A laminate for a transition section with high fatigue strength in a bifurcated area and its usage method

Abstract

The present invention belongs to the technical field of composite material design for helicopter rotors, and discloses a ply for a transition section with high fatigue strength in a bifurcated area, which includes V-shaped glass cloth and Y-shaped glass cloth. Both the V-shaped glass cloth and the Y-shaped glass cloth are ±45° epoxy resin glass fiber fabric prepregs. Among them, the acute-angle end of the V-shaped glass cloth wraps around the tip of the filling block of the helicopter blade, and the acute-angle end of the Y-shaped glass cloth is wrapped outside the sharp angle of the V-shaped glass cloth, and the other end of the Y-shaped glass cloth extends into the bifurcated groove of the beam band of the helicopter blade. The ply for the transition section with high fatigue strength in the bifurcated area provided by the present invention can greatly enhance the fatigue strength while ensuring the same structural stiffness, effectively improving the service life of the blade root. Compared with the traditional ply, this kind of ply has better processability, and the glass fibers of the beam are not prone to wrinkles during the molding process. This solution has strong operability and extremely low additional cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of helicopter rotor composite material design, and relates to the design technology of a high fatigue strength transition section in the bifurcation area of helicopter rotor blades. Specifically, it relates to a ply arrangement for a high fatigue strength transition section in the bifurcation area and its usage method. Background Art

[0002] In a helicopter rotor system, the blade root or the root of the flexible beam mainly consists of a metal bushing, a filling block, and a beam strap. The form in which the beam strap bifurcates at the tip of the filling block and extends to wrap around the filling block can effectively maintain the shape of the root and efficiently transmit loads. The loads applied to the blade or the flexible beam can be divided into flapping, lead-lag, and torsion. Among them, the flapping load causes the tip of the filling block to squeeze towards the beam at the bifurcation, generating a stress perpendicular to the fiber direction. Since most of the current blade beams are made of unidirectional tape materials, they have a strong load-bearing capacity in the fiber direction but a weak load-bearing capacity perpendicular to the fiber direction. Therefore, cracks will continuously expand at the beam bifurcation, resulting in fatigue failure.

[0003] Currently, for the main rotor flexible beam of a certain type of helicopter, cracks often first appear in the bifurcation area during the flapping fatigue test, leading to the end of the test. During use, cracks often appear in the bifurcation area of the tension-torsion bar within the service life. By statistically analyzing the fatigue failure characteristics of the blades, more than half of the failure problems occur in the beam bifurcation area at the blade root. Therefore, solving the stress concentration problem at this location will effectively extend the service life of the rotor system.

[0004] Existing design techniques often aim to reduce the extrusion stress by increasing the cross-sectional area at the tip of the filling block. However, as the cross-sectional area increases, the transition here will become more severe, the bifurcation angle of the beam will be larger, and the load transmission will become more difficult, and the fatigue performance will also decline accordingly. Therefore, this method is not ideal. Some university research groups in China are studying a three-dimensional braiding method to braid fibers perpendicular to the beam fiber direction in the bifurcation area to enhance the strength in this direction. However, this method is still in the exploratory stage, there are no successful cases yet, and the cost is huge, making mass production impossible. In the current and the next few years, three-dimensional braiding cannot be applied to the development of domestic rotor composite materials. Summary of the Invention

[0005] To solve the above problems, based on the structural characteristics of rotor composite materials, the present invention proposes a ply arrangement for a high fatigue strength transition section in the bifurcation area and its usage method. This ply structure consists of two layers of epoxy resin glass cloth prepregs, which effectively converts the stress perpendicular to the beam fiber direction into the stress in the beam fiber direction, improving the fatigue performance of the bifurcation area.

[0006] The technical solution of the present invention:

[0007] A laminate for a transition section with high fatigue strength in a forked area, comprising a V-shaped fiberglass cloth and a Y-shaped fiberglass cloth. Both the V-shaped fiberglass cloth and the Y-shaped fiberglass cloth are ±45° epoxy resin fiberglass fabric prepregs. Among them, the sharp end of the V-shaped fiberglass cloth wraps around the tip of the filling block of the helicopter blade, and the sharp end of the Y-shaped fiberglass cloth is wrapped outside the sharp corner of the V-shaped fiberglass cloth. The other end of the Y-shaped fiberglass cloth extends into the forked groove of the beam band of the helicopter blade.

[0008] Further, the width of the tip of the filling block is 0.3 mm to 0.4 mm, and the angle does not exceed 20°.

[0009] Further, the V-shaped fiberglass cloth is a continuous and uncut fiberglass fabric.

[0010] Further, the Y-shaped fiberglass cloth is formed by bonding two fiberglass cloths.

[0011] Further, the bonding part between the tip of the forked section of the Y-shaped fiberglass cloth and the V-shaped fiberglass cloth has two chamfers that are convex on the top and concave on the bottom.

[0012] Further, the filling block, the V-shaped fiberglass cloth, and the tip of the Y-shaped fiberglass cloth facing the beam band all have chamfers.

[0013] A method for using a laminate for a transition section with high fatigue strength in a forked area, comprising the following steps:

[0014] Step 1, prefabricate a cured filling block of the helicopter blade;

[0015] Step 2, lay the V-shaped fiberglass cloth at the sharp corner of the filling block of the helicopter blade, and then lay the Y-shaped fiberglass cloth;

[0016] Step 3, bond the beam band outside the sharp corner of the filling block of the helicopter blade wrapped with the V-shaped fiberglass cloth and the Y-shaped fiberglass cloth;

[0017] Step 4, integrally form by compression molding and heat curing.

[0018] Further, the beam band in Step 3 is an epoxy resin fiberglass prepreg tape.

[0019] Advantages of the present invention:

[0020] 1. The laminate for the transition section with high fatigue strength in the forked area provided by the present invention can greatly enhance the fatigue strength while ensuring the same structural stiffness, effectively improving the service life of the blade root.

[0021] 2. Compared with the traditional laminate, this laminate has better processability, and the fiberglass of the beam is not prone to wrinkles during the compression molding process.

[0022] 3. This solution has strong operability and extremely low additional costs. Description of the Drawings

[0023] Figure 1 Schematic diagram of the ply layout of the transition section with high fatigue strength in the forked area;

[0024] Among them, 1—V-shaped fiberglass cloth, 2—Y-shaped fiberglass cloth, 3—filling block, 4—beam belt. Specific implementation mode

[0025] This part is an embodiment of the present invention, which is used to explain and illustrate the technical solution of the present invention. Without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0026] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicating directions or position relationships are the azimuth or position relationships given by the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or case must have a specific azimuth, be constructed and operated in a specific azimuth, and therefore cannot be understood as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include more than one such feature. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0027] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installation", "connection", and "connection" should be interpreted in a broad sense. For example, it can be a fixed connection, a detachable connection or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0028] A ply for the transition section with high fatigue strength in the forked area includes a V-shaped fiberglass cloth 1 and a Y-shaped fiberglass cloth 2. Both the V-shaped fiberglass cloth 1 and the Y-shaped fiberglass cloth 2 are ±45° epoxy resin fiberglass fabric prepregs. Among them, the acute end of the V-shaped fiberglass cloth 1 wraps the tip of the filling block 3 of the helicopter blade, the acute end of the Y-shaped fiberglass cloth 2 is wrapped outside the sharp angle of the V-shaped fiberglass cloth 1, and the other end of the Y-shaped fiberglass cloth 2 extends into the forked groove of the beam belt 4 of the helicopter blade.

[0029] The width of the tip of the filling block 3 is 0.3 mm to 0.4 mm, and the angle does not exceed 20°.

[0030] The V-shaped glass cloth 1 is a continuous and uncut fiberglass fabric.

[0031] The Y-shaped glass cloth 2 is formed by bonding two glass cloths.

[0032] The bonding area between the tip of the bifurcated section of the Y-shaped glass cloth 2 and the V-shaped glass cloth 1 has two chamfers with a convex upper part and a concave lower part.

[0033] The filling block 3, the V-shaped glass cloth 1, and the Y-shaped glass cloth 2 all have chamfers at the tips facing the girder strip 4.

[0034] A method of using a laminate for a transition section with high fatigue strength in a bifurcated area includes the following steps:

[0035] Step 1, prefabricate a cured helicopter blade filling block;

[0036] Step 2, lay the V-shaped glass cloth at the sharp corner of the helicopter blade filling block, and then lay the Y-shaped glass cloth;

[0037] Step 3, bond the girder strip outside the sharp corner of the helicopter blade filling block wrapped with the V-shaped glass cloth and the Y-shaped glass cloth;

[0038] Step 4, integrally form by molding and hot curing.

[0039] The girder strip in Step 3 is an epoxy fiberglass prepreg tape.

