This work investigates the microstructure evolution during the rotary friction welding (RFW) of Inconel 718 alloy. A cellular automata (CA) approach is implemented to evaluate a cylindrical component (at weld center and edge wall), predicting dynamic recrystallization (DRX) and grain size of friction welds. The input variables for RFW were rotational speed (500, 1000, and 1200 rpm), feed rate (2 mm/s), and feed distance (3.6 mm). The CA model is based on the Laasraoui-Jonas model and explains intricate grain transformation in terms of microstructure, temperature, strain, and strain rate. Calculated grain consists of very fine grain structure at the stir zone followed by the thermo-mechanical affected zone, where partial recrystallized microstructure was present. The average grain size was 2.5 µm, which is comparable to reported experimental values. The grain analysis revealed that temperature and strain are most affecting factors to attain a refined microstructure. The strain rates predicted for both center and edge locations of the weld were found to be higher as rotational speed increased. A steady strain distribution is noted at greater temperature for all the rotational speeds. The results of this work contribute toward the understanding of microstructure and mechanical response for RFW of Inconel 718.

Ductile iron (DI) can acquire various properties with the addition of alloying elements and through heat treatment. In this work, the effects of vanadium and molybdenum on the microstructure and corrosion resistance of DI and austempered ductile iron (ADI) were studied. Corrosion resistance was evaluated by potentiodynamic polarization techniques in 0.5 M H2SO4, 0.5 M NaCl, and 05 M NaOH as electrolyte. The ADI alloyed with vanadium presented anupper ausferritic microstructure consisting of broad ferrite needles, while the combination of vanadium and molybdenum allows obtaining a fine microstructure composed of ausferrite and thin needles of ferrite; this microstructure improves the corrosion resistance in NaCI and NaOH. The DI’s showed corrosion due to the galvanic pair between the graphite nodule and the ferrite; however, a high amount of carbide increases the corrosion resistance in H2SO4.

In this work, the evaluation of tunnel defects in Al-7075 T6 sheets processed by friction stir welding (FSW) is explored using computed tomography (CT) and the finite element method (FEM). The effect of axial force and temperature generated during the FSW was assessed using four rotary speeds (1600, 1700, 1800 and 1900 rpm), each at two different welding speeds (15 and 30 mm/min). These joints were CT-scanned, reconstructing the voxels from the X-Ray images. A voxel size of 46 m, a spot size of 59 m and a magnification of 4.35 using a Cu filter of 0.5 mm were selected. The 3D images of the welds showed the forms, places and levels of the detected defects. The tunnel defects were found at 2 mm from the bottom edge of the weld plates, and the tendency for the defects formation was reduced at 1900 rpm based on CT scans. The numerical results of FSW revealed that with a higher rotational speed, the generated heat and strain were increased, while the stress decreased for higher welding speeds. The coupling of CT and numerical results provide an in-depth understanding of material flow and defect formation during friction process.

This work presents a mathematical and numerical framework for the design and analysis of a remotely operated vehicle (ROV) intended for shallow-water reef exploration. The vehicle consists of an open-frame structure with a sealed pressure housing and a four-thruster propulsion system that enables omnidirectional maneuverability and stable low-speed operation. The hydrodynamic behavior of the ROV is modeled using the incompressible Reynolds-averaged Navier–Stokes equations, which are solved numerically to obtain the velocity and pressure fields around the vehicle. Thruster-induced flow is represented through a Multiple Reference Frame (MRF) formulation, allowing thrust generation and momentum exchange to be resolved directly from the governing equations without prescribing artificial source terms. The propulsion model is supported by experimental bollard-pull characterization of T200 thrusters, from which quadratic thrust laws were identified. A quantitative validation against published experimental data shows deviations within 6–9% and a root-mean-square error (RMSE) of approximately 1.6 N, confirming the accuracy of the proposed thrust model. The CFD-predicted axial force ($F_Z\approx -17.60\mathrm{N}$) was further shown to be consistent with the experimentally derived thrust law when evaluated at the corresponding equivalent operating condition. Structural response is evaluated through a one-way fluid–structure interaction (FSI) strategy, in which the hydrodynamic loads obtained from the CFD solution are transferred to a linear elastic structural model. The validity of the one-way coupling assumption is supported by explicit displacement-to-length ratios in the range $\delta /L\sim$ 10⁻⁵–10⁻³, confirming negligible geometric feedback on the flow field. The results show that the combined CFD–FSI formulation provides physically consistent predictions while remaining computationally efficient. The aluminum configuration exhibited a maximum von Mises stress of approximately 21.1 MPa, remaining safely within the elastic regime, whereas the ABS configuration reached a maximum displacement of 2.9 mm, indicating substantially higher structural compliance. Overall, the experimentally validated propulsion model, quantitatively supported CFD predictions, and asymptotically justified one-way FSI coupling constitute the main contributions of this study, providing a reproducible and physically consistent methodology for the analysis and optimization of reef-class ROVs.