Method and apparatus for reworking structures using resin infusion of fiber preforms

#This disclosure generally relates to techniques for reworking structures, especially composites, and deals more particularly with a method and apparatus for reworking areas of structures using resin infusion of fiber preforms.

#Composite structures sometimes have localized areas containing one or more inconsistencies that may require rework in order to bring the structure within design tolerances. One technique for reworking localized areas of structures involve placing a patch over the area and securing it to the parent structure using mechanical fasteners, however fasteners may increase aircraft weight and/or drag on the aircraft, and may be esthetically undesirable in some applications. Another rework technique involves bonding the rework patch to the parent structure however this technique may also require the use of mechanical fasteners to provide secondary load paths forming an arrestment mechanism to limit the growth of an inconsistency. Still another technique for reworking structures, referred to as a wet layup technique, involves hand layup of wet plies with fiber reinforcement, such as a woven or knitted fabric and applying wet resin to the plies as they are laid up. The wet layup technique may result in air entrapment within the patch which may result in porosities in the reworked area. The wet layup technique may also be labor intensive, requires repair technicians to come into proximity with wet resin and may require excessive cleanup activity.

#Accordingly, there is a need for a method and apparatus for reworking structures, especially composites, that result in a high quality rework meeting desired performance standards which reduces or eliminates porosities due to air entrapment. There is also a need for a repair method which may reduce labor.

#FIG. 1 is an illustration of a perspective view of a structure having an inconsistency requiring rework.

#FIG. 2 is an illustration similar to FIG. 1 but showing the structure having been reworked using a resin infused fiber patch according to the disclosed method.

#FIG. 3 is an illustration of a sectional view taken along the line 3-3 in FIG. 1.

#Referring first to FIGS. 1 and 3, a composite structure 18 may have a localized area 20 containing one or more inconsistencies 21 that requires rework in order to bring the structure 18 within design or performance tolerances and/or specifications. In the illustrated example, the structure 18 comprises a composite aircraft skin 22 having a thickness “t”, with an outer first side 22a and an inner second side 22b. The structure 18 may comprise other shapes and materials, including, without limitation, ceramics, metals and metal composites. The inconsistencies 21 may comprise, for example and without limitation, impact damage, cracks, fractures, or porosities occurring at the time of manufacture or while the structure is in service. The inconsistency 21 may partially or fully penetrate the thickness “t” of the skin. Referring also to FIGS. 2 and 8, in accordance with the disclosed embodiments, a method is provided of reworking the area 20 to bring it into design or performance specifications, using a rework patch 24, sometimes also referred to herein as a “fiber preform”, before being infused with resin and cured.

#Referring now to FIG. 3, according to the disclosed method, rework of the localized area 20 begins with removing a portion 27 of the skin 22 which includes the inconsistency 21. The process of removing a portion 27 of the skin 22, sometimes also referred to as “scarfing”, results in a depression or scarfed area 25 in the skin 22, as shown in FIG. 4. In the illustrated example, the scarfed area 25 is shown as having a cross sectional profile that is substantially continuously tapered, from the outer edges 25a to the center 25b of the scarfed area 25. However, the scarfed area 25 may have other cross sectional profiles, including a stepped scarf (not shown). In a process step discussed later, a rework patch 24 is used to substantially fill the scarfed area 25.

#Referring to FIG. 5, after the scarfed area 25 has been formed in the outer side 22a of the skin 22, a resin flow through hole 26 is formed in the skin 22, within the scarfed area 25, passing from the outer side 22a of the skin through the skin 22 to the skin's inner side 22b. The hole 26 may be formed by drilling or other suitable methods. In the illustrated example, the through hole 26 is located generally in the center 25b of the scarfed area 25, however other locations within the scarfed area 25 are possible, depending on the application. Also, while a single through hole 26 is shown in the illustrated embodiment, more than one through hole 26 may be employed at multiple locations within the scarfed area 25, depending upon the size and shape of the scarfed area 25.