International Journal of Mechanical and Materials Engineering最新文献

This study explores how expanded thermoplastic polyurethane (ETPU) responds to temperature and compression at various temperatures. Dynamic mechanical thermal analysis (DMTA) was used to understand the temperature influence at small deformations. To investigate the deformation behavior at different compression stages we employed in-situ CT measurements and 3D strain mapping. Through quasi-static compression tests at temperatures from − 50 to 120 °C, we determined the influence of temperature on compression modulus, elastic stress, stress at 50% deformation, densification, and energy absorption. Remarkably, ETPU demonstrates robust recovery after compression, particularly within the − 50 to 60 °C temperature range. Subsequent compression tests show consistent or even slightly increased compression properties, such as a 10% increase in energy absorption for samples previously tested at − 40 °C, indicating that ETPU can withstand prior exposure to different temperatures.

To ascertain upon the ideal configuration of physico-mechanical qualities, efficient processing techniques, and network stability of the prepared bio-composite films in real-world applications, the polymeric materials shall be subjected to a careful manipulation. Such bio-composite films have outstanding combinations of biocompatibility and toxicity-associated safety qualities. Such research interventions will be beneficial for the packaging, pharmaceutical, and biomedical industries that wish to target and adopt them for commercial applications. In this article, three alternate organic acids, i.e., citric acid (CA), tartaric acid (TA), and malic acid (MA), are blended separately into polyvinyl alcohol (PVA)-starch (St)-glycerol (Gl) composite films and for the targeted purpose of enhanced crosslinking, plasticizing, and antibacterial capability of the polymer network. The organic acid-based bio-composite polymeric films were assessed in terms of swelling index (SI), in vitro degradation, tensile strength (TS), percentage elongation (%E), antibacterial activity, and cytotoxicity attributes. Among these, the MA-based PVA composite films outperformed the CA-based PVA composite film in terms of absorbency (SI 739.29%), mechanical strength (TS 4.88 MPa), and elasticity (%E 103.68%). Furthermore, following a 24-h incubation period, the MA-based films exhibited the highest proliferative effect of 215.59% for the HEK cells. In conclusion, the MA has been inferred to be the most relevant organic acid for the desired optimality of film composition, physical and biological properties, and cost.

On account of their unique shape memory effect (SME), pseudoelasticity, and biomedical applications, shape memory alloys (SMAs) have gained significant acceptance in the industrial trade and biomedical applications over the past few decades. Due to their affordable constituent parts and the availability of large-scale methods that are commonly employed for the manufacturing of stainless steels, Fe-based shape memory alloys offer benefits in commercial production, owing to their low cost compared to NiTi. The increasing insistence on stronger, lighter, and more functional materials paved the way for active materials. SMAs are a distinct grade of active materials. They exhibit attractive attributes like the potential to provide considerable recoverable strain while mechanical loading (superelasticity), shape recovery during heating (shape memory effect), and biocompatibility, which ultimately prove them to be one of the appropriate actuators for applications in the biomedical industry. This paper gives a review of the Martensitic transformation of some of the compositions of Fe-based SMAs, their potential to be used in civil structures as strengthening materials, their applications, and future research needs. This paper also focuses on the application of iron-based SMAs in different fields and the necessity to work on this SMA in the future since results show that Fe-based SMAs have shown good potential and can serve as an apt alternative to Ni-based shape memory alloys, which on the other hand has quite a lot of disadvantages, the key one being costly. Fe-based SMAs are comparatively lower in cost and have a greater scope to work with in the near future.

CuMn₂O₄ (CMO) thin films are produced using a simple hydrothermal method. The influence of reaction duration on the electrodes’ electrochemical performance is investigated. XRD data shows improved crystal structure after 24-h reaction time, with a crystallite size of 12.17 nm. Distinct vibrational peaks associated with Cu–O and Mn–O are observed in the ATR-FTIR spectra, corroborating the spinel formation after 24 h. XPS analysis shows a compositional shift over time, starting with copper hydroxide at 12 h, evolving into a mix of copper and manganese oxides, hydroxides, and oxyhydroxides by 18 h, and achieving the desired spinel composition by 24 h. Microscopic analysis reveals CMO is arranged as small sheet structures, with 4.95 ± 2.92 µm in length after 24-h reaction. The CMO_24h electrode displays a maximum specific capacitance of 1187.50 Fg⁻¹ at a scan rate of 1 mVs⁻¹ in 1 M Na₂SO₄ electrolyte. The electrochemical performance of the synthesized CMO electrodes reveals a high potential for energy storage applications.

Thin films reinforced with chitosan and cellulose nanocrystals (CNC) were produced using the casting process. In this study, the impact of plasticisers and sizing agents such as glycerol and polyvinyl alcohol (PVA) respectively on morphological, structural, thermal, and mechanical properties was investigated. The results showed the blends of CNC/PVA/glycerol gave better results when compared to films produced by blends of chitosan/PVA/glycerol films and chitosan/CNC/PVA/glycerol films. The UV spectroscopy showed 65% transmittance for chitosan/PVA/glycerol films, while the film of CNC/PVA/glycerol showed transmittance of 40%. The transmittance of chitosan/CNC/PVA/glycerol showed 75%. The films formed by the combination of CNC/PVA/glycerol showed better stress/strain properties than other films. The films of all combinations showed good thermal stability between the range of 350 and 450 °C. The morphological study using SEM revealed smooth texture for all the films. The study suggests that the films produced may be used for the food packaging applications due to its thermal stability and stress/strain properties.

The insulating oil serves the dual purpose of providing insulation and cooling within transformers. This investigation aims to explore the impact of various nanoparticles on the dielectric breakdown voltage (BDV) of dielectric oils. The study examines the effect of the concentration of magnetic nanoparticles on the dielectric breakdown voltage of insulating oils. Nanoparticles such as iron (II, III) oxide (Fe₃O₄), cobalt (II, III) oxide (CO₃O₄), and ferrous phosphide (Fe₃P) were utilized to create nanofluids with carrier mediums consisting of mineral oil and synthetic ester oil. BDV determination was conducted using a VDE and S–S electrode system according to IEC 60156 standards. Nanofluid were prepared using a two-step method, and their concentrations ranged from 0.01 g/L, 0.02 g/L, and 0.04 g/L in base oils. Twelve iterations were conducted for each prepared nanofluid, and breakdown voltage measurements were recorded. The results indicate a noteworthy enhancement in the breakdown voltage of nanofluids. The statