Abstract:
An article is made by co-curing a lay up on a composite bond jig of fiber-reinforced composite materials having a lower layer, at least one elongated hollow mandrel of a stiffened graphite fabric having its lower surface adhered to the upper surface of the lower layer, and an upper layer adhered to the top and side surfaces of the hollow mandrel and at least portions of the upper surface of the bottom layer.

Description:
CROSS RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/087,488 filed Jun. 1, 1998 under 35 U.S.C. 119(e). 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of fabricating advanced composite aerostructure articles and more particularly, but not by way of limitation, to a method for fabricating an advanced composite aerostructure article having an integral co-cured fly away hollow mandrel. 
     2. Prior Art 
     There is a growing trend in the aerospace industry to expand the use of advanced composite materials for a diverse array of structural and dynamic aerostructural applications because of the strength-to-weight advantage provided by composite materials. One particular application for the use of such advanced composite materials lies in the fabrication of advanced composite articles such as panels for nacelles for aircraft jet engine propulsion systems. Such structural articles as fan cowls generally comprises inner and outer composite skins, which are formed from composite materials such as graphite or an aromatic polyamide fiber of high tensile strength that are embedded in a resinous matrix, e.g., epoxy, having a honeycomb core material interposed therebetween in the instance of a fuselage panel. 
     In the instance of an aerospace article such as a fan cowl, one or more stiffening members are affixed to the outer skin and covered with an inner skin for efficiently transmitting and/or reacting axial and/or bending loads to which the fan cowl is subjected. 
     There are two techniques currently employed for bonding through autoclave processing a composite stiffening member in combination with a composite structural panel: (1) the co-cured bonding method and (2) the secondary bonding method. Both methods are disadvantageous in requiring costly non-recurring tooling and/or costly recurring manufacturing steps. 
     A typical composite sandwich panel intended for use as an aerostructure article is normally fabricated using two autoclave cured inner and outer composite skins that are formed by using a curing cycle with heat, pressure, and a unique tool for each skin. A sandwich panel is then made up using a composite bond jig, tool or fixture with the pre-cured face skin laid-up on the bond jig tool followed by a ply of film adhesive, a honeycomb aluminum or non-metallic core of a given thickness, another ply of film adhesive and finally the previously pre-cured inner skin. The bond jig that is used to fabricate the sandwich panel is generally the same tool that was used to create the outer composite skin. A plurality of closure plies of uncured composite material are layed up and the assembled sandwich panel are cured during their final assembly stage. This sandwich panel is then vacuum bagged to the composite bond jig and again cured in an autoclave under high pressure and heat. 
     Thus, at least three very expensive and man-hour consuming cure cycles have gone into the fabrication of this exceptionally strong but lightweight composite/honeycomb core sandwich panel. At least two different and expensive tools are needed in this process. Manufacturing flow time is very long, energy use is high and the manufacturing floor space required is excessive. 
     The co-curing method envisions curing the composite inner and outer skins that are laid-up with a layer of adhesive film and honeycomb core in one cure cycle in the autoclave. A co-cured panel is desirable in that it is less expensive to fabricate since only one bond jig tool is required, only one cure cycle is needed, it is less labor intensive, it requires less floor space to accomplish, and a much shorter manufacturing flow time is achieved. However, co-curing an aerostructure panel has never achieved wide spread acceptance because of the large loss of panel strength and integrity that is lost due to the lack of compaction of the composite plies placed over and under the honeycomb core details. The composite plies dimple into the center of each core cell with nothing but the cell walls to compact the composite skins. The only way to overcome this knockdown factor is to add extra plies which creates both unwanted weight and excess cost. Thus, because of these constraints co-cured aerostructure panels are not widely manufactured in the aerospace industry. 
     There are other particular problems when a honeycomb core element is used to provide a stiffening element for an aerospace article such as a fan cowl. As Hartz et al described in U.S. Pat. No. 5,604,010 concerning a “Composite Honeycomb sandwich Structure”, with a high flow resin system, large amounts of resin can flow into the core during the autoclave processing cycle. Such flow robs resin from the laminate, introduces a weight penalty in the panel to achieve the desired performance, and forces over-design of the laminate plies to account for the flow losses. To achieve the designed performance and the corresponding laminate thickness, additional plies are necessary with resulting cost and weight penalties. Because the weight penalty is severe in terms of the impact on vehicle performance and costly in modem aircraft and because the flow is a relatively unpredictable and uncontrolled process, aerospace design and manufacture dictates that flow into the core be eliminated or significantly reduced. In addition to the weight penalty from resin flow to the core, it was discovered that microcracking that originated in the migrated resin could propagate to the bond line and degrade mechanical performance. Such microcracking potential has a catastrophic threat to the integrity of the panel and dictates that flow be eliminated or, at least, controlled. 
     Unfortunately, the use of honeycomb core as a stiffener for elements in a aerostructure article such as a fan cowl, or in a structural panel has other deleterious effects, two of the greatest drawbacks to aluminum core being its inherent significant cost and corrosion. To minimize galvanic corrosion of the core caused by contact with the face skins, isolating sheets are interposed between such aluminum core and the face skins. Also, the aluminum core has an inherent cost and also must be machined to a desired shape in an expensive process. The honeycomb core may also be subject to crush during manufacture and thereby limits the pressures that may be used in autoclave processing. Also, the honeycomb core if damaged in use has a spring back effect which makes the detection of such damage more difficult. Thus, the processing of an aerospace advanced composite article is limited to an autoclave pressure of not greater than 35 psi rather than an advanced pressure that would increase the strength of the resultant advanced composite article. 
     In providing reinforcing mandrels for stiffener elements, such as hat sections, for aerospace advanced composite structural panels it is also known to provide a composite stiffening member in the form of a polyimidide foam mandrel fabricated by machining a core mandrel to a desired shape. Obviously, the machining of the core mandrel is expensive and time consuming and further introduces the problem of properly bonding the core mandrel to inner and outer skins. 
     Therefore, a great need has arisen for a practical method of readily producing stiffened, fiber-reinforced composite structures useful in the construction of integrally stiffened components for aerospace applications which are cost and labor efficient and which save time in the fabrication process. 
     Accordingly, it is an object of the present invention to provide a method for fabricating aerostructure advanced composite articles that eliminates honeycomb core in stiffening elements, provides a lighter weight assembly and is easier to repair. 
     Another object of the present invention is to reduce the layup cost of known advanced composite co-cure assemblies by at least 15% and to increase assembly strength over such existing co-cure assembly by being able to utilize advanced pressures in autoclave processing. 
     Yet another object of the present invention is to improve the quality of assembly of such co-cured advance composite assemblies and thereby increase customer satisfaction. 
     A further object of the present invention is to provide a process that provides an assembly that can be manufactured in one manufacturing cell from raw material to final product. 
     Yet further objects of the present invention are to reduce the cost of post bond and final assembly work for the final co-cured assembly, which assembly will readily indicate damage to an improved stiffening element. 
     The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiments in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings. 
     SUMMARY OF THE INVENTION 
     The foregoing problems are overcome and other advantages are provided by a new and improved method for fabricating an advanced composite aerostructure article from fiber reinforced composite material and incorporating a hollow stiffened graphite fabric mandrel that becomes an integral part of such article. 
     In accordance with a preferred embodiment of the present invention, a suitable lay-up mandrel or composite bond jig (COBJ) having a predetermined upper lay-up surface receives a first composite uncured layer to provide one surface of a composite aerostructure article, the first uncured layer having at least one uncured resin-impregnated laminate layer. A bond jig may be referred herein as a tool or fixture or lay up mandrel. A hollow mandrel having a predetermined cross sectional shape is layed up on and adhesively tacked to the upper surface of such first uncured composite layer which preferably forms the outer skin of an aerospace article. The hollow mandrel is preferably a spirally wound longitudinally extending shaped formed of a stiffened graphite fabric layer. A second uncured composite layer additional plies of uncured campsite layers is assembled by lay up over the upper outer surface of the bond jig and at least a portion of the first uncured composite layer, the second uncured layer having at least one uncured resin-impregnated layer and, preferably, a plurality of plies that does not cover the open ends of the hollow mandrel. 
