Composite structural elements

Abstract

The composite structural element comprises a flat main portion defining a coordinate system having a first axis extending along the longitudinal axis of the structural element and a second axis perpendicular to the longitudinal axis and defining an angle of +90° with the first axis, the structural element comprising a layup having single plies each consisting of a fiber reinforced composite material having a unidirectional fiber orientation, the layup comprising N plies arranged from top to bottom in the following form, N being a positive integer equal to or greater than 5: [[α, β] M ; [γ] K ; [β, α] M ], α, β and γ represent the angles enclosed by a ply between the first axis and the corresponding unidirectional fiber orientation of a ply, [x] y refers to y layers each with an angle x; [x, y] z Refers to z pairs of plies, each pair of plies having angles x and y, respectively; α = -20°, β = 40°, γ = -75° or α = 20°, β = -40°, γ = 75°, each angle having a tolerance of -5° to +5°; K is a positive integer equal to or greater than 1, M is a positive integer equal to or greater than 1, and N = 4·M+K.

Description

Technical Field

[0001] The present disclosure generally relates to a composite structural element (eg, for use as a rib or spar) having high resistance to shear buckling and post-buckling.

[0002] For example, the present disclosure also relates to shear loaded composite laminates. These are suitable for aircraft components, such as spars and ribs, for example, but not limited thereto. Shear loaded panels are also widely used in fields such as civil engineering, automotive or ship design. Background Art

[0003] Figure 1 A graphical representation of the behavior of a composite element under shear loading as defined in the present disclosure is shown. That is, the term "buckling" refers to a loss of structural (mechanical) stability. This means that for a certain load level (the so-called eigenvalue level), a non-planar deflection of the in-plane loaded panel may occur. The directions of the 0° and 90° ply orientation angles are also given by Figure 1 The arrows on the right show that the angles of a fiber reinforced composite material having a ply with a substantially unidirectional fiber orientation can be defined relative to the 0° direction.

[0004] Figure 1 The first buckling mode of a long angle-ply (with the angle of -45° or +45°, which can be arranged in alternating ply pairs) with 16 plies and belonging to a symmetrically laid-up 2 mm thick panel is shown for in-plane shear loading (large arrow). The shear flow is constant.

[0005] Furthermore, the term "post-buckling" refers to the deformation of a structure in the form of both deflection and in-plane displacement under loads above the buckling level.

[0006] In the prior art, there is a conventional lay-up of laminates with angles of 0° / 45° / 90° / 135°. This means laminating plies with angles of 0°, 45°, 90° and 135° respectively.

[0007] According to US 7,840,389 B2 and US 7,668,701 B2, there is prior art in the field of layup selection for composite boards / panels referring to post-buckling. However, this prior art does not contain a specific solution with layup angle values.

[0008] According to US 8,306,789 B2 there is also prior art in the field of layup selection methods for composite panels not concerned with post-buckling in general. The prior art only describes a design optimization method / process without any specific solution with layup angle values ​​(for post-buckling resistance).

[0009] According to US 8,556,213 B2 there is prior art in the field of layup selection methods for composite panels designed only to resist buckling without taking post-buckling into account.

[0010] Furthermore, the lay-up solution disclosed herein is based on patent EP 2 910 365 B1 assigned to the present applicant (hereinafter referred to as “prior art document 1”) and on the theoretical results of the paper by S. Selyugin entitled “ON LAY-UP OPTIMIZATION OF ANISOTROPIC COMPOSITE PLATES IN POST-BUCKLING” in the proceedings of the 17th European Conference on Composites (ECCM17) in Munich from June 26 to 30, 2016 (hereinafter referred to as “prior art document 2”). Summary of the invention

[0011]

[0006] Therefore, there is a need for implementation of a solution that avoids one or more of the problems discussed above or other related problems.

[0012] This disclosure is intended to:

[0013] • Providing a symmetrical layup of composite structural elements with high resistance to both shear buckling and post-buckling. That is, the present disclosure is directed to providing an optimized layup solution for shear loaded composite laminates operating in the "above buckling" range post-buckling.

[0014] As indicated above, a shear loaded (bidirectional) panel with a symmetrically laid-up rectangle is considered. Without loss of generality, it is assumed that the panel according to the disclosure operates above buckling without breaking (with loads up to 1.5 times the buckling level). It must be noted that this value is only an example applied, for example, to aviation, and is by no means a limitation of the present disclosure.

[0015] For example, such a plate could model the interval between the stiffeners of the ribs and spar of an aircraft vertical tail plane (VTP).

[0016] In addition, the present disclosure achieves the following advantages:

[0017] The proposed lay-up solution significantly improves the post-buckling load carrying capacity of a structural element (eg a composite structural element) in two shear loading plane directions, where the buckling load levels in these loading directions are nearly equal and close to the maximum level.

[0018] The proposed solution can result in structural weight savings of up to 10% compared to prior art designs.

[0019] • For the same level of shear loading (in both directions), the solution of the present disclosure results in approximately 50% lower maximum post-buckling deflection and maximum post-buckling minimum principal strain (compared to the prior art angle-ply construction).

