Design method for strength of reinforced composite panel connections based on strength calculation

Abstract

The application provides a design method for enhancing the connection strength of a composite wall plate based on strength calculation, and the method comprises the following steps: geometric models of a lifting connector and a composite frame web of an aircraft body are respectively established; entity unit finite element models are respectively established according to the geometric models of the lifting connector and the composite frame web of the aircraft body, and RBE2 units are used to simulate the connection of the connector; stress analysis and stiffness distribution are performed based on the established finite element models; whether the connector of the second connector and the mounting hole of the composite frame web of the aircraft body meet the strength requirement is respectively judged; if the mounting hole of the composite frame web of the aircraft body does not meet the strength requirement, two corner boxes are added on the back plate of the back surface of the composite frame web of the aircraft body, and the strength of the mounting hole of the composite frame web of the aircraft body is checked. The technical scheme of the application can solve the technical problem that the load transmission strength of the connector between the composite material connections in the prior art is difficult to accurately check.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of structural design simulation, and particularly relates to a design method for connection strength of reinforced composite wallboard based on strength calculation. BACKGROUND

[0002] In composite material structure design, 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 high specific strength and specific stiffness, strong designability, good fatigue resistance and many other advantages, and aircraft and aerospace structures are extremely sensitive to weight. 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 contents of composite material structure design. The connection part is usually the weak link of 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 complex.

[0004] At present, the design and analysis method for increasing the connection strength of the composite wallboard usually adopts the following method: the existing wallboard connection local structure is tested by using the test method, the stress characteristics and the maximum bearing capacity of the connection area are determined through the test, if the strength of the connection area does not meet the design requirements, an improvement scheme is proposed based on the stress characteristics and the maximum bearing capacity of the connection area, and the improvement scheme meeting the design requirements is determined by using the test method again. This method has the disadvantages of long development cycle and high development cost. SUMMARY

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

[0006] According to an aspect of the present application, there is provided a design method for enhancing the connection strength of a composite wallboard based on strength calculation, comprising: establishing a geometric model of a lifting connector and a geometric model of a composite frame web of a fuselage respectively; wherein the lifting connector comprises a first connector and a second connector, the first connector is used to bear a lifting load, the second connector is located between the first connector and the composite frame web of the fuselage, the second connector is fixed to the composite frame web of the fuselage through a plurality of connecting pieces, and the first connector is fixed to the second connector and the composite frame web of the fuselage through a plurality of connecting pieces; a back plate is fixed to the back of the composite frame web of the fuselage through a plurality of connecting pieces; a solid element finite element model is established according to the geometric model of the lifting connector and the geometric model of the composite frame web of the fuselage respectively, and RBE2 elements are used to simulate the connection of the connecting pieces; stress analysis and stiffness distribution are performed based on the established finite element model, wherein the reaction force of the first connector is taken as the driving force of the second connector, the strength of the first connector and the second connector and the load transmission of the connecting pieces are calculated respectively; whether the connecting pieces of the second connector and the mounting holes of the composite frame web of the fuselage meet the strength requirement is judged respectively; if the mounting holes of the composite frame web of the fuselage do not meet the strength requirement, two corner boxes are added to the back plate on the back of the composite frame web of the fuselage, and the corner boxes are fixed to the back plate, the edge strip, and the upper longitudinal beam and the middle longitudinal beam through a plurality of connecting pieces; the stiffness of the connecting piece load transmission area is taken as a maximum value, the load distribution of the connecting piece load transmission area is improved to 100%, and the strength of the mounting holes of the composite frame web of the fuselage is checked.

[0007] Further, the connecting pieces are metal bolts.

[0008] Further, the materials of the lifting connector and the connecting pieces are 30CrMnSi.

[0009] Further, the finite element model of the lifting connector is simulated by solid elements.

[0010] According to another aspect of the present application, there is provided a structure for enhancing the connection strength of a composite wallboard, which is designed by using the design method for enhancing the connection strength of a composite wallboard based on strength calculation as described above; the structure comprises two corner boxes, which are located on the back of the composite frame web of the fuselage opposite to the front surface where the lifting connector is mounted, and the corner boxes are fixed to the web, the edge strip, and the upper longitudinal beam and the middle longitudinal beam through a plurality of connecting pieces.

