Abstract:
Methods for repairing composite containment casings involving providing a composite containment casing having an integrated abradable system, the abradable system having at least one damaged portion, and including a sandwich structure, and at least one abradable layer, removing the damaged portion of the abradable system to leave a hole, shaping a sandwich structure segment to produce a shaped sandwich structure, placing the shaped sandwich structure into the hole in the abradable system, infusing a resin into the shaped sandwich structure, and curing the containment casing having the shaped sandwich structure, and applying at least one abradable layer to the shaped sandwich structure to produce the containment casing having a repaired integrated abradable system.

Description:
TECHNICAL FIELD 
     Embodiments described herein generally relate to methods for repairing composite containment casings. More specifically, embodiments herein generally describe methods for repairing composite fan casings having integrated abradable systems. 
     BACKGROUND OF THE INVENTION 
     In gas turbine engines, such as aircraft engines, air is drawn into the front of the engine, compressed by a shaft-mounted compressor, and mixed with fuel in a combustor. The mixture is then burned and the hot exhaust gases are passed through a turbine mounted on the same shaft. The flow of combustion gas expands through the turbine which in turn spins the shaft and provides power to the compressor. The hot exhaust gases are further expanded through nozzles at the back of the engine, generating powerful thrust, which drives the aircraft forward. 
     Because engines operate in a variety of conditions, foreign objects may undesirably enter the engine. More specifically, foreign objects, such as large birds, hailstones, ice, sand and rain may be entrained in the inlet of the engine where they may impact the engine or a fan blade therein. Sometimes these impacts can result in a portion of the contacted blade being torn loose from the rotor, which is commonly known as fan blade out. The loose fan blade may then impact the interior of the fan casing. Similarly, in cold weather and at high altitudes, ice can form and accumulate on the fan blades. When engine speed is rapidly accelerated, or altitude is decreased, the ice can shed, also resulting in an impact with the interior of the fan casing. 
     In recent years composite materials have become increasingly popular for use in a variety of aerospace applications because of their durability and relative lightweight. Although composite materials can provide superior strength and weight properties, and can lessen the extent of damage to the fan casing during impacts such as ice shedding and fan blade outs, there remains room for improvement. 
     Current composite containment technology, such as that used to make fan casings, typically employs a thick, monolithic hardwall design that is capable of withstanding an impact caused by ice and/or released fan blades, and also fragmentizing the ice or released fan blades, breaking them into smaller pieces. These fragmentized pieces can then be purged from the engine without causing significant damage to either the engine or the body of the aircraft. The construction of the fan casing provides for the dissipation of impact energy using any of a number of mechanisms including fiber/matrix interference failure, matrix microcracking and ply delamination. 
     More specifically, current hardwall designs generally consist of an abradable system having an abradable layer attached to a substrate structure that includes a glass/epoxy composite face sheet bonded to a Nomex® honeycomb core, which can be very lightweight. See U.S. Pat. No. 5,344,280 to Langenbrunner et al. However, such honeycomb cores are typically not designed to provide significant energy absorption during a fan blade out event. More specifically, the design of the honeycomb core results in an abradable system having radial weakness. Thus, released fan blades will have a tendency to simply cut through the honeycomb core upon impact, leaving roughly 99% of the impact energy to be absorbed by the fan casing body. Moreover, because the current abradable systems require numerous layup, bonding, cure, and machining cycles, the fabrication of such systems can be labor intensive, costly, and can result in a heavier than desired fan casing because of the multiple layers of construction. Additionally, because the abradable system is fabricated separately from, and then attached to, the fan casing, the two parts function independently, rather than as a unitary system. 
     Accordingly, there remains a need for methods for repairing integrated abradable systems for containment fan casings that can provide improved impact resistance without the previously described time, labor, weight and cost issues. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Embodiments described herein generally relate to methods for repairing composite containment casings comprising providing a composite containment casing having an integrated abradable system, the abradable system having at least one damaged portion, and comprising a sandwich structure, and at least one abradable layer, removing the damaged portion of the abradable system to leave a hole, shaping a sandwich structure segment to produce a shaped sandwich structure, placing the shaped sandwich structure into the hole in the abradable system, infusing a resin into the shaped sandwich structure, and curing the containment casing having the shaped sandwich structure, and applying at least one abradable layer to the shaped sandwich structure to produce the containment casing having a repaired integrated abradable system. 
