This study investigates the dual solution existence and the associated temporal stability of magnetohydrodynamic hybrid nanofluid (HNF) flow over a bidirectional shrinking sheet. The working fluid consists of an Al₂O₃–Cu/water HNF subjected to suction, magnetic field effects, and porous medium resistance. The reduced coupled ordinary differential governing equations are solved using the Galerkin weighted residual method. A temporal stability analysis based on eigenvalue formulation is conducted to distinguish physically realizable solutions from unstable ones. The effects of emerging parameters on the skin friction coefficients and the Nusselt number are examined with the concentration given on magnetic effect. The results reveal the dual solution existence in a critical range of suction values, beyond which no solutions exist, indicating boundary-layer separation. Stability analysis confirms that only the upper-branch solution is stable and physically admissible. Enhanced magnetic field strength, delay boundary-layer separation and improve thermal performance. The present results show excellent agreement with previously reported limiting cases, demonstrating the accuracy and robustness of the proposed method.
The impact of periodic mechanical vibration on the phase transitional property of VO 2 based thermal sensing thin film synthesized on AT-cut quartz has been investigated in this paper. VO 2 were found to go through phase transition due to effect of heat, and display reduction of film resistivity and transmitted infrared power at a specific transition temperature, typically around 60-70°C. But sometimes the transmitted infrared power has been observed to decrease at a significantly lower temperature compared to the similar phenomenon for resistivity reduction. In order to correctly validate the transition temperature, the derivative of the transmitted optical power signal is measured, and it has been found that this measurement is experimentally possible when the VO 2 film is subjected to a moderate to high frequency periodic mechanical vibration. It has also been observed that the variation of the mechanical vibration frequency has a direct effect on the derivative signal, which indicates the sharpness of the phase transition and magnitude of change of the transmitted infrared power depending on the width of the extrema lobe of the derivative.
This work focuses on the modeling and prediction of the optical absorption coefficient in GaAs 2D nanostructure subjected to hydrostatic pressure. The database is generated from numerical calculations describing the optical absorption of exciton confined in GaAs 2D nanostructure. The obtained data are exploited to develop predictive models based on machine learning such as Decision Tree and Gradient Boosting techniques, in order to establish an accurate relationship between the incident photon energies and the optical absorption coefficient. The quality of the proposed approaches is examined using standard statistical metrics, considering the mean absolute, squared errors, and root mean squared error, as well as the coefficient of determination. The obtained results demonstrate an excellent agreement between the predicted and numerical values, with very low errors and strong generalization capability. these approaches therefore represent an efficient alternative to conventional numerical methods for the rapid prediction of the optical properties of discoidal quantum dots and offers promising perspectives for the optimization of optoelectronic devices.
The limbs of compound bows are subjected to highly complex and intensive mechanical loads throughout the entire shooting cycle. Due to the operation of the cam system, forces acting on the limbs may exceed the applied draw force by several times, particularly near maximum draw. Extreme dynamic loads can be generated during dry firing, which may result in sudden and often fiber-directional failure of composite limbs. Local stress levels are further increased by stress concentration effects arising from geometric and material inhomogeneities. In this study, the forces acting on the cam system and the bow limbs were determined through preliminary analytical calculations. The Euler–Bernoulli beam theory was applied to estimate limb deflection analytically. The analysis was refined using the Timoshenko beam model to account for shear deformation and cross-sectional rotation. Cross-sectional second moments of area and relevant material properties were determined to ensure accurate results. The calculated deflections, although small in magnitude, were shown to have a significant influence on the stress state of the limbs. Based on the numerical results, it was concluded that compound bow limbs operate close to, or in some cases beyond, their material limit under severe loading conditions.
This study is part of my doctoral research and investigates the sustainable recycling of aluminum waste through the development of aluminum-containing polymer hybrid materials. The study aims to understand how the type, structure, and distribution of these reinforcements influence the mechanical strength and overall behavior of the composites. The increasing demand for lightweight, high-performance, and environmentally friendly materials in various industries - such as automotive, construction, and packaging - has driven the exploration of metal-polymer composites. In this context, aluminum, due to its low density, corrosion resistance, and recyclability, presents a promising candidate for reinforcement in polymer matrices. Special attention was given to how the particle size and distribution affect the elasticity, flexibility, and structural integrity of a selected PU-foam. The study aims to contribute to the broader field of circular materials engineering by offering insights into how industrial aluminum waste can be effectively reused in high-value polymer systems.
Thermodynamic behavior and phase stability of binary and ternary alloy systems containing Fe, Al, and Ni are systematically investigated. Formation enthalpies (ΔH) of solid solutions and intermetallic compounds in the Fe–Al, Fe–Ni, Al–Ni, and Fe–Al–Ni systems were calculated using Miedema’s semi-empirical model implemented in the Materials Analysis Applying Thermodynamics (MAAT) software. Overall, the results indicate that solid solutions in the binary systems are thermally stable, and when the concentration of alloying elements is increased, solids solutions demonstrate a low change in thermal behavior while compounds exhibit more complex thermodynamic behavior and require higher energy for formation. The ternary Fe–Al–Ni system also exhibits exothermic and endothermic reactions according to the molar ratio of elements. The electronic and vibrational properties of the Fe₈₀Al₁₅Ni₅ alloys are theoretically simulated using DFT and TD-DFT for UV–Visible calculations, and the spectroscopic features are interpreted in correlation with the thermodynamic stability predicted by Miedema’s semi-empirical model. No experimental spectroscopic measurements were performed in this study.
Conventional crosslinking agents for Epoxidized Natural Rubber (ENR) are typically synthesized chemicals that pose toxic threats to living organisms and the environment. Glycerol, a major byproduct from waste palm oil biodiesel production, remains largely underutilized. This study aims to identify a novel, environmental-friendly crosslinking agent for Epoxidized Natural Rubber (ENR). While waste palm oil is commonly utilized for biodiesel production, its major byproduct, glycerol, remains largely underutilized. Consequently, this research investigates the potential of glycerol to serve as a crosslinking agent for ENR. Experimental results confirm that a crosslinking reaction successfully occurs between ENR and glycerol. This is substantiated by Fourier Transform Infrared Spectroscopy (FTIR) analysis, which reveals crosslinking via the opening of the ENR oxirane rings. Significant peaks observed at 1032 cm⁻¹, 3340 cm⁻¹, and 2900 cm⁻¹ correspond to C-O-C, O-H, and C-H bonds, respectively. Furthermore, results from gel fraction analysis and Moving Die Rheometer (MDR) testing corroborate the crosslinking interaction between ENR and glycerol, indicating that crosslinking density increases with higher glycerol loading. Mechanical property testing further demonstrates that the tensile strength of glycerol-crosslinked ENR improves in correlation with the increased degree of crosslinking.
Microelectromechanical systems (MEMS) are widely used in flexible and stretchable applications employing polymeric substrates such as PDMS, PET, and Polyimide. In this study, the mechanical behavior of PVDF thin films on PDMS substrates is numerically investigated under uniaxial tensile loading using Finite Element Analysis (FEA). The developed FEA model is first validated using established experimental results before being applied to the main specimen. Mesh-independent analyses are performed for PVDF film thicknesses of 50, 75, 100, and 125 µm with a 1 mm thick PDMS substrate under different elastic modulus conditions. Results show that thicker PVDF films require higher elastic strain to reach yielding. Furthermore, interfacial shear stresses are maximum at the laminate ends and decrease toward the center. These findings provide useful insights into the mechanical behavior and failure characteristics of PVDF–PDMS laminates for flexible MEMS applications.
Acrylonitrile–butadiene–styrene (ABS) is widely used for structural housings, but its stiffness and strength can be limiting. Here, a particulate-reinforced ABS composite was fabricated by casting using polymer-derived ceramic (PDC) powder as reinforcement. A liquid polysilazane (PSZ) precursor was cured, milled to ~1–10 μm powder, and pyrolyzed at 700–1200 °C to obtain SiCNO-based ceramic filler. ABS pellets and SiCNO powders were melt-mixed at 250 °C and cast into ASTM-standard specimens for tensile (ASTM D638), compression (ASTM D695), and flexural (ASTM D790) tests. For tensile specimens with 10 wt.% filler, tensile strength increased from 23.89 MPa (neat ABS) to 36.74 MPa at 1100 °C pyrolysis, while Young’s modulus increased from 1.71 GPa to 2.61 GPa. At higher pyrolysis temperature (1200 °C), tensile performance degraded, consistent with increased ceramic crystallization and/or interfacial weakening. Compression tests (5–30 wt.% filler) showed monotonic increases in modulus with filler loading, but resilience dropped sharply between 10–20 wt.%, indicating a brittle–ductile transition window. Flexural strength improvements were modest; the best case was 10 wt.% filler pyrolyzed at 900 °C, giving 55.05 MPa vs. 51.35 MPa for neat ABS. SEM fracture surfaces revealed a transition from ductile fibrillation in neat ABS to layered fracture with embedded ~1–5 μm ceramic particles in the composite. These results demonstrate that castable ABS/PDC composites can deliver substantial tensile stiffening and strengthening when carefully selected pyrolysis temperature and filler fraction are used.
As the climate challenges worsen and the need to reduce carbon emissions becomes more urgent, timber is undergoing a remarkable revival as a sustainable material, driven by shifting societal attitudes. However, this renewed reliance on wood also raises important questions about how to reforest in ways that are ecologically responsible. With global demand for timber projected to rise, the expansion of managed plantations has become inevitable, positioning agroforestry at the centre of both commercial and scientific attention.Paulownia, renowned as the fastest-growing tree species globally, plays a pivotal role in this transition. Its dense foliage enables unparalleled CO 2 sequestration, earning it the moniker of a "climate tree". While native to China, it is now cultivated across the globe, though not without controversy - its invasive tendencies have spurred demand for domesticated strains with reduced ecological impact. Crucially, such cultivars must retain robust mechanical performance, including vibration damping properties, a key determinant of acoustic suitability.This research evaluated strain-dependent damping characteristics through analysis of the logarithmic decrement in free-decaying flexural vibrations. Specimens included a conventional Paulownia variant (cultivated in Georgia, Italy, and Spain) alongside a novel German-cultivated strain - notably the first such harvest recorded in the country.Given the microstructure’s reliance on local soil nutrients and its critical role in damping behaviour, the study quantified the resulting variability in strain response. The results identified distinct regimes within the damping curves: a strain-independent plateau followed by a strain-dependent area. Calculated bending moduli, derived from resonant frequencies, ranged from 1024 N/mm² to 5873 N/mm². This wide dispersion is attributed to heterogeneity in the fibril alignment - a factor that also influences energy dissipation.
Additive manufacturing techniques such as Fused Deposition Modelling (FDM) and Stereolithography (SLA) enable the production of smart composites with complex geometries. In these materials, the bonding strength between ferromagnetic shape memory alloy (FSMA) microparticles and the polymer matrix is critical for efficient strain transfer. Matrix stiffness also plays a key role: it must be high enough to transmit stress, yet soft enough to allow magnetic twin boundary motion without exceeding the blocking stress. This study analyses the temperature-dependent shear modulus of composites containing Ni 45 Mn 36.7 In 13.3 Co 5 microparticles embedded in polycaprolactone (PCL) and photocurable bisphenol A-glycidyl methacrylate (Bis-GMA) matrices using dynamic mechanical analysis (DMA). The experimental results were fitted using modified Rule of Mixtures (ROM) and Halpin-Tsai (HT) models. The elastic energy transfer was also calculated to evaluate the strain transfer capability from the microparticles to the matrix during the martensitic transformation. These results underscore the substantial impact of matrix properties on mechanical response and provide modelling tools for the design of FSMA-based actuators, sensors, energy generation devices based on the harvesting of vibrational energy and damping systems.
