JPH04232400A - Composite air wheel having improved shearing capacity - Google Patents

Abstract

PURPOSE: To provide an airfoil blade which comprises layers of non-metal composite laminates buried in resin base material and has great tolerance to impact damage caused by foreign matters and a method to manufacture such airfoil blade for fluid flow machines. CONSTITUTION: A blade comprises a plurality of layers of composite laminates sandwiching at least one layer of a less than rigid bonding agent. The elastic bonding agent allows the relative movement between adjacent layers allowing the loading of the laminate to its full potential strain. In one form, the elastic agent is selectively positioned between layers of laminates at different predetermined locations of the blade. The blade 10 includes an air foil section 12 including a tip 14 and a root section 16, and the air foil section has a front surface 22 and a successive surface 20. A part of the composite laminate layer extends to the whole of the air foil and the rest of the composite laminate layer extends to the root section.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD This invention relates to blades for fluid flow machines, and more particularly to blades comprising a non-metallic composite laminate embedded in a resin matrix and having increased ability to withstand foreign object impact.

0002

BACKGROUND OF THE INVENTION Propellers and gas turbine engine fan blades made of composite materials such as graphite and glass fibers are expected to replace metal blades. These composite materials have excellent strength properties and are significantly lighter than their metal counterparts. However, one area in which composite blades are not as satisfactory as metal blades is their resistance to foreign object impact. Composite blades are prone to delamination when subjected to impact, primarily at the laminate-to-resin interface.

[0003] To manufacture composite braids, typically multiple substantially parallel filament laminates are bonded together. Standard methods applicable to blades include the use of high strength fibers and reinforced resins. These methods increase the blade's resistance to foreign object damage, but do not increase the blade's ability to resist delamination. Each laminate consists of a single layer of generally longitudinal fiber elements. These laminates are bonded together with a resin matrix. If the structure is loaded perpendicular to the laminate direction, the load should be transferred through the thickness of the structure by shear forces through the resin system. Resins are more susceptible to shear than fibers and therefore become weak links in the structure when subjected to transverse loads. Additionally, resins are inherently brittle and do not stretch (yield) and break. Impact loads caused by birds, ice, and other foreign objects impose extremely high transverse loads on the blade fiber layers, resulting in blade failure. The construction and processing of the blade also creates areas that experience delamination under impact loads. These areas are usually between laminates, between laminates and fibers, formers,
It is found where the strength or shearing capacity varies greatly, such as between spars. Figure 1 shows a typical transition area. That is, where the two overlying unidirectional high-strength laminate layers 8, 9 transition to the fabric 7, an interface with a large load transition is created.

[0004] As a solution to impact loads, it has been proposed to make the blades from a base material with higher impact strength (tougher). Although these materials have a very high threshold for the onset of delamination, they do not prevent delamination from proceeding. These materials themselves are hard and difficult to process due to the reinforcing additives.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus that eliminates the drawback of delamination occurring when a composite blade is subjected to impact.

Another object of the invention is to provide fan (prop) blades with the ability to withstand high impact energies of foreign objects (increasing the delamination threshold, ie, toughness), and to provide fan (prop) blades with the ability to withstand high impact energies of foreign objects (increasing the delamination threshold, ie, toughness), and to The objective is to ensure the integrity of the blade (to prevent delamination from progressing).

Broadly speaking, the present invention accomplishes the above objects and is a composite air foil blade comprising a plurality of composite laminate layers interleaved with alternating layers of elastic bonding material in preselected areas. In one embodiment, the alternating regions of the blade layers are sewn together with high strength elastic thread to interconnect the layers prior to forming the blade. In another form, the laminate is braided into a three-dimensional matrix and the resin is injected into the matrix by resin transfer molding. Braiding the laminate increases the load carrying capacity with the base fiber elements. Some fiber laminates have significantly different properties compared to adjacent laminates, and in these cross-sections, a relatively pliable adhesive layer is placed between the laminates,
Transfer and distribute loads.

[0008] In order to better understand the present invention, a specific configuration of the present invention will be explained below with reference to the drawings.

