Abstract:
A structural component for an aircraft or spacecraft, comprising: a planar member; a reinforcing member which projects from the planar member and is rigidly connected thereto; the reinforcing member comprising at least a foam layer and a cover layer, a plurality of pins extending at least through the foam layer and the cover layer, and at least the pins and the cover layer comprising a curable matrix.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of and claims priority to PCT/EP2011/067464 filed Oct. 6, 2011 which claims the benefit of and priority to U.S. Provisional Application No. 61/390,793, filed Oct. 7, 2010 and German patent application No. 10 2010 042 128.6, filed Oct. 7, 2010, the entire disclosures of which are herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a structural component, an aircraft or spacecraft and a method. 
       BACKGROUND OF THE INVENTION 
       [0003]    Although applicable to any desired structural components and aircraft or spacecraft, the present invention and the set of problems on which it is based are described in greater detail in relation to a fuselage structure of an aircraft. 
         [0004]    Carbon-fibre-reinforced plastics material (CFRP) fuselage structures generally consist of planar members, in particular skin members, which are shaped in the manner of a tube. The planar members are reinforced internally in the longitudinal and peripheral direction by reinforcing members, in particular stringers and formers. The reinforcement members provide the required stability and rigidity, taking a considerable proportion of the loads. 
         [0005]    Modern CFRP fuselage structures generally reflect the construction of older metal fuselage structures. Because of the very different material properties, this approach leads to high manufacturing costs for CFRP fuselage structures. The high manufacturing costs result in particular from the fact that the methods used to manufacture the metal fuselage structures are not really applicable to a fibre composite material, in particular a thermosetting one Moreover, these “black metal” fuselage structures cannot fully exploit the typical advantages of anisotropic fibre composite materials, since they evolved from isotropic metals. For example, mass-produced parts, such as angle brackets, clips or the like, cannot really be made cost-effectively from fibre composite material. 
         [0006]    Further, sandwich constructions are used in the field of aviation, and are formed from an upper and a lower cover layer between which a honeycomb core structure is located to increase the rigidity. As an alternative to the honeycomb core structure, it has also become known to form the core structure from a rigid foamed material. As regards the thermal and acoustic insulation and the component manufacture, inter alia, the use of rigid foamed materials of this type has advantages over the use of honeycomb core structures. The poor mechanical properties by comparison with the honeycomb core structures are a drawback of the rigid foamed material core structures. Stitching processes, in which fibres are introduced into the cover layers and the rigid foamed foam, are used to compensate for these poor mechanical properties. After a resin infiltration process, the fibres which are embedded in the resin contribute to the mechanical reinforcement of the rigid foamed material, the fibres, along with the resin, forming what are known as “pins”. A method of this type is disclosed for example in DE 10 2005 024 408 A1. 
         [0007]    The use of sandwich constructions, as described above, is already a first step towards producing components which exploit the specific material properties of fibre composite materials. Currently, however, there are still no adequate solutions available which provide a structural component comprising a planar member and comprising a reinforcing member reinforcing said planar member, and which simultaneously exploit the specific material properties of fibre composite materials. 
       SUMMARY OF THE INVENTION 
       [0008]    An aspect of the present invention is therefore to provide a structural component, an aircraft or spacecraft, and a method which meet the aforementioned requirements. 
         [0009]    Accordingly, a structural component for an aircraft or spacecraft is provided, comprising: a planar member; a reinforcing member which projects from the planar member and is rigidly connected thereto; the reinforcing member comprising at least a foam layer and a cover layer, a plurality of pins extending at least through the foam layer and the cover layer, and at least the pins and the cover layer comprising a curable matrix. 
         [0010]    An aircraft or spacecraft comprising the structural component according to the invention is further provided. 
         [0011]    A method, in particular for manufacturing the structural component according to the invention, is further provided, comprising the steps of: applying a cover layer to a foam layer; introducing a plurality of pins into the foam layer and the cover layer; arranging the foam layer, the cover layer and the pins on a planar member so as to form a reinforcing member projecting from the planar member; infiltrating at least the cover layer and the pins with a curable matrix and curing said matrix; and connecting the reinforcing member to the planar member. 
