Patent Description:
A problem during design of for example a ship, encountered today is that if for example a hull of a ship is manufactured with modern alloys and design, the hull becomes lightweight and strong. But the deck and the various vertical and horizontal walls used in the construction of a ship becomes heavy weight if standard design is used. Therefore, a need for lightweight and sturdy panels of various dimensions and areas exists.

A promising design for such panels is disclosed in <CIT> which provides a solution that involves either extrusion of panels or additive/subtractive manufacturing. If extrusion is used the available materials for construction is rather limited and a lightweight alloy, such as an alumina alloy would be the most likely candidate. However, if the hull of the ship is manufactured in stainless-steel there is a problem related to joining alumina alloys and stainless steel. There exists an alternative to manufacture panels using additive/subtractive manufacturing, but this alternative is rather expensive if large panels are desired.

Furthermore, the truss design used in <CIT> is rather weak and leaves room for improvement. One of its advantages is that the core of the sandwich material may be formed by bending a metal net to a pyramidal lattice. It is well known in solid mechanics that this truss structure is far from optimal from a structural strength point of view, for example if one of the base corners of the pyramidal lattice is subjected to momentum.

In document <CIT>) a structure having a symmetric tetrahedron with <NUM>° sloping sides. The structure uses an "octa-tetra" arrangement where every second volume is an octaeder rather than a tetrahedron. The structure has the disadvantage of not being fully triangulated. Further disadvantages are bending at joints and difficulties in forming square blocks using the structure.

In document <CIT>) a core <NUM> that inserted into a hollow shell <NUM> having strictly symmetrical interior tetrahedrons is shown. , each side of the symmetrical interior tetrahedrons having sides with equilateral triangles. This have similar disadvantages as described above.

In document <CIT>) a single-row beam of tetrahedrons formed from creasing a cylindrical tube is shown. The structure uses folding and creasing of sheets and tubes, limiting the structure to soft and malleable materials.

In document <CIT>) a structure including carbon fiber spring members in the shape of beams not having fully triangulated sections. This have similar disadvantages as described above.

It is an object of the present invention to provide a solution that is compatible with modern ship design that involves lightweight hulls.

It is another object of the present invention to provide a more robust and sturdy sandwich construction that simultaneously provides very low density.

It is another object of the present invention to provide a sandwich construction that provides excellent resistance against corrosive agents or environments.

According to the present invention, the above mentioned objects and other advantages are obtained by providing a sandwich construction element according to the independent claim.

The terms "flat", "close packed", and "unit cell" as used herein are to be interpreted in a broad sense. The term "flat" should be interpreted as essentially flat. The term "close packed" should be interpreted as fully packed, unit cell should be interpreted as an element used to close pack a volume i.e., to completely fill the volume with unit cells.

A more complete understanding of the invention, as well as further features and advantageous thereof, will be obtained by reference to the following detailed description and drawings.

The following description is for illustration and exemplification of the invention only and is not intended to limit the invention to the specific embodiments described.

Unless defined otherwise, technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

The meaning of the terms "flat", "close packed" and "unit cell" as used herein are as follows.

The term "flat" should be interpreted as essentially flat.

The term "close packed" means that a volume is completely filled with a basic construction in a symmetric and repetitive way.

The "unit cell" is the basic geometry used for close packing of a volume.

<FIG> shows an exploded perspective view of a sandwich construction element, generally designated <NUM>, according to a first embodiment of the present invention. The sandwich construction element <NUM> comprises a first element <NUM> with a flat face and a second element <NUM> with a flat face being parallel and facing the flat face of the first element <NUM>. The sandwich construction element further comprises an open core structure <NUM> arranged between the first element <NUM> and the second element <NUM>. The open core structure <NUM> is operatively connected to the first element <NUM> and the second element <NUM>.

The open core structure <NUM> comprises a plurality of close packed tetrahedrons structures <NUM>.

