Selective reinforcement with metal matrix composites

Abstract

A selectively reinforced structure may be produced by embedding at least two metal matrix composite tapes in a non-planar relationship to one another and in a predetermined region of a structure to selectively reinforce the structure. Further, a method for selectively reinforcing a structure or part includes positioning at least two metal matrix composite tapes in a substantially fixed non-planar relationship in a predetermined location within a mold and filling the mold with a material such as a metal, metal alloy, polymer, foam, glass, or ceramic such that the MMC tapes are embedded within the material. A reinforced structure is produced that has at least two metal matrix composite tapes selectively positioned within the structure.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 60/593,624, filed Jan. 31, 2005, which is herein specifically incorporated by reference in its entirety.

SUMMARY OF THE INVENTION

The present invention is directed to selectively reinforced structure where at least two metal matrix composite reinforcements are maintained in a relatively fixed, non-planar relationship to one another within the structure. In certain embodiments, a selectively reinforced structure may include a body of material and at least two metal matrix composite tapes, each having a longitudinal axis, a planar surface, and a maximum width, wherein the planar surfaces are substantially mutually non-parallel and the longitudinal axes are substantially mutually parallel, and wherein the at least two metal matrix composite tapes are embedded within the material of the body and extend within the body a distance of at least five times the maximum width of the tape. The metal matrix composite tape may include aluminum oxide fibers in an aluminum matrix. Further, the aluminum oxide fibers may be continuous fibers. In certain embodiments, the body of the structure may be include a material such as metal, metal alloy, glass, polymer, foam, and a castable ceramic. Further, the metal matrix composite tape may include aluminum oxide fibers in an aluminum matrix and the body material of the structure may include aluminum.

Still further, the invention may include a method for selectively reinforcing a structure. The method may include the steps of positioning at least two metal matrix composite tapes having a longitudinal axis, a planar surface, and a maximum width within a mold such that the planar surfaces are substantially mutually non-parallel and the longitudinal axes are substantially mutually parallel; and filling the mold with a material, wherein the at least two metal matrix composite tapes are embedded within the material and extend within the material a distance of at least five times the maximum width of the tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of I-beam end plugs.

FIG. 2 is a perspective view of an I-beam metal matrix composite tape insert.

FIG. 3 is a perspective view a casting with metal matrix composite reinforcement in an I-beam configuration.

FIG. 4 is a plot of flexural load vs. displacement curves for unreinforced aluminum (A), square reinforced aluminum (B), I-beam reinforced aluminum (C), and aluminum reinforced with vertical, parallel metal matrix composite tapes (D).

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Selective reinforcement of structure is a method by which strength and stiffness of regions of the structure can be improved by adding metal matrix composite (MMC) materials with higher strength and stiffness in the desired amount where it is beneficial. Accordingly, MMC tape may be incorporated in a structure, thereby providing selectively strengthened regions. Materials used for the structure may include but are not limited to, metal, metal alloys, plastic, glass, ceramic, foams or other moldable or castable materials. As used herein, a metal matrix composite (“MMC”) is a material made of continuous reinforcing fibers in a matrix of metal where the continuous fibers are infiltrated with the matrix metal. Fibers may include aluminum oxide, glass, quartz, carbon, or other similar fibers. The matrix metal may include any castable metal or metal alloy that is compatible with the selected fibers. The matrix metal may include aluminum, magnesium, copper, zinc, iron, and alloys thereof as well as other metals known to be used in forming metal matrix composite tapes. MMC tape made of aluminum oxide fibers in aluminum or aluminum alloys is available under the name METPREG® from Touchstone Research Laboratory, Ltd., Triadelphia, West Va.

Structures that incur concentrated loads usually require the application of high margins of safety to the entire structure. This requirement leads to an increase in overall weight and size of the structure beyond what is needed by the bulk of the structure in order to ensure adequate load-carrying capacity in the highly stressed areas. Incorporating at least two MMC tapes in the body of structure in a relatively fixed and substantially non-planar relationship provides for enhanced physical properties, such as increased stiffness. Typically, each MMC tape has thickness, a width and a length. The width of the tape defines a planar surface of the tape. A longitudinal axis extends along the length of the tape and is parallel to the planar surface.

At least two MMC tapes are positioned within the body of a structure such that the planar surfaces are substantially mutually non-parallel and the longitudinal axes are substantially mutually parallel. The particular non-parallel configuration for the MMC tapes is not limited and may include any variety of non-parallel relationships. The at least two metal matrix composite tapes are embedded within the material of the body making up the structure and extend within the body a distance of at least five times the maximum width of the tape.

Selectively incorporating MMC tapes allows the designer and fabricator the opportunity to add stronger MMC tape material in specific regions of the structure to selectively reinforce the structure. Providing accurate and precise positioning of the MMC tape in the structure improves the ability to selectively reinforce the structure. MMC tapes can be positioned and held in place during the fabrication process of the structure. A method may include inserting at least two MMC tapes in a relatively fixed and non-planar relationship as discussed above in a predetermined region of a structure to selectively reinforce the structure. Another method may include positioning at least two MMC tapes in a relatively fixed and non-planar relationship as described above in a selected location within a mold and filling the mold with a material around the positioned tapes such that the MMC tapes are embedded within the material and thereby achieving selective reinforcement of the structure defined by the mold. The filling step may include, but is not limited to, a molding process, a casting process, or other similar process for forming the material around the MMC tape.

