Composite sandwich panels, cores for composite sandwich panels, methods of joining panels, and methods of assembly

Abstract

A core for a composite sandwich panel, a composite sandwich panel, and a method forming a composite sandwich panel, the composite sandwich panel including a core pic properties and to increase a shear strength density scaling, the core defining a generally planar element having a front side and an opposing rear side, a frame that outlines a perimeter of the core, shims received within the frame and configured to accommodate mechanical fasteners, and a skin composed of a thin material having a high tensile strength, a width sufficient to provide reinforcement for joinery, and where the core includes bonding surfaces that extend generally parallel to the skin and provide increased area contact for enhanced adhesion to the skin.

Description

[0001] COMPOSITE SANDWICH PANELS, CORES FOR COMPOSITE SANDWICH PANELS, METHODS OF JOINING PANELS, AND METHODS OF ASSEMBLY

[0002] CROSS REFERENCE TO RELATED APPLICATION nation

[0003] Serial Number 63 / 471,699 filed on June 07, 2023, the entire contents of which are herein incorporated by reference.

[0004] TECHNICAL FIELD more particularly, composite sandwich panels formed from a plurality of materials, a core for such panels, methods of joining, and methods of assembly.

[0005] BACKGROUND t but strong structure is required, for example, in transport vehicles, shipping containers, etc.

[0006] Such composite sandwich panels typically utilize a structure comprised of a core of high density polyethylene (HDPE) foam (or other resins) with steel skins (or other high stiffness / strength skins, e.g., aluminum or fiber-reinforced polymers) affixed to the core. agth (i.e. stiffness to weight and strength to weight ratios, respectively), these panels still typically weigh between 70 and 90 pounds in standard configurations, thus adding weight to the resulting structure. This is disadvantageous, particularly in shipping and transportation applications where increases in weight are associated with a rise in fuel consumption, a decrease in freight efficiency, and an overall increase in costs. Alternative materials like lightweight polystyrene (PS) foam or polypropylene (PP) honeycomb can further decrease weight but suffer from several structural drawbacks. Particularly, PS foam has low shear strength and thus fails prematurely. PP honeycomb has issues are of the core requires custom mechanical fasteners to join panels together, thus complicating assembly and correspondingly increasing costs.

[0007] Some composite sandwich panels utilize cellular core materials. However, these cellular materials, despite being lightweight and cost efficient at large scale, suffer from several dlular cores have utilized honeycomb geometries and open unit cell configurations formed of repeated intersecting polygonal planes, for example, as disclosed in International Patent Application Number PCT / US2021 / 038932 entitled, “Material with Proisotropic Stress Response Structure”, the content of which is incorporated herein by reference in its 2a that is available for bonding to the flat surface of the skin of a composite sandwich panel.

[0008] Moreover, these cores are generically composed of flat / polygonal facets, and often require specialized edge fasteners to join the panels together, thus complicating assembly of a corresponding structure. lly sufficient, and which may be assembled and affixed to adjacent panels in a simple and cost efficient manner.

[0009] BRIEF SUMMARY ibed herein that generally integrates performance enhancing improvements to the central region of the cellular core, in the form of non-developable wall geometry, increased surface area for bonding to skins, and a panel with a solid frame perimeter surrounding the core. In one instance, this design is achieved through a thermoforming process that creates a trough in the perimeter around the cellular core, and solid materials of the same plastic resin arc then placed into the trough. This configuration facilitates robust fastening using conventional, md custom mechanical fastening methods, and provides a reduced weight panel with high structural integrity. In other embodiments, the trough and / or the solid materials placed into the trough may be formed of substances different from each other and / or different from the substance(s) used to form the body of the panel. osed of a plurality of intersecting polygonal facets configured to promote isotropic properties and to increase a shear strength density scaling, the core defining a generally planar element having a front side and an opposing rear side, a frame that outlines a perimeter of the core, shims received within the frame and configured to accommodate mechanical fasteners, and in the front side and the real' side of the core, where the frame has a width sufficient to provide reinforcement for joinery, and where the core includes bonding surfaces that extend generally parallel to the skin and provide increased area contact for enhanced adhesion to the skin. Here, the shear strength density is the quantitative relationship between shear

