This invention, in general, relates to a composite structure. More particularly, the composite structure is relates to a composite with a honeycomb core structure with three dimensional fiber continuity.
Honey comb structures are most commonly used in applications where light weight materials are desirable, for example, in interiors of aircrafts, in paperboard honeycombs used in paper pallets, glass flooring systems, etc. Improvements in aerospace design, motor vehicle equipment, and light-weight construction formed the foundation for the advancement of honeycomb structures. The benefit of the honeycomb structures lies in their low weight, combined with their tremendous structural strength. Honeycomb structures are typically used as shock absorbing layers both in automobile manufacture and in sports equipment such as sports shoes owing to the anti-shock mechanical property exhibited by such structures. Honeycomb structures are apt for design and architectural applications as a result of their ratio of mass to their load carrying capacity and bend strength. Moreover, the composite material, which generally comprises a honeycomb core, can be adapted for specific requirements with regard to strength and selection of materials.
In the furniture industry, honeycomb structures are used extensively. For example, for low load bearing furniture table tops or furniture walls, 3 mm thin medium-density fiberboards (MDFs) are glued to an internal paper honeycomb core. However, in the current art of honeycomb based composites, strength failure is caused due to a lack of in-plane shear strength and tendency of the material to delaminate owing to the mixture in the material layer and structure.
Currently, a three dimensional fiber arrangement is achieved through stitching of upper and lower face sheets, or through complex knitting. Such stitching and knitting processes are cumbersome and expensive. It is cost prohibitive to use complex three dimensionally stitched or knitted composites in commonplace applications. There is a need for a faster and less costly process to achieve three dimensional fiber reinforcement, which will enable the use of three dimensional oriented fibers in commonplace composite applications in the furniture and building industry.
Hence, there is a long felt but unresolved need for a composite comprising a honeycomb structure with three dimensional fiber continuity that improves adhesion between face sheets and a core of the honeycomb structure, improves the in-plane shear strength, and reduces the risk of delamination between the core and face sheets of the honeycomb structure.
This summary is provided to introduce a selection of concepts in a simplified form that are further described in the detailed description of the invention. This summary is not intended to identify key or essential inventive concepts of the claimed subject matter, nor is it intended for determining the scope of the claimed subject matter.
The composite disclosed herein addresses the above mentioned needs for a honeycomb structure with three dimensional fiber continuity that improves adhesion between face sheets and a core of a honeycomb structure, improves the in-plane shear strength, and reduces the risk of delamination between the core and the face sheets of the honeycomb structure.
The composite disclosed herein comprises a core comprising a cellular structure and reinforcing fibers, an upper face sheet, and a lower face sheet. The cellular structure comprises multiple cells composed of a carrier material. The cells are, for example, of a honeycomb type, with a hexagonal geometry, having a mix of shapes and cell sizes, for example, square or sinusoidal shapes. In an embodiment, the carrier material is cellulosic paper. In another embodiment, the carrier material comprises an inorganic material. The outer walls of the cells are adhered to each other to form the cellular structure. The cellular structure is a honeycomb structure comprising strips of the carrier material arranged in an x direction in an x-y plane and adhered together at alternate and spaced areas of the strips of carrier material. The honeycomb structure is formed by expanding the strips of carrier material in the x direction after the adhesion.
The reinforcing fibers are externally bonded onto the outer walls of each of the cells of the cellular structure in a z direction. In an embodiment, the reinforcing fibers comprise organic fibers of an extended length, that is, longer than the height of the outer walls of the cells of the cellular structure. In an embodiment, the reinforcing fibers comprise inorganic fibers. The inorganic fibers comprise, for example, one or more of glass fibers and carbon fibers. The reinforcing fibers conform to a shape of the cellular structure along the adhered outer walls of the cells of the cellular structure. An upper portion of the reinforcing fibers is configured to extend outwardly from the upper edges of the cells of the cellular structure. A lower portion of the reinforcing fibers is configured to extend outwardly from the lower edges of the cells of the cellular structure. In an embodiment, the length of the upper portion and the lower portion of the reinforcing fibers extending outwardly from the upper edges and the lower edges of the cells of the cellular structure respectively is greater than the width of one of the cells of the cellular structure.
The upper face sheet is configured to be bonded to the upper portion of the reinforcing fibers that extends outwardly from the upper edges of the cells of the cellular structure in the z direction. The upper portion of the reinforcing fibers that extends outwardly from the upper edges of the cells of the cellular structure in the z direction is continued in an x-y plane by the bonded upper face sheet. The lower face sheet is configured to be bonded to the lower portion of the reinforcing fibers that extends outwardly from the lower edges of the cells of the cellular structure in the z direction. The lower portion of the reinforcing fibers that extends outwardly from the lower edges of the cells of the cellular structure in the z direction is continued in the x-y plane by the bonded lower face sheet.