         [0012]    The idea behind the present invention is to reinforce a planar member with a reinforcing member comprising a foam layer and pins. The reinforcing member is accordingly no longer formed in the manner conventional for “black metal” constructions, since reinforcing members of “black metal” constructions of this type have for example a T-shaped or Ω-shaped cross-section and are formed entirely of CFRP, whilst the invention provides a solution which takes into account the specific material properties of fibre composite materials. The pins advantageously contribute to the reinforcement of the structural component, in such a way that a highly mechanically efficient structure is achieved. 
         [0013]    Advantageous configurations of the invention are provided in the dependent claims. 
         [0014]    In the present context, a “pin” means a pin-shaped formation comprising fibres which extend in the longitudinal direction of the pin and are embedded in a matrix, in particular an epoxide and/or thermoplastic matrix. The pins may, as described in the introduction, be produced in the reinforcing member by a stitching process and a subsequent resin infiltration process. Alternatively, however, it is also possible to produce the pins in advance and subsequently to introduce them into the reinforcing member. For example, the pins may be produced in advance and pierced through the cover layer and the foam layer. 
         [0015]    In the present context, “curable matrix” is intended also to include a matrix which is already fully cured. 
         [0016]    It should be noted that the steps in the method according to the invention can be carried out in any desired order, and this order should not be considered to be predetermined by the use of any of the specific articles. Thus, for example, the step of infiltrating the cover layer and the pins with the curable matrix and curing said matrix may take place before the cover layer and pins are arranged, along with the foam layer, on the planar member. 
         [0017]    In one configuration of the structural component according to the invention, the pins also extend through the planar member, at least in part. This provides an even more stable structural component, since the pins are thus also anchored in the planar member. 
         [0018]    In a further configuration of the structural component according to the invention, the foam and/or the pins are connected, in particular glued, directly to the planar member. This results in a construction which is easy to manufacture. This is particularly appropriate if the foam layer is produced directly on the planar member, the cover layer is subsequently applied to the side of the foam layer remote from the planar member, and the pins are subsequently produced. In this case, the cover layer is preferably stitched to the planar member, the pins being produced by subsequent resin infiltration. 
         [0019]    In a further configuration of the structural component according to the invention, the reinforcing member comprises a further cover layer, which is arranged between the planar member and the foam layer and connected thereto, the cover layer likewise comprising a curable matrix. A construction of this type is particularly appropriate in a solution in which the reinforcing member is initially constructed from the cover layer, the foam layer, the further cover layer and the pins. For example, the cover layer may be stitched to the foam layer and if applicable to the further cover layer to produce the pins, and subsequently undergo resin infiltration. Subsequently, the reinforcing member formed in this manner is applied, in particular glued, directly to the planar member. 
         [0020]    In a further configuration of the structural component according to the invention, the pins extend through the further cover layer. Anchoring the pins in the further cover layer results in an even more stable structural component. 
         [0021]    In a further configuration of the structural component according to the invention, the cover layer, the further cover layer, the planar member and/or the pins comprise a fibrous material, in particular an interlaid scrim, woven fabrics and/or rovings, which is infiltrated by the respective matrix. An epoxy resin and/or thermoplastic matrix may be considered for the matrix. 
         [0022]    In a further configuration of the structural component according to the invention, two of the reinforcing members are provided, and cross at a crossing point, and at the crossing points, fibres which extend in the longitudinal direction of the respective reinforcing members are exclusively those which extend over the entire length of a respective reinforcing member. This prevents the fibres from being doubled up in the region of the crossing points, making it possible to reduce the weight and save material. 
         [0023]    In a further configuration of the structural component according to the invention, the planar member is formed as a skin portion and/or a plurality of reinforcing members are provided and together form a grid structure, in particular a diamond structure. With a grid structure of this type, a very stable structural component can be produced. The structural component is preferably formed as a fuselage barrel. 
         [0024]    In a further configuration of the method according to the invention, the pins are introduced by inserting prefabricated rigid pins, by stitching in fibres and/or incorporating fibres at least into the foam layer and the cover layer. With the aforementioned configuration, the pins can be produced in a simple manner. 
         [0025]    In a further configuration of the method according to the invention, a further cover layer is provided between the foam layer and the planar member and connected thereto. The further cover layer increases the stability of the structural component. 
         [0026]    In a further configuration of the method according to the invention, the pins are initially inserted into the foam layer and the cover layer and if applicable into the further cover layer, subsequently the foam layer or if applicable the further cover layer is connected to the planar member or the foam layer and the cover layer and if applicable the further cover layer are arranged on the planar member, and subsequently the pins are introduced into the foam layer, the cover layer, the planar member, and if applicable the further cover layer. This provides various efficient ways of producing the planar member comprising the reinforcing member. 
         [0027]    In a further configuration of the method according to the invention, the cover layer and if applicable the further cover layer are formed from a fibrous material, in particular a fibrous interlaid scrim, fibres of the fibrous material in particular extending exclusively in a respective longitudinal direction of two reinforcing members which are to be manufactured and parallel to this direction, triangular, diamond or rectangular regions being cut out of the fibrous material, longitudinal edges of the regions extending parallel to the respective longitudinal directions of the reinforcing members which are to be manufactured. This makes it possible to prevent fibres from being doubled up at crossing points of the reinforcing members in a simple manner, as described previously above. 
         [0028]    In a further configuration of the method according to the invention, the cover layer, the pins and if applicable the further cover layer are infiltrated with the matrix and/or cured at a first time, and the planar member is infiltrated with the matrix and cured at a second time, the first and second times being the same or different times. In other words, it is thus possible initially to cure the reinforcing member in advance and subsequently to apply it to the planar member, which has already been cured. Alternatively, the planar member and the reinforcing member can be cured simultaneously. For this purpose, the planar member and the reinforcing member are joined together while each uncured or only partially cured, and be cured together. As a further alternative, the at least incompletely cured reinforcing member can be applied to the cured planar member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    The invention is described in greater detail in the following by way of embodiments, with reference to the appended drawings, in which: 
           [0030]      FIG. 1  is a perspective view of a detail of a structural component according to an embodiment of the present invention; 
           [0031]      FIG. 2  is an enlarged view A from  FIG. 1 ; 
           [0032]      FIG. 3  is a section B-B from  FIG. 2  in one state of a method according to an embodiment of the present invention; 
           [0033]      FIG. 4  is the section B-B of  FIG. 3  in accordance with a variant B′-B′ of the method; and 
           [0034]      FIG. 5  is a plan view of a fibrous material for manufacturing reinforcing members of the structural component of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    In the figures, like reference numerals denote like or functionally equivalent components unless otherwise stated. 
         [0036]      FIG. 1  is a perspective view of a detail of a structural component  1  of an aircraft generally denoted as  2 . 
         [0037]    The structural component  1  comprises a planar member  3  and reinforcing members  4 ,  4 ′. The reinforcing members  4 ,  4 ′ are firmly attached to the planar member  3 . The reinforcing members  4 ,  4 ′ form a diamond structure having an angle α—see FIG.  2 —of between for example 15 and 45°, preferably between 30 and 40°. The angle α is the acute angle of a respective diamond  5 . 
         [0038]      FIG. 2  is an enlarged view A from  FIG. 1 . 
         [0039]    The reinforcing members  4 ,  4 ′ project from the planar member  3 . In other words, an underside  6 , concealed in  FIG. 2 , of each of the reinforcing members  4 ,  4 ′ lies on the planar member  3 , and an upper side  7  thereof is spaced apart from the underside  6  or upper side of the planar member  3  by a height H. The height H may for example be between 25 and 35 mm. Further, the reinforcing members  4 ,  4 ′ may have a width W of for example 35 to 70 mm. The height H and the width W relate in the above to a cross-section Q of a respective reinforcing member  4 ,  4 ′. In the present embodiment, the cross-section Q is rectangular in shape. However, other cross-sections are equally conceivable. The length L of a respective reinforcing member  4 ,  4 ′ can be anything from a few centimetres to several metres. 
         [0040]      FIG. 3  is a section B-B from  FIG. 2  in one state of a method according to an embodiment of the present invention. 
         [0041]    It can be seen from  FIG. 3  that the reinforcing member  4  is composed of an upper cover layer  11 , a lower cover layer  12 , and a foam layer  13  arranged between the cover layers  11 ,  12 . The cover layers  11 ,  12  each comprise a fibrous material  14 , described in greater detail below with reference to  FIG. 5 , which is embedded in an epoxy resin matrix. The foam layer  13  may in particular be a rigid foam. 
         [0042]    In the method steps preceding the state shown in  FIG. 3 , the cover layers  11 ,  12  are stitched to the foam layer  13  positioned between them by way of a stitching thread  15 , as is shown highly schematically on the left-hand side of  FIG. 3  by way of a dashed line. The stitching thread  15  is for example formed as roving, and therefore comprises a plurality of individual threads. The reinforcing member  4  formed in this manner is infiltrated with an epoxy resin matrix, the fibrous material  14  of the cover layers  11 ,  12  being infiltrated as well as the stitching thread  15 . Subsequently, the reinforcing member formed in this manner is cured, forming stable pins  16 . The pins  16  are of an elongate shape and may in particular be formed with a circular cross-section. The fibres in the respective pins  16  extend along the longitudinal direction L 1  thereof. The longitudinal direction L 1  of the respective pins  16  is preferably oblique to a normal S to the planar member  3 , for example at an angle β of between 10 and 80°. The stitching preferably takes place in the longitudinal direction of a respective reinforcing member  4 ,  4 ′, and this results in two parallel rows of pins  16 , as can be seen particularly clearly from  FIG. 2 . 
         [0043]    Subsequently, the formed reinforcing member  3  is cured. To provide the reinforcing member  4  with a corresponding shape, it can be oriented on a correspondingly contoured laminated device before being cured. In this way, a curved shape of the reinforcing member  4  can for example be achieved. 
         [0044]    After the reinforcing member  4  is cured, it is applied to the planar member  3 . The planar member  3 , which is in particular a fuselage outer skin, preferably likewise comprises a fibrous material which is embedded in an epoxy resin material. The planar member  3  is thus formed for example as a prepreg. After the reinforcing member  4  is applied to the planar member  3 , the planar member  3  is cured, whereupon the epoxy resin matrix in the planar member  3  connects it firmly to the reinforcing member  4 . 
         [0045]    However, a number of variants are possible in this context. For example, the cover layers  11 ,  12  may comprise a prepreg. Accordingly, the pins  16  may also be formed with an epoxy resin matrix which has not yet been cured. The reinforcing member  4  which has not yet been cured may thus be applied to the planar member  3  while still flexible. In a subsequent step, the structural component  1  formed in this manner is cured as a whole. As a further alternative, the reinforcing member  4 , which is provided with the matrix but has not yet been cured, could be placed on the planar member  3  which has already been cured, whereupon the structural component  1  formed in this manner is cured as a whole. 
         [0046]      FIG. 4  shows the section B-B of  FIG. 3  in accordance with a variant B′-B′ of the method. 
         [0047]    In this variant, the reinforcing member  4  is constructed on the planar member  3 . For this purpose, the foam layer  13  is applied directly to the planar member  3 . However, it would equally be possible also to apply the lower cover layer  12  to the planar member  3  beforehand, and only subsequently to apply the foam layer  13  to the lower cover layer  12 . Subsequently, the upper cover layer  11  is applied to the foam layer  13 . Subsequently, the upper cover layer  11 , the foam layer  13  and the planar member  3  are stitched together by means of the stitching thread  15 . After a corresponding infiltration with an epoxy resin matrix, the pins  16  are formed. The configurations and variants which were described previously in connection with  FIG. 3  can be applied correspondingly to the embodiment of  FIG. 4 . 
         [0048]    Instead of the stitching process, it is further conceivable to use a different type of process, in which the pins  16  are prefabricated so as already to be stable, and are subsequently inserted into the composite consisting of the upper cover layer  11 , the foam layer  13  and the planar member  3 . The prefabricated pins  16  are thus already cured. After the pins  16  are inserted, the epoxy resin matrix of the upper cover layer  11  of the planar member  3  and if applicable the lower cover layer  12  are subsequently cured. 
         [0049]    The pins  16  may moreover be formed by incorporating the fibrous material  15  into at least the foam layer  13  and the upper cover layer  11  by means of a needle, as disclosed in DE 10 2005 024 408 A1, of which the content to this effect is also the subject-matter of the present application. 
         [0050]    In the embodiments of  FIGS. 4 and 5 , the pins  16  may each extend through the upper cover layer  11 , the lower cover layer  12  and the planar member  3 , as is shown for two pins  16  in  FIG. 4 . 
         [0051]      FIG. 5  is a plan view of the fibrous material  14  for forming the grid-like reinforcing members  4 ,  4 ′. 
         [0052]    The fibrous material  14  is composed of fibres  21 ,  22 . The fibres  21  and  22  extend at the angle α to one another—see  FIGS. 2 and 5 . The fibres  21  and  22  may be interwoven. Alternatively, the fibres  21  and  22  may be part of different interlaid scrims which are positioned one above the other. The fibres  21  and  22  initially form a planar formation, for example an approximately rectangular formation.  FIG. 5  only shows parts of this formation. 
         [0053]    Subsequently, the diamond-shaped regions  5  are cut out from the formation—see  FIGS. 2 and 5 . For this purpose, the fibres  21  and  22 , shown in dashed lines in  FIG. 5 , are cut to length, in such a way that merely the fibres  21  and  22  shown as a solid line in  FIG. 5  remain. In  FIGS. 2 and 5 , the longitudinal direction of the reinforcing member  4  is denoted by the reference numeral L 2  and the longitudinal direction of the reinforcing member  4 ′ is denoted by the reference numeral L 3 . The cutting lines  26  and  27  parallel to the longitudinal directions L 2  and L 3 , for cutting out a respective diamond-shaped region  5 , are shown as a dot-dash line in  FIG. 5  for merely one of the regions  5 . 
         [0054]    In a plan view, the fibrous material  14  produced in this manner corresponds to the progression of the reinforcing member  4 ,  4 ′—see  FIG. 2 . The fibrous material  14  is distinguished in that there are no fibres doubled up at the crossing points  23 —see FIGS.  2  and  5 —between the fibres  24 , associated with the reinforcing member  4  and extending in the longitudinal direction L 2  thereof, and the fibres  25 , associated with the reinforcing member  4 ′ and extending in the longitudinal direction L 3  thereof. 
         [0055]    The fibrous material  14  may subsequently be used to form the upper cover layer  11  and if applicable the lower cover layer  12 . The fibre formation  14  is infiltrated with an epoxy resin matrix and subsequently used as described in connection with  FIGS. 3 and 4 . 
         [0056]    The presently used fibres are preferably carbon fibres, although inclusions of other fibres such as aramid fibres are also conceivable. Whenever reference is made to an epoxy resin matrix in the present document, this may also comprise a proportion of thermoplastic. 
         [0057]    Although the invention has been disclosed by way of preferred embodiments, it is not limited thereto, but can be modified in various ways. The embodiments and developments disclosed for the structural component according to the invention apply correspondingly to the aircraft or spacecraft according to the invention and to the method according to the invention, and vice versa. It should further be noted that in the present document, the term “a” does not exclude a plurality.