The present invention relates generally to the fabrication of composite structures and components, and more specifically to a fiber precursor for such structures and components.
There are numerous processes and technologies for fabrication of composite structures and components. These include 3-D printing technologies, autoclave curing, out-of-autoclave (“OOA”) curing, injection molding, liquid molding and hot pressing. Each of these technologies requires one or more fiber precursors to serve as the basis for the fabricated composite structure.
One technology for creating such precursors is tailored fiber placement (“TFP”). TFP was first developed in the 1990's, enabling the production of arbitrarily-shaped fiber precursors. TFP involves positioning and securing a bundle of fibers, referred to as a roving, upon a base substrate material, to form an integrated precursor for a fiber-reinforced composite structure. Typically, the strength and stiffness of such a fiber-reinforced structure is greatest along the direction in which the component fibers are aligned. The appropriate offset of the component fiber alignment within the precursor results in a structure exhibiting quasi-isotropic strength and stiffness along the plane of the composite structure. However, such structure will exhibit far less strength and stiffness with regard to forces applied orthogonally to the fiber placing plane.
TFP has proven to be effective for fabricating complex, arbitrarily-shaped composite components, and for providing structural reinforcement of composite structures. The pattern of the roving upon the substrate can be calculated so as to optimize this reinforcement to compensate for localized or directed stresses that the resulting composite structure may be exposed to. Examples of particular methods for performing and optimizing roving placement for structural reinforcement are disclosed in Spickenheuer, A., et al. “Using tailored fibre placement technology for stress adapted design of composite structures,” Plastics and Rubber Composites, vol. 37, pp. 227-232 (March 2008) and Gliesche, K, et al., “Application of the tailored fibre place (TFP) process for a local reinforcement on an ‘open hole’ tension plate from carbon/epoxy laminates,” Comp. Sci. and Tech., vol. 63, pp. 81-88 (2003), which are incorporated by reference herein. The roving material itself is typically comprised of a grouping or bundle of colinear fiber filaments, running substantially parallel to the axis of the length of the roving. As stated previously, the strength and stiffness of a fiber-reinforced structure is greatest along the direction in which the fibers are aligned. Consequently, the maximum stiffness and greatest strength of such a fiber roving applied to a structure will be exhibited along the plane of that structure, not in a plane orthogonally situated to that of the structure. Present roving and roving processes are incapable of fully exploiting the physical and mechanical qualities of the fibers within the roving so as to maximize the orthogonal strengthening of a structure. The inability to take full advantage of these physical and mechanical properties within the roving itself is also presented in additive manufacturing processes such as fused filament fabrication; the fused filament does not possess the full strength and stiffness it might otherwise possess in the direction perpendicular to the printing direction.
Disclosed herein is an improved fiber precursor, and methods for employing such to enhance the structural reinforcement of composite structures. The precursor is comprised of one or more fibrous filaments positioned within the precursor so that the filaments within each fiber are oriented at an angle offset from the axis of the length of the precursor. The offset of these filaments can be accomplished, for example, by twisting a plurality of filaments into a continuous spiral to form the precursor, or by wrapping a collection of colinear filaments about a central core, or by braiding plurality of filaments to form the precursor. The angle of offset at which the twisted, braided or wrapped fibers are positioned can be varied as a function of the twisting, braiding or wrapping process (angle of wrap, tension upon the twisting or wrapping fibers, degree of rotational twisting applied to the fibers per length of precursor, etc.). The offset angle can be arbitrarily chosen to achieve the desired shear properties based upon the particular composite structure, the manufacturing method(s) being employed, and the environment in which the precursor will be utilized.
In one example the fiber precursor includes a plurality of fibers arranged to form a continuous cylindrical element, where the fibers are predominantly aligned to a fixed angle offset from a longitudinal axis of the cylindrical element. The fiber precursor includes comingled resin and reinforcement fibers. One example of resin fibers is thermoplastic fibers. One example of reinforcement fibers is carbon fibers. In one example the fiber precursor is formed by twisting the fibers about the longitudinal axis to form the continuous cylindrical element. The fiber precursor may include about 1,000 to about 50,000 fibers.
In one embodiment the fixed angle is offset from the longitudinal axis of the cylindrical element by 45 degrees.
Also described herein is an additive manufacturing process, including the steps of: heating the fiber precursor to a temperature at which the precursor becomes nominally plastic such that the fiber precursor will retain the shape imposed on it by the applied forces. The additive manufacturing process may also include depositing the heated fiber precursor upon a build surface in a controlled pattern. The heated fiber precursor may be deposited using a nozzle. In one embodiment, the additive manufacturing process includes depositing the heated fiber precursor in a controlled pattern to create a three-dimensional object. The heated fiber precursor may be cooled prior to being heated.
