Design method for enhancing connection strength of composite wallboard based on strength calculation

Abstract

The invention provides a design method for enhancing the connection strength of a composite wallboard based on strength calculation. The method comprises the following steps: respectively establishing a geometric model of a hoisting joint and a geometric model of a fuselage composite frame web; entity element finite element models are established according to the geometric model of the hoisting connector and the geometric model of the fuselage composite material frame web respectively, and connection of connecting pieces is simulated through RBE2 units; carrying out stress analysis and rigidity distribution based on the established finite element model; respectively judging whether the connecting piece of the second joint and the mounting hole of the web of the fuselage composite material frame meet the strength requirement or not; and if the mounting hole of the fuselage composite material frame web does not meet the strength requirement, two corner boxes are additionally arranged on a back plate on the back surface of the fuselage composite material frame web, and the strength of the mounting hole of the fuselage composite material frame web is checked. By means of the technical scheme, the technical problem that in the prior art, the load transfer strength of connecting pieces between composite material connections is difficult to check accurately can be solved.

Description

Technical Field

[0001] The invention relates to the technical field of structural design simulation, and in particular to a design method for enhancing the connection strength of composite wall panels based on strength calculation. Background Art

[0002] In the design of composite material structures, the integrity of the structure is always one of the means to reduce the weight of the structure and improve the efficiency of the structure. Advanced composite materials have many advantages such as high specific strength and specific stiffness, strong designability, good fatigue resistance, etc. Aircraft and aerospace structures are extremely sensitive to weight requirements. For these structures, composite materials are undoubtedly an ideal structural material and are being used more and more widely.

[0003] Connection design and analysis is one of the important aspects of composite material structure design. The connection part is usually the weak link in the static strength and fatigue strength of the composite material structure. This is because the composite material has the characteristics of anisotropy and brittleness, which makes the stress concentration of the composite material connection part more serious than that of metal. These characteristics determine that the composite material connection strength problem becomes complicated.

[0004] At present, the design and analysis methods for increasing the connection strength of composite wall panels are usually carried out as follows: the local structure of the existing wall panel connection is tested by experimental methods, and the stress characteristics and maximum bearing capacity of the connection area are determined through experiments. If the strength of the connection area does not meet the design requirements, an improvement plan is proposed based on the stress characteristics and maximum bearing capacity of the connection area, and an improvement plan that meets the design requirements is determined through re-testing. This method has the disadvantages of long development cycle and high development cost. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art.

[0006] According to one aspect of the present invention, a design method for strengthening the connection strength of composite wall panels based on strength calculation is provided, the method comprising: establishing a geometric model of a lifting joint and a geometric model of a fuselage composite material frame web respectively; wherein the lifting joint comprises a first joint and a second joint, the first joint is used to bear the lifting load, the second joint is located between the first joint and the fuselage composite material frame web, the second joint is fixed to the fuselage composite material frame web through a plurality of connectors, and the first joint is fixed to the second joint and the fuselage composite material frame web through a plurality of connectors; a back plate is fixed to the back of the fuselage composite material frame web through a plurality of connectors; a solid unit finite element model is established according to the geometric model of the lifting joint and the geometric model of the fuselage composite material frame web respectively, and R The BE2 unit simulates the connection of the connector; force analysis and stiffness distribution are performed based on the established finite element model, wherein the support reaction force of the first joint is used as the main force of the second joint, and the inherent strength of the first joint and the second joint and the load transfer of the connector are calculated respectively; it is judged whether the connector of the second joint and the mounting holes of the fuselage composite frame web meet the strength requirements respectively; if the mounting holes of the fuselage composite frame web do not meet the strength requirements, two corner boxes are added to the back plate on the back of the fuselage composite frame web, and the corner boxes are fixed to the back plate, edge strips, upper longitudinal beams and middle longitudinal beams through a number of connectors; the stiffness of the connector load transfer area is taken as the maximum value, the load distribution of the connector load transfer area is increased to 100%, and the strength of the mounting holes of the fuselage composite frame web is checked.

[0007] Furthermore, the connecting piece adopts a metal bolt.

[0008] Furthermore, the materials of the lifting joint and the connecting piece are both 30CrMnSi.

[0009] Furthermore, the finite element model of the lifting joint is simulated using solid elements.

[0010] According to another aspect of the present invention, there is provided a structure for enhancing the connection strength of composite wall panels, which is designed using the design method for enhancing the connection strength of composite wall panels based on strength calculation as described above; the structure comprises two corner boxes, which are located on the back side opposite to the front side of the fuselage composite material frame web installation lifting joint, and the corner boxes are fixed to the web, edge strips, and upper longitudinal beams and middle longitudinal beams by a number of connectors.

[0011] Furthermore, the structure also includes a back plate, which is located on the back side of the fuselage composite material frame web and between the fuselage composite material frame web and the corner box.

[0012] Further, the corner box is made of the same material as the back panel.

[0013] Further, the thickness of the corner box material is the same as the thickness of the back panel.

[0014] By applying the technical solution of the present invention, a design method for enhancing the connection strength of composite wall panels based on strength calculation is provided. The method analyzes the connection strength between the lifting joint and the fuselage composite frame web. Based on the force analysis and stiffness distribution principle, the support reaction force of the first joint is used as the main force of the second joint. The inherent strength of the first joint and the second joint and the load transfer of the connecting parts are calculated respectively to determine the specific scheme for enhancing the connection strength. The improved connection area is checked using a strength verification method considering extreme conditions to ensure that the connection scheme has sufficient strength and reduce design iterations. The present invention uses strength calculation instead of experimental development, which is low in cost, good in versatility, and suitable for engineering applications. Compared with the prior art, the technical solution of the present invention can solve the technical problem in the prior art that the load transfer strength of the connecting parts between composite material connections is difficult to accurately verify. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The included drawings are used to provide a further understanding of the embodiments of the present invention, which constitute a part of the specification, are used to illustrate the embodiments of the present invention, and together with the text description, explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 It shows a schematic structural diagram of a lifting joint provided according to a specific embodiment of the present invention;

[0017] Figure 2 A schematic diagram of a geometric model of a lifting joint and a fuselage composite material frame web provided according to a specific embodiment of the present invention is shown;

[0018] Figure 3 A schematic diagram of the bolt support reaction force of the first joint provided according to a specific embodiment of the present invention is shown;

[0019] Figure 4 A schematic diagram of constraint conditions of a second joint provided according to a specific embodiment of the present invention is shown;

[0020] Figure 5 A schematic diagram of shear force of bolts on the fuselage composite material frame web connection surface provided according to a specific embodiment of the present invention is shown;

[0021] Figure 6 A schematic diagram of installing a corner box according to a specific embodiment of the present invention is shown;

[0022] Figure 7 A schematic diagram of a corner box structure provided according to a specific embodiment of the present invention is shown;

[0023] Figure 8A back plate load application diagram according to a specific embodiment of the present invention is shown;

[0024] Fig. 9 A schematic diagram of the shear force connection between the back plate and the web hole provided according to a specific embodiment of the present invention is shown.

[0025] The above drawings include the following reference numerals:

[0026] 1. First joint; 2. Second joint; 3. Fuselage composite material frame belly plate; 4. Back plate; 5. Corner box. DETAILED DESCRIPTION

[0027] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present invention. Meanwhile, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, and therefore, once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0030] According to a specific embodiment of the present invention, a design method for enhancing the connection strength of composite wall panels based on strength calculation is provided, and the method includes:

[0031] The geometric model of the lifting joint and the geometric model of the fuselage composite frame web 3 are established respectively; wherein the lifting joint includes a first joint 1 and a second joint 2, the first joint 1 is used to bear the lifting load, the second joint 2 is located between the first joint 1 and the fuselage composite frame web 3, the second joint 2 is fixed to the fuselage composite frame web 3 through a plurality of connectors, and the first joint 1 is fixed to the second joint 2 and the fuselage composite frame web 3 through a plurality of connectors; a back plate 4 is fixed to the back of the fuselage composite frame web 3 through a plurality of connectors;

[0032] Solid unit finite element models are established according to the geometric models of the lifting joint and the fuselage composite frame web 3, respectively, and RBE2 units are used to simulate the connection of the connectors;

[0033] Based on the established finite element model, force analysis and stiffness distribution are performed, wherein the support reaction force of the first joint 1 is used as the main force of the second joint 2, and the strength of the first joint 1 and the second joint 2 and the load transfer of the connecting parts are calculated respectively;

[0034] Determine whether the connecting piece of the second joint 2 and the mounting hole of the fuselage composite material frame web 3 meet the strength requirements;

[0035] If the mounting holes of the fuselage composite material frame web 3 do not meet the strength requirements, two corner boxes 5 are added to the back plate 4 on the back of the fuselage composite material frame web 3, and the corner boxes 5 are fixed to the back plate 4, the edge strip, and the upper longitudinal beam and the middle longitudinal beam through a number of connectors;

[0036] The stiffness of the load-transferring area of ​​the connector is taken as the maximum value, the load distribution in the load-transferring area of ​​the connector is increased to 100%, and the strength of the mounting holes of the fuselage composite material frame web 3 is checked.

[0037] By applying this configuration, a design method for enhancing the connection strength of composite wall panels based on strength calculation is provided. The method analyzes the connection strength between the lifting joint and the fuselage composite frame web. Based on the force analysis and stiffness distribution principle, the support reaction force of the first joint is used as the main force of the second joint. The strength of the first joint and the second joint and the load transfer of the connecting parts are calculated respectively, and the specific scheme for enhancing the connection strength is determined. The strength verification method considering the limit case is used to verify the improved connection area to ensure that the connection scheme has sufficient strength and reduce design iterations. The present invention uses strength calculation instead of experimental development, which is low in cost, good in versatility, and suitable for engineering applications.

[0038] As a specific embodiment of the present invention, the connecting member can be a metal bolt. The lifting joint is connected to the fuselage composite material frame web 3 by a metal bolt, which is a typical composite material connection form. Composite materials have the characteristics of anisotropy and brittleness, so that the stress concentration of the fuselage composite material frame web 3 is more serious than that of metal.

[0039] As a specific embodiment of the present invention, the material of the lifting joint and the connecting bolts can both be 30CrMnSi.

[0040] As a specific embodiment of the present invention, the finite element model of the lifting joint is simulated using solid elements.

[0041] According to another aspect of the present invention, a structure for enhancing the connection strength of composite wall panels is provided, and the structure is designed using the design method for enhancing the connection strength of composite wall panels based on strength calculation as described above; the structure includes two corner boxes 5, the corner boxes 5 are located on the back side opposite to the front side of the fuselage composite material frame web 3 where the lifting joint is installed, and the corner boxes 5 are fixed to the web 3, the edge strip, and the upper longitudinal beam and the middle longitudinal beam through a plurality of connecting parts.

[0042] In the present invention, the structure designed by the design method for enhancing the connection strength of composite wall panels based on strength calculation as described above has sufficient connection strength, which can ensure a reliable connection between the lifting joint and the fuselage composite material frame web 3.

[0043] In order to have a further understanding of the present invention, the design method of the present invention is described in detail below in conjunction with specific embodiments.

[0044] 1. Establishment of geometric model

[0045] The corresponding geometric model is established for the lifting joint and fuselage composite frame web 3 of a certain type of aircraft. The first joint 1 is fixed to the second joint 2 and the fuselage composite frame web 3 by 4 bolts. The second joint 2 is connected to the front of the fuselage composite frame web 3 by 4 bolts and to the side of the fuselage composite frame web 3 by 3 bolts. A back plate 4 is connected to the back of the fuselage composite frame web 3 by 8 bolts. The lifting joint and bolt materials are both 30CrMnSi, the bolt diameter is 6mm, and the reinforcement area frame structure and nail arrangement are shown in Figure 1 , strengthen the geometric model of the front structure such as Figure 2 shown.

[0046] 2. Establishment of finite element model

[0047] Solid unit finite element models are established according to the geometric models of the lifting joint and the fuselage composite frame web 3, respectively. RBE2 units are used to simulate the connection of the connectors, and the finite element model of the lifting joint is simulated by solid units.

