FIELD OF THE INVENTION

The present invention generally relates to sandwich structures having relatively high strength to weight ratios. More particularly this invention relates to sandwich structures having a plurality of intersected cores and methods for making such sandwich structures.

BACKGROUND OF THE INVENTION

Sandwich structured materials are widely used in the industry, for instance in constructions and manufacturing. Sandwich structure involves a light weight core material that supports the faces and transfers the load between them. In the prior art we account for four types of sandwich cores: foam or air bubbles based cores, corrugated cores, closed cores (usually honeycomb) and truss cores.

Each of the prior art sandwich cores have their advantages and their shortcomings. Sandwich materials with foam or air bubbles cores are generally of low cost and easy to manufacture, although they have low compression strength. Sandwich materials with corrugated cores are generally considered of moderate manufacturing costs having higher compression strength than the foam cores, but having uneven mechanical properties in the orthogonal directions of the face plane. Sandwich materials with honeycomb cores have high stiffness and very good mechanical properties, however they have very high manufacturing costs, with manufacturing processes that requires generally batch type processing and complex bonding procedures to attach the honeycomb cores to the face sheets. Sandwich materials with truss cores are often considered as a compromise alternative between corrugated and honeycomb cores. The manufacturing process of truss cores are generally less expensive than the honeycomb cores however is considerably more complex than manufacturing the corrugated cores, more specifically the bonding process of the truss cores to the faces is fairly complex. Moreover, the truss cores offer lower mechanical properties than the honeycomb cores.

EU Pat Application 0631023 A1 to F. Vadillo discloses sandwich material claimed to be obtained my means of folding, molding or extrusions where the structure is composed of two superimposed structures which are composed of a series of pyramidal structures. The core with the pyramidal structure allegedly may be obtained by means of folding where a laminar sheet is pressed in between two molds the first with the a series of pyramids and the second with the series of inverted(void) pyramids. The shortcoming of Vadillo's design is that a material, not having any cuts or openings, needs to have very high elastic properties to be able to be folded as described above without tearing the material's fabric. A material with such elastic properties implies a sandwich material with very low compression strength. Accordingly the Vadillo design may be practical only by means of molding or extrusions which requires batch processes, multiple steps and manual assembly.

US Pat Application 0177635 A1 submitted by T. P. Pepe discloses a sandwich material which comprise opposed planar sheets having interlocking protrusions. In contrast to the above mentioned Vadillo design, Pepe's design suggests that these protrusions are relatively small and having a certain distance between them as to allow their creation by folding means without tearing the material fabric. The sandwich material in Pepe's design is more suited for materials with certain elastic properties such as thin plastic foils, which will place its core material in the category of the air bubbles cores, which involves the above stated shortcomings.

PCT Application WO2009087304 submitted by Leylekian discloses another sandwich core composed of two superimposed structures where the first has a pattern of pyramidal structures and the second has a regular corrugated structure. The pyramidal structure pattern is suggested to be done by means of folding in accordion manner. As a pre-requisite to such folding, in order to prevent any tearing, the material is cut with a corresponding series of diamond openings. One of the shortcoming of this design is in the amount of waste material resulted from those cuts in diamond openings. This shortcoming is common to any other truss cores made via a similar process of cutting large openings in an initial flat sheet. Another shortcoming of Leylekian design is the fact that the initial flat surface of the pyramidal structures as well as the initial flat surface of the corrugated structure are significantly larger than the surface of the end product.

U.S. Pat. No 3,227,600 to K. M. Holland under the title "formable honeycomb" discloses an expandable pack of multi-cellular honeycomb type core made from stacks of pre-corrugated ribbons having the corrugations of triangular shapes. Holland's invention shares the above mentioned shortcoming and complexities to arrive at the final product which is the sandwich material.

Priluck, in U.S. Pat. 5,527,590, 5,679,467, and 5,962,150 (hereafter referred to as the Priluck patents) discloses a truss core structural material having a lattice configuration manufactured from a plurality of segments, which are typically welded together in order to fix their position. The lattice is generally configured in the shape of uniformly stacked pyramids in a three-dimensional array Manufacturing of the structural materials disclosed in the Priluck patents, however, tends to be highly complex. Fabrication of the truss core alone generally requires multiple steps, including injection molding, manual assembly, casting, and welding. Attachment of solid face sheets generally adds additional manufacturing steps. As a result the material disclosed in the Priluck patents tends to be expensive.

U.S. Pat. No. 6,644,535 B2 to Wallach et al. discloses a truss core sandwich material and an automated methodology for fabricating such truss core sandwich panel. The shortcoming of the Wallach truss core is the complexity to create the interwoven wires and to bond them to the faces in an uniform way which leads to uneven structural properties of the sandwich panel.

Axxion Technology B.V. in EP 2258544, 2197662, 160160 and WO/2009/045095 (hereafter referred to as the Axxion patents) discloses various methods to continuously produce honeycomb cores and to attach them to the face sheets. The shortcoming of the Axxion patents is in the complexity of the bending and twisting the material to arrive at the honeycomb structure core. Moreover, these patents share with any other honeycomb core sandwich material the same complexity of attaching the faces sheets to the cores.

There is therefore a need for a structural sandwich material that has a high strength to weight ratio, which can be produced relatively easy in a continuous process and where the face sheets are easy to attach solidly to the core material in order to prevent future de-laminations.

OBJECTS OF THE INVENTION

It is a preferred object of the present invention to provide a new type of core material for structural sandwich panels; more particularly this invention discloses sandwich structures having a plurality of intersected cores.

It is a further preferred object of the invention to provide a method for making such sandwich structures in a continuous automated process.

SUMMARY OF THE INVENTION

The present invention discloses a novel structural sandwich material and a method for making such sandwich material in a continuous automated process. The structural sandwich material includes two face sheets and a core. The core includes a plurality of parallel core sheets which have a plurality of cut out sections, each cut out section defining a hole and a plurality of angled sections adjacent to said hole in the core sheet, where two by two adjacent core sheets have their angled sections in contact in a complementary pattern as such that an angled section from one core sheet is in contact with at least one angled section from the corresponding adjacent core sheet. The surface of the angled sections is smaller than the adjacent hole as such that the angled sections may be virtually folded inside the adjacent hole in the core sheet. The angled sections are at an angle from the core sheet surface and provide to the core sheets a significant structure compared to that same core sheet without any angled sections. However, such a core sheet alone usually do not offer the required structure for a sandwich material since the angled sections may fold, under pressure, at the core sheet surface level. The intersection in complementary patterns of the angled sections of two adjacent core sheets will generate a proper structural firmness to the sandwich material. The intersected angled sections are, preferably, bonded at their contact points using any of the various bonding methods known in the art, including, but not limited to, glues, resins, solvents, welding. The bonding of the angled sections at their contact points prevents the angled sections to fold, under pressure, at the core sheet surface level. The rigidity of the core is provided by the intersection of the angled sections.

The angled sections may be obtained, preferably, by means of folding or by any other means known in the art, such as, but not limited to, molding, injection-molding, roto- molding, thermo-forming, vacuum-forming.

In one embodiment, the core is composed of two core sheets, hereafter referred as the lower core and the upper core. The core sheets are in parallel planes to each other and parallel to the face sheets of the sandwich material. The surface of each core sheet is covered with a pattern of elementary components inside which we retrieve the sections at an angle from the core sheet plane.

In this embodiment, the cut-out section hereafter referred as elementary component of the pattern is a hexagon with an equilateral triangle hole having its center in the center of the hexagon and the angled sections are triangles smaller than the said equilateral triangle hole.

The triangular angled sections of this embodiment may be obtained by folding means, in the following way: • in the core sheet consider an equilateral triangle,

• divide the equilateral triangle in three equal triangles united in the center of the said equilateral triangle,

• cut three segments starting from the center of the equilateral triangle and ended at each vertex of the equilateral triangle,

• each of the three triangles having cuts on two edges is folded orthogonally to the elementary component plane. Preferably, all angled sections in a core sheet, and subsequently in an elementary component, are folded in the same orthogonal direction; more specifically all up for the lower core and all down for the upper core. Accordingly, the elementary component of the lower core has three triangles folded up and a resulting equilateral triangle hole. In the same way the elementary component of the upper core has three triangles folded down and a resulting equilateral triangle hole.

To obtain an elementary core component, in this embodiment, the elementary component of the upper core is placed on top of the elementary component of the lower core in such a way that the vertex of each angled section, triangle in this embodiment, in an elementary component (upper or lower) is placed in between two angled sections of the respectively opposite elementary component (lower or upper). In this way, in a view from the top, the two resulting equilateral triangle holes are intertwined in complementary pattern, more specifically from a top view the holes are intertwined in a hexagram shape.

In this embodiment, each angled section in an elementary component is in contact with two angled section of the opposite elementary component and the vertex of any angled section in an elementary component do not reach the plane of the respectively opposite elementary component.

This embodiment discloses the angled sections as being of triangular shape, however it is understood that the angled sections may have, in other embodiments, different shapes, such as, but not limited to, rectangles, squares, hexagons, trapezoids, irregular polygons or may have curved edges or surfaces.

In another embodiment the hole in the core sheet has a squared shape and the angled sections have an obtuse angle from the core sheet plane in such a way that, when the lower elementary component is assembled with the upper elementary component, the angled sections of an elementary component are in contact over the entire length of the of the angled edges with the adjacent angled sections of the opposite elementary component. In this embodiment the bonding of the complementary patterns of the angled sections is done over a larger section of their periphery compared to the previously mentioned embodiment. Moreover in this embodiment the assembled angled sections of two opposite elementary components create a closed structure with eight faces, which bears similarities with the regular honeycomb structures. It is apparent to a person skilled in the art that such closed structure may have different polygon holes, larger the number of edges in the polygon hole less obtuse the angle of the angled sections.

In a preferred embodiment, the angled edges of the angled sections contain a series of recesses at the future intersection points of the orthogonally angled sections. The intent of these recesses is twofold:

• first, with proper calculation of the depth of the opening, it will allow the vertex of any angled section in an elementary component to reach over the plane of the respectively opposite elementary component. The corresponding portion extending over the plane of the opposite elementary component, hereafter referred as "extending-vertex", is further angled parallel and at the same level with the plane of the elementary component and is to be bonded to the face sheets of the sandwich panel.

• second, with proper design of the recesses, it will provide better rigidity of the intersection between the angled sections. More specifically, it will provide better support at the intersection points to prevent the angled sections to fold, under pressure, at the core sheet surface level.

In such preferred embodiment, the surface of each core sheet is covered with a virtual regular tessellation of hexagonal tiling of elementary components and with angled sections adjacent to equilateral triangles holes; holes having their center in the center of the hexagons and being arranged in such a way to not touch to each other. Moreover the equilateral triangles holes are arranged in a repetitive pattern and, preferably, a pattern that is self-complementary as it may be used for the surface of the opposite core sheet, with a simple translation or rotation.

A person skilled in the art understands that the core sheets may be covered by any type of tessellation being that regular, semi-regular, aperiodic or any other type of tessellations. Moreover, there may be no specific tessellation as the important part is the pattern of the polygons of the holes adjacent to the angled sections. These polygons are preferably regular polygons, meaning equiangular and equilateral polygons, to allow a constant distance between the core sheets, when the angled sections are, preferably, created by folding means. The pattern of these polygons, preferably regular polygons, have to be in such a way that they do not touch to each other and the complementary pattern for the opposing core sheet is also in such a way that the polygons do not touch to each other.

In a preferred embodiment, the method of producing the above described sandwich panel is a continuous automated process that includes:

• feeding rolls with the sheets for the upper and lower cores.

• cutting stations to cut the edges and the recesses of the angled sections.

Each-one of the sheets may have its own cutting station or the cuttings of the core sheets may be combined in only one station.

• folding stations to orthogonally fold the angled sections and their extending- vertices. The folding process is a two steps process. The first step is to fold the extending-vertex of each angled section orthogonally to the core sheet plane. In the preferred embodiment, the extending-vertices of the lower core are folded down and the extending-vertices of the upper core are folded up. The second step is to fold the angled sections orthogonally to the core sheet plane. The angled sections of the lower core are folded up and the angled sections of the upper core are folded down.

• an assembly station for the upper and lower core sheets where each angled section will intersect the corresponding angled sections of the opposite core sheet according to the designed complementary patterns. The assembly station preferably includes a bonding method of the contact points of the angled sections.

• feed rolls with the sheets for the upper and lower faces.

• an assembly station for upper and lower faces to the assembled cores. The assembly station includes a bonding method of the core sheets to their adjacent face sheet and of the extending-vertices to the opposite face sheet.

• preferably an operations control module which typically includes a processor- actuatable motor or servo for controlling the rotation rate and timing of rollers, for controlling the relative position and operation of the cutting and folding stations, for controlling the advancement of the core sheets at the cores assembly station and the preferably timing for the bonding process, for controlling the advancement of the core and the face sheets at the faces assembly station and for controlling the bonding process at the faces assembly station.

The invention as well as its numerous advantages will be better understood by reading the following non-restrictive description of preferred embodiments made in reference to the appending drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a cut-out section of a lower core, referred as elementary component of the lower core, according to a preferred embodiment of the present invention.

FIG. 2 is a perspective view of an assembled elementary core component where the elementary component of the lower core shown in FIG. 1 intertwines in complementary pattern with the elementary component of an upper core.

FIG. 3A is a top view of the frame elements of the assembled elementary core component from FIG 1 , showing the resulting equilateral triangle holes intertwined in the complementary pattern of a hexagram shape.

FIG. 3B,C,D are top views of the frame elements of other assembled elementary core component showing different shapes for the elementary components and of the intertwined polygonal holes.

FIG. 4 is a perspective view of FIG 3A.

FIG. 5 is a top view of a core sheet as per FIG. 3A covered with the regular hexagonal tessellation and with the equilateral triangles arranged in a repetitive and self complementary pattern.

FIG. 6 is similar to the FIG. 5 having a different shape for the recesses.

FIG. 7 is a perspective view of a rectangular section of the lower core sheet ready to be assembled to the corresponding upper core sheet, according to a preferred embodiment of the present invention.

FIG. 8 is a perspective view of a rectangular section of the assembled core, according to a preferred embodiment of the present invention. FIG. 9 is a front view of the assembled sandwich material, according to a preferred embodiment of the present invention.

FIG. 10 is a schematic representation of an apparatus for an automated process to fabricate the sandwich material, according to a preferred embodiment of the present invention.

FIG. 11A is a perspective view of different embodiment of the cut-out section having an irregular hexagon shape for the angled sections.

FIG. 11 B is a perspective view of the assembly of two opposing cut-out sections shown in FIG. 11A and FIG. 2.

FIG. 12A is a perspective view of different embodiment of the cut-out section having different shapes for the angled sections.

FIG. 12B is a perspective view of the assembly of two opposing cut-out sections shown in FIG. 12A.

FIG. 12C is a perspective view of a different embodiment showing the possibility of multiple layers assembly.

FIG. 13A is a perspective view of different embodiment of the cut-out section having other shapes for the angled sections.

FIG. 13B is a perspective view of the assembly of two opposing cut-out sections shown in FIG. 13A.

FIG. 14A is a perspective view of different embodiment of the cut-out section where the angled sections form an acute angle with the core sheet surface.

FIG. 14B is a perspective view of the assembly of two opposing cut-out sections shown in FIG. 14A.

FIG. 15A is a perspective view of different embodiment of the cut-out section where the angled sections form an obtuse angle with the core sheet surface.

FIG. 15B is a perspective view of the assembly of two opposing cut-out sections shown in FIG. 15A. DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective view of the cut-out section of the lower core, referred as elementary component of the lower core where its elementary component pattern is a virtual hexagon 5 on the lower core sheet surface 2. In the representation of FIG. 1 the angled surfaces have a substantially trapezoidal shape and are adjacent to an equilateral triangle hole which has its vertices congruent to three of the virtual hexagon 5 vertices. It must be noted that such congruence is not obligatory. Preferably, there will be a congruence between the center of the hexagon and the equilateral triangle.