[0011] Further, the structure further comprises a back plate, which is located on the back of the composite frame web of the fuselage and between the composite frame web of the fuselage and the corner boxes.

[0012] Further, the materials of the corner boxes and the back plate are the same.

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

[0014] The technical scheme of the present application provides a design method for connection strength of a reinforced composite wallboard based on strength calculation, which analyzes the connection strength between a lifting joint and a composite material frame web of an aircraft body, takes the reaction force of the first joint as the driving force of the second joint based on stress analysis and stiffness distribution principle, calculates the strength of the first joint and the second joint and the load transmission of the connecting piece respectively, determines the specific scheme for reinforcing the connection strength, checks the improved connection area by using the strength checking method considering the limit condition, ensures that the connection scheme has sufficient strength, and reduces design iteration. The present application uses strength calculation instead of test development, has low cost, good universality, and is suitable for engineering application. Compared with the prior art, the technical scheme of the present application can solve the technical problem that the load transmission strength of the connecting piece between the composite material connections is difficult to accurately check. BRIEF DESCRIPTION OF DRAWINGS

[0015] The accompanying drawings, which are included to provide a further understanding of the embodiments of the application and constitute a part of the specification, illustrate the embodiments of the application and together with the text description serve to explain the principles of the application. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0016] Figure 1 A structure diagram of a lifting joint provided by a specific embodiment of the present application is shown;

[0017] Figure 2 A geometric model diagram of a lifting joint and a composite material frame web of an aircraft body provided by a specific embodiment of the present application is shown;

[0018] Figure 3 A bolt reaction force diagram of a first joint provided by a specific embodiment of the present application is shown;

[0019] Figure 4 A constraint condition diagram of a second joint provided by a specific embodiment of the present application is shown;

[0020] Figure 5 A bolt shear force diagram of a connection surface of a composite material frame web of an aircraft body provided by a specific embodiment of the present application is shown;

[0021] Figure 6 An installation diagram of a corner box provided by a specific embodiment of the present application is shown;

[0022] Figure 7 A structure diagram of a corner box provided by a specific embodiment of the present application is shown;

[0023] Figure 8A backplane load application diagram is shown provided in accordance with specific embodiments of the present application;

[0024] Figure 9 A backplane to web hole connection shear diagram is shown provided in accordance with specific embodiments of the present application.

[0025] Wherein the above figures include the following reference numerals:

[0026] 1. First joint; 2. Second joint; 3. Fuselage composite frame web; 4. Backplane; 5. Corner box. DETAILED DESCRIPTION

[0027] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0028] It should be noted that the terms used herein are only intended to describe specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form, unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in the specification, there is a reference to the presence of a feature, step, operation, device, component and / or combinations thereof.

[0029] Unless specifically stated otherwise, the relative arrangements of the components and steps illustrated in these embodiments and the numerical expressions and values are not limiting of the scope of the application. It should be understood that the various parts of the drawings are not necessarily drawn to scale relative to each other. The techniques, methods, and devices known to those of ordinary skill can not be discussed in detail because they can unnecessarily obscure the application. In all examples shown and discussed herein, any specific value should be interpreted as merely an example, and not as a limitation. Thus, other examples of the exemplary embodiments can have different values. It should be noted that like reference numerals and letters refer to like items in the following drawings, and thus, once an item is defined in one drawing, it need not be discussed further in subsequent drawings.

[0030] The design method for enhancing the connection strength of a composite wallboard based on strength calculation according to the specific embodiment of the present application comprises:

[0031] A geometric model of the lifting joint and a geometric model of the composite frame web 3 of the fuselage are respectively established; wherein the lifting joint comprises 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 composite frame web 3 of the fuselage, the second joint 2 is fixed to the composite frame web 3 of the fuselage through a plurality of connecting pieces, and the first joint 1 is fixed to the second joint 2 and the composite frame web 3 of the fuselage through a plurality of connecting pieces; a back plate 4 is fixed to the back of the composite frame web 3 of the fuselage through a plurality of connecting pieces;

[0032] The entity element finite element model is respectively established according to the geometric model of the lifting joint and the geometric model of the composite frame web 3 of the fuselage, and the RBE2 element is used to simulate the connection of the connecting pieces;

[0033] The stress analysis and stiffness distribution are performed based on the established finite element model, wherein the support reaction force of the first joint 1 is used as the active force of the second joint 2, and the strength of the first joint 1 and the second joint 2 and the load transmission of the connecting pieces are calculated respectively;

[0034] Whether the connecting pieces of the second joint 2 and the mounting holes of the composite frame web 3 of the fuselage meet the strength requirement is respectively judged;

[0035] If the mounting holes of the composite frame web 3 of the fuselage do not meet the strength requirement, two corner boxes 5 are added to the back plate 4 on the back of the composite frame web 3 of the fuselage, 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 plurality of connecting pieces;

[0036] The stiffness of the load transmission area of the connecting pieces is taken as the maximum value, the load distribution of the load transmission area of the connecting pieces is improved to 100%, and the strength of the mounting holes of the composite frame web 3 of the fuselage is checked.

[0037] By using this configuration mode, a design method for enhancing the connection strength of a composite wallboard based on strength calculation is provided. The connection strength between the lifting joint and the composite frame web of the fuselage is analyzed, the support reaction force of the first joint is used as the active force of the second joint based on the stress analysis and stiffness distribution principle, the strength of the first joint and the second joint and the load transmission of the connecting pieces are calculated respectively, the specific scheme for enhancing the connection strength is determined, the improved connection area is checked by using the strength checking method considering the limit condition, the connection scheme has sufficient strength, the design iteration is reduced, and the strength calculation is used instead of the test development, so that the cost is low, the universality is good, and the method is suitable for engineering application.

[0038] As a specific embodiment of the present application, the connecting member can adopt a metal bolt. The lifting lug is connected with the fuselage composite frame web plate 3 by a metal bolt, which is a typical composite material connection form. The composite material has anisotropy and brittleness, so that the stress concentration of the fuselage composite frame web plate 3 is more serious than that of metal.

[0039] As a specific embodiment of the present application, the materials of the lifting lug and the connecting member bolt can adopt 30CrMnSi.

[0040] As a specific embodiment of the present application, the finite element model of the lifting lug adopts a body element simulation.

[0041] According to another aspect of the present application, a structure for enhancing the connection strength of a composite wall plate is provided, which is designed by using the design method for enhancing the connection strength of a composite wall plate based on strength calculation as described above; the structure comprises two corner boxes 5 located on the back surface opposite to the front surface where the lifting lug is installed on the fuselage composite frame web plate 3, and the corner boxes 5 are fixed on the web plate 3, the edge strip, and the upper and middle longitudinal beams by a plurality of connecting members.

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

[0043] In order to further understand the present application, the design method of the present application is described in detail below in combination with specific embodiments.

[0044] I. Establishment of geometric model

[0045] The corresponding geometric models of the lifting lug and the fuselage composite frame web plate 3 of a certain type of aircraft are established. The first lug 1 is fixed on the second lug 2 and the fuselage composite frame web plate 3 by 4 bolts, the second lug 2 is connected with the front surface of the fuselage composite frame web plate 3 by 4 bolts, and is connected with the side surface of the fuselage composite frame web plate 3 by 3 bolts. On the back surface of the fuselage composite frame web plate 3, a back plate 4 is connected by 8 bolts. The materials of the lifting lug and the bolts are 30CrMnSi, the diameter of the bolt is 6mm, and the reinforcing area frame structure and the pin arrangement form are shown in Figure 1 The geometric model of the structure before reinforcement is shown in Figure 2 .

[0046] II. Establishment of finite element model

[0047] The solid element finite element models are established according to the geometric model of the lifting lug and the geometric model of the fuselage composite frame web plate 3 respectively, the connection of the connecting member is simulated by using RBE2 element, and the finite element model of the lifting lug adopts a body element simulation.

[0048] III. Analysis of the force and strength of the connection area

[0049] Figure 1 In the lifting connector shown, the first connector 1 bears the lifting load, and when the lifting weight is 3 tons, the force on the lifting connector before lifting is 56553 N, which is borne by two lifting connectors, so the force on a single lifting connector is 28276.5 N, upward along the Y axis, and applied to the hanging point.