     A suitable flexible tube bag is then positioned within the hollow mandrel and extends beyond its open ends. A suitable vacuum bag is then placed over the lay-up assembled on the lay-up mandrel or bond jig and removably secured to such lay-up assembly and to the ends of the tube bag as by a suitable sealant tape which permits the ends of the hollow mandrel to remain open. The vacuum bag is exhausted to secure the lay-up assembly upon the lay up mandrel. The lay up assembled on the lay-up mandrel is then subjected in a suitable autoclave to a cure cycle of predetermined pressure and temperature to cure such resin impregnated layers to form a unitary co-cured one piece aerostructure article having a reinforcing hollow hat section provided therein. Since the ends of the hollow mandrel remain open during the cure cycle the lay-up assembly may be subjected to an increased pressure to strengthen the resultant article. Following the cure cycle the bond jig is removed from the autoclave and the co-cured article is removed from the bag and trimmed as desired. 
     The cross sectional area of the hollow mandrel may be varied as desired to provide a preferred shape that may provide a cross sectional area that may be changed to accommodate other structures that may be in close vicinity to such article in its ultimate use. 
     To accommodate the need to further strengthen the aerostructure article in certain areas where the configuration of aerospace article or part does not allow access for a tube bag to reach the outer periphery of a hollow mandrel, a hollow mandrel containing a suitable tube bag may be secured to the surface of the first uncured skin layer and in contact with spaced longitudinally extending reinforcing hat sections prior to application of the subsequent composite layers. In this instance, the internal air bag is provided with a suitable vent means extending through the hollow mandrel, the uncured “hat” plies of the second uncured layer and the primary vacuum bag to permit the interior of such bag to freely communicate with the atmosphere in the interior of the autoclave so that the pressure provided within such transversely provided hollow mandrel portion is the same as that pressure experienced on the exterior surface of the lay-up assembly. 
     A suitable tooling means such as a “throw in block” may be inserted in an end of a hollow mandrel during lay up, the tooling block being configured to allow installation of a tube bag through such block and the hollow mandrel and to provide a particular configuration for such end during the curing process. Thus, a suitable mechanical attachment such as a hinge or latch member may be easily secured to the end of the co-cured hat section without the necessity of providing shimming members as is now required for honeycomb core hat sections for advanced composite aerostructure articles. 
     The foregoing has outlined rather broadly the more pertinent and important features of the present invention in order the detailed description of the invention that follows may be better understood so that the present contribution to the art may be more fully appreciated. Additional features of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the disclosed specific embodiment may be readily utilized as a basis for modifying or designing other structures and methods for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions and methods do not depart from the spirit and scope of the invention as set forth in the happened claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a perspective of a co-cured aerospace article that has been fabricated by the method of a preferred embodiment of the present invention. 
     FIG. 2 is a cross sectional view of a longitudinal hat section of the article seen in FIG.  1 . 
     FIG. 3 is a cross sectional view of a hat section of the article seen in FIG.  1  and extending between spaced longitudinally extending hat sections. 
     FIG. 4 is a perspective of the hat section arrangement of FIG. 3 as disposed transversely between longitudinally extending reinforcing hat sections as shown in FIG.  2 . 
     FIG. 5 is perspective of the hollow mandrel used to reinforce the hat sections of FIGS. 2 and 3 and illustrating how it may be desirably deformed to provide desired form for such hat sections. 
     FIG. 6 is a perspective that illustrates the insertion of a removable tooling means into the end of a hollow mandrel to insure precise molding of such end. 
     FIG. 7 is a perspective of a typical mechanical means, such as a hinge attachment that may be inserted into such molded end of the hat section and secured to a co-cured aerostructure article. 
     FIG. 8 is a perspective that illustrates how a mechanical attachment may be inserted into and attached to the molded end of a hat section and also attached to a reinforcing longeron member. 
     FIG. 9 is a perspective that illustrates the insertion of a tube bag into and through the removable tooling means, seen in FIG. 8, that was inserted into a hollow mandrel. 
     FIG. 10 is a perspective that illustrates the sealing of a tube bag to a vacuum bag and the sealing of the vacuum bag to a bond jig. 
    
    
     Similar numerals refer to similar parts in the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings in detail and in particular to FIG. 1, the reference character  10  generally designates an aerostructure article constructed in accordance with a preferred embodiment of the invention. The article  10  is an advanced composite co-cured structure having a unitary skin  12  and circumferentially extending spaced reinforcing hat sections  14 ,  16 , and  18  for the illustrated exemplary part. The article  10  is shown as generally arcuate in shape since the illustrative example of the invention  10  shown in FIG. 1 is representative of a fan cowl for a aircraft turbofan jet engine but the use of the invention for the fabrication of aerostructure articles may extend to other shapes and applications. 
