Composite sandwich panel, core for composite sandwich panel, method of joining panels and method of assembling

Abstract

A core for a composite sandwich panel, a composite sandwich panel, and a method of forming a composite sandwich panel, the composite sandwich panel comprising: a core having properties to increase shear strength density scale, the core defining a generally planar element having a front side and an opposing rear side; a frame following the contour of the periphery of the core; a shim received within the frame and configured to receive a mechanical fastener; and a skin comprised of a thin material having a high tensile strength and having a width sufficient to provide enhanced bonding, and wherein the core includes a bonding surface extending substantially parallel to the skin and providing increased area contact to enhance adhesion to the skin.

Description

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

[0001] Citations of relevant applications

[0002] The entire contents of patent application No. 63 / 471,699 are incorporated herein by reference. Technical Field

[0003] This disclosure specifically relates to composite sandwich panels formed of multiple materials, cores for such panels, joining methods, and assembly methods. Background Technology

[0004] For example, robust structures are required in transport vehicles and shipping containers.

[0005] Such composite sandwich panels typically utilize a core consisting of high-density polyethylene (HDPE) foam (or other resins) and a steel skin (or other high-stiffness / high-strength skin, such as aluminum or fiber-reinforced polymers) attached to the core. (Considering stiffness to weight ratio and strength to weight ratio separately) These panels typically still weigh between 70 and 90 pounds in standard configurations, thus increasing the weight of the resulting structure. This is disadvantageous, especially in shipping and transportation applications where increased weight is associated with higher fuel consumption, reduced freight efficiency, and overall increased costs. Alternative materials such as lightweight polystyrene (PS) foam or polypropylene (PP) honeycomb structures can further reduce weight, but several structural drawbacks exist. Specifically, PS foam has low shear strength and therefore fails prematurely. PP honeycomb structures have some issues, and the nature of the core requires custom mechanical fasteners to join the panels together, complicating assembly and correspondingly increasing costs.

[0006] Some composite sandwich panels utilize segmented core materials. However, while these segmented materials are lightweight and cost-effective on a large scale, they have several drawbacks. Known segmented cores utilize honeycomb geometry and open-cell configurations formed by repeating intersecting polygonal planes, for example, as disclosed in International Patent Application No. PCT / US2021 / 038932 entitled “Material with Proisotropic Stress Response Structure,” the entire contents of which are incorporated herein by reference. This relates to the area of ​​flat surfaces that can be used to bond to the skin of composite sandwich panels. Furthermore, these cores are typically constructed of flat / polygonal surface structures and often require specialized edge fasteners to join multiple panels together, thus complicating the assembly of the corresponding structures.

[0007] It needs to be sufficient and can be assembled and attached to adjacent boards in a simple and cost-effective manner. Summary of the Invention

[0008] This document describes a composite panel that generally integrates performance enhancements to the central region of a segmented core in the form of a non-developable curved wall geometry, increased surface area for bonding to the skin, and a panel with a solid frame perimeter surrounding the core. In one example, the design is achieved via a thermoforming process that forms grooves in the perimeter of the segmented core and then places a solid material of the same plastic resin into the grooves. This configuration facilitates robust fastening using conventional mechanical fastening methods and provides a weight-reduced panel with high structural integrity. In other embodiments, the grooves and / or the solid material placed in the grooves may be made of different substances and / or different substances from those used to form the panel body.

[0009] The composite sandwich panel includes: a core composed of a plurality of intersecting polygonal facets configured to improve isotropic properties and increase shear strength density scale, the core defining a generally flat element having a front side and a back-to-back rear side; a frame following the periphery of the core; a spacer sheet received within the frame and configured to accommodate mechanical fasteners; and a skin disposed on the front and rear sides of the core, wherein the frame has a width sufficient to provide reinforcement for the joint, and wherein the core includes a bonding surface extending generally parallel to the skin and providing increased area contact to enhance adhesion to the skin. Here, shear strength density is a quantitative relationship between shear values.

[0010] This document also provides a core for a composite sandwich panel, the core comprising: a plurality of intersecting polygonal surface structures configured to improve isotropic properties and increase shear strength density scale; and a plurality of bonding surfaces formed on the surface structures.

[0011] This disclosure also provides a method for manufacturing a composite sandwich panel, the method comprising: providing a core composed of a plurality of intersecting polygonal surface structures; arranging the surface structures to improve isotropic properties and increase the shear strength density scale of the core; forming a bonding surface on the surface structures, the bonding surface providing increased area contact to enhance adhesion; forming a frame that follows the contour of the periphery of the core; providing spacer sheets within the frame and arranging the spacer sheets to accommodate mechanical fasteners; and providing a skin composed of a thin material; and attaching the skin to the bonding surface. Attached Figure Description

[0012] To gain a more complete understanding of this disclosure, reference is now made to specific embodiments, wherein like reference numerals denote like parts, wherein: FIG1 shows an assembled composite sandwich panel in an exemplary embodiment; FIG2 is an exploded view thereof; FIGS. 4a and 4b show perspective views thereof and their partial enlarged views; FIG5 is a front view of a core including spacer sheets disposed around its periphery; FIGS. 6a and 6b show perspective views thereof and their partial enlarged views; FIGS. 7a and 7b show exploded views thereof and partial enlarged views of the core; along axis AA; FIG9 is a portion of the core. A front view showing an exemplary embodiment of the core geometry; Figure 10 is a perspective view thereof; Figures 11a and 11b show side views viewed from the top and right side of Figure 9, respectively, including illustrative dimensions; Figures 12a and 12c show multiple views of an alternative composite sandwich panel; Figures 13a, 13b, and 14 show multiple views of the composite sandwich panel in the alternative embodiment; Figures 15a and 15c show multiple views of the composite sandwich panel in the alternative embodiment; and the composite sandwich panel. Detailed Implementation

[0013] Figures 1 and 2 illustrate an exemplary, non-limiting composite sandwich panel 10. The core 12 has a front side 14 and a rear side 16 facing away from each other. The panel 10 also includes a skin 18 disposed on each of the front side 14 and the rear side 16. In this example, the core 12 is generally formed as a three-dimensional flat element with a straight profile. That is, the front side 14 and the rear side 16 of the core 12 are substantially square or rectangular in shape. This is merely exemplary. The core 12, its various faces and profiles, and the larger panel 10 can be formed from any desired polygonal or curved shape or a combination thereof.

[0014] As illustrated in Figures 1 and 2, the skin 18 is a thin planar member having a generally square shape and including opposing inner surfaces 20 and outer surfaces 22, wherein the outer surface 22 is oriented away from the core 12 and faces the exterior of the plate 10. Like the core 12, the skin 18 can have any desired shape, and the skin 18 can be shaped to complement the shape of the core 12, or it can have a different shape than the core.

[0015] The skin has a strength of 150 ksi and a thickness of 0.013 inches to 0.016 inches. This steel is processed in accordance with industry standards, with representative alloys including, but not limited to, ASME A653 galvanized annealed steel or hot-dip galvanized steel, with appropriate backing or primer coating, paint and / or other surface treatments.

[0016] Continuous fibers with high tensile strength (e.g., glass, carbon, borosilicate, basalt). Such fibers can be embedded within a substrate (e.g., thermoplastic polymers such as PE, PP, TPO, PEEK, ABS, aPET, PETG). These skins 18 can be applied to the core 12 as unidirectional strips or bonded into multilayer laminates using directional layup.

[0017] The skin 18 is attached to the front 14 and rear 16 of the core 12 using a bonding process. For example, if the skin 18 is made of steel, bonding can be achieved using a structural adhesive, such as an epoxy primer using a one-component, moisture-curing polyurethane. As described, the skin 18 is formed of a fiber-reinforced polymer. Alternatively, if the skin 18 is formed of a fiber-reinforced polymer matrix, an adhesive can be used, or the skin can be thermally welded to the core.

[0018] Figure 3 shows a detailed view of the rear side 16 of the core 12. Figure 4a shows a perspective view of the rear side 16, and Figure 4b shows an enlarged partial view thereof. The frame follows the outer periphery of the core 12. The central region 24 contains a plurality of intersecting polygonal facet structures 28, which are repeated to form an array joined by the frame 26. As discussed further herein, the facet structures 28 are designed to promote isotropic properties and increase the shear strength density scale and increase the contact area to enhance adhesion to mating surfaces. The frame 26 is a flat element having a flat surface 30 on the rear side 16 of the core 12, which is coplanar with the outer extensions of the polygonal facet structures 28, i.e., some facet structures 28 are coplanar with the flat surface 30 of the frame 26.