High voltage bare conductor surfaces were tested by spray method of IEC TS 63073. Theconductors have different surface properties: a standard conductor with untreated surface, a paintedone, a sand-blasted surface and three old conductors after long service life was tested. The oldconductors operate in significantly different areas of Hungary which makes the surfacecontamination and the rate of atmospheric corrosion different. For comparable tests specializedequipment was developed, which makes the spray test in the same way and with same parameters inall tests. The equipment contains digital cameras to make photos from the conductor’s surfacewhich can be compared to the chart of technical specification. The tests were conducted usingdifferent water qualities. The surface treated and old conductors show good hydrophilicity in alltests while the untreated and painted conductors wettability was wrong. The related technicalspecification designates classes where HC7 means the water film on the surface, while HC1 meanslarge drops of water on the surface. The surface treatment makes HC7 class surface of theconductors. The contamination and atmospheric corrosion also make HC6-HC7 class surface. Theas-manufactured or painted surface were evaluated as HC2-HC4. Acidic additions make thewettability class larger.
Three-dimensional (3D) printing enables the fabrication of smart composite materials by embedding ferromagnetic shape memory alloy (FSMA) microparticles into a ductile polymer matrix, thus overcoming the intrinsic brittleness of most FSMA materials. In this work, the effects of thermal treatments near the melting temperature upon the damping mechanism in the low-temperature region are studied both in the 3D-printed PCL samples and in the 3D-printed (PCL/Ni 45 Mn 36.7 In 13.3 Co 5 ) composites, focusing on the interactions processes between the microparticles and the polymer chains. 3D-printed PCL and 3D-printed composites were obtained by means Fused Deposition Modelling (FDM) and were studied by mechanical spectroscopy (MS). The deconvolution of the damping spectra revealed the appearance of two relaxation mechanisms in 3D-printed PCL samples and three relaxation mechanisms in 3D-printed composites.
Applications of 3D printed metallic alloy materials like Ti6Al4V or Ti64 offer significant advantages for certain applications and incorporates complex geometries like lattice structures achieving material optimization. This study analyzes the thermal processing of i-SLS 3D-printed Ti6Al4V-PA12 composites with varying lattice structures (Solid, Gyroid, and Sinusoid). This paper analyzes the chemical barriers and morphological indicators of the sintered composites using SEM-EDX and Optical Microscopy, Pearson Correlation is calculated for statistical analysis. Results among the varying sintering profiles showed that sintering at 1250 °C (Intermediate Temperature Profile) has progress on initial Ti64 contact. Outcomes are dependent with the high surface-area-to volume ratio of the geometric shapes, leading to higher residual carbon decomposition, but prone to surface oxidation. Oxidation and carbon residues are factors interfering with the necking between Ti6Al4V particles. Thus, high temperature treatment for Ti6Al4V sintering under high purity argon atmosphere showed a lack of densification and failed to reach a sintered state.
This study aims to predict the effective Young’s modulus of Ti6Al4V lattice structures based on strut thickness and strut length using regression-based machine learning methods. Four predictive models, Linear Regression (LR), Polynomial Regression (PR), Support Vector Regression (SVR), and Gaussian Process Regression (GPR), were developed and compared in MATLAB using 25 sets of simulation data. Among these models, PR and GPR demonstrated the most promising performance in the actual versus predicted comparison, achieving the lowest root mean square error (RMSE) and the highest coefficient of determination (R²) for the given data size. Optimal training size for all models was around 36% to 52% of the total data set, which has a critical significance for data efficiency. To evaluate data sufficiency and model reliability, 5-fold Cross Validation was performed, and learning curves were generated to analyze how prediction error varies with the number of training samples. In the Learning curve, the PR model achieved its lowest RMSE, followed by GPR, which had the second best RMSE at its optimal training size. LR performed well for comparatively linear data, whereas SVR showed great variations and many shortcomings with the limited dataset.
