Amalia Moutsopoulou

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SCIEPublish is an international open-access journal publishing service provider run by SCIE Publishing Limited, dedicated to supporting and inspiring scientists or institutions/societies who aspire to publish high-quality journals.

The use of polyamide-12 (PA12) thermoplastics in additive manufacturing (AM) is promising owing to their mechanical properties and printability. However, in load-bearing applications, improvements in mechanical strength and stiffness are sought after. Herein, the reinforcement efficiency of silicon nitride (Si₃N₄) nanoparticles in the PA12 matrix was explored. The filler loading varied between 2.0 wt. % and 10.0 wt. %. The nanocomposites were extruded into filament using melt compounding for subsequent material extrusion (MEX) 3D printing. PA12/Si₃N₄ nanocomposites were examined for their thermal, rheological, morphological, and structural characteristics. For mechanical characterization, flexural, tensile, microhardness, and Charpy impact data were obtained. For structural examination, porosity and dimensional deviation were assessed. Scanning electron microscopy (SEM) was used to investigate morphology and chemical composition. The results indicate that Si₃N₄ nanopowder significantly improved all mechanical properties, with a greater than 20% increase in tensile strength and elastic modulus when compared to neat PA12. The structural characteristics were also improved. These findings indicate that Si₃N₄ nanoparticles provide a viable reinforcement filler for PA12 for use in lightweight, robust structural components fabricated using MEX AM. Furthermore, it can be stated that ceramic–polymer nanocomposites further improve the applicability of PA12, where high mechanical performance is required.

Recently, significant attention has been paid to the use of multirole materials in additive manufacturing (AM). Polyvinylidene fluoride (PVDF) is an ideal candidate material that has been selected for examination because of its unique characteristics. This study establishes a correlation between the macroscopic mechanical behavior and microscopic structural mechanisms, enabling the utilization of the deformation rate in tailoring the mechanical response of printed PVDF components. This research focuses on testing AM PVDF samples under different strain rates (10–300 mm/min), aiming to report their behavior under loading conditions compatible with the stochastic nature of real-life applications. The thermal (thermogravimetric analysis and differential scanning calorimetry) and rheological (viscosity and melt flow rate) properties were investigated along with their morphological characteristics (scanning electron microscopy). The response under combined dynamic and thermal loading was investigated through dynamic mechanical analysis, and the structural characteristics were investigated using spectroscopic techniques (Raman and energy-dispersive spectroscopy). The properties examined were the ultimate and yield strengths, modulus of elasticity, and toughness. Sensitivity index data are also provided. For completeness, the flexural strength, Charpy impact strength, and Vickers hardness were also evaluated, suggesting that the AM PVDF samples exhibit a resilient nature even when subjected to extremes regarding their strain rate versus their overall mechanical characteristics. PVDF exhibited a strain-hardening response with an increase in its strength of up to ~25% (300 mm/min) and a stiffness of ~15% (100 mm/min) as the loading speed of testing increased.

Structural control techniques can be used to protect engineering structures. By computing instantaneous control forces based on the input from the observed reactions and adhering to a strong control strategy, intelligent control in structural engineering can be achieved. In this study, we employed intelligent piezoelectric patches to reduce vibrations in structures. The actuators and sensors were implemented using piezoelectric patches. We reduced structural oscillations by employing sophisticated intelligent control methods. Examples of such control methods include H-infinity and H₂. An advantage of this study is that the results are presented for both static and dynamic loading, as well as for the frequency domain. Oscillation suppression must be achieved over the entire frequency range. In this study, advanced programming was used to solve this problem and complete oscillation suppression was achieved. This study explored in detail the methods and control strategies that can be used to address the problem of oscillations. These techniques have been thoroughly described and analyzed, offering valuable insights into their effective applications. The ability to reduce oscillations has significant implications for applications that extend to various structures and systems such as airplanes, metal bridges, and large metallic structures.

Herein, silicon nitride (Si₃N₄) was the selected additive to be examined for its reinforcing properties on high-density polyethylene (HDPE) by exploiting techniques of the popular material extrusion (MEX) 3D printing method. Six different HDPE/Si₃N₄ composites with filler percentages ranging between 0.0–10.0 wt. %, having a 2.0 step, were produced initially in compounds, then in filaments, and later in the form of specimens, to be examined by a series of tests. Thermal, rheological, mechanical, structural, and morphological analyses were also performed. For comprehensive mechanical characterization, tensile, flexural, microhardness (M-H), and Charpy impacts were included. Scanning electron microscopy (SME) was used for morphological assessments and microcomputed tomography (μ-CT). Raman spectroscopy was conducted, and the elemental composition was assessed using energy-dispersive spectroscopy (EDS). The HDPE/Si₃N₄ composite with 6.0 wt. % was the one with an enhancing performance higher than the rest of the composites, in the majority of the mechanical metrics (more than 20% in the tensile and flexural experiment), showing a strong potential for Si₃N₄ as a reinforcement additive in 3D printing. This method can be easily industrialized by further exploiting the MEX 3D printing method.

In this study, we introduce progress in intelligent control for reducing structural vibrations. The field of intelligent control for dampening structural vibrations is evolving rapidly, driven by advancements in materials science, AI, and actuator technology. These innovations have led to more efficient, reliable, and adaptable vibration-control systems with applications ranging from civil engineering to aerospace. The use of smart materials has opened new avenues for vibration control of piezoelectric materials. When mechanical stress is applied to these materials, an electric charge response is formed, allowing for precise control over the vibrations. Improved computational models and simulations play crucial roles in the design and testing of vibration-control systems. Finite element analysis helps in accurately predicting the behavior of structures under various loads, thereby aiding in the design of effective vibration-control systems. In our work, we use intelligent control theory to dampen structural vibrations in engineering structures.