[0009]

[Specific Structure] One form of a fan blade to which the present invention can be applied is shown at 10 in FIG. We refer to "fan blades" here, but this is not the same as the term "fan" or "propeller".
are synonymous and interchangeable terms. Additionally, although described with application to propeller or fan blades, the invention has application to other types of air foil blades, e.g.
It can be applied to both ducted and ductless fan blades in gas turbine engines, as well as compressor blades. Blade 10 has an airfoil portion 12 including a tip 14 and a root portion 16. Airfoil portion 12 has a leading surface 22 and a trailing surface 20. The blade 10 is comprised of a plurality of composite laminate layers with continuous fibers embedded in a matrix material laminated at an angle. In a specific embodiment, the continuous fibers of the composite laminate extend throughout the airfoil, some on the leading surface 22.
to the trailing surface 20, and a portion extends radially from the root portion 16 to the tip portion 14, thus forming a swept-air propeller fan blade shape. edge 22,
The surfaces 20, 14, and 16 define are an airfoil pressure side surface 18 and an airfoil suction side surface 24. In some embodiments, surfaces 18 and 24 form a composite shell that includes a foam/metal blade spar 26 to form the blade or to provide a structural attachment to the blade hub. Insert and bond to inner laminate.

Typically, the fibers in composite laminates are unidirectional, parallel to each other, semi-ductile, low strength,
Consolidated with low modulus matrix material. The base material is
The effects of cutting one fiber are transferred and localized by redistributing the load near the cut fiber to the adjacent fibers. The elastic modulus of fiber is approximately 10x10 in the case of glass.
6 psi, about 44x for modern graphite
106 psi. Typical fibers are graphite,
Made of boron or S-glass. Elastic modulus approximately 44x10
6 psi graphite fibers are preferred. Higher modulus, and therefore stronger, fibers have greater compatibility with geometries such as high recession and low edge thickness. The matrix material is typically a thermoset resin, but can also be thermoplastic.

When laminating the laminate, the fibers of each layer are arranged in an alternating pattern, for example at -45° to the reference axis.
, 0°, +45°, 0°. Two successive layers may be laminated at the same angle. This form of lamination results in an aeroelastically stable blade with well-tuned vibrational modes. FIG. 1 shows two adjacent layers 8, 9 forming an alternating pattern. The fibers may be braided three-dimensionally so that some of the fibers enter the intermediate layer of the composite to increase delamination resistance.

Composite blades may be formed as solid composite blades or may include foamed, hollow, or other inserts to reduce weight, metal inserts to increase strength, or blade hub coupling media. It's okay. One example configuration is disclosed in commonly assigned US patent application Ser. No. 13DV-9601. The fabric 7 of FIG. 1 can be a foam insert, spar or transition layer to the outer surface of the blade.

Turning to FIG. 3, this replaces the blade of FIG.
- It is a sectional view cut in the 3-line direction. The blade 10 is
It can be seen that it consists of a plurality of laminates 30. These laminates may be laminate layers as shown at 8 and 9 in FIG. The laminates 30 are bonded together with an epoxy matrix 32. In the blade of this invention, the laminate 30 is bonded in selected areas with a non-rigid adhesive material. Preferably, the adhesive material is somewhat elastic. Suitable bonding materials are thermoplastic or thermosetting bonding agents, such as polyurethanes, which have rubber-like properties, ie materials that do not break when deformed. FIG. 4 is an enlarged view of the circled area 28 of FIG. 3 to better illustrate the intermediate adhesive layer 32 of elastic material between the laminates 30. FIG. Layer 32 is no thicker than laminate 30. The thickness of the laminate is typically about 10 mils, but can vary from 5 to 20 mils. The resilient material of layer 32 is selectively placed between the laminates 30 during the blade layup process. These selected positions can be determined by destructive testing of the airfoil, for example by impacting the blade with an object, or by analytical methods. Although the use of a resilient layer 32 increases the ability of the fan blade to withstand higher impact loads without delamination, it does not prevent delamination from developing once it begins.

[0014] It has been found that sewing the laminate layers together is an effective way to prevent the development of delamination. Figure 5 shows the same blade as Figure 2, with the suture indicated by dashed line 3
Indicated by 4. Before final joining or shaping of the blade,
The laminate layers may be sewn together at selected locations using high strength synthetic threads. Although suturing alone does not increase the ability of the blade to prevent the initiation of (local) delamination, it does increase the blade's ability to prevent the development of delamination due to external stimuli such as blade vibration. Sutures allow for shocks greater than those that cause delamination to begin,
Absorption capacity is also greatly increased without further delamination.

