International Journal of Mechanical and Materials Engineering最新文献

Nitrogenated amorphous C (a-C:N) coatings with an intermediate sp³ C fraction of 30%–55% and N content of 0–5 at.% were deposited on single-crystal silicon wafer substrates via intermittent filtered cathode vacuum arc deposition. Some of the coated specimens were annealed at 300 and 600 °C for 4 h in a 5-Pa vacuum. The morphologies, microstructures, and the bonding structure of the specimens were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy, and micro-Raman spectroscopy. The mechanical characteristics of the coatings, including the residual stress and hardness, were measured. Of the doped N content in the coatings, 60%–70% formed a pyridine- and pyrrole-like ring configuration of sp² C = N bonds. As the N content was increased, the fraction of pyridine-like bonds decreased, and the pyrrole-like configuration gradually became dominant. Compared to the N-free coatings, the thermally stable temperature of the nitrogenated coatings decreased to approximately 300 °C, and their surface roughness increased after annealing at 600 °C. The increase in the ratio of pyridine-like to pyrrole-like bonds (R_pyd-pyr) in the coatings increased the number of voids and pinholes in the surface layer. However, the top surface of the a-C:N coating with 3.4 at.% N annealed at 600 °C remained smooth almost without voids, which could be ascribed to its suitable R_pyd-pyr and high sp² C = C fraction.

Graphical Abstract

In this paper the Poly (aniline-co–o-methoxy aniline) (PAOMA) copolymer coatings, as well polyaniline (PANI) and poly (o-methoxy aniline) (POMA) individual polymer coatings, were synthesized on copper (Cu) substrates from an aqueous solution of sodium salicylate. A series of PAOMA copolymer coatings were deposited by electrochemical copolymerization of aniline (ANI) with o-methoxy aniline (OMA) using different monomer feed ratios under cyclic voltammetric conditions. A comparative analysis of the cyclic voltammograms (CVs) recorded during polymerization of aniline, o-methoxy aniline, and their copolymer clearly reveals the effect of the monomer ratio on the formation of the copolymer, polymer, and the quality of the coatings. All the resulting coatings were characterized by cyclic voltammetry, UV–visible absorption spectroscopy, scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The synthesis of the copolymer, using a mixture of monomers in the aqueous sodium salicylate solution, was confirmed through a comparative study of the results obtained from the polymerizations, as well with the characterizations of the individual monomers, aniline and o-methoxy aniline. Corrosion resistant characteristics of resulting coatings were evaluated by potentiodynamic polarization measurement in aqueous solution of 3% NaCl solution. It extracts the values of corrosion potential (E_corr), corrosion rate (CR), porosity (P) and protection efficiency (%PE). The analysis of these results imply that the copolymer PAMOA-5 coating provides effective protection to Cu against corrosion in aqueous 3% NaCl as compared to that of the other copolymers and also than the corresponding homopolymers. For PAOMA-5 coated Cu it was found that the remarkable positive shift of 344 mV in E_corr, substantial reduction in corrosion rate 875 times lower than that observed for bare Cu, lowest value of porosity (0.44 × 10^–6) and highest protection efficiency of 99.9%.

The CuCo₂O₄ and CuCo₂O₄/MWCNT nanocomposites were synthesized using hydrothermal techniques as an electrode material for supercapacitor applications. Structural characterization, including XRD, SEM, and EDX, confirmed the successful fabrication of nanocomposites. Electrochemical analysis revealed that CuCo₂O₄/MWCNTs exhibit excellent oxygen (OER) and hydrogen (HER) evolution catalytic activity, with enhanced cyclic stability, high-rate capability, and better specific capacitance compared to pure CuCo₂O₄ electrodes. The synergistic interaction between CuCo₂O₄ and MWCNTs significantly improves electrochemical performance, highlighting the potential of these nanocomposites as an electrode material for energy storage and electrocatalytic applications.

Some physical properties of Sn₅Ge₁₀Se_85-xPb_x; (x = 2.5, 5, 10, 15 17.5 and 20 at. %) chalcogenide glasses, namely average coordination number (CN), deviation of stoichiometry (r), floppy modes (f), cross-linking density (X), average number of constraints (Ncon), lone pair electrons (Lp), overall mean bond energy ( < E˃), and average heat of atomization (Hs), are depicted. The experimental and theoretical values of the optical band gap E_op for different contents of Pb were found to be very close to each other. The dispersion properties, such as complex dielectric function (widetilde{varepsilon }), optical conductivity ({sigma }_{op}), single oscillator E_o, and dispersion energies E_d, are investigated. On the other hand, electrical conductivity is studied. Our results are based on the Tauc equation, Wemple and Di-Domenico (WDD) model, Pankove method, Tichy and Ticha relationship, and Miller’s rule. The values of the first-order χ⁽¹⁾ and third-order χ⁽³⁾ of optical susceptibility and the nonlinear refractive index (n₂) were found to increase with the increase of Pb content, which has a maximum value, hence decreasing thereafter with the increase of the latter.

The utilization of rubber and fibrous materials in the fabrication of sports equipment constitutes the foundation of this study. The judicious integration of materials science with the materials employed in sports equipment manufacturing is instrumental in propelling the field forward and enhancing athletic performance. A theoretical analysis of existing graphene technology and its applications to rubber and fibrous materials can provide a foundation for exploring the potential of graphene technology in sports equipment. This analysis can facilitate an organic integration of the materials (graphene) field and the sports field at the theoretical level, thereby promoting the application of graphene technology in the sports field. The present study aims to modify the substrate with graphene functional materials in rubber and fibrous materials to achieve the objective of enhancing the performance of sports equipment and improving athletes' performance in the manufacture of sports equipment.

