This invention relates to composite materials and, more particularly, to burn resistant composite materials for use in structures such as gas turbine engines.
Machines such as gas turbine engines or other structures create or are exposed to relatively high temperatures that can, on occasion, result in ignition. For example, imbalance within a compressor of a gas turbine engine may cause a rotating compressor blade to rub against an outer compressor case surrounding the compressor. Friction between the blade and the compressor case may cause temperatures greater than 2700 F (1482 C) and possibly even result in ignition of certain materials used within the compressor and temperatures as high as 6000 F (3300 C).
In conventional compressor arrangements, the compressor is surrounded by a compressor case and, depending on the type of engine, an outer case that defines a duct radially outwards of the compressor. One or both of the cases are made of a metallic alloy, such as a titanium alloy. Although conventional cases have a containment capacity that is effective for containing flames and debris, there is opportunity to enhance the containment capacity. For example, if the temperature within the compressor were to exceed an ignition temperature or a melting temperature of the metallic alloy, the metallic alloy may ignite or liquefy and thereby result in loss of containment capacity.
Accordingly, there is a need for a case that provides enhanced burn and thermal resistance for maintaining containment capacity, including molten metal containment, of the case at elevated temperatures. This invention addresses those needs while avoiding the shortcomings and drawbacks of the prior art.
An example burn resistant composite article includes at least one composite layer having first fibers within a first organic resin matrix. At least one burn resistance layer is disposed adjacent the at least one composite layer. The burn resistance layer includes second fibers within a second organic resin matrix. The composite layer and the burn resistance layer each have an associated thermal resistance, and the thermal resistance of the burn resistance layer is greater than the thermal resistance of the composite layer. In one example, the second fibers include inorganic fibers, aramid fibers, or combinations thereof.
In one example, the burn resistant composite article is a compressor case adjacent a tip of at least one rotatable compressor blade within a gas turbine engine wherein the case may contain a seal. In another example, the burn resistant composite article is an outer case that defines a fan bypass passage.
An example method of manufacturing the burn resistant composite article includes the steps of forming the at least one composite layer, and forming the at least one burn resistance layer adjacent the at least one composite layer. For example, the composite layer and the burn resistance layer are formed from pre-impregnated layers.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.
A compressor case 26 generally surrounds the compressor section 16 to form a central duct or passage there through. The shape of the compressor case 26 may vary depending on a design of the compressor section 16, but generally the compressor case 26 is a sleeve-like structure arranged about the compressor blades 22 and vanes 24. The compressor case 26 may include a single wall, a double wall having an inner and outer wall, or a single wall section in combination with a double wall section.
The gas turbine engine 10 may also include other case structures, such as a turbine case 28 and an outer case 30 (e.g., a nacelle). The outer case 30 generally surrounds the compressor case 26 and forms a radially outer wall of a fan bypass passage 31 from the fan 14 of the engine 10. The shape of the outer case 30 may vary by engine type and design but is generally a sleeve like structure having a single wall.
As can be appreciated, the properties and functions of the various cases 26, 28, and 30 may vary depending upon structural requirements, containment requirements, or other design factors. For example, the disclosed compressor case 26 and outer case 30 provide containment capability within the compressor section 16, where temperatures are expected to peak between 2700° F. (1482° C.) and 6,000° F. (3,316° C.) under certain blade rub conditions. Given this description, one of ordinary skill in the art will recognize the application of the disclosed examples to meet the needs of their particular use.
As is known, the air compressed in the compressor section 16 is mixed with fuel in the combustion section 18 and is burned to produce hot gasses that are expanded in the turbine section 20 to drive the fan 14.
The composite layer 40 and the burn resistance layer 42 each have a characteristic thermal resistance. For example, the thermal resistance can be characterized by a burn resistance of each of the layers 40 and 42, or by a mechanical property at a pre-selected temperature (e.g., strength at a certain temperature), or by another suitable method. The thermal resistance of the burn resistance layer 42 is greater than the thermal resistance of the composite layer 40, which allows the burn resistance layer 42 to withstand elevated temperatures without significant degradation or melting to maintain a desired degree of containment capability.
