Browse Topic: Advanced composite materials
The demand for carbon fiber reinforced polymers (CFRPs) is growing, especially for use in high-performance applications. Components manufactured of CFRP are made by layering sheets of carbon fibers within a resin matrix. Due to the fibers’ brittle nature, CFRPs are difficult to shape into complex forms, limiting adoption of the material in applications such as vertical lift systems. To address this limitation, researchers at Montana State University, Bozeman (MSU) are developing a new form of carbon fiber called stretch broken carbon fiber (SBCF). SBCF maintains the strength of continuous carbon fibers, while allowing for fiber slip that is used to create a pseudo-plastic strain response needed in most forming processes. Dome and bulge tests were used for comparing the formability response of IM7 MSU SBCF/977-3 with continuous Hexcel IM7 12K/977-3. Results showed increased formability of the MSU SBCF ones due to their ability to stretch under an applied load.
Maintaining the operational readiness of military helicopters demands repair solutions that are fast, reliable, and adaptable. This paper presents the integration of Gamma Alloys' advanced metal matrix composites (MMCs) into additive manufacturing (AM) techniques - specifically Cold Spray and Friction Stir Additive Manufacturing (FSAM) - as a transformative approach to helicopter repair and replace for the US Army.
Gamma Alloys manufactures aluminum matrix composite bearing liners for helicopter transmissions that have the performance of steel liners at one third the weight. These bearing liners have diameters between 2.5 and 24 inches. Our composites are made by blending aluminum powders with spheroidized alumina particles. These powders are then vacuum hot pressed into billets. These billets are then extruded into shapes that can be machined into bearing liners. The extrusion process transforms the powder metallurgy product into a wrought product. Over 2000 liners have been made and are currently flying in R&D vehicles since 2018 with no maintenance issues.
The emerging Advanced Air Mobility (AAM) market is an increasingly important area of research and development within vertical lift. AAM operations will be characterized by short- to mid-range flight that will include urban and suburban corridors and high utilization business models such as on-demand ride-share and package delivery operations. AAM operations also have an enhanced need for durability of vehicle components with respect to impact and fatigue within unsteady environments such as urban canyons. Further business model constraints include the minimization of scheduled maintenance, while maintaining safety levels. A university leadership initiative (ULI), Innovative Manufacturing, Operation, and Certification of Advanced Structures for Civil Vertical Lift Vehicles (IMOCAS), combined research and software development to address these operational aspects. Another major focus of the ULI was the development of processes to integrate new advanced composite materials into AAM designs. These new composites, such as thermosets and thermoplastics, offer equal or enhanced performance at lower weights than traditional aviation materials. This paper provides an overview of the outcomes of the ULI, introducing new software, processes, and data available to the community for the AAM market, crosscutting large passenger operations and smaller medical or commercial cargo operations.
Carbon fiber reinforced polymer composites (CFRP) are extensively used as structural components in rotorcraft applications. Here, we report considerable improvement in the fatigue life of CFRP through the infiltration of nanoscale silica particles into the epoxy resin matrix (nanoCFRP). Fumed silica nanoparticles were initially added to the epoxy resin to prepare epoxy-silica nanocomposites, which were demonstrated to have superior fracture and fatigue properties. Fractographic analysis indicated presence of various key toughening mechanisms including crack deflection, plastic void growth as well as a hitherto unreported heterogeneity induced mesoscale toughening effect. The epoxy-silica nanocomposite resin was then used as the matrix material to fabricate nanoCFRP. Cyclic flexural bending tests indicate significant fatigue life enhancement for the nanoCFRP. The enhancement is especially pronounced in the high cycle fatigue regime. This enhancement in high cycle fatigue is indicative of transfer of small-scale toughening mechanisms from the silica-epoxy nanocomposite resin to the nanoCFRP system. Such nanoCFRP show promise to improve the fatigue life and reduce the operational/maintenance cost for next generation rotorcraft.
The complex dynamics of rotorcraft structures under varying operational and environmental conditions demand the development of accurate and robust-to-uncertainties structural health monitoring (SHM) approaches. The inherent uncertainty within monitoring data makes it difficult for conventional methods to accurately and robustly detect and quantify damage without the need for a large number of data sets. In addition, due to the time-varying nature of rotorcraft operations, such conventional metrics might still fail even with abundance of data. In this paper, we propose a unified probabilistic damage detection and quantification framework for active-sensing, guided-wave SHM that focuses on monitoring rotorcraft structural "hotspots". The proposed framework involves three stages: The first stage incorporates statistical damage detection based on stochastic non-parametric time series (NP-TS) models of ultrasonic wave propagation signals within a hotspot sensor network configuration. The second stage involves the statistical path selection, where a NP-TS representation is used for the sole purpose of identifying damage-intersecting signal (wave propagation) paths, that is the paths that are most sensitive to damage, in order to use them in the subsequent damage quantification stage. That last stage achieves probabilistic damage quantification, where the results of the NP-TS models are used to train Bayesian Gaussian Process regression and classification models. This unified framework ensures accurate and robust damage detection and quantification in a data-efficient manner since only damage-intersecting paths are selected and used in the analysis. The performance of the proposed framework is compared to that of conventional state-of-the-art damage indices (DIs) in detecting and quantifying simulated damage in two representative coupons: a Carbon Fiber Reinforced Polymer (CFRP) coupon and a stiffened aluminum (Al) panel. It is shown that the proposed framework outperforms conventional DI-based active-sensing guided-wave SHM methods.
For high end composite manufacturing in a rapid development environment, the long lead item is often the hard tooling, in particular the cure mold. A traditional metal mold takes in the neighborhood of four to nine months to design, fabricate and validate. With high temperature capable print materials, and larger and faster printers, Additive Manufacturing (AM) appears to have high potential in this area of advanced composites manufacturing. Sikorsky has used AM very successfully on a scale up to approximately 3'x3' and cure temperatures of 350°F. Though long-term durability is still to be determined; the materials, technologies, and techniques Sikorsky has employed for AM autoclave cure molds on this scale have consistently exceeded expectations. AM tools along the scale of main rotor blades could be leveraged to realize even more significant cost and schedule gains from AM autoclave tooling, and in this area, there are still more questions than answers when it comes to a dependable tooling solution. Rotorcraft development, in particular Future Vertical Lift (FVL), programs offer an opportunity to realize the significant schedule and cost benefits AM can provide for composite tooling.
Current rotorcraft gas turbine engines typically use titanium alloys and steel for compressor section and single-crystal nickel superalloys for the hot-section turbine stator vanes and rotor blades. However, these material selections are rapidly changing due to increased requirements on power-density and efficiency. Future Army gas turbine engines will be using ceramic matrix composites for many high temperature engine components due to their low density and improved durability in high temperature environment. The gas turbine industry is also actively developing adaptive concept technologies for production and assembly of modular gas turbine engine components with integrated sensing. In order to actively monitor engine components for extended seamless operation and improved reliability, it is essential to have intelligent embedded sensing to monitor the health of critical components in engines. Under this U.S. Army Foreign Technology Assessment Support (FTAS) program funded research project, surface bonded and embedded sensor patches from a U.K.-based company, Epsilon Optics Ltd., were experimentally evaluated to measure temperature responses on typical propulsion component material coupons. The temperature responses from this foreign technology sensor were assessed using a thermomechanical fatigue tester with a built-in furnace to conduct thermal cycling durability experiments. The experimental results obtained from the durability performance of this fiber-optic based embedded sensor are reported in this paper. This sensor technology upon maturation to higher TRL (Technology Readiness Level) levels can greatly reduce the lifecycle cost of future Army gas turbine engines.
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