[0019] Figures 5 through 7 show multiple views of the front side 14 of the core 12. The view of the central region 24 on the front side 14, and the polygonal surface structure 28, is the opposite of what is seen at the rear side 16. The frame 26 on the front side 14 of the core 12 and the rear side 16 of the core 12 are also visible. As best seen in Figures 7a and 7b, the frame 26 includes an inner boundary 34 and an outer boundary 36. The inner boundary 34 is a thin protruding element extending from the flat surface 32 of the frame 26, extending around the central region 24, and is positioned to contact the polygonal surface structure 28. The outer boundary 36 is also thin. The inner boundary 34 and the outer boundary 36 extend substantially orthogonally from the flat surface 32 of the frame 26 and are parallel to each other.

[0020] Both the inner boundary 34 and the outer boundary 36 include an outermost surface 38, which is disposed away from the flat surface 32 of the frame 26, wherein these outermost surfaces 38 are coplanar. The coplanarity of the frame elements and the polygonal surface structure is clearly visible in the enlarged partial cross-section of the core 12. Specifically, dashed line BB illustrates that the rear flat surface 30 of the frame 26 is coplanar with the mating surface 40 of the polygonal surface structure 28. Similarly, dashed line CC illustrates the outermost surface 38 of the inner boundary 34.

[0021] As can be specifically seen in Figures 7a-7b and Figure 8, the protruding inner boundary 34 and outer boundary 36 of the frame 26, along with the front flat surface 32, combine to form a groove. That is, these elements have a U-shaped cross-section, a portion of which is visible in Figure 8. As seen in Figure 7a, the groove extends around the periphery of the core 12, thereby enclosing the central region 24. The groove is configured to receive at least one liner, and in the illustrated embodiment, four liners are provided: liner 42 and 44 arranged opposite each other, and liner 46 and 48 arranged opposite each other. Liners 42 to 48 are received by friction fit, or loosely disposed therein and secured by abutting the flat surface 32 with a skin 18 mounted on top of them, as discussed below. Liners 42 to 48 are essentially prismatic portions designed to at least partially or completely fill the groove and receive and retain the engaging hardware. In one embodiment, liner 42 to 48 are formed of the same material. Filler pieces 42 and 44 have equal lengths, and filler pieces 46 and 48 have equal lengths, wherein the lengths of filler pieces 46 and 48 are greater than the lengths of filler pieces 42 and 44. Here, filler pieces 46 and 48 extend the entire length of the core 12, and filler pieces 42 and 44 extend perpendicularly therebetween. This configuration is, of course, exemplary. In the case of a square-shaped core 12, filler pieces 42 to 48 may all have equal lengths, or some or all of filler pieces 42 to 48 may have different lengths, or any other desired configuration in which they are received by and substantially fill the slots of the frame 26.

[0022] Returning to the cross-section of Figure 8, it can be seen that the suturing piece 42 is located in the groove of the frame 26. The suturing piece 42 has an equal or slightly smaller thickness. The suturing pieces 42 to 48 are completely located within the groove of the frame 26 and do not protrude from it.

[0023] Figures 9 through 11 show multiple views of a portion of the core 12. Here it can be seen that the polygonal surface structure 28 includes a plurality of mating surfaces 40 extending across the front side 14 of the core 12 and correspondingly, mirror-image, extending across the rear side 1 and the length of the shown portion of the core 12. See Figure 9. This arrangement of Figures 9 through 10 is repeated throughout the core 12 to form a herringbone pattern (see, for example, Figure 5). Specifically, as shown in Figures 11a and 11b, the mating surfaces 40 at the front side 14 of the core 12 are coplanar with each other, and the mating surfaces 40 at the rear side 16 of the core are also coplanar with each other. Along the entire length of the core 12, the mating surfaces 40 alternate between the front side 14 and the rear side 16 and are connected by alternating inclined polygonal portions 50. In the example shown, the inclined polygonal portions 50 are at a 135° angle relative to the mating portions 40. o Similarly, as shown in Figure 9, the intersecting axes DD form a repeating V-shaped pattern on the portion of core 12 shown in Figures 9 and 10.

[0024] Exemplary dimensions are included in Figures 11a and 11b. The core thickness is 0.220 inches. The thickness of the bonding surface 40 is 0.063 inches. The formed depth shown has a length of 3.074 inches and a width of 2.934 inches. These dimensions are exemplary and may vary depending on the application.

[0025] As mentioned above, the composite sandwich panel 10 is formed by attaching the skin 18 to both the front side 14 and the rear side 16 of the core 12. In a preferred embodiment, the skin 18 contacts the inner boundary 34 and the outer boundary 36 of the frame 26, contacts the filler pieces 42 to 48 disposed in the slots of the frame 26, and also contacts the bonding portion 40 of the polygonal surface structure 28. Some of these surfaces in contact with the skin 18 facilitate the bonding and attachment of the skin 18 to the core 12.

[0026] An increased contact area between the core 12 and the skin 18 is provided to enhance adhesion. In the illustrated embodiment, the bonding portion 40 has a flat planar surface positioned to engage the skin when the skin 18 is disposed on the core 12. In other embodiments, the outward-facing surface of the bonding portion 40 may include non-planar elements (such as recesses) to further facilitate adhesion to the skin 10.

[0027] As shown, the core 12 includes a plurality of intersecting polygonal surface structures 28, which are designed to promote isotropic properties and increase the shear strength density scale. The core may fall into the type described in U.S. Patent Application No. 18 / 012,047, the entire contents of which are incorporated herein by reference. Specifically, the core provides an optimal shear strength density scale, promotes isotropic material properties, has in-plane tensile properties to maximize fatigue life and impact resistance, and is designed to include a periphery modified to include a filler plate to accommodate mechanical fasteners. Embodiments of the core disclosed herein encompass these aspects but are merely exemplary.

[0028] In this paper, the "shear strength density scale" refers to the relationship between a material's shear strength and its density. This concept is used to determine how density variations affect a material's shear strength, which is crucial for optimizing material properties. By understanding this scale, materials can be designed to achieve desired balance. The various geometries and configurations of the core 12 discussed in this paper are specifically configured to contribute to isotropic properties and increase the shear strength density scale.

[0029] Skin 10 is described herein as extending over the entire extent of the front and rear sides, extending only over a portion of the core, and / or extending beyond the perimeter of the core on one or more faces. 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 at a location between the inner and outer boundaries of the frame. Adjacent panels may include skins extending beyond their perimeters to lie on the aforementioned adjacent panels. In this way, the extended skins of one panel may overlap and extend on top of the frame of the adjacent panel to facilitate joining them in an “overlapping” manner.

[0030] Figures 12 through 14 illustrate several exemplary embodiments of composite sandwich panels that are joined together in an overlapping manner. Specifically, Figures 12a and 12c show two adjacent panels 10', 10'', each panel including a core 12 with a frame 28 having sprue tabs 42 to 48 and a skin 18 fixed thereto, as described above. However, unlike the aforementioned skin, the skin on the front side 14 of panel 10' is offset to the right (as shown), which exposes the frame 28 on one side of panel 10' and forms an extension 52 of the skin 18 on the other side of panel 10'. The skin 18 on the rear side 16 is aligned with the core. Panel 10'' is constructed similarly to panel 10'. In this way, the frame 28 of the panel overlaps with the extension 52 of panel 10' when the two panels are joined. The extension 52 of panel 10' can be secured to the frame 28 of panel 10'' using adhesives, mechanical fasteners, or a combination thereof to secure panels 10', 10'' together. Additional plates of the same construction can be fixed in pairs.

[0031] In the examples of Figures 12a to 12c, the skin 18 on the rear side 16 of plate 10' extends from the edge of the underlying core 12 to the edge. However, in other embodiments, the skin 18 on the rear side 16 of plate 10' may be biased in a direction opposite to the bias direction of the skin 18 on the front side 14 of plate 10', to form another extension 52. The skins 18 on the front sides 14 of plates 10' and 10'' are biased as described with respect to Figures 12a to 12c. However, here, the skins 18 on the rear side 16 of plates 10' and 10'' are biased in opposite directions. This forms extensions 52 on the front side 14 and rear side 16 of plates 10' and 10'' for the plates to abut against each other. The skins 18 can be secured to the frame at multiple locations on the front and rear sides of the respective plates by adhesives and / or mechanical fasteners.

[0032] Figure 13b illustrates an alternative configuration of a composite sandwich panel 100 comprising a core 12 and a skin 18, wherein the skin 18 extends edge-to-edge throughout the core 12. However, on the front side 14 of the panel 100, the skin 18 extends to the right edge (as shown) and then extends beyond the core 12 to form an extension 52. Similarly, on the rear side 16 of the panel 100, the skin 18 extends to the left edge (as shown) and then extends beyond the core 12. In Figure 13b, the extension 52 of one of the skins 18 extends over the skin 18 of the adjacent panel 100 on both the front side 14 and the rear side 16. This overlap provides an interface at which the skin can be secured by adhesives and / or mechanical fasteners. This configuration can be used with or without the frame 28.

[0033] A protective film 102 is disposed above the outer surface 22 of the skin 18. In one example, the protective film 102 may be made of polyethylene terephthalate (PET). Other suitable materials may be used to provide a protective layer for the sheet and to facilitate bonding with the skin 18.

[0034] In this configuration, the skin 18 on the front side 14 and rear side 16 of plate 150 is not aligned with the core 12, such that on the first side (left side of the figure), the frame 28 is exposed, and on the other side (right side of the figure), the skin 18 on the front side 14 and rear side 16 of plate 150 protrudes to form an extension 52. This forms a "mortise and tenon" that overlaps and abuts the exposed frame 28 by inserting a portion of the frame 28 of one plate 150 into the protruding extension 52 of the other plate 150. This overlapping area can receive adhesives and / or mechanical fasteners to attach adjacent plates 150 in the manner discussed above.

[0035] The core 12 includes a portion 152 with a smaller cross-sectional area and a portion 154 with a larger cross-sectional area. A skin 18 is fitted to the alternately shaped core 12 and extends to the end portion 152 of the core 12, and extends beyond the larger portion 154 of the core 12 to form an extension 52. The resulting plates 150 are secured together using the mortise and tenon joint method described above.

[0036] Figure 16b shows an alternative edge-to-edge arrangement of the composite sandwich panel 200. However, at one edge (left side of the figure), the skin 18 on the front side 14 of the panel 200 is bent at approximately ninety degrees and extends to the rear side 16, where the skin 18 is bent again at ninety degrees to protrude from the panel 200, thus forming an extension 52. The skin 18 on the rear side 16 of the panel 200 is arranged opposite to each other and includes two vertical bends on the other side of the core 12 to traverse to the front side 14 and protrude, thus forming the extension 52. Adjacent panels 200 can be fitted together by overlapping and attaching two adjacent extensions 52, as shown.

[0037] Figure 16c illustrates an arrangement of two plates 10 with skin 18. Here, a stake 220 is placed between adjacent plates 10 and includes: a portion 222 extending over the front side 14 of one of the plates 10; a portion 224 extending over the rear side 16 of the adjacent plate 10; and a portion 226 connecting portions 222 and 224. Portions 222 and 224 are positioned close to the respective frame 28 and allow the two plates to be joined together.

[0038] Figure 16d shows a similar configuration using two-part piles 250 to accommodate two adjacent composite sandwich panels 10. A first portion 252 of the pile 250 extends over the frame 28 on the front side 14 of the panel 10 and continues thereafter. Another portion extending over the frame 28 on the rear side 16 of the panel 10 engages with the first portion 252. Due to this advantageous arrangement, the first portion 252 and the second portion 254 of the pile 250 can be secured to the frame 28 of the panel 10 and fixed to each other, thereby achieving the adjacency of the panels 10.

[0039] Figure 16e illustrates another configuration utilizing two-part piles 250, wherein a first portion 252 extends substantially coplanar with the core 12 of the adjacent plate 10 and is secured to offset frame portions 256. These portions 256 are similar to the frames 28 described herein; however, the portions 256 extend non-coplanarly with respect to the core 12, while the frames 28 are substantially coplanar with their respective cores 12. See, for example, Figure 8. The offset frame portions 256 are positioned relative to the core 12 and thus secure two adjacent plates 10 while maintaining coplanar alignment of the skin 18 on the front side 14 of the plate 250.

[0040] To date, the frame 12 of the composite sandwich panel has been described as being formed by repeating polygonal facets 28 having multiple flat bonding surfaces 40. This configuration is, of course, exemplary, and many geometries are contemplated within the broad scope of this disclosure.

[0041] Figure 17 illustrates another exemplary embodiment of the geometry for core 12, which includes a flat surface similar to the flat surface of the previously described polygonal facet structure 28. The flat surface in Figure 18 has been rounded to provide additional strength and stiffness. That is, the flat surface of the geometry in Figure 17 is transformed into a non-developable surface in Figure 18. Figure 19 shows another geometric embodiment in which the top of the non-developable surface in Figure 18 is flattened, further increasing the bonding area and modifying the geometry to address plate-specific failure modes. The composite sandwich panels described herein may include any of the disclosed geometries, variations, or combinations thereof.

[0042] The frame area of ​​the disclosed composite sandwich panel has sufficient width to receive and hold the joining elements and fasteners used when adjacent panels are abutted in the manner discussed above.

[0043] Composite sandwich panels are described herein as including an extended frame. However, as illustrated, for example, with respect to Figures 13b, 14, and 16a-16b, there are embodiments of the disclosed composite sandwich panels without a frame, and these embodiments are designed to abut adjacent panels through a unique arrangement and utilization of skins disposed on the core to form the panels. Other alternative embodiments that do not surround the perimeter of the panels also exist. For example, the core may include a frame only on one or more, but not all, sides.

[0044] The composite sandwich panel described in this article solves the aforementioned problems and shortcomings by providing a panel that is both lightweight and structurally sound.

[0045] Embodiments of the present invention are described herein with reference to the accompanying drawings. Alternative embodiments may be devised without departing from the scope of the invention. It should be noted that various connections and positional relationships are shown in the description and drawings. These connections and / or positional relationships (unless otherwise specified) may be direct or indirect, and the invention is not intended to be limiting in this respect. Thus, the connection of entities may refer to a direct connection or an indirect connection, and the positional relationship between entities may be direct.

[0046] The term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations or designs. The terms "at least one" and "one or more" are understood to include any integer greater than or equal to one, i.e., one, two, three, four, etc. The term "multiple" is understood to include any integer greater than or equal to two, i.e., two, three, four, five, etc. Terms (such as "connected to," "attached to," etc.) can include both indirect and direct.

[0047] Various embodiments of the invention have been described for illustrative purposes, but are not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments, as well as to practical applications or technical improvements to technologies found in the market, or to enable those skilled in the art to understand the embodiments disclosed herein.

[0048] Figure Labels

[0049] 10 Composite sandwich panels

[0050] 12-core

[0051] The rear side of the 16 cores

[0052] 18 Skin

[0053] 20. Inner surface of the skin

[0054] 22. Outer surface of the skin

[0055] 26 Frames

[0056] 28. Polygonal surface structure

[0057] 30. The rear flat surface of the frame

[0058] 32. Front flat surface of the frame

[0059] 36 Outer Boundary

[0060] 38. The outermost surface of the boundary

[0061] 40 Bonding Surface

[0062] 42-48 Gap Filler Plate

[0063] 52 Extension

[0064] 100 Composite Sandwich Panel

[0065] 102 Protective Film

[0066] 150 Composite Sandwich Panel

[0067] 154. Sections with larger cross-sections

[0068] 200 Composite Sandwich Panel

[0069] 220 integrated pile

[0070] Part of pile 222

[0071] 226 Connection Part

[0072] 250 Two-part piles

[0073] 252 Part 1

[0074] 254 Part Two

Claims

1. A composite sandwich panel, comprising: The core is composed of multiple intersecting polygonal facets, and the core is configured to define a generally flat element having a front side and a back-to-back rear side. The frame follows the contour of the periphery of the core; A sprue is received within the frame and configured to accommodate mechanical fasteners; and a skin is disposed on the front and rear sides of the core; wherein the width of the frame is sufficient to provide reinforced engagement; wherein the core includes a plurality of engagement surfaces that extend substantially parallel to the skin and provide increased area contact to enhance adhesion to the skin.

2. The composite sandwich panel according to claim 1, wherein, The frame includes a slot for receiving and holding the gap filler piece.

3. The composite sandwich panel according to claim 2, wherein, The groove is defined by an outer boundary of the core, an inner boundary that protrudes from the front side of the core and extends substantially collinearly with the outer boundary, and a flat surface on the frame extending between the outer and inner boundaries on the front side of the core. The frame is continuous with the central region of the core, which contains the plurality of polygonal surface structures, and the groove has a generally U-shaped cross-section.

4. The composite sandwich panel according to claim 2, wherein, The gap filler plate comprises one or more parts.

5. The composite sandwich panel according to claim 3, wherein, The plurality of bonding surfaces are disposed on the plurality of polygonal surface structures and located on the front and rear sides of the core, wherein the bonding surface on the front side of the core is coplanar with the inner boundary and the outer boundary, and a portion of the frame is formed on the rear side of the core.

6. The composite sandwich panel according to claim 6, wherein, Multiple mating surfaces on the front side of the core are coplanar with each other, and wherein the mating surfaces on the front side of the core are arranged parallel to the mating surfaces on the rear side.

7. The composite sandwich panel according to claim 7, wherein, The bonding surface at the front side of the core is connected to the bonding surface at the rear side of the core via an inclined portion.

8. The composite sandwich panel according to claim 8, wherein, The inclined polygonal portions extend at an angle of approximately 135 degrees relative to the plurality of bonding surfaces. Some facet structures extend parallel to each other on the front side of the plate, wherein a second group of the plurality of polygonal facet structures extends parallel to each other and at an angle to the first group on the front side of the plate, wherein the first group and the second group intersect at an intersecting axis to form a repeating V-shape.

9. The composite sandwich panel according to claim 8, wherein, The angle of intersection is approximately 135 degrees.

10. The composite sandwich panel according to claim 1, wherein, The skin is made of thin-gauge high-strength steel.

11. The composite sandwich panel according to claim 1, wherein, The skin comprises several materials.

12. The composite sandwich panel according to claim 1, wherein, The core is designed to have in-plane tensile properties to maximize fatigue life and impact resistance. Multiple intersecting polygonal facets are configured to improve isotropic properties and increase the shear strength density scale; and multiple mating surfaces are formed on the facets, defining an increased contact area to enhance adhesion to mating surfaces.

13. The core according to claim 13, wherein, The plurality of bonding surfaces include a plurality of surfaces that are coplanar with each other on the front side of the core and a plurality of surfaces that are coplanar with each other on the rear side of the core, wherein the bonding surfaces on the front side of the core are arranged parallel to the bonding surfaces on the rear side.

14. The core according to claim 14, wherein, The bonding surface at the front side of the core is connected to the bonding surface at the rear side of the core via an inclined polygonal portion, wherein the inclined polygonal portion extends at an angle of approximately 135 degrees relative to the plurality of bonding surfaces.

15. The core according to claim 14, wherein, The first group of the plurality of polygonal facet structures extends parallel to each other on the front side of the composite sandwich panel, wherein the second group of the plurality of polygonal facet structures extends parallel to each other on the front side of the composite sandwich panel and at an angle to the first group, wherein the first group and the second group intersect at an intersecting axis to form a repeating V-shape, wherein the angle of intersection is approximately 135 degrees.

16. The core of claim 13, further comprising a frame extending around a plurality of sprue plates configured to receive mechanical fasteners.

17. A method for manufacturing a composite sandwich panel, the method comprising: Provide a core composed of multiple intersecting polygonal surface structures; increase the strength density scale of the core; Multiple bonding surfaces are formed on the surface structure, the multiple bonding surfaces providing increased area contact to enhance adhesion; a frame is formed, the frame following the contour of the periphery of the core; Mechanical fasteners; The core is provided with a skin on its front and rear sides, the skin being made of a thin material with high tensile strength; and the skin is attached to the plurality of bonding surfaces.

18. The method of claim 18, further comprising forming a groove in the frame for receiving the filler piece by the steps of: causing an outer boundary to protrude from the front side of the core and extending the outer boundary around the periphery of the core, causing an inner boundary to protrude from the front side of the core and extending the inner boundary substantially collinearly, the inner boundary being located on the front side of the core.

19. The method of claim 19, further comprising: The plurality of mating surfaces are formed on the polygonal surface structure on the front and rear sides of the core, the inner boundary and the outer boundary are arranged, the plurality of mating surfaces on the rear side of the core are arranged to be coplanar with each other and coplanar with the flat surface of the frame on the rear side of the core, the mating surfaces on the front side of the core are arranged to be parallel to the mating surfaces on the rear side, and the mating surfaces are connected to the front side of the core.

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