The angled sections 1 may be obtained by folding means in the following way:

• in the initial (unfolded) lower core sheet surface 2 consider an equilateral triangle,

• the initial (unfolded) lower core sheet surface 2 is cut in three segments starting from the center of the equilateral triangle and ended at each vertex of the equilateral triangle,

• the angled sections 1 are all folded up substantially orthogonally to the lower core sheet surface 2. By folding the angled sections 1 the result is a equilateral triangle hole in the lower core sheet surface 2.

In a preferred embodiment, the angled edges of the angled sections 1 contain a series of recesses 3 at the future contact points of the angled sections 1 with the angled sections of the upper core.

In a preferred embodiment, a proper calculation of the depth of the recess 3 allows the extending-vertices 4 to be angled parallel to the lower core sheet surface 2 of the elementary component.

FIG. 2 is a perspective view of an assembled elementary core component where the elementary component of the lower core intertwines in complementary pattern with the elementary component of the upper core. The elementary virtual hexagon 10 of the upper core is placed on top of the elementary virtual hexagon 5 of the lower core in such a way that the each angled section 6 of the elementary component of the upper core is placed, in a preferred embodiment, in between two angled sections 1 of elementary component of the lower core. In this way, the two resulting equilateral triangle holes are intertwined in complementary pattern of a hexagram shape not visible in this figure. In a preferred embodiment, the angled sections 1 of the lower core intersect two angled sections 6 of the upper core at the contact points 11 which are retrieved on the recesses 3 of the lower core and the recesses 8 of the upper core. The angled sections 1 and 6 are bonded at their contact points 1 1 using any of the various bonding methods known in the art, including, but not limited to, glues, resins, solvents, and spot-welding. The bonding of the angled sections contact points prevents the angled sections to fall back, under pressure, to their unfolded flat level. The rigidity of the elementary core component is provided by the intersection of the angled sections.

In the case where the angled sections are obtained by means of folding as explained above, a proper calculation of the depth of the recesses 3 allows the extending- vertices 4 of the lower core to be angled parallel and at the same level with the upper core sheet surface 7. Similarly, the extending-vertices 9 of the upper core are angled parallel and at the same level with the lower core sheet surface 2.

FIG. 3A is a top view of the frame elements of the assembled elementary core components showing the resulting equilateral triangle holes intertwined in the complementary pattern of a hexagram shape. The frame of the virtual hexagon 10 of the upper elementary core component is substantially on top of the virtual hexagon 5 of the lower elementary core component, the virtual hexagon 10 and virtual hexagon 5 being in different parallel planes. The frames of the angled sections 1 of the lower elementary component and the frames of the angled sections 6 of the upper elementary component outline two equilateral triangle holes which are intertwine in a complementary pattern of a hexagram shape.

The extending-vertices 4 of the lower elementary core component are angled parallel and at the same level with the plane of the virtual hexagon 10 of the upper core. Similarly, the extending-vertices 9 of the upper core are angled parallel and at the same level with the plane of the virtual hexagon 5 of the lower core.

FIG. 3B,C,D are top views of the frame elements of the assembled elementary core component showing different shapes for the elementary components and of the intertwined polygonal holes. FIG 3B shows intertwined squares in a hexagonal elementary component for a regular hexagonal tessellation. The FIG 3C shows intertwined pentagons in a squared elementary component for a regular squared tessellation. The FIG 3D shows intertwined hexagons in a circle elementary component for no specific tessellation.

FIG. 4 is a perspective view of FIG 3A showing more clearly the fact that the virtual hexagon 10 and the virtual hexagon 5 are in different parallel planes. Moreover, in this view it is shown from a different perspective the preferred complementary pattern where each angled section 6 of the elementary component of the upper core is placed in between two angled sections 1 of elementary component of the lower core and vice-versa, having their contact points 11 on the corresponding recesses 3 and 8 of, respectively, the lower elementary core component and of the upper elementary core component.

In addition, FIG. 4 shows the extending-vertices 4 of the lower elementary core component angled substantially orthogonal to the surface of the angled sections 1 , having the surface of the extending-vertices 4 at the same level with the plane of the virtual hexagon 10 of the upper elementary core component. Similarly the extending- vertices 9 of the upper elementary core component are folded substantially orthogonal to the plane of the angled sections 6, having the surface of the extending- vertices 9 at the same level with the plane of the virtual hexagon 5 of the lower elementary core component.