[0020] Buckling levels (two loading directions approximately equal) are within a few % and much higher than in prior art angle-ply layups. The plies in the proposed layup above several [-75°] plies close to the mid-plane are subjected mainly to bending-distortion due to shear buckling as starting point for post-buckling analysis. They are pairs of plies [-20°, +40°] (with possible deviations of + / -5°). The plies near the mid-plane are subjected to 2D strains in the best way and the later strains are important for post-buckling.

[0021] • The lay-up solution according to the present disclosure can be implemented for shear loaded composite structural elements, particularly VTP ribs and spars.

[0022] • The lay-up solution according to the present disclosure improves the post-buckling load carrying capacity of the structural element in both loading directions, where the buckling load levels of these loading directions are nearly equal and close to the maximum level.

[0023] • The lay-up solution according to the present disclosure combines both buckling and post-buckling high performance for both loading directions.

[0024] One or more of the problems stated above are solved by the subject-matter of the independent claims. Developments are set forth in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the technology presented herein are described below with reference to the accompanying drawings, in which:

[0026] Figure 1 A diagram showing the behavior of a composite element under shear loading as defined in the present disclosure;

[0027] Figure 2 shows a main device embodiment of a composite structural element according to the present disclosure;

[0028] Figure 3 A modification of the composite structural element of the present disclosure is shown;

[0029] Figure 4 shows a rib according to a first embodiment example of a composite structural element according to the present disclosure;

[0030] Figure 5 shows a spar according to a second embodiment example of a composite structural element according to the present disclosure;

[0031] Figure 6shows a torsion box according to a third embodiment example of a composite structural element according to the present disclosure;

[0032] Figure 7 A first embodiment of a ply arrangement for a composite structural element is shown;

[0033] Figure 8 A second embodiment of a ply arrangement for a composite structural element is shown;

[0034] Fig. 9 A third embodiment of a ply arrangement for a composite structural element is shown;

[0035] Fig.10 A fourth embodiment of a ply arrangement for a composite structural element is shown; and

[0036] Fig.11 A fifth embodiment of a ply arrangement of a composite structural element is shown. DETAILED DESCRIPTION

[0037] Without loss of generality, the present disclosure can be summarized as follows: The purpose of the present disclosure is, for example, to give engineers simple rules for selecting symmetrical non-conventional lay-ups with high resistance to both buckling and post-buckling. The lay-up solution significantly improves the post-buckling load carrying capacity of structural elements in both loading directions, where the buckling load levels for these loading directions are nearly equal and close to the maximum level. According to current analysis, the proposed solution can lead to structural weight savings of up to 10% compared to today's designs.

[0038] According to a first aspect, a composite structural element is disclosed, comprising a substantially flat main portion defining a coordinate system having a first axis extending along a longitudinal axis of the structural element and a second axis extending in the flat main portion perpendicular to the longitudinal axis and defining an angle of +90° with the first axis, wherein the structural element comprises a layup having single plies each consisting of a fiber reinforced composite material having a substantially unidirectional fiber orientation, wherein the layup comprises N plies arranged from top to bottom in the following form, N being a positive integer equal to or greater than 5: [[α, β] M ; [γ] K ; [β, α] M ], where α, β and γ represent the angles enclosed by one ply between the first axis and the corresponding unidirectional fiber orientation of the one ply, [x] y refers to y layers each with an angle x, [x, y] zIt refers to z pairs of plies, each pair of plies has an angle x, y, α = -20°, β = 40°, γ = -75° or α = 20°, β = -40°, γ = 75°, each angle has a tolerance of -5° to +5°, and K is a positive integer equal to or greater than 1, and M is a positive integer equal to or greater than 1, as shown below: N = 4·M+K.

[0039] According to a first improvement of the first aspect, the composite structural element preferably has the following structure: [[α, β] M ; [α]; [γ] K ; [α]; [β, α] M ], where N = 2 + 4·M + K.

[0040] According to a second improvement of the first aspect, the composite structural element preferably further comprises at least one additional ply having an angle δ enclosed between the first axis and the unidirectional fiber orientation of the at least one additional ply, wherein δ is preferably 90° near the mid-plane, -20° away from the mid-plane or any other value, and the at least one additional ply is inserted between one or more of the N plies, and the stacking comprises N+P plies, P being a positive natural number equal to or greater than 1 and specifying the number of additional plies. In this case, the stacking preferably comprises N plies arranged from top to bottom in the following form: [[α, β] M , [δ] L , [γ] K , [δ] P , [γ] K , [δ] L , [β, α] M ], where N = 4*M + 2*L + 2*K + P. In addition or alternatively, K is preferably equal to or lower than N / 3, more preferably equal to or lower than N / 4. This second improvement leads to a general lay-up in which the basic lay-up has some limitations despite the symmetry and covers all possible numbers of layers in the lay-up under the condition that the number of layers with angle γ = -75° becomes too high. And, for manufacturing stability reasons, several (preferably a few) plies (plies with an angle of preferably 90° near the mid-plane, plies with an angle of preferably -20° away from the mid-plane, or plies with preferably other orientations) are added to the laminate between some layers, but the symmetry of the entire lay-up is maintained. This more general lay-up is preferably defined as: [[α, β] M , [δ] L , [γ] K , [δ] P , [γ] K , [δ] L , [β, α] M]. In this respect, the following preferably applies: α=-20°, β=40°, γ=-75°, δ=-20° or 90° or any other angle, preferably 90° close to the center (or midplane) and -20° away from the center (or midplane), wherein each angle has a tolerance of -5° to +5°, and K is a positive integer equal to or greater than 1, and M is a positive integer equal to or greater than 1, L has a value of 0 or 1, and P has a value of 0, 1 or 2. The layup comprises N=4*M+2*L+2*K+P.

[0041] According to a second aspect, there is provided a torsion box for use in an aircraft structural component, the torsion box comprising at least one rib being a composite structural element according to the first aspect and at least one spar being a composite structural element according to the first aspect.

[0042] According to a third aspect, there is provided an aircraft comprising a torsion box according to the second aspect.

[0043] Furthermore, it will be appreciated by those skilled in the art that the services, functions, and steps explained herein may be implemented using software acting in conjunction with a programmed microprocessor, or using an application specific integrated circuit (ASIC), a digital signal processor (DSP), or a general purpose computer. It will also be appreciated that, while the following embodiments are described in the context of methods and apparatus, the techniques presented herein may also be implemented in a computer program product, and in a system comprising a computer processor and a memory coupled to the processor, wherein the memory is encoded with one or more programs that perform the services, functions, and steps disclosed herein. This is particularly applicable to aspects of (adaptively) controlling the manufacturing process and / or analysis process of the composite structural elements pertaining to the present disclosure.

[0044] In the following description, for purposes of explanation rather than limitation, specific details are set forth in order to provide a thorough understanding of the technology presented herein. It will be apparent to one skilled in the art that the technology may be practiced with other embodiments that deviate from these specific details.

[0045] In the following, the so-called post-buckling ratio (PBR) (i.e., the load level above a predetermined high buckling load) is considered up to 1.5. This is a level used, for example, in the aerospace industry to analyze load carrying capacity in post-buckling. Simple support boundary conditions (as the most conservative) are considered throughout this disclosure.

[0046] Figure 2 A main device embodiment of a composite structural element according to the present disclosure is shown.

[0047] like Figure 6The composite structural element 12, 14 is used, for example, as a rib 12 or a spar 14 (described later). The structural element 12, 14 comprises a substantially flat main portion 22 (see also Figure 4 ), which defines a coordinate system having a first axis a extending along the longitudinal axis L of the structural elements 12, 14 and a second axis b extending perpendicularly to said longitudinal axis L in the flat main portion and defining an angle of +90° with the first axis a.

[0048] Further, the structural element 12, 14 comprises a layup 28 having individual plies 30, 34, 36, 38 each consisting of a fiber reinforced composite material having a substantially unidirectional fiber orientation 32, wherein the layup 28 comprises N plies (N being a positive integer equal to or greater than 5) arranged from top to bottom in the following form: [[α, β] M ; [γ] K ; [β, α] M ].

[0049] Here, α, β and γ represent the angles that a ply 30, 34, 36 has between the first axis a and the corresponding unidirectional fiber orientation 32 of the ply, such as Figure 2 In addition, the symbol “[x] y " refers to a number y of plies each having an angle x, and the notation "[x, y] z " refers to a number of z pairs of plies, each pair of plies having angles x and y, respectively. Figure 2 As shown, the order of x, y specifies the order of lamination (defined from top to bottom): [α, β] represents a ply with angle α followed by a ply with angle β, while [β, α] represents a ply with angle β followed by a ply with angle α.

[0050] Furthermore, the angle α is equal to -20°, the angle β is equal to 40°, and the angle γ is equal to -75°. Alternatively, the angle α is equal to 20°, the angle β is equal to -40°, and the angle γ is equal to 75°. The tolerance of each of the above angles is -5° to +5°.

[0051] Finally, the parameters of the above formula are set as follows. K is a positive integer equal to or greater than 1, and M is a positive integer equal to or greater than 1. Further, N is equal to 4·M+K.

[0052] In other words, the final layup 28 preferably has a [[[-20°, +40°] M ; [-75°] K ] S ] type arrangement, where the symbol [x] S This means that the ply arrangement x is mirrored relative to the plane of symmetry or the midplane, see e.g. Figure 7 .

[0053] It is worth noting that the following layup 28 solution is also valid when mirrored about the X axis a or Y axis b:

[0054] [[[20°, -40°] M ; [75°] K ] S ]or

[0055] That is, in other words, based on the inventors' research, the following layup 28 selections are proposed. The layup 28 that results in the best post-buckling performance (for both deflection and compressive strain) and high buckling loads is as follows. As a constraint, without loss of generality, the overall laminate thickness preferably ranges from 5 plies up to a total thickness of 5 mm, and the panel aspect ratio preferably ranges between 1.5 and 4. The panel preferably models the entire span of, for example, an aircraft VTP rib and wing spar. The PBR is preferably up to 1.5. The individual ply thickness is preferably equal to or less than 0.25 mm.