Polytetrafluoroethylene (PTFE) is widely utilized in engineering applications due to its low friction, self-lubricating properties and chemical inertness. However, its tribological performance under variable loading conditions has been insufficiently studied. This research investigates the influence of variable loading on the wear and friction characteristics of PTFE under dry sliding conditions, particularly within the context of rolling and sliding contact bearings. A modified pin-on-disk tribometer equipped with a variable loading assembly was used to simulate fluctuating load scenarios commonly encountered in bearing applications. The results show that PTFE experiences wear rates that fall between those observed under mean and maximum constant loading conditions, with a notable increase in wear and specific wear rate compared to mean static loads. However, no similar trend was observed for the friction coefficient. These results provide insightful information on the optimization of PTFE performance in dynamic environments including bearings, biomedical implants, and mechanical seals.

Due to current challenges related to global warming and the ecological impact of materials, the industry is considering natural-fibre-reinforced thermoplastic composites for their low weight and sustainability. However, to be considered for structural applications, their mechanical behaviour and damage mechanisms need to be fully understood. Regarding Flax-Polypropylene (Flax-PP) composites, damage mechanisms are successfully identified in the literature; however, their initiation and propagation up to final failure are not well described yet. The present study focuses on a spread-tow woven Flax-PP composite and aims to investigate the damage mechanisms and their evolution in two configurations — namely with fibres of the top ply being either parallel or perpendicular to the loading direction. The damage mechanisms are first identified via SEM analysis of fracture surfaces after standard tensile testing. Then, for both configurations, the evolution of damage mechanisms is studied by in situ SEM micro-tensile testing. In both cases, crack initiation at fibre tips and fibre debonding is the primary failure mechanisms, leading to subsequent fibre pullout and preferred crack path. Results show that the crack path is more in the case of top ply fibres parallel to the loading direction than in the case of transversal fibres. The greater occurrence of fibre pullout compared to fibre breakage is attributed to the weak interfacial strength between the fibres and the matrix, which is typical for natural fibre composites. The present study used in situ investigation to propose a detailed sequence of damage evolution related to tensile loading.

This study investigates the development and characterization of a novel multifunctional honeycomb core composite comprising multi-walled carbon nanotube (MWCNT)-reinforced Hemp-Glass blended epoxy for advanced structural applications. The research employs dynamic mechanical analysis (DMA), analytical modeling, FEM using higher-order shear deformation theory, and experimental validation to evaluate material properties and structural performance. Dynamic mechanical analysis demonstrated that 2% MWCNT specimens exhibited superior extension modulus at 40–50 °C, while 1% MWCNT specimens performed better above 65 °C. The transverse shear properties of MWCNT-filled specimens (0%, 1%, and 2% weight fractions) were systematically characterized, revealing storage shear moduli ranging from 105–135 MPa (Gxz direction) to 100-–125 MPa (Gyz direction). Finite element modeling of GFRP-skinned sandwich cylindrical shells revealed that the natural frequencies increased with MWCNT weight fraction due to enhanced transverse shear stiffness, while decreased shell curvature also improved frequencies through passive stiffness contributions. Temperature effects showed natural frequencies declining above 60 °C due to viscoelastic behavior, though MWCNT incorporation significantly preserved thermal stability by maintaining epoxy resin viscosity. Modal damping characteristics increased above 60 °C, reflecting enhanced viscoelastic behavior with MWCNT reinforcement. The critical buckling load analysis demonstrated progressive improvement with increasing MWCNT content, with 2% MWCNT specimens showing maximum buckling resistance up to 60 °C. The study revealed significant differences in natural frequencies and modal loss factors between various shell curvatures and temperatures, particularly under clamped boundary conditions. The successful integration of sustainable hemp fibers with high-performance glass fibers and MWCNT reinforcement presents a promising pathway for environmentally conscious composite materials without compromising structural performance, offering designers flexible solutions for wind turbine components, aerospace structures, helicopter blades, automotive parts, and advanced sporting equipment.

The increasing demand for sustainable and eco-friendly materials has driven research into developing biocomposites as alternatives to conventional plastics. This study addresses the challenge of optimizing the properties of biocomposite panels made from high-density polyethylene (HDPE) and short flax straw fibers (FSF) at low content ratios. The aim of the study was to fabricate and characterize biocomposite panels to evaluate their potential for large-scale production. A comprehensive methodology was employed, including the use of Fourier transform infrared (FTIR), thermogravimetric and derivative thermal gravimetric (TGA-DTG), mechanical property testing, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), water contact angle measurements, ultrasonic testing, water absorption (WA) analysis, and chemical resistance evaluation. Remarkable results revealed that graft copolymerization occurred between HDPE and FSF, as confirmed by FTIR, while SEM indicated the successful incorporation of FSF into the HDPE matrix. The mechanical properties, including tensile strength, elastic modulus, and elongation, were significantly influenced by the presence of FSF. Thermal stability decreased slightly with the addition of FSF, and DSC analysis showed a minor shift in the melting point. Water contact angle values increased with higher FSF content, while XRD results indicated a reduction in HDPE intensity. Water absorption increased with higher FSF content, suggesting a trade-off between fiber content and hydrophobicity. The significance of this study lies in demonstrating that these biocomposite panels exhibit promising properties for large-scale production, offering a sustainable alternative to traditional composites in various industrial applications.