[0048] 3. Stress analysis and strength analysis of the connection area

[0049] Figure 1 In the lifting joint shown, the first joint 1 bears the lifting load. When the lifting weight is 3 tons, the force on the joint before lifting is 56553N, which is borne by two lifting joints. Therefore, the force on the single-side lifting joint is 28276.5N, which is applied to the hanging point upward along the Y-axis.

[0050] After the first joint 1 is subjected to the hanging load, the four nail holes transmit the force to the four nail holes on the web 3 and the second joint 2 (which is connected back to back with the first joint 1 on the web 3). Therefore, the strength of the first joint 1 is calculated first to obtain the reaction force of the nail holes of the first joint 1. According to the finite element model of the first joint 1, it is calculated that the stress of the first joint 1 itself and the nail transmission load both meet the strength requirements.

[0051] Figure 3 is the support reaction force of the 4 bolts of the first joint 1. These 4 groups of support reaction forces are transmitted to the 4 joints of the web 3 and the second joint 2. According to the force analysis, it can be known that the 4 joints of the second joint 2 bear 2 / 3 of the load. Therefore, 2 / 3 of the 4 groups of support reaction forces of the first joint 1 are applied to the second joint 2 as the load condition of the second joint 2. At the same time, the other 7 bolts of the second joint 2 (including the 4 bolts on the front and the 3 bolts on the side) are constrained according to the actual situation. The loading and constraints of the second joint 2 are as follows: Figure 4 shown.

[0052] Figure 5 is the shear force on the bolts of the second joint 2 (connecting surface with the web 3), the maximum shear force is 6090N, which is less than the shear limit of the 6mm steel nail. The thickness of the composite plate is 3mm, the hole diameter is 6mm, and the corresponding hole extrusion stress is 333Mpa. According to the hole extrusion limit of 350Mpa, the hole extrusion margin is -0.08, which is less than 0, indicating that the hole extrusion margin of the composite plate is insufficient, the web 3 is in danger of being torn apart, and the strength requirement is not met.

[0053] 4. Improved design based on strength analysis

[0054] In the analysis in step 3, it was found that the web 3 connected by the lifting joint was weak. In order to prevent the web 3 from being damaged by hole extrusion and causing oil leakage, two corner boxes 5 were added to the original corner boxes on the back of the original fuselage composite frame web 3 at each hanging point. They were connected to the back plate 4, edge strips and upper middle longitudinal beams of the frame web 3 through rivets to disperse the force transmission and reduce the stress level of the web 3. Figure 6 and Figure 7 shown.

[0055] 5. Stress analysis of the structure after strengthening

[0056] The material and thickness of the corner box 5 used for reinforcement are consistent with those of the back plate 4. For example, both materials are steel. Therefore, the stiffness distribution of the corner box 5 and the back plate 4 is 1:1, that is, the back plate 4 can reduce half of the load after reinforcement. According to the above analysis, the web 3 has insufficient stiffness due to unreasonable layer design. Therefore, 350Mpa is selected as the hole extrusion limit value. At the same time, in order to check the hole extrusion of the connection between the edge of the back plate 4 and the web 3 under extreme conditions, the working condition that the back plate 4 bears all the loads transmitted by the joint is selected. The constraint conditions of the back plate 4 are the same as Figure 4 All the loads transmitted by the joint are applied to the back plate 4. Then, due to the existence of the reinforced corner box 5, half of the load is taken as the final load and applied to the back plate 4. The load conditions are as follows: Figure 8 shown.

[0057] Depend on Figure 8 It can be seen that according to the 1:3 relationship between the stiffness of the web 3 and the back plate 4, the applied load should be 0.75*0.5=0.375 times the maximum load. In order to examine it under extreme conditions, the applied load coefficient is changed to 1*0.5=0.5 times the maximum load.

[0058] Fig. 9 is the shear force diagram of the connection hole between the back plate 4 and the web plate 3, Fig. 9 It can be seen that the maximum shear force on the back plate 4 under extreme conditions is 4090N, which is much smaller than the shear limit of the 8mm steel nail. At the same time, the hole extrusion is 4090N / 3mm / 8mm=227Mpa. According to the hole extrusion limit of 350Mpa, the hole extrusion margin is 350Mpa / 227Mpa / 1.5-1=0.34. The margin is greater than 0, which meets the strength requirements.