[0015] Sutures must be used carefully on fan or prop blades. From a maintenance standpoint, it must be able to withstand average impacts (small to medium-sized birds between 4 ounces and 2.5 pounds) with no damage or only damage that does not lead to secondary failure over time. Must be. For large impacts such as 4-8 pounds, safety is extremely important. In the case of open rotor systems, large impacts must not cause the entire part to dislodge. This is because detachment of parts may cause other damage. Therefore, delamination of the blade is desirable in such situations. When a large impact is applied, the delamination of the structure absorbs energy rather than tearing the blade, which can lead to the detachment of large blade fragments. The sutures are effective in preventing delamination from routine events that can damage the leading edge 22, trailing edge 24 and tip region 14 of the blade. Stitching is undesirable in the main airfoil body of the blade so that the delamination described above occurs in situations where impact loads must be absorbed to prevent detachment of the entire blade or blade assembly.

FIG. 6 is a cross-sectional view taken along line 6--6 of FIG. 5, illustrating the placement of suture or thread 34 through the blade. FIG. 7 is a sectional view taken along the line 7-7 in FIG. 5, again showing the state of suture formation in the blade 10. Figure 8 shows
7 is an enlarged view of the circled area 36 of FIG.
0, showing semi-ductile matrix layer 32 and sutures 34. For blades 10 that use suturing to prevent propagation of delamination, injection or compression molding can be used to bond the blades together after suturing.

Although compression molding or autoclaving and injection molding or resin transfer molding can be used to carry out the above-described method, resin transfer molding is preferred as a method of joining the blades using a stitching method.

Although the principle of the present invention has been explained using a specific example, in carrying out the invention, the principles shown in the above description should be used in order to develop other suitable embodiments suitable for specific operating conditions. It will be apparent to those skilled in the art that various changes in structure, arrangement and components may be made.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a pair of composite overlay layers placed in an alternating pattern and an intermediate fabric fibrous layer transitioning from the composite layer to the blade insert.

FIG. 2 is a plan view of an example of an air foil blade to which the present invention can be applied.

FIG. 3 shows the structure of the blade according to the present invention.
- It is a 3-line sectional view.

FIG. 4 is an enlarged view of area 28 of FIG. 3;

5 is a plan view of another embodiment of the blade of FIG. 2 demonstrating seams that help prevent delamination of the blade layers; FIG.

FIG. 6 is a sectional view taken along line 6-6 in FIG. 5;

FIG. 7 is a sectional view taken along line 7-7 in FIG. 5;

8 is an enlarged view of area 36 of FIG. 7. FIG.

[Explanation of symbols]

7 Cloth 8, 9 Laminate layer 10 Blade 12 Air foil part 14 Tip part 16 Root part 18 Pressure side surface 20 Successive surface 22 Preceding surface 24 Suction side surface 30 Laminate layer 32 Elastic material layer 34 Suture

Claims (11)

[Claims] 1. An air foil blade comprising a plurality of overlay layers of non-metallic composite materials, wherein at least one layer of non-rigid material is disposed between adjacent composite laminate layers in preselected areas of the blade, such that the blade Air foil blade with alternating layers of composite laminate and non-rigid material in preselected areas. 2. The air foil blade of claim 1, wherein a plurality of layers of non-rigid bonding material are selectively disposed between the composite laminate layers. 3. The air foil blade of claim 1, wherein said composite material is selected from the group consisting of graphite composites, glass composites, and boron composites. 4. The air foil blade of claim 1, wherein said elastic material is a thermoplastic or thermoset binder. 5. The air foil braid of claim 1, wherein said braid is sewn with a plurality of rows of flexible threads interconnecting said plurality of layers. 6. The air foil blade of claim 4, wherein said thread is comprised of aromatic polyamide. 7. The air foil blade according to claim 1, wherein the composite material layer has a structure in which fibers are three-dimensionally knitted, and some of the fibers are included in the intermediate layer. 8. The air foil blade of claim 1, wherein said elastic layer comprises a resin material deposited on said layer of composite material before placing said layer of composite material on a former. 9. Each layer of the composite material has a thickness of about 5 to
The air foil blade of claim 1 which is 20 mil. 10. The air foil blade of claim 8, wherein the thickness of the elastic layer is less than or equal to the thickness of the composite material layer. 11. A plurality of layers of non-metallic composite material and at least one layer of elastic bonding material are alternated in preselected areas, and the layers of composite material and the layer of elastic material are sewn together to form a preformed blade. A method for manufacturing an air foil blade, including the step of: