CORE FOR SLIDEBOARD AND ASSOCIATED SLIDEBOARD

Abstract

The invention relates to a core (1000) for a board, comprising a lower face defining a plane (P) having a longitudinal axis oriented along the length of the board and a transverse axis oriented along the width of the board, the core (1000) having a thickness measured along a direction perpendicular to said lower face of the core (1000), said core (1000) comprising: at least one plywood element of a first type (100) having alternating layers (101) having wood fibers oriented along the longitudinal axis and layers (102) having wood fibers oriented along the transverse axis, and at least one plywood element of a second type (110) having alternating layers (111) of wood fibers oriented along the longitudinal axis and layers (112) having wood fibers oriented along the thickness of the core (1000). Figure for the abstract: Fig 1

Description

Title of the invention: CORE FOR SLIDE BOARD AND ASSOCIATED SLIDE BOARD technical field

[0001] The invention relates to the field of sliding boards, in particular snow sliding boards.

[0002] More specifically, it aims at a new core structure comprising plywood elements, enabling the board to have good mechanical properties, particularly in terms of resistance to compression, torsion, and bending. Prior techniques#:

[0003] Generally, a ski board has a core extending over almost the entire length of the board, and whose role is essentially to give thickness to the ski, by separating mechanical reinforcements and keeping them away from the neutral fiber.

[0004] The cores can be formed by injecting components that react together to form a foam into the board mold or into a specific mold for obtaining the core. Another technique consists of cutting and machining the core prior to molding. The invention relates more specifically to this family of cores.

[0005] These cores can therefore be made of various materials, such as, for example, a polymer foam or, more frequently, wood.

[0006] These cores are therefore produced during a pre-molding operation, and they are cut and machined so that their external contours correspond to the desired volume, in order to sufficiently separate the fibrous reinforcements that come into contact with it.

[0007] Generally, prior art wood-based cores are formed from a set of wood strips oriented along a longitudinal axis of the board and glued together. The resulting panel is called a laminated / glued panel.

[0008] By way of example, document FR843973 describes a ski consisting of a wooden core formed by wood strips oriented along the longitudinal axis of the board and glued together. These wood strips are made from solid wood with wood fibers oriented along the axis of the board's thickness. The board also comprises a thinner bottom and top layer with wood fibers oriented longitudinally; these layers act as reinforcements, a base, and a top layer.

[0009] Such a core provides the board with good compressive strength. However, the board is not suitable for resisting significant torsion or bending.

[0010] There are also cores formed from thin layers of wood superimposed and bonded together during molding.

[0011] Thus, document DE 295 02 290 describes a snowboard incorporating a core made up of a superposition of layers of wood whose wood fibers are oriented, in turn, along the longitudinal axis of the snowboard, along the transverse axis^ 90°, and along the diagonals, i.e. about plus or minus 45°.

[0012] Such a stacking allows for uniform behavior of the board on snow or water, since the wood fibers have several preferred orientations, angularly distributed. Furthermore, the manufacture of such a snowboard requires particularly meticulous and delicate handling, which increases the manufacturing cost.

[0013] However, such a core does not allow the board to have good resistance to compression, nor to improve the mechanical properties of the board, particularly in bending and torsion.

[0014] The technical problem that the invention aims to solve is therefore to develop a core giving a board good mechanical properties in compression, bending and torsion. Description of the invention

[0015] To solve this problem, the invention proposes to develop a core for a sliding board, comprising an upper face and an lower face intended to come into contact with the sliding base, the lower face defining a plane comprising a longitudinal axis oriented along the length of the board and a transverse axis, oriented along the width of the board, the core having a thickness measured along a direction perpendicular to said lower face of the core.

[0016] Such a kernel comprises:

[0017] - at least one plywood element of a first type comprising a alternating layers with wood fibers oriented along the longitudinal axis and layers with wood fibers oriented along the transverse axis, and - at least one plywood element of a second type comprising alternating layers of wood fibers oriented along the longitudinal axis and layers with fibers oriented along the thickness of the core.

[0018] In other words, the element of the first type, which comprises an alternation of wood fibers oriented along the transverse axis and along the longitudinal axis of the core, makes it possible to provide resistance to torsion and bending.

