A composite material multi-dimensional variable stiffness casing structure

Abstract

The present invention discloses a composite material multi-dimensional variable stiffness casing structure, which relates to the field of aero-engines. The casing structure has multi-dimensional variable stiffness characteristics of in-plane and out-of-plane variable stiffness; in-plane variable stiffness, the laying angle of the composite material fiber changes in the form of a continuous curve, and when the continuous curve fiber is wound, the fiber has a tensile stress to provide prestress for the casing containment area structure; out-of-plane variable stiffness, the stiffness change of the composite material along the thickness direction is achieved by alternating layers of two or more materials, and the laying angle of the fibers in the layer changes alternately, and the number of layers, the thickness of the layers and the density of the fibers can be adjusted to achieve the best mechanical properties. The present invention optimizes the variable stiffness characteristics of each area of ​​the casing structure according to numerical simulation and experimental test results, and realizes fine control of multi-dimensional variable stiffness and local strength under the premise of ensuring the structural strength safety and lightweight goals, thereby solving the problem of insufficient stiffness strength and weight reduction space of the traditional metal engine casing structure.

Description

Technical Field

[0001] The invention relates to the technical field of aeroengines, and in particular to a composite material multi-dimensional variable stiffness casing structure. Background Art

[0002] At present, the casings of large mechanical equipment such as aircraft are made of a large amount of metal materials, and the main problems are excessive weight, high manufacturing cost, poor corrosion resistance, etc. Due to its lightweight advantage, the all-composite casing has been used in the latest generation of large bypass ratio turbofan engines in the world, greatly improving the performance and fuel efficiency of the engine, and has become an important embodiment of the advancement of aviation engines. It is one of the key technologies that my country urgently needs to break through.

[0003] The aircraft engine casing needs to be strong enough to withstand the various loads and vibrations from the aircraft during flight, as well as the impact of high-pressure airflow. The aircraft engine casing also needs to have sufficient rigidity to maintain the stability of its shape and size under various working conditions. The aircraft engine casing has extremely high requirements for the sealing of oil, gas, and liquid to ensure that the airflow in the casing will not leak during high-speed flight. It needs to carry additional components and additional mass such as installation pipelines and APU (auxiliary power unit), and at the same time prevent external impurities such as dust and moisture from entering the casing, thereby affecting the normal operation of the engine.

[0004] Variable stiffness composite materials can better improve the matching of process, mechanical properties and structural geometric appearance and improve design efficiency by optimizing the distribution of structural stiffness. By integrating automatic fiber placement and hybrid fiber molding processes and combining multi-scale and multi-level ideas, variable stiffness can be achieved in-plane and out-of-plane simultaneously to achieve "variable stiffness", give full play to the lightweight advantages of composite materials, and realize low-cost manufacturing of variable stiffness composite casings, which has great application potential.

[0005] The composite material layup angles used in traditional aircraft engine casings are relatively fixed and the wall thickness is uniform, which limits the improvement of the containment performance and weight reduction potential of composite material casings. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a composite material multi-dimensional variable stiffness casing structure, which solves the practical problems of traditional metal casing structures due to material property constraints, such as inflexible stiffness design and insufficient room for improvement in strength and weight reduction design.

[0007] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: a composite material multi-dimensional variable stiffness casing structure, comprising a containing area, an engine component installation area, a casing structure transition area and a casing installation edge area connected in sequence;

[0008] The containing area, the engine component installation area, the casing structure transition area and the casing installation edge area all have multi-dimensional variable stiffness characteristics;

[0009] The multi-dimensional variable stiffness characteristics are embodied in: variable stiffness in the plane and variable stiffness out of the plane, and in the variable thickness area, the variable stiffness in the plane and out of the plane are used simultaneously;

[0010] The in-plane variable stiffness is a continuous curve fiber variable stiffness, and the laying angle of the composite fiber changes in the form of a continuous curve in the plane, and the fiber winding direction is based on the geometric shape of the structure to achieve a gradual change in stiffness. When the continuous curve fiber is wound, the fiber has an initial tension, which provides prestress for the casing containment area structure and enhances its working strength;

[0011] The out-of-plane variable stiffness is a discrete variable stiffness. Two or more materials are alternately laid to achieve stiffness changes along the thickness direction. The interlayer fiber laying angles are alternately changed. The number of layers, layer thickness and fiber density can be adjusted.

[0012] The thickness gradient area with in-plane and out-of-plane variable stiffness is composed of alternating continuous curve angles and discrete straight fiber layers. In addition, the prepreg volume content can be increased or decreased to increase or decrease the thickness.

[0013] Furthermore, the containing area is thick in the middle and thin on both sides, and has in-plane and out-of-plane variable stiffness characteristics. With the thickest point as the center, the fiber winding angle gradually changes towards the thinning areas on both sides, and the layer thickness gradually decreases.

