Patent Application
20130164498
The present invention relates generally to composite materials, and, more particularly, to an improved thermoplastic composite prepreg for automated fiber placement.
Reinforced thermoplastic and thermoset materials have wide application in, for example, the aerospace, automotive, industrial/chemical, and sporting goods industries, etc. Thermoplastic or thermosetting resins are impregnated into reinforcing fibers to form a “prepreg” tape that is used to form completed structures. Thermoplastic prepregs may be melt bonded together in-process avoiding the expensive and time-consuming procedure of curing that is required for thermoset prepregs. These thermoplastic prepreg tapes are growing in popularity among all segments of the composites industry due to their higher performance and versatility. However, process rates, surface finish, and some properties such as void content are lower for in-process consolidated thermoplastic prepregs. It is therefore desirable to have an improved thermoplastic composite prepreg for automated fiber placement.
Embodiments of the present invention provide an improved thermoplastic composite prepreg for automated fiber placement. The prepreg in accordance with an embodiment of the present invention has a substantially uniform geometry. In some embodiments, a susceptor layer is disposed on a composite tape. A resin layer is disposed over the susceptor, and the susceptor absorbs energy, for example, from electromagnetic waves, such as light from a laser, or ultrasonic energy from an ultrasonic energy source. It will be recognized that any and all feasible energy sources are included within the scope of the invention. The susceptor then heats up the resin which allows for more effective formation of multilayer composite shapes. Methods in accordance with embodiments of the present invention create structures using this prepreg without the need for costly and time-consuming autoclave processes.
In one embodiment, a multilayered composite material is provided, the material comprising, a fiber tape comprising fibers held together with a thermoplastic polymer matrix, a susceptor layer disposed on a first side of the fiber tape, and a polymer surface layer disposed on the susceptor layer.
In another embodiment, a multilayered composite material is provided, the material comprising, a fiber tape comprising fibers held together with a thermoplastic polymer matrix, a polymer surface layer disposed on the fiber tape, wherein a susceptor is intermixed in the polymer surface layer.
In another embodiment, a multilayered composite material is provided, the material comprising, a fiber tape comprising fibers held together with a thermoplastic polymer matrix, a first susceptor layer disposed on a first side of the fiber tape, a first polymer surface layer disposed on the first susceptor layer, a second susceptor layer disposed on a second side of the fiber tape, and a second polymer surface layer disposed on the second susceptor layer.
The drawings are not necessarily to scale. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering may represent like elements.
Embodiments of the present invention provide an improved thermoplastic composite prepreg tape. The prepreg tape is optimized for high-speed, high quality in-situ consolidation during automated fiber placement. Embodiments of the prepreg tape have substantially uniform dimensions (cross section, width and thickness, etc.), substantially uniform energy absorption, substantially uniform surface roughness, and sufficient resin at the surface to affect a bond between layers. Embodiments of the present invention provide a multilayered composite material. The multilayered composite material comprises a fiber tape comprising: fibers held together with a thermoplastic polymer matrix; a susceptor layer disposed on at least one side of the fiber tape; and a polymer surface layer disposed on the susceptor layer. Benefits include being able to fabricate components (e.g. aircraft parts and the like) using automated fiber placement without the need for costly and time-consuming post processes such as an autoclave.
The larger the HAZ, the more time it takes to cool and the more residual stresses are induced. The prepreg shrinks as it cools due to its Coefficient of Thermal Expansion (CTE) at varying rates depending on factors, non-limiting examples of which include the type of fiber, matrix, and the direction (e.g. fiber direction or cross-fiber direction) in which shrinkage is measured. The currently applied tape 308, heat source 304, and associated tape supply mechanism travel in direction D to apply the tape. In some embodiments, this motion may be repeated as necessary or desirable to build up a composite shape.
One way to achieve a small HAZ 302 is to use a high intensity energy source such as a laser. If the laser energy is of a wavelength that is absorbed by the polymer (such as CO2 lasers at 10.6 μm), then the high intensities that are needed for high process rates tend to vaporize or otherwise damage the polymer on the surface resulting in poor bond quality. Therefore, with the non-uniform fiber distribution and/or surfaces of the prior art prepreg tapes, uneven heating and poor bond quality can result. If the laser energy is of a wavelength to which the polymer is transparent (such as, for example, diode lasers or fiber lasers at 1060 nm) then an absorbing material is needed to create the HAZ.
The susceptor layer 404 absorbs the energy from a laser or other source to create the heat needed to bond adjacent layers of the prepreg tape 400. The choice of material for the susceptor may depend, in part, on the energy source used for creating the HAZ. For example, if laser energy at 1060 nm is used, the absorber 404 may be comprised of carbon black, nanotubes, nanoclay, graphene, nanoparticles, whiskers, carbon fiber dust, or any other suitable means. CLEARWELD coating (Produced by Gentex, Carbondale, Pa.) may also be used, as it contains energy absorbing materials designed for operating in the 940 nm-1100 nm wavelength range. Clearweld coatings form thin, uniform layers of the energy absorbing materials onto the fiber tape 406. When laser energy is applied to the area that has been coated, the Clearweld material absorbs this energy and converts it to heat. This results in a localized melting of the prepreg tape layers and the formation of a weld.
A variety of methods may be used for making polymer surface layer 402. Such methods may include, but are not limited to, extrusion, film coating, powder coating, casting, solution coating, plasma spray, flame spray, sintering, vapor deposition, any combination thereof, or any other suitable means. In one embodiment, the polymer surface layer 402 has a thickness ranging from approximately 1 micrometer to approximately 15 micrometers, and a surface roughness, Ra, ranging from approximately 0.1 micrometers to approximately 1.3 micrometers. It will be recognized that any other feasible thicknesses and surface roughnesses are included within the scope of the invention. The polymer surface layer may be comprised of PE (Polyethylene), PP (Polypropylene), PET (Polyethylene terephthalate), PEEK (Polyether ether ketone), PEKK (Polyetherketoneketone), PI (Polyimide), PAI (Polyamide-imide), any combination thereof, or any other suitable polymer.
It is preferable to provide a uniform coating that achieves intimate contact with the surface to which it is being bonded, and has sufficient thickness to affect the bond, but not so thick as to adversely affect the performance of the overall structure by significantly reducing fiber volume fraction. Since the fibers produce the desirable strength and/or stiffness in a typical composite structure, it is desirable to maximize the amount of fibers available per unit volume. This parameter is referred to as “fiber volume.”
In one embodiment, the fiber volume, which is a percentage of fiber volume to total volume for a given cross-sectional volume of the tape, ranges from 55% to 65% with one standard deviation ranging from about 2% to about 4%, and more preferably about 3%. It will be recognized that any other feasible fiber volumes are included within the scope of the invention.
Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, certain equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more features of the other embodiments as may be desired and advantageous for any given or particular application.
This application claims priority to 61/578,386 filed on Dec. 21, 2011, and is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61578386 | Dec 2011 | US |