Furthermore, the open core structure comprises at least two flat elements <NUM>, <NUM> arranged between the first element <NUM> and the second element <NUM>. The at least two flat elements <NUM>, <NUM> are arranged perpendicular to the flat faces of the first element <NUM> and the second element <NUM>, and facing each other with a first distance between the two flat elements <NUM>, <NUM>.

The two flat elements <NUM>, <NUM> and the first element <NUM> and the second element <NUM> define a box shaped volume. This volume is filled with unit cells <NUM> in a repetitive pattern as shown exploded in <FIG>.

In <FIG> the sandwich construction element <NUM> is shown with the unit cells <NUM> packed together. In this <FIG> it is shown that by packing the unit cells together the box shaped volume is close packed filled with tetrahedron structures <NUM>. In this figure the first element <NUM> and the second element <NUM> are not shown since they would obstruct the perspective view of the tetrahedron structures <NUM>. In <FIG> an additional flat element <NUM> is added to the at least two flat elements <NUM>, <NUM> at a distance equal to the first distance, and the volume defined by the flat elements <NUM>, <NUM> is close packed with tetrahedron structures. By adding more flat elements and unit cells panels of arbitrary sizes can be formed in a repetitive pattern.

In <FIG> the unit cell <NUM> is shown in a perspective view with an added imaginary dotted box <NUM> as a help structure. The dotted box <NUM> has a width of b, a depth of d and a height of h in arbitrary units. In a first corner <NUM> is a coordinate system defined with an X axis along the base line of the width direction of the box <NUM>, a Y axis extends along the baseline of the depth direction of the box <NUM>, and a Z axis extends along the baseline of the height direction of the box <NUM>. In order to define the unit cell <NUM> six points are needed. These six points are as follows p1=[<NUM>,<NUM>,<NUM>], p2=[b/<NUM>,<NUM>,h], p3=[<NUM>,d,h], p4=[b/<NUM>,d,<NUM>], p5=[b,d,h], and p6=[b,<NUM>,<NUM>], where [x coordinate, y coordinate, z coordinate].

As can be seen from <FIG>, the six points in the unit cell, defined above, define two tetrahedrons sharing a diagonal spine. The tetrahedrons may have an XZ plane that is perpendicular to the XY plane and are thus asymmetric tetrahedrons.

<FIG> shows that a first parallelogram <NUM> is formed by point's p2, p3, p4 and p6. A second parallelogram <NUM> is formed by p1, p2, p5, and p4. These two flat parallelograms <NUM>, <NUM> are arranged in an overlapping intersecting relation along a diagonal d between point's p2 and p4, with an angle <NUM> between the two flat parallelograms <NUM>, <NUM>. From this figure a triangle is identified in the XZ-plane between point's p1, p2 and p6 and from a solid mechanics point of view this triangle is most preferably an equilateral triangle.

In a unit cell according to the present disclosure, a volume is formed between the tetrahedrons, which is asymmetric and have two of the planes perpendicular. This has the advantage that a pattern with unit cells that alternate orientation can create a rectangular parallelepiped. a volume with parallel sides which is good or advantageous, e.g. for generating sheets, plates, columns and beam profiles. This is in contrast to a unit cell based on symmetric tetrahedrons. A symmetric tetrahedron is defined as having four equilateral triangle faces, where every in-plane angle is <NUM>° and every edge is of equal length. Symmetric tetrahedrons cannot easily be assembled in a pattern that gives flat, parallel sides. Now with reference made to <FIG> different embodiments of the parallelograms <NUM>, <NUM> will be discussed.

In <FIG> a first embodiment of a parallelogram 400a is disclosed. The parallelogram 400a comprises a slit <NUM> along the diagonal d of the parallelogram from a corner to at least the center <NUM> of the parallelogram.

The slit <NUM> is configured to receive a corresponding parallelogram 400a with a slit <NUM> such that the two parallelograms are joined along the diagonal of each parallelogram, such that the end portions of the slit of the two parallelograms overlaps.

