BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view showing an example of a structural member, a preform, and an aircraft skin assembly in accordance with this invention.
FIG. 2 is a transverse sectional view of the structural member of FIG. 1.
FIG. 3 is sectional view of the assembly of FIG. 1, taken along the line 3-3 of FIG. 4, and showing adhesive being injected.
FIG. 4 is a transverse sectional view of the assembly of FIG. 1, after or during the injection of adhesive.
FIG. 5 is a sectional view of the assembly of FIG. 1, taken along the line 5-5 of FIG. 4.
FIG. 6 is a schematic view of a weave pattern of the woven preform of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, a structural member 11 is shown being joined to a second member 13, which typically comprises the skin of an aircraft. In one example, an interface member 15 provides an interface to bond structural member 11 with skin 13. In one embodiment, interface member 15 comprises a woven preform, however other members could alternately be used.
Structural member 11 may comprise a variety of aircraft frame components such as a spar or beam of a wing or fuselage, a bulkhead, or a bracket. The word “structural” is used for convenience and not in a limiting manner. In this embodiment, both structural member 11 and skin 13 are formed of laminated resin composite material. That is, each is formed of multiple layers of fiber, such as carbon, laid up one upon the other. Some of the layers may be unidirectional and other layers woven or otherwise configured. Alternatively, structural member 11 could be a metal. Preferably, structural member 11 and skin 13 are cured prior to assembly.
Structural member 11 has two flat sides 19 that face opposite directions. Each side 19 has a recess or groove 17 formed therein. As shown in FIGS. 2 and 4, groove 17 is preferably rectangular in transverse section, but other shapes are feasible. Also, in this example, groove 17 undulates in a longitudinal or axial direction, having peaks and valleys, defining a general sine wave configuration. This undulating groove can also be varied to create other shapes with an increase in recess area, for instance, two sine wave shapes can be placed back to back, resulting in a diamondback pattern. Grooves 17 extend along the length of structural member 11.
A plurality of communication channels 21 are formed in structural member 11. As shown in FIGS. 3 and 4, each communication channel 21 has a side section 21a that is formed in each side 19 and intersects one of the grooves 17. Side section 21a extends to the base edge of structural member 11. Communication channel 21 has a base section 21b that extends along the base edge of structural member 11 and joins the two side sections 21a. Communication channels 21 are spaced apart from each other at selected points along the length of structural member 11.
As shown in FIGS. 2 and 4, a hole 23 is formed in structural member 11 approximately midway between sides 19 and extends upward from the base edge of structural member 11 a selected distance. Each hole 23 intersects base section 21b of one of the communication channels 21. As shown in FIGS. 1-3, a temporary locator pin 25 is inserted into each hole 23 prior to assembly. Grooves 17, communication channels 21, and holes 23 are preferably formed in structural member 11 during its molding process.
In this embodiment, preform 15 is a composite fiber member that is woven. FIG. 6 illustrates one example of a suitable weave pattern for preform 15, showing one-half of preform 15. Parallel warp fibers 27 are looped or woven together with fill fibers 28. In this example, preform 15 is “pi-shaped”, having a flat base 29 and two parallel legs 31 (FIGS. 1, 4) that are perpendicular to base 29, defining a clevis. FIG. 6 shows one-half of base 29 and one leg 31, which is shown folded over base 29 during the weaving process. Base 29 and legs 31 are woven at the same time and interlinked with fill fibers 28. There are four layers in base 29 and leg 31 in this embodiment, and each of the layers is interlinked with the others by means of the fill fibers 28. After weaving, legs 31 are straightened to an orthogonal orientation, and perform 15 is pre-impregnated with a resin.
Referring again to FIG. 1, base 29 of preform 15 has one side that abuts skin 13. The inside surface of each leg 31 has a recess or groove 33 for mating with groove 17. Grooves 33 and 17 have the same configuration and undulate in the same manner. When aligned, grooves 17 and 33 define a cavity that is elongated and extends from one end to the other end of the assembly. Holes 35 (FIGS. 4, 5) are formed in base 29 at the same distance apart as holes 23 in structural member 11. During assembly holes 23 will align with holes 35. Preferably, holes 35 and grooves 33 are formed in a molding process prior to assembly with a multi-piece die that inserts between legs 31. Holes 39 (FIGS. 4, 5) are formed in skin 13 at the same distance apart from each other as holes 23 and 35. Holes 39 align with holes 23 and 35 during assembly.
Referring to FIG. 1, during assembly, locator pins 25 are pressed into holes 23 (FIGS. 2, 4). Preform 15 is placed on skin 13 with holes 35, 39 (FIGS. 4, 5) in alignment, and cured or bonded together. Structural member 11 is inserted between legs 31 and locator pins 25 are stabbed through holes 35, 39. The technician will clamp structural member 11 to skin 13 with a jig or fixture.
Then the technician removes the first two locator pins 25 and connects a hose adapter 41 to the first one of the skin holes 39, as illustrated in FIG. 3. The technician pumps adhesive 37 (FIGS. 4 and 5) through holes 35, 39 and communication channel sections 21a, 21b into the cavity defined by grooves 17, 33. Adhesive 37 flows along grooves 17, 33 to the second set of holes 35, 39 and communication channels 21.
Once adhesive 37 begins to flow out the second hole 39, the operator ceases pumping adhesive 37, removes adapter 41 and plugs the first hole 39. Subsequently, the technician removes the third and fourth locator pins 25 and repeats the process of pumping adhesive 37. Adhesive 37 flows through communication channel sections 21a, 21b to grooves 17, 33 and flows between the third and fourth locator pins 25. Some of the adhesive 37 may flow the opposite direction to the second hole 39. The operator repeats the process until grooves 17, 33 are substantially filled with adhesive 37.
The operator then cures the bond in a conventional manner, typically by heat. Vacuum bagging may be employed if desired. Optionally, an adhesive film may be located between base 29 and skin 13. Although believed not needed, paste adhesive could also be placed between preform legs 31 prior to insertion of structural member 11, if desired.
The invention has significant advantages. The elongated groove between the bonding surfaces provides an adhesive rib that interlocks the pieces together, increasing the shear strength of the joint. The undulations increase shear strength both in directions perpendicular to the lengths as well as along the lengths. The method allows the members to be set up in a fixture while in a dry condition, which speeds up the process.
While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but it is susceptible to various changes without departing from the scope of the invention. For example, although shown to be a pi-shaped preform, a preform with different configurations, such as a T, X or L shape, could be employed in different applications. In some instances, the preform could be eliminated, with the grooves being formed in two structural members to define a cavity. If the grooves were short enough, only two communication channels may be needed. Further, the communication channels could be formed in the woven perform instead on in the structural member.
Patent Application
20070261787