[0014] Furthermore, the engine component installation area is an area of ​​equal thickness, has an in-plane variable stiffness characteristic, and the in-plane stiffness distribution characteristics are controlled by continuous curved fiber laying, and the angles of the curved fibers in adjacent layers are mirror-antisymmetric.

[0015] Furthermore, the thickness of the transition area of ​​the casing structure gradually increases, and it has both in-plane variable stiffness and out-of-plane variable stiffness characteristics. The inner layer is continuous curved fiber winding or discrete straight fiber laying, and discrete straight fiber laying is alternately added between layers, thereby ensuring a smooth transition of the structural mechanical characteristics without increasing the complexity of the process.

[0016] Furthermore, the casing mounting edge area has a high axial load and a thick structural wall, and has an out-of-plane variable stiffness characteristic. The axial stiffness is enhanced in the plane by discrete straight fibers, and plies are added between layers, and the angles of the straight fibers between adjacent layers are arranged alternately and axially symmetrically.

[0017] The beneficial effects of the present invention are as follows: the multi-dimensional variable stiffness composite material can be customized according to the load-bearing requirements of the structure. By optimizing the distribution of structural stiffness, the matching of process, mechanical properties and structural geometric appearance can be better improved, and the design efficiency can be improved, thereby giving full play to the lightweight advantages of composite materials, improving the containment performance efficiency of the composite material casing structure, and solving the problems of fixed fiber angles, insufficient stiffness strength and weight reduction in traditional composite material casings, and having great application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the variable stiffness casing structure.

[0019] Figure 2 This is a schematic diagram of the receiver area.

[0020] Figure 3 Schematic diagram of the ply layup of the variable stiffness part within the surface of the variable stiffness composite engine casing.

[0021] Figure 4 Schematic diagram of the layup of the variable stiffness out-of-plane composite engine casing.

[0022] Figure 5 Schematic diagram of the thickness change part.

[0023] Figure 6 Schematic diagram of the in-plane variable stiffness fiber cylinder.

[0024] Among them: 1. Containment area; 2. Engine component installation area; 3. Casing structure transition area; 4. Casing installation edge area. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0026] like Figure 1 and Figure 2 As shown, a composite material multi-dimensional variable stiffness casing structure comprises a containing area 1, an engine component installation area 2, a casing structure transition area 3 and a casing installation edge area 4 connected in sequence;

[0027] The containing area 1, the engine component installation area 2, the casing structure transition area 3 and the casing installation edge area 4 all have multi-dimensional variable stiffness characteristics;

[0028] The multi-dimensional variable stiffness characteristics are embodied in: variable stiffness in the plane and variable stiffness out of the plane, and in the variable thickness area, the variable stiffness in the plane and out of the plane are used simultaneously;

[0029] The in-plane variable stiffness is a continuous curve fiber variable stiffness, and the laying angle of the composite fiber changes in the form of a continuous curve in the plane, and the fiber winding direction is based on the geometric shape of the structure to achieve a gradual change in stiffness. When the continuous curve fiber is wound, the fiber has an initial tension, which provides prestress for the structure of the casing containing area 1 and enhances its working strength;

[0030] like Figure 3 As shown in the figure, in the in-plane variable stiffness ply, the angle of the continuous curved fiber of the single layer changes continuously, so that the stiffness can be gradually changed, which improves the stiffness of the load-bearing area and reduces the weight at the same time. When the curved fiber is wound, tension is added to make the structure prestressed, and the radial and circumferential stiffness are increased accordingly, thereby improving the local stiffness and strength; by adjusting the resin matrix content in the prepreg, the thickness of the single layer can be changed, so the thickness of the casing section changes gradually, which can effectively improve the overall mechanical properties of the structure and the balance of the mechanical properties of each part of the structure, achieve the optimal stiffness and strength characteristics, and reduce the weight of the structure at the same time.

[0031] The curved fiber trajectory adopts a polynomial function or a non-uniform rational B-spline curve, and the fiber curve changes continuously along the circumference of the surface and the axial direction of the structure at the same time.

[0032] The out-of-plane variable stiffness is a discrete variable stiffness. Two or more materials are alternately laid to achieve stiffness changes along the thickness direction. The interlayer fiber laying angles are alternately changed. The number of layers, layer thickness and fiber density can be adjusted.

[0033] like Figure 4 As shown in the figure, in the out-of-plane variable stiffness design, the fibers in a single layer are straight fibers, and multiple layers are stacked and laid in sections. The fiber angles, sizes, and quantities of different layers are determined by the working stress of the casing structure. Using two or more materials at the same time can effectively improve the overall mechanical properties of the structure and the balance of the mechanical properties of each part of the structure, achieve optimized stiffness and strength characteristics, and reduce the self-weight of the structure.