If burn resistance is used to characterize the thermal resistance, the burn resistance of the burn resistance layer 42 is greater than the burn resistance of the composite layer 40. Burn resistance can be estimated qualitatively or quantitatively from the compositions of the layers 40 and 42 or be determined experimentally. For example, when exposed to a flame, the burn resistance layer 42 self-extinguishes in a shorter amount of time than the composite layer 40 or further, when exposed to molten metal, the burn resistant layer is not penetrated.
In the disclosed example, the composite layer 40 includes reinforcing fibers 44 within an organic resin matrix 46, such as polyimide, epoxy, or bismaleimide. For example, the reinforcing fibers 44 may include organic aramid fibers, glass fibers, graphite fibers, ceramic fibers or combinations thereof. The reinforcing fibers 44 may be distributed within the organic matrix 46 in a manner suitable for providing the composite layer 40 with a desired degree of strength and rigidity. In one example, the reinforcing fibers 44 are woven in a predetermined pattern and later impregnated with the organic resin matrix 46.
The burn resistance layer 42 also includes fibers 48 disposed within an organic resin matrix 50, such as polyimide, epoxy, or bismaleimide. The fibers 48 provide the burn resistance layer 42 with its thermal and burn resistance properties. For example, the fibers 48 are made of a heat resistant and/or burn resistant material. In one example, the fibers 48 are inorganic fibers, aramid fibers, or combinations thereof. In a further example, the fibers 48 are inorganic fibers made from alumina (Al2O3), silica (SiO2), various silicates (examples include MSiO4, MSi2O7, MSiO3, etc. where “M” denotes single or multiple cations species), mullite (3Al2O3-2SiO2), zirconia (ZrO2), or combinations thereof. The relatively high thermal resistance of such fibers, compared to other materials such as metals and some polymers, allows them to maintain mechanical integrity and resist oxidation and burning under compressor conditions that may peak between 2700° F. (1482° C.) and 6,000° F. (3,316° C.).
The fibers 48 may all be made of a single type of ceramic or inorganic fiber, such as the alumina, silica, silicates, mullite, or zirconia fibers described above. Alternatively, the fibers 48 may include at least two different types of the inorganic fibers, or inorganic fibers and organic fibers such as aramid fibers. The different types of the fibers 48 may be woven in a predetermined pattern, such as plain, twill, basket, Leno, satin, herringbone, or other known pattern.
As shown in
The burn resistant coating 52 may include any type of thermal or self-extinguishing burn resistant material that is suitable for being deposited onto the fibers 48. For example, the burn resistant coating 52 includes an inorganic material such as a silicate. Given this description, one of ordinary skill in the art will recognize other suitable types of burn resistant coatings.
In the illustrated example, the compressor case 26 includes a single composite layer 40 and a single burn resistance layer 42.
Additionally, the arrangement of the composite layers 40 and the burn resistance layers 42 in a radial direction relative to the engine centerline 12 may be selected based upon design considerations of the particular compressor section 16. For example, one of the burn resistance layers 42 may be used as a radially innermost layer of the compressor case 26, 26′, 26″ to protect one or more of the composite layers 40 that are radially outwards of the burn resistance layer 42 from exposure to elevated temperatures or flames within the compressor section 16. Alternatively, one or more of the composite layers 40 may be located radially inwards of one or more of the burn resistance layers 42 to enhance structural rigidity or strength of the compressor case 26, 26′, 26″, for example.
At step 68, the stacked pre-impregnated sheets 62 and 64 are co-cured, such as by heating at a predetermined temperature for a predetermined period of time. Optionally, a pressure P may be applied to the stack of the pre-impregnated sheets 62 and 64 to mold the pre-impregnated sheets 62 and 64 into a desired shape and “squeeze” excess organic matrix resin from the fibers 44 and 48, for example. One or more post curing steps 70, such as machining, may be used to smooth the compressor case 26 or shape it into a desired dimension.
Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.
This invention was made with government support under Contract No. N00019-02-C-3003 awarded by the United States Air Force. The Government therefore has certain rights in this invention.