The parallelogram is also asymmetric as two of the sides are longer than the other two, thereby forming a tilted rectangle. When two such parallelograms are joined, e.g. by bringing one into the other via the slits, they create a cross that shape or form the diagonal back of two tetrahedrons.

In <FIG>, a second embodiment of a parallelogram 400b is disclosed. This parallelogram 400b comprises recesses 404b arranged at distance from the diagonal d. In this particular embodiment the recesses are triangles but other shapes are of course possible such as holes 404b and 404c as disclosed in <FIG>.

The purpose of the recesses may be to provide a more lightweight structure, or for allowing fluid communication between the unit cells. In one embodiment the at least two flat elements comprises recesses for the same purposes.

The parallelogram may also comprise tabs along the sides of the parallelogram facing the at least two flat elements, wherein the flat elements comprises corresponding recesses. In this way, the unit cells may be operatively connected to the at least two flat elements. In one embodiment the unit cells are operatively connected to the first and the second element, with for example a welded joint or an adhesive. <FIG> discloses a flat array <NUM> of parallelograms <NUM>, <NUM> with intermediate parallelograms <NUM>. This flat array <NUM> forms a repeating triangular wave pattern by a first parallelogram <NUM> having a first edge <NUM> operatively connected to an edge of an intermediate parallelogram <NUM>.

In one embodiment, the flat array may comprise folding lines along the common edges <NUM>,<NUM> between adjacent first parallelogram and intermediate parallelogram, wherein the intermediate parallelogram comprises a folding line along its short diagonal.

By bending the parallelograms of a first flat array and a second flat array, along the edges <NUM> in a first angle and the intermediate parallelograms along the short diagonals in a second angle, a bended array that can be used to obtain an array of unit cells is formed.

In <FIG> is a bended first array <NUM> arranged opposite a bended second array <NUM>, with corresponding recesses aligned to each other. By joining theses arrays <NUM>, <NUM> an array of unit cells are formed. This has the effect that a large number of unit cells may be efficiently manufactured.

In one embodiment, the sandwich construction element comprises sheet metal. And in a preferred embodiment the sheet metal is stainless steel. This way the sandwich construction element may be efficiently integrated with a modern hull of a ship.

In one embodiment of the sandwich construction, the unit cells of the open cell core is operatively connected to the at least two flat elements by means of tabs extending from the unit cells into corresponding grooves in the at least two flat elements.

In one embodiment of the sandwich construction element the unit cells of the open cell core is operatively connected to the first element and the second element by means of an adhesive.

In one embodiment of the sandwich construction element the unit cells of the open cell core is operatively connected to the first element and the second element by means of welding.

Claim 1:
A sandwich construction element (<NUM>), comprising:
- a first element (<NUM>) with a face, extending in a longitudinal direction with a thickness and a height being smaller than the longitudinal length;
- a second element (<NUM>) with a face, extending in the same longitudinal direction as the first element with a thickness and a height being smaller than the longitudinal length, wherein the second element is facing the face of the first element (<NUM>);
- an open core structure (<NUM>) arranged between, and operatively connected to the first element (<NUM>) and the second element (<NUM>), wherein the open core structure comprises a plurality of close packed tetrahedron structures (<NUM>), wherein the tetrahedron structures (<NUM>) are asymmetric and are arranged to form one or more unit cells (<NUM>) with six points defining two tetrahedrons sharing a diagonal spine, wherein each tetrahedron has a plane that is perpendicular to another, wherein each tetrahedron is an asymmetric tetrahedron, wherein a volume is formed by said two tetrahedrons and wherein said two tetrahedrons define two parallelograms (<NUM>, <NUM>, 400a-c), arranged in an overlapping intersection relation along a diagonal wherein each of the parallelograms (<NUM>, <NUM>, 400a-c) comprises a slit (<NUM>) along said diagonal (<NUM>) from a corner to at least a center (<NUM>) of the parallelogram, wherein the slit is configured to receive a corresponding parallelogram with a slit (<NUM>) such that the end portions of the slit of the two parallelograms overlap.