The present paper reports for the synthesis of fine-grained corundum ceramics by the method of diffusion dominated solid state sintering at temperature relatively low for corundum materials - 1300 °C, 1450 °C and 1500 °C, using specially introduced additives as follows: 3.0 wt. % T i O 2 , graphene nanostructures - 2.0 wt. % GnP or 20.0 wt. % G3 and nanosized A l 2 O 3 . The initial powders and the ceramics synthesized from them were characterized mainly by the methods of Infrared spectroscopy (FT-IR), X-ray phase analysis (XRD), Scanning electron microscopy (SEM). The results obtained from the conducted research show that the introduction of special additives in a certain amount has an impact on the sintering temperature and recrystallization processes in ceramics. The X-ray phase analysis proved that the main crystalline phase in the ceramics synthesized from blends G1, A1 and C0 was corundum. The main functional groups present in the compositions of the ceramic samples synthesized were determined by FT-IR spectroscopy. Using SEM, it was proved that the introduced nano-additives initiated the formation of fine-grain and fine-pore structure with corundum grain sizes ranging from 0.2 to 2.0 μm. The decreased ceramics synthesis temperature, in this case, was mainly due to the additive T i O 2 (3.0 wt. %) included in the initial blends and the high dispersity of the initial materials. The specific additives introduced into the resulting ceramic ( T i O 2 , G3, GnP, nano- A l 2 O 3 ) lead to a significant reduction in the synthesis temperature. The corundum-based samples containing additives were studied to determine the more important physical-mechanical properties, e.g. water absorption ( W A , % ), apparent density ( ρ a p p , g / c m 3 ) and apparent porosity ( P a p p , % ). Given the characteristics of the synthesized corundum samples, they can be studied and applied as filtering elements and adsorbents in the purification of wastewater from various pollutants, such as dyes and some heavy metals.
Aortic valve disease is a major cause of cardiovascular deaths worldwide. Aortic stenosis increases the workload on the heart and severely alters hemodynamic function by impairing effective blood flow. In recent years, extrusion-based bioprinting technologies have made significant progress in producing patient-specific, biocompatible cardiovascular structures, opening up new opportunities for advanced therapeutic applications. In this study, a commercially available FDM-type 3D printer (ENDER-3 Pro) was mechanically and electronically modified into a fully functional, low-cost bioprinter capable of depositing alginate-gelatin hydrogels with high structural fidelity, despite their low viscosity. The redesigned system integrates a NEMA-17 driven syringe extrusion module equipped with a TR8X8 lead screw, enabling high-resolution pressure-controlled deposition of viscoelastic bioinks. A three-leaflet aortic valve geometry was digitally reconstructed and simplified using Fusion 360 to ensure printability while preserving essential anatomical features. The printing parameters were systematically investigated according to the alginate-based bioinks and set to a nozzle diameter (0.6 mm), layer height (0.6 mm), extrusion multiplier (0.02), and printing speed (5 mm/s). Quantitative shape fidelity assessment, including top-down geometric deviation analysis, confirmed that the bioprinted aortic valve constructs successfully maintained the nominal CAD boundaries. By dynamically optimizing slicing parameters, specifically the extrusion multiplier, rheologically driven deformations such as excessive lateral spreading were effectively mitigated. Although comprehensive evaluation of hemodynamic performance requires future in vitro experiments and coupled fluid–structure interaction (FSI) simulations, the present study establishes a robust and accessible biofabrication framework capable of producing highly complex cardiovascular geometries. Cost-effective and adaptable bioprinting platforms, derived from consumer-grade fused deposition modeling (FDM) systems, can achieve the geometric fidelity and structural stability necessary for advanced cardiovascular tissue engineering. This approach significantly enhances the accessibility of high-precision bioprinting technologies, thereby facilitating broader adoption in both research and translational applications.
Understanding the influence of hole geometry on the elastoplastic behavior of fiber-reinforced composites is critical for designing lightweight, high-performance structural components. This study introduces an efficient framework that combines a simplified theory of small elastoplastic deformations for transversely isotropic media with the finite element method, enabling accurate prediction of stress and strain localization in perforated composites. The material is modeled as an elastoplastic continuum composed of stiff reinforcing fibers embedded in a softer matrix, capturing key anisotropic effects while avoiding costly multiscale simulations. A systematic parametric study of circular, elliptical, and crack-like holes reveals that hole geometry dramatically alters stress concentration patterns. In particular, when the ratio of the semi-axes of an elliptical hole falls below 0.2, maximum shear stresses localize near the lateral surfaces, creating a high risk for matrix–fiber separation and damage initiation. The findings provide quantitative design guidelines for optimizing hole shapes in reinforced composites and demonstrate a practical method to bridge the gap between idealized elastic models and computationally intensive full-scale elastoplastic simulations. This approach offers direct relevance for aerospace, automotive, and energy applications, where stress concentrators critically impact structural reliability.
Selective Compliance Assembly Robot Arm (SCARA) manipulators are extensively employed in automated manufacturing due to their ability to deliver high-speed, precise, and repeatable motion in assembly tasks. This study presents kinematic modeling and validation of a four-degree-of-freedom SCARA with an RRPR (Revolute-Revolute-Prismatic-Revolute) configuration. The forward and inverse kinematic equations were formulated by applying the Denavit-Hartenberg convention, with algebraic and geometric approaches to ensure accurate mapping between joint parameters and end-effector positions. The accuracy of the kinematical models was validated in a MATLAB-based simulation environment with the GUIDE interface, enabling visualization of joint behavior and end-effector trajectory in a 3D workspace. A full factorial design experiment (3³), consisting of 27 joint parameter combinations, assessed the positional output (Px, Py, Pz) under different configurations. In addition, optimal trajectory planning moved the robot between specified points in 4.5 seconds using a fixed time step and 451 interpolated points. Cross-validation using RoboAnalyzer demonstrated high fidelity in spatial and temporal trajectory generation. Finally, a workspace simulation with 250,000 random joint variable samples confirmed the complete workspace and mechanical constraints of the manipulator. The MATLAB workspace boundary closely agreed with RoboAnalyzer, validating the derived kinematic model for robotic motion analysis and industrial automation applications.
Bending and buckling deformations of very thin beams with curved cross-sections are discussed. Nonconvex strain-energy density functions are considered, and the critical loads and corresponding critical conditions are defined. The Euler-Lagrange equation with Weierstrass-Erdmann corner conditions is acceptable for globally stable deformations. The deformations are defined in the context of globally stable equilibrium deformations. Regions of low and high strain are revealed, separated by a discontinuity in the curvature of the elastic curve. Since the curvature is almost zero in one section, when combined with the other section, the beam will be treated as two separate sections. The one remaining is undeformed, and the other is deformed with constant curvature. Those phenomena are easily observed in the metallic measuring bands.
