International Journal of Mechanical and Materials Engineering最新文献

This study presents an integrated theoretical approach combining ab initio density functional theory (DFT) simulations with a new analytical model of the ferroelectric phase transition that accounts for interactions between both first and second neighbors in pure and magnesium-doped lithium niobate (LiNbO₃, LN). This framework enables the characterization of the evolution of ionic conductivity as a function of temperature and Mg concentration, as well as the variation of the Curie temperature (T_C) with doping level. In parallel, DFT calculations provide insight into the effect of Mg doping on the electronic density of states (DOS) and band structure. By applying vacancy-based models (a mixed model and two models referred to as 1 and 2) to both pure and Mg-doped LiNbO₃, we obtain good agreement with experimental data for ionic conductivity and Curie temperature. At constant temperature, the ionic conductivity of Mg-doped LiNbO₃, increases up to a critical Mg concentration of approximately 3.4%, which is attributed to a reduction in Nb antisite defects (Nb_Li) and a narrowing of the band gap, leading to an effective n-type behavior. Beyond this threshold, the conductivity gradually decreases due to band gap widening and the formation of additional structural defects. Overall, this integrated approach advances the understanding of transport mechanisms in Mg-doped LiNbO₃, and provides valuable guidance for optimizing acoustic and optoelectronic devices based on this material.

This study presents the first exploration of natural dye extracted from Rumex abyssinicus for crayon formulation, leveraging its local availability and environmental sustainability. The work focused on evaluating the effects of paraffin wax, talc, extracted dye, and temperature on the crayon's properties. Characterization techniques, including UV–vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), tensile strength testing, visibility, and durability assessments, were employed to analyze the formulated crayon. A Box-Behnken design within the Response Surface Methodology framework was used to optimize the formulation by varying paraffin wax (4, 6 and 8 g), dye (0.5, 1.25 and 2 g), talc (5, 7 and 9 g), and temperature (80, 90 and 100 °C), while keeping stearic acid (0.5 g) and beeswax (1 g) constant. UV–vis spectroscopy revealed a maximum absorbance of 0.830 at λ_max of 298.7 nm, indicating strong pigment retention. The crayon exhibited a tensile strength of 1.48 N/mm² and a percentage elongation at break of 1.34%, reflecting its durability and flexibility. These findings demonstrate the feasibility of utilizing Rumex abyssinicus dye in eco-friendly crayon production, offering a sustainable alternative with desirable mechanical and aesthetic properties.

Building insulation is currently one of the biggest challenges to reduce energy consumption. Saving energy also means reducing the human impact on Environment. In order to reduce this impact, the manufacturing of the building materials is of importance. Moreover, policies, laws and regulations keep evolving in this direction. Mineral insulation foams are mainly composed of cement or gypsum. In mentioned context, an evolution of mineral insulating foams is necessary. This paper proposes promising low carbon mineral foams. The insulating foam, produced by a direct foaming method, aims at having a thermal conductivity lower 0.065W/m/K combined with a compressive strength higher than 0.2 MPa. Therefore, in this research, binder has been replaced by hydraulic lime and used with a bio-sourced foaming agent, locally produced. Limestone Clay Fines (LCF), considered as waste, have been added in the formulation up to 25% of the binder and LCF addition also improved the foaming of the mixture by more than 70%. 12,5% of Sulfo-Aluminous Cement (SAC) was used and has a key role in the setting process. Superplasticizer was also used to reduce water consumption, which accounts for half of the total mass of raw materials, and allows quantity adjustment of SAC. Mixing process choices and more precisely mixing equipment, can also have a significant impact. Indeed, the use of whisk, in place of a blade, produces more quickly a 28% lighter foam. Comparing with other insulating materials, this mineral foam presents one of the lowest CO₂ equivalent emissions and also one of the lowest drinking net water consumptions. Moreover, the specificities of this insulating foam pores give to this new material interesting acoustic performances. Indeed, the processed foams are five times better acoustically than aerated concrete. In fact, the internal structure of the mineral foam absorbs up to 80% of low wavelengths.