[0010] Further provided herein is a core for a composite sandwich panel, including a plurality of intersecting polygonal facets configured to promote isotropic properties and to increase a shear strength density scaling, and a plurality of bonding surfaces formed on the facets that

[0011] Additionally provided in the present disclosure is a method of manufacturing a composite sandwich panel, the method including providing a core composed of a plurality of intersecting polygonal facets, arranging the facets to promote isotropic properties and to increase a shear strength density scaling of the core, forming bonding surfaces on the facets that provide increased area contact for enhanced adhesion, forming a frame that outlines a perimeter of the core, disposing shims within the frame and arranging the shims to accommodate mechanical fasteners, and disposing a skin composed of a thin material ing the skin to the bonding surfaces.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a more complete understanding of this disclosure, reference is now made to the id detailed description, wherein like reference numerals represent like parts, in which:

[0014] FIG. 1 shows an assembled composite sandwich panel in one exemplary embodiment;

[0015] FIG. 2 is an exploded view thereof;

[0016] FIGS. 4a-b show a perspective view thereof and a partial enlarged view thereof;

[0017] FIG. 5 is a front view of the core including shims disposed at a perimeter thereof;

[0018] FIGS. 6a-b show a perspective view thereof and a partial enlarged view thereof;

[0019] FIGS. 7a-b show an exploded view thereof and a partial enlarged view of the core; n along the axis A-A;

[0020] FIG. 9 is a front view of a portion of the core showing one exemplary embodiment of a core geometry; FIG. 10 is a perspective view thereof;

[0021] FIGS. 1 la-b show a side view taken from the top of FIG. 9 and a side view taken from the right of FIG. 9, respectively, including illustrative dimensions;

[0022] FIGS. 12a-c show various views of a composite sandwich panel in an alternate

[0023] FIGS. 13a-b and 14 show various views of composite sandwich panels in an alternate embodiments;

[0024] FIGS. 15a-c show various views of a composite sandwich panel in an alternate embodiment; and composite sandwich panels.

[0025] DETAILED DESCRIPTION

[0026] FIGS. 1-2 illustrate a composite sandwich panel 10 in one exemplary, non-limiting core

[0027] 12 having a front side 14 and an opposing rear side 16. The panel 10 further includes a skin 18 disposed on each of the front and real' sides 14, 16. In this example, the core 12 is generally formed as a three-dimensional planar element having rectilinear profiles. That is, the front and rear sides 14, 16 of the core 12 are substantially square or rectangular in nerely exemplary. The core 12, its various sides and profiles, and the greater panel 10, may be formed of any desired polygonal or curvilinear shape, or combinations thereof.

[0028] The skin 18, as illustrated in FIGS. 1-2, is a thin planar member having a generally square shape and including opposing interior and exterior surfaces 20, 22, where the interior panel 10, and where the exterior surface 22 is oriented way form the core 12 and faces an exterior of the panel 10. As with the core 12, the skin 18 may assume any desired shape, and the skin 18 may be shaped complementary to the shape of the core 12, or may diverge therefrom. to 150ksi, and 0.013” to 0.016” in thickness). Such steel is treated in a manner consistent with industry standards, representative alloys include but are not limited to ASME A653 galvannealed or hot dip galvanized steel, with appropriate backer or primer coatings, paint, and / or other surface treatments. continuous fibers having a high tensile strength (e.g. glass, carbon, borosilicate, basalt). Such fibers may be embedded within a substrate such as thermoplastic polymer (e.g. PE, PP, TPO, PEEK, ABS, aPET, PETG). These skins 18 can be applied to the core 12 as unidirectional tapes, or consolidated into multi-ply laminates with orientational layup

[0029] 0.

[0030] The skin 18 is affixed upon the front and rear 14, 16 of the core 12 through a bonding process. For example, where the skin 18 is formed of the steel material, bonding may be achieved utilizing structural adhesives, such as an epoxy primer using a one-part moisture cure urethane. As noted, where the skin 18 is formed of the fiber-reinforced polymer

[0031] Alternatively, where the skin 18 is formed of the fiber-reinforced polymer matrix, an adhesive may be used or the skin may be thermally welded to the core.

[0032] FIG. 3 shows a detailed view of the rear side 16 of the core 12. FIG. 4a shows a perspective view of the rear- side 16, and FIG. 4b shows an enlarged partial view thereof. on 24 and tracing an outer perimeter of the core 12. The central region 24 contains a plurality of intersecting polygonal facets 28 which repeat to form an array bonded by the frame 26. As discussed further herein, the facets 28 are designed to promote isotropic properties and to increase a shear strength density scaling and increased contact area for enhanced adhesion to mating surfaces. The frame 26 is a planar clement having a flat surface 30 on the rear side 16 of the core 12 which is coplanar with an outward extent of the polygonal facets 28. i the flat surface 30 of the frame 26.

[0033] FIGS. 5-7 show various views of the front side 14 of the core 12. The central region 24 is visible on the front side 14, along with a view of the polygonal facets 28, opposite from that seen at the rear side 16. The frame 26 can also be seen on the front side 14 of the core t the rear side 16 of the core 12. As best seen in FIGS. 7a-b, the frame 26 includes an inner border 34 and an outer border 36. The inner border 34 is a thin protruding element that extends from the flat surface 32 of the frame 26, extends around the central region 24, and is disposed in contact with the polygonal facets 28. The outer border 36 is likewise a thin inner and outer borders 34, 36 extend generally orthogonally from the flat surface 32 of the frame 26 and parallel to one another.

[0034] The inner and outer borders 34, 36 each include an outermost surface 38, disposed distally from the flat surface 32 of the frame 26, where these outermost surfaces 38 are coplanar partial cross-section of the core 12 in which the coplanar nature of the frame elements and the polygonal facets is made clear. Particularly, dashed line B-B illustrates that the rear flat surface 30 of the frame 26 is coplanar with a bonding surface 40 of the polygonal facet 28. Similarly, a dashed line C-C illustrates that the outermost surface 38 of the inner border 34

[0035] As can be seen particularly in FIGS. 7a-b and 8, the protruding inner and outer borders 34, 36 and the front flat surface 32 of the frame 26 combine to form a trough. That is, these elements have a U-shaped cross section, a portion of which is visible in FIG. 8. As seen in FIG. 7a, this trough extends around the perimeter of the core 12, surrounding the central region 24. The trough is configured to receive at least one shim and, in the illustrated embodiment, four shims arc provided, shims 42 and 44 arranged opposite from one another, and shims 46 and 48 arranged oppositely. The shims 42-48 are received within rugh a friction fit, or disposed loosely therein and secured against the flat surface 32 by the skin mounted there atop 18 as discussed below. The shims 42-48 are essentially prismatic portions designed to fill, at least partly or fully, the trough and to receive and retain joinery hardware. In one embodiment, the shims 42-48 are formed of the same material as the rd shims 46 and 48 are of equivalent length where the length of shims 46 and 48 is greater than the length of shims 42 and 44. Here, the shims 46, 48 extend across a length of the core 12 and the shims 42, 44 extend perpendicularly therebetween. This configuration is of course exemplary. The shims 42-48 may each be of equal length, in the case of a square ;e 12, or some or all of the shims 42-48 may be of different lengths, or any other desired configuration which would be received by and substantially fill the trough of the frame 26.

[0036] Returning again to the cross-section of FIG. 8, the shim 42 can be seen located in the trough of the frame 26. The shim 42 has a thickness which is equal to or less than the ; 42-48 arc located fully within the trough of the frame 26 and do not protrude therefrom.

[0037] FIGS. 9-11 show various views of a portion of the core 12. Here it can be seen that the polygonal facets 28 comprise a plurality of the bonding surfaces 40 extending across the front side 14 of the core 12 and, correspondingly, in mirror like fashion, across the rear jrses a length of the illustrated portion of the core 12. See, FIG. 9. This arrangement of FIGS. 9- 10 is repeated across the core 12 to form a herringbone-like pattern (see, e.g., FIG. 5). As shown particularly in FIGS. 1 la-b, the bonding surfaces 40 at the front side 14 of the core 12 are coplanar with one another, and the bonding surfaces 40 at the rear side 16 of the core are coplanar with one another. Across the length of the core 12, the bonding surfaces 40 alternate between the front side 14 and the rear side 16 and are connected by alternating angled polygonal portions 50. In the illustrated example, the angled polygonal portions 50 extend at 135° relative the bonding portions 40. Likewise, as shown in FIG. 9, the bonding he intersection axis D-D form a repeating V-shape pattern on the portion of the core 12 shown in FIGS. 9-10.

[0038] Exemplary dimensions are included in FIGS. 1 la-b. A thickness of the core is 0.220 inches. A thickness of the bonding surfaces 40 is 0.063 inches. A depth formed by the shown has a length and width of 3.074 inches and 2.934 inches. These dimensions are exemplary and may be varied by application.

[0039] As mentioned above, the composite sandwich panel 10 is formed by affixing the skin 18 on both the front and rear sides 14, 16 of the core 12. In a preferred embodiment, the skin doing, the skin 18 contacts the inner and outer borders 34, 36 of the frame 26, the shims 42-48 which are disposed in the trough of the frame 26, and also the bonding portions 40 of the polygonal facets 28. These many surfaces in contact with the skin 18 promote the bonding and affixation of the skin 18 onto the core 12. e increased contact area between the core 12 and skin 18 for enhanced adhesion. In the illustrated embodiment, the bonding portion 40 has a flat planar surface positioned to engage the skin 18 when disposed upon the core 12. In other embodiments, the outwardly facing surface of the bonding portion 40 may include non-planar elements such as recesses rther facilitate adhesion with the skin 10. As demonstrated, the core 12 comprises a plurality of intersecting polygonal facets 28 designed to promote isotropic properties and increase shear strength density scaling. The core may be of the type described in U.S. Patent Application No. 18 / 012,047, the content of which is incorporated herein by reference in its entirety. Particularly, the core is ptimal shear strength density scaling, to promote isotropic material properties, to have in-plane auxetic properties to maximize fatigue life and impact resistance, and to include a perimeter modified to include shims to accommodate mechanical fasteners. The embodiments of the core disclosed herein contain these aspects, but are merely exemplary

[0040] Herein, "shear strength density scaling" refers to the relationship between a material's shear strength and its density. This concept is used to determine how changes in density affect the shear strength of the material, which is crucial for optimizing material performance. By understanding this scaling, materials can be engineered to achieve a desirable balance materials. The various geometries and configurations of the structure of the core 12 discussed herein are specifically configured for, and result in, the promotion of isotropic properties and an increase in the shear strength density scaling.

[0041] The skin 10 has been described herein as extending across the full extent of the front and ily partially across the core and / or may extend beyond the perimeter of the core on one or more sides. For example, a composite sandwich panel may include a skin that terminates on one or both of the front and rear sides of the core in a location between the inner and outer borders of the frame. An adjacent panel may include a skin that extends beyond its kin on the aforementioned adjacent panel. In this manner, the extending skin of one panel may overlap and extend atop the frame of the adjacent panel in order to facilitate the joining thereof in ‘shiplap’ manner. FIGS. 12-14 show various exemplary embodiments of composite sandwich panels adjoined in the shiplap manner. Particularly, FIGS. 12a-c show two adjoined panels 10’, 10”, each including a core 12 having a frame 28 with shims 42-48, and skins 18 secured thereto, as described hereinabove. However, unlike previous embodiments where the skins ont side 14 of the panel 10’ is skewed to the right (as shown in the drawing) which exposes the frame 28 on one side of the panel 10’ and creates an extension 52 of the skin 18 on the other side of the panel 10’. The skin 18 on the rear side 16 is aligned with the core. The panel 10” is constructed similarly to the panel 10’. In this way, the frame 28 of the panel extension 52 of the panel 10’ when the two panels are brought into engagement. The extension 52 of the panel 10’ may be secured to the frame 28 of the panel 10” with adhesives, mechanical fasteners, or combinations thereof in order to secure together the panels 10’, 10”. Additional panels of the same construction can be secured to the paired

[0042] In the example of FIGS. 12a-c, the skin 18 on the real’ side 16 of the panel 10’ extends from edge to edge of the underlying core 12. However, in other embodiments, the skin 18 on the rear side 16 of the panel 10’ may be skewed in the opposite direction from that of the skin 18 on the front side 14 of the panel 10’ so as to create another extension 52 the skins 18 on the front sides 14 of the panels 10’ and 10” arc skewed as described with regard to FIGS. 12a-c. However, here, the skins 18 on the bottom sides 16 of the panels 10’ and 10” are skewed in the opposite direction. This creates extensions 52 on the front and real’ sides 14, 16 of the panels a 10’, 10” which, when the panels are adjoined to each way, the skins 18 may be secured to the frames by adhesives and / or mechanical fasteners at multiple locations on the front and rear sides of the respective panels.

