if the SDEG value is greater than 0, it is considered that the adhesive layer starts to enter into damage, and if the SDEG value is greater than or equal to 0.99, it is considered that the adhesive layer is completely damaged; and finally determining the damage initial part and the final damage form of the adhesive layer by observing the SDEG values of different adhesive layer units.
The invention firstly obtains basic data of the mechanical property of the composite material paper honeycomb core material through experiment measurement, then inputs the obtained basic data into ABAQUS simulation software for simulation calculation, and finally forecasts the load condition of a typical part in the forming process of the material honeycomb sandwich structure according with the simulation result. The invention can forecast the stress of materials such as honeycomb and the like in all directions in the forming of the composite material honeycomb sandwich structure in advance, is beneficial to analyzing the cause of defects, is convenient for technologists to improve the production process, improves the product percent of pass and has better practicability.
The rest of this embodiment is the same as embodiment 1 or 2, and therefore, the description thereof is omitted.
Example 4:
a stress analysis method in a honeycomb sandwich structure forming process comprises the following steps:
step S1: and testing the elastic modulus, the tensile strength and the thermal expansion coefficient of the honeycomb structure in each direction at normal temperature, testing the elastic modulus and the tensile strength of the honeycomb structure at high temperature, and inputting the elastic modulus and the tensile strength as material parameters into ABAQUS simulation software, wherein various moduli and strengths are obtained by converting a load-displacement curve into a stress-strain curve, and the thermal expansion coefficient is obtained by taking a test value.
Step S2: measuring the peel strength or fracture toughness of the node adhesive bonding of the honeycomb structure, and analyzing the failure mode of the aramid paper when the aramid paper is bonded and peeled through the node adhesive, wherein when the paper is broken, the broken interface is fibrous and is relatively rough; when the glue is damaged, the damaged interface is smoother. When the adhesive layer is damaged, the adhesive layer is simulated by the aid of the chemical unit in the mold building process.
Step S3: testing the normal temperature modulus, the high temperature modulus and the thermal expansion coefficient of the aramid fiber paper, and inputting the measured values into ABAQUS simulation software as material parameters, wherein various types of modulus are obtained by converting a load-displacement curve into a stress-strain curve, and the thermal expansion coefficient is a test value.
Step S4: constructing a structural finite element model of a composite material honeycomb sandwich component, converting a three-dimensional geometric model into a three-dimensional mechanical finite element model, discussing effective unit types of beams, ribs, skins, honeycombs and rubber materials, wherein in the equivalent model, the skins use shell units, the beams and the honeycomb cores use three-dimensional solid units, and a detail model of the honeycomb sandwich plate is established for a part with a higher stress level of the equivalent model; the detail model only intercepts the area with higher stress level in the equivalent model, the model is relatively smaller, the application of boundary conditions is facilitated by adopting the entity unit, therefore, the skin is adopted for modeling by adopting the entity unit, in addition, in order to further improve the calculation precision, the equivalent model is consistent with the size of a prototype, the exposed part of the skin and the core on one side is completely supported, the size of the honeycomb cell of the detail model is consistent with the actual structure, the surface of the skin on one side is supported, and the constraint condition is consistent with the constraint condition in the forming process of the honeycomb sandwich structure.
Step S5: and (4) applying uniform pressure load on the basis of the model established in the step S4 to perform simulation calculation, analyzing stress distribution and stress component size of the key part, particularly W-direction stress of the honeycomb core, extracting the W-direction stress in the stress cloud chart, comparing the W-direction stress with the strength value converted from the test data in the step S2, wherein if the W-direction stress is lower than the strength value, the key part is not damaged, and otherwise, the key part is damaged.
Step S6: the method comprises the steps of researching the stress redistribution problem under thermal coupling aiming at thermal shrinkage stress caused by pressure and temperature change in the forming process, comparing the stress redistribution problem with a stress analysis result without thermal influence, researching and analyzing the influence of thermal shrinkage, and extracting an SDEG cloud picture of a glue layer unit from a simulation result. When the value of SDEG is greater than 0, the adhesive layer is considered to start entering into damage, and when the value of SDEG is not less than 0.99, the adhesive layer is considered to be completely damaged. By observing the SDEG values of different glue layer units, the damage initial position and the final damage form (slow damage or instant damage) of the glue layer, namely the cracking mechanism of the honeycomb core, are determined.
The invention firstly obtains the basic data of the mechanical property of the composite material paper honeycomb core material through experiment measurement, then inputs the obtained basic data into ABAQUS simulation software for simulation calculation, and finally forecasts the load condition of a typical part in accordance with the material honeycomb sandwich structure forming process through a simulation result. The invention can forecast the stress of materials such as honeycomb and the like in all directions in the forming of the composite material honeycomb sandwich structure in advance, is beneficial to analyzing the cause of defects, is convenient for technologists to improve the production process, improves the product percent of pass and has better practicability.
Example 5:
a method for analyzing the stress of honeycomb sandwich structure in its shaping procedure includes such steps as measuring the basic data of mechanical performance of composite paper honeycomb core, inputting the obtained data to a calculation model for simulation calculation, and forecasting the load of typical part in the procedure of shaping honeycomb sandwich structure. As shown in fig. 1, the method specifically comprises the following steps:
step 1: testing the elastic modulus and tensile strength of the honeycomb structure in each direction at normal temperature and high temperature, and testing the thermal expansion coefficient of the honeycomb structure; testing the peeling strength or fracture toughness (tensile strength in the W direction of the honeycomb structure) of the adhesive joint of the honeycomb structure; and (3) testing the elastic modulus and the thermal expansion coefficient of the aramid paper at normal temperature and high temperature, and analyzing the failure mode (paper failure or glue failure) of the aramid paper when the aramid paper is bonded and peeled by the node glue. The above modulus and strength are obtained by calculating the displacement-load curve in the test results.
And 2, step: modeling was performed in ABAQUS as follows: the equivalent model is composed of a skin and a honeycomb core. The skins are constructed of S4R cells, and the honeycomb core is obtained by solid stretching, the cell type being C3D 8R. Then, finite element meshing is carried out on the part, and material parameters are set. The whole model is combined on an ABAQUS assembly interface and is consistent with the actual model. And 6 degrees of freedom are limited at one side of the model and the exposed part of the honeycomb core. And selecting the outputs of stress, strain, displacement, force, damage coefficient and the like from the calculation output. On the established model, uniformly distributed pressure stress is applied to the equivalent model respectively aiming at the pressure of the hot tank and the weak vacuum pressure, and simulation calculation is carried out. All calculation results are stored in an odb file, a stress cloud picture in a simulation result is called through an ABAQUS post-processing interface, and the structural performance change part can be accurately positioned according to the color distribution of the cloud picture. Determining the position with larger stress as the key position, analyzing the stress distribution and the relation between the stress component and the test strength of the key position, and establishing a simplified detailed model for the key position. Fig. 2 shows the modeling effect of the equivalent model, fig. 3 and fig. 4 show stress cloud charts of the internal honeycomb along 3 axial directions, and the part with larger stress in the cloud charts is taken as a key part and modeled.
And step 3: as shown in fig. 5, modeling is performed in ABAQUS as follows: the detail model is composed of a panel, a honeycomb core and an adhesive layer. The panel is obtained through solid stretching modeling, the cell type is C3D8R, the middle honeycomb core is formed by S4R cells with included angles of 120 degrees facing up and down, the glue layer is obtained through solid stretching, and the glue layer cell type adopts a coherent interface cell in ABAQUS. Then, the component is subjected to finite element meshing, material parameters are set, and the material direction normal direction of the adhesive layer is required to be perpendicular to the normal direction of the adhesive layer close to the shell unit. The whole model is combined on an ABAQUS assembly interface, the glue layer is used for bonding and molding the honeycomb core in the middle of the shell units which face up and down, and the panel is tightly attached to the upper surface and the lower surface of the honeycomb core, so that uniform pressure can be applied conveniently. The internal pressure boundary conditions of the local cells are analyzed, and assuming that one of the cells has an internal pressure, in this example, the cell having the internal pressure is set as the center position of the model so as to observe the influence of the internal pressure on the cells of the surrounding cells. Under the fixed honeycomb, Tie constraint is established between nodes at the upper end and the lower end of the Z direction of the honeycomb core and the inner surfaces of the upper panel and the lower panel by utilizing the Tie function of ABAQUS, so that relative displacement is prevented.
Step S4: in addition to the load and the boundary condition setting in step S3, outputs such as stress, strain, displacement, force, damage coefficient, and the like are selected among the calculation outputs. In this example, all the calculation results are stored in the odb file, and through the post-processing interface of the ABAQUS, a stress cloud picture, a displacement cloud picture, a damage coefficient (SDEG) cloud picture and the like in the simulation result can be adjusted, so that the structural performance change part can be accurately positioned according to the color distribution of the cloud picture. In the example graph, after 0.1Mpa internal pressure is applied, obvious honeycomb core cell wall surface stress change and influence on surrounding honeycomb core cells can be observed, in addition, the damage condition of the glue layer can also be clearly observed through a damage coefficient cloud graph of the glue layer coherent unit, the parts with SDEG >0 are all damaged parts of the glue layer, and the damage condition is more serious when the SDEG is larger. FIG. 6 shows the bond line SDEG results after 0.1MPa application to the center core grid of the detail model. According to the honeycomb core lattice detail model, when 0.1Mpa internal pressure (air blocking) is applied to the side wall surface of the honeycomb core, SDEG >0 in a stress cloud chart causes the adhesive layer to be peeled and damaged, and the honeycomb core is cracked.