[0019] The element of the second type, which comprises an alternation of wood fibers oriented in the direction of the thickness and along the longitudinal axis of the core, makes it possible to provide resistance to compression and bending.

[0020] Thus, the combination of these two elements within the core makes it possible to obtain good resistance in all three spatial directions, that is, in the direction of the core's thickness, length, and width. The core's mechanical resistance is thus improved in compression, bending, and torsion.

[0021] In addition, the choice of the arrangement of the elements, in relation to each other, makes it possible to favor areas of the core which require particular reinforcement.

[0022] For example, the center of the boot (CM), which designates a reference point on the ski indicating to the boot fitter where to place the binding device so that the ski boot is approximately centered around this reference point, can be reinforced. Indeed, this area of ​​the ski corresponds to the area subjected to the greatest compressive stress, as it is the skier's point of support. It is therefore desirable to prioritize a large proportion of the second type of element in this area.

[0023] On the contrary, the front contact point (PA), which designates the point of contact of the ski with the ground, can be reinforced against bending. Indeed, this area of ​​the ski corresponds to the area subjected to the most bending and torsional stresses, for example, to follow the geometry of the ski slope. It is therefore desirable to prioritize a large proportion of the first type element in this area.

[0024] Furthermore, plywood is a robust material, easy to work with, and does not warp under the effects of heat or humidity. Since skis, snowboards, and surfboards are subjected to humid environments such as snow or seawater, the properties described above make plywood an ideal material for constructing board sports equipment.

[0025] Plywood is also preferred because it fits in with the current trend towards a return to more durable, environmentally friendly, and easily recyclable materials.

[0026] In practice, the layers forming the plywood elements are between 1 and 3 mm thick. The thinness of each layer allows for greater flexibility and better cohesion between the different layers. Choosing the thickness of each layer of plywood allows for adjusting the rigidity in bending / compression or bending / torsion of the plywood elements used to form the core.

[0027] According to another characteristic, the elements of the first and second type each have an odd number of layers.

[0028] An odd number of layers allows the same type of layer to be found on the outer walls of the element in question. The plywood element It thus features a plane of symmetry at its center, with the layers distributed symmetrically around this plane. Consequently, the mechanical properties of the plywood element are also symmetrical about this plane, which reduces the risk of damaging the core. Indeed, unevenly distributed stresses on the core can create irreversible cracks or deformations, degrading the board's performance or even rendering it unusable.

[0029] The elements of the first and second type can be positioned in the ski mold directly on top of each other or next to each other without any particular interface element.

[0030] In practice, in order to facilitate their assembly or mechanical connection with each other, the elements of the first and second type can advantageously be separated by an intermediate layer of adhesive.

[0031] Alternatively, the elements of the first and second type are preferably separated by an intermediate reinforcing layer that can be made of a material included in the group including metals and high-tenacity fibers such as glass fibers and basalt fibers.

[0032] High-tenacity fibers have excellent tensile and compressive strength, while maintaining good flexibility and lightness. In addition, the fiber impregnation resin can also provide a bonding function.

[0033] The addition of an intermediate layer thus allows a degree of flexibility and a certain freedom of movement between two elements of different types, in order to improve the transmission of forces between these two elements.

[0034] Depending on the number and arrangement of the elements of the first and second type, the intermediate layer may comprise fibers oriented along the longitudinal axis or fibers oriented along the transverse axis. Thus, the mechanical strength properties are improved in the preferred fiber direction.

[0035] In a particular embodiment, the intermediate layer may comprise both fibers oriented along the longitudinal and transverse axes.

[0036] There are several embodiments that allow the development of kernels that meet the problems stated above.

[0037] According to a first embodiment, the core comprises an element of the first type and an element of the second type, the element of the first type being at least partially covered by the element of the second type.

[0038] Such a core therefore comprises an element of the first type, covering the entire width of the core and intended to absorb the torsional and bending forces suffered by the board in order to stabilize the race of a user, and an element of the second type, superimposed on the element of the first type, narrower and intended to resist the compressive forces exerted on the sliding board.

[0039] In practice, at the median longitudinal level of the core, the second type element covers between 30 and 80% of the upper surface of the first type element. The mid-length of the core is intended to be located near the support area of ​​the ski boot. Thus, due to its proximity to the boot's support area, this zone requires compression reinforcement, which explains the coverage ratio of the second type element.

[0040] In certain embodiments of this first embodiment, the element of the first type may have a constant thickness, the element of the second type then having a variable thickness to follow the thickness profile of the core.

[0041] Alternatively, the element of the second type may have a constant thickness, the element of the first type having a variable thickness to adapt to the thickness of the core.

[0042] According to a second embodiment, the core comprises two elements of the first type and one element of the second type, the element of the second type being arranged in the central area of ​​the core, the elements of the first type being arranged on either side of the element of the second type.

[0043] Such a core therefore comprises a central element designed to resist the compressive forces exerted on the board. The lateral elements are designed to absorb the torsional and bending forces experienced by the board in order to stabilize the user's movement.

[0044] In a particular embodiment of this second embodiment, the element of the second type may have a height greater than that of the lateral elements of the first type.

[0045] This specific shape of the element of the second type adapts to the final thickness of the board and makes it possible to prioritize the compressive strength of the core.

[0046] Furthermore, according to another characteristic, at the median longitudinal level of the core, the element of the second type covers between 50 and 70% of the total width of the core.

[0047] According to the invention, the median longitudinal plane of the core corresponds to the mid-length of the core. In various embodiments, the mid-length of the core may not correspond to the mid-length of the ski. In practice, the mid-length of the core is generally located at the front of the ski's runner, that is, at the front of the ski boot's support area. Thus, preferably, due to its proximity to the boot's support area, this area is reinforced in compression, which explains the occupancy rate of the second type of element.

[0048] In certain embodiments, the element of the second type may have a constant width along the entire length of the core, while the elements of the first type have a variable width to follow the profile of the dimension line. The element The first type is then, preferably, parallelepiped in shape, the elements of the second type having an internal side of straight shape and an external side of curved shape, to follow the dimension line.

[0049] In the context of the invention, the core sidecut corresponds to the profile of the core's width evolution along the core's longitudinal axis. Preferably, the core sidecut corresponds to that of the ski.

[0050] Alternatively, the elements of the first type may have a constant width along the entire length of the core, while the element of the second type has a variable width to follow the profile of the dimension line. The element of the first type then has two curved sides, and the elements of the second type also have two curved inner sides and one curved outer side, to follow the shape of the element of the first type. The elements of the first type are then curved to conform to the curved lateral shapes of the central element of the second type.

[0051] According to another aspect, the invention relates to a sliding board comprising a core as described above. Brief description of the figures

[0052] The invention will be well understood, and its advantages and various other features will become apparent, from the following description of some non-limiting embodiments, with reference to the accompanying schematic drawings, in which:

[0053] [Fig. 1] [Fig. 1] is a perspective view of a portion of the core of the invention according to a first embodiment,

[0054] [Fig.2] Fig.2 is a perspective view of a portion of the core of the invention according to a second embodiment,

[0055] [Fig.3] [Fig.3] is a cross-sectional view at the middle of the shoe, of a sliding board including a core according to the first embodiment of [Fig.1].

[0056] [Fig.4] The [Fig.4] is a cross-sectional view at the middle of the shoe, of a sliding board including a core according to a variant of the first embodiment of the [Fig.1],

[0057] [Fig. 5] [Fig. 5] is a top view of the embodiment of the core illustrated in [Fig. 1], and

[0058] [Fig.6] [Fig.6] is a side view of the embodiment of the core illustrated in [Fig.1]. Description of the implementation methods

[0059] For clarity, we define a frame Oxyz and planes xy, yx and xz defined from the non-collinear vectors x, y and z of the frame Oxyz.

[0060] The core 1000, 2000, as illustrated in Figures 1 and 2, has a lower face intended to be aligned with the board's sliding base, and an upper face, aligned with the lower face. The lower face defines a plane P parallel to the xz plane described previously. Plane P has a longitudinal axis, oriented along the z-axis, in the length of the board, and a transverse axis, oriented along the x-axis, in the width of the board. The core 1000, 2000 therefore has a thickness measured along a direction perpendicular to said lower face, that is, along the y-axis, and corresponding to the distance separating the lower face from the upper face of the core 1000, 2000.