     An article  10 , as illustrated, may typically be provided with an aperture  20  for insertion of an access door (not shown) with reinforcing hat sections  22  and  24  extending transversely to and in fixed integral contact with the circumferentially extending reinforcing hat sections  16  and  18 . Suitable mechanical attachments  26  are provided to mate with and be fixedly secured to ends  28  of circumferentially extending hat sections  14 , 16  and  18 . The ends of such hat sections are precisely formed, as will be set forth in detail hereinafter, to permit attachment of the mechanical attachments  26  without requiring the use of shimming. In the particular illustration of the invention  10  in FIG. 1, the mechanical attachments  26  are shown as combined with an integral longeron member  30  for reinforcement purposes. The attachments  26  may be used for hinging the article  10  to another structure or for latching two such articles together or for other desired purposes. 
     Referring now to FIG. 2, the specific novel method of the present invention that is used to provide the novel reinforcing hat sections seen in FIG. 1 will be described. A suitable lay-up mandrel or composite bond jig (COBJ)  32  having a predetermined shape, such as that used to provide the arcuate shape of the skin  12  of the article  10  is provided for receiving a lay-up assembly for co-curing. A first uncured composite layer  34  is assembled on an upper surface of the lay-up mandrel  32  to provide the shape of at least one surface of the composite aerostructure article  10 . The first uncured layer  34  having at least one uncured resin-impregnated laminate layer that is generally a graphite or aramid fabric laminate layer that is termed a “pre-preg” in the advanced composite manufacturing industry. The first uncured composite layer  34 , which may have a plurality of uncured resin-impregnated laminate plies, will be seen to provide the outer skin of the article  10 . 
     A lightweight circumferentially extending hollow mandrel  36  is layed up on the first composite preform layer  34  by a suitable uncured tacking adhesive, not shown, such as EA9689 made by The Dexter Corp., Hysol Aerospace Products, 2850 Willow Pass Road, P.O. Box 3123, Bay Point, Calif. The hollow mandrel  36  is, in effect, “tacked” to the first preform layer  34  by the adhesive. As can be seen in FIG. 5, the hollow mandrel  36  is a pre-stiffened flexible spirally arranged shape that longitudinally extends along the upper surface of the layer  34 . The cross sectional shape of the hollow mandrel  36  may be determined to provide optimal stiffening of the hat section  14  of the article  10 . A preferred cross sectional form for the hollow mandrel  36  would be trapezoidal to provide the greatest strength but other shapes such as square, rectangular or round could be provided as desired. Another desirable feature of the hollow mandrel  36  is that the cross sectional shape may be varied during the length of a hat section to accommodate other needs. For example, if the article  10  were to be a fan cowl for an aircraft turbofan engine enclosure then the height of the hollow mandrel  36  could be decreased in areas to accommodate the space requirements of equipment carried by the core engine. 
     As seen in FIG. 5, the spiral wound configuration of the hollow mandrel  36  permits it to be flexed in a desirable direction, such as the arcuate shape of FIG. 1, or the sinuous shape of the mandrel as seen in FIG. 5. A pre-stiffened hollow mandrel  36  may be procured from AIRTECH International Inc., 2542 East Del Amo Blvd., P.O. Box 6207, Carson, Calif. The hollow mandrel  36  is pre-stiffened to the extent required to provide a desired hat configuration during the continuing fabrication of the article  10  as described hereinafter. 
     A second uncured composite layer  38  is then assembled on the lay up mandrel over the upper outer surface of the hollow mandrel  36  and over at least a portion of the first composite layer  34 . However, it should be recognized that the corners of the cross sectional shape of the hollow mandrel  36  are not sharp but are rounded as would be expected in the formation of the spirally wound hollow mandrel  36 . While the strength of a hat section fabricated with a hollow mandrel having rounded corners is sufficiently strong, the strength of such a hat section can be improved by providing, in effect, a fillet  37  along the longitudinal length of the intersection of the bottom of the hollow mandrel  36  and the first composite preform layer  34 . This fillet  37  may be advantageously provided by positioning a very small roll of graphite fiber fabric material or a small roll of unidirectional material or longitudinally extending strands of such material in the small circumferentially extending gap provided by a rounded corner of a hollow mandrel  36  and the first uncured composite layer  34 . The graphite fiber material of the fillet  37  may either uncured resin impregnated graphite material or a resin free graphite material. 