     Embodiments herein also generally relate to method for repairing composite containment casings comprising providing a composite containment casing having an integrated abradable system, the abradable system having at least one damaged portion, and comprising a sandwich structure and at least one abradable layer, removing the damaged portion of the abradable system to leave a hole, shaping a sandwich structure segment to produce a shaped sandwich structure, infusing a resin into the shaped sandwich structure, curing the shaped sandwich structure, bonding the shaped sandwich structure in the hole in the abradable system, and applying at least one abradable layer to the shaped sandwich structure to produce the containment casing having a repaired integrated abradable system. 
     These and other features, aspects and advantages will become evident to those skilled in the art from the following disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the invention, it is believed that the embodiments set forth herein will be better understood from the following description in conjunction with the accompanying figures, in which like reference numerals identify like elements. 
         FIG. 1  is a schematic cross-sectional view of one embodiment of a gas turbine engine in accordance with the description herein; 
         FIG. 2  is a schematic cross-sectional view of a portion of one embodiment of a fan casing having an integrated abradable system in accordance with the description herein; 
         FIG. 3  is a schematic perspective view of one embodiment of a mandrel having a pocket in accordance with the description herein; 
         FIG. 4  is a schematic cross-sectional view of a portion of the mandrel of  FIG. 3  taken along line A-A having a sandwich structure positioned in the pocket and material wrapped thereabout in accordance with description herein; and 
         FIG. 5  is a schematic cross-sectional view of a portion of one embodiment of a fan casing having an integrated abradable system and the system&#39;s position relative to a fan blade in accordance with the description herein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments described herein generally relate to methods for repairing composite containment casings having integrated abradable systems. Those skilled in the art will understand that the following description is applicable to all types of gas turbine engines, including but not limited to Low Bypass Fan Engines, High Bypass Fan Engines and Ultra-High Bypass Fan Engines. 
     Turning to the figures,  FIG. 1  is a schematic representation of one embodiment of a conventional gas turbine engine  10  that generally includes a fan assembly  12  and a core engine  14 . Fan assembly  12  may include a composite fan casing  16  having a body  17 , and an array of fan blades  18  extending radially outwardly from a rotor disc  20 . Core engine  14  may include a high-pressure compressor  22 , a combustor  24 , a high-pressure turbine  26  and a low-pressure turbine  28 . Engine  10  has an intake end  30  and an exhaust end  32 . 
     As previously described, embodiments herein may comprise a fan casing  35  having an integrated abradable system  34  adjoined thereto that can lessen the damage resulting from a fan blade out or other like event. While the abradable system  34  may take a variety of configurations, it may generally comprise a sandwich structure  36  and at least one abradable layer  38 , as shown in  FIG. 2 . As used herein, “sandwich structure” refers to a multi-layered structure generally comprising a first facesheet  33 , and a second facesheet  33  positioned about at least one core layer  37 , as shown in  FIG. 2 . First and second facesheet  33 , as well as core layer  37 , may comprise any woven, braided, or non-crimp fabric capable of being infused with a resin and cured to produce a composite material, such as carbon fibers, graphite fibers, glass fibers, ceramic fibers, and aramid polymer fiber. Moreover, the material used in core layer  37  can have non-isotropic properties, and may include cell, columnar, and truss configurations. A plurality of core layers  37  may be desirable to permit tailoring of the orthotropic properties of sandwich structure  36  as a function of the fan casing  35  radius or thickness. 
     Some examples of materials suitable for use as sandwich structure  36  can include, but should not be limited to, TYCOR® (WebCore Technologies, Inc., Miamisburg, Ohio, see U.S. Patent Application 2005/0074593) shown in  FIG. 2 , or 3-D woven truss configurations (Bally Ribbon Mills, Bally, Pa., see U.S. Pat. Nos. 6,742,547 and 6,892,766) shown in  FIGS. 4 and 5 . 
