Patent Description:
A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-pressure and temperature exhaust gas flow. The high-pressure and temperature exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section may include low and high pressure compressors, and the turbine section may also include low and high pressure turbines.

Airfoils in the turbine section are typically formed of a superalloy and may include thermal barrier coatings to extend temperature capability and lifetime. Ceramic matrix composite ("CMC") materials are also being considered for airfoils. Among other attractive properties, CMCs have high temperature resistance. Despite this attribute, however, there are unique challenges to implementing CMCs in airfoils.

<CIT> discloses a prior art gas turbine engine component as set forth in the preamble of claim <NUM>.

<CIT> discloses a prior art gas turbine engine thin wall composite vane airfoil.

<CIT> disclose a prior art ceramic matrix composite (CMC) hollow blade and a method of forming such a blade.

<CIT> discloses a prior art ceramic matrix composite airfoil trailing edge arrangement.

<CIT> discloses a prior art CMC turbine component.

<CIT> discloses a prior art gas turbine engine seal assembly with a ductile wear liner.

<CIT> discloses a prior art composite filler.

From one aspect, there is provided a gas turbine engine component as recited in claim <NUM>.

There is also provided a gas turbine engine as recited in claim <NUM>.

The various features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description.

The engine parameters described above and those in this paragraph are measured at this condition unless otherwise specified. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about <NUM>, or more narrowly greater than or equal to <NUM>. The "Low corrected fan tip speed" as disclosed herein according to one non-limiting embodiment is less than about <NUM> ft / second (<NUM> meters/second), and can be greater than or equal to <NUM> ft / second (<NUM> meters/second).

<FIG> illustrates selected portions of a sectioned view of a gas turbine engine component <NUM>, namely component wall <NUM>. According to the invention, the component <NUM> is an airfoil, such as a turbine vane or turbine blade, and a leading edge of the airfoil is shown.

In the illustrated example, the component wall <NUM> has an exterior core gaspath side 64a and an opposed interior side 64b. The gaspath side 64a is exposed to hot combustion gases in the core flow path C of the engine <NUM>. The interior side 64b borders an internal passage in the component <NUM>, such as a core cavity or cooling passage.

The component wall <NUM> is formed of a ceramic matrix composite (CMC) that includes a plurality of fiber plies <NUM> that are disposed in a ceramic matrix. For example, the CMC may be, but is not limited to, a SiC/SiC CMC in which SiC fiber plies are disposed within a SiC matrix. A fiber ply is a <NUM>-dimensional sheet of woven fiber tows. For example, the fiber plies <NUM> may have a harness weave structure.

The component wall includes a corner section 68a that connects first and second wall sections 68b/68c. The fiber plies <NUM> extend continuously through the first wall section 68b, the corner 68a, and the second wall section 68c. The fiber plies <NUM> are in a stacked contiguous arrangement in the first and second wall sections 68b/68c. In the illustrated example, the corner section 68a is acute in that the angle formed between the interior side 64b of the wall sections 68b/68c is less than <NUM>°. The term "stacked" refers to the plies <NUM> being arranged one on top of another. The term "contiguous" refers to the plies being in contact from one ply to the next. That is, the plies are stacked back-to-back.

At least some of the fiber plies <NUM> separate from one another in the corner 68a to define one or more void pockets <NUM> there between. According to the invention, there are at least two void pockets <NUM>, and one of the void pockets <NUM> is inboard of the other relative to the exterior gaspath side 64a. The void pockets <NUM> are thin, relative to the thickness of a single one of the fiber plies <NUM>. According to the invention, the maximum thickness t of each void pocket <NUM> is less than the thickness of a single one of the plies <NUM>. In general, the thickness t is equal to or less than <NUM> micrometers. The thickness t, however, may be varied to adapt the design for a particular airfoil geometry without compromising cavity radius or to increase cavity radius if desired. The bending of the fiber plies <NUM> bend in the corner 68a give the void pockets <NUM> an arced shape. For instance, each void pocket <NUM> is divergent-convergent in that between its endpoints it diverges from one endpoint to the maximum thickness and then converges from the maximum thickness to the other endpoint.

The void pockets <NUM> serve to facilitate reductions in thermal gradients and reductions in interlaminar stresses. For instance, the void pockets <NUM> serve as insulation regions and thereby reduce thermal transfer from the exterior gaspath side 64a to the interior side 64b. If additional cooling is desired, the void pockets <NUM> can be provided with cooling air flow, such as bleed air from the compressor section <NUM>. The void pockets <NUM> also locally reduce geometric constraints on the fiber plies <NUM>. For instance, under thermal stresses that are representative of the thermal conditions in the engine <NUM>, the void pockets <NUM> permit unconstrained local thermal growth of the fiber plies <NUM> and thereby reduce interlaminar tension. Interlaminar shear may increase, however, shear may be more tolerable than tension. In contrast, in a similar configuration of the same corner radius and ply thickness that does not have the void pockets <NUM>, the plies constrain one another and thus geneate comparatively higher interlaminar stresses. The void pockets <NUM> may also facilitate damage tolerance. For instance, if the outer fiber plies <NUM> at the exterior gaspath side 64a were to become damaged, such as from a foreign object impact, the void pockets <NUM> may act as a buffer to isolate the damage to those plies. Moreover, if there is cracking from damage or normal use, such crack progression may occur in stages, where void pockets <NUM> provides points of arrest rather than progressing through an entire ply stack.

In the illustrated example, the number and arrangement of the fiber plies <NUM> is also configured to facilitate increased strength and durability. For example, the fiber plies <NUM> are arranged in groups, represented at 66a/66b/66c. Each of the groups 66a/66b/66c has two of the fiber plies <NUM> that are contiguous. The first group 66a separates from the second group 66b in the corner 68a and the second group 66b separates from the third group 66c in the corner 68a. As discussed above, the void pockets <NUM> between the groups 66a/66b/66c facilitate reductions in thermal gradients and reductions in interlaminar stresses. The use of two fiber plies <NUM> in each group 66a/66b/66c facilitates increasing stiffness and strength.

The void pockets <NUM> may also facilitate formation of acute corners. For example, during layup of the fiber plies <NUM> in fabrication of the component <NUM>, the void pockets <NUM> provide the fiber plies <NUM> space to bend without constraint from adjacent fiber plies <NUM>. In some examples, however, to keep the void pockets <NUM> from collapsing during fabrication and/or to control the geometry of the void pockets <NUM>, consumable mandrels may be used. The fiber plies <NUM> are laid up around the consumable mandrels, and the mandrels are later dissolved or otherwise removed, leaving the void pockets <NUM> in their place.

An alternate method that does not use consumable materials may be used to form the void pockets <NUM>. For example, an adhesive is used to temporarily attach plies together around a mandrel or other shaping tool to retain a desired shape prior to insertion into a graphite tool and subsequent densification in a furnace. The void pockets <NUM> are created in the preform stage by maintaining a separation in the desired area and selectively applying the adhesive to hold the plies in place. For instance, the adhesive is applied at least at the ends of the void pockets <NUM> to prevent the pockets from collapsing. The graphite tool and mandrels may have to be modified to create pinch points at the ends to constrain the pre-form to retain the void, since the pre-form tends to expand and may cause the voids to close during the densification process due to high temperatures. Given this description, one of ordinary skill in the art will be able to determine tolerancing of the tooling to achieve the desired void pocket <NUM> size. If there is some collapsing of the void pockets <NUM> during this processing, consumable material may be selectively used in those areas to limit collapse.

Claim 1:
A gas turbine engine component (<NUM>) comprising:
a component wall (<NUM>) that has an exterior core gaspath side (64a) and an opposed interior side (64b), the component wall (<NUM>) being formed of a ceramic matrix composite that includes a plurality of fiber plies (<NUM>) disposed in a ceramic matrix, the component wall (<NUM>) including a corner (68a) connecting first and second wall sections (68b, 68c), the fiber plies (<NUM>) extending continuously through the first wall section (68b, 68c), the corner (68a), and the second wall section (68b, 68c), the fiber plies (<NUM>) being in a stacked contiguous arrangement in the first and second wall sections (68b, 68c) and at least some of the fiber plies (<NUM>) separating from one another in the corner (68a) to define one or more void pockets (<NUM>) therebetween,
wherein there are at least two of the void pockets (<NUM>) wherein, relative to the exterior core gas path side (64a), a first one of the void pockets (<NUM>) is inboard of a second one of the void pockets (<NUM>),
characterised in that:
the corner (68a) is a leading edge of an airfoil; and
the void pockets (<NUM>) each have a maximum thickness (t) which is less than a thickness of a single one of the plies (<NUM>).