FIG. 5 is a top view of a core sheet with a regular virtual hexagonal 5 tessellation and with equilateral triangles arranged in a repetitive and self complementary pattern. This view may be useful for the case where the angled sections 1 are obtained by means of folding. In FIG. 5 the recesses 3 are represented by simple circles. The equilateral triangles having their center in the center of the virtual hexagon 5 are arranged in such a way to not touch to each other. Moreover the equilateral triangles are arranged in a repetitive pattern that is self-complementary as such that by flipping that pattern 180 degrees in the vertical plane we obtain the pattern for the surface of the opposite core sheet. In this figure it is represented how to obtain the angled section 1 by having cuts in each of the equilateral triangles of the hexagonal 5 elementary core component. These cuts are starting from the center of each equilateral triangle and ended at each vertex of that equilateral triangle.

In FIG 5 the angled sections 1 are of triangular shape, however it is understood that the angled sections may have, in other embodiments, different shapes, such as, but not limited to, rectangles, squares, hexagons, trapezoids, irregular polygons or may have curved edges or surfaces.

The core sheet material represented in this view by the core sheet surface 2 may be constructed of any suitable materials which may be metallic, non-metallic or a combination thereof, where preferably the material has suitable folding mechanical properties. A metallic core material may be constructed of substantially any metal and/or alloy including, but not limited to, aluminum, chromium, copper, iron, magnesium, nickel, titanium, and combinations thereof. Desirable metals and alloys typically include iron alloys, such as stainless steels and plain carbon steels, aluminum alloys, magnesium alloys and copper alloys.

The core sheet material may also be constructed of non-metallic materials such as, but not limited to, paper, cardboard, polymers, polymer composites, plastics, and ceramics. For example, polymer composite materials may be used, such as fiber composite wires impregnated with a resin; fiber composites which may include carbon, glass, hemp, cotton and/or other fibres, nano-reinforced materials with nano- fibres or polymers with nano-powders such as carbon nanotubes, fullerenes or other nano-structures.

FIG. 6 is similar to FIG 5 having a different shape for the recesses 13. In this case the recesses 13 are designed to have vertical walls when the angled sections are in a substantially orthogonal angled position. These vertical walls of the recesses 13 will provide better rigidity of the intersection between the angled sections. More specifically, it will provide better support at the intersection points to prevent the angled sections to fold, under pressure, at the core sheet surface level.

It is understood that the core sheets may be covered by any type of tessellation being that regular, semi-regular, aperiodic or any other type of tessellations. Moreover, there may be no specific tessellation as the important part is the pattern of the polygonal holes adjacent to the angled sections. These polygonal holes are preferably regular polygons, meaning equiangular and equilateral polygons as shown in FIG. 3A,B,C,D, to allow, when the angled sections are created by means of folding, for a constant distance between the core sheets. The pattern of these polygons, preferably regular polygons, have to be in such a way that they do not touch to each other and the complementary pattern for the opposing core sheet is also in such a way that the polygons do not touch to each other. FIG. 7 is a perspective view of a rectangular section of the lower core sheet ready to be assembled to the corresponding upper core sheet. The angled sections offer to the core sheets a significant structure compared to that same core sheet without any angled sections. However, such a core sheet alone cannot offer the required structure for a sandwich material as the angled sections may fold, under pressure, to the core sheet surface level.

This view discloses the preferred embodiment of the lower core sheet where the angled sections are all angled orthogonally in the up direction. The pattern of the angled sections and the pattern of the equilateral triangles holes adjacent to the angled sections create a structure that has fairly uniform mechanical properties in any orthogonal directions of the core sheet plane.

It is apparent that, when the angled sections are obtained by means of folding, the surface of the initial unfolded core sheets is substantially equal with the surface of the resulting core, having none or very little waste material, which is a great advantage over all other folded cores from the previous art.

