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BR-102021003589-B1 - METHOD FOR MANUFACTURING A MONOLITHIC BOX-SHAPED STRUCTURE FOR AIRCRAFT FUSELAGS AND WINGS USING A FIBER-REINFORCED POLYMER MATRIX PREPREG MATERIAL

BR102021003589B1BR 102021003589 B1BR102021003589 B1BR 102021003589B1BR-102021003589-B1

Abstract

METHOD FOR MANUFACTURING A MONOLITHIC STRUCTURE, AND, MONOLITHIC STRUCTURE IN BOX SHAPE. The invention relates to a method for manufacturing a monolithic box-shaped structure (1) having a cavity (8) by subjecting a fiber-reinforced prepreg material to a curing operation. The method comprises the step of using two or more support tools (15) that are elongated and internally hollow, having a conformation complementary to that of the cavities (8) to be manufactured and a composition based on suitable reinforcing material and polymer to allow the transition from a rigid state to a flexible elastomeric state and vice versa in response to heating/cooling; the support tools (15) allow, in the rigid state, the direct lamination of the prepreg material on their outer walls (16) and are configured to consolidate the flexible elastomeric state at a temperature below the curing temperature and above 50°C; During the curing operation, curing pressure is applied both externally to the structure (1) being formed and internally to the support tools (15), whose walls (16) have become flexible, to push the prepreg material to be cured.

Inventors

  • STEFANO GIUSEPPE CORVAGLIA
  • Nicola Gallo
  • Danila FUGGIANO

Assignees

  • LEONARDO S.p.A

Dates

Publication Date
20260317
Application Date
20210225
Priority Date
20200226

Claims (8)

  1. 1. Method for fabricating a monolithic box-shaped structure (1) for aircraft fuselages (3a) and wings (3b) (4) using a fiber-reinforced polymer matrix prepreg material, the structure (1) comprising: an upper wall (5); a lower wall (6) facing the upper wall (5) and set back a non-zero amount from the upper wall (5); and at least one interconnecting element (7) extending transversely between the upper (5) and lower (6) walls, connected to them and delimiting with the upper (5) and lower (6) walls themselves the respective elongated cavities (8), the method comprising the steps of: a) providing at least two elongated support tools (15), each having a cross-section with an external polygonal profile complementary to the profile of the cavities (8) to be formed in the structure (1); b) externally arranging, on three adjacent walls (16) of each support tool (15), an elongated profiled bar (11) made of prepreg material, having a C-shaped cross-section and comprising a back part (12) and two end appendages (13) that protrude transversely from the back part (12) and arranged on the same side as the back part itself (12); c) joining the profiled bars (11) along their respective back parts (12) by placing the tools side by side. support (15) so that the profiled bars (11) themselves have opposite concavities; d) laminating one or more layers of prepreg material onto a lower plate (22) of a forming mold (21) to form a lower lining (6a) intended to constitute the lower wall (6) of the structure (1); e) insert the assembly formed by the support tools (15) and the profiled bars (11) in step c) into the lower lining (6a) carried by the lower plate (6) of the forming mold (21) and between the respective side plates (24) delimiting the forming mold itself (21), the profiled bars (11) being arranged with their respective end appendages (13) coplanar in contact with the lower lining (6a); f) laminate one or more layers of the pre-impregnated material onto an upper plate (23) of the forming mold (21) to form an upper lining (5a) intended to constitute the upper wall (5) of the structure (1); g) mount the upper plate (23) onto the side plates (24) of the forming mold (21) in a position facing the lower plate (22) so that the upper lining (5a) is placed in contact with the end appendages (13) of the profiled bars (11) opposite the appendages of end (13) in contact with the lower coating (6a); h) take the forming mold (21) thus prepared and filled with the upper and lower coatings (5a, 6a) and with the profiled bars (11) to autoclave to perform a curing operation at predefined curing temperature and pressure; characterized in that: the support tools (15) are internally hollow and have a composition based on reinforcing material and polymer suitable to allow the passage from a rigid state to a flexible elastomeric state and vice versa in response to heating and respectively cooling; the support tools (15) are configured to consolidate the flexible elastomeric state at a temperature lower than the curing temperature and higher than 50°C; step b) is performed by laminating the prepreg directly onto the outer surface of the walls (16) of the support tools (15) in a rigid state; during phase h), the curing pressure is applied both inside the forming mold (21) and inside the support tools (15), whose walls (16) are made flexible by the transition from the rigid state to the flexible elastomeric state and are therefore pushed by the curing pressure itself to adhere to the profiled bars (11) and to the lower (6a) and upper (5a) coatings.
  2. 2. Method according to claim 1, characterized in that it further comprises, prior to step h), the steps of: i) inserting into each support tool (15) at least one tubular bag (30) that protrudes from the respective opposite front and rear end portions (15a) of the support tool (15) itself; l) sealing, at each of the opposite front and rear ends (27, 28) of the forming mold (21), a first axial end (31) of a respective external tubular bag (32) suitable for positioning in use around the respective front and rear end portions (15a) of the support tools (15) that protrude from the forming mold (21) itself; em) seal the adjacent ends of the tubular bags (30) that protrude from the respective support tools (15) to each other and to the respective second axial ends (33) of the respective outer tubular bags (32) opposite the first axial ends (31), the curing pressure being applied inside the tubular bags (30).
  3. 3. Method according to claim 1 or 2, characterized in that step b) is preceded only by a step n) of applying a first resin-based adhesive agent at least to the parts of the walls (16) of the support tools (15) in the rigid state intended to receive the prepreg material.
  4. 4. Method according to any one of claims 1 to 3, characterized in that steps d) and f) are preceded by a step o) of applying a second resin-based adhesive agent at least to the lower (22) and upper (23) parts of the forming mold (21) intended to receive the prepreg material.
  5. 5. Method according to any one of claims 1 to 4, characterized in that the polymer of the support tools (15) is a thermosetting polymer or thermoplastic with shape memory.
  6. 6. Method according to any one of claims 1 to 5, characterized in that the reinforcing material of the support tools (15) includes one or more elastic fibers.
  7. 7. Method according to any one of claims 1 to 6, characterized in that at least two interconnecting elements (7) are formed, wherein, in step a), at least three elongated support tools (15) are provided, and, wherein, in step b), on the walls (16) of at least one of the support tools (15) two profiled bars (11) are directly rolled on opposite sides.
  8. 8. Method according to any one of claims 1 to 7, characterized in that it further comprises, after step h), a step p) of heating the support tools (15) to bring them into the flexible elastomeric state and extracting them from the respective cavities (8) of the newly formed structure (1).