     The second uncured composite layer  38  is comprised of at least one ply of an uncured resin-impregnated graphite or aramid fabric material. Commonly, as is seen in FIG. 2, the first uncured composite layer  38  may comprise three layers, or as many as desired, of uncured resin-impregnated graphite or aramid fabric material or, as is commonly termed, “prepreg” material and provides the outer skin of the article  10 . 
     The lay-up assembly provided thus far by the novel method is then covered by a suitable vacuum bag  40  which is removably sealingly secured to the outer surface of the lay-up assembly and to the lay-up mandrel  32  as by a suitable sealant tape. The vacuum bag  40  is secured to the ends of the tube bag  48  and to the periphery of the bond jig  32  to permit the interior of a hollow mandrel  36  to communicate with the exterior of the vacuum bag  40  as will be described in greater detail with relation to FIG.  10 . The vacuum bag  40  is then exhausted to secure the lay up assembly upon the upper surface of the lay up mandrel or tool  32 . 
     The lay up assembly arranged on the mandrel  32  is then placed in a suitable autoclave and subjected to a suitable curing cycle having an elevated temperature and elevated pressure over a desired time period to provide for curing of the first and second composite layers  34  and  38  and the hollow mandrel  36  into a unitary co-cured one piece aerostructure article. Since the interior of the hollow mandrel  36  is open to the atmosphere of the autoclave, an increased pressure may be exerted upon the lay up assembly during the cure cycle since the increased pressure within the autoclave will be balanced by the pressure within the hollow mandrel  36  since the expanded tube bag  41  will conform to the interior shape of the hollow mandrel  36 . 
     Characteristically, an ultimate pressure of no greater than 45 psi may be used in the curing of an aerostructure article having a honeycomb core type hat section because of the possibility of crushing the core or causing dimpling of the plies overlying the core. In the practice of the novel method of the present invention this pressure in the autoclave can be increased to fall within a range of 45-70 psi for the curing cycle for resin impregnated graphite or aramid fabric material. Other higher pressures could be used for the curing cycle, as may be desired for other advanced composite materials. The use of an increased pressure provides for greater quality of the article and increased physical properties. It will be seen that the curing process will provide for the resins of the first and second composite preform layers  34  and  38  to penetrate the graphite fabric material of the hollow mandrel  36  and the tacking adhesive of flows as well to provide an integral co-cured article. 
     After the curing cycle has been completed in the autoclave the lay up mandrel is removed from the autoclave and the vacuum bag  40  is removed from the article  10  and the mandrel  32 . The article  10  may then be removed from the lay up mandrel  32  and suitably trimmed for further use. 
     As seen in FIG. 1, the present invention also provides for the interposing of reinforcing hat sections, such as hat sections  22  and  24  that are transversely disposed to circumferentially reinforcing hat sections  16  and  18 . Referring now to FIGS. 3 and 4, it will be seen that a pre-stiffened reinforcing hollow mandrel  42  of the hat section  24 , for example, is positioned on the first uncured composite layer  34  and extends transversely to and in contact with the adjacent sidewalls of the cross sectional shapes of the pre-stiffened hollow mandrels  44  and  46  that are respectively disposed in the hat sections  16  and  18  of the article  10 . The hollow mandrel  42  is composed of the same pre-stiffened graphite fabric material as the mandrels  44  and  46  and is trimmed to assure complete contact of its opposing end edges with the sidewalls of the mandrels  44  and  46 . To assure that the pressure experienced within the hollow mandrel  42  is the same as that provided within a curing autoclave a suitable flexible tube bag  48  is positioned within the hollow mandrel  42  before that mandrel is secured to first uncured composite layer  32  with a suitable adhesive. The flexible tube bag  48  is provided with a suitable vent means which is illustrated as a copper tube  50  or spru that extends from the interior of the flexible tube bag  48  through the second uncured composite layer and is sealed to the vacuum bag  40 . Thus, when the lay up assembly on the mandrel  32  is positioned within an autoclave and subjected to a curing cycle of elevated temperature and pressure, the ramp up of pressure within the autoclave will similarly be ramped up within the tube bag  48  with the tube bag  48  expanding to completely fill the cavity within the hollow mandrel  42  and preclude any portion of the mandrel  42  not be supported by a complementary air pressure during such cure cycle. 
