Mobin Vandadi

This study investigates the indentation size effect (ISE), strain rate sensitivity (SRS) and incipient plasticity in CrCoNi medium-entropy alloys (MEAs) through a combination of nanoindentation experiments and molecular dynamics (MD) simulations. Microstructural characterization reveals grain refinement and twin formation dependent on processing conditions, with significant effects on mechanical response. Nanoindentation results confirm classic ISE behaviour at the microscale, but show pronounced deviations at nanoscale depths, accompanied by discrete pop-in events indicative of homogeneous dislocation nucleation. An SRS of m=0.083 and an activation volume of 40–60 b3 suggest that thermally activated dislocation glide is governed by Peierls friction rather than forest hardening. MD simulations incorporating realistic short-range order (SRO) demonstrate reduced dislocation activity and elevated critical stresses compared to randomly distributed atomic configurations. The presence of SRO modulates deformation mechanisms, suppresses phase transformation and enhances twinning-dominated plasticity. These findings highlight the synergistic role of atomic-scale chemical ordering and geometric confinement in controlling plasticity and strengthen the case for SRO-informed design strategies in next-generation high-performance alloys.

Reinforced concrete remains integral to modern infrastructure, yet traditional designs, relying on longitudinal reinforcing bars and stirrups, face limitations in adaptability and performance optimization. This study explores the integration of auxetic structures with negative Poisson ratios (NPRs) as reinforcement for concrete, leveraging advances in additive manufacturing to achieve enhanced mechanical properties. Three auxetic geometries, brick‐and‐mortar, bowtie, and tubular, are fabricated using aluminum, stainless steel, and polylactic acid (PLA) and are evaluated experimentally and numerically. Stainless steel tubular structures achieve a record compressive strength of 233 MPa, exceeding high‐performance fiber‐reinforced concrete (HPFRC) at similar reinforcement volumes. In particular, auxetic aluminum tubular reinforcements demonstrate a specific compressive strength of 149 kJ g ⁻¹ , equivalent to steel fiber reinforced concrete. Bowtie geometries improve toughness by redistributing stress, and tubular structures exhibit superior energy absorption and load redistribution. Finite element simulations reveal stress concentration mitigation and delay crack propagation, corroborating the experimental results. These findings highlight the significant impact of reinforcement geometry on structural performance and demonstrate that auxetic reinforcements can outperform conventional designs in strength, stiffness, and energy dissipation. This work establishes auxetic designs as a viable and promising strategy for next‐generation reinforced concrete systems aimed at improving resilience and mechanical efficiency.

This study explored a sustainable method for depositing carbon-based coatings on Ni-Invar and Ti-6Al-4V metallic substrates using a pack carburization process with cyanide-rich Manihot esculenta (cassava) leaves as the carbon source. Comprehensive experimental and computational analyses were performed to investigate the composition, structure, and tribological performance of the coatings. Characterization using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electron microscopy (SEM), and lateral force microscopy (LFM) revealed that the Ni-Invar substrate developed turbostratic multilayer graphene coatings with minimal carbide formation, achieving ultralow coefficient of friction (COF) values of 0.08 (macroscale) and 0.0033 (nanoscale). In contrast, Ti-6Al-4V substrates formed coatings rich in titanium carbide and metal carbonates with more disordered carbon structures, resulting in higher COF values of 0.1 and 0.0147, respectively. Monte Carlo simulations illustrated an island growth mechanism on Ni-Invar driven by dominant carbon-carbon interactions, while Ti-6Al-4V exhibited uniform layer growth due to stronger carbon-substrate affinity. Density Functional Theory (DFT) calculations provided further insight, showing that Ti had a strong affinity for graphene, with a binding energy of -1.1440 × 10³ eV, whereas Ni and Fe exhibited stronger self-affinity (-1.6250 × 10³ and -1.7190 × 10³ eV, respectively), favoring metal-metal bonding over carbon-metal bonding. These integrated experimental and numerical analyses offer detailed insights into carbon coating structures and their growth mechanisms. The results underscore the critical role of substrate chemistry in determining coating morphology and tribological behavior, highlighting Ni-Invar as a promising candidate for achieving superlubricity through carbon-based surface engineering.

Understanding and controlling the diffusion of ions and chemicals within the secondary plant cell walls are pivotal in various applications of biomasses. Recent studies have shown that inorganic ion diffusion through secondary cell walls is controlled by a moisture-induced glass transition in amorphous polysaccharides, including amorphous cellulose and hemicelluloses. Understanding the diffusion of ions in these structures has been the subject of numerous recent experiments; however, a deep understanding of the underlying mechanisms of interactions between ion atoms and water/hemicellulose molecules is still lacking. This study uses molecular dynamics simulations to elucidate the diffusion mechanisms of potassium and chloride ions in the cell walls under varying moisture content. The results reveal that a higher moisture content leads to the formation of solvent layers around the ions and reduces the charge interaction between the functional groups of wood polymers and ions. Hence, a higher moisture content results in an improved diffusion rate of ions within the domain. The simulation results also show that higher moisture content lowers the glass transition temperature, promoting diffusion of ions in the system. In contrast, increases in the ion concentration increase the glass transition temperature of the system and degrade the diffusion of ions in the system.