     It is envisioned that during the fabrication process, sandwich structure  36  can be designed to be strong radially and weak circumferentially. Radial strength will allow for the absorption and dissipation of impact energy generated by a released fan blade, as well as the alteration of the released blade&#39;s flight trajectory. Circumferential weakness will allow for sandwich structure  36  to become crushed and deformed when impacted by a fan blade due to unbalanced rotor orbiting. Taken together, this radial strength and circumferential weakness can allow the sandwich structure  36  to help absorb energy generated by a released fan blade, thereby reducing the energy that will need to be absorbed by the fan casing  35 . This can lead to the fabrication of a thinner, lighter fan casing  35 . Additionally, sandwich structure  36  can maintain its mechanical integrity, thereby reducing the likelihood the released fan blade will contact and/or significantly damage the fan casing  35 . 
     Abradable layer  38  refers to the radially innermost layer of integrated abradable system  34  and provides a region against which the fan blades may occasionally rub throughout engine operation. Abradable layer  38  may generally comprise any low-density, syntactic film epoxy suitable for use in a clearance control application that can be resistant to damage from ice impact and can be easily repaired/replaced throughout the service life time of the fan casing  35 , as explained herein below. One example of a suitable material for use as abradable layer  38  is Hysol® EA 9890, though the embodiments herein should not be limited to such. Additionally, abradable layer  38  can be bonded to the fan casing  35  so as to cover sandwich structure  36 . Any conventional bonding materials and techniques known to those skilled in the art may are acceptable for use herein. 
     In general, a fan casing  35  having an integrated abradable system  34  can be made using conventional composite manufacturing processes. However, some modifications to the tooling used in the process are required. As shown in  FIG. 3 , a mandrel  40  may be provided for fabricating embodiments of the fan casing  35  described herein. Mandrel  40  may be similar to conventional tools used in fan casing fabrication, see for example, U.S. Patent Application No. 2006/0134251 to Blanton et al., with the exception that mandrel  40  can have a pocket  42  disposed circumferentially thereabout for receiving truss core layer  37  of abradable system  34 . Mandrel  40  can be “substantially cylindrical,” and may be generally shaped like a cylinder, either with or without a contour. 
     More specifically, and as shown in  FIG. 3 , pocket  42  may have any dimension that corresponds to the desired dimensions of sandwich structure  36  of abradable system  34 . However, in general, pocket  42  (and therefore sandwich structure  36 ) can have a width W of from about one to about three times the axial chord length L of fan blade  18  as indicated in  FIG. 1 , and a depth D of from about one to about five times the radial thickness T of fan casing  35 , which is measured at the thickest cross-section of the fan casing  35  as shown in  FIG. 5 . As an example, if fan blade  18  comprises an axial chord length L of about 12 inches (about 30.4 cm) and a preform  46  ( FIG. 4 ) of the fan casing  35  comprises a radial thickness T of about 1 inch (about 2.54 cm), then pocket  42  may have a width W of from about 12 inches (about 30.4 cm) to about 36 inches (about 91.4 cm) and a depth D of from about 1 inch (about 2.54 cm) to about 5 inches (about 12.7 cm). Moreover, because abradable system  34  functions to absorb impact from a released fan blade, pocket  42  can be positioned along mandrel  40  such that sandwich structure  36 , and therefore abradable system  34 , will be adjacent to fan blades  18  when the fan assembly of the engine is assembled, as shown in  FIG. 5 . 
     Fabrication of fan casing  35  having integrated abradable system  34  can be accomplished in a couple of ways. In one embodiment, sandwich structure  36  having the desired number of core layers  37  may first be positioned within pocket  42  of mandrel  40 , as shown in  FIG. 4 . Next, at least one ply of a material  44  may be continuously applied about mandrel  40  having pocket  42  containing sandwich structure  36  until the desired thickness is obtained. Similar to facesheet  33  of sandwich structure  36 , material  44  may comprise any woven, braided, or non-crimp fabric capable of being infused with a resin and cured to produce a composite material. In one embodiment, the material may comprise carbon fibers, graphite fibers, glass fibers, ceramic fibers, and aramid polymer fibers. Additionally, each fiber tow may comprise from about 3000 to about 24,000 individual fiber filaments. 
     The resulting fan casing preform  46  having an integrated sandwich structure  36 , may be treated with any suitable resin, such as epoxy, using conventional techniques for infusing the resin throughout the fan casing preform  46  and the integrated sandwich structure  36 . Once the resin has been infused, fan casing preform  46  may then be cured using traditional curing methods known to those skilled in the art. 
     In an alternate embodiment, fan casing preform  46  can be layed up about a conventional mandrel using conventional techniques, followed by resin infusion and curing. The resulting fan casing  35  may then have sandwich structure  36 , which has been previously resin-infused and cured, bonded to interior  19  thereof. Like the previous embodiment, sandwich structure  36  can be positioned adjacent to fan blades  18  when the fan assembly of the engine is assembled, as shown in  FIG. 5 . 
     Whichever method of fabrication is selected, to complete fan casing  35  having abradable system  34 , at least one abradable layer  38  may be applied over sandwich structure  36 , as shown in  FIG. 5 , using any suitable method, including, but not limited to, adhesively bonding or mechanically attaching. Further finishing steps conventional to all fan casing fabrication processes, such as the application of one or more acoustic panels  48 , may then be carried out. 
     The integrated abradable systems of the fan casing embodiment described herein can provide several benefits in addition to those previously discussed. For example, the fan casing embodiments herein can require significantly fewer layup, bonding, cure, and machining cycles than conventional fan casings due to the integrated nature and construction of the abradable system. Moreover, because the sandwich structure core layer(s) can be made from any non-metallic, composite materials, the abradable systems herein can better absorb impact energy, yet still be lightweight. In particularly, the embodiments of abradable system described herein can absorb up to about 25% of the impact energy generated by a released fan blade, leaving only about 75% of the impact energy to be absorbed by the body of the fan casing. By “impact energy,” it is meant the kinetic energy of the released fan blade. This allows the thickness and, therefore, the weight, of fan casing  35  to be reduced. 
     Another benefit provided by the presently described embodiments is ease of repair. Those skilled in the art will understand that the entire abradable system  34  need not be removed and reapplied if the damage is limited to only a portion thereof. Rather, should a portion of the abradable system  34  become damaged by ice shedding, a fan blade out, or other like occurrence, that portion only can be replaced. Similar to fabrication, repair may be carried out in a couple of ways. In one embodiment, the damaged portion of the abradable system  34  can be machined, or cut, out of the fan casing  35  using conventional methods leaving a hole in the abradable system  34 . A sandwich structure segment, which can comprise any number of core layers  37  and facesheets  33  as needed, may then be shaped to the proper dimensions needed to fill the hole and to create a shaped sandwich structure  36 . The shaped sandwich structure  36  may then be positioned within the hole in the abradable system  34  and resin may be infused therein. The shaped sandwich structure  36  may then be cured to produce a fan casing  35  having a repaired integrated abradable system  34 . 
     In an alternate embodiment, the damaged portion of the abradable system  34  can again be machined out using conventional methods to create a hole in the abradable system  34 . A sandwich structure segment may be shaped to the proper dimensions need to fill the hole in the abradable system  34  and to create a shaped sandwich structure  36 . In this embodiment, the shaped sandwich structure  36  may first be infused with resin and cured before being placed into hole and bonded to the abradable system  34  to produce a fan casing  35  having a repaired integrated abradable system  34 . Those skilled in the art will understand that any acceptable adhesive or other like material may be used to bond the shaped sandwich structure  36  in the hole on the abradable system  34 . 
     Regardless of the method of repair utilized, after bonding the filler sandwich structure to the fan casing, a new abradable layer may be applied to the filler sandwich structure in the manner described previously. 
     The repaired fan casing having the integrated abradable system can provide all of the benefits described previously. In addition, the ability to repair only the damaged portion of the fan casing can reduce the time and expense that would otherwise be involved in replacing the entire abradable system. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.