A dynamic failure simulation method for composite-metal joint structure test piece

Abstract

The present invention discloses a method for simulating dynamic failure of a composite material-metal connection structure test piece, comprising the steps of S1. studying the failure mode and failure criterion of a high-lock bolt fastener under composite dynamic loading to obtain a failure equation with universal applicability; S2. studying the dynamic failure mechanism and failure criterion of the composite material-metal connection structure; S3. studying the dynamic failure numerical simulation and modeling method of the composite material-metal connection structure test piece; S4. studying the application of the composite material-metal connection numerical simulation method in fuselage structure crash simulation; the method studies the influence of load action mode and different loading rates on its failure mode, reveals its failure mechanism and failure criterion under the action of crash load, so as to study its numerical simulation method, break through its modeling technology, and conduct application research in the finite element model of the lower structure of the cargo hold floor, which has academic significance and scientific value for guiding engineering practice.

Description

Technical Field

[0001] The invention relates to the field of mechanical engineering and test technology, and in particular to a dynamic failure simulation method for a composite material-metal connection structure test piece. Background Art

[0002] Due to the superior properties of composite materials such as high specific strength, high specific stiffness and strong designability, the proportion of composite materials used in military and civilian aircraft structures has been greatly increased in recent years, and their application sites have gradually transitioned from secondary load-bearing structures such as active surfaces to primary load-bearing structures such as fuselages and wings; although aircraft composite structures are developing in the direction of integrated design and manufacturing, due to the requirements of structural design, manufacturing, use and maintenance, necessary process separation surfaces and maintenance covers must be designed, so connection structures are still inevitable; composite material connection structures usually appear in the transition area of ​​components, which are manifested as structural shape discontinuities and material discontinuities in the connection area, which easily lead to high stress concentration in the local structure, so the connection structure becomes a key link in the overall structural design of the aircraft, and its connection design is one of the most challenging tasks in aircraft structural design;

[0003] The factors that affect the strength of composite material connection structures are more complex than those of metals, and some of these factors are essentially different. For example, metals are plastic isotropic materials, while composites are brittle anisotropic materials. The failure of metal materials is independent of the coordinate direction, while the failure of composite materials is related to the coordinate system, and the stiffness and strength degrade layer by layer. Therefore, fiber-reinforced composite materials often have more and more complex failure modes than traditional metal materials. Therefore, the ideas and methods of metal structure connection design cannot continue to be used, otherwise, large errors will occur, or even serious design accidents. Therefore, it is necessary to conduct extensive research on fiber-reinforced composite connection structures, study the influence of connection methods on connection strength and failure modes, and provide useful references for the optimal design of corresponding composite connectors.

[0004] However, the main load-bearing components in the current aircraft structures are still mainly made of metal materials, which inevitably requires the connection of composite structural parts and metal structural parts. Due to the anisotropy and multi-mode damage of composite materials, the connection between them and metal becomes the weak point of the entire structure. More than 70% of the damage of aircraft composite-metal structural parts occurs at the connection. Therefore, the study of composite-metal connection performance is of great engineering significance. Summary of the invention

[0005] In view of the above-mentioned problems, the present invention aims to provide a dynamic failure simulation method for a composite material-metal connection structure test piece. This method studies the influence of load action mode and different loading rates on its failure mode, reveals its failure mechanism and failure criterion under the action of crash load, so as to further study its numerical simulation method, break through its modeling technology, and carry out application research in the finite element model of the cargo hold floor substructure, which has academic significance and scientific value for guiding engineering practice.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for simulating dynamic failure of a composite material-metal joint structure test piece, comprising the steps of:

[0008] S1. Study the failure mode and damage criterion of high-lock bolt fasteners under complex dynamic loading, and obtain a universal failure equation;

[0009] S2. Based on the failure equation of high-lock bolt fasteners, the dynamic failure mechanism and failure criterion of composite-metal joint structures are studied;

[0010] S3. Research on numerical simulation and modeling methods of dynamic failure of composite-metal joint structure test pieces;

[0011] S4. Research on the application of numerical simulation method of composite-metal connection in fuselage structure crash simulation.

[0012] Preferably, the process of studying the failure mode and damage criterion of high-lock bolt fasteners under composite dynamic loading in step S1 includes:

[0013] S101. Using the typical titanium alloy high-lock bolt fastener CFBL1001 used in aircraft fuselage structure, and using a high-speed hydraulic servo material testing machine as the test platform, load failure experiments were carried out under 30° tension-shear coupling, 45° tension-shear coupling, 60° tension-shear coupling, pure tension, pure shear and other loading modes and different loading rates;

[0014] S102. In the dynamic composite loading test, the actual load on the high-lock bolt fastener during the tensile process can be decomposed into a component along the tensile direction and a component along the shear direction:

[0015] T(α)=Fcosα (1)

[0016] N(α)=Fsinα (2)

[0017] In equations (1) and (2), F is the actual load of the high-lock bolt fastener during the tensile process, α is the loading angle, that is, the angle between the tensile direction and the nail rod, T(α) and N(α) are the components along the tensile direction and the components along the shear direction, respectively;

[0018] S103. According to the results of pure tension, 30° compound loading, 45° compound loading, 60° compound loading and pure shear test, the failure surface of the high-lock bolt fastener is obtained. When the tensile component and shear component of the load borne by the high-lock bolt fastener are located inside the failure surface, the high-lock bolt fastener does not fail. Otherwise, the high-lock bolt fastener fails. Then the failure equation of the high-lock bolt fastener is obtained:

[0019]

[0020] In formula (3), Tu and Nu are the maximum tensile load and the maximum shear load, respectively. The values ​​of a and b can be obtained by numerical fitting based on the test data of 30° composite loading, 45° composite loading, and 60° composite loading.

[0021] Preferably, the research process of the dynamic failure mechanism and failure criterion of the composite material-metal connection structure described in step S2 includes:

[0022] S201. Based on the carbon fiber reinforced resin matrix composite material connection parent material and the typical aluminum alloy connection parent material, high locking bolt fastener CFBL1001 is used to design composite-metal mechanical connection structure test pieces with different structures;

[0023] S202. Using a high-speed hydraulic servo material testing machine as a test platform, conduct dynamic failure tests of composite-metal mechanical connectors at a loading rate of 0.01m / s-10m / s to obtain mechanical property data of the connection structure test pieces;

[0024] S203. At the same time, digital imaging technology is used to record the entire test process of the dynamic failure test, and the dynamic strain field on the surface of the test piece is obtained. The deformation of the two motherboards is observed, and the dynamic failure load and failure deformation information of the connection structure under different working conditions are analyzed in combination with the speckle situation to reveal its destructive failure mechanism.

[0025] Preferably, the research process of the dynamic failure numerical simulation and modeling method of the composite material-metal connection structure test piece described in step S3 includes:

[0026] S301. Use LS-DYNA finite element analysis software and fully integrated Belytschko-Tsay shell elements to mesh the motherboard. Set the mesh size of the overlapped part of the motherboard to 1 mm and the rest to 4 mm. Set multiple integration points on the thickness.

[0027] S302. The metal motherboard adopts the JC failure model or the GISSMO damage model, and the composite motherboard adopts the Chang-Chang failure criterion. Two interlayer modeling methods, adhesive unit and interlayer contact, are used respectively. By identifying key parameters, the parameter values ​​are determined; the hexahedral cluster entity unit is used to simulate the fastener. The hexahedral cluster unit is a combination of multiple hexahedrons to transmit force and load. When the load of the hexahedral cluster reaches the failure condition, the hexahedral cluster is deleted;

[0028] S303. Evaluate the accuracy of the composite-metal mechanical connection structure simulation results through correlation analysis between the simulation results and the failure test results, and verify the established composite-metal mechanical connection structure model.

[0029] Preferably, the application research process of the composite material-metal connection numerical simulation method described in step S4 in the fuselage structure crash simulation includes:

[0030] S401. Establish a finite element model of the composite pillar assembly at the bottom of the aircraft cargo hold. The double pillar structure is a composite structure, and the other structures are metal structures. The metal structure adopts the JC failure model or the GISSMO damage model, and the composite pillar structure adopts the Chang-Chang failure criterion.

[0031] S402. Evaluate the crash simulation results of the composite column assembly at the lower part of the aircraft cargo hold, compare the crash simulation results of the metal column assembly, and evaluate the established composite-metal mechanical connection structure model;

[0032] S403. Change the angle and thickness of the composite column to evaluate the crash resistance of the composite column structure at the bottom of the aircraft cargo hold.

[0033] The beneficial effects of the present invention are as follows: the present invention discloses a dynamic failure simulation method for a composite material-metal connection structure test piece. Compared with the prior art, the improvements of the present invention are as follows:

[0034] (1) The present invention designs a dynamic failure simulation method for a composite-metal connection structure test piece. The method designs a composite column structure under the cargo hold floor of the fuselage and a composite-metal mechanical connection method, and establishes a finite element model of the aircraft fuselage structure. The numerical simulation method and simulation technology of the composite-metal mechanical connection structure are applied to the modeling and simulation of the aircraft fuselage structure. Based on factors such as crash simulation calculation accuracy, calculation efficiency, and failure mode simulation, the modeling method and simulation technology of the composite-metal bolt connection in the aircraft fuselage structure are studied, and guidance is provided for the simulation analysis of the crash resistance of the composite fuselage structure of the aircraft, which has certain engineering significance and value.

[0035] (2) This method studies the failure modes and damage criteria of aviation composite-metal mechanical connection structures under dynamic loading conditions, reveals the influence of loading rate on the failure modes and physical mechanisms of composite-metal mechanical connection structures, obtains dynamic damage criteria for composite-metal mechanical connections under general conditions, and constructs a universal dynamic failure constitutive equation for composite-metal mechanical connection structures. This provides theoretical support for dynamic failure analysis and evaluation of composite-metal mechanical connections under low and medium strain rates, and has certain academic significance and scientific value in guiding engineering practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention is a flow chart of a method for simulating dynamic failure of a composite material-metal connection structure test piece.

[0037] Figure 2 This is a test piece diagram of a single high-locking bolt single lap joint of the present invention.

[0038] Figure 3 This is a test piece diagram of multiple high-locking bolt single lap joints of the present invention.

[0039] Figure 4 This is a diagram of a metal column assembly according to the present invention.

[0040] Figure 5 This is a diagram of a composite material column assembly according to the present invention.

[0041] Figure 6 It is a structural diagram of the lower part of the aircraft cargo hold floor with columns of different inclination angles according to the present invention.

[0042] Among them, Figure 2 In the figure, Figure (a) is a single lap joint test piece, Figure (b) is an L-type pull-off test piece, and Figure (c) is a butt-jointed peeling test piece;

[0043] exist Figure 6 In the figure, Figure (a) is a lower structural diagram of the aircraft cargo hold floor with columns under the condition of 0°, Figure (b) is a lower structural diagram of the aircraft cargo hold floor with columns under the condition of 45°, Figure (c) is a lower structural diagram of the aircraft cargo hold floor with columns under the condition of 65°, and Figure (d) is a lower structural diagram of the aircraft cargo hold floor with columns under the condition of 150°. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0045] Example 1: Refer to the attached Figure 1-6 A dynamic failure simulation method for a composite material-metal joint structure test piece is shown, comprising the steps of:

[0046] S1. The failure mode and damage criterion of high-lock bolt fasteners under composite dynamic loading are studied, and a universal failure equation is obtained:

[0047] S101. Using the typical titanium alloy high-lock bolt fastener CFBL1001 used in aircraft fuselage structure, and using a high-speed hydraulic servo material testing machine as the test platform, load failure experiments were carried out under 30° tension-shear coupling, 45° tension-shear coupling, 60° tension-shear coupling, pure tension, pure shear and other loading modes and different loading rates;

[0048] S102. In the dynamic composite loading test, the actual load on the high-lock bolt fastener during the tensile process can be decomposed into a component along the tensile direction and a component along the shear direction:

[0049] T(α)=Fcosα (1)

[0050] N(α)=Fsinα (2)

[0051] In equations (1) and (2), F is the actual load of the high-lock bolt fastener during the tensile process, α is the loading angle, that is, the angle between the tensile direction and the nail rod, T(α) and N(α) are the components along the tensile direction and the components along the shear direction, respectively;

[0052] S103. According to the results of pure tension, 30° compound loading, 45° compound loading, 60° compound loading and pure shear test, the failure surface of the high-lock bolt fastener is obtained. When the tensile component and shear component of the load borne by the high-lock bolt fastener are located inside the failure surface, the high-lock bolt fastener does not fail. Otherwise, the high-lock bolt fastener fails. Then the failure equation of the high-lock bolt fastener is obtained:

[0053]

[0054] In formula (3), Tu and Nu are the maximum tensile load and the maximum shear load, respectively. The values ​​of a and b can be obtained by numerical fitting based on the test data of 30° composite loading, 45° composite loading, and 60° composite loading.

[0055] S2. Based on the failure equation of high-lock bolt fasteners, the dynamic failure mechanism and failure criteria of composite-metal connection structures are studied:

[0056] S201. Based on the carbon fiber reinforced resin matrix composite material connection parent material and the typical aluminum alloy connection parent material, the high-lock bolt fastener CFBL1001 is used to design composite-metal mechanical connection structure test pieces with different structures. Considering a single high-lock bolt, lap joint test pieces, L-type pull-off test pieces, and butt peel test pieces are designed; considering multiple high-lock bolts, two-bolt lap joints with horizontal and longitudinal arrangements, and four-bolt lap joints with rectangular and diamond arrangements are designed, such as Figure 2-3 As shown;

[0057] S202. Using a high-speed hydraulic servo material testing machine as a test platform, conduct dynamic failure tests of composite-metal mechanical connectors at a loading rate of 0.01m / s-10m / s to obtain mechanical property data of the connection structure test pieces;

[0058] S203. At the same time, the entire test process of the dynamic failure test is recorded by using digital image technology, and the dynamic strain field on the surface of the test piece is obtained, the deformation of the two motherboards is observed, and the dynamic failure load and failure deformation information of the connection structure under different working conditions are analyzed in combination with the speckle situation to reveal its destructive failure mechanism;

[0059] S3. Research on numerical simulation and modeling methods of dynamic failure of composite-metal joint structure test pieces:

[0060] S301. Use LS-DYNA finite element analysis software and fully integrated Belytschko-Tsay shell elements to mesh the motherboard. Set the mesh size of the overlapped part of the motherboard to 1 mm and the rest to 4 mm. Set multiple integration points on the thickness.

[0061] S302. The metal motherboard adopts the JC failure model or the GISSMO damage model, and the composite motherboard adopts the Chang-Chang failure criterion. Two interlayer modeling methods, adhesive unit and interlayer contact, are used respectively. By identifying key parameters, the parameter values ​​are determined; the hexahedral cluster entity unit is used to simulate the fastener. The hexahedral cluster unit is a combination of multiple hexahedrons to transmit force and load. When the load of the hexahedral cluster reaches the failure condition, the hexahedral cluster is deleted;

[0062] S303. Through correlation analysis between simulation results and failure test results, comparison of failure morphology and load-displacement curves, etc., the simulation accuracy of the finite element model of the composite-metal mechanical connection structure is evaluated, and a finite element modeling method and model that can accurately reproduce the test results are established.

[0063] Example 2: S4. Application of composite-metal joint numerical simulation method in fuselage structure crash simulation

[0064] S401. Based on the metal aircraft cargo hold lower column assembly, the aircraft cargo hold lower composite column assembly is designed by using the strength equivalence criterion. The double column structure is a composite structure, and the fuselage bulkhead and cargo hold floor beams and other structures are metal structures. The composite column is connected to the metal fuselage bulkhead and the metal cargo hold floor beam respectively by high-locking bolts; a finite element model of the column assembly is established, the metal structure adopts the JC failure model or the GISSMO damage model, the composite column structure adopts the Chang-Chang failure criterion, and a high-locking bolt connection is established based on the above-mentioned verified composite-metal mechanical connection structure modeling method;

[0065] S402. Conduct crash simulation analysis of the composite column assembly at the lower part of the aircraft cargo hold, compare the crash simulation failure mode, load displacement curve, energy absorption curve and other results of the metal column assembly, evaluate the crash simulation results of the composite column assembly, and confirm the validity of the composite-metal mechanical connection structure model in the composite column assembly;

[0066] S403. Based on the composite column assembly, a finite element model of the fuselage cargo hold floor lower structure containing the composite column structure is established, different composite column angles, column thicknesses, etc. are set, and crash simulations are performed at different impact velocities. By evaluating the crash resistance of the composite column structure at the bottom of the aircraft cargo hold, the finite element modeling method and technology of the composite-metal mechanical connection structure in the fuselage frame section are further analyzed, so as to provide technical support and guidance for the crashworthiness design, simulation analysis and evaluation of the aircraft composite fuselage structure;

[0067] The composite-metal connection simulation method can effectively improve the accuracy of dynamic failure simulation of high-lock bolt connections and save computing costs. At the same time, this method is applied to fuselage structure crash simulation, which can effectively improve simulation accuracy and computing efficiency.