[0059] Aiming at the calculation of nail transfer load in actual structure, the present invention proposes a design method for enhancing the connection strength of composite wall panels based on strength calculation, and determines the specific scheme for enhancing the connection strength on this basis to reduce the stress concentration in the connection area. The improved connection area is checked by using the strength verification method considering the limit case to ensure that the connection scheme has sufficient strength. It is considered that the stiffness of the nail transfer area is the maximum value, and the load distribution in the nail transfer area is increased from 75% to 100%. Verification under such conditions can ensure that the connection scheme has sufficient strength and reduce design iterations. The results obtained by this method are relatively accurate and can be used for the connection strength verification and improved design between the lifting joint and the fuselage composite web of general aircraft, replacing experimental development, shortening the development cycle, and improving work efficiency, providing a theoretical basis and design guidance for structural design and strength analysis.

[0060] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0061] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A design method for enhancing the connection strength of composite wall panels based on strength calculation, characterized in that: The method comprises: The geometric model of the lifting joint and the geometric model of the fuselage composite material frame web are established respectively; wherein the lifting joint includes a first joint and a second joint, the first joint is used to bear the lifting load, the second joint is located between the first joint and the fuselage composite material frame web, the second joint is fixed to the fuselage composite material frame web through a plurality of connectors, and the first joint is fixed to the second joint and the fuselage composite material frame web through a plurality of connectors; a back plate is fixed to the back of the fuselage composite material frame web through a plurality of connectors; Solid unit finite element models are established according to the geometric models of the lifting joint and the fuselage composite frame web, and RBE2 units are used to simulate the connection of the connectors. Based on the established finite element model, force analysis and stiffness distribution are performed, wherein the support reaction force of the first joint is used as the main force of the second joint, and the strength of the first joint and the second joint and the load transmitted by the connecting parts are calculated respectively; respectively determining whether the connecting piece of the second joint and the mounting hole of the fuselage composite material frame web meet the strength requirements; If the mounting holes of the fuselage composite material frame web do not meet the strength requirements, two corner boxes are added to the back plate on the back of the fuselage composite material frame web, and the corner boxes are fixed to the back plate, the edge strip, and the upper and middle longitudinal beams through a number of connectors; The stiffness of the load-transferring area of ​​the connector is taken as the maximum value, the load distribution in the load-transferring area of ​​the connector is increased to 100%, and the strength of the mounting holes of the fuselage composite material frame web is checked.

2. The design method for enhancing the connection strength of composite wall panels based on strength calculation according to claim 1 is characterized in that: The connecting parts are made of metal bolts.

3. The design method for enhancing the connection strength of composite wall panels based on strength calculation according to claim 1 or 2, characterized in that: The materials of lifting joints and connecting parts are 30CrMnSi.

4. The design method for enhancing the connection strength of composite wall panels based on strength calculation according to any one of claims 1 to 3, characterized in that: The finite element model of the lifting joint is simulated using solid elements.

5. A structure for enhancing the connection strength of composite wall panels, characterized in that: The structure is designed using the design method for enhancing the connection strength of composite wall panels based on strength calculation as described above; the structure includes two corner boxes, which are located on the back side opposite to the front side of the fuselage composite frame web installation lifting joint, and the corner boxes are fixed to the web, edge strips, upper longitudinal beams and middle longitudinal beams through a number of connecting parts.

6. The structure for enhancing the connection strength of composite wall panels according to claim 5 is characterized in that: The structure further comprises a back plate, which is located on the back side of the fuselage composite material frame web and between the fuselage composite material frame web and the corner box.

7. The structure for enhancing the connection strength of composite wall panels according to claim 5 is characterized in that: The corner boxes are made from the same material as the back panel.

8. The structure for enhancing the connection strength of composite wall panels according to claim 5 is characterized in that: The thickness of the corner box material is the same as the thickness of the back panel.

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