The upper portion and the lower portion of the reinforcing fibers extending from the upper edges and the lower edges of the cells of the cellular structure provide the following functions. Firstly, three dimensional continuity of the reinforcing fibers is established between a surface of contact between the core, the upper face sheet, and the lower face sheet. Such three dimensional continuity improves delamination resistive performance of the composite. Secondly, in some cases, it is sufficient to only coat the extending reinforcing fibers with an adhesive to bond to the upper face sheet and the lower face sheet, instead of applying adhesive to the entire upper face sheet and the lower face sheet, thereby reducing adhesive consumption.
Disclosed herein is also a second composite with a three dimensional continuity of reinforcing fibers. The second composite comprises strips of reinforcing fibers arranged in an x direction along an x-y plane and adhered together at alternate and spaced areas of the strips of reinforcing fibers. The arranged and adhered strips of reinforcing fibers are expanded in the x direction to create a honeycomb structure. The strips of reinforcing fibers are adhered to each other in a first binder matrix and substantially oriented in a z direction. An upper portion of the reinforcing fibers is configured to extend outwardly from the upper edges of the cells of the honeycomb structure in the z direction. The upper portion of the reinforcing fibers extending outwardly from the upper edges of the cells of the honeycomb structure in the z direction is configured to be set in a second binder matrix. The extended upper portion of the reinforcing fibers is continued in the x-y plane by the second binder matrix.
A lower portion of the reinforcing fibers is configured to extend outwardly from the lower edges of the cells of the honeycomb structure in the z direction. The lower portion of the reinforcing fibers extending outwardly from the lower edges of the cells of the honeycomb structure in the z direction is configured to be set in the second binder matrix. The extended lower portion of the reinforcing fibers is continued in the x-y plane by the second binder matrix. A three dimensional continuity of the reinforcing fibers is established between the first binder matrix and the second binder matrix. Hence, the second composite is created with three dimensional fiber continuity between an upper surface, a core, and a lower surface. In the above case, the upper surface is created by reinforcing fibers in the second binder matrix, the core is composed of reinforcing fibers in the first binder matrix, and the lower surface is composed of reinforcing fibers in the second binder matrix.
In an embodiment of the second composite, the upper portion of the reinforcing fibers extending outwardly from the upper edges of the cells of the honeycomb structure in the z direction is configured to be bonded to an upper face sheet and is thereby continued in the x-y plane by the bonded upper face sheet. The lower portion of the reinforcing fibers extending outwardly from the lower edges of the cells of the honeycomb structure in the z direction is configured to be bonded to a lower face sheet and is thereby continued in the x-y plane by the bonded lower face sheet.
Disclosed herein is also a method for manufacturing a composite with a three dimensional continuity of reinforcing fibers. Sheets of reinforcing fibers, an adhesive, a first fiber binder resin, and a second fiber binder resin are provided. The first fiber binder resin and the second fiber binder resin comprise, for example, epoxy, polyester resins such as orthothalic polyester resin, polyurethanes, vinyl esters, phenolic resins, urea formaldehyde, etc. Each of the sheets of reinforcing fibers is coated with the first fiber binder resin along multiple selected linear paths to create multiple coated areas and non-coated areas on the sheets of reinforcing fibers. The coated areas on the sheets of reinforcing fibers constitute a first binder matrix. Examples of methods of resin coating on the sheets of reinforcing fibers are, for example, roller coating, spray on systems, etc. The adhesive is applied on equally spaced areas along a length of the coated areas of each of the sheets of reinforcing fibers after allowing the sheets of reinforcing fibers to cure. Each of the sheets of reinforcing fibers are arranged, one on top of another to form a bundle of sheets of reinforcing fibers.
The bundle of sheets of reinforcing fibers is sliced from an upper surface to a lower surface of the bundle of sheets of reinforcing fibers along a line passing through the non-coated areas on the sheets of reinforcing fibers to form separate strips of reinforcing fibers. Each of the strips of reinforcing fibers is expanded in an x direction in an x-y plane to create a honeycomb structure. The created honeycomb structure comprises reinforcing fibers oriented in a z direction in the first binder matrix. An upper portion and a lower portion of the reinforcing fibers extend outwardly from the upper edges and the lower edges of the cells of the honeycomb structure. The upper portion and the lower portion of the reinforcing fibers extending outwardly from the upper edges and the lower edges of the cells of the honeycomb structure respectively are flattened along the x-y plane.
The flattened upper portion and lower portion of the reinforcing fibers extending outwardly from the upper edges and the lower edges of the cells of the honeycomb structure respectively are wetted along the x-y plane using the second fiber binder resin to form a second binder matrix, thereby establishing a three dimensional fiber continuity of the reinforcing fibers between the first binder matrix and the second binder matrix, after curing of the composite. In an embodiment, the method for manufacturing the composite with a three dimensional continuity of reinforcing fibers comprises orienting and adhering additional reinforcing fibers in a direction perpendicular to the z direction, to the strips of reinforcing fibers oriented in the z direction. The strips of reinforcing fibers oriented in the z direction are high density reinforcing fibers and the adhered additional reinforcing fibers oriented perpendicular to the strips of reinforcing fibers oriented in the z direction are low density reinforcing fibers. The number and the density of the additional reinforcing fibers are less than the number and the density of the reinforcing fibers oriented in the z direction respectively.
The foregoing summary, as well as the following detailed description of the invention, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, exemplary constructions of the invention are shown in the drawings. However, the invention is not limited to the specific methods and components disclosed herein.
The upper face sheet 108 is configured to be bonded to the upper portion 101a of the reinforcing fibers 101 that extend outwardly from the upper edges 105b of the cells 106 of the cellular structure 105 in the z direction. The upper portion 101a of the reinforcing fibers 101 extending outwardly from the upper edges 105b of the cells 106 of the cellular structure 105 in the z direction is continued in an x-y plane by the bonded upper face sheet 108. The lower face sheet 109 is configured to be bonded to the lower portion 101b of the reinforcing fibers 101 extending outwardly from the lower edges 105c of the cells 106 of the cellular structure 105 in the z direction. The lower portion 101b of the reinforcing fibers 101 extending outwardly from the lower edges 105c of the cells 106 of the cellular structure 105 in the z direction is continued in the x-y plane by the bonded lower face sheet 109. A three dimensional continuity of the reinforcing fibers 101 is established between a surface of contact between the core 107, the upper face sheet 108, and the lower face sheet 109.
The methods of resin coating over the reinforcing fibers 101 are, for example, roller coating, spray on systems, etc.
A lower portion 101d of the reinforcing fibers 101 is configured to extend outwardly from the lower edges 111b of the cells 106 of the honeycomb structure 111 in the z direction. The lower portion 101d of the reinforcing fibers 101 extending outwardly from the lower edges 111b of the cells 106 of the honeycomb structure 111 in the z direction is configured to be set in the second binder matrix 113. The extended lower portion 101d of the reinforcing fibers 101 is continued in the x-y plane by the second binder matrix 113. A three dimensional continuity of the reinforcing fibers 101 is therefore established between the first binder matrix 112 and the second binder matrix 113.
In an embodiment, the upper portion 101c of the reinforcing fibers 101 extending outwardly from the upper edges 111a of the cells 106 of the honeycomb structure 111 in the z direction is configured to be bonded to an upper face sheet 108. The extended upper portion 101c of the reinforcing fibers 101 is continued in the x-y plane on the upper surface of the honeycomb structure 111 by the bonded upper face sheet 108. The lower portion 101d of the reinforcing fibers 101 extending outwardly from the lower edges 111b of the cells 106 of the honeycomb structure 111 in the z direction is configured to be bonded to a lower face sheet 109. The extended lower portion 101d of the reinforcing fibers 101 is continued in the x-y plane on the lower surface of the honeycomb structure 111 by the bonded lower face sheet 109.
The bundle of sheets of reinforcing fibers 101 is sliced 705 from an upper surface to a lower surface of the bundle of sheets of reinforcing fibers 101 along a line passing through the non-coated areas on the sheets of reinforcing fibers 101 to form separate strips of reinforcing fibers 101. Each of the strips of reinforcing fibers 101 is expanded 706 in an x direction in an x-y plane to create a honeycomb structure 111 comprising the reinforcing fibers 101 oriented in a z direction in the first binder matrix 112. The upper portion 101c and the lower portion 101d of the reinforcing fibers 101 extend outwardly from the upper edges 111a and the lower edges 111b of the cells 106 of the honeycomb structure 111. The upper portion 101c and the lower portion 101d of the reinforcing fibers 101 extending outwardly from the upper edges 111a and the lower edges 111b of the cells 106 of the honeycomb structure 111 respectively, are flattened 707 along the x-y plane. The flattened upper portion 101c and lower portion 101d of the reinforcing fibers 101 extending outwardly from the upper edges 111a and the lower edges 111b of the cells 106 of the honeycomb structure 111 respectively are wetted 708 along the x-y plane using the second fiber binder resin to form a second binder matrix 113, thereby establishing 709 a three dimensional fiber continuity of reinforcing fibers 101 between the first binder matrix 112, the core 107 exemplarily illustrated in
Example 1: A sheet of reinforcing fibers 101, for example, organic jute fibers, oriented substantially in the z direction is placed on a planar surface. Narrow strips of Kraft paper 1 inch wide are cut and adhered to both sides of the sheet of reinforcing fibers 101. These strips of Kraft paper are positioned parallel to one another, with a spacing of two inches between them. Adhesives are applied every three inches along the paper strips. The sheet of reinforcing fibers 101 with adhered strips of Kraft paper are placed one above the another, staggered lengthwise by 1.5 inches. After the adhesive cures, the above bundle of sheets of reinforcing fibers 101 are further cut into stacked strips of reinforcing fibers 101 by making a cut along the center of the two inch gap between the paper strips. Each of the stacked strips of reinforcing fibers 101 are expanded to create a honeycomb structure 111, wherein loose fibers extend out of the upper edges 111a and the lower edges 111b of the cells 106 of the honeycomb structure 111. The loose extending reinforcing fibers 101 are then coated with an adhesive and thereafter attached to a 3 mm thick top and 3 mm thick bottom medium density fiberboard (MDF) sheet. A 24% increase in modulus of rupture (MOR) performance was achieved with the above three dimensional fiber arrangement, when compared to the case without the use of reinforcing fibers 101.
Example 2: A sheet of reinforcing fibers 101, for example, woven glass fibers of 450 grams per square meter weight is positioned on a roller. The sheet of reinforcing fibers 101 is sent through a roll coater, where orthothalic polyester resin is coated along 1 inch strips on the sheet, with three inches spacing between the coated strips. Hence, on the glass fiber sheet, 3 inch bands of uncoated glass fibers are followed by 1 inch polyester coated glass fibers. After the polyester resin cures, epoxy adhesive is applied every three inches along the polyester coated glass fiber area. In the above manner, ten feet long, and four feet wide sheets of glass fibers, with epoxy strips alternatively located, are placed one above the other, and pressed using a ten ton press. After the epoxy cures, a cut is made along the center line of the uncoated 3 inch wide glass fiber area. Hence, multiple stacks of strips of reinforcing fibers 101 are created, and each stack unit is expanded in the x direction to create a honeycomb structure 111 with an uncoated sheet of reinforcing fibers 101 extending out of the coated polyester walls of the honeycomb structure 111 in the z direction. The extending uncoated sheet of reinforcing fibers 101 on the upper surface of the honeycomb structure 111 is then wetted with a polyester resin and flattened out as the upper surface of the honey comb structure 111. Similarly, the extending uncoated reinforcing fibers 101 on the lower surface of the honeycomb structure 111 is then wetted with a polyester resin and flattened out as the lower surface. In this example, the reinforcing fibers 101 are flattened out in the above mentioned x direction. The flattening process is carried out by pressing two Teflon® coated sheets onto the upper surface and the lower surface of the honeycomb structure 111. In the above example, a sheet of reinforcing fibers 101, for example, a specially woven glass sheet with greater density reinforcing fibers extending in one direction and lower density reinforcing fibers 114 extending in a corresponding perpendicular direction exemplarily illustrated in
The composites 100a, 100b, and 100c, exemplarily illustrated in
The foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the invention disclosed herein. While the invention has been described with reference to various embodiments, it is understood that the words, which have been used herein, are words of description and illustration, rather than words of limitation. Further, although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein; rather, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. Those skilled in the art, having the benefit of the teachings of this specification, may affect numerous modifications thereto and changes may be made without departing from the scope and spirit of the invention in its aspects.
Number | Date | Country | Kind |
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4356/CHE/2011 | Dec 2011 | IN | national |
This application is a national phase application of PCT application number PCT/IN2012/000812 titled “3D Fiber Composite”, filed in the Indian Patent Office on Dec. 11, 2012, which claims priority to and the benefit of provisional patent application number 4356/CHE/2011 titled “3D Fiber Composite”, filed in the Indian Patent Office on Dec. 13, 2011. The specifications of the above referenced patent applications are incorporated herein by reference in their entirety.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IN2012/000812 | 12/11/2012 | WO | 00 | 5/13/2014 |