Composite turbine blades are currently fabricated by laying up multiple layers of fibers in the form of either unidirectional prepregs or thin woven cloth. Composites formed in this manner have poor through-thickness strength. It is also difficult, if not impossible, to form trailing edges as thin as necessary for optimum engine performance.
A method was developed to produce integrally woven preforms of reinforcing fibers for ceramic composite turbine blades. The preforms contain reinforcing fibers in a 3D arrangement that avoids failure by delamination, and allows formation of thin trailing edges.
Two versions of the design were developed. The complex nature of the weave structures in the walls of the airfoil and in the trailing edge region mandates the use of a Jacquard head loom to produce the preform, rather than the more common Dobby loom. In the first version, a reduced weft fiber count in the tapered trailing edge region was produced by drawing weft tows out of the woven preform during weaving, and removing them by cutting after weaving. In the second version, the paths of the weft fiber tows were modified to make them turn in a staggered pattern within the trailing edge region, thus avoiding the need for cutting any tows.
The 3D arrangement of the fibers in walls and the trailing edge allows the design of hollow blades that can contain high-pressure cooling air without the danger of splitting the trailing edge region. It also allows formation of thinner trailing edges, and can be optimized for different loads in different applications. The 3D arrangement also can be adjusted to produce blades that taper in cross-section from the base to the tip. Formation of the trailing edge without cutting circumferential fibers gives more uniform surface texture and reduced manual steps in producing the preform.
This work was done by Brian Cox and David Marshall of Teledyne Scientific Co. for Glenn Research Center.
Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steven Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-19170-1.