Impact resistant blade

#This invention relates to composite blades for use in fluid flow machines and, more particularly, to increasing their tolerance to foreign object impact.

#For many years attempts have been made to replace the relatively heavy, homogeneous metal blades and vanes of fluid flow machines such as gas turbine engine compressors with lighter composite materials. The primary effort in this direction has been toward the use of high strength, elongated filaments composited in a lightweight matrix. Early work involved glass fibers, and more recent efforts have been directed toward the utilization of boron, graphite and other synthetic filaments. These later materials have extremely high strength characteristics as well as high moduli of elasticity which contributes to the necessary stiffness of the compressor blades and vanes.

#Many problems have confronted the efforts to utilize these filaments, particularly in adapting their unidirectional strength characteristics to a multidirectional stress field. To a large extent, these problems have been overcome and composite blades have been demonstrated with performance characteristics, in many areas, equal to or better than their homogeneous metal counterparts in addition to providing the expected and significant weight reductions.

#While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as part of the present invention, it is believed that the invention will be more fully understood from the following description of the preferred embodiment which is given by way of example with the accompanying drawings, in which:

#FIG. 1 is a perspective view of a composite gas turbine engine compressor blade embodying the present invention;

#FIG. 2 is a cross-sectional view of a single composite laminate;

#Referring to the drawings wherein like numerals correspond to like elements throughout, attention is first directed to FIG. 1 wherein a composite blade 10 for use in a fluid flow machine and constructed according to the present invention is illustrated. While not so limiting, the blade 10 is adapted for use in axial flow gas turbine engine compressors and fans. It will become apparent to those skilled in the art that the present invention offers an improvement for many bladed structures and that rotor blade 10 is merely meant to be illustrative of one such application. Accordingly, rotor blade 10 is shown to comprise an airfoil portion 12, generally of radially variant camber and stagger, and a dovetail tang 14 which enables the blade to be mounted on and retained by a rotatable disc or hub in a conventional manner. A typical flow path defining platform, not shown, could be mounted between the airfoil 12 and the dovetail 14 portions of the blade.

#The major portion, or primary structure, of the blade comprises laminates of elongated, continuous filaments having high strength and high modulus of elasticity embedded in a lightweight matrix. The filament laminates are laid and bonded together in essentially parallel relationship to each other to form the airfoil portion 12 of blade 10. In the preferred embodiment involving predominantly metallic material, the blade would comprise bonded boron filament laminates in an aluminum matrix. It is anticipated, however, that the structure could comprise any nonmetallic system, including graphite filaments and an epoxy resin. Further, it is understood that the present invention anticipates the use of any fiber embedded in any binder, such as an organic resin, for its structure.

#Focusing now upon a single filament composite ply or laminate, attention is directed to the cross-sectional view of FIG. 2. Therein, a single layer of collimated, elongated boron filaments 16 is sandwiched between two layers of aluminum foil 18a, 18b of preferred metals/alloys to be discussed later. These constituents have been diffusion bonded in the known manner to form the unitized ply 20 as depicted. It is to be recognized that while a boron/aluminum composite system is discussed for sake of example, it will become clear that the present invention is not so limiting.