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This study investigated the influence of moisture absorption on the electromagnetic (EM) wave absorption performance and mechanical strength of a radar-absorbing structure (RAS) with nickel-coated pristine glass fibers and polyamide 6. To construct the RAS, nickel was deposited on pristine glass fibers via electroless plating, and the RAS was fabricated using a hot-press process. An environmental test was conducted under a high humidity of 85%, and the EM wave absorption capacity of the RAS was measured at 2-week intervals. Moreover, compressive and interlaminar shear tests were conducted to verify the degradation of mechanical strength and the effect of the nickel coating on moisture absorption resistance. The test results revealed that immersion in moisture degraded the EM absorption capacity of the RAS. Nevertheless, an improvement in the mechanical strength of the RAS after saturation was observed due to the nickel coating. [ABSTRACT FROM AUTHOR]

In this study, a novel multifunctional film known as susceptor, containing silver nanoparticles, was proposed to improve the induction welding performance of unidirectional carbon fiber-reinforced polyetherketoneketone (CF/PEKK) thermoplastic composites. A group of Ag/PEKK films was synthesized with different amounts of silver nanoparticles. Good thermal performance was obtained, including the maximum temperature and thermal growth time constant, leading to the selection of films with 60 wt.% and 70 wt.% silver nanoparticles. In addition, the mechanical performance was evaluated for single-lap joints fabricated with the selected films and stainless-steel mesh. Specifically, the highest interlaminar shear strength and single-lap shear strength of 25.2 MPa and 20.9 MPa, respectively, were achieved with a susceptor containing 60 wt.% silver nanoparticles. The mechanism of these increases in thermal and mechanical performance is discussed using numerical and experimental methods (non-destructive test and optical microscope observation). In conclusion, the multifunctional heating film incorporated into the adhesive can improve the thermal and mechanical efficiency of single-lap joints of thermoplastic composites fabricated using the induction welding method. [ABSTRACT FROM AUTHOR]

In the field of composite materials, many reports have shown that catastrophic structural damage is caused by lightning strikes. In this study, new design concepts were proposed for the lightning-strike protection of nickel-coated glass/epoxy foam-core composites. Instead of using a neat metal mesh, glass fibers were modified with nickel particles via a plating technique to improve their thermal and electrical conductivities. In addition, a thin Invar plate was inserted at the middle of the structure and a foam core was introduced to reduce damage to the structure. Three models with different materials and stacking sequences were used in this study. Severe damage was experimentally observed following artificial lightning at a peak current of approximately 150 kA when considering a waveform A. Furthermore, numerical prediction was performed to identify the damage mechanisms of the structures. Besides the heat flux source, a mechanical source known as the shock wave overpressure was investigated separately as a new factor for dielectric materials. These two sources of lightning were determined as minor reasons for the structural damage. The failure modes were analyzed for further discussion about the failure mechanism in this study. [ABSTRACT FROM AUTHOR]

Nickel coating of reinforcing fibers via electroless plating can provide superior properties to polymer composites, particularly for radar stealth, although its effect on thermomechanical properties and thermal cycling response are relatively unverified. Thermal cycling of strained nickel‐coated glass fiber epoxy laminates was performed to evaluate its effect through in‐plane shear mechanical testing and fiber‐matrix interface region microscopic observations. Laminates were subjected to 4000 cycles of thermal conditioning (regular and strained). Subsequent in‐plane shear tensile tests revealed a ~10% increase in their ultimate shear strength, which was credited to polymer relaxation and increased plastic energy storage capacity. Atomic force microscopy in force modulation mode showed the most significant fiber‐matrix interface region changes for strained thermal cycled specimens, which we attribute to their higher stress during conditioning and plastic deformation. A relatively short fiber‐matrix interface region length was observed, which we attribute to the lower surface energy of Ni‐glass fiber. Thermomechanical analysis (TMA) revealed a glass‐transition temperature range of 71–110°C, and coefficients of thermal expansion (CTE) were evaluated for several laminate configurations. [ABSTRACT FROM AUTHOR]

Promising carbon fiber-reinforced thermoplastic (CF/polyetherketoneketone (PEKK)) composites were fabricated by the state-of-the-art technology known as "Automated Fiber Placement." The mechanical properties of CF/PEKK were evaluated for four different postprocessing methods: in situ consolidation, annealing, vacuum bag only (VBO), and hot press (HP). The evaluation was performed by narrowing down the relevant processing parameters (temperature and layup speed). Furthermore, the void content and crystallinity of CF/PEKK were measured to determine the effect of these postprocessing processes. The HP process resulted in the best quality with the highest interlaminar shear strength, highest crystallinity degree, and lowest void content. The second most effective method was VBO, and annealing also realized an improvement compared with in situ consolidation. The correlation between the postprocessing method and the void content and crystallinity degree was also discussed. [ABSTRACT FROM AUTHOR]