The invention firstly obtains the basic data of the mechanical property of the composite material paper honeycomb core material through experiment measurement, then inputs the obtained basic data into ABAQUS simulation software for simulation calculation, and finally forecasts the load condition of a typical part in accordance with the material honeycomb sandwich structure forming process through a simulation result. The method can forecast the stress of the honeycomb and other materials in all directions in the forming of the composite material honeycomb sandwich structure in advance, is beneficial to a technologist to analyze the cause of some defects, is convenient for the technologist to improve the production process, improves the product percent of pass, and has better practicability.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications and equivalent variations of the above embodiments according to the technical spirit of the present invention are included in the scope of the present invention.
Claims (3)
1. A stress analysis method in a honeycomb sandwich structure forming process is characterized by comprising the following steps:
step S100: basic data of mechanical properties of the honeycomb sandwich structure are tested in an experiment, and ABAQUS simulation software is input as material parameters for simulation modeling;
step S200: testing the peel strength or fracture toughness of node adhesive bonding of the honeycomb sandwich structure, analyzing a failure mode of the aramid paper when the aramid paper is bonded and peeled through the node adhesive, and if the failure mode is a glue layer failure mode, selecting a correct unit of ABAQUS simulation software to simulate the glue layer during modeling;
step S300: testing the normal temperature modulus, the high temperature modulus and the thermal expansion coefficient of the aramid paper, and inputting ABAQUS simulation software as material parameters to carry out simulation modeling;
step S400: constructing a finite element model of the honeycomb sandwich structure, and converting the three-dimensional geometric model into a three-dimensional mechanical finite element model; during modeling, the equivalent model comprises a skin, a beam and a honeycomb core, wherein in the equivalent model, the skin adopts a shell unit, and the beam and the honeycomb core adopt a three-dimensional entity unit; establishing a detail model of the honeycomb sandwich board at a key part with a higher stress level of the equivalent model, wherein the detail model comprises a panel, a honeycomb core and a glue layer, the skin adopts a three-dimensional solid unit, the honeycomb core adopts a shell unit, and the glue layer adopts a cohesive unit;
step S500: applying uniform pressure load to the finite element model constructed in the step S400 for simulation calculation, analyzing stress distribution and stress components of key parts, extracting W-direction stress in a stress cloud picture, and comparing the W-direction stress with the peeling strength value in the step S200, wherein if the W-direction stress is smaller than the peeling strength value, the key parts are not damaged, otherwise, the key parts are damaged;
step S600: the method comprises the following steps of (1) researching the stress redistribution problem under thermal coupling aiming at thermal shrinkage stress caused by pressure and temperature changes in the honeycomb sandwich structure forming process, and carrying out comparative analysis through a simulation result and a stress analysis result without thermal influence;
the basic data in the step S100 include the elastic modulus, tensile strength, and thermal expansion coefficient of the honeycomb sandwich structure in each direction at normal temperature and high temperature; in the step S200, the fracture toughness of the node adhesive bonding of the honeycomb sandwich structure is the tensile strength of the honeycomb sandwich structure in the W direction; in the step S200, if the paper destruction mode is adopted, the destruction interface is fibrous, and the interface is rough; if the glue is in a glue failure mode, the failure interface is smoother;
the equivalent model is completely consistent with the structure size of an actual part, and the model is large, so that the calculation efficiency can be improved by adopting a shell unit for the skin; because the detail model only intercepts the region with higher stress level in the equivalent model, the model is relatively small, and the application of boundary conditions is facilitated by adopting solid units, the skin is modeled by adopting the solid units; in addition, in order to further improve the calculation accuracy, the equivalent model is consistent with the size of a prototype, the exposed parts of the skin and the core on one side are completely fixed and supported, the size of the honeycomb cell of the detail model is consistent with the actual structure, the surface of the skin on one side is fixed and supported, the constraint condition is consistent with that in the forming process of the honeycomb sandwich structure, and the accuracy of later-stage stress analysis is ensured.
2. The method for analyzing the stress of the honeycomb sandwich structure in the forming process according to claim 1, wherein in the step S400, uniform distribution of compressive stress is applied to the equivalent model, simulation calculation is performed, and all calculation results are stored in an odb file; and (3) calling a stress cloud picture in the simulation result, accurately positioning the structural performance change part according to the color distribution of the cloud picture, determining the part with high stress as a key part, and establishing a detail model for the key part.
3. The method for analyzing the stress of the honeycomb sandwich structure forming process according to claim 1 or 2, wherein in the step S600, in the simulation result, an SDEG cloud chart of a glue layer unit is extracted, if an SDEG value is larger than 0, the glue layer is considered to start to enter a damage mode, and if the SDEG value is larger than or equal to 0.99, the glue layer is considered to be completely damaged; and finally determining the damage initial position and the final damage form of the adhesive layer by observing the SDEG values of different adhesive layer units.
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