[0068] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for simulating dynamic failure of a composite material-metal joint structure test piece, characterized by: Included steps S1. Study the failure mode and failure criterion of high-lock bolt fasteners under combined dynamic loading, and obtain the failure equation of lock bolt fasteners; S2. Based on the failure equation of high-lock bolt fasteners, the dynamic failure mechanism and failure criterion of composite-metal joint structures are studied; S3. Study the dynamic failure numerical simulation and modeling methods of composite-metal joint structure test pieces; S4. Study the application of composite-metal connection numerical simulation method in fuselage structure crash simulation; The process of studying the failure mode and damage criterion of high-lock bolt fasteners under combined dynamic loading as described in step S1 includes: S101. Using a typical titanium alloy high-lock bolt fastener CFBL1001, and a high-speed hydraulic servo material testing machine as the test platform, load failure experiments were carried out under 30° tension-shear coupling, 45° tension-shear coupling, 60° tension-shear coupling, pure tension, pure shear loading modes and different loading rates; S102. In the dynamic composite loading test, the actual load on the high-lock bolt fastener during the tensile process is decomposed into a component along the tensile direction and a component along the shear direction: （1） （2） In formula (1) and formula (2), is the actual load of the high-lock bolt fastener during the tension process, is the loading angle, that is, the angle between the tensile direction and the nail rod, and are the component along the tensile direction and the component along the shear direction respectively; S103. According to the results of pure tension, 30° compound loading, 45° compound loading, 60° compound loading and pure shear test, the failure surface of the high-lock bolt fastener is obtained. When the tensile component and shear component of the load borne by the high-lock bolt fastener are located inside the failure surface, the high-lock bolt fastener does not fail. Otherwise, the high-lock bolt fastener fails. Then the failure equation of the high-lock bolt fastener is obtained: （3） In formula (3), Tu and Nu are the maximum tensile load and the maximum shear load, respectively. The values ​​of a and b are obtained by numerical fitting based on the test data of 30° composite loading, 45° composite loading, and 60° composite loading.

2. A dynamic failure simulation method for a composite material-metal joint structure test piece according to claim 1, characterized in that: The research process of the dynamic failure mechanism and failure criterion of the composite material-metal connection structure described in step S2 includes: S201. Based on the carbon fiber reinforced resin matrix composite material connection parent material and the typical aluminum alloy connection parent material, high locking bolt fastener CFBL1001 is used to design composite-metal mechanical connection structure test pieces with different structures; S202. Using a high-speed hydraulic servo material testing machine as a test platform, conduct dynamic failure tests of composite-metal mechanical connectors at a loading rate of 0.01m / s-10m / s to obtain mechanical property data of the connection structure test pieces; S203. Use digital imaging technology to record the entire test process of the dynamic failure test in step S202, obtain the dynamic strain field on the surface of the test piece, observe the deformation of the two motherboards, and analyze the dynamic failure load and failure deformation information of the connection structure under different working conditions in combination with the speckle situation to reveal its destructive failure mechanism.

3. The method for simulating dynamic failure of a composite material-metal joint structure test piece according to claim 1, characterized in that: The research process of the dynamic failure numerical simulation and modeling method of the composite material-metal connection structure test piece described in step S3 includes: S301. Use LS-DYNA finite element analysis software and fully integrated Belytschko-Tsay shell elements to mesh the motherboard. Set the mesh size of the overlapped part of the motherboard to 1 mm and the rest to 4 mm. Set multiple integration points on the thickness. S302. The metal motherboard adopts the JC failure model or the GISSMO damage model, and the composite motherboard adopts the Chang-Chang failure criterion. Two interlayer modeling methods, adhesive unit and interlayer contact, are used respectively. By identifying key parameters, the parameter values ​​are determined; the hexahedral cluster entity unit is used to simulate the fastener. The hexahedral cluster unit is a combination of multiple hexahedrons to transmit force and load. When the load of the hexahedral cluster reaches the failure condition, the hexahedral cluster is deleted; S303. Evaluate the accuracy of the composite-metal mechanical connection structure simulation results through correlation analysis between the simulation results and the failure test results, and verify the established composite-metal mechanical connection structure model.

4. The method for simulating dynamic failure of a composite material-metal joint structure test piece according to claim 1, characterized in that: The application research process of the composite material-metal connection numerical simulation method described in step S4 in the fuselage structure crash simulation includes: S401. Establish a finite element model of the composite pillar assembly at the bottom of the aircraft cargo hold. The double pillar structure is a composite structure, and the other structures are metal structures. The metal structure adopts the JC failure model or the GISSMO damage model, and the composite pillar structure adopts the Chang-Chang failure criterion. S402. Evaluate the crash simulation results of the composite column assembly at the lower part of the aircraft cargo hold, compare the crash simulation results of the metal column assembly, and evaluate the established composite-metal mechanical connection structure model; S403. Change the angle and thickness of the composite column to evaluate the crash resistance of the composite column structure at the bottom of the aircraft cargo hold.

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