Description

TECHNICAL FIELD [001] The present invention relates to a monolithic box-shaped structure made of composite material for aircraft fuselages and wings, in particular, for an aircraft horizontal stabilizer, to which the following description will explicitly refer without thereby losing generality. [002] The present invention also relates to a method for manufacturing the aforementioned monolithic box-shaped structure. FUNDAMENTALS [003] As is known, the horizontal stabilizer is a structural component with fixed surfaces that is generally part of the tail portion of an aircraft fuselage. [004] The stabilizer has inside a monolithic box-shaped structure made of composite material and essentially comprising: - an upper wall; - a lower wall facing the upper wall and set back a non-zero distance from it; and - a plurality of interconnecting elements or stringers that extend between the upper and lower walls and delimiting between themselves and the aforementioned upper and lower walls the respective elongated cavities, each extending between a front opening and a rear opening arranged in planes transverse to the walls themselves and to the stringers. [005] The use of composite material makes it possible to reduce the overall weight of the aircraft while at the same time obtaining very strong structures. [006] The upper and lower walls are approximately parallel and more precisely slightly convergent towards each other at the front openings or at the back openings. [007] The stringers consist of partitions that are substantially orthogonal, or more generally transverse, to the upper and lower walls. [008] The described structure is manufactured by means of a known method comprising the steps indicated below from a prepreg with a thermosetting matrix (resin) reinforced by fibers of different nature such as carbon fibers, aramid fibers, glass fibers, etc. [009] Firstly, each stringer, in the prepreg condition, is preformed in suitable preforming tools producing two elongated profiled bars having C-sections and consisting of a back part and two wings that project orthogonally from opposite end edges of the back part; in order to form a stringer, the two C-shaped profiled bars are joined together along their respective back parts so as to have opposite concavities. [0010] In particular, each C-shaped profiled bar is rolled on three flat faces of a preforming tool with a substantially parallelepiped profile; a first face of the tool is completely coated by the prepreg, while two other faces adjacent to the first face, orthogonal to it and parallel to each other, are coated only for a stretch. [0011] After the necessary vacuum consolidation and at a predetermined temperature, the C-shaped profiled bars are joined two by two in the manner described above to form the desired number of stringers, which are held in the predetermined position and distance for the subsequent curing step by the respective rigid support tools in the form of elongated pins. [0012] The preforming operation is a vacuum and temperature application process that allows the prepreg material to acquire a consolidated shape without undergoing a polymerization process. [0013] Each support tool consists of a rigid and solid elongated body, substantially parallelepiped-shaped, bounded by flat faces and having a cross-section corresponding to the shape of the elongated cavities of the structure to be manufactured. [0014] Before positioning each stringer, still in the form of a pre-formed prepreg, between two support tools, these are subjected to a preparation operation consisting of the following successive steps: - applying a layer of separation agent, for example, in the form of a film, to each support tool to facilitate the subsequent extraction of the support tool itself from the respective elongated cavity; - fitting a tubular bag into each support tool thus prepared, leaving an excess of this at each end of the support tool itself for a subsequent sealing operation; - wrapping each support tool and outside the tubular bag with a ventilation fabric, securing the flaps with a sealant; - fitting a tubular separation film into each support tool thus prepared, also leaving an excess of this at each end of the support tool itself for the subsequent sealing operation; - sealing the ends of the tubular bag and the tubular separation film by means of a sealant; - applying vacuum and waiting for the tubular separation film to contract the entire preparation on the relative support tool. [0015] At this point, the pre-formed stringers, each consisting of two C-shaped profiled bars joined together along their respective backs, are positioned between the support tools previously subjected to the preparation operation described above; in particular, each pre-formed stringer is arranged so that: - the backs of the relative pair of C-shaped profiled bars that constitute them are arranged between two facing flat faces of two mutually adjacent support tools; and - the win