FIG. 8 is a perspective view of a rectangular section of the assembled core. The intersection of the complementary patterns of the angled sections of the lower and of the upper core sheets will generate a firm structure for the sandwich material. Moreover, the core sheets portion that are not part of the angled sections offers a significant surface to allow a strong bonding with the corresponding face sheet of the sandwich material. That strong bonding can be achieved using relatively simple bonding methods known in the art and it will prevent future delaminations between the core and the face sheets, which addresses the delaminations shortcomings of the prior art honeycomb sandwich materials.

FIG. 9 is a front view of the assembled sandwich material, in the preferred embodiment, where it is shown the lower face sheet 12 bonded to the lower core sheet surface 2 and similarly the upper face sheet 14 bonded to the upper core sheet surface 7. Moreover, it is presented the front view of the angled sections 1 of the lower core which are in contact with the angled sections 6 of the upper core, having their contact points 11 on the corresponding recesses 3 and 8 of, respectively, the angled sections 1 of the lower core and of the angled sections 6 of the upper core. The lower face sheet 12 and the upper face sheet 14 may be constructed of the same material as the core sheet 2 and 7 or it may be constructed of any other suitable materials and may be metallic, non-metallic or a combination thereof. Moreover, the face sheets may be constructed from materials not necessarily suitable, in the preferred embodiment, for the core sheets, such as, but not limited to, glass, ceramics, marble, stones, rubber, wood or a combination thereof.

From FIG. 9 it is apparent that the resulted core structure it is not in the category of closed cores, such as the honeycomb cores, however it is neither in the open cores category, nor in any other previously known categories for core sandwich materials. The sandwich material of this invention do not present any particular open direction parallel to the core sheet surface, however it allows the air or any other fluid to flow freely between its intersected angled sections. Such fluid flow characteristics may provide for advantageous heat transfer in some applications (e.g., for providing a heat sink in a manufacturing environment). Moreover, in some applications it may be suitable to fill the core space with foam for improved rigidity and increased bonding between the angled sections 1 of the lower core and the angled sections 6 of the upper core and between the assembled core and the face sheets.

It is understood that the sandwich material core structure may be constructed with a plurality of such assembly presented in FIG. 9, where the plurality of assemblies are stacked one on top of the other in a multi-layer arrangement.

FIG. 10 is a schematic representation of an apparatus for an automated process to fabricate the sandwich material; the method which includes:

• feeding rolls 15 and 20 with the lower core sheet 16 and respectively the upper cores sheet 21.

• cutting station 17 to cut the edges and the recesses of the angled sections for the lower core sheet 16. Similarly there is the cutting station 22 for the upper core sheet 21. It is understood that the schematic representation shows two stations when in reality there may be only one cutting station for both sheets.

• folding station 18 to fold the angled sections and their extending-vertices for the lower core sheet 16 and similarly the folding station 23 for the upper core sheet 21. The folding process is a two steps process. The first step is to fold the extending-vertex of each angled section substantially orthogonally to the core sheet plane. In the preferred embodiment, the extending-vertices of the lower core sheet 16 are to be folded down and the extending-vertices of the upper core 21 are to be folded up. The second step is to fold the angled sections substantially orthogonally to the core sheet plane. The angled sections of the lower core sheet 16 are to be folded up and the angled sections of the upper core sheet 21 are to be folded down.

The folding stations 18 and 23 may include a step for the conditioning of the sheet material before and/or after the folding, such as anodizing step for metal sheets.

• a first assembly station 25 where the lower core sheet with angled sections 19 is intersected with the upper core sheets with angled sections 24 according to the designed complementary patterns. The assembly station 25 preferably includes a bonding method of the intersection points of the angled sections. The assembly station may include a step to inject foam or expandable resin in the assembled core.

• feed roll 27 with the lower face sheet 28 and feed roll 29 with the upper face sheet 30.

• a second assembly station 31 to assemble the upper face 30 and lower face 28 to the assembled cores 26 in order to achieve the intended result of the sandwich material 32. The assembly station 31 includes a bonding method of the core sheets to their adjacent face sheet and of the extending-vertices to the opposite face sheet.