[0061] As illustrated in Figures 1 and 2, the core 1000, 2000 of the invention is formed of at least two distinct elements 100, 110, 200, 210 made of plywood.

[0062] A plywood element 100, 110, 200, 210 thus comprises alternating layers 101, 102, 111, 112, 201, 202, 211, 212, also called plies, held together by gluing. For example, the glue used may be urea-formaldehyde, melamine, phenolic, or resorcinol glue.

[0063] The thickness of a plywood element 100, 110, 200, 210 generally varies between 5 and 50 mm depending on the configuration, typically between 5 and 30 mm for alpine skis, touring skis, or snowboards, and between 5 and 50 mm for cross-country skis. The width varies between 30 and 150 mm for cross-country skis, alpine skis, or touring skis, and between 150 mm and 500 mm for wide skis or snowboards. Layers 101, 102, 111, 112, 201, 202, 211, and 212 preferably have a thickness between 1 and 3 mm.

[0064] Layers 101, 102, 111, 112, 201, 202, 211, 212 are obtained by cutting thin sheets from wood panels. The wood used can come from any type of tree, with a preference for poplar. Layers 101, 102, 111, 112, 201, 202, 211, 212 therefore have wood fibers with a preferred orientation, which depends on the wood used and how the cutting is carried out.

[0065] According to a first embodiment illustrated in [Fig. 1], the core 1000 comprises two distinct elements 100,110 made of plywood.

[0066] The first type element 100 is formed by a stacking, along the thickness axis of the core 1000, of layers 101 having wood fibers oriented along the longitudinal axis of the core 1000 and of layers 102 having wood fibers oriented along the transverse axis of the core 1000.

[0067] In other words, the fibers of successive layers 101,102 have an orientation in the plane at 0°, then 90°, then again 0° with respect to the longitudinal axis of the core 1000.

[0068] In practice, the element of the first type 100 comprises between 1 and 10 layers, preferably with an odd number of layers and preferably 3 or 5 layers.

[0069] In the example of [Fig. 1], the element of the first type 100 has a constant thickness of 5 mm and consists of a superposition of three layers 101,102,101 of a constant thickness of 1.66 mm.

[0070] Preferably, for ease of manufacturing, the element of the first type 100 has a constant thickness. However, alternatively, the thickness can vary along the longitudinal axis of the core 1000, in order to adapt to the thickness of the core 1000. For example, in the case of alpine skis or touring skis, the thickness of the element of the first type 100 can be between 3 and 15 mm, the thinnest being located at the ends of the core 1000, while the thickest is located near the central area of ​​the core 1000.

[0071] Furthermore, as illustrated in [Fig. 5], the first-type element 300 can have a variable width along the longitudinal axis of the core 3000, to follow the profile of the sidecut. The width can thus vary between 5 and 600 mm depending on the type of ski and / or the embodiment. For example, in the case of alpine or touring skis, the width of the first-type element 300 can be between 50 and 120 mm, with the narrowest width located near the central area of ​​the core 3000, while the widest width is located at the ends of the core 3000.

[0072] The element of the second type 110 is formed by a juxtaposition, along the transverse axis of the core 1000, of layers 112 having wood fibers oriented along the axis of the thickness of the core 1000 and of layers 111 having wood fibers oriented along the longitudinal axis of the core 1000.

[0073] In practice, the element of the second type 110 comprises an odd number of layers. Preferably, the element of the second type 110 comprises between 10 and 50 layers for alpine or touring skis, between 5 and 30 layers for cross-country skis, and between 100 and 200 layers for a snowboard, which is a sliding board much wider than a ski.

[0074] In the example of [Fig. 1], the element of the second type 110 has a constant width of 60 mm and is made up of 5 layers 111, 112 of a constant thickness of 12 mm. Alternatively, in a preferred embodiment corresponding to an alpine ski or a touring ski, the element of the second type 110 can comprise 27 layers 111, 112, formed by 3 stringers of 9 layers 111, 112 of 2.2 mm each and also has a constant width of 60 mm.

[0075] Alternatively, the width of the element of the second type 110 can be between 50 and 100 mm, or even 150 mm for wide sliding boards and can vary along the longitudinal axis to follow the profile of the sideline.

[0076] Furthermore, the element of the second type 110 can have a height between 1 and 10 mm, advantageously variable along the longitudinal axis of the core 1000 , to follow the thickness profile of the core 1000. As an example, as illustrated in [Fig.6], the thinnest part of the second type element 410 is located at the ends of the core 4000, while the thickest part of the second type element 410 is located near the central area of ​​the core 4000.

[0077] As illustrated in [Fig. 1], the second type element 110 at least partially overlaps the first type element 100. Typically, the second type element 110 covers between 30 and 80% of the upper surface of the first type element 100, due to the non-constant width of the ski, and in particular its sidecut. Alternatively, the second type element 110 can cover the entire upper surface of the first type element 100, the two elements then having the same width.

[0078] The two elements 100, 110 are bonded to each other by an intermediate bonding layer, for example made with a urea-formaldehyde, melamine, phenolic, or resorcinol adhesive, or a bio-based adhesive. Advantageously, the two elements 100, 110 can be separated by an intermediate reinforcing layer 115, visible in [Fig. 3], with a thickness of between 0.1 and 1 mm. This intermediate reinforcing layer 115 is made of a metallic material or of a material belonging to the group of high-tenacity fibers, such as glass fibers or basalt fibers.

[0079] By way of example, the intermediate reinforcing layer 115 is made of glass fibers oriented along the longitudinal axis of the core 1000. Alternatively, the intermediate reinforcing layer 115 is made of basalt fibers oriented along the transverse axis of the core 1000. In other embodiments, the intermediate reinforcing layer 115 may comprise both fibers oriented along the longitudinal axis of the core 1000 and along the transverse axis of the core 1000. These fibers are preferably impregnated with a resin, in particular epoxy, to ensure bonding with the various constituent elements of the ski.

[0080] As illustrated in Figures 3 and 4, a board such as a ski 1100, 1200 including a core 1001, 1002 of the invention comprises a base 140, at the ends of which the edges 130 are arranged. A first layer of metallic or high-tenacity fibrous reinforcement 180 is arranged between the edges 130, on the base 140. This first layer of fibrous reinforcement 180 is composed, for example, of 720 g / m² of warp fibers oriented in the longitudinal direction of the core and 80 g / m² of weft fibers oriented in the transverse direction of the core. This first layer of fibrous reinforcement 180 has a thickness of approximately 1 mm.

[0081] On [Fig. 3], a second layer of metallic or fibrous reinforcement to High tenacity 190 covers the first reinforcement layer 180 and the edges 130. This second fibrous reinforcement layer 190 has a thickness of approximately 1mm.

[0082] The first type element 100 covers the reinforcement layer(s) 180,190 over a width less than the base 140, to allow the edges 120 to be placed on either side of the first type element 100. In the embodiments of Figures 3 and 4, the edges 120 have almost the same height as the first type element 100. Alternatively, the edges 120 may have a height less than or greater than that of the first type element 100; typically, the edges 120 may have the same height as the core 1001,1002, that is to say, a height equal to the sum of the heights of the first type element 100 and the second type element 110.

[0083] In the example of [Fig.3], an intermediate reinforcing layer 115 is disposed on the upper surface of the squares 130 and the lateral and upper faces of the first type element 100.

[0084] The second type element 110 is arranged on the intermediate reinforcement layer 115, which covers the first type element 100. Advantageously, at the ski 1100,1200, a metal plate 160, preferably made of Titanal® or Zycral®, with a thickness between 0.1 and 2 mm, is inserted on the core 1001,1002 to allow the ski and boot to be unbridled.

[0085] A new layer of metallic or fibrous reinforcement 150 covers the upper and lateral walls of the core 1001,1002. This reinforcement layer 150 is covered by a protective top 160 intended for the protection and decoration of the ski 1100,1200.