[0056] Therefore, the proposed layup 28 is one in which, symmetrically, a number of plies close to the mid-plane are [-75°] plies (having a practically small effect on the buckling level), the other plies counted from the mid-plane are pairs of [-20°, +40°] (these pairs represent average, layup-imparted, equal buckling levels for both loading directions). The permissible deviation for all the above angles is + / -5°. Further, up to 25% of the plies close to the mid-plane are preferably [-75°] plies. In other words, the above parameter K is preferably equal to N / 4 but lower than N / 3. The higher the PBR, the larger K must be.

[0057] Furthermore, in the composite structural element 12, 14, the more general layup 28 preferably has the following structure: [[α, β] M ; [α]; [γ] K ; [α]; [β, α] M ], where N = 2 + 4·M + K.

[0058] In other words, the layup 28 preferably also has an arrangement of an odd number of plies, such as [[-20°, +40°] M ;-20°;[-75°] K ; -20°; [+40°, -20°] M ] or [[-20°, +40°] M ; [-75°] K ; [+40°, -20°] M], where K is an odd number in the latter case. It is worth noting that the more general solution of stacking 28 also works when mirrored about the X axis a or Y axis b: [[20°, -40°] M ; 20°; [75°] K ; 20°; [-40°, 20°] M ] or [[20°, -40°] M ; [75°] K ; [-40°, +20°] M ], where K is an odd number in the latter case.

[0059] Figure 3 A modification of the composite structural element of the present disclosure is shown.

[0060] This improvement leads to a general lay-up in which the basic lay-up has some limitations despite the symmetry and covers all possible numbers of plies in the lay-up under the condition that the number of plies with angle γ = -75° becomes too high. Also, for manufacturing stability reasons, several (a few) plies (plies with angle preferably 90° near the mid-plane, plies with angle preferably -20° away from the mid-plane, or plies with preferably other orientations) are added to the laminate between some plies, but the symmetry of the whole lay-up is maintained.

[0061] The general tiling is preferably defined as: [[α, β] M , [δ] L , [γ] K , [δ] P , [γ] K , [δ] L , [β, α] M ], where α = -20°, β = 40°, γ = -75°, δ = -20°, 90° or another value, preferably 90° near the center and -20° away from the center. Preferably, each angle has a tolerance of -5° to +5°, and K is a positive integer equal to or greater than 1, while M is a positive integer equal to or greater than 1, L has a value of 0 or 1, and P has a value of 0, 1 or 2. The lay-up preferably comprises N = 4*M+2*L+2*K+P. Furthermore, K is preferably equal to N / 4 and lower than N / 3.

[0062] That is, the composite structural element preferably further comprises at least one additional ply 38 having an angle δ enclosed between the first axis (a) and the unidirectional fiber orientation 32 of the at least one additional ply. δ is preferably 90° near the center and -20° away from the center or any other value. Without loss of generality, as Figure 3As shown, a ply 38 is preferably inserted between the outermost ply 36 having an angle γ and the ply 34 having an angle β (or the top single ply 30 having an angle α), while another ply 38 is preferably inserted centrally between several plies 36 having an angle γ, but always following the symmetry of the entire layup.

[0063] That is, the at least one additional ply 38 is preferably inserted between one or more of the N plies. Further, the stack preferably includes N+P plies, where P is a positive natural number equal to or greater than 1 and specifies the number of additional plies 38 .

[0064] Figure 4 The rib 12 of the first embodiment example of the composite structural element according to the present disclosure is shown, and Figure 5 A spar 14 is shown according to a second embodiment example of a composite structural element of the present disclosure. Figure 6 Further shown is a torsion box 10 according to a third embodiment example of a composite structural element according to the present disclosure.

[0065] That is, the torsion box 10 (eg, for use in an aircraft structural component such as a VTP) includes at least one rib 12 as the above-mentioned composite structural element and at least one spar 14 as the above-mentioned composite structural element.

[0066] In this regard, Figure 6 1 is a perspective view of a torsion box 10, for example, for a vertical tail plane (VTP) of an aircraft. The torsion box 10 comprises two types of composite structural elements (as described above), which are designed to have a generally longitudinal shape and take the form of a respective Figure 6 The form of the ribs 12 and the spar 14 is shown in relation to the longitudinal axis L.

[0067] In the following, the torsion box 10, the ribs 12 and the spar 14 will be described in the context of an aircraft embodiment. Therefore, the present disclosure also covers an aircraft comprising the torsion box 10 described in the present disclosure. However, this does not exclude the possibility of other fields of implementation. For example, the present disclosure is preferably applicable to a ship structure comprising at least one composite structural element as described herein. Further, the present disclosure is preferably applicable to a beam or a shear connector plate used in civil engineering or the automotive industry, comprising at least one composite structural element as described herein.

