COMPOSITE CORE STRUCTURE AND METHOD

A composite core structure includes a core having a plurality of elongated fibers and a plurality of spherical members, the elongated fibers and spherical members consolidated into a desired molded shape. The composite core structure also includes a matrix material encapsulating the elongated fibers and spherical members.

BACKGROUND

The embodiments herein relate to composite structures and, more particularly, to core materials for such structures, as well as a method of forming composite core structures.

Composite core materials are typically either honeycomb or closed cell foam. The honeycomb option is supplied in uniform thickness sheets and is difficult to shape to contour or cut into complex forms. Closed cell foam materials are more easily shaped, relative to honeycomb structures, but have limited structural properties. Therefore, distinct disadvantages are associated with each of the two primary composite core materials, with a tradeoff between shape flexibility and structural property flexibility imposing constraints on composite structure manufacturers.

BRIEF DESCRIPTION

According to one embodiment, a composite core structure includes a core having a plurality of elongated fibers and a plurality of spherical members, the elongated fibers and spherical members consolidated into a desired molded shape. The composite core structure also includes a matrix material which integrates the elongated fibers and spherical members into a monolithic structure.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the spherical members are hollow.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the plurality of elongated fibers includes a plurality of lengths.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the spherical members are formed of thermoplastic.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the elongated fibers are formed of carbon fiber.

According to another embodiment, a slurry for forming a composite core structure includes a suspension medium. The slurry also includes a plurality of elongated fibers disposed in the suspension medium. The slurry further includes a plurality of spherical members disposed in the suspension medium.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the suspension medium is a fluid.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the spherical members are hollow.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the plurality of elongated fibers includes a plurality of lengths.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the spherical members are formed of thermoplastic.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the elongated fibers are formed of carbon fiber.

According to yet another embodiment, a method of forming a composite core structure is provided. The method includes providing a slurry comprising a suspension medium, a plurality of elongated fibers disposed in the suspension medium, and a plurality of hollow spherical members disposed in the suspension fluid. The method also includes drawing the slurry into a mold form with a porous base. The method further includes filtering the suspension medium out of the mold form through the porous base. The method yet further includes consolidating the elongated fibers and the hollow spherical members into the desired form. The method also includes infusing a matrix material into the mold form for mixing with the elongated fibers and the hollow spherical members. The method further includes hardening the matrix material, elongated fibers and hollow spherical members into a monolithic structure.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the elongated fibers and the hollow spherical members are consolidated in the mold form under vacuum.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that any residue of the suspension medium is removed through a flushing step after consolidation.

In addition to one or more of the features described above, or as an alternative, further embodiments may include customizing the structural properties of the composite core structure based on modification of at least one structural factor.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the at least one structural factor comprises at least one of density of the elongated fibers, size of the hollow spherical members and constituent materials.

DETAILED DESCRIPTION

Referring toFIGS. 1-3, a composite structure is illustrated at various stages of manufacture. More specifically, a composite core structure10is shown. The composite core structure10described herein may be employed in any application that benefits from the use of composite structures. In some embodiments, the composite core structure10is employed in the aerospace industry, such as in association with a rotary wing aircraft, for example.

As will be appreciated from the description herein, the composite core structure10is manufactured in a manner that provides a manufacturer with flexibility related to both shaping and structural properties. In other words, the composite core structure10may be contoured or cut into complex geometries, while still being formed in a customizable manner with regard to structural properties, such as strength or elastic modulus, for example.

The composite core structure10includes a plurality of elongated fibers12and a plurality of spherical members14that are randomly mixed with each other during manufacture of the composite core structure10. The elongated fibers12may be formed of various materials, including carbon fiber in some embodiments. The elongated fibers12are of different lengths in some embodiments. In such embodiments, some or all of the fibers have lengths that differ from the other fibers. The spherical members14are hollow in some embodiments. In some embodiments, the spherical members14are formed of a low density material. The spherical members14may be formed of various contemplated materials. In one embodiment, the spherical members14are formed of thermoplastic. While the geometric configuration of a sphere is illustrated and primarily described herein, it is to be understood that deviations from a sphere are contemplated. For example, an oval structure may be employed or any suitable alternative.

FIG. 1illustrates the composite core structure10in a first stage of manufacture. In particular, a slurry16is illustrated. The slurry16includes the elongated fibers12and the spherical members14suspended in a suspension medium18to establish a random mix of the elongated fibers12and the spherical members14. In some embodiments, the suspension medium18is a fluid in the form of a liquid or gas. Two-phase substances (i.e., liquid-gas or liquid-solid) are also contemplated.

FIG. 2illustrates the composite core structure10in a second stage of manufacture. The above-described slurry16is drawn into a mold form20that is shaped to a desired geometry. The mold form20includes a porous base that facilitates removal of the suspension medium18from the slurry16while disposed in the mold form20. The porous base allows filtering out of the suspension medium18to leave a homogenous interlocking mix of the elongated fibers12and the spherical members14in the mold form20. The suspension medium18is completely removed and the remaining mass of elongated fibers and spherical members14is consolidated. Removal of the suspension medium18and consolidation of the elongated fibers12and the spherical members14is done under vacuum in some embodiments.

FIG. 3illustrates the composite core structure10in a third stage of manufacture. Once the elongate fibers12and the spherical members14are consolidated into the desired shape in the mold form20, a matrix material22is infused into the void space to coat and encapsulate the elongated fibers12and the spherical members14. Once the matrix material22is settled in the mold form20, the elongated fibers12, the spherical members14and the matrix material22are hardened to form the final composite core structure10. Exemplary materials that the matrix material22comprises are resin, concrete, thermoplastic and metal. The preceding list is merely illustrative and not limiting. Some materials are hardened by curing, while others do not require curing.

Referring now toFIG. 4, a flow diagram schematically illustrates a summary of a method50of forming the composite core structure10according to an embodiment. The method50includes providing52the slurry16that includes the suspension medium18, the elongated fibers12and the spherical members14. The slurry16is drawn54into the mold form20. The suspension medium18is filtered56out of the mold form20through the porous base and the remaining elongated fibers12and spherical members14are consolidated58. The matrix material22is infused60into the mold form20for mixing with the elongated fibers12and the spherical members14. The matrix material22, the elongated fibers12and the spherical members14are hardened62to form the final composite core structure10.

Advantageously, the composite core structure10has isotropic properties and is able to be molded into any desired shape during manufacturing with strength based on the capability of the embedded fiber rather than traditional materials. A composite core structure10manufactured in this manner possesses a wide range of customizable properties, including moduli, based on at least one structural factor that may be manipulated by a manufacturer to obtain desired properties. The at least one structural factor may include strength or density of the elongated fibers, size of the spherical members and/or constituent materials used.