[This corrects the article DOI: 10.3389/frabi.2026.1772871.].
Solid-state welding processes, particularly friction-stir welding (FSW), offer significant advantages for joining different aluminum alloys due to their good mechanical performance, energy efficiency, and cost-effectiveness. The FSW of the AA5052-H32 and AA6261-T6 alloys has not been previously reported. In this study, the effects of the main FSW process parameters on the mechanical behavior of different AA5052/AA6261 alloy joints were systematically investigated. A full factorial experimental design was applied, considering the tool rotation speed (900–1800 rpm) and the welding speed (56–252 mm/min) as control factors, along with their ratio (Rs/Ws). The results of the tensile tests reveal that the joint strength is strongly affected by the interaction between the rotation and welding speeds, with the Rs/Ws ratio is identified as a key parameter governing material flow, plastic deformation, and defect formation. The maximum tensile strength, approximately 198 MPa, corresponding to a mechanical efficiency of 84.4%, was achieved at 1800 rpm and 7 rev/mm, a condition that favored effective material mixing and a defect-free interfacial bond (≈162–186 MPa). The microhardness profiles showed a minimum of approximately 40–50 HV within the TMAZ, on the advancing side. In general, clear quantitative relationships were established between the process parameters and the mechanical properties, which allowed for the identification of optimal operating conditions to produce high-quality FSW joints between the dissimilar materials AA5052/AA6261.
This study presents a two-dimensional computational fluid dynamics analysis of a vertical-axis Savonius-type wind turbine under atmospheric conditions representative of an educational environment located in the Ecuadorian Andean region. Unlike previous studies conducted under sea-level meteorological conditions, this research is performed under high-altitude conditions (2723 m a.s.l.). The unsteady flow around the rotor was simulated using a two-dimensional approach based on the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations, discretized with the finite volume method and coupled with the k–ω Shear Stress Transport (SST) turbulence model. The rotor rotation was modeled using sliding mesh technique, employing a second-order implicit time scheme to ensure numerical stability and adequate temporal resolution. The numerical model was configured for a tip speed ratio of 0.8 and a wind speed of 3.9 m/s. The time step was defined based on a constant angular advancement of the rotor per time iteration, ensuring numerical stability and adequate temporal resolution. The aerodynamic torque was obtained by integrating the pressure and viscous forces acting on the blades, allowing the calculation of the mechanical power generated and the power coefficient. The results showed a periodic and stable torque behavior after the initial transient cycles, yielding an average torque of 0.7687 N·m and a mechanical power of 5.17 W, while the power coefficient reached a value of 0.2102. Analysis of the flow fields revealed the formation of a low-velocity wake downstream of the rotor, regions of high turbulent kinetic energy associated with periodic vortex shedding, and a significant pressure difference between the advancing and returning blades, confirming that turbine operation is dominated by drag forces. The numerical results were validated through comparison with previous studies, showing good agreement and demonstrating the reliability of the proposed Computational Fluid Dynamics (CFD) approach. This study highlights the potential of Savonius turbines for low-power applications in urban and educational environments, as well as the usefulness of CFD as a tool for evaluating and optimizing their aerodynamic performance.
Concrete remains one of the most widely utilized construction materials, valued particularly for its exceptional compressive strength. However, exposure to fire can compromise both its internal microstructure and external integrity. This research investigates the behavior of concrete manufactured with recycled concrete coarse aggregate (RCA) derived from construction waste, aiming to establish experimental evidence of fire’s impact on compressive strength. We employed the Optimal Density Method to design mix proportions targeting 24 MPa compressive strength. The experimental program comprised 45 cylindrical samples distributed across three replacement levels: 0%, 15%, and 30% natural aggregate substitution with RCA. Following 28 days of curing, samples underwent direct fire exposure in a melting furnace. Temperature progression was monitored using a pyrometer, ranging from ambient (0 °C) through 250 °C, 400 °C, 600 °C, to 800 °C, with controlled exposure duration at each level. Three samples were tested at each temperature. After fire exposure, samples were cooled for 24 h at ambient temperature before compression testing. The densities of the fresh specimens were determined to be 2254.06 kg/m3 for HS-0AR%, 2210.09 kg/m3 for HS-15AR%, and 2180.85 kg/m3 for HS-30AR%, with a percentage density variation with respect to HS-0AR% of 1.95% and 3.25%, respectively. Finally, in relation to the compressive strength of concrete, a reduction of 4.34% was observed for 15% AGR and 5.72% for 30%, suggesting that the variations may be due to factors such as the water/cement ratio, the quality of the aggregate, and the curing conditions of concrete. In addition, several pathologies were observed, such as cracking, fissures, color changes, and spalling.
