The present invention relates to a lightweight periodic cellular structure fabricated using stacked arrays of wires or tubes that can be used as a multifunctional lightweight structural core for structural panels. More particularly, the present invention relates to a method of manufacturing such a lightweight periodic cellular structure using stacking and bonding techniques resulting in lightweight stacked arrays of hollow or solid structural elements and the resulting stacked arrays and pyramidal arrays resulting from this method.
The state of the art in the open-cell lightweight cellular structure industry is to utilize stochastic open cell metal foams as the core for such structural elements. Stochastic open cell foams lack the stiffness and strength of closed-cell (non-porous) metal foams but they possess characteristics that can be exploited in multifunctional applications. In addition to basic mechanical load support, these open cell foams possess good heat dissipation characteristics because of the ability to pump fluids through the pores in their open internal structure, they also have a high surface to volume ratio and are often used as electrodes in electrochemical cells. Such open cell foams are also being investigated for high-temperature supports for catalytic operations.
Manufacturing techniques for open cell stochastic foams include chemical or physical vapor deposition, electrolytic deposition, investment casting, and sintering processes. In most processing techniques, open cell polymer foams are used as the parent template onto which the metal foams are formed. These foams are available from a large number of manufacturers in a variety of cell sizes (typically measured as pores per inch). In addition, the various cell parameters can be modified by different techniques yielding overall foam property changes such as changes in relative density and modification of the cell size and structure within the foam.
The method of producing conductive metal porous sheet in Vaccarro, U.S. Pat. No. 5,738,907, herein incorporated by reference, accomplishes the production of open cell stochastic metal foam that can be formed into a continuously isotropic form.
The shortcomings in this technique, however, in that it does not result in a metal foam with predictable structural mechanical characteristics due to the overall lack of predictability in the metal foam's overall mechanical structure. The pores formed result in an overall isotropic structure while retaining conductivity, however, the exact shapes of pores as well as the cross-sectional shapes of the solid members surrounding the pores are unpredictable. This results therefore in an unpredictable bending modulus, tensile strength, and overall load-bearing capacity.
There are a number of methods for manufacturing periodic cellular metals as well that provide structural cores with regularly-spaced pores or channels suitable for multifunctional applications. These methods include investment casting, lattice block construction, constructed metal lattice, and metal textile lay-up techniques.
The truss panel in Hardigg, U.S. Pat. No. 4,757,665, herein incorporated by reference, discloses a structure of alternating pyramidal truss formed by a molding technique that result in a predictably-shaped and controlled structural shape.
This method however, does not provide for, among other things, precisely shaped hollow structural members that allow for directed flow of fluids to facilitate heat transfer throughout the structure of the truss panel.
There exists a need in the art for an open-cell periodic structure that has the advantages of open cell stochastic metal foams (including hollow open pores and provisions for a variety of structural shapes) with the precisely predictable mechanical properties that are currently unattainable in open cell stochastic foams. There also exists a need for a method of manufacture for such an open-cell periodic structure that allows for the maximum flexibility in construction such that a variety of geometries can be accommodated in manufacturing the periodic structure.
According to the invention, the lightweight periodic cellular structure has a stacked array of hollow or solid structural elements that are bonded at their contact points in order to form a stacked lattice structure. Further arrays may be stacked onto the stacked lattice structure in order to form a periodic cellular structure of varying thickness and depth. Also, structural panels may be added to parallel exterior edges of the stacked lattice structure to form a structural panel.
Further, the hollow structural elements are provided with wicking elements along their interior walls to facilitate heat transfer through the periodic cellular structure. Liquid may also be introduced into the hollow structural elements to further facilitate heat transfer through the periodic cellular structure. Also, the cellular structure may be utilized as light weight current collectors, such as electrodes, anodes, and cathodes.
The method of manufacturing the periodic cellular structure can accommodate a variety of cross-sectional shapes for the hollow structural members. In addition, the method may introduce a variety of stacking offset angles to vary the lattice shape and resultant mechanical characteristics of the periodic cellular structure. Finally, the method also allows for the bending of the array of hollow or solid structural elements into an array of hollow pyramidal truss elements that can be used to form a stacked pyramidal structure to serve as an alternative core of the periodic cellular structure.
In one aspect, the present invention lightweight periodic cellular structure provides a first array of hollow and/or solid structural elements located in a first plane along a first axis; and a second array of hollow and/or sold structural elements located in a second plane along a second axis, wherein the second array is stacked immediately on top of the first array and wherein the first axis and the second axis are offset at a desired offset angle, and wherein the second array is bonded to the first array at points of contact where the first array and the second array meet to form a stacked lattice structure.
In another aspect, the present invention provides a method of constructing a lightweight periodic cellular structure comprising the steps of: arranging a first array of parallel hollow and/or solid structural elements in a first plane along a first axis; stacking a second array of parallel hollow and/or solid structural elements in a second plane along a second axis, wherein the first axis and the second axis are offset at a desired offset angle and the second plane is parallel and disposed on the first plane at a plurality of contact points; and bonding the second array to the first array at the plurality of contact points to form a stacked lattice structure.
In another aspect, the present invention arranging a first array of hollow and/or solid parallel structural elements in a first plane along a first axis; stacking a second array of hollow and/or parallel structural elements in a second plane along a second axis, wherein said first axis and said second axis are offset at a desired offset angle and said second plane is parallel and disposed on the first plane at a plurality of contact points; bonding the second array to said first array at said plurality of contact points to form a stacked lattice structure; and bending said stacked lattice structure to a desired bending angle at a select number of said contact points to form a pyramidal cellular core.
The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.
The foregoing and other objects, features and advantages of the present invention, as well as the invention itself, will be more fully understood from the following description of preferred embodiments, when read together with the accompanying drawings, in which:
Turning now to the drawings, the subject invention, as shown In
The resulting stacked lattice structure 10 as shown in
In addition, according to the design criteria discussed throughout, other hollow structural designs of the present invention are provided. As shown in co-pending and co-assigned PCT International Application No. PCT/US01/22266, entitled “Heat Exchange Foam,” filed on Jul. 16, 2001, and corresponding U.S. application Ser. No. 10/333,004, filed Jan. 14, 2003, of which are hereby incorporated by reference herein in their entirety, there is provided other ways of forming the structural elements that includes a core that is comprised of an open cell having solid or hollow ligaments, foam, and/or interconnected network. The resultant hollow ligaments that have a substantially circular (rounded) cross section will require an internal wicking structure to effect a heat pipe. Otherwise, an interconnected cellular or truss network that has hollow ligaments having a triangular or cusp-like shaped cross section, or an acute-angled corner will not require an internal wicking mechanism to effect a heat pipe. The corner regions of the heat pipe act as return channels or groves.
According to the design criteria discussed throughout, other two-dimensional and three-dimensional structures may be implemented with the present invention as shown in co-pending and co-assigned PCT International Application No. PCT/US02/17942, entitled “Multifunctional Periodic Cellular Solids and the Method of Making thereof,” filed on Jun. 6, 2002, of which is hereby incorporated by reference herein in its entirety.
According to the design criteria discussed throughout, other two-dimensional and three-dimensional structures may be implemented with the present invention as provided in co-pending and co-assigned PCT International Application No. PCT/US01/17363, entitled “Multifunctional Periodic Cellular Solids and the Method of Making thereof,” filed on May 29, 2001, and corresponding U.S. application Ser. No. 10/296,728, filed Nov. 25, 2002, of which are hereby incorporated by reference herein in their entirety.
In addition, because of the tubes being hollow, additional functionality can be readily integrated into the structures described in this document. For example, the hollow nature of the tubes allow for the structure to become a very lightweight current collector for the integration of power storage devices such as batteries. For example, according to the design criteria discussed throughout, as shown in co-assigned PCT International Application No. PCT/US01/25158, entitled “Multifunctional Battery and Method of Making the Same,” filed on Aug. 10, 2001, and corresponding U.S. application Ser. No. 10/110,368, filed Jul. 22, 2002, of which are hereby incorporated by reference herein in their entirety, there is provided other ways of forming current collectors.
There are numerous other functionalities, which can be added into these structures making them ideal candidates for “structure plus” multifunctional materials.
As shown in
As shown in
We turn now to an alternate embodiment of the subject invention as shown in
The resulting pyramidal structure 12 as shown in
As shown in
It should be appreciated that the parallel structural panels 8 as discussed throughout can be planar, substantially planar, and/or curved shape, with various contours as desired.
Similarly,
As shown in
Finally, we turn to the methods for producing the above embodiments of the subject invention. The method for producing the stacked lattice structure 10 as shown in
The method for producing the alternate embodiment stacked pyramidal structure 12 as shown in
The embodiments and methods of manufacture for the embodiments described above provide a number of significant advantages. First of all, the methods of producing these periodic cellular structures allows for infinite variation in the cross-sectional size and shape of the arrays of hollow and solid structural elements 1,2 and the arrays of hollow and solid pyramidal truss elements 12 that make up the resulting stacked lattice structures 10 and stacked pyramidal structures. This flexibility is accomplished while still allowing for hollow passageways within the arrays of hollow structural elements 1, 2 whereby wicking elements 11 and fluids may be introduced in order to obtain optimum heat transfer performance within the periodic cellular structure. While the prior art open cell stochastic metal foams allow for improved heat transfer in their open pores, the unpredictable nature of the size and shape of the resultant pores makes them unpredictable and unreliable as load bearing structures. The present invention provides for the best heat transfer properties of open cell stochastic metal foams with the geometric and structural certainty of an engineered truss structure.
In addition, the subject invention provides for easy construction using a variety of bonding techniques. Where open cell stochastic metal foams require some stretching and temperature processing to achieve the slightest isotropic tendencies, the present invention provides for exacting control over all of the mechanical properties of the resulting periodic cellular structure by adjustment of: the cross sectional shapes of the arrays of hollow structural elements 1,2, the desired offset angle 15 between the first and second arrays 1,2 and the desired bending angle 16 in the case of the pyramidal structure 12 described above as the alternate embodiment. In addition, the structural rigidity and surface area of the wicking elements contained within the periodic cellular structure by increasing the density of parallel hollow structural elements within the stacked arrays 1,2 and pyramidal truss elements 12.
Overall, the subject invention provides a way to combine the best heat transfer capabilities of the open cell stochastic metal foam with the structural integrity and predictability of engineered truss shapes in a method that is simple and inexpensive to perform.
Of course it should be understood that a wide range of changes and modifications could be made to the preferred and alternate embodiments described above. It is therefore intended that the foregoing detailed description be understood that it is the following claims, including all equivalents, which are intended to define the scope of this invention.
This application claims priority from U.S. Provisional Application Ser. No. 60/384,341 filed on May 30, 2002, entitled “Method for Manufacture of Periodic Cellular Structure and Related Structure thereof,” and Application Ser. No. 60/422,550 filed on Oct. 31, 2002, entitled “Method for Manufacture of Periodic Cellular Structure and Related Structure thereof,” the entire disclosures of which are hereby incorporated by reference herein.
This invention was made with United States Government support under Grant No. N00014-00-1-0342, awarded by the Defense Advanced Research Projects Agency/Office of Naval Research. The United States Government has certain rights in the invention.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US03/16844 | 5/29/2003 | WO | 11/23/2004 |
Number | Date | Country | |
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60384341 | May 2002 | US | |
60422550 | Oct 2002 | US |