Multi-stage debulk and compaction of thick composite repair laminates

A method for fabricating a repair laminate for a composite part having an exposed surface includes applying a release film to the exposed surface and forming an uncured ply stack assembly on the release film. The uncured ply stack assembly is formed by forming and compacting a series of uncured ply stacks. The release film and ply stack assembly is then removed from the exposed surface. A bonding material is then applied to the exposed surface, and the uncured ply stack assembly is applied to the bonding material. The ply stack assembly and bonding material are then cured.

TECHNICAL FIELD

The present invention relates to methods of fabricating laminates made from polymeric-matrix composite materials.

DESCRIPTION OF THE PRIOR ART

Parts made from polymeric-matrix composite materials form many components in modern automotive, aeronautical, and marine vehicles, as well as components in many other types of equipment and structures. Such parts may, from time to time, become damaged, thus requiring repair or replacement. It is often required or at least more cost effective to repair a damaged part than to replace the part. Conventional methods of repairing polymeric-matrix composite parts require the use of specialized tooling and double vacuum tool/processes, which require multiple staging operations and cure cycles, or specialized lay-up tools and autoclave processing, which is expensive and often impractical when used to facilitate a repair.

There are many ways to repair damaged polymeric-matrix composite parts that are well known in the art; however, considerable shortcomings remain.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention represents a method for multi-stage debulking and compaction of thick composite repair laminates made from one or more polymeric-matrix composite materials. In one embodiment, the method is applied to the repair of an existing composite part. The method provides a composite part meeting the same laminate quality requirements as a thick laminate made using highly-pressurized autoclave processing. For the purposes of this disclosure, the term “thick laminate” means a laminate made from more than about 10 plies of polymeric-matrix composite material.

Referring toFIG. 1in the drawings, a pre-existing composite part101is shown. It should be noted that composite part101may be planar or non-planar in form. A layer of release film103is applied to composite part101and a first plurality of uncured plies105(only one labeled inFIG. 1for clarity) of polymeric-matrix composite material is applied to release film103. In a preferred embodiment, the number of uncured plies105making up the first plurality of uncured plies105is no more than about ten plies. The first plurality of uncured plies105makes up a first ply stack107. Uncured plies105may comprise “wet lay-up” plies or pre-impregnated, i.e., “pre-preg” plies.

Referring now toFIG. 2, bleeder material (not shown) and a sealing bag201is applied over first ply stack107and release film103in a conventional manner. Sealing bag201is attached to an exposed surface203of composite part101to create a substantially air tight seal between exposed surface203and sealing bag201. A vacuum port205extends through sealing bag201to allow gases to be withdrawn from sealing bag201within the substantially air tight seal between sealing bag201and exposed surface203. A vacuum assembly (not shown) is attached to vacuum port205, which evacuates gases, as represented by arrow207, from within the sealed volume of sealing bag201. In a preferred embodiment, vacuum at a level of two to three inches of mercury is applied to the sealed volume of sealing bag201. In addition to applying vacuum, a heat source209heats at least first ply stack107to a desired debulking and compaction temperature. In a preferred embodiment, sufficient heat is applied to first ply stack107by heat source209to raise the temperature of first ply stack107to a temperature of about 125 degrees Fahrenheit. First ply stack107is maintained at the desired temperature, e.g., about 125 degrees Fahrenheit, under vacuum, e.g., about one to two inches of mercury, for a time period sufficient to debulk and partially compact first ply stack107. In a preferred embodiment, first ply stack107is maintained at the desired temperature and under vacuum for about one hour. Subsequently, first ply stack107is preferably maintained at the desired temperature under full vacuum, e.g., about 28 inches of mercury, for a period of time of about 30 minutes to further compact first ply stack107. After the desired period of debulking and compaction time, sealing bag201, the breather material, and any other ancillary processing materials are removed from first ply stack107and composite part101. First ply stack107is now debulked and compacted.

It should be noted that the debulking and compaction temperature is a temperature below a curing temperature of the polymer-matrix composite material.

Referring now toFIG. 3, a plurality of ply stacks, such as first ply stack107, a second ply stack301, and a third ply stack303, are combined to form a ply stack assembly305. Ply stack assembly305may comprise any suitable, desired number of ply stacks, such as ply stacks107,301, and303. In the illustrated embodiment, second ply stack301is formed by applying a plurality of plies, preferably no more than about ten plies, to first ply stack107. A bag, such as sealing bag201, is then applied to first ply stack107and second ply stack301. Vacuum and heat are then applied to bagged first ply stack107and second ply stack301according to the method described herein concerningFIG. 2. Third ply stack303, as well as any desired ply stacks in addition to third ply stack303, are formed by the same method as second ply stack301.

Referring toFIG. 4, release film103(shown inFIGS. 1-3) is removed and replaced with a bonding material401. Bonding material401is disposed between ply stack assembly305and exposed surface203of composite part101. Note that in this one method of bonding ply stack assembly305to exposed surface203. Bonding material401also includes, and is not limited to: a layer of adhesive paste or a layer of adhesive film disposed between ply assembly305and exposed surface203; and/or, adhesive material disposed within ply stack assembly305.

As depicted inFIG. 5, bleeder material and a sealing bag501is applied over ply stack assembly305and bonding material401in a conventional manner. Sealing bag501is attached to exposed surface203of composite part101to create a substantially air tight seal between exposed surface203and sealing bag501. A vacuum port503extends through sealing bag501to allow gases to be withdrawn from sealing bag501within the substantially air tight seal between sealing bag501and exposed surface203. A vacuum assembly (not shown) is attached to vacuum port503, which evacuates gases, as represented by arrow505, from within the sealed volume of sealing bag501. In a preferred embodiment, full vacuum, e.g., about 28 inches of mercury, is applied to the sealed volume of sealing bag501. In addition to applying vacuum, a heat source507heats at least ply stack assembly305to a desired curing temperature, which is dependent upon the particular composite material being used. In one embodiment, sufficient heat is applied to ply stack assembly305by heat source507to raise the temperature of ply stack assembly305to a temperature of about 250 degrees Fahrenheit. Ply stack assembly305is maintained at the desired temperature under full vacuum for a time period sufficient to sufficiently cure ply stack assembly305and bonding material401to form composite laminate601, shown inFIG. 6. In a preferred embodiment, ply stack assembly305is maintained at the desired temperature and under vacuum for about two hours. After the desired curing time, sealing bag501, the breather material, and any other ancillary processing materials are removed from composite laminate601, as depicted inFIG. 6. The cured ply stack assembly305and the previous composite part101now form parts of composite laminate601, as the cured ply stack assembly305is adhesively bonded to the pre-existing form of composite part101.

It should be noted that the present method may also be applied to the fabrication of a new composite part, rather than to the repair of a composite part. For example, composite part101may be replaced with a lay-up tool. Release film103is not replaced with bonding material401prior to curing ply stack assembly305, so cured composite laminate601can be removed from the lay-up tool.

It should also be noted that a damaged composite part701, shown inFIG. 7, may be machined or scarfed to define a recess703into which a ply stack assembly705is received, cured, and adhesively bonded to composite part701to form composite laminate707.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the description. It is apparent that an invention with significant advantages has been described and illustrated. Although the present invention is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof.