Patent Description:
Carbon/carbon ("C/C") composites consist of carbon fibers in a carbon matrix. C/C composites are used to form parts in various industries. For example, C/C parts may be employed in aerospace applications due to the superior high temperature characteristics of C/C. However, carbon fiber is unique in that it has a negative CTE. Differences in the expansion of a C/C part and the expansion of a component mounted to the C/C part, due to the CTE of C/C part being different from the CTE of the component, can generate stress, which may lead to separation and/or damage to the parts. Similarly, variations in the expansion of a C/C part and a coating applied to the C/C part can lead to cracks in the coating. Finally, the accuracy of aerospace guidance and/or dimensionally stable equipment can be affected by thermal expansion of the structure to which the equipment is attached.

<CIT> discloses carbon-carbon composite materials.

<CIT> discloses a carbon-carbon grid for ion engines.

In accordance with an aspect of the present invention, there is provided a composite structure in accordance with claim <NUM>.

Optionally, the second fiber layer further includes a second carbon fiber tow having the first coefficient of thermal expansion. In various embodiments, the non-carbon fiber tow of the second fiber layer is at least one of a silicon carbide fiber or a silicon nitride fiber.

Optionally, a first portion of the fiber reinforced composite material comprises a first number of fiber layers, and a second portion of the fiber reinforced composite material comprises a second number of fiber layers greater than the first number of fiber layers.

Optionally, a fastener is located through the second portion of the fiber reinforced composite material, and a coefficient of thermal expansion of the fiber reinforced composite material in the second portion of the fiber reinforced composite material is approximately equal to a coefficient of thermal expansion of the fastener.

Optionally, a coefficient of thermal expansion of the fiber reinforced composite material in the first portion of the fiber reinforced composite material is different from a coefficient of thermal expansion of the fiber reinforced composite material in the second portion of the fiber reinforced composite material.

Optionally, a coating may be applied over the fiber reinforced composite material. The coefficient of thermal expansion of the fiber reinforced composite material is approximately equal to a coefficient of thermal expansion of the coating.

Optionally, a coefficient of thermal expansion of the fiber reinforced composite material is approximately zero.

According to another aspect of the present invention, there is provided a method of making a composite structure for use in conjunction with an aerospace component having a target coefficient of thermal expansion in accordance with claim <NUM>.

Optionally, a first fiber layer of the plurality of fiber layers includes a first carbon fiber tow having the first coefficient of thermal expansion, and a second fiber layer of the plurality of fiber layers includes a non-carbon fiber tow having the second coefficient of thermal expansion.

Optionally, the method further comprises forming the second fiber layer by weaving the non-carbon fiber tow with a second carbon fiber tow having the first coefficient of thermal expansion.

Stacking the plurality of fiber layers includes interleaving a plurality of carbon fiber layers with a plurality of non-carbon fiber layers.

Optionally, the method further comprises forming each fiber layer of the plurality of fiber layers by weaving a carbon fiber tow having the first coefficient of thermal expansion with a non-carbon fiber tow having the second coefficient of thermal expansion.

Optionally, stacking the plurality of fiber layers includes forming a first portion of the fiber reinforced composite material having a first number of fiber layers and forming a second portion of the fiber reinforced composite material having a second number of fiber layers greater than the first number of fiber layers. The second portion of the fiber reinforced composite material includes the coefficient of thermal expansion that is approximately equal to the target coefficient of thermal expansion of the aerospace component.

Optionally, the aerospace component is formed of at least one of a metal or a metal alloy.

Optionally, the method further comprises dispersing a plurality of ceramic particles in the carbon matrix of the fiber reinforced composite material.

According to another aspect of the present invention, there is provided an aerospace component in accordance with claim <NUM>.

Optionally, a plurality of ceramic particles is dispersed in the carbon matrix.

The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the inventions, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this invention and the teachings herein. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option.

With reference to <FIG>, an aerospace component <NUM> is illustrated. In various embodiments, aerospace component <NUM> includes a first structure <NUM> and a composite structure <NUM> mounted to the first structure <NUM>. A composite structure <NUM> is formed of a fiber reinforced composite material <NUM>. In various embodiments, a coating <NUM> may be applied over fiber reinforced composite material <NUM>. First structure <NUM> is formed of a first material <NUM>. In various embodiments, first material <NUM> may be a metal or a metal alloy. For example, first material <NUM> may be titanium, a titanium-alloy, a nickel-alloy, or a nickel-based super alloy, such as INCONEL.

In accordance with various embodiments, a CTE of the fiber reinforced composite material <NUM> of composite structure <NUM> is tailored to match a target CTE. Stated differently, the CTE of fiber reinforced composite material <NUM> may be approximately equal to the target CTE. As used in the previous context only, "approximately equal" means the CTE of fiber reinforced composite material <NUM> is within ± <NUM>% of the target CTE. In various embodiments, the target CTE is the CTE of first material <NUM>. In various embodiments, the target CTE is the CTE of coating <NUM>. In various embodiments, the target CTE is zero.

In accordance with various embodiments, fiber reinforced composite material <NUM> includes fibers <NUM> and a matrix <NUM> surrounding fibers <NUM>. In accordance with various embodiments, fibers <NUM> include a plurality of carbon (or first) fibers 110a and a plurality of non-carbon (or second) fibers 110b. As used herein, "carbon fiber" refers to a fiber that is formed essentially of only carbon (e.g., a fiber that is at least <NUM>% carbon, at least <NUM>% carbon, at least <NUM>% carbon, at least <NUM>% carbon, at least <NUM>% carbon, and/or at least <NUM>% carbon). As used herein, "non-carbon fiber" refers to a fiber that includes elements other than, or in addition to, carbon. In this regard, "non-carbon" does not mean devoid of carbon. For example, in various embodiments, non-carbon fibers 110b include silicon carbide (SiC) fibers. In various embodiments, non-carbon fibers 110b include silicon nitride fibers. In accordance with various embodiments, non-carbon fibers 110b have a CTE that is greater than the CTE of carbon fibers 110a. For example, non-carbon fibers 110b may have a CTE of greater than <NUM> × <NUM>-<NUM>/°C.

In various embodiments, fiber reinforced composite material <NUM> includes a plurality of stacked fiber layers. With additional reference to <FIG>, in various embodiments, fiber reinforced composite material <NUM> may be formed by stacking a plurality of fiber layers, such as, first fiber layer 114a, second fiber layer 114b, third fiber layer 114c, fourth fiber layer 114d, and fifth fiber layer 114e (collectively fiber layers <NUM>) to form a fiber layup <NUM>. Fiber layers <NUM> include carbon fibers 110a (also referred to as carbon tows) and non-carbon fibers 110b (also referred to a non-carbon tows).

Fiber layup <NUM> may be formed utilizing either oxidized polyacrylonitrile (PAN) fibers (referred to as "OPF" fibers) or carbonized carbon fibers for carbon fibers 110a. Carbon fibers 110a and non-carbon fibers 110b are used to fabricate a preform using a needle punching process. For example, carbon fibers 110a and non-carbon fibers 110b are layered in a selected orientation to form fiber layup <NUM> of a selected geometry. Typically, two or more layers of fibers are layered onto a support and are then needled together simultaneously or in a series of needling steps. This process interconnects the horizontal fibers with a third direction (also called the z-direction). The fibers extending into the third direction are also called z-fibers. This needling process may involve driving a multitude of barbed needles into the fibrous layers to displace a portion of the horizontal fibers into the z-direction.

In various embodiments, at least one of the fiber layers <NUM> includes both carbon fiber 110a and non-carbon fiber 110b. For example, in various embodiments, at least one of the fiber layers <NUM> may include a woven fiber layer having a weft formed of carbon fiber 110a and warps formed of non-carbon fiber 110b.

In various embodiments, one or more of fiber layers <NUM> may include a woven fiber layer, where the weft fibers are non-carbon fibers and the warp fibers are carbon fibers. In various embodiments, one or more of fiber layers <NUM> may include a woven fiber layer, where the weft fibers include non-carbon fibers and carbon fiber and the warp fibers are carbon fibers. In various embodiments, one or more of fiber layers <NUM> may include a woven fiber layer, where the warp fibers include non-carbon fibers and carbon fibers and the weft fibers are carbon fibers. In various embodiments, one or more of fiber layers <NUM> may include a woven fiber layer, where the weft fibers and the warp fibers each include non-carbon fibers interleaved with carbon fibers. The weaving pattern of the carbon and non-carbon fibers of the weft fibers and/or of the warp fibers is/are selected based on the target CTE. In this regard, the weft fibers and/or the warp fibers may include multiple carbon fiber tows between adjacent non-carbon fiber tows and/or multiple non-carbon fiber tows between adjacent carbon fiber tows. In various embodiments, each of the fiber layers <NUM> is woven with both carbon fibers 110a and non-carbon fibers 110b.

In various embodiments, at least one the fiber layers <NUM> is formed of only carbon fiber tows 110a (i.e., is devoid of non-carbon fibers 110b) and at least one of the fiber layers <NUM> is formed of only non-carbon fiber tows 110b (i.e., is devoid of carbon fibers 110a). For example, fiber layup <NUM> includes non-carbon fiber layers interleaved with carbon fiber layers. In various embodiments, fibers layers <NUM> may include at least one fiber layer <NUM> formed of only carbon fiber tows 110a and at least one fiber layer <NUM> formed of weaved carbon fiber tow 110a and non-carbon fiber tow 110b.

After stacking the desired number of fiber layers <NUM>, fiber layup <NUM> is densified. Returning to <FIG>, during the densification operation, carbon matrix <NUM> is deposited around and between the fibers 110a, 110b. Densification may be done using chemical vapor infiltration (CVI) or any other suitable carbon deposition method.

In accordance with various embodiments, the locations of carbon fibers 110a and non-carbon fibers 110b, the weave pattern of carbon fibers 110a and non-carbon fibers 110b in each fiber layer <NUM> (<FIG>), and/or the ratio of carbon fibers 110a to non-carbon fibers 110b is/are selected to create a desired CTE profile through fiber reinforced composite material <NUM>. In this regard, the locations of carbon fibers 110a and non-carbon fibers 110b, the weave pattern of carbon fibers 110a and non-carbon fibers 110b, and/or the ratio of carbon fibers 110a to non-carbon fibers 110b are configured such that the CTE of fiber reinforced composite material <NUM> is approximately equal the target CTE.

With reference to <FIG>, an aerospace component <NUM> is illustrated. In various embodiments, aerospace component <NUM> includes a first structure <NUM> and a composite structure <NUM> mounted to the first structure <NUM>. Composite structure <NUM> is formed of a fiber reinforced composite material <NUM>. One or more fastener(s) <NUM> is/are located through fiber reinforced composite material <NUM>. In accordance with various embodiments, the CTE profile of fiber reinforced composite material <NUM> is configured such that a first portion <NUM> of fiber reinforced composite material <NUM> includes a first CTE and a second portion <NUM> of fiber reinforced composite material <NUM> includes a second CTE, different from the first CTE. In various embodiments, the CTE of second portion <NUM> is approximately equal to the CTE of fasteners <NUM>. Fasteners <NUM> may be formed of a metal or metal alloy. For example, fasteners <NUM> may include titanium, a titanium-alloy, a nickel-alloy, and/or a nickel-based super alloy, such as INCONEL.

Fiber reinforced composite material <NUM> includes carbon fibers 220a and non-carbon fibers 220b, which are similar to previously described carbon fibers 110a and non-carbon fibers 110b, respectively. In various embodiments, a ratio of carbon fibers 220a to non-carbon fibers 220b is greater in first portion <NUM> as compared to the ratio of carbon fibers 220a to non-carbon fibers 220b in second portion <NUM>. For example, the weft fibers and/or the warp fibers in second portion <NUM> may include a greater ratio of non-carbon fibers 220b to carbon fibers 220a as compared to the ratio of non-carbon fibers 220b to carbon fibers 220a in first portion <NUM>. Stated differently, in various embodiments, a greater percentage of the fibers located in second portion <NUM> may be non-carbon fibers 220b as compared to the percentage of fibers in first portion <NUM> that are non-carbon fibers 220b.

