REFERENCE TO RELATED APPLICATIONS

This application claims priority to co-pending U.S. patent application serial number 13/804, 164, filed March 14, 2013, entitled "SPLIT END TUBE CONNECTOR", which claims one or more inventions which were disclosed in Provisional Application Number 61/723,057, filed November 6, 2012, entitled "SPLIT END TUBE

CONNECTOR". The benefit under 35 USC § 119(e) of the United States provisional application is hereby claimed, and the aforementioned applications are hereby

incorporated herein by reference. BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The invention pertains to the field of tube connectors. More particularly, the invention pertains to connectors for fiber reinforced composite tubes.

DESCRIPTION OF RELATED ART Tube connectors and tube splices are well known across many applications. Very few innovations exist, however, that are specific to connecting fiber reinforced tubes, and in particular carbon fiber tubes.

U.S. Patent No. 2,878,039 (Hoegee) discloses a collet and ferrule type clamp hose coupling intended for inflight aircraft refueling. U.S. Patent No. 5,082,314 (Aubry) discloses a joint for connecting composite tubes using an annular metallic ferrule with a flat portion, as well as a curved portion.

U.S. Patent No. 5,346,237 (Wang) discloses a bicycle frame constructed from carbon fiber tubes joined by metal connectors. The metal connectors include threaded sockets and metal connecting members. U.S. Patent No. 8,262,825 (Fahey) discloses a method for axially connecting filament wound composite tubes by winding bands of fibers around an underlying end- fitting.

In addition, adjustable and tightening tube splices are available, such as the Splice- Lock™ connections from The Wagner Companies (Milwaukee, WI), which insert into the end of a tube and mechanically expand, putting pressure on the tube wall to prevent the splice from pulling out.

SUMMARY OF THE INVENTION

A split end tube connector connects fiber reinforced composite tubes. In preferred embodiments, the fiber reinforced composite tubes are made of carbon fiber. The tube connector end inserted into the carbon fiber tube is split lengthwise to alleviate peel stresses caused by thermal contraction of the connector as a result of temperature changes. In a preferred embodiment, the split end tube connector is made from a metal, such as aluminum, steel, or titanium.

In one preferred embodiment, a split end tube connector includes an external end and a first internal end. The first internal end fits into a first tube and includes two or more longitudinal slots. In some preferred embodiments, the first internal end also includes at least one ridge substantially perpendicular to the slots. In some embodiments, the first tube is preferably made of carbon fiber. In some preferred embodiments, the external end includes a second internal end that fits inside a second tube and includes two or more longitudinal slots. In some preferred embodiments, the second internal end also includes at least one ridge substantially perpendicular to the slots.

In another preferred embodiment, a split end tube connector system includes at least one split end tube connector with a first internal end and an external end and at least one first tube having a first end and a second end, where the first internal end of the split end tube connector is bonded into a first end of the first tube. The first internal end includes two or more longitudinal slots. In some preferred embodiments, the first internal end also includes at least one ridge substantially perpendicular to the slots. In preferred embodiments, the first tube is made of carbon fiber. In other preferred embodiments, the external end includes a second internal end that is bonded inside a second tube and includes two or more longitudinal slots. In some preferred embodiments, the second internal end also includes at least one ridge substantially perpendicular to the slots.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a split tube connector with a blank external end.

FIG. 2 shows an alternate view of the split tube blank connector of FIG. 1.

FIG. 3 shows a side view of the split tube blank connector of FIG. 1.

FIG. 4 shows a split tube connector with the blank end machined to be a single male external connection.

FIG. 5 shows a split tube connector with the blank end machined to be a single female external connection.

FIG. 6 shows a split tube connector with a four-slotted male external connection.

FIG. 7 shows a split tube connector with a four-bladed female external connection.

FIG. 8 shows a split tube connector with the blank end machined to be a single outside blade.

FIG. 9 shows a tube connector with both ends split for internal use. FIG. 10 shows a truncated single-slotted female connector. FIG. 1 1 shows a base plate.

FIG. 12 shows a single-bladed / single-slotted yoke connection. FIG. 13 shows a 3-connector in-plane triple connection. FIG. 14 shows a 3-connector right-angle connection.

FIG. 15 shows a single-slot female-to-female connection via a single-bladed male-to-male adapter. FIG. 16 shows a four-slotted female-to-female connection via a four-bladed male-to-male adapter.

FIG. 17 shows a base plate and truncated single-slotted female connector added to a right- angle joint with three connectors.

FIG. 18 shows the connector system of FIG. 17, but with the tubes hidden.

DETAILED DESCRIPTION OF THE INVENTION

Tube connectors and tube splices are well known across many applications. Within the field of fiber reinforced composite tubes, and in particular carbon fiber tubes, there exists a challenge whereby the coefficient of thermal expansion for the carbon fiber tube and the tube connector may be very different. This is the case if a metal or plastic tube connector is utilized with a carbon fiber tube. Since the coefficient of thermal expansion for the carbon fiber tube is much smaller than that for the metal or plastic part, there is the potential, under changing temperature, and in particular cold temperature, for the tube connector to shrink, thus creating a peel stress on the adhesive bond between the tube and connector. As a result, delamination of the tube connector from the tube inner wall surface may occur.

The tube connectors described herein alleviate this problem by using a split end for the portion of the tube connector inserted and bonded into the carbon fiber tube. Figures 1-3 show the basic tube connector 100 with a blank external end 101 (i.e. no specific connection method on the external end 101 used to attach the tube connector 100 to either another tube connector or an accessory). In Figure 1, the tube connector has an internal end 102 that is split longitudinally, and is inserted into the carbon fiber tube and bonded into place with an adhesive, such as epoxy. Figure 2 shows an alternate view of the internal end, which is tubular in construction. By splitting the tubular end of the connector, additional compliance is offered in the case where large temperature changes occur. That is, if the temperature drops, the tube connector material will shrink; however, the longitudinal slots 103 cause the tube connector to be locally weakened in the radial direction, thus the amount of peel stress the tube connector 100 can impart on the adhesive bond is reduced, decreasing the chances of a peel failure. The longitudinal slots 103 created by the split tube construction also increase the bond surface area perpendicular to the tube surface. These surfaces act to maintain the bond strength in the shear direction. Since adhesive shear strength is typically one to two orders of magnitude greater than adhesive peel strength, this greatly improves the strength of the bond overall. While six longitudinal slots are shown in the figures, any number of slots are possible in alternative embodiments. For example, in some preferred embodiments, there are two to eight longitudinal slots 103 on the tube connectors described herein. In addition, ridges 104 may be added to the internal end 102, which further increase the surfaces acting in shear, thus offering additional resistance to peel failures. Figures 4-8 show various external connection ends. Figures 4 and 5 show a single- bladed male connection 40 and a single-slotted female connection 50, respectively. The single-bladed male connection 40 has a single external connection blade 41, which mates with the single slot 51 on the single-slotted female connection 50. Figures 6 and 7 show a four-bladed male connection 60 and a four-slotted female connection 70, respectively. The four-bladed male connection 60 has four external connection blades 61, which mate with the four slots 71 on the four-slotted female connection 70. In another embodiment, a single outside blade connector 80, which contains a single outside blade 81, can be utilized, as shown in Figure 8. While one and four bladed male connections are shown in the figures, in preferred embodiments, the bladed male connectors have one to eight blades. Similarly, while one and four slotted female connections are shown in the figures, in preferred embodiments, the slotted female connectors have one to eight slots.

Alternatively, the external end can instead be utilized as another split end internal connection, as shown in Figure 9, for insertion directly into another tube. In this case, the tube connector is being used as a tube splice 90, with two internal ends 91, 92. In another embodiment of the connector 105, shown in Figure 10, instead of an internal end 102, the end 106 is truncated and flattened, with a threaded hole and bolt 107 for connection to another tube connector or base plate 110 (shown in Figure 1 1).

Figures 12-16 show how these connectors are attached to one another and the tubes 121 with fasteners 122 in various configurations. Figure 12 shows a single-bladed / single-slotted yoke connection 120. Figure 13 shows a three connector in-plane triple connection. Figure 14 shows a three connector right-angle connection. The tube connector 141 includes a flat external end like the end 106 shown in Figure 10. Figure 15 shows a single-slot female-to-female connection via a single-bladed male-to-male adapter 151. Figure 16 shows a four-slotted female-to-female connection via a four-bladed male- to-male adapter 161.

Figure 17 shows a base plate 110 and truncated single-slotted female connector 105 added to a right-angle joint including three connectors 40, 80, 171. The tube connector 171 includes an external end 40 and a flattened end 106. Figure 18 shows the connector system of Figure 17, with the tubes 121 hidden.

In preferred embodiments, the split end tube connectors are made from a metal, such as aluminum, steel, or titanium. In other embodiments, the split tube connector is plastic. In preferred embodiments, the material for the tubes is carbon fiber. In other embodiments, the tubes are made of fiberglass or another fiber reinforced plastic.

Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention.

Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.