This study investigates the Al6061-TiB2-Gr hybrid composites developed by high-energy stir casting with varying TiB2 (5, 10, 15, and 20 wt.%) and fixed graphite (2 wt.%). The research focuses on both chemical and tribological characterization. The phase composition and elemental analysis were examined using SEM and EDS, confirming uniform distribution and strong bonding of reinforcements. Wear tests were conducted using a pin-on-disc setup under different loads (5–15 N) and sliding distances (1000–3000 m). The response surface methodology (RSM) and ANOVA were employed to model the effects of reinforcement content, load, and sliding distance on wear rate and friction coefficient. The Al6061-20TiB2-2Gr composite exhibited a 68% reduction in wear rate and 71% lower friction compared with the base alloy. The combination of hard TiB2 and self-lubricating graphite enhanced surface protection, resulting in smoother wear morphology. The study confirms that the optimized hybrid composite provides superior tribological performance and chemical stability, suitable for eco-efficient engineering applications.

In this study, Nb-doped V₂O₅/rGO composites were synthesized via the hydrothermal method, with reduced graphene oxide contents ranging from 0 to 15% to evaluate their photocatalytic performance in the degradation of methyl orange (MO), rhodamine B (RhB), and malachite green (MG) under UV light. XRD analysis with Rietveld refinement confirmed the stabilization of the orthorhombic alpha-V2O5 phase, where the presence of Nb₂O₅ signals and a shift in diffraction peaks evidenced lattice expansion induced by doping. Furthermore, XPS analysis revealed the coexistence of mixed oxidation states (V⁴⁺/V⁵⁺) and the formation of oxygen vacancies, which are critical for charge transfer. Morphological characterization by SEM showed a structural evolution from microplates in the rGO-free material to a porous network of interconnected nanosheets at 15% rGO. Although thermal stability improved with rGO content, the 5% rGO composite exhibited the optimal photocatalytic activity, achieving removal efficiencies exceeding 90% for RhB and MG. The degradation of malachite green was found to be strongly pH-dependent, suggesting that electrostatic interactions govern the adsorption mechanism. These results point to a synergistic effect between Nb-doping and the rGO network, promoting an efficient Z-scheme charge transfer mechanism.

This study presents a novel approach to improving the performance of domestic vapor compression refrigeration systems (VCRS) through a bio-synthesized nano-lubricant derived from periwinkle shells, a biodegradable waste material. Periwinkle-shell-derived CaO-rich nanoparticles (PSD–CaO nanoparticles) were synthesized via a sustainable method Al₂(SO₄)₃ as a precursor, marking the first application of PSD–CaO nanoparticles in refrigeration. Although bulk composition shows significant SiO₂ inherited from the shell matrix, the active nanomaterial consists of crystalline CaO domains responsible for the observed performance enhancement. Experimental evaluation showed that at 0.1 M concentration, the 0.036 wt.% CaO-rich nanoparticle + mineral oil (M.O.) blend achieved the lowest energy consumption (0.3832 kWh) and power consumption, attributed to enhanced thermal conductivity and reduced friction. Conversely, pure M.O. outperformed nano-lubricant blends at 0.3 M concentration, where nanoparticle agglomeration increased viscosity and reduced lubrication efficiency. At 0.1 M, the 0.06 wt.% CaO-rich nanoparticle + M.O. achieved the lowest pressure ratio, indicating optimal lubrication. Cooling capacity was highest at 0.05 wt.% CaO-rich nanoparticle + M.O. (0.3 M) and 0.08 wt.% CaO-rich nanoparticle + M.O. (0.1 M). The coefficient of performance (COP) peaked at 0.05 wt.% (0.3 M) and 0.024 wt.% (0.1 M), underscoring the importance of nanoparticle dispersion in maximizing thermal efficiency. However, none of the tested configurations met the ISO requirement for pull-down to –12 °C, highlighting limitations in deep cooling capability. The key novelty lies in the eco-friendly synthesis of CaO-rich nanoparticles from waste periwinkle shells, demonstrating a pathway toward waste valorization and energy efficiency. Aligned with Sustainable Development Goals (SDGs) 11.6 and 13.3, this research shows the potential of bio-derived nano-lubricants to enhance VCRS performance, with optimal nanoparticle concentration being central to sustainable refrigeration design.

This study presents an integrated experimental and analytical investigation of the electromagnetic interference (EMI) shielding effectiveness (SE_T) of carbon black (CB)-reinforced epoxy composites. Composites were fabricated using a simple hand lay-up technique with CB filler contents ranging from 4 wt.% to 40 wt.%. SE_T was evaluated in the X-band frequency range (8–12 GHz) using a calibrated Vector Network Analyzer (VNA), relevant to radar, satellite, and wireless communication applications. An analytical model based on classical electromagnetic wave theory was developed to predict total shielding by incorporating reflection, absorption, and multiple internal reflections. Results revealed that absorption dominated the overall shielding response, contributing more than 80–85% of the total attenuation, confirming the material’s suitability for high-frequency EMI suppression. The model showed strong agreement with experimental results, with a mean absolute deviation of 10.16 dB, confirming its validity for preliminary design assessments. Increasing CB content significantly enhanced shielding performance, achieving a maximum SET of 47.48 dB at 25 wt.% representing nearly a 40% improvement relative to low-loading composites. HFSS field simulations further verified strong electromagnetic attenuation and absorption-driven energy dissipation within the composite structure. Minor deviations between model and experiment underscored the importance of uniform filler dispersion. Overall, the findings demonstrate that CB/epoxy composites offer a lightweight, cost-effective, and efficient alternative to traditional metallic EMI shields, providing a rare multiscale correlation across experimental, analytical, and numerical domains.

Miscibility gap alloys (MGAs) are promising candidates for high‑temperature thermal energy storage owing to their high latent heat and intrinsic phase separation. In this study, the liquid–liquid phase separation and subsequent solidification of Fe–Cu alloys were experimentally investigated using an aerodynamic levitator in a reducing atmosphere to suppress oxidation. In situ observations using a high-speed camera revealed that Fe‑rich liquid domains separated first from the undercooled homogeneous liquid, followed by the formation of Cu‑rich liquid domains. These observations are consistent with the asymmetry of the Gibbs free energy of mixing in liquid Fe–Cu alloys. The energy densities of these alloys exceeded the upper range of IRENA’s 2050 target (50–85 kWh m⁻³) for high-temperature latent-heat storage at Cu concentrations above 40 at. % (Fe60Cu40 and higher), indicating the potential of Fe–Cu alloys as high‑temperature latent heat storage materials. Our results provide insights into the role of microstructural control and, together with favorable thermal properties, offer a promising strategy for the design of MGA‑based thermal energy storage materials produced by casting.

This study examines the impact of post-weld heat treatment (PWHT) on TIG-welded Inconel 625 alloy. Seven TIG welding passes under pure argon shielding gas were utilized to join 10 mm-thick plates prepared with V-groove edge machining. Welded plates were subsequently sectioned into ASTM E8/E8M-compliant dog bone and disc specimens for mechanical testing. The PWHT involved solution annealing at 1060 °C for 2 h followed by rapid quenching, controlled furnace cooling, and a sub-critical temperature soak at 600–800 °C. Mechanical properties were evaluated through tensile testing, pin-on-disc wear tests, and Vickers microhardness measurements. Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDX) analyses of the base and fusion zones revealed dissolution of detrimental Laves and δ phases, a homogenized γ-matrix structure, and restored elemental uniformity. However, previous studies have not clearly connected these microstructural changes to the corresponding mechanical and tribological behavior across different weld zones. Heat-treated samples exhibited consistent hardness, maintained tensile strength, improved ductility, and a significant reduction (15%) in friction coefficient. These enhancements confirm the suitability of optimized thermal cycles for restoring solid-solution strengthening and dimensional stability, making the alloy particularly suitable for demanding aerospace and power generation applications exposed to high temperatures and corrosive environments.

This work presents a transfer learning approach for the forward design of composite unit cells of metasurfaces and frequency-selective surfaces (FSS). As a specific application, we target reconfigurable intelligent surfaces (RIS) for wireless communication. We demonstrate that forward models for dual-dipole unit cells can be trained using significantly fewer data by reusing pre-trained models of simpler, single-dipole structures. Our architecture reduces the required training data by up to a factor of 25 while maintaining a mean squared error (MSE) on the order of (10^{-2}). After establishing the forward model for the dual-dipole RIS, we use it in an inverse design framework to synthesize a composite 2-bit RIS unit cell operating at 26.5 GHz. The resulting RIS provides phase modulation in a 270(^circ) range by tuning the reverse bias voltage of integrated varactor diodes. Numerical simulations confirm the validity of the proposed approach, establishing transfer learning as a data-efficient and practical method for the design of composite unit cell structures.