[0043] FIG. 13b shows an alternate configuration of a composite sandwich panel 100 which includes the core 12 and the skins 18, where the skins 18 extend across the entirety of the core 12, from edge to edge. However, on the front side 14 of the panel 100, the skin 18 extends to the right edge (as shown in the drawing) and then extends beyond the core 12 to create the extension 52. Similarly, on the on the rear side 16 of the panel 100, the skin 18 extends to the left edge (as shown in the drawing) and then extends beyond the core 12 to G.

[0044] 13b, the extension 52 of one of the skins 18 extends over the skin 18 of the adjacent panel 100 on the front side 14 and rear side 16 of the adjoined panels 100. This overlap provides an interface at which the skins may be secured by way of adhesives and / or mechanical fasteners. This configuration may be used with or without the frames 28.

[0045] J in which a protective film 102 is placed over the exterior surface 22 of the skins 18. In one example, the protective film 102 may be composed of polyethylene terephthalate (PET). Other substances suitable to provide a protective layer to the panel and to facilitate bonding with the skins 18 may be utilized.

[0046] Therein, the skins 18 on the front side and rear sides 14, 16 of the panel 150 are non- aligned with the core 12 such that at a first side (left in the drawing), the frame 28 is exposed and at the opposite side (right in the drawing), the skins 18 on the front and rear sides 14, 16 of the panel 150 project to create the extensions 52. This forms a ‘tongue and osed portion of the frame 28 of one panel 150 into the protruding extensions 52 of the other panel 150 such that the extensions 52 overlap the exposed frame 28. This overlapping area may receive adhesives and / or mechanical fasteners in order to affix the adjacent panels 150 in the manner discussed above. i in which the core 12 includes a portion 152 having a smaller cross-sectional area and a portion 154 having a larger cross-sectional area. The skins 18 are fitted to the alternately shaped cores 12 and extend to the terminal end of the core 12 at the smaller portion 152, and extend beyond the core 12 at the larger portion 154 in order to form the extensions 52. The resulting panels 150 are secured together in the tongue and groove manner described above.

[0047] FIG. 16b shows an alternate arrangement for a composite sandwich panel 200 in which the .00, from edge to edge. However, at one edge (lefts side of drawing), the skin 18 on the front side 14 of the panel 200 turns about ninety degrees and extends to the real- side 16 where the skin 18 turns ninety degrees again so as to protrude from the panel 200 thus forming the extension 52. The skin 18 on the rear side 16 of the panel 200 is oppositely arranged r side of the core 12 includes the two perpendicular turns in order to traverse to the front side 14 and to protrude, thus forming the extension 52. Adjacent panels 200 may mated by overlapping and affixing two adjacent extensions 52 as illustrated.

[0048] FIG. 16c illustrates a means of adjoining two of the panels 10 having skins 18 on front and s 52.

[0049] Here, a post 220 is placed between the adjacent panels 10 and includes a portion 222 which extends atop the front side 14 of one of the panels 10, a portion 224 which extends over the rear side 16 of the adjacent panel 10, and a portion 226 that connects the portions 222 and 224. The portions 222 and 224 are disposed proximate to the frames 28 of the respective oin the two panels together.

[0050] FIG. 16d is a similar configuration which utilizes a two pail post 250 in order to mate two adjacent composite sandwich panels 10. A first portion 252 of the post 250 extends on the front sides 14 of the panels 10 over the frames 28 and then extends in a substantially

[0051] >0 extends on the rear sides 16 of the panels 10 over the frames 28 and engages with the first portion 252. As a result of this advantageous disposition, the first and second portions 252 and 254 of the post 250 can be secured to the frames 28 of the panels 10 and to one another, thus resulting in the adjoining of the panels 10.

[0052] FIG. 16e shows another configuration utilizing a two-part post 250 in which the first portion 252 extends generally coplanar with the cores 12 of adjacent panels 10, and the mors, that secure the first portion 252 to offset frame portions 256. These portions 256 are similar to the frames 28 described herein, however the portions 256 extend in a non- coplanar manner with respect to the cores 12, whereas the frames 28 are substantially coplanar with their respective cores 12. See, e.g., FIG. 8. The offset frame portions 256 oplanar disposition relative to the cores 12 and to thus secure two adjacent panels 10 while maintaining the coplanar alignment of the skins 18 on the front side 14 of the panels 250.

[0053] Thus far, the frame 12 of the composite sandwich panel has been described as being formed of repeating polygonal facets 28 having a plurality of flattened bonding surfaces 40 text.

[0054] This configuration is of course exemplary and many geometries are contemplated within the broad scope of the disclosure.

[0055] FIG. 17 illustrates a further exemplary embodiment for a geometry of the core 12 which includes flattened surfaces similar to those of the previously described polygonal facets 28.

[0056] FIG.

[0057] 17, but with the flattened surfaces have been rounded in order to provide additional strength and stiffness. That is, the flattened surfaces of the geometry of FIG. 17 are converted to non -develop able surfaces in FIG. 18. FIG. 19 shows a further geometry embodiment in which the tops of this non-developable surface of FIG. 18 are flattened in bonding area has been increased further and the geometry is modified to address panelspecific failure modes. The composite sandwich panels described herein may include any of the disclosed geometries, variations, or combinations thereof. The frame area of the disclosed composite sandwich panel is of a width sufficient to receive and retain joinery elements and fasteners and the like utilized in adjoining adjacent panels in the manner discussed hereinabove.

[0058] Composite sandwich panels have been described herein as comprising a frame that extends

[0059] However, as noted for example with regard to FIGS. 13b, 14, and 16a-b, embodiments of the disclosed composite sandwich panel exist without the frame and are designed to be adjoined to adjacent panels through unique arrangements and utilizations of the skins that are disposed upon the core to form the panels. Still further alternate embodiments exist in perimeter of the panel. For example, the core may include a frame only one side, or multiple sides but not all sides.

[0060] The composite sandwich panel described herein addresses the problems and deficiencies noted above by providing a panel that is both lightweight and structurally sufficient, and it manner.

[0061] Various embodiments of the present invention are described herein with reference to the related drawings. Alternative embodiments can be devised without departing from the scope of this invention. It is noted that various connections and positional relationships description and in the drawings. These connections and / or positional relationships, unless specified otherwise, can be direct or indirect, and the present invention is not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or

[0062] The teim "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or design described herein as "exemplary" is not necessarily to be constmed as preferred or advantageous over other embodiments or designs. The terms "at least one" and "one or more" are understood to include any integer number greater than or equal to one, i.e. one, two, three, four, etc. The terms "a plurality" arc understood to include any integer number greater than or equal to two, i.e. two, three, four, five, etc. Terms such as "connected to", “affixed to”, etc., can include both an

[0063] The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described JS of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the ail to understand the embodiments disclosed herein.

Claims

CLAIMS:

1. A composite sandwich panel, comprising: a core composed of a plurality of intersecting polygonal facets configured to defining a generally planar' element having a front side and an opposing rear side; a frame that outlines a perimeter of the core; shims received within the frame and configured to accommodate mechanical fasteners; and sposed on the front side and the rear’ side of the core; wherein the frame has a width sufficient to provide reinforcement for joinery; and wherein the core includes bonding surfaces that extend generally parallel to the skin and provide increased area contact for enhanced adhesion to the skin.

2. The composite sandwich panel of claim 1, wherein the frame comprises a trough which receives and retains the shims.

3. The composite sandwich panel of claim 2, wherein the trough is delimited by an outer jr of the core, an inner boundary that protrudes from the front side of the core and extends generally collinear with the outer border, and a flat surface on the frame which extends between the outer border and the inner border on the front side of the core. i and continuously with a central region of the core that contains the polygonal facets, and wherein the trough has a generally U-shaped cross-section.