[0086] Any other type of ski structure, composed of composite and / or metallic reinforcements or even layers of wood positioned above and below the core, can be considered. Preferably, these reinforcements will have lower weights than those conventionally used in skis, due to a core that is more mechanically efficient than usual. Indeed, the core according to the invention contributes to the ski's flexural and torsional rigidity more significantly than when using a conventional laminated wood core or a polyurethane core. For example, the reinforcements are made of only 600 g / m² of unidirectional glass fibers or 420 g / m² of unidirectional basalt fibers. In skis manufactured conventionally, the reinforcements are not unidirectional but are reinforced in both the warp and weft and have a total glass weight exceeding 700 g / m², and most often equal to or greater than 800 g / m².Thus, reducing the weight of fibers used results in a weight saving on the total weight of the ski, and also reduces the environmental impact by decreasing the proportion of non-recyclable material.

[0087] The invention also relates to a second embodiment illustrated in [Fig. 2]. In this embodiment, the core 2000 comprises three wooden elements 200, 210 plywood. A central element of the second type 210 and two lateral elements of the first type 200, arranged on either side of the central element of the second type 210.

[0088] The element of the second type 210 is formed by a juxtaposition, along the transverse axis of the core 2000, of layers 212 having wood fibers oriented along the axis of the thickness of the core 2000 and of layers 211 having wood fibers oriented along the longitudinal axis of the core 2000.

[0089] In practice, the element of the second type 210 comprises between 1 and 50 layers, preferably with an odd number of layers.

[0090] In the example of [Fig.2], the element of the second type 210 has a constant width of 60 mm over the entire length of the core and is made up of 5 layers 211, 212. In an example giving good results on an alpine ski, the element of the second type 210 can comprise 27 layers 211, 212, formed by 3 stringers of 9 layers 211, 212 of 2.2 mm each and also has a constant width of 60 mm.

[0091] The width of the element of the second type 210 can be between 50 and 150 mm, can be constant over the entire length of the core and / or the ski or vary along the longitudinal axis to follow the profile of the sideline of the ski or another profile.

[0092] In addition, the element of the second type 210 can have a height between 1 and 50mm, depending on the type of sliding board, advantageously variable along the longitudinal axis of the core 2000, to follow the thickness profile of the core 2000.

[0093] The elements of the first type 200 are formed by a stacking, along the axis of the thickness of the core 2000, of layers 201 having wood fibers oriented along the longitudinal axis of the core 2000 and of layers 202 having wood fibers oriented along the transverse axis of the core 2000.

[0094] In other words, the fibers of successive layers 201, 202 have an orientation in the plane at 0°, then 90°, then again 0° with respect to the longitudinal axis of the core 2000.

[0095] In practice, the elements of the first type 200 comprise between 1 and 10 layers, preferably with an odd number of layers.

[0096] In the example of [Fig.2], the elements of the first type 200 consist of a superposition of three layers 201, 202, 201.

[0097] The thickness of the first type 200 elements can be between 2 and 70 mm and the thickness can vary along the longitudinal axis of the core 2000, in order to adapt to the thickness of the core 2000. Alternatively, the thickness of the first type 200 elements can be constant over the entire length of the core and preferably less than the thickness of the second type 210 element over the entire length of the core. In particular, the thickness of the first type 200 elements can be identical to the thickness of the second type 210 element. Alternatively, the second type 210 element can have a greater height than the first type 200 elements. Typically, the element of the second type 210 can protrude by 2 to 10 mm compared to the elements of the first type 200.

[0098] Furthermore, the elements of the first type 200 can have a variable width along the longitudinal axis of the core 2000, as illustrated in [Fig. 5], to follow the profile of the dimension line. The width can thus vary between 5 and 300 mm depending on the embodiment.

[0099] Elements 200, 210 are bonded to each other, for example using a urea-formaldehyde, melamine, phenolic, or resorcinol adhesive. Alternatively, elements 200, 210 may be separated by an intermediate bonding layer with a thickness between 0.1 and 1 mm. This intermediate layer may be made of a material belonging to the group of high-tenacity fibers, such as glass fibers or basalt fibers.