[0034] The characteristic of segmented laying in out-of-plane variable stiffness is that the thickness of each section of composite material is controlled by the matrix and fiber reinforcement material, and the amount of resin matrix in the prepreg is gradually increased / decreased to increase / decrease the thickness, thereby achieving fine control of the section thickness.

[0035] The use of two or more materials in out-of-plane variable stiffness is specifically: high stiffness / high strength materials are used in the high load-bearing areas of the receiver, and lightweight materials are used in the non-load-bearing areas to compensate for and avoid excessive deformation or failure, thereby optimizing the structural stiffness distribution.

[0036] The above points can be flexibly combined to achieve multi-dimensional variable stiffness of high-performance composite materials, maximize the lightweight advantages of composite materials, and improve the containment performance efficiency of the composite casing structure.

[0037] In this embodiment, the casing structure has multi-dimensional variable stiffness characteristics in different areas according to functional characteristics. The discrete and continuous curved fiber laying methods and the initial prestress effect provided by fiber pre-tensioning can effectively improve the overall mechanical properties of the structure and the balance of the mechanical properties of each part of the structure, achieve optimized stiffness and strength characteristics, and reduce the self-weight of the structure.

[0038] The division of the engine casing structure area is determined by the function and dimensional characteristics of each part of the casing, and the variable stiffness scheme is determined according to the stress-strain, load-bearing requirements, and dynamic response characteristics under the working conditions of the divided area.

[0039] The containing area 1 is thick in the middle and thin on both sides, and has the characteristics of variable stiffness in and out of the plane. With the thickest part as the center, the fiber winding angle gradually changes towards the thinning areas on both sides, and the layer thickness gradually decreases.

[0040] In the containment area 1, the in-plane curved fibers continuously change in the circumferential direction along the outer contour of the casing, and the interlayer curved fiber laying forms can be alternated in sequence. In addition, the curved fibers are wound in a tensioned manner to provide prestress for the structure of the containment area 1 of the casing, thereby enhancing its working strength.

[0041] The engine component installation area 2 is an area of ​​equal thickness and has an in-plane variable stiffness characteristic. The in-plane stiffness distribution characteristics are controlled by continuous curved fiber laying, and the angles of the curved fibers in adjacent layers are mirror-antisymmetric.

[0042] The thickness of the transition area 3 of the casing structure gradually increases, and it has two characteristics: in-plane variable stiffness and out-of-plane variable stiffness. The inner layer is continuous curved fiber winding or discrete straight fiber laying, and the layers are alternately increased with discrete straight fiber laying, such as Figure 5 As shown, a smooth transition of the structural mechanical properties is ensured without increasing the complexity of the process.

[0043] Local circumferential winding is used at bolt connections and openings to reduce stress concentration and ensure the bearing capacity of the bolt holes.

[0044] The casing mounting edge region 4 has a high axial load and a thick structural wall, and has an out-of-plane variable stiffness characteristic. The axial stiffness is enhanced in the plane by discrete straight fibers, and plies are added between layers, and the angles of the straight fibers between adjacent layers are alternately arranged in an axially symmetrical manner.

[0045] In one embodiment of the present invention, it is considered that the fiber is laid at 0° along the circumferential direction and 90° along the axial direction. The typical laying scheme is shown in Table 1:

[0046] Table 1 Typical laying scheme

[0047]

[0048] Schematic diagram of curved fiber with in-plane variable stiffness Figure 6As shown in the figure, combined with the initial prestress effect provided by fiber pre-tensioning, the stiffness and strength of the composite material casing can be better optimized; the out-of-plane variable stiffness uses two or more unidirectional laminates to alternately lay layers to achieve changes along the casing thickness direction, and uses two or more materials to alternately lay layers to achieve a variable stiffness structure of the composite casing shell. The above two variable stiffness can be flexibly combined to effectively improve the performance of the composite casing structure and reduce the overall quality of the casing structure to a greater extent.

[0049] After the variable stiffness design scheme is determined, prototype production and testing are carried out. The casing prototype is produced and physical properties tests and processing performance tests are carried out. The design parameters and processes are fine-tuned and adjusted according to the experimental results.

[0050] In one embodiment of the present invention, the composite material is mainly for continuous fiber resin-based composite materials, and its in-plane laying method adopts automatic fiber placement technology (AFP), and 3D printing technology can also be used to achieve a variable stiffness laying process with spatial angle changes, and resin transfer molding technology (RTM) curing process can be used to achieve the combination of fiber and resin substrate. The specific in-plane variable stiffness scheme selection needs to first clarify the force characteristics and stiffness strength requirements of the engine casing structure to achieve the purpose of lightweight and high performance of the composite engine casing.