5. The composite sandwich panel of claim 2, wherein the shims comprise one or more6. The composite sandwich panel of claim 3, wherein the bonding surfaces are disposed on the polygonal facets on the front side and rear side of the core, wherein the bonding surfaces on the front side of the core are coplanar with the inner and outer borders, and ice of the frame formed on the rear' side of the core.

7. The composite sandwich panel of claim 6, wherein the bonding surfaces on the front side of the core are coplanar with one another, and wherein the bonding surfaces on the t side of the core being arranged parallel to the bonding surfaces on the rear side.

8. The composite sandwich panel of claim 7, wherein the bonding surfaces at the front side of the core are connected to the bonding surfaces at the rear side of the core by angled9. The composite sandwich panel of claim 8 wherein the angled polygonal portions extend from the bonding surfaces at an angle of about one-hundred and thirty-five degrees. d facets extends across the front side of the panel in parallel to one another, wherein a second group of the polygonal facets extends across the front side of the panel in parallel to one another and at an angle to the first group, where the first and second groups intersect at an intersection axis to form a repeating V-shape.

9. The composite sandwich panel of claim 8, wherein the angle of intersection is about one-hundred and thirty-five degrees.

10. The composite sandwich panel of claim 1, wherein the skin material is composed of a thin gauge, high strength steel.

11. The composite sandwich panel of claim 1, wherein the skin material is composed of a12. The composite sandwich panel of claim 1, wherein the core is designed to have inplane auxetic properties to maximize fatigue life and impact resistance. a plurality of intersecting polygonal facets configured to promote isotropic properties and to increase a shear strength density scaling; and a plurality of bonding surfaces formed on the facets that define an increased contact area for enhanced adhesion to mating surfaces.

14. The core of claim 13, wherein the bonding surfaces comprise surfaces on a front side of the core that are coplanar with one another, surfaces on a rear- side of the core that are coplanar with one another, wherein the bonding surfaces on the front side of the core are arranged parallel with the bonding surfaces on the rear side.

15. The core of claim 14, wherein the bonding surfaces at the front side of the core are connected to the bonding surfaces at the rear side of the core by angled polygonal portions, wherein the angled polygonal portions extend from the bonding surfaces at an angle of about one-hundred and thirty-five degrees.

16. The core of claim 14, wherein a first group of the polygonal facets extends across the front side of the panel in parallel to one another, wherein a second group of the polygonal facets extends across the front side of the panel in parallel to one another and at an angle the first group, where the first and second groups intersect at an intersection axis to form arepeating V- shape, wherein the angle of intersection is about one-hundred and thirty-five degrees.

17. The core of claim 13, further comprising a frame extending around the plurality of r more shims configured to accommodate mechanical fasteners.

18. A method of manufacturing a composite sandwich panel, the method comprising: providing a core composed of a plurality of intersecting polygonal facets;;rength density scaling of the core; forming bonding surfaces on the facets that provide increased area contact for enhanced adhesion; forming a frame that outlines a perimeter of the core; mechanical fasteners; and disposing a skin composed of a thin material having a high tensile strength on a front side and on a rear side of the core; and adhering the skin to the bonding surfaces.

19. The method of claim 18, further comprising forming a trough in the frame for receiving the shims by protruding an outer border from the front side of the core and extending the outer border around the perimeter of the core, protruding an inner boundary from the front side of the core and extending the inner border generally collinear with the the inner border on the front side of the core.

20. The method of claim 19, further comprising forming the bonding surfaces on the polygonal facets on the front side and the rear side of the core, arranging the ith theinner and outer borders, arranging the bonding surfaces on the rear side of the core coplanar to each other and coplanar with a flat surface of the frame on the rear side of the core, arranging the bonding surfaces on the front side of the core to be parallel with the bonding surfaces on the rear side, and connecting the bonding surfaces at the front side of ins.REFERENCE NUMERALS10 composite sandwich panel12 core16 rear side of core18 skin20 interior surface of skin22 exterior surface of skin26 frame28 polygonal facets30 rear flat surface of frame32 front flat surface of frame36 outer border38 outermost surface of border40 bonding surface42-48 shim52 extension100 composite sandwich panel102 protective film150 composite sandwich panel154 portion having larger cross-section200 composite sandwich panel220 one-part post222 portion of post226 connecting portion250 two-part post252 first portion254 second portion

Images