Fabrication of Fiber-Metal Laminates with Non-Autoclave Processes

NASA's plasma-deposition process provides the ability to tailor various properties while designing functional parts by selecting specific materials and processing parameters to meet the end goal. Specifically, the plasma process deposits metal particles that are heated as they travel axially at low velocity through an inert gas plasma. The accelerated powder particles become molten, strike the substrate fabric (uniaxial, biaxial, and multiaxial) and rapidly solidify, imparting very little heat to the substrate while forming a metal-to-fiber bond, as well as a metal-to-metal bond. The resulting metal-coated fabric is porous, so the polymer matrix can pass through the product precursor during the infusion process. The amount of metal deposited can be controlled, as can the number of plies of fabric that are ultimately stacked to produce the preform for the polymer matrix infusion process. A variety of infusion processes can be utilized to prepare the FML, including resin transfer molding (RTM), resin film infusion (RFI), and vacuum-assisted resin transfer molding (VARTM). The tailorable aspect of the process allows for specific product design. By varying the combination of metal particle, fiber, fabric type, metal layer thickness, fabric direction, number of layers, polymer matrix resin, infusion process, and cure conditions, the characteristics of the final part can meet the needs of various applications.

Fiber-Metal Laminates (FMLs) are composite materials that consist of conventional fiber reinforced plastics with the addition of a metal component, typically a foil or mesh layer(s). The metal component offers the advantage of incorporating metal-like properties to the composite construction. While a range of potential advantages and applications have been discussed for FMLs, the primary application to date has been for aircraft structures, with one potential advantage being the lightning strike protection (LSP) offered by the improved electrical conductivity. As aircraft construction has moved to composite structures, there has been an increasing need for such conductive composites. Similarly, with increasing use of composites for other large structures, e.g. wind turbines, there are an increasing number of potential applications for lightning strike protection materials. Other advantages of FML are improved impact and fire resistance. This innovation provides a method for making FML materials that incorporate nanotube reinforcement. The method involves the use of RF plasma spray to directly form and deposit nanotube materials onto fibers/fabrics, which can then be manufactured into composite structures by infiltrating the fiber with resin, and consolidating the structure via autoclave processing or via the use Vacuum Assisted Resin Transfer Molding (VARTM) composite manufacturing methods. Nanotubes incorporated into the structure in this manner can be of several types, for example boron nitride or carbon nanotubes. The objective of this innovation is to incorporate the nanotube materials in the FML in order to improve the mechanical properties.

This NASA invention enables several benefits that mitigate limitations associated with conventional ATP systems, including the following: (1) avoids obtuse head rotation or cross-tool translation when laying adjunct tape plies, (2) simultaneously places tape on both sides of a part via two robots, (3) eliminates external anchoring frame requirements, and (4) translates parts during build while also translating the applicator head. The ability to perform simultaneous layup on opposite sides of the component, as well as reduction of head rotation reversal during bidirectional tape layup, offers increased layup speed. The invention offers increased placement accuracy as a result of reduced movement between tape layup operations and the eliminated need for an anchoring frame (facilitated by simultaneous pressure extrusion of prepreg by the two robots). NASAs automated tow/tape placement system has two key unique features: the use of two opposed ATP cars to enable a tool-less process, and an on-the-fly reversal tape/tow laydown tooling head. The system uses two opposing (i.e., underside-to-underside) ATP cars, and can build parts vertically, horizontally, or at any other angle, depending on the workspace available. The ATP die wheels can be reversed or turned to draw the composite back and forth at different angles to create a layer-by-layer composite structure. Both cars can dispense TPC tape thus, either car can function as an opposing tool surface while the other performs prepreg lay-up. For structures that do not vary in thickness, both cars can lay tape at the same time doubling layup speed. Current ATP robots must rotate the large tooling head, or traverse panels without layering tape to achieve bidirectional layup, where each additional movement introduces alignment error. To increase layup rate while simultaneously minimizing misalignment, NASAs system incorporates an on-the-fly reversal tape/tow laydown tooling head to enable efficient bidirectional layup.

In order to improve the properties of monolithic metallic materials, alloying additions are made that create secondary phases and/or precipitate structures. These improvements must occur during melt solidification and are governed by the thermodynamics of the process. That is, optimizing the metallic alloy is possible only as much as thermodynamics allow. Developing novel methods to combine metallic compositions/alloys into a fully dense material is of interest to create materials with novel property combinations not available with monolithic alloys.While various approaches for layering two-dimensional materials exist, their capabilities are typically limited and non-isotropic. Further, while three-dimensional composites may be formed with conventional powder metallurgy processes, it is generally very difficult to control the arrangement of the phases, for example due to randomness created by mixing powders. This invention is method for creating a multiple alloy composite structures by forming a three-dimensional arrangement of a first alloy composition, in which the three-dimensional arrangement has a substantially open and continuous porosity. The three-dimensional arrangement of the first alloy composition is infused with at least a second alloy composition. The three-dimensional arrangement is then consolidated into a fully dense solid structure.

The simulation combines existing fracture mechanics based damage propagation techniques with a discrete approach to modeling discontinuities in finite elements. Additionally, the use of an advanced laminate theory recovers deformation and stress information that would normally require a high fidelity model. To accomplish this, the same theoretic and analytical concepts that a high fidelity numerical simulation tool utilizes for laminate damage simulation are placed in the context of a low fidelity finite element. In taking this approach, a laminate can be modeled as a single layer low fidelity shell mesh that has the ability to locally increase fidelity and represent a delamination based damage process but only if it is determined that one should occur. The numerical simulation tool's performance has been validated against numerical benchmarks as well as experimental data.