None.
The present invention generally relates to struts. More particularly, the present invention relates to a lightweight strut utilizing advanced composites and manufacturing techniques.
Struts of the present invention can be aerospace components including landing gear brake rods, stay bars, linkages and wingbox structural components to name a few. Metal components are currently used due to reliability and proven lifespan; however, composite materials are desired for weight reduction. Partial composite components are used for some components such as brake rods but include metal end fittings. The disadvantage with metal end fittings in any composite solution is the inherent weak point, stiffness mismatch and CTE (coefficient of thermal expansion) mismatch at the metal-composite joint. Such a joint with metal ends and its inherently different stiffnesses between materials is a source of fatigue failure. Furthermore, this does not allow the full use of the composite's strength because the continuous composite fiber is cut at a joint.
U.S. Pat. No. 10,464,656 shows metal end fittings which suffer the problems as previously explained. The single shear bond (as identified in claim 11 and column 2, lines 27-32 of the '656 Patent) between the composite tube and metal end fitting is a weak point that the present invention overcomes.
U.S. Patent Publication 2005/0056117 uses a conventional filament winding operation that is not optimized for strength due to alignment of the fibers. After the strut body is wound then its forked ends are formed with openings designed to receive load transfer inserts.
Accordingly, there still exists a need for even lighter and stronger struts that can ultimately lead to substantial weight savings, especially considering the numerous amounts of struts that may be utilized in a particular vehicle, such as an airplane. The present invention fulfills these needs and provides other related advantages.
The solution of the present invention is a continuous reinforced composite strut. The strut of the present invention has an integrated composite end to withstand the load with minimal, if any, metal in the entire structure. The present invention solves the problem of heavyweight and complicated designed metal end components usually required for highly loaded structural elements. The continuous reinforced composite strut offers sufficient mechanical strength and stiffness, while reducing component weight significantly, by ½ or up to a ⅔ weight reduction.
The present invention allows continuous fibers to traverse the entire length of the structural element without cutting the fiber and puts the composite fibers in the direction of load, as well as in-plane loading along the main section. At the ends, the composite strut is put in a load scenario ideal for it, i.e., with thru-wall compression. With this, load can be transferred from a separate component, a metal pin for example, from out-of-plane stress into the composite and then to in-plane stress within the composite along the length of the component. This is different than usual joints which require metal and require to shear in the load causing high interlaminar and damaging loads to the composite. This invention avoids that problem altogether and takes thru-wall out-of-plane stress at the ends and directly loads the fibers in-plane.
The process of the present invention utilizes robotic fiber placement of continuous fiber thermoplastic composites to place a continuous fiber tape, continuously around both ends of a structural linkage. This, plus internal composite components to help boost compression and torsion loads on the linkage, are the essence of the invention that is unmatched to date. The composite is in its ideal load state, with minimal interlaminar loading compared to in-plane loading, and limited distortional loading compared to in-plane loading. This cannot be accomplished with metal end fittings and cutting fibers as done with traditional composite designs.
U.S. Publication 2005/0056117 uses a filament winding, whereas the present invention uses fiber placing in-situ (on the fly melt processed) bringing inherent different properties. With the present invention no post process heat cycle is required. A heat cycle allows materials with different thermal expansion rates to grow and shrink back at different rates upon return to room temperature, allowing them to become de-bonded.
Tension winding during the in-situ fiber placement process can be employed to prestress the strut, reducing deflection along axis of strut, the primary load direction, during service. With no post-processing, as required with thermoset materials under tension winding, the strut does not change dimensions as it cycles through high temperatures, as it would with thermoset based material. This is unique to in-situ AFP of thermoplastic CFRPs (carbon fiber-reinforced plastics).