[0068] With respect to, for example, a forward flight direction Fd of an aircraft, when installed in the aircraft, the torsion box 10 is arranged with the spars 14 extending substantially transversely to the forward flight direction Fd and the ribs 12 extending substantially parallel to said forward flight direction Fd. Figure 6In the embodiment of the present invention, the left spar 14 thus defines the trailing edge and the right spar 14 thus defines the leading edge of the torsion box 10. The ribs 12 are preferably arranged to extend between the spars 14 and are preferably connected thereto, for example by conventional means. Thus, the ribs 12 and the spars 14 are preferably arranged in a substantially cross-direction or net-like / grid-like manner to define the torsion box 10. Thus, two adjacent ribs 12 and two opposing portions of the spars 14 preferably define a substantially rectangular hollow space 16 within the torsion box 10.

[0069] The torsion box 10 is preferably Figure 6 The wing box 10 is completed by thin-walled sheets or skins, not shown, covering the top and bottom surfaces of the torsion box 10. These skins are preferably further reinforced by girders extending substantially parallel to the spar 14.

[0070] like Figure 6 As further shown in FIG. 1 , the ribs 12 and the spars 14 are preferably equipped with a plurality of stiffeners 18 extending substantially transversely to the respective longitudinal axes L and distributed along these longitudinal axes L. In the following, the area between two adjacent stiffeners 18 is referred to as an “interval 19 ”. For the purpose of illustration, only one stiffener 18 and one interval 19 are provided with reference numerals for only one of these ribs 12 and these spars 14 .

[0071] Figure 5 Describes in more detail Figure 1 The spar 14 of the torsion box, the orientation of which corresponds to Figure 6 The orientation of the right spar 14 in FIG. Figure 5 In the figure, without loss of generality, the spar 14 is shown in a partial perspective view and is configured to have a C-shaped profile. The spar 14 thus comprises upper and lower flange portions 20, and a flat main portion 22 configuring a web portion of the spar 14, extending between the flange portions and substantially transverse to the flange portions. Within the flat main portion 22, the stiffener 18 is preferably arranged to delimit a plurality of zones 19.

[0072] In addition, the main loads imposed on the spar 14 during aircraft operation and the stresses generated thereby are Figure 5 14. The top row of arrows A pointing upwards indicates the direction of the main air loads acting on the spar 14. In addition, two arrows B extending parallel to the longitudinal axis L indicate additional forces exerted on the spar 14. The main shear forces generated by the forces according to arrows A and B are indicated by arrows C with asymmetric tips extending in different directions within the flat main portion 22 and the interval 19. Of course, there may be additional loads acting on the spar 14, for example, compressive forces in the direction opposite to arrow A, which are mainly compensated by the reinforcement 18.

[0073] Moreover, in Figure 5 , a coordinate system is shown, comprising a first axis a extending along the longitudinal axis L and defining an angle of 0° and a second axis b extending perpendicularly to the longitudinal axis L in the flat main portion 22. Thus, the second axis b defines an angle of +90° with the first axis a. Figure 5 As shown, the second axis b is parallel to the arrow A and extends in the direction of the corresponding main air load. Figure 5 The coordinate system of is consistent with the coordinate system described above in the context of composite structural elements.

[0074] With respect to this coordinate system, direct shear loading resulting in positive shear forces and shear flows is defined as resulting in a positive shear angle in the coordinate system, i.e., according to Figure 5 The shear angle caused by the force of arrow B in FIG. The opposite shear loading leading to negative shear flow occurs in the opposite case, that is, when arrows B point in opposite directions, respectively.

[0075] With respect to the prevailing stresses within the flat main portion 22, it is therefore apparent that high resistance to buckling is preferred to counteract both direct and opposite shear loading.

[0076] Figure 4 yes Figure 6 Detailed view of the ribs 16 of the torsion box 10 and the main loads and stresses associated therewith. In order to avoid repetitions, identical features are associated with the same reference symbols in the following compared to the previous description.

[0077] Figure 4 1 shows a side view of the rib 12 as shown through the extension of the longitudinal axis L. The rib 12 is preferably configured to have a slightly oval shape and an I-shaped cross section ( Figure 4 ). Therefore, in Figure 4 At the upper and lower edges in the rib 12, the rib 12 is preferably provided with a flange portion 20, and a main plane portion 22 forming a web portion extending therebetween. At the outer end of the rib 12 along the longitudinal axis L, a connecting portion 24 is provided, which is complementarily shaped relative to the C-shaped profile of the spar 14 for connection thereto. In addition, along the flange portion 20, several receiving portions 21 are preferably provided to receive the longitudinal beams, respectively, when attached to the top and bottom panels, which form the skin of the torsion box 10.

[0078] Similar to combining Figure 5The spar 14 in question exerts a main air load indicated by arrow A on the rib 12 in a direction substantially transverse to the longitudinal axis L. Furthermore, the force indicated by arrow B is exerted in the direction of the longitudinal axis L, thereby causing main shear forces according to arrows C in the web portion 22 of the rib 12 in two different directions. Likewise, the coordinate system is defined by a first axis a extending along the longitudinal axis L of the rib 12 and defining an angle of 0°, while a second axis b extends perpendicularly to said longitudinal axis in the flat main portion 22 and defines an angle of 90° with the first axis a. In the case shown, the second axis b extends parallel to the arrow A and therefore in the direction of the corresponding main air load.

