Patent Application: US-61921109-A

Abstract:
biomimetic tendon - reinforced ” composite structures feature improved properties including a very high strength - to - weight ratio . a basic structure comprises a plurality of spaced - apart stuffer members , each having a first end and a second end defining a length . a plurality of tendon elements interconnect with the first and second ends of the stuffer members in alternating fashion , such that the tendon elements criss - cross each other between the stuffer members . a first panel is bonded or attached to the first ends of the stuffer members , and a second panel is bonded or attached to the second ends of the stuffer members . in the preferred embodiments , the first panel , the second panel , or both the first and second panels are curved . an efficient manufacturing process based upon hollow stuffers and tendon elements in the form of bent wires is also disclosed .

Description:
this invention uses a methodology called “ function - oriented material design ,” or fomd , to design materials for the specific , demanding tasks . in order to carry out a fomd , first the functions of a particular structure are explicitly defined , such as supporting static loads , dissipating or confining vibration energy , or absorbing impact energy . these functions are then quantified , so as to define the objectives ( or constraint functions ) for the optimization process . additional constraints , typically manufacturing and cost constraints , may also need to be considered in the optimal material design process . the fomd system has resulted in a number of innovative structural material concepts , including the btr ( biomimetic tendon - reinforced ) composite materials described in this specification . the original concept of the btr composite was obtained through a topology optimization process which maximizes the out - plane stiffness of a composite made of carbon fiber and epoxy matrix material . the result shows that the fiber should be concentrated and oriented along the most effective load paths identified through the topology optimization process . according to this new composite concept , which is different from the traditional fiber - reinforced laminate composites , fibers are evenly distributed in the matrix material . the analyses also showed that the materials in tension and materials in compression can be treated differently in the composite , and can be selected and designed separately with respect to their functionalities in the composite material . additional covering and filling materials can also be added into the composite , and the further development of the concept through prototyping , testing , and developing fabrication method resulted in a wide range of new btr composites . an example btr design process is illustrated in fig1 . the goal here is to optimize the out - plane stiffness of the composite material for a given amount of the fiber and matrix materials . as shown in fig1 a , a static load was applied at the middle of a design domain fixed at its two ends . the objective function considered in the optimization problem is to minimize the total strain energy stored in the composite . this is equivalent to maximize the out - of - plane stiffness ( resisting the out - of - plane load ). fig1 b shows the optimum layout of the composite obtained using fomd methods . the optimum structural configuration of the composite has several key components , including : fiber , stuffer , and joint , as shown in fig1 b . note that the optimum structure obtained from the concept design implies that the fibers should be concentrated and optimally arranged along the load paths where the reinforcements are most needed . unlike traditional woven materials , in which the fibers are almost evenly distributed in one plane in the matrix materials , the new material will be reinforced by allocating concentrated fibers , such as fiber ropes , along load paths so as to increase transverse stiffness . in practical applications , a matrix or filling material may ( or may not ) be used to enhance structural performance , as shown in fig2 . one typical btr composite structure , shown in fig3 , includes six fundamental components : tendons / muscles ( represented by fiber cables and / or actuators ), ribs / bones ( represented by metallic , ceramic , or other stuffers and struts ), joints ( including knots ), flesh ( represented by filling polymers , foams , thermal and / or acoustic materials , etc . ), skins ( represented by woven composite layers or other thin covering materials ), and shell ( represented by hard and stiff materials , such as metal or ceramic .) in different embodiments , the two - dimensional material concept may be extended to a three - dimensional lattice , as shown in fig4 . the preferred structure is made of various raw materials , for example , steel frame , steel columns , carbon - fiber ropes , and carbon fiber / epoxy cover panels . a potential fabrication procedure is shown in fig5 . here , bent - wire tendon elements 502 are inserted into the ends of stuffer members 504 to create linear structures 506 . these , in turn , may be replicated to create a planar structure 510 . if panels 512 , 514 are added , a lightweight yet rigid structure 516 results . fig6 illustrates possible structures using the basic btr idea . fig6 a shows a flat panel such as that depicted in fig5 . fig6 b shows a curved cylindrical section , and fig6 c shows a curved spherical section . fig6 d shows a complete cylinder may be formed using the process . fig7 further illustrates example prototypes with a wide range of material variations . fig8 illustrates a design toolkit developed at mkp inc ., while an example finite element model of the btr material shown in fig4 is shown in fig9 . the top and bottom plates may be metal carbon fiber / epoxy panel layers . the stuffers may be steel , aluminum or ceramic , and the tendon elements may be carbon fiber ropes . the panels are glued to the frames using epoxy to form the final btr structure as shown in fig4 . the dimension of the sample lattice structure is 100 mm × 100 mm × 12 mm . note that commercial 1 - ea codes can also provide an estimate for the response of the btr under various loads . fig8 illustrates an extension of the btr concept to develop a composite armor , which consists of stuffer , fiber ropes , woven fiber panels , and ceramic layers . since the btr structure is ultra - light , the proposed composite armor would benefit the future combat system in the total weight reduction as well as in the energy absorption . the carbon - rope reinforcement plan is optimized to withstand an actual impact . in some btr structures , the carbon ropes may be stitched to the frame structure . fig9 shows how fiber elements 1102 , 1104 may be passed through stuffer tubes 1106 . fig1 shows elongated panel stuffer members 1202 . fig1 shows a sandwich btr structure using spheroid stuffer members 1302 , at least in one plane . fig1 illustrates potential knot designs for assembling special btr composites , including two - dimensional and three - dimensional structures . an advantage of the btr composite is the use of embedded fiber tendons . when a load carrying carbon - fiber tendon in a well - designed btr composite is broken , the neighboring fiber tendons can act as the safety members to preserve the integrity of the whole btr structure provided the tendons are properly placed . in a practical application , several layers of the proposed btr structure can be stacked together to provide even better out - of - plane performance when needed . while certain of the embodiments so far described have depicted stuffer members and tendon elements disposed between flat , parallel tiles , non - parallel flat panels and non - flat panels may alternatively be used . as one example , fig1 illustrates an embodiment wherein the stuffer members ( i . e ., 1502 ) and tendon elements ( i . e ., 1504 ) are disposed between curved panels 1506 , 1508 . in this case , panels 1506 , 1508 share a common radius of curvature from point “ p ” such that the panels are equidistant . further in this embodiment the stuffer members are uniformly spaced and aligned along spokes extending radially outwardly from the common center point . although a 2 - dimensional structure is shown ( i . e ., one set of stuffer members in a plane ), it will be appreciated that in this and all other embodiments 3 - dimensional structures may be used , in which case addition groups of stuffers would be present in the spaces into and / or out of the plane . additionally , although panels 1506 , 1508 are hemispherical , in this and all other embodiments using curved panels , non - hemispherical surfaces may be used , including parabolic , hyperbolic , and compound surfaces as shown in fig2 . fig1 depicts an embodiment of the invention including two curved panels , 1602 , 1604 one having a radius curvature from point “ p ” and the other having a different radius of curvature based upon “ p ′.” the stuffer members are shown extending radially outwardly from point “ p ” but in this case they vary in length because the panels are not equally spaced apart . fig1 is a drawing which shows two curved panels , also with two radii , but in this case the stuffers are aligned along spokes emanating from “ p ′.” other stuffer alignments are possible , including arrangements based upon a center of curvature other than “ p ” and “ p ′,” including a center midway between them . curved and flat panels may also be intermixed in accordance with the invention . fig1 for example depicts an embodiment of the invention having one flat panel 1802 and one panel 1804 having a convex outer surface . in this case the stuffer elements are parallel to one another , but as shown in fig1 , the stuffers may be arranged along lines extending from a common center of curvature . fig1 depicts an embodiment of the invention having one flat panel 2002 and one panel 2004 having a concave outer surface . the stuffers are arranged along lines extending from a common center of curvature , but other arrangements may be used including parallel positioning . fig1 shows two curved panels 2102 , 2104 , both having concave outer surfaces with the same radius of curvature ( i . e ., r 1 = r 2 ). fig2 illustrates two curved panels , both with concave outer surfaces , but wherein the radius of curvature of one of the panels is different from that of the other ( i . e ., r 1 ≠ r 2 ). fig2 depicts an embodiment of the invention having two curved panels 2302 , 2304 with convex outer surfaces and the same radius of curvature , whereas fig2 shows two curved panels with convex outer surfaces and different radii of curvature . the stuffers are preferably parallel in the embodiments of fig1 - 22 . fig2 shows how panels 2502 , 2504 with complex / compound shapes may be accommodated in accordance with the invention . such structures may be optimized , for example , to fabricate vehicular , aerospace and marine body parts . fig2 shows how , in all embodiments , the stuffer members and tendon elements may be embedded in a hardened matrix material 2610 such as epoxy . fig2 shows how , in all embodiments , the stuffer members need not be spaced apart from one another by equal distances , and fig2 shows how , in all embodiments , the tendon elements may be tied , stitched , glued , or otherwise bonded at the points where they cross , thereby forming “ joints ” 2810 . fig2 a illustrates the use of hollow stuffer members 2902 and tendon elements in the form of bent wires 2904 . fig2 b shows how the components of fig2 a appear when assembled from a side view perspective . fig2 c is a top - down view showing four bent - wire tendon elements and a stuffer member having a round cross - section , and fig2 d is a top - down drawing showing four bent - wire tendon elements and a stuffer member having a non - round cross - section , such as a square . the use of hollow stuffer members and bent - wire tendons simplifies manufacture and may even be automated using pick - and - place robotics , for example . fig2 illustrates additional configurations and options for assembling the stuffer members and bent - wire tendons . in all bend - wire configurations , small pieces such as those shown in fig2 a - 27d may be used or , alternatively , the longer pieces of fig5 may be used . as with all embodiments described herein , the staffers may be composed of any suitable materials , including ceramic , metal or plastic , preferably semi - rigid or rigid . although four bent - wire tendon elements are shown inserted into each end of the stuffer members , other arrangements such as three tendon elements may be used , in which case a top - down view of a two - dimensional structure could show multiple triangles or hexagons as opposed to squares , diamonds or parallelograms . it will also be appreciated that the use of hollow stuffer members and bend - 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