[0050] After the first connector 1 bears the hanging load, the force is transmitted to the four pin holes on the web plate 3 and the second connector 2 (connected back-to-back with the first connector 1 on the web plate 3) through the four pin holes. Therefore, the strength of the first connector 1 is calculated first to obtain the reaction force of the pin hole of the first connector 1. According to the finite element model of the first connector 1, it is calculated that the stress of the first connector 1 itself and the pin transmission load all meet the strength requirements.

[0051] Figure 3 The four groups of support reactions of the four bolts of the first connector 1 are transmitted to the four connectors of the web plate 3 and the second connector 2. According to the force analysis, it is known that the four connectors of the second connector 2 bear 2 / 3 of the load, so 2 / 3 of the four groups of support reactions of the first connector 1 are applied to the second connector 2 as the load condition of the second connector 2, and at the same time, the other seven bolts of the second connector 2 (including the four bolts on the front and the three bolts on the side) are constrained according to the actual situation. The loading and constraint of the second connector 2 are shown in Figure 4 .

[0052] Figure 5 The maximum shear force borne by the bolts of the second connector 2 (connected to the web plate 3) is 6090 N, which is less than the shear limit of a 6 mm steel pin. The thickness of the composite plate is 3 mm, and the hole diameter is 6 mm. The corresponding hole extrusion stress is 333 Mpa. According to the hole extrusion limit of 350 Mpa, the hole extrusion margin is -0.08, which is less than 0. It is indicated that the hole extrusion margin of the composite plate is insufficient, and the web plate 3 is in danger of being pulled apart, which does not meet the strength requirements.

[0053] IV. Improved design based on strength analysis

[0054] In the analysis in step three, it is found that the web plate 3 connected by the lifting connector is relatively weak. In order to prevent the web plate 3 from being damaged due to hole extrusion and causing oil leakage, two corner boxes 5 are added to each hanging point on the basis of the original corner box on the back of the original composite material frame web plate 3. The corner boxes 5 are connected with the back plate 4, the edge strip and the upper and middle longitudinal beams of the frame web plate 3 through rivets to disperse the force and reduce the stress level of the web plate 3, as shown in Figure 6 and Figure 7 .

[0055] V. Force analysis of the strengthened structure

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

[0057] As shown in Figure 8 , according to the stiffness ratio of 1:3 between the web plate 3 and the back plate 4, the applied load should be 0.75*0.5=0.375 times the maximum load, and in order to investigate under the limit condition, the load coefficient is changed to 1*0.5=0.5 times the maximum load.

[0058] Figure 9 The shear force diagram of the joint hole between the back plate 4 and the web plate 3 is shown in Figure 9 , it can be known that the maximum shear force of the back plate 4 under the limit condition is 4090N, which is far less than the shear limit of 8mm steel nails, and 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 requirement.

[0059] The present application proposes a design method for enhancing the connection strength of a composite wall plate based on strength calculation, which is used to determine the specific scheme of enhancing the connection strength, so as to reduce the stress concentration in the connection area, and the improved connection area is checked by using the strength checking method considering the limit condition, so as to ensure that the connection scheme has sufficient strength. It is considered that the stiffness of the nail transmission area is the maximum value, the load distribution of the nail transmission area is increased from 75% to 100%, and the checking under this condition can ensure that the connection scheme has sufficient strength, and at the same time, the design iteration is reduced. The result obtained by the method is more accurate, and can be used for checking and improving the connection strength between the lifting joint of a general aircraft and the composite web plate of the aircraft, replacing the test development, shortening the development cycle, improving the work efficiency, and providing a theoretical basis and design guidance for structural design and strength analysis.

[0060] For purposes of the description hereinafter, spatial or directional terms, for example, "above", "below", "upper", "lower", and the like, can be used, and relate to the device as illustrated in the figures. However, it is to be understood that no absolute or relative orientation of the device is intended or implied, unless specifically described as such. Terms concerning attachments, coupling and the like, such as "connected" and "coupled" and the like, are to be construed in accordance with their normal meanings, that is, as referring to an indirect or direct connection or coupling. Any reference to "comprising" or "containing" is to be construed as meaning "comprising or containing, but not limited to". Any reference to "comprising" or "containing" is to be construed as meaning "comprising or containing, but not limited to".