[0079] To compensate for the primary shear loads as discussed with reference to the previous figures, the ribs 12 and spars 14 are constructed as unitary components (composite structural elements) and are made from a layup 28 having a single ply of fiber composite material as described above and further below.

[0080] Figure 7 A first embodiment of a ply arrangement of composite structural elements 12, 14 following a basic lay-up is shown.

[0081] like Figure 7 As shown, the first row of the table evaluates the general prior art with respect to positive and negative loading (as described above). The general prior art teaches that for this experiment, a symmetrical layup consists of plies in the form of: [-45°, 45°] 4S , which means that (from top to bottom) 4 pairs of [-45°, 45°] plies are arranged, followed by 4 pairs of [-45°, -45°] pairs.

[0082] Furthermore, as shown in the second row of the table, an arrangement as in Patent Document 1 was evaluated. This arrangement has a ply arrangement of the following type: [-20°, 40°] 4S (meaning that 4 pairs of [-20°, 40°] plies are arranged (from top to bottom), followed by 4 pairs of [20°, -40°] pairs), resulting in almost equal high buckling levels in both loading directions (Prior Art Document 1). In the embodiments of the present disclosure, this arrangement is used as an initial analysis reference.

[0083] That is, a direct search for a solution according to the present disclosure with high resistance to post-buckling was conducted by varying the ply orientation near the mid-plane. The results further presented correspond to a target accuracy of 1%-2% (the minimum values ​​of the maximum deflection and the maximum compressive strain become below 5·10 -3 ).

[0084] With respect to the present application shown in the third row, the analysis performed showed that the orientation angle values ​​of several near mid-plane layers should be equal to each other and equal to [-75°], as described above.

[0085] In summary, the composite structural element 12, 14 based on 16 plies preferably has the following structure: [[-20°, 40°] 3; [-75°] 4; [40°, -20°] 3]. Other possible arrangements of other thicknesses and numbers of plies are preferably:

[0086] [[-20°, 40°] 5, [-75°] 4, [40°, -20°] 5] or

[0087] [[-20°, 40°]2, [-75°]2, [40°, -20°]2].

[0088] As experimental constraints, the material chosen was 0.125 mm T300 / 5208 type tape and a symmetrical lay-up was used. The plate thickness was t=2 mm, the plate dimensions were 200 x 600 mm and a shear flow loading of 50 N / mm was applied (both positive and negative directions).

[0089] As shown above, the evaluation is constructed as:

[0090] First row: As above, apply [-45°, +45°] 4S The conventional prior art of arrangement.

[0091] · Second row: As mentioned above, the prior art arrangement of Patent Document 1 is [-20° / 40°] 4S .

[0092] Third row: the preferred arrangement of the present disclosure, in this case [[-20°, 40°]3, -75°, -75°] S , meaning a symmetrical arrangement of (from top to bottom) 3 [-20°, 40°] ply pairs, followed by 4 [-75°] plies, and in turn followed by 3 [40°, -20°] ply pairs.

[0093] The first entry in each cell shows the maximum deflection (mm), while the second entry shows the maximum compressive strain (a dimensionless quantity).

[0094] The corresponding eigenvalues ​​for this angle-ply solution (depending on the sign of the loading) are 1.39 / -1.79. As further shown in the table, the load level corresponds to PBR = 1.5 times level 1.75, or 2.625.

[0095] The lay-up 28 solution (third row) outperforms the conventional state-of-the-art in terms of maximum deflection and maximum compressive strain [-45°, +45°]4S method and provides a considerable improvement over the method of Patent Document 1 (second row). It is thus documented that the insertion of multiple [-75°] plies provides a surprising beneficial effect in terms of post-buckling elasticity.

[0096] Figure 8 A second embodiment of a ply arrangement for a composite structural element is shown, which follows a more general formula. Figure 8 As shown, the composite structural elements 12, 14 preferably have the following structure:

[0097] [[-20°, 40°] 4, [-20°], [-75°] 6, [-20°], [40°, -20°] 4]

[0098] Another example layup 28 is:

[0099] [[-20°, 40°]2, [-75°]2, [40°, -20°]2] or

[0100] [[-20°, 40°] 4, [-20°], [-75°] 6, [-20°], [40°, -20°] 4] or

[0101] [[-20°, 40°] 4, [-75°] 2, [90°] 2, [-75°] 2, [40°, -20°] 4] or

[0102] [[-20°, 40°]4, [-75°], [-90°], [-75°]2, [-90°], [-75°], [40°, -20°]4].

[0103] As experimental constraints, the material chosen was 0.125 mm T300 / 5208 type tape and a symmetrical lay-up was used. In this case, the plate thickness was t=3 mm, the plate dimensions were 200 x 600 mm, and a shear flow loading of 50 N / mm was applied (both positive and negative directions).

[0104] As shown above, the evaluation is constructed as:

[0105] First row: As above, apply [-45°, +45°] 4S The conventional prior art of arrangement.

[0106] · Second row: As mentioned above, the prior art arrangement of Patent Document 1 is [-20° / 40°] 4S .