[0040] The structure of the laminate for the transition section with high fatigue strength in the bifurcated area consists of two glass cloths, the filling block 3, and the girder strip 4. The shapes of the two glass cloth prepregs are V-shaped and Y-shaped respectively, which successively wrap the tip of the filling block 3. The girder strips 4 on both sides are bonded to the glass cloth and the filling block 3, and the whole is formed by molding and hot curing. The structural layout is as shown in the appendix Figure 1 shown. The two glass cloths are ±45° epoxy fiberglass fabric prepregs, the filling block 3 is an epoxy chopped fiber pre-cured part, the girder strip 4 is an epoxy fiberglass prepreg tape, and the whole is formed by molding and hot curing.

[0041] The tip width of the filling block of the transition section laminate is very small, ranging from 0.3 mm to 0.4 mm, and the angle does not exceed 20°.

[0042] The V-shaped glass cloth is a continuous cloth and shall not be cut.

[0043] The Y-shaped glass cloth is formed by bonding two glass cloths.

[0044] The bonding area between the tip of the bifurcated section of the Y-shaped glass cloth and the V-shaped cloth needs to be chamfered twice; without chamfering, the girder fibers will wrinkle at the sharp corner due to uneven transition. After one chamfer, the girder fibers may still wrinkle at the subsequent sharp corner, but after two chamfers, that is, first chamfering downwards and then upwards, the girder fibers will no longer wrinkle.

[0045] The main beam belt bifurcates at the tip of the Y-shaped glass cloth.

[0046] For example, chamfers are required at the filling blocks, the V-shaped cloth, and the tip of the Y-shaped cloth, which is also to prevent the main beam fibers from wrinkling due to uneven transition at the sharp corners and to prevent stress concentration.

[0047] As described above, only the specific embodiments of the present invention are described in detail, and the unelaborated parts are conventional techniques. However, the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. The protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A laminate for a transition section with high fatigue strength in a bifurcated area, characterized in that, it includes a V-shaped fiberglass cloth (1) and a Y-shaped fiberglass cloth (2), and both the V-shaped fiberglass cloth (1) and the Y-shaped fiberglass cloth (2) are ±45° epoxy resin fiberglass fabric prepregs; wherein, the acute-angle end of the V-shaped fiberglass cloth (1) wraps the tip of the filling block (3) of the helicopter blade, and the acute-angle end of the Y-shaped fiberglass cloth (2) is wrapped outside the sharp angle of the V-shaped fiberglass cloth (1), and the other end of the Y-shaped fiberglass cloth (2) extends into the bifurcated groove of the beam band (4) of the helicopter blade.

2. The laminate for a transition section with high fatigue strength in a bifurcated area according to claim 1, characterized in that, the width of the tip of the filling block (3) is 0.3 mm to 0.4 mm, and the angle does not exceed 20°.

3. The laminate for a transition section with high fatigue strength in a bifurcated area according to claim 1, characterized in that, the V-shaped fiberglass cloth (1) is a continuous and uncut fiberglass fabric.

4. The laminate for a transition section with high fatigue strength in a bifurcated area according to claim 1, characterized in that, the Y-shaped fiberglass cloth (2) is formed by bonding two fiberglass cloths.

5. The laminate for a transition section with high fatigue strength in a bifurcated area according to claim 1, characterized in that, the bonding part between the tip of the bifurcated section of the Y-shaped fiberglass cloth (2) and the V-shaped fiberglass cloth (1) has two chamfers that are convex on the upper side and concave on the lower side.

6. The laminate for a transition section with high fatigue strength in a bifurcated area according to claim 1, characterized in that, the tips of the filling block (3), the V-shaped fiberglass cloth (1) and the Y-shaped fiberglass cloth (2) facing the beam band (4) all have chamfers.

7. A method for using a laminate for a transition section with high fatigue strength in a bifurcated area, using any one of the laminates for a transition section with high fatigue strength in a bifurcated area according to claims 1-6, including the following steps: Step 1, prefabricate a cured filling block of the helicopter blade; Step 2, lay the V-shaped fiberglass cloth at the sharp angle of the filling block of the helicopter blade, and then lay the Y-shaped fiberglass cloth; Step 3, bond the beam band outside the sharp angle of the filling block of the helicopter blade wrapped with the V-shaped fiberglass cloth and the Y-shaped fiberglass cloth; Step 4, integrally form by molding and hot curing.

8. The method for using a laminate for a transition section with high fatigue strength in a bifurcated area according to claim 7, characterized in that, the beam band in step 3 is an epoxy resin fiberglass prepreg tape.

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