Open-die forging is an incremental bulk metal forming process for producing large, safety-relevant components such as turbine and generator shafts. Besides achieving the target geometry, the process improves mechanical properties through grain refinement and the elimination of casting-related defects. With the increasing use of high-alloy steels, precise process control is required to prevent surface and internal cracking caused by material damage. However, predictive models for damage evolution under the thermo-mechanical conditions of open-die forging remain limited, particularly with respect to high-temperature recrystallization and the incremental process character with inherent pause times. In this work, a recrystallization-sensitive damage model was developed and validated for open-die forging. The parameters of the Lemaitre damage formulation were determined for the cold work tool steel D2 (1.2379, X155CrVMo12-1) using hot tensile tests over the relevant forging temperature range. Dynamic recrystallization kinetics were characterized by hot compression tests and described using an Avrami-type JMAK formulation, while static recrystallization behavior was analyzed by stress relaxation experiments and also modeled with JMAK kinetics. These results enabled the quantification of recrystallized fractions as functions of strain, temperature, strain rate, and dwell time. To link microstructural evolution with damage development, tailored recrystallization states were generated in dilatometer experiments and examined metallographically with respect to void formation and healing. The extended model was implemented in a finite element framework and validated through open-die forging experiments on demonstrator geometries, showing its capability to predict damage initiation under industrially relevant conditions.
This study investigates the electric dipole effect at Al₂O₃/SiO₂ interfaces deposited by Atomic Layer Deposition (ALD) on 4H-silicon carbide (SiC) substrates for threshold voltage (V T ) modulation. By incorporating an ultrathin 3nm Al₂O₃ layer onto ALD-deposited 30nm SiO₂, they created an electric dipole that produces a 0.65±0.15V positive shift in threshold voltage after N₂O post-deposition annealing. The dipole-induced voltage shift was validated through both MOS capacitor measurements and lateral MOSFET characterization. Importantly, the threshold voltage enhancement occurred without degradation in field-effect mobility, demonstrating that the dipole effect does not introduce additional scattering centers. This technique offers an effective approach for threshold voltage tuning in alternative semiconductor devices where thermal SiO₂ growth is not feasible, addressing critical challenges in SiC power electronics that require high threshold voltages (>3V) for reliable operation.
Liquid Composite Molding (LCM) processes, used for producing high-quality, complex composite parts, rely on the uniform infiltration of liquid resin into fibrous fabrics. These fabrics possess a dual-scale structure: highly porous inter-tow spaces surrounding denser fiber tows. The resulting disparity in permeability and flow rates is a primary cause of defect formation, such as voids. To minimize these defects, accurate simulation, incorporating the critical influence of capillary pressure on resin infiltration within the fiber tows, is essential. This work presents a robust numerical model developed to simulate the two-phase resin flow and impregnation dynamics within a digitized, real plain-weave E-glass reinforcement obtained via X-ray micro-computed tomography (CT). The simulation utilizes the open-source multiscale multiphase solver, hybridPorousInterFoam , which employs a Darcy-Brinkman approach, transitioning between Darcy's law in porous regions and Navier-Stokes in free space. A key methodological enhancement involved modifying the advection algorithm using the isoAdvector scheme to mitigate numerical instabilities caused by the high viscosity ratio between the resin and air. Capillary effects at the mesoscale are incorporated through multiscale parameters, specifically the drag and surface tension forces. The key findings demonstrate that the modified solver successfully handles the fluid-fluid interface advection for high viscosity ratios. A parametric study highlighted the significant effect of capillary pressure on multiphase flow within the dual-scale porous media. The numerical results for flow front advancement showed very good agreement when compared against dedicated experimental validation data, confirming the model's high predictive accuracy and its potential for optimizing LCM injection conditions.