[0061] In addition, it should be pointed out that the use of the terms "first", "second" and the like, to describe various elements, is merely intended to differentiate the elements from one another, and does not connote any special order or order of precedence, unless otherwise specifically indicated. Thus, the use of the terms "first", "second" and the like, is not intended to limit the scope of the present application, and is not intended to connote any special order or order of precedence.

[0062] The preferred embodiments herein disclosed are not intended to limit or restrict the scope of the application, but merely convey the best mode contemplated by the inventors of carrying out the claimed application. Modifications can be made by those skilled in the art, which yet fall within the scope of the present application. Therefore, it is, therefore, to be understood that any variations made to the application are to be considered as being within the scope of the present application as defined by the appended claims, if any, and their equivalents.

Claims

1. A design method for calculating the strength of a connection of a reinforced composite wall panel based on strength, characterized by, The method comprises: geometric models of the lifting joint and the composite material frame web of the fuselage are respectively established; the lifting joint comprises a first joint and a second joint, the first joint is used for bearing the lifting load, the second joint is located between the first joint and the composite material frame web of the fuselage, the second joint is fixed on the composite material frame web of the fuselage through a plurality of connecting pieces, and the first joint is fixed on the second joint and the composite material frame web of the fuselage through a plurality of connecting pieces; a back plate is fixed on the back of the composite material frame web of the fuselage through a plurality of connecting pieces; entity unit finite element models are respectively established according to the geometric models of the lifting joint and the composite material frame web of the fuselage, and RBE2 units are used to simulate the connection of the connecting pieces; stress analysis and stiffness distribution are performed based on the established finite element models, wherein the support reaction force of the first joint is used as the active force of the second joint, and the strength of the first joint and the second joint and the load transmission of the connecting pieces are calculated; whether the connecting pieces of the second joint and the mounting holes of the composite material frame web of the fuselage meet the strength requirement is judged respectively; if the mounting holes of the composite material frame web of the fuselage do not meet the strength requirement, two corner boxes are added on the back plate on the back of the composite material frame web of the fuselage, and the corner boxes are fixed on the back plate, the edge strip, and the upper longitudinal beam and the middle longitudinal beam through a plurality of connecting pieces; the stiffness of the load transmission area of the connecting pieces is taken as the maximum value, the load distribution of the load transmission area of the connecting pieces is improved to 100%, and the strength of the mounting holes of the composite material frame web of the fuselage is checked.

2. The design method of the strength of the connection of the reinforced composite wall panel based on the strength calculation according to claim 1, characterized by, The connecting pieces are metal bolts.

3. The design method of the strength of a connection of a fiber-reinforced composite wall panel based on strength calculation according to claim 1 or 2, characterized by, The materials of the lifting joint and the connecting pieces are 30CrMnSi.

4. The design method of the strength of a connection of a fiber-reinforced composite wall panel based on strength calculation according to claim 1 or 2, characterized by, The finite element model of the lifting joint is simulated by using body units.

5. A structure for enhancing the strength of a composite panel connection, characterized by, The structure is designed by using the design method for enhancing the connection strength of the composite material wall plate based on strength calculation in any one of claims 1 to 4; the structure comprises two corner boxes, the corner boxes are located on the back surface opposite to the front surface of the composite material frame web of the fuselage on which the lifting joint is mounted, and the corner boxes are fixed on the web, the edge strip, and the upper longitudinal beam and the middle longitudinal beam through a plurality of connecting pieces.

6. The structure for enhancing the connection strength of a composite wall panel according to claim 5, wherein The structure further comprises a back plate, the back plate is located on the back of the composite material frame web of the fuselage and between the composite material frame web of the fuselage and the corner boxes.

7. The structure for enhancing the connection strength of a composite wall panel according to claim 5, wherein The materials of the corner boxes and the back plate are the same.

8. The structure for enhancing the connection strength of a composite wall panel according to claim 5, wherein The thickness of the corner box material is the same as that of the back plate.

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