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    Multi-Scale mechanical behavior of Liquid Elium® based thermoplastic matrix composites reinforced with different fiber types: Insights from fiber–matrix adhesion interactions
    (Korean Fiber Society, 2024-11-19) Kaybal, Halil Burak; Ulus, Hasan; Cacik, Fatih; Eskizeybek, Volkan; Avci, Ahmet
    Elium® liquid thermoplastic resin, with room-temperature curing and recyclability, enables large-scale production. However, limited research exists on the fiber–matrix interface, and understanding micro-scale interactions is key to influencing the composite’s macro-scale mechanical properties. This study investigates the interfacial adhesion of glass, carbon, basalt, and aramid fibers-reinforced liquid Elium® thermoplastic matrix composites at micro-, meso-, and macro-scales. Contact angle measurements show 53-56º for glass fibers, indicating superior wettability with the Elium® matrix, while carbon, aramid, and basalt fibers exhibit 58-62º, 73-74º, and 79-86º, respectively. Micro-bond tests demonstrate the highest load-carrying capacity in the interface between glass fibers and the matrix, with glass fibers carrying 11.4% more load than carbon fibers and 25.8% more than basalt fibers. Fiber bundle tests, including transverse and 45° fiber bundle tests, highlight the superior load-carrying performance of glass fibers, with all fiber types showing increased load-carrying capacities in the 45° tests. The micro-scale and meso-scale data obtained from micro-bond and fiber bundle tests corroborated the results of the macro-scale interlaminar shear stress (ILSS) tests, confirming the significant influence of the fiber–matrix interface on the mechanical integrity of the composites. The shear strength at the glass/Elium® interface was 47.54 MPa, which was 8.5% higher than carbon, 20.3% higher than aramid, and 25.9% higher than basalt interfaces. These findings advance our understanding of the mechanical behavior and interfacial adhesion in thermoplastic matrix composites. They underscore the crucial role of the fiber/matrix interface in determining the mechanical properties of composites and offer insights into the compatibility of diverse fiber reinforcements with the innovative Elium® matrix. © The Author(s), under exclusive licence to the Korean Fiber Society 2024.
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    Rectified control barrier functions for high-order safety constraints
    (Institute of Electrical and Electronics Engineers Inc., 2024-12-16) Ong, Pio; Cohen, Max H.; Molnar, Tamas G.; Ames, Aaron D.
    This letter presents a novel approach for synthesizing control barrier functions (CBFs) from high relative degree safety constraints: Rectified CBFs (ReCBFs). We begin by discussing the limitations of existing High-Order CBF approaches and how these can be overcome by incorporating an activation function into the CBF construction. We then provide a comparative analysis of our approach with related methods, such as CBF backstepping. Our results are presented first for safety constraints with relative degree two, then for mixed-input relative degree constraints, and finally for higher relative degrees. The theoretical developments are illustrated through simple running examples and an aircraft control problem. © 2017 IEEE.
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    Studying flame-retardancy, smoke and toxicity of fiber-reinforced composites manufactured via modified resins and metallic coatings
    (Elsevier B.V., 2025-01-02) Murad, Md Shafinur; Hamzat, Abdulhammed K.; Bahçeci, Ersin; Asmatulu, Eylem; Bakir, Mete; Asmatulu, Ramazan
    This study focuses on the development of flame-retardant fiber-reinforced polymer (FRP) composites, which are typically fire-intolerant despite their excellent mechanical, chemical, and thermal properties. Incorporating modified resins, metallic surface coatings, and graphene powder improved the composite's fire resistance and reduced smoke emissions properties. The composites were fabricated using a wet-layup process under vacuum. Thermal stability, flammability, and smoke production characteristics were evaluated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), thermomechanical analysis (TMA), UL94 vertical flame test, and standardized smoke and toxicity tests. The addition of 9,10-dihydro-9-oxo-10-phosphaphenanthrene-10-oxide (DOPO) and Cu film surface coating led to superior smoke suppression with negligible smoke production (maximum Ds of 0–4, VOF4 of 1 at 180–240 s), whereas unmodified composites showed significant smoke development (maximum Ds of 759 at 240 s, VOF4 of 1157). Because DOPO and matrix interacted to form a char layer, the modified test samples passed the UL 94 vertical flame tests with a V0 rating. The metal films also enhanced fire-shielding and heat-dissipation, which resulted in a synergistic effect of chemical and physical protection with minimum release of toxic gases. This research could lead to composites with reduced emissions of harmful gases and minimal smoke formations with better fire-retardant properties. © 2025 The Authors
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    Impact of nanoparticle size and loading on printability of composite inks for direct ink writing
    (John Wiley and Sons Inc, 2024-12-28) Li, Yun; Flynn, Aidan; Masternick, Christopher; Kolanovic, Brandon; Li, Bin; Li, Bo
    Direct ink writing (DIW) using polymer-particle composite inks is a new research area enabling a wide range of new functionalities. Despite extensive studies, there remains a need for a deeper understanding of how particle size and loading specifically influence printability, especially in the nano range. This work aims to systematically evaluate the effects of SiO2 nanoparticle size (26–847 nm) and loading on printability within a polydimethylsiloxane (PDMS) matrix. For the single-layer printing process, which is influenced by the substrate properties, a 3D printing line analysis (3D-PLA) is developed to monitor the top and side views of printed lines. It is found that line width varies with ink composition and substrate, while the line height decreases with solvent evaporation, indicating a strong confinement effect from the substrate. For multilayer structures, dual-layer printing analysis (DLPA) is utilized to evaluate the printability. It is shown that DLPA is independent of the substrate and can be used to compare the printabilities from different inks. Both 3D-PLA and DLPA can be correlated to the rheological behavior of the ink through ink rheology analysis (IRA). Finally, this research defined the design space for DIW by benchmarking the minimum and maximum particle loadings for printable composite inks. © 2024 Wiley-VCH GmbH.
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    Disturbance-robust backup control barrier functions: Safety under uncertain dynamics
    (Institute of Electrical and Electronics Engineers Inc., 2024-12-09) Van Wijk, David E. J.; Coogan, Samuel; Molnar, Tamas G.; Majji, Manoranjan; Hobbs, Kerianne L.
    Obtaining a controlled invariant set is crucial for safety-critical control with control barrier functions (CBFs) but is non-trivial for complex nonlinear systems and constraints. Backup control barrier functions allow such sets to be constructed online in a computationally tractable manner by examining the evolution (or flow) of the system under a known backup control law. However, for systems with unmodeled disturbances, this flow cannot be directly computed, making the current methods inadequate for assuring safety in these scenarios. To address this gap, we leverage bounds on the nominal and disturbed flow to compute a forward invariant set online by ensuring safety of an expanding norm ball tube centered around the nominal system evolution. We prove that this set results in robust control constraints which guarantee safety of the disturbed system via our Disturbance-Robust Backup Control Barrier Function (DR-bCBF) solution. The efficacy of the proposed framework is demonstrated in simulation, applied to a double integrator problem and a rigid body spacecraft rotation problem with rate constraints. © 2017 IEEE.