Also described herein is a fiber precursor including a straight core having a longitudinal axis that includes a first bundle of a plurality of colinear fibers and at least one additional bundle of a plurality colinear fibers wrapped around the straight core so as to form a coil about the straight core, where each section of the coil is offset from the longitudinal axis of the straight core by the same fixed angle (e.g. 45 degrees). In one embodiment, the first bundle and the at least one additional bundle have circular cross-sections. The cross-sectional diameter of the first bundle may be less than, substantially equal to or greater than the cross-sectional diameter of the at least one additional bundle. In another embodiment, the first bundle has a rectangular cross-section and the at least one additional bundle has a circular cross-section. In another embodiment, the first bundle has a rectangular cross-section and the at least one additional bundle includes a flexible tape. The first bundle and the at least one additional bundles may include comingled resin (e.g. thermoplastic fibers) and reinforcement fibers (e.g. carbon fibers). The fiber precursor of this embodiment is formed by wrapping the at least one additional bundle of fibers around the straight core of colinear fibers.
In other embodiments, the fiber precursor includes three or more bundles of a plurality of colinear fibers interlaced with each other to form an interlocking, repeating pattern. Examples of repeating patterns include flat braids, regular braids, three-dimensional braids, tubular braids. The number of fibers in a bundle is about 1000 fibers to about 50,000 fibers.
The features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings in which:
Increasing V1 will reduce offset angle ΘT, increasing twisting rate ω1 will increase ΘT, and reducing in the distance (dr) between roller sets 206 and 208 decreases ΘT. These variables can be altered depending upon the desired offset angle, the physical characteristics of the fibers being drawn, the desired density of the resulting precursor, as well as other considerations that might arise based upon the specific apparatus being employed to perform the formation of the precursor and the environmental conditions in which it is being formed.
As stated above, the particular offset angle, ΘT, can be varied by manipulating V1, ω1, and dr. Although the offset angle is not restricted to any particular value, well-known and generally accepted design theory for fiber composites, such as those set forth in Chou, T., Microstructural Design of Fiber Composites, Thermoplastic behavior of laminated composites, pp. 39-46, FIG. 2.4 (Cambridge University Press 1992), which is incorporated by reference herein, prescribe that an offset angle of 45°, with respect to the plane of the substrate surface to which the precursor is affixed, would maximize the shear property of the resultant precursor/substrate structure. Note that the surface of the substrate would be aligned with the longitudinal axis of precursor affixed thereto in the manner illustrated in
Comingled fibers 202 utilized to form the twisted precursor are typically comprised of both reinforcing fibers and thermoplastic resin fibers. Reinforcing fibers include fibers comprised of materials such as carbon, glass, aramid, ultra-high molecular weight polyethylene (UHMPE), boron, steel, copper, and carbon nanotubes. Thermoplastic resin fibers include fibers comprised of materials such as nylon 66, nylon 6, nylon 12, polypropylene (“PP”), polyethylene (“PE”), polyester, polyether ether ketone (“PEEK”), polyphenylene sulfide (“PPS”), polyetherimide (“PEI”), and polyvinylidene difluoride (“PVDF”). The distribution of these two types of fibers within the twisted precursor is critical with respect to the resultant precursor/substrate structure, as this ratio determines the fiber/volume make-up of that structure. This ratio can be adjusted based upon the particular application and environment for which the precursor/laminate structure is being fabricated. However, regardless of the particular ratio, it is desirable to ensure that there is a uniform distribution of the thermoplastic resin fibers among the reinforcing fibers within the precursor. This uniform distribution provides for a precursor that exhibits predictable, consistent characteristics throughout the fabrication process of the structure, and consistent performance with respect to mechanical properties, such as shear strength, once incorporated into the structure.
An additional embodiment of the invention is illustrated in
The diameters of the straight core and colinear fiber, as well as the wrapping angle can be varied as needed for particular applications. In
It will be understood that although
Yet another embodiment of the invention is depicted in
Each of the embodiments of the precursor invention discussed above have been described as being primarily utilized in the fabrication of precursor structure. These structures typically require additional manufacturing processes, such as injection molding, autoclave curing, out-of-autoclave (“OOA”) curing, liquid molding and hot pressing, to be performed upon the precursor/substrate structures before a finished product or component is created.
The precursors disclosed may also be employed in manufacturing processes not requiring the introduction of, or attachment to, a substrate. For example, the twisted precursor of
In FFF, a precursor filament 802 is deposited from a deposition nozzle 804 onto build surface 806. A twisted precursor (such as the one illustrated in
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.