Holding the MMC tapes in a selected configuration may be accomplished by using machined end plugs to position the tapes within the mold while molten metal or other material that will make up the structure is poured into the mold. The end plugs are machined with non-parallel slots such that the ends of the MMC tape may be inserted in the slots to hold the MMC tape in the desired configuration within the mold. The end plugs may be made out a material that is machinable and can hold the configuration of the MMC tapes during the molding process. One such material for end plugs includes graphite or other similar materials used in the molding process. When the MMC tapes are inserted in the mold with the end caps, gaps between the end caps and the mold allow for the material to enter the mold and surround the MMC tapes.

For casting metals, the mold may be kept above the melting temperature of the casting metal for several minutes in order to achieve a good interface between the tape and casting metal. This may be accomplished by holding the mold under the molten casting metal or using an auxiliary heat source around the mold. While the metal is still molten within the mold, the mold may be moved, vibrated, or agitated to encourage encapsulation and wetting of the tapes by the casting metal. The mold may then be removed from the heat and subjected to directional cooling or quenching in order to reduce the formation of shrinkage porosity within the casting, as desired. The cast part may then be removed from the mold and allowed to cool to room temperature before handling.

EXAMPLE

MMC tapes were positioned in castings in the form of a square, an I-beam, and parallel rows within the cast part. The MMC tape, which was manufactured in a separate process, consisted of continuous Nextel 610 fibers in a matrix of pure aluminum, with the fibers oriented along the length of the tape. The MMC tapes were held in place by graphite blocks that had grooves machined into them to hold the MMC tapes in the desired position. Multiple tapes were stacked together in each position. For example the I-beam reinforcement consisted of four tapes stacked together in each segment of the I-beam. FIG. 1 shows the graphite end plugs 10 with grooves 12 that were used to hold the tapes in the shape of an I-beam-reinforcement. FIG. 2 shows a tape insert 14 where MMC tapes 16 were held together with very fine stainless steel wire 18 to help keep the tapes positioned properly during the casting process. The casting metal was pure aluminum and was inserted into the mold by attaching a handle to the mold and submerging the mold into a large crucible containing the molten aluminum. The mold was pre-heated by partially submerging it in the molten metal for several minutes. The mold was then completely submerged to allow it to fill with molten metal. Alternatively, the mold may be inserted into a furnace, such as a vertical tube furnace, to pre-heat the mold and then filled by ladling the molten metal into the mold from a separate melting furnace.

After filling the mold with molten metal, the mold was shaken and turned to make sure the tapes were wetted by the molten metal. While the shaking step was included for these examples, it is not necessary to provide a cast structure with MMC reinforcements. FIG. 3 is an illustration of one of the finished castings. The finished casting 20 included the MMC tapes 16 within a cast aluminum body 22. The samples were tested to determine the effect on flexural strength and the results are shown in FIG. 4. Castings reinforced with non-planar MMC tapes showed significant improvement in load compared to unreinforced aluminum and reinforced aluminum with planar MMC tape orientation.

While these samples consisted of tape with pure aluminum and Nextel 610 fibers and casting metal of pure aluminum, MMC tape with other alloys and other fiber types could be used. Similarly, other alloys could be used for the casting metal. For example, castings were also made by incorporating tape into 2014 aluminum alloy castings. In addition, other methods of holding the tapes in position could be utilized in order to achieve the same results.

While the invention has been described in detail with respect to certain preferred embodiments, the invention is limited only be the appended claims.

Claims

1. A method for selectively reinforcing a structure, comprising the steps of:

positioning at least two metal matrix composite tapes having a longitudinal axis, a planar surface, and a maximum width within a mold such that the planar surfaces are substantially mutually non-parallel and the longitudinal axes are substantially mutually parallel; and

filling the mold with a material, wherein the at least two metal matrix composite tapes are embedded within the material and extend within the material a distance of at least five times the maximum width of the tape.

2. The method of claim 1, wherein the metal matrix composite tape comprises aluminum oxide fibers in an aluminum matrix.

3. The method of claim 1, wherein the material is selected from the group consisting of a metal, metal alloy, polymer, glass, foam, and a castable ceramic.

4. The method of claim 1, wherein the metal matrix composite tape comprises aluminum oxide fibers in an aluminum matrix and wherein the material comprises aluminum.

5. A selectively reinforced structure comprising a body of material and at least two metal matrix composite tapes, each having a longitudinal axis, a planar surface, and a maximum width, wherein the planar surfaces are substantially mutually non-parallel and the longitudinal axes are substantially mutually parallel, and wherein the at least two metal matrix composite tapes are embedded within the material of the body and extend within the body a distance of at least five times the maximum width of the tape.

6. The selectively reinforced structure of claim 5, wherein the metal matrix composite tape comprises aluminum oxide fibers in an aluminum matrix.

7. The selectively reinforced structure of claim 5, wherein the aluminum oxide fibers are continuous fibers.

8. The selectively reinforced structure of claim 5, wherein the body comprises a material selected from the group consisting of a metal, metal alloy, glass, polymer, foam, and a castable ceramic.

9. The selectively reinforced structure of claim 5, wherein the metal matrix composite tape comprises aluminum oxide fibers in an aluminum matrix and wherein the body material comprises aluminum.