[0051] In the present invention, the fiber angles of different curved fiber paths are determined by the containment requirements of the casing containment area or the safety factor of the non-containment area, so that different areas exhibit different stiffness characteristics. Tension is added during the winding of the curved fibers to produce prestress in the structure, increase radial stiffness, and improve interface strength. There are both continuous curved variable angle plies and discrete straight fiber plies in the thickness gradient area, and the number of plies is increased to increase thickness. Discrete straight fibers are laid in sections in the transition area 3 and the casing installation edge area 4 of the casing structure with complex shapes and complex loads. The thickness of each section is adjusted according to the working conditions, and the thickness of each area is flexibly controlled. The amount of resin matrix in the prepreg is gradually increased / decreased to increase / decrease the thickness, thereby achieving fine control of the cross-sectional thickness. At the same time, the stiffness of the matrix participates in the adjustment of the overall stiffness of the casing, and variable stiffness is achieved in conjunction with the changes in fibers and plies. Two or more materials are used to alternately lay layers to optimize stiffness and strength, while achieving the purpose of thickness change.

[0052] The present invention improves the uniform mechanical properties of traditional composite material casings. By finely adjusting the stiffness, the performance of the casing under various working conditions can be improved to avoid excessive deformation or failure. The casing can better adapt to different operating conditions, effectively resist stress changes under different working conditions, and effectively reduce the weight of the casing, thereby improving the overall engine efficiency.

[0053] The composite multi-dimensional variable stiffness casing designed by the present invention has the following three advantages over the traditional casing: improving casing strength, reducing casing weight, and increasing casing structure reliability. Variable stiffness can be achieved by changing the angle of curved fibers and adding structural prestress, which can maximize the performance of composite materials. Compared with the constant stiffness composite material structure, the performance of the variable stiffness composite material structure can be improved by 10 to 30%.

[0054] The composite casing of the present invention can solve the problems of excessive weight, high manufacturing cost, poor corrosion resistance, etc. of the traditional metal casing. The variable stiffness composite casing of the present invention not only has better strength and stiffness than metal materials, but also has better corrosion resistance and lighter weight, which can significantly improve the maneuverability and fuel economy of the aircraft.

[0055] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the invention.

Claims

1. A composite material multi-dimensional variable stiffness casing structure, characterized in that: It comprises a containing area (1), an engine component installation area (2), a casing structure transition area (3) and a casing installation edge area (4) which are connected in sequence; The containing area (1), the engine component installation area (2), the casing structure transition area (3) and the casing installation edge area (4) all have multi-dimensional variable stiffness characteristics; The multi-dimensional variable stiffness characteristics are embodied in: variable stiffness in the plane and variable stiffness out of the plane, and in the variable thickness area, the variable stiffness in the plane and out of the plane are used simultaneously; The in-plane variable stiffness is a continuous curve fiber variable stiffness, wherein the laying angle of the composite fiber changes in the form of a continuous curve in the plane, the fiber winding direction is based on the geometric shape of the structure to achieve a gradual change in stiffness, and when the continuous curve fiber is wound, the fiber has an initial tension, providing prestress for the structure of the casing containing area (1), thereby enhancing its working strength; The out-of-plane variable stiffness is a discrete variable stiffness. Two or more materials are alternately laid to achieve stiffness changes along the thickness direction. The interlayer fiber laying angles are alternately changed. The number of layers, layer thickness and fiber density can be adjusted. The thickness gradient region with in-plane and out-of-plane variable stiffness is characterized by alternating continuous curve angles and discrete straight fiber layers. In addition, the prepreg volume content can be increased or decreased to increase or decrease the thickness. The engine component installation area (2) is a region of equal thickness and has an in-plane variable stiffness characteristic. The in-plane stiffness distribution characteristics are controlled by laying continuous curved fiber layers, and the angles of the curved fibers in adjacent layers are mirror-imaged and anti-symmetric. The thickness of the transition area (3) of the casing structure gradually increases, and it has both in-plane variable stiffness and out-of-plane variable stiffness. The layers are continuous curved fiber winding or discrete straight fiber laying, and discrete straight fiber laying is alternately added between the layers, so as to ensure a smooth transition of the mechanical characteristics of the structure without increasing the complexity of the process. The casing mounting edge region (4) has a high axial load and a large structural wall thickness, has an out-of-plane variable stiffness characteristic, and the axial stiffness is enhanced in the plane by discrete straight fibers, with additional plies between layers and the angles of the straight fibers between adjacent layers being arranged alternately and axially symmetrically.

2. The composite material multi-dimensional variable stiffness casing structure according to claim 1, characterized in that: The containing area (1) is thick in the middle and thin on both sides, and has the characteristics of variable stiffness in-plane and out-of-plane. With the thickest part as the center, the fiber winding angle gradually changes towards the thinning areas on both sides, and the layer thickness gradually decreases.

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