Integrated variable stiffness member

Abstract

An oblong stiffening member such as a sail batten having a tapered geometry formed by a pair of parallely spaced apart oblique circular cones interconnected by a webbing strip. The member can be made from a unitary piece of fiber composite material such as a carbon fiber infused polymer wherein the orientations of the fibers are varied to provide both bending and torsional strength and stiffness that varies along the length of the member. Such properties can be useful in sail battens due to the rigorous dynamical forces subjected to such structures.

Claims

1. An improved variable stiffness structural member comprises: said member having an oblong shape in a longitudinal direction; said member having a proximal end and a distal end; a first zone between said proximal end and said distal end; wherein said first zone comprises a first fiber reinforced material having a first set of plural fiber orientations; wherein first fiber reinforced material has a first longitudinal stiffness and a first latitudinal stiffness different from said first longitudinal stiffness.

2. The member of claim 1, wherein said member further comprises: a second zone between said proximal end and said distal end; wherein said second zone comprises a second fiber reinforced material having a second set of plural fiber orientations different from said first set of plural fiber orientations; wherein said second fiber reinforced material has a second longitudinal stiffness different from said first longitudinal stiffness.

3. The member of claim 2, wherein said first set of plural fiber orientations comprises a first fiber layer orientation rotated a first non-zero angle with respect to a second fiber layer orientation.

4. The member of claim 3, wherein said first set of plural fiber orientations further comprises a third fiber layer orientation rotated a second non-zero angle with respect to said second fiber layer orientation, and wherein said second non-zero angle is different from said first non-zero angle.

5. The member of claim 4, wherein said second set of plural fiber orientations comprises a fourth fiber layer orientation rotated a third non-zero angle with respect to a second fiber layer orientation.

6. The member of claim 5, wherein said first non-zero angle is at least 90 degrees, said second non-zero angle is at least 45 degrees, and said third non-zero angle is at least 30 degrees.

7. The member of claim 2, wherein said first set of plural fiber orientations and said second set of plural fiber orientations have a least one fiber layer in common.

8. The member of claim 1, wherein said member further comprises: a pair of substantially parallel, oblong, spaced-apart rods, laterally joined by a webbing strip; and, wherein each of said pair of rods gradually tapers from said proximal end toward said distal end.

9. The member of claim 8, wherein said first one of said pair of rods comprises an axial hollow.

10. The member of claim 9, wherein said first one of said rods has a substantially conical shape; and wherein said axial hollow has a substantially conical shape.

11. The member of claim 1, wherein said member has a variable cross-sectional geometry along a logitudinal length of said member.

12. The member of claim 1, wherein said member further comprises: said member having a first cross-sectional area near said proximal end and a second cross-sectional area near said distal end; wherein said first cross-sectional area is larger than said second cross-sectional area.

13. The member of claim 12, wherein said first cross-sectional area is substantially barbell shaped.

14. The member of claim 12, wherein said first cross-sectional area comprises a pair of spaced apart, interconnected, diametrically symmetric geometric shapes selected from the group consisting of: circles, ellipses, triangles, squares, rectangles, trapezoids, pentagons, hexagons, heptagons, octagons, nonagons, and decagons.

15. The member of claim 1, wherein said member is formed by a unitary piece of composite material.

16. The member of claim 8, wherein said rods have a substantially oblique circular conical shape.

17. The member of claim 8, wherein both of said pair of rods are similarly shaped and dimensioned.

18. The member of claim 12, wherein said first cross-sectional area has a width dimension corresponding to said webbing strip, and a height dimension corresponding to an outer diameter of said one of said rods, and wherein said width dimension is equal to or greater than said diameter dimension.

19. The member of claim 1, wherein said member further comprises: said member having a first width dimension at said proximal end and a second width dimension at said distal end; and, wherein said first width dimension is equal to or greater than said second width dimension.

20. The combination of a sailing craft having a sail and a plurality of sail battens, wherein at least one of said battens comprises: a fiber reinforced composite structural member having a first set of plural fiber orientations; wherein said member comprises: a pair of substantially parallel, spaced-apart tapering rods, laterally joined by a webbing strip.

21. An improved variable stiffness structural member comprises a fiber reinforced material having plural fiber orientations selected to adjust a longitudinal stiffness different from a latitudinal stiffness.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] FIG. 1 is a diagrammatic perspective view of an improved fiber reinforced composite structural member used as a sail batten on a sailing vessel.

[0054] FIG. 2 is a diagrammatic front view of a fiber reinforced composite structural member according to an exemplary embodiment of the invention.

[0055] FIG. 3 is a diagrammatic partial elevational front view thereof.

[0056] FIG. 4 is a diagrammatic partial elevational side view thereof.

[0057] FIG. 5 is a diagrammatic distal end view thereof.

[0058] FIG. 6 is a diagrammatic cross-sectional end view taken along a medial section thereof.

[0059] FIG. 7 is a diagrammatic proximal end view thereof.

[0060] FIG. 8 is a diagrammatic partial, cross-sectional front view of a fiber reinforced composite structural member having rod lumens according to an alternate exemplary embodiment of the invention.

[0061] FIG. 9 is a diagrammatic distal end view of the member of FIG. 8.

[0062] FIG. 10 is a diagrammatic cross-sectional end view taken along a medial section of the member of FIG. 8.

[0063] FIG. 11 is a diagrammatic proximal end view of the member of FIG. 8.

[0064] FIG. 12 is a diagrammatic partial perspective view of fiber composite layers having differential orientations.

[0065] FIG. 13 is a diagrammatic top view of a fiber composite member showing the variously selected fiber orientations.

[0066] FIG. 14 is a diagrammatic top view of a fiber composite member showing plural zones of variously selected fiber orientations.

[0067] FIG. 15 is a diagrammatic cross-sectional views of various rod geometries.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0068] Referring now to the drawing, there is shown in FIG. 1 a multidimensionally reinforced fiber composite lightweight stiffening member 11 according to an exemplary embodiment of the invention as implemented on a batten 12 carried within a transverse pocket 13 of a sail 14 of a sailing vessel 15 where the batten urges the sail into a more optimum aerodynamic shape. FIG. 2 shows the member 11 removed from the sail and laid flat. The member has an oblong, substantially rectangular shape extending logitudinally from a proximal end 16 or base, to be located near the mast 10 of the sailing vessel, to an opposite distal end 17, to be located near the trailing edge 9 of the sail.

[0069] The word substantially is used throughout this specification to mean that minor inaccuracies due to low tolerances, and manufacturing and material defects can lead to inexactitude of various parameters. Those skilled in the art will readily appreciate such inexactitude in the context in which the described stiffening member is used.

[0070] Referring now to FIGS. 2-7, the member 11 includes a pair of parallelly spaced apart, solid rods 21,22 forming the opposite lateral edges 24,25 of the member and extending along substantially the entire longitudinal length L of the member from the proximal end 16 to the distal end 17. Each of the rods can have a substantially conical shape having a substantially circular cross-section where the diameter Dr varies according to its longitudinal position on the member, gently and gradually tapering from a wider proximal diameter Dp to a narrower distal diameter Dd. The substantially conical shape can be characterized by a ratio between these two diameters Dd/Dp which ranges from between about 0.05 to 0.5. The conical shape can be an oblique circular cone so that cross-sections perpendicular to the elongation axis of the member form circles. Alternately, the conical shape can be a right circular cone where cross-sections perpendicular to the elongation axis of the member form ellipses, albeit ones with very low eccentricity.

[0071] The rods 21,22 are interconnected by a medial webbing strip 23 having generally parallel trapezoidal front and back surfaces. Thus, the webbing strip can be substantially planar, having a substantially uniform thickness T along the entire longitudinal length of the member.

[0072] The rods can be angled outwardly so that the lateral extent of the member remains substantially uniform. In other words, the overall width W of the member can remain constant. This also causes the width of the webbing strip Ww to vary between a narrower width at the proximal end of the member to a wider width at the distal end of the member. Thus the width of the member can be defined as W=Ww+2(Dr).

[0073] Referring now to FIG. 7, by making both rods 21,22 substantially identically shaped and dimensioned, the member 11 can be made to be symmetric about a plane 31 perpendicularly bisecting the webbing strip 23. In this way, the symmetrical member can be conveniently loaded in the pocket without regard to whether which rod is located on the top side. It shall be noted that the transition between each rod and webbing strip can be gradual in the form of a concave fillet 27 having a radius of between approximately 5% to 25% of the cross-sectional diameter of the rod at the point of contact with the fillet. Although the member is shown having a barbell shaped cross-section where the rods form a pair of circles, other shapes are available, such as for example, ellipses, rounded squares, rectangles ovals, or other polygons having rounded vertices.

[0074] Referring now to FIGS. 8-11, the member 40 can be further adapted so that the rods 41,42 are hollow, each having a central lumen 43,44 extending the length of the respective rod. The medial webbing strip 45 interconnecting the rods can remain solid. The shape and dimensioning of the lumen can be selected so that the wall formed between the outer surface of the rod and the inner surface facing the lumen is ring-shaped having a circular outer surface cross-section and a circular inner surface cross-section. The wall thickness can thus be angularly uniform at every cross-section and linearly uniform from end to end. The lumen can terminate in apertures at the distal and proximal ends. Alternately, the lumens can terminate in a closed cup at the distal extremity of the lumen. The lumens can serve to reduce the mass and amount of material contained in the member while maintaining adequate bending and torsional stiffness and strength.

[0075] The stiffness properties of the member can be adjusted by forming the member from fiber-resin composite materials such as a carbon-fiber epoxy resin composite. The uncured epoxy is combined with carbon fibers using techniques well known in the art. In this example a thermosetting preimpregnated resin tape or prepreg is used such as unidirectional fiber tape available from American Cyanamid Co. of Wayne, N.J. Layers of the tape are successively wrapped onto one another to form into an uncured member body corresponding to the desired size of the sail batten. Once cured the body becomes the unitary fiber composite member.

[0076] The orientation of the fibers can be selected to enhance stiffness with respect to bending moments apart from the elongation direction of the member.

[0077] As shown diagrammatically in FIGS. 12 and 13, successive layers 61,62,63 of tape can be applied where the orientation or direction of fibers in each layer are different from the direction of fibers in each successive layer to adjust stiffness properties to forces applied from various directions and magnitudes over time. For example, a first layer 61, can be oriented at 0 degrees so that the elongation direction of the embedded fibers are parallel with the elongation axis 65 of the member 60. A second layer 62, can be oriented so that the elongation direction 66 of the embedded fibers are at an angle A1 of about 45 degrees with respect to the elongation axis of the member. Similarly, a third layer 63, can be oriented so that the elongation direction 67 of the embedded fibers are at an angle A2 of about 90 degrees with respect to the elongation axis of the member. A fourth layer, can be oriented so that the elongation direction 68 of the embedded fibers are at an angle A3 of about 135 degrees with respect to the elongation axis of the member. In this way, the fiber reinforced material forming the member can have a set of fiber orientations where a first layer is rotated a first non-zero angle with respect to a second layer, and a third layer rotated a second non-zero angle with respect to the first layer, and so on. It has been found that a variable stiffness member can be made having the first angle A1 being at least 15 degrees, the second angle A2 being at least 30 degrees, and the third angle A3 being at least 45 degrees. Successive layers can have even greater angles as shown below.

[0078] Referring now to FIG. 14, the structural member can be divided into a plural number of zones where the fiber orientation of the various layers within each zone can be different from the orientations on other zones in order to selectively and preferentially rigidize the different zones of the member differently. In other words, each zone can have a fiber reinforced material having a set plural fiber orientations that are the same or different from the set of fiber orientations of the material in another zone.

[0079] By way of example, the member 70 can be divided along its longitudinal dimension into three discrete latitudinal zones 71,72,73 where the first distal zone 71 can have a set of fiber layers oriented in the 0 degree direction and in the 30 degree and 150 degree directions. A second medial zone 72 can have a set of fiber layers oriented in the 0 degree direction and in the 45 degree and 135 degree directions. A third proximal zone 73 can have a set of fiber layers oriented in the 0 degree direction and in the 45 degree, 90 degree, and 135 degree directions. Thus, the set of fiber layers in a particular zone results in that set having a plural number of different fiber orientations.

[0080] Further, as detailed above, plural fiber orientations of one set can be different from the plural fiber orientations of another set. These differential fiber orientation sets combined over the length of the member can preferentially rigidize the proximal zone to greater bending and torsional loads than the distal zone. Of course adjacent zones can share a layer having a particular orientation. For example, a single layer can have the 0 degree orientation and extend across all three zones as shown. In addition layers from one zone can, and in practice often do partially overlap into an adjacent zone. It has been found that a variable stiffness member can be made of latitudinally separated zones, each having a set of fiber orientations which include different layers being rotated at least 15 degrees with respect to one another. In the above example a first zone 73 can have a first set of fiber orientations where some layers are rotated at least 90 degrees with respect to one another, and other layers rotated at least 45 degrees with respect to one another, and another zone 71 sharing the 0 degree layer and having a second set of fiber orientations where some layers are rotated at least 30 degrees with respect to one another.

[0081] Referring now to FIG. 15, as previously shown, the cross-sectional shape of the member 80 can include rods 81,82 having a substantially circular shape. However, other shapes may be useful for other structural members depending on the application for which the members are used, and due to manufacturing concerns. For example, the rods can have an elliptical shape 83, or a quadrangular shape, including squares and rectangles 84. Rods having other diametrically symmetrical polygonal shapes such as hexagons 85, octagons, and decagons can be used to provide a member cross section which is symmetric about the side-to-side transverse axis 86, and the front-to-back transverse axis 88. Other shapes can be used which are diametrically symmetric depending on orientation such as trapezoids 88, pentagons, and heptagons. Myriad other more complex shapes which provide symmetricity with respect to both transverse axes are available such as substantially half-moon shapes 89. For sail batten applications such symmetricity is preferred in order to ease installation of the battens in the sails. However, non-symmetric rod cross-sections can be used depending on the application.

[0082] The above-described members can provide bending stiffness as a function of distance from the proximal end of the member according to the geometry of the lateral rods, fiber orientation within the various zones of the member, and the thickness of the interconnecting webbing strip.

[0083] It has been found that the properties exhibited by the above described structural member can be useful in sail battens due to the rigorous dynamical moments subjected to such structures and the variable stiffness of the member along its length.

[0084] While the preferred embodiments of the invention have been described, modifications can be made and other embodiments may be devised without departing from the spirit of the invention and the scope of the appended claims.