In various embodiments, fiber reinforced composite material <NUM> may be formed by forming a fiber layup, as described above with reference to fiber layup <NUM>. Fiber reinforced composite material <NUM> may be formed by stacking a plurality of first fiber layers <NUM> and a plurality of second fiber layers <NUM>. In various embodiments, second fiber layers <NUM> are located in second portion <NUM>. In this regard, a greater number of fiber layers may be located in second portion <NUM> as compared to the number of fiber layers in first portion <NUM>. In various embodiments, one or more of the second fiber layers <NUM> include(s) only non-carbon fibers 220b and one or more of the first fiber layers <NUM> include(s) only carbon fibers 220a. In various embodiments, one or more of the second fiber layers <NUM> include(s) non-carbon fibers 220b and carbon fibers 220a, and one or more of the first fiber layers <NUM> include(s) only carbon fibers 220a. In various embodiments, one or more of the second fiber layers <NUM> include(s) only non-carbon fibers 220b, and one or more of the first fiber layers <NUM> include(s) carbon fibers 220a and non-carbon fibers 220b. In various embodiments, one or more of the first fiber layers <NUM> and one or more of the second fiber layers <NUM> each include both carbon fibers 220a and non-carbon fibers 220b.

The interleaving pattern of second fiber layers <NUM> and first fiber layers <NUM> and the ratio of carbon fibers 220a to non-carbon fibers 220b in second portion <NUM> is selected based on the CTE of fastener <NUM>. In this regard, the locations of carbon fibers 220a and non-carbon fibers 220b, a weave pattern of carbon fibers 220a and non-carbon fibers 220b, and the ratio of carbon fibers 220a to non-carbon fibers 220b in second portion <NUM> of fiber reinforced composite material <NUM> are selected such that the CTE of fiber reinforced composite material <NUM> in second portion <NUM> is approximately equal to the CTE of fasteners <NUM>. As used in the previous context, "approximately equal" means the CTE of fiber reinforced composite material <NUM> is within ± <NUM>% of the CTE of fasteners <NUM>.

With reference to <FIG>, a method <NUM> of making a composite structure for use in conjunction with an aerospace component having a target CTE is illustrated. In various embodiments, method <NUM> may include forming a fiber reinforced composite having a CTE approximately equal to the target CTE (step <NUM>). In various embodiments, step <NUM> may include stacking a plurality of fiber layers (step <NUM>) and forming a carbon matrix surrounding the plurality of fiber layers (step <NUM>). The plurality of fiber layers includes a plurality of carbon fibers and a plurality of non-carbon fibers. In various embodiments, step <NUM> includes interleaving a plurality of carbon fiber layers with a plurality of non-carbon fiber layers.

In various embodiments, step <NUM> may further include forming one or more of the fiber layers of by weaving together a non-carbon fiber tow and a carbon fiber tow. In various embodiments, step <NUM> may further include forming each of the fiber layers by weaving together a carbon fiber tow and a non-carbon fiber tow. In various embodiments, step <NUM> includes interleaving a plurality of carbon fiber layers with a plurality of non-carbon fiber layers.

With reference to <FIG>, in various embodiments, step <NUM> includes forming a first portion of the fiber reinforced composite material having a first number of fiber layers (step 312A), and forming a second portion of the fiber reinforced composite material having a second number of fiber layers greater than the first number of fiber layers (step 312B). In various embodiments, the second portion of the fiber reinforced composite material comprises a CTE that is approximately equal to the target CTE. In various embodiments, step <NUM> may include dispersing a plurality of ceramic particles in the carbon matrix.

Claim 1:
A composite structure (<NUM>; <NUM>), comprising:
a fiber reinforced composite material (<NUM>; <NUM>) including:
a plurality of fiber layers (<NUM>; <NUM>, <NUM>); and
a carbon matrix (<NUM>) surrounding the plurality of fiber layers (<NUM>; <NUM>, <NUM>);
wherein a first fiber layer (<NUM>) of the plurality of fiber layers (<NUM>; <NUM>, <NUM>) includes a first carbon fiber tow (110a; 220a), and a second fiber layer (<NUM>) of the plurality of fiber layers (<NUM>; <NUM>, <NUM>) includes a non-carbon fiber tow (<NUM>10b; 220b),
wherein the first carbon fiber tow (110a; 220a) has a first coefficient of thermal expansion, and the non-carbon fiber tow (110b; 220b) has a second coefficient of thermal expansion that is greater than the first coefficient of thermal expansion,
characterised in that:
the plurality of fiber layers (<NUM>; <NUM>, <NUM>) includes a plurality of carbon fiber layers interleaved with a plurality of non-carbon fiber layers, the plurality of carbon fiber layers including the first fiber layer (<NUM>), and the plurality of non-carbon fiber layers including the second fiber layer (<NUM>).