Patent Application
20050084379
This application claims priority to German Patent Application DE10326719.0 filed Jun. 6, 2004, the entirety of which is incorporated by reference herein.
This invention relates to a compressor blade root for engine blades of aircraft engines which comprise a fiber-composite core with metallic enclosure and which is held in a recess of a compressor disk.
In order to save weight, the fan blades (compressor blades) of gas turbine engines are, as is generally known, made of fiber-reinforced plastic with a metallic enclosure. The blade is firmly attached via a dovetail-style, longitudinally curved blade root in a conformal recess of the compressor disk (rotor). Centrifugal forces, gas pressure and vibrations of the airfoil excited by the flow medium subject the compressor blades of turbomachines to considerable stresses which, in the case of aircraft engines, can become excessive in the event of a bird strike, i.e. an impingement of a bird onto the rotor wheel, leading to the destruction of the respective blade and to serious consequential damage.
Patent Specification EP 0 353 672 B1, for example, describes a blade made of fiber-reinforced material with a blade core and a blade shaft which extends radially to the rotor and is firmly attached to the rotor. An essentially radial fiber strand extends through the blade shaft and the blade core and is covered by an outer skin which, at the transition to the rotor, is designed as a flange which is fixed to the rotor.
In the case of a fiber-material compressor blade known from Specification U.S. Pat. No. 4,040,770, reinforcing wedges made of a homogenous material, for example titanium, are arranged in the area of the dovetail-style blade root between the fiber layers in order to provide a load-carrying structure in this highly loaded area. On the outside of the blade root, a bearing made of the same homogenous material is provided to protect the fiber layers and to obtain a uniform transfer of forces between the blade root and the compressor disk. The dovetail-style blade root features longitudinal, plane faces at its sides and is, thus, firmly fixed in the conformal recess of the compressor disk, enabling the latter to fully take up the loads acting upon the blade. Between the fiber material and the inserts, or bearings, made of homogenous material, a transition layer is provided whose modulus of elasticity is greater than that of the fiber material and smaller than that of the material of the inserted wedges or bearings. The purpose of this transition layer material is to avoid thermal stresses at the interface between the fiber material and the homogenous reinforcing or bearing material, to improve the load-carrying capacity of the blades and to prolong their service life.
The specific problem with known compressor blades, in particular those featuring a carbon-fiber reinforced plastic core, is the inability of this composite material, or the respective compressor blade, to take up and transfer the high forces occurring under extreme loads. Firstly, fatigue stability and dynamic strength of the fiber-composite core are inadequate, with the high tensile forces encountered by the blade not being properly transferred to the blade root, i.e. from the composite material to the metallic portion of the blade root and from there to the compressor disk. Secondly, the fiber-composite material is not capable of taking up the high bending loads resulting from a bird strike. Finally, high clamping forces and local surface pressures occur at the attachment of the blade root to the compressor disk which result in both fatigue of the fiber-composite material and high fretting wear between the blade root and its location in the compressor disk.
It is a broad aspect of the present invention to provide an engine blade whose compressor blade root features a fiber-composite core and a metallic enclosure such that the blade is capable of taking up and transferring high forces while having a long service life.
It is a particular object of the present invention to provide solution to the above problems by a compressor blade root designed in accordance with the features described herein. Further features and advantageous embodiments of the present invention will become apparent from the description below.
In other words, the concept underlying the present invention with respect to a compressor blade root of the type mentioned above is to have the pressure loads present at the blade root directly act upon the fibers in that the fibers are compressed and the matrix material is infiltrated into the minute cavities subsequently to compression and to introduce the forces transferred by the fiber-composite core to the blade root via an as intimate as possible contact between the fiber-composite core and the enclosure, this intimate contact being produced by a micro-structure applied to the inner surfaces of the enclosure. Since this design of a fiber-composite core is not capable of withstanding high bending loads, it is pendularly located within a limited angular range and frictionally dampened in the recess for the location of the blade root in the compressor disk.
This fiber-composite core enables, on the one hand, high forces to be taken up and transferred to the enclosure in the area of the blade root, i.e. introduced in the metallic part of the blade root. On the other hand, the bending load of the fiber material is reduced by the frictionally dampened pendular movement of the blade root allowed within a limited range in the recess of the compressor disk.
A compressor blade featuring such a compressor blade root is very light, which is favorable for the operation of the gas turbine engine. Such a compressor blade is nevertheless capable of withstanding and transferring, without damage, the high forces to which it is exposed. It has high dynamic strength and fatigue stability, as well as a long service life. Stress and wear in the recess locating the blade root are reduced.
