NIAR Research Publications

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    Effects of manufacturing defects on composite seat pans at static and dynamic strain rates
    (American Institute of Aeronautics and Astronautics Inc, AIAA, 2024) Bhasin, Akhil; Maichan, Tanat; Gomez, Luis M.; Olivares, Gerardo; Keshavanarayana, Suresh R.
    The use of composite materials in aircraft primary seat structures has increased and requires additional standards to maintain the current level of aircraft seat safety. The presence of manufacturing defects or service damage could undermine the load-carrying capabilities of these structures at dynamic loading rates. In the current work, the effects of out-of-plane fiber waviness/wrinkle on representative aircraft seatpans has been investigated. The seatpans are tested at both quasi-static and elevated strain rates. The performance of seatpans with defects is compared against pristine seatpans. All the experiments were conducted using a high-rate test frame and were supported with high-speed Digital Image Correlation (DIC). A comparison of load, displacement, strain, and strain rate at failure between different configurations is reported. © 2024 by Akhil Bhasin, NIAR AVET.
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    High energy dynamic impact analysis of thermoplastic composite laminates
    (American Institute of Aeronautics and Astronautics Inc, AIAA, 2024) Ravi, Aswini Kona; Bhasin, Akhil; Gomez, Luis M.; Olivares, Gerardo
    In this paper, the numerical analysis of thermoplastic laminates subjected to high-energy dynamic impact conditions is discussed. The ballistic experiments were conducted at NASA Glenn on two different thermoplastic material systems at a range of impact velocities. The material system considered for the research presented in this paper is Solvay APC AS4D/PEKK-FC. The test outcomes included projectile containment and penetration into the composite laminate. For the numerical analysis, two different modeling approaches with varying fidelity levels were considered. The first modeling approach is a simplified definition of the composite laminate using a single shell layer and is referred to as the basic fidelity level. The second modeling approach is more extensive, with all the plies in the composite laminate modeled distinctly and is referred to as the moderate fidelity level. Both the modeling approaches presented an acceptable correlation with test data when it comes to the projectile residual velocity and the panel displacement data. This paper aims to present the differences between the predictive capabilities of the simulations when the composite laminate is modeled using different fidelity levels and when a medium fidelity composite material model is chosen. © 2024 by Aswini Kona Ravi, NIAR AVET.
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    Characterization of thermoplastic composites made by oven consolidation and stamp forming
    (The Composites and Advanced Materials Expo (CAMX), 2023) Rubesinghe, Lakshan; Heil, Joseph P.
    The introduction of reinforced thermoplastic materials for large aerospace structural applications has been a developmental effort, as the benefits they offer have been overshadowed by the more established thermoset composites. While thermoset composites require a long curing process that cannot be reversed, thermoplastic composites can be rapidly processed and reshaped multiple times without significantly degrading the material or its properties. They also offer superior toughness and resistance to environmental factors. However, the quality and processability of unidirectional prepreg material for thermoplastic composites is not well understood, leading to variability in end part quality. This paper presents research studies conducted on two different industry-wide used thermoplastic materials. Materials were examined for their prepreg qualities as well as consolidated laminate properties that were fabricated using two common out of autoclave (OOA) methods: oven consolidation and stamp forming. Key goals of this research are to understand laminate quality and processability when OOA methods are used. Standard autoclave consolidations of thermoplastics provide a reliable baseline dataset, a comparative understanding of the materials can be obtained by comparing out of autoclave processing methods with autoclave results. Out of Autoclave post processing significantly eliminates cost and time factors and assists high-rate manufacturing of composites. Industry could utilize the set of specific processing parameters provided in this paper as a guideline for novel, sustainable and efficient high-rate manufacturing techniques in hopes of assisting the current and future requirements for aerospace industry. Copyright © 2023. Used by CAMX - The Composites and Advanced Materials Expo. CAMX Conference Proceedings.
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    Structural batteries challenges for emerging technologies in aviation
    (Association of American Publishers, 2023) Di, Mauro G.; Guida, M.; Olivares, Gerardo; Gomez, L.M.
    In a global context where modern societies need to move towards greater environmental sustainability, ambitious targets to limit pollutant emissions and combat climate change have been set out. Concerning the aviation sector, research centers and industries are carrying out new aircraft designs with increased use of electrical energy onboard aircraft both for non-propulsive and propulsive purposes, leading to the concepts of More Electric Aircraft (MEA), Hybrid Electric Aircraft (HEA) and All-Electric Aircraft (AEA). Despite the expected flight emissions reduction, new potential air transportation missions, safer flights, and enhanced design flexibility, there are some drawbacks hindering the trend to HEA solutions, strictly bounded to the limited performance of traditional battery systems. The reference is to low energy and power densities, which impact on aircraft weight and flight performances. A new technology, namely structural battery, combining energy storage and load-bearing capacity in multifunctional material structures, is now under investigation since capable to mitigate or even eliminate barriers to the electrification of air transport sector. Although, the deployment of this technology raises relevant questions regarding airworthiness requirements, which need to be applied when considering such multifunctional materials. The purpose of the presented activity is to take a step towards the definition of aircraft certification requirements when dealing with structural batteries, considering them both as a structure and as a battery, to maintain unchanged or even improve the level of safety in all normal and emergency conditions.
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    Failure Analysis of Composite C-Spars Under Inter-Laminar Tensile (ILT) Configurations: An Experimental & Numerical Evaluation
    (DEStech Publications, 2023-09) Shafie, Mohamed Z.; Seneviratne, Waruna P.; Tomblin, John S.; Rathnaweera, Ruchira; Nadason, Harishanker
    In designing composite structures, it is fundamental to understand critical areas of structural deficiencies that lead to failures. One such critical design element is the failure caused by out-of-plane loads propagating through the bending of a composite laminate. In such cases, load offsets and element heights are generally the primary contributors to moments and forces leading to the degree of bending. In curved beams, these load conditions result in inter-laminar tension (ILT) type failures between plies, resulting in delamination and eventual failure. This work investigates such an ILT failure mechanism on composite C-Spars. The C-Spar specimen was constructed entirely of a quasi-isotropic [45/0/-45/90]4S layup and consisted of two 90-degree radii along with straight web sections defining the height of the element. To examine the contribution of the bending moment, resultant force, and rotation on the unfolding radii, varying loading arm configurations were investigated with a pinned load applicator. High-fidelity finite element (FE) analysis using B-Spline Analysis Method (BSAM), developed under the Air Force Research Laboratories (AFRL), was also utilized to predict failure of the C-Spars. The FE models showed good agreement with that of the experimental data and predicted failure loads within 10% on multiple configurations while also mimicking the geometric nonlinearity under larger deformation. Having successfully modeled the rotation and failure of the C-Spar configuration, this enables further investigation into the critical inter-laminar stresses induced within the design of such structures.