An exemplary embodiment of a composite strut, includes: a first end opposite a second end separated by a strut distance along a longitudinal axis, the first end defining a first aperture and the second end defining a second aperture; a compression block extending along the longitudinal axis disposed between the first aperture and the second aperture, the compression block defining a top side opposite a bottom side disposed between a right side opposite a left side; a tension strap comprising a first continuous fiber reinforced plastic composite wrapped repeatedly around the first aperture, along the top side of the compression block, around the second aperture and along the bottom side of the compression block at least two times, wherein fibers of the tension strap are oriented extending parallel to the longitudinal axis between the first and second apertures; and an overwind comprising a second continuous fiber reinforced plastic composite wrapped repeatedly around the first continuous fiber reinforced plastic composite and the compression block between the first end and second end at least two times, wherein fibers of the overwind are oriented extending around the longitudinal axis.
Other exemplary embodiments may include a left side filler block extending along the longitudinal axis between the first and the second apertures disposed between the compression block and the overwind on the left side of the compression block, the left side filler block in cross section along the longitudinal axis defining a left side chord length adjacent to the left side of the compression block, the left side chord length opposite a left side curvature. Likewise, this exemplary embodiment may include a right side filler block extending along the longitudinal axis between the first and the second apertures disposed between the compression block and the overwind on the right side of the compression block, the right side filler block in cross section along the longitudinal axis defining a right side chord length adjacent to the left side of the compression block, the right side chord length opposite a right side curvature. The compression block, the left side filler block and the right side filler block may be separately manufactured parts or the compression block, the left side filler block and the right side filler block may be integrally manufactured as a single part.
The first continuous fiber reinforced plastic composite may be wrapped repeatedly at least 3 times, at least 5 times, or at least 10 times.
The compression block, tension strap and the overwind may utilize a common base resin.
A first end and a second end of the compression block may be at least partially cylindrically shaped.
The compression block may be rectangular in cross section along the longitudinal axis.
The first and the second apertures may be cylindrically shaped.
The composite strut may exclude (i.e., not comprise) any metal part throughout.
The compression block may comprise a chopped fiber filled thermoplastic composite.
Other features and advantages of the present invention will become apparent from the following more detailed description, when taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.
The accompanying drawings illustrate the invention. In such drawings:
A compression block 17 extends along the longitudinal axis and is disposed between the first aperture and the second aperture. The compression block is best seen in
As best shown in
Similarly, the right side filler block 31 extends along the longitudinal axis between the first and the second apertures disposed between the compression block and the overwind on the right side of the compression block. The right side filler block in cross section along the longitudinal axis defines a right side chord length 32 adjacent to the left side of the compression block. The right side chord length is opposite a right side curvature 33, which is similarly circular in shape.
Referring to
In this embodiment, the compression block, the left side filler block and the right side filler block are separately manufactured parts. However, in an alternative embodiment the compression block, the left side filler block and the right side filler block may be integrally manufactured as a single part.
The compression block, tension strap and the overwind utilize a common base resin. This aids in preventing delamination and reduces and/or eliminates any mismatches between coefficients of thermal expansion.
In this embodiment, the compression block is rectangular in cross section along the longitudinal axis. However, other shapes could be used such as square or octagonal, as an octagonal shape would incorporate the left and right side filler blocks.
The composite strut of claim 1, wherein the compression block may comprise a chopped fiber filled thermoplastic composite.
In this embodiment, the entire strut does not comprise a metal part.
Although several embodiments have been described in detail for purposes of illustration, various modifications may be made to each without departing from the scope and spirit of the invention. Accordingly, the invention is not to be limited, except as by the appended claims.
10 strut
11 first end, strut
12 second end, strut
13 distance, strut
14 longitudinal axis, strut
15 first aperture
16 second aperture
17 compression block
18 top side, compression block
19 bottom side, compression block
20 right side, compression block
21 left side, compression block
22 tension strap
23 first continuous fiber reinforced plastic composite
24 orientation parallel to longitudinal axis
25 overwind
26 second continuous fiber reinforced plastic composite
27 oriented extending around longitudinal axis
28 left side filler block
29 left side chord length, left side filler block
30 left side curvature, left side filler block
31 right side filler block
32 right side chord length, right side filler block
33 right side curvature, right side filler block
34 removable pins