     The arrangement seen in FIG. 4 is then covered with the second uncured composite layer  38  covering the hollow mandrels  42 ,  44  and  46  and at least a portion of the first uncured composite preform layer  34 . The vacuum bag  40  is provided over the lay up assembly and secured to the lay up mandrel  32  as before, with the ends of the tube bags positioned within the hollow mandrels  44  and  46  remaining open, and exhausted to firmly position the bond jig  32  prior to the lay up mandrel  32  being positioned in a suitable autoclave for subjecting the lay up assembly to a suitable co-cure cycle of elevated temperature and pressure. Following the cure cycle in the autoclave the bond jig  32  is removed from the autoclave and the vacuum bag  40  is removed from the co-cured aerostructure article and the vent means  50  may be removed, as desired, from the transversely extending hat section  42 . 
     Another advantageous feature of the present invention is illustrated in FIGS. 6 to  8 . Referring first to FIG. 6, it will be seen that novel invention is especially advantageous in providing for precise configurations of the end areas of the reinforcing hat sections for ease in positioning and securing desired mechanical attachments to the hat section and the co-cured first and second uncured composite layers. Such mechanical attachments may be used, as in the example of the fan cowl shown in FIG. 1, to provide hinge and latch connections for such fan cowl. After the hollow mandrel, shown by way of example to be mandrel  36 , has been tackingly adhesively secured to the first composite layer  34  and, either before or after the second composite layer  38  has been placed over the hollow mandrel  36  and a portion of the first composite layer, a suitable tooling means  52 , commonly termed a “throw-in block” is removably inserted into an end section of the hollow mandrel  36 . The dimensions of the tooling means  52  are chosen so as to provide a smooth precise interior surface of the interior of the hollow mandrel  36  following the curing cycle and a precise outer molded surface of the second composite layer  38 . 
     As seen, the tooling means  52  is provided with a suitable aperture  54  that permits the insertion of a tube inside the hollow mandrel  36  to provide communication of atmosphere imposed on the exterior of the lay up assembly with the interior of the hollow mandrel  36  during the cure cycle. Thus, when the curing cycle is completed the tooling means  52  is easily removed from the interior of the hollow mandrel  36 . A suitable mechanical attachment, such as the hinge member  56  shown in FIG. 7, may be easily inserted into the molded end portion of the hollow mandrel  36 . The hinge member  56  is provided with a hollow hat section portion  58  that may be inserted into the hollow mandrel  36  and an integral flange surface  60  that may be positioned on the first composite layer  34 , which is now the outer skin layer  12  of FIG. 1, by the illustrated mechanical attachments  62 . The hinge member  56  may also be provided with an additional flange surface  64  that may also be secured to a suitable longeron member  66  as shown in FIG. 8 for further reinforcement of the article  10 . It is to be understood that the particular arrangements illustrated in FIGS. 1 and 8 for attaching the aerostructure article  10  to other aerostructure components is intended to be exemplary and not limiting in any manner. 
     Referring now to FIG. 9 which is a perspective of the skin layer  34  having a fly away hollow mandrel  36  positioned thereon and an overlying hat section  38  laid thereover. A flexible tube bag  48  is seen extending through the hollow mandrel  36  and extending beyond the outer end of the throw in block  52  positioned in the end of the hollow mandrel  36 . While the flexible tube bag  48  is shown in its deformed state during assembly of the lay up on the bond jig  32  it is to be understood that after the lay up assembly has been vacuum bagged and positioned in an autoclave (not shown) the tube bag  48  will expand against the inner wall of the hollow mandrel  36  as the pressure within such autoclave is increased. 
     As seen in FIG. 10, after the lay up assembly of the aerospace article  10  has been completed the tube bag  48  is sealed to the mandrel  32  and to the overlying vacuum bag  40  by a suitable double sided sealant tape, which double sided sealant tape is also used to seal the vacuum bag at its periphery to the bond jig  32  in a manner known in the art. The bagged lay up assembly of the aerospace article  10  is then ready to be placed in a suitable autoclave for curing. 
     The present disclosure includes that contained in the appended claims as well as that of the foregoing description. Although this invention has been described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and numerous changes in the details of construction and combination and arrangement of parts and method steps may be resorted to without departing from the spirit and scope of the invention.