• preferably an operations control module 33 which typically includes a processor-actuatable motor or servo for controlling the rotation rate and timing of rollers 15, 20, 27, 29 and the advancement of the core sheets 16 and 21 , for controlling the relative position and operation of the cutting stations 17 and 22 and the folding stations 18 and 23, for controlling the advancement of the core sheets 19, 24 at the cores assembly station 25 and preferably the timing for the bonding process, for controlling the advancement of the assembled core 26 and the face sheets 28, 30 at the faces assembly station 31 and for controlling the bonding process at the faces assembly station 31.

FIG. 11A is a perspective view of different embodiment of the cut-out section having an irregular hexagon shape for the angled sections 34, that not taking into account the recesses 3. In this embodiment cut-out section pattern is a virtual square 35 that may be used in a regular squared tessellation of the core sheet surface.

FIG. 11 B shows the assembly of two opposing cut-out sections shown in FIG 11A and FIG. 2. In this assembly the lower core component have the angled sections 34 with an irregular hexagon shape as shown in FIG 11A where the angled sections 6 of the upper core component have a trapezoidal shape as shown in FIG. 2. The shapes of the angled sections that are in contact with each other may be dissimilar.

FIG. 12A is a perspective view of different embodiment of the cut-out section having different shapes for the angled sections. In this embodiment the adjacent hole to the angled section is a square. On the periphery of the squared hole two opposing angled sections 36 have a trapezoidal shape and the other two opposing angled sections 37 have a rectangular shape. In this embodiment it shows that the recesses 38 may have substantially vertical walls. As mentioned above, the angled sections may have different shapes, such as, but not limited to, rectangles, squares, hexagons, trapezoids, irregular polygons or may have curved edges or surfaces. Moreover, the shapes of the angled sections on a core sheet may be dissimilar to each other.

FIG. 12B shows the assembly of two opposing cut-out sections shown in FIG 12A. FIG. 12C shows the possibility of multiple layers assembly.

FIG. 13A is a perspective view of different embodiment of the cut-out section having other shapes for the angled sections. In this embodiment the adjacent hole to the angled section is a square. Two angled sections 39 have a rectangular shape and two angles sections 40 have a substantially squared shape. The angled sections 39 have two recesses 38 and the angled sections 40 have only one recess 38. Assembling two such opposite elementary components the angled sections 40 will be in contact with only one angled section of the opposing core sheet.

FIG. 13B shows the assembly of two opposing cut-out sections shown in FIG. 13A.

FIG. 14A is a perspective view of different embodiment of the cut-out section where the angled sections 1 form an acute angle with the core sheet surface. FIG. 14A shows that the recesses 41 may have different shapes, in this case the walls of the recess 41 are not parallel.

FIG. 14B shows the assembly of two opposing cut-out sections shown in FIG. 14A. FIG. 15A is a perspective view of different embodiment of the cut-out section, referred as elementary component, where the adjacent hole to the angled sections 42 is a square. The angled sections 42 form an obtuse angle with the core sheet surface in such a way that, when the lower elementary component is assembled with the upper elementary component, the angled sections of an elementary component are in contact over the entire length of the of the angled edges with the adjacent angled sections of the opposite elementary component.

FIG. 15B shows the assembly of two opposing cut-out sections shown in FIG. 15A. In this embodiment the bonding of the complementary patterns of the angled sections 42 and 43 is done over a larger portion 44 of their periphery compared to the previously mentioned embodiment. Moreover in this embodiment the assembled angled sections of two opposite cut-out sections create a closed structure with eight faces, which bears similarities with the regular honeycomb structures.

Embodiments of the disclosed core material for structural sandwich panels of the present invention may be used in a wide variety of applications, especially for those in which a high strength to weight ratio is required. For example, candidate uses may include cardboard packaging, construction panels, floors and decks in residential, commercial or military applications. Further, the sandwich panels having relatively complex curvature may enable these materials to be used advantageously in applications such as boat hulls, aircraft wing and body skins, pressure vessels and containers, and the like materials to be used in industrial applications, such as chemical processing, energy generation, or in industries such as automobile, transportation, aeronautical and aerospace. For example, flat panels may be used to fabricate frame and/or firewall components, while curved panels may be used for high strength/low weight body panels.

The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.