According to the present invention, the bending stresses acting upon the compressor blade are compensated by a frictionally dampened pendular movement of the compressor blade with respect to the compressor disk, which is enabled by the circularly arched side flanks of the longitudinally straight blade root sliding on correspondingly circularly arched bearing areas of the recess in the compressor disk against a frictional resistance.
The present invention is more fully described in light of the accompanying drawing showing an embodiment, with the only figure illustrating, in sectional side view, a bottom part of a compressor blade comprising a fiber-composite core and a metallic enclosure, with the root of the compressor blade conformally mating a recess provided on the periphery of a compressor disk.
The compressor blade 1 comprises an airfoil 2 and a blade root 3 and includes a fiber-composite core 4 and a metallic enclosure 5 with a thin-walled portion 5a in the area of the airfoil 2 and with a thick-walled portion 5b in the area of the blade root 3. In the blade root 3, a reinforcing wedge 6 divides the fiber-composite core 4 into two partial strands 4a, 4b to provide for high strength in the root area and to enable the high tensile forces acting upon the airfoil 2 to be effectively introduced into the blade root 3. Upon infiltration, a metal plate 12 is attached (for instance, by welding or other means) at the bottom end of the blade, preferably to the reinforcing wedge, to take up the clamping forces produced by the centrifugal loads and, thus, to reduce the mechanical pressure load on the carbon fibers.
Preferably, a large end of the wedge 6 is positioned below a fit of the blade root 3 to the compressor disk 10 to avoid delamination forces under centrifugal load.
The metallic enclosure 5 and the reinforcing wedge 6 are here made of titanium, while a composite of carbon fibers embedded in plastic is used for the fiber-composite core 4. The fiber-composite core 4 is, however, manufactured such that a fiber strand compressed in transverse direction to the compressor blade 1 is initially produced under high pressure and that a plastic is infiltrated into the remaining cavities of the strand subsequently to the high compression of the fiber material. The high packing density of the fiber structure within the plastic matrix with a relatively low plastic share enables the compressor blade 1, i.e. the fiber material, to take up high tensile forces, with high dynamic strength and fatigue stability being ensured since the compressive stresses have to be transmitted only partially via the plastic matrix.
For the generation of a large specific surface for the purpose of an intimate contact and transfer of forces between the fiber-composite core 4 and the metallic enclosure 5, the inner surfaces of the metallic enclosure 5 are micro-structured at least in the area of the blade root 3 by means of a mechanical treatment such as glass-bead peening or a sand blasting process, or by means of a welded-on fine wire mesh 7, or by other processes/mechanisms, either mechanical, chemical or electrical. Also, the outer surfaces of the reinforcing wedge 6 mating with the fiber structure can be micro-structured by means of such a wire mesh 7, or by means described above or in a different manner.
As becomes apparent from the drawing, the blade root 3 is located via circularly arched bearing faces 8 in a recess 9 of a compressor disk 10 whose two sideward bearing areas 11 are conformally rounded. The radii R1 of the laterally opposite rounded bearing faces 8 are identical, but do not have a common center, i.e. the centers M1, M2 of the circularly arched bearing faces 8 are remote from each other to radially center the blade under centrifugal load. For the functioning of the blade root 3 in the above-described form, it is crucial that the blade root 3 is straight. This shape allows the compressor blade 1 to perform a pendular movement in the recess 9 of the compressor disk 10 which, however, is limited by the different centers M1 and M2, with these remote centers M1, M2 also having the centering effect described above. If the airfoil 2 is subject to a shock, for example in the event of a bird strike, the shock effect is absorbed by the pendular movement of the airfoil 2 within the limited range available and by the friction on a large surface between the bearing faces 8 of the blade root 3 and the bearing areas 11 in the recess 9. Thus, the fiber-composite material, which does not endure bending loads, is relieved to a considerable extent. To increase the friction between the bearing faces of the blade root and the bearing areas 11 of the recess 9, the surfaces of one or both of the bearing faces 8 and the bearing areas 11 can be micro-structured in one of the manners discussed above, or in another manner.
The combination of the above features, i.e. the transversely compressed fiber material with low matrix share, the arrangement of the reinforcing wedge, the surface enlargement at the mating faces between the fiber-composite material, the blade root and the reinforcing wedge and the longitudinally straight blade root with opposite, arched bearing and friction faces, provides a low-weight compressor blade which is capable of effectively transmitting forces and, despite the high loads applied, has a long service life.
List of Reference Numerals
| Number | Date | Country | Kind |
|---|---|---|---|
| DE 103 26 719.0 | Jun 2003 | DE | national |
