Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-12-19
2003-12-02
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S066000, C156S092000, C156S293000
Reexamination Certificate
active
06656299
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method and apparatus for structural repair and, more particularly, to a method and apparatus for repairing a damaged or defective area of a structure.
BACKGROUND OF THE INVENTION
It is well known to implement patch repairs to damaged composite structures (such as aircrafts and/or spacecrafts) that are generally made up of sandwich reinforced materials having outer fiber-reinforced composite layers separated by a lightweight core made up of metallic or non-metallic honeycomb, structural foams, and/or wood fibers (e.g. balsa). Generally, damage areas (usually recesses) are formed in these composite structures as a result of fabrication defect(s) or impact(s) from an object. These recesses usually extend at least through an outer composite layer and into the central core of the composite structure.
Conventional repair of these composite structures generally involves drilling holes through the damaged outer composite layer and subsequently injecting adhesive and/or filler material into the core through these holes. This injection of adhesive is generally followed by bonding a pre-cured or co-cured patch to the repair area. While the adhesive which holds the patch to the repair area is drying, the patch is usually held in position using one or both a vacuum bag and tape. Use of the vacuum entails sealing the vacuum bag around the repair area and changing the pressure to approximately 1 atmosphere (up to 14.7 psi); while use of the tape to hold the patch in place should be obvious to those of ordinary skill in the art.
The use of tape and vacuums to provide compressional force on the patch has demonstrated ineffective results when these repair areas were tested for sheer and peel strength. Such ineffectiveness is due, at least in part, to conventional tape and vacuum methods only providing up to about 14.7 psi of force at sea level (and less at higher altitudes). Maximum bond strength cannot be attained at these conventional levels of compressional force. Further, it has been shown that the use of vacuum bags can reduce the bond strength of the adhesive between the patch and the repair area by up to 35%. Such a reduction in bond strength is due to incomplete chemical reactions undergone by the adhesives in a vacuum environment.
Other methods have attempted to increase compressional forces, but have sacrificed structural integrity of the original composite structure in the process. For example, one method consists of drilling a hole through the entirety of the composite structure and creating a vice-type apparatus to increase the compressional force on the patch. Such a method obviously results in an undesirable hole through the entirety of the composite structure. In practical terms, drilling a hole from the outside of an airplane into the fuselage would not promote the structural wellbeing of that aircraft. Yet another method of repair utilizes a plurality of pins which go through the entirety of the patch and into the composite structure. This pin method also has a drawback in that an increased number of holes are put into the outer composite layer of the structure, weakening the structure, with every attempt to strengthen the composite structure. Accordingly, the integrity of the composite structure is sacrificed every time another pin is driven into the structure. It would therefore be desirable to have a method of repairing composite structures that provides greater compressional forces than conventional methods without sacrificing additional integrity of the composite structure.
SUMMARY OF THE INVENTION
The present invention is generally directed to a method and apparatus for structural repair. More specifically, the present invention is generally directed to a method and apparatus for repairing a damaged or defective area of a structure, such as any general composite structure. The repair method and structure of the present invention desirably addresses the lack of appropriate clamping force imposed on repaired areas of composite structures using conventional repair methods. Accordingly, any appropriate type/configuration of damaged or defective structure may benefit from performing repairs on such a structure utilizing the repair method and/or apparatus of the present invention. One particularly desirable application is the repair of the outer shell of a launch vehicle, an aircraft, a spacecraft, a rocket, or any other aerodynamic body that flies.
A first aspect of the present invention includes a method for repairing a structure having a damaged or defective area. The repair method generally includes forming a recess on an exterior surface of the structure. Once the recess exists, a threaded insert is placed in the recess and a first material is deposited in the recess. The particular order in which the threaded insert and the first material are placed in the recess is not critical. This first material is generally cured after it has been placed in the recess. After both the first material and threaded insert have been positioned in the recess, a patch is usually positioned over the recess. A compression fixture is then generally placed over the patch which covers the first material-filled recess. The compression fixture is then compressed against the exterior surface of one or both the structure and the first material by directing a threaded fastener through the compression fixture and into the threaded insert.
Various refinements exist of the features noted in relation to the subject first aspect of the present invention as well. Further features may also be incorporated in the subject first aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. For instance, the recess can be formed by the outer surface of the structure obtaining a nick, notch, depression, dent, slit, cut, or the like. Some recesses can be intentionally formed and/or shaped to promote optimal repair of a damaged area of the structure. Generally, the size and shape of the original recess preferably encompasses the damaged area, but exceptions exist wherein the outer surface of the structure is augmented to change the size or shape of the original recess/damaged area. These recesses can be formed/shaped by machining, milling, hole-sawing, routing, and any other methods known in the art for forming and/or shaping a recess in a structure. Regardless of how the recess is formed, the depth of the recess is ideally limited to less than a wall thickness of the structure in which the recess is formed (i.e., the recess preferably does not extend through the wall thickness of the structure). In variations where the structure is a composite having first and second peripheral face sheets and an internal core, a residual thickness of the internal core material can be left in the recess to form a bottom surface of the recess.
Upon the threaded insert being placed in the recess in the first aspect, the threaded insert may be positioned in spaced relation to a bottom of the recess. In other words, the threaded insert may be positioned to avoid contact with the base/floor/bed of the recess. Additionally, the threaded insert may be positioned interiorly of a plane of the exterior surface of the structure. Put another way, the threaded insert may be positioned in the recess so that no portion of the threaded insert extends beyond the plane that contains the outer surface of the structure. In another embodiment, the threaded insert is positioned in the recess so that an end portion of the threaded insert and the outer surface of the structure are at least substantially coplanar. Other variations which reflect at least a portion of the threaded insert protruding from the recess and extending beyond the plane of the outer surface of the structure are contemplated.
The order in which the first material and the threaded insert are disposed in the recess in the case of the first aspect may be generally dependent upon, amongst other factors, the chemical and physical properties of the first
Grosskrueger Duane D.
Hora Keith Y.
Krohn Michael D.
Orsini Vittorio C.
Ball Michael W.
Corcoran Gladys
Lockheed Martin Corporation
Marsh & Fischmann & Breyfogle LLP
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