[0107] Third row: preferred arrangement of the present disclosure, in this case [[-20°, 40°]3, -20°, [-75°]3] S, meaning a symmetrical arrangement of (from top to bottom) 4 [-20°, 40°] ply pairs, followed by 1 [-20°] ply, followed by 6 [-75°] plies, followed by 1 additional [-20°] ply, and in turn followed by 4 [40°, -20°] ply pairs.

[0108] The first entry in each cell shows the maximum deflection (mm), while the second entry shows the maximum compressive strain (a dimensionless quantity).

[0109] The corresponding eigenvalues ​​for this angle-ply solution (depending on the sign of the loading) are 4.92 / -5.84. As further shown in the table, the load level corresponds to PBR=1.3 (for the "weak" direction of the conventional arrangement in the first row) times the level 4.92, or 6.396.

[0110] Here too, the lay-up 28 solution (third row) outperforms the conventional state-of-the-art in terms of maximum deflection and maximum compressive strain [-45°, +45°] 4S method and provides a considerable improvement over the method of Patent Document 1 (second row). It is thus documented that the insertion of multiple [-75°] plies provides a surprising beneficial effect in terms of post-buckling elasticity.

[0111] for Figure 8 To become more realistic in implementation, it is preferred to add some extra plies between the [-75°] plies in order to increase manufacturing stability.

[0112] Fig. 9 A third embodiment of a ply arrangement for a composite structural element is shown. Figure 8 In agreement, the composite structural elements 12 , 14 preferably have the following structure: [[α, β] 4; [α] 1; [γ] 6; [α] 1; [β, α] 4].

[0113] As experimental constraints, the material chosen was 0.125 mm T300 / 5208 type tape and a symmetrical lay-up was used. In this case, the plate thickness t = 3 mm, the plate dimensions in this case were 200 x 400 mm, and 50 N / mm shear flow loading (both positive and negative directions) was applied.

[0114] As shown above, the evaluation is constructed as:

[0115] First row: As above, apply [-45°, +45°] 4S The conventional prior art of arrangement.

[0116] · Second row: As mentioned above, the prior art arrangement of Patent Document 1 is [-20° / 40°] 4S .

[0117] Third row: preferred arrangement of the present disclosure, in this case [[-20°, 40°] 4, -20°, [-75°] 3] S , meaning a symmetrical arrangement of (from top to bottom) 4 [-20°, 40°] ply pairs, followed by 1 [-20°] ply, followed by 6 [-75°] plies, followed by 1 additional [-20°] ply, and in turn followed by 4 [40°, -20°] ply pairs.

[0118] The first entry in each cell shows the maximum deflection (mm), while the second entry shows the maximum compressive strain (a dimensionless quantity).

[0119] The corresponding eigenvalue (depending on the sign of the loading) for this angle-ply solution is 5.5 / -6.5. As further shown in the table, the load level corresponds to PBR=1.3 (for the "weak" direction of the conventional arrangement in the first row) times the level 5.5, or 7.16.

[0120] Here too, the lay-up 28 solution (third row) outperforms the conventional state-of-the-art in terms of maximum deflection and maximum compressive strain [-45°, +45°] 4S method and provides a considerable improvement over the method of Patent Document 1 (second row). It is thus documented that the insertion of multiple [-75°] plies provides a surprising beneficial effect in terms of post-buckling elasticity.

[0121] for Fig. 9 The solution is similar to Figure 8 Further, with Figure 8 Consistently, in order to make the solution more realistic in terms of implementation, it is preferred to add some extra plies between the [-75°] plies in order to increase manufacturing stability.

[0122] Fig.10 A fourth embodiment of a ply arrangement of a composite structural element is shown. The composite structural element preferably has the following structure: [[α, β] 3; [γ] 4; [β, α] 3].

[0123] As experimental constraints, the material chosen was 0.125 mm T300 / 5208 type tape and a symmetrical lay-up was used. The plate thickness t = 2 mm, in this case the plate dimensions were 200 x 400 mm and a 50 N / mm shear flow loading (both positive and negative directions) was applied.

[0124] As shown above, the evaluation is constructed as:

[0125] First row: As above, apply [-45°, +45°] 4SThe conventional prior art of arrangement.

[0126] · Second row: As mentioned above, the prior art arrangement of Patent Document 1 is [-20° / 40°] 4S .

[0127] Third row: preferred arrangement of the present disclosure, in this case [[-20°, 40°] 3, [-75°] 2] S , meaning a symmetrical arrangement of (from top to bottom) 3 [-20°, 40°] ply pairs, followed by 4 [-75°] plies, and in turn followed by 4 [40°, -20°] ply pairs.

[0128] The first entry in each cell shows the maximum deflection (mm), while the second entry shows the maximum compressive strain (a dimensionless quantity).

[0129] The corresponding eigenvalue (depending on the sign of the loading) for this angle-ply solution is 1.56 / -2.00. As further shown in the table, the load level corresponds to PBR = 1.5 times level 1.83, or 2.745.

[0130] The lay-up 28 solution (third row) outperforms the conventional state-of-the-art in terms of maximum deflection and maximum compressive strain [-45°, +45°] 4S method and provides a considerable improvement over the method of Patent Document 1 (second row). It is thus documented that the insertion of multiple [-75°] plies provides a surprising beneficial effect in terms of post-buckling elasticity.

[0131] Fig.10 The result is similar to Figure 7 The results in which the dimensions of the strip are 200x600 mm.

[0132] Fig.11 A fifth embodiment of a ply arrangement for a composite structural element is shown. In particular, Fig.11 The weight saving capability is shown as the prior art + / -45° 16 plies can be replaced by 15 plies according to the present disclosure.The composite structural elements 12, 14 preferably have the following structure: [[α, β] 3; [γ] 3; [β, α] 3].

[0133] As experimental constraints, the material chosen was 0.125 mm T300 / 5208 type tape and a symmetrical lay-up was used. The plate thickness t = 2 mm, in this case the plate dimensions were 200 x 400 mm and a 50 N / mm shear flow loading (both positive and negative directions) was applied.

[0134] As shown above, the evaluation is constructed as:

[0135] First row: As above, apply [-45°, +45°] 4S The conventional prior art arrangement of has a total of 16 plies.

[0136] · Second row: The preferred arrangement of the present disclosure, in this case [-20°, 40°]3, [-75°]3, [-20°, 40°]3, meaning a symmetrical arrangement of (from top to bottom) 3 [-20°, 40°] ply pairs, followed by 3 [-75°] plies, and in turn followed by 3 [40°, -20°] ply pairs, with a total of 15 plies.

[0137] The first entry in each cell shows the maximum deflection (mm), while the second entry shows the maximum compressive strain (a dimensionless quantity).

[0138] The corresponding eigenvalue (depending on the sign of the loading) for this angle-ply solution is 1.56 / -2.00. As further shown in the table, the load level corresponds to PBR = 1.5 times level 1.56, or 2.184.

[0139] The Lay-up 28 solution (second row) is significantly different from the conventional state-of-the-art in terms of maximum deflection and maximum compressive strain at [-45°, +45°] 4S Methods are comparable, but provide improvements in weight savings: The results of this table show that the method of the present disclosure has a 6.3% weight reduction compared to the conventional prior art. It is therefore documented that the insertion of multiple [-75°] plies provides a surprising benefit not only in terms of post-buckling resilience, but also in terms of weight savings.

[0140] It is believed that from the foregoing description, the advantages of the technology presented herein will be fully understood, and it will be apparent that various changes can be made to the form, construction and arrangement of the exemplary aspects of the present disclosure without departing from the scope of the present disclosure or sacrificing all of its beneficial effects. Because the technology presented herein can be varied in many ways, it should be recognized that the present disclosure should be limited only by the scope of the appended claims.

Claims

1. A composite structural element (12, 14) comprising a substantially flat main portion (22) defining a coordinate system having a first axis (a) extending along a longitudinal axis (L) of the composite structural element (12, 14) and a second axis (b) extending perpendicularly to the longitudinal axis (L) within the flat main portion and defining an angle of +90° with the first axis (a), wherein the composite structural element (12, 14) comprises a layup (28) having single plies (30, 34, 36) each consisting of a fiber reinforced composite material having a substantially unidirectional fiber orientation (32), wherein the layup (28) comprises N plies arranged from top to bottom in the following form, N being a positive integer equal to or greater than 5: [[a, b] M ;[c] K ;[b, a] M ], among them: α, β and γ represent the angles one ply (30, 34, 36) has between said first axis (a) and the corresponding unidirectional fiber orientation (32) of said one ply, [x] y refers to y plies each having an angle x; [x, y] z It refers to z pairs of plies, each pair of plies having angles x and y respectively; α=-20°, β=40°, γ=-75° or α=20°, β=-40°, γ=75°, wherein each angle has a tolerance of -5° to +5°; and K is a positive integer equal to or greater than 1, and M is a positive integer equal to or greater than 1, as shown below: N=4·M+K.

2. The composite structural element according to claim 1, having the following structure: [[a, b] M ;[a];[c] K ;[a];[b,a] M ], among them: N=2+4·M+K.

3. The composite structural element according to claim 1, further comprising: at least one additional ply (38) having an angle δ enclosed between the first axis (a) and the unidirectional fiber orientation (32) of the at least one additional ply, wherein: δ is -20°, 90° or another value; The at least one additional ply is interposed between one or more of the N plies; and The stack includes N+P plies, where P is a positive natural number equal to or greater than 1 and specifies the number of additional plies (38).

4. The composite structural element according to claim 3, wherein the layup (28) comprises N plies arranged from top to bottom in the following form: [[a, b] M ,[d] L ,[c] K ,[d] P ,[c] K ,[d] L ,[b, a] M ], among them: L is 0 or 1; P is between 0 and 2; and N=4*M+2*L+2*K+P.

5. A composite structural element according to any one of the preceding claims, wherein: K is equal to or lower than N / 3.

6. The composite structural element according to claim 5, wherein: K is equal to or lower than N / 4.

7. A torsion box (10) for use in an aircraft structural component, comprising: at least one rib (12) which is a composite structural element (12, 14) according to any one of the preceding claims; as well as At least one spar (14) being a composite structural element (12, 14) according to any one of the preceding claims.

8. An aircraft comprising a torsion box according to claim 7.

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