[0100] In conclusion, the invention makes it possible to develop a core that gives a ski board good mechanical properties in compression, bending, and torsion by combining two elements of the first and second types, thus optimizing the board's mechanical resistance in all three spatial dimensions. The resulting core is therefore more robust and allows for a reduction in the thickness and / or weight of the mechanical reinforcements usually added. Ultimately, the invention makes it possible to reduce the number of materials used in ski manufacturing and to favor natural materials, moving increasingly towards eco-designed ski boards that are more environmentally friendly and more easily recyclable.

Claims

Demands

1. Core (1000, 1001, 1002, 2000, 3000) for a sliding board (1100, 1200), comprising an upper face and a lower face intended to be aligned with the sliding base (140), the lower face defining a plane (P) having a longitudinal axis oriented along the length of the board and a transverse axis oriented along the width of the board, the core (1000, 1001, 1002, 2000, 3000) having a thickness measured along a direction perpendicular to said lower face of the core (1000, 1001, 1002, 2000, 3000), said core (1000, 1001, 1002, 2000, 3000) comprising: - at least one plywood element of a first type (100, 200) comprising alternating layers (101, 201) with wood fibers oriented along the longitudinal axis and layers (102, 202) with wood fibers oriented along the transverse axis, and - at least one element of plywood of a second type (110,210) comprising alternating layers (111, 211) of wood fibers oriented along the longitudinal axis and layers (112, 212) with wood fibers oriented along the thickness of the core (1000, 1001, 1002, 2000, 3000).

2. Core according to claim 1, characterized in that the layers (101, 102, 201, 202, 111, 112, 211, 212) forming the elements (100, 110, 200, 210) in plywood have a thickness of between 1 and 3mm.

3. Core according to claim 1 or 2, characterized in that the elements of the first and second type (100, 110, 200, 210) each comprise an odd number of layers (101, 102, 201, 202, 111, 112, 211, 212).

4. Core according to any one of claims 1 to 3, characterized in that the elements of the first and second type (100, 110, 200, 210) are separated by an intermediate bonding layer.

5. Core according to any one of claims 1 to 4, characterized in that the elements of the first and second type (100, 110, 200, 210) are separated from an intermediate reinforcing layer (115) made of a material included in the group including metals, high-tenacity fibers such as glass fibers and basalt fibers.

6. Core according to claim 5, characterized in that the intermediate reinforcing layer (115) comprises fibers oriented along the longitudinal axis and / or oriented along the transverse axis.

7. Core according to any one of claims 1 to 6, characterized in that it comprises an element of the first type (100) and an element of the second type (110), the element of the first type (100) being covered at least partially by the element of the second type (110).

8. Core according to claim 7, characterized in that at the median longitudinal level of the core (1000), the element of the second type (100) covers between 30 and 80% of the upper face of the element of the first type (110).

9. Core according to claim 7 or 8, characterized in that the element of the first type (100) has a constant thickness, the element of the second type (110) has a variable thickness to follow the thickness profile of the core.

10. Core according to any one of claims 7 to 9, characterized in that the element of the second type (110) has a constant width, the element of the first type (100) has a variable width to follow the profile of the dimension line.

11. Core according to any one of claims 7 to 10, characterized in that the element of the second type (110) has a constant thickness, the element of the first type (100) has a variable thickness to adapt the thickness of the core.

12. Core according to any one of claims 1 to 6, characterized in that it comprises two elements of the first type (200) and one element of the second type (210), the element of the second type (210) being disposed in the central area of ​​the core (2000), the elements of the first type (200) being disposed on either side of the element of the second type (210).

13. Core according to claim 12, characterized in that the element of the second type (210) has a height greater than that of the lateral elements of the first type (200).

14. Core according to claim 12 or 13, characterized in that at the median longitudinal level of the core (2000), the element of the second type (210) covers between 50 and 70% of the total width of the core (2000).

15. Core according to any one of claims 12 to 14, characterized in that the element of the second type (210) has a constant width along the entire length of the core (2000), the elements of the first type (200) featuring a variable width to follow the profile of the contour line.

16. Core according to any one of claims 7 to 9, characterized in that the elements of the first type (200) have a constant width over the entire length of the core (2000), the element of the second type (210) having a variable width to follow the profile of the dimension line.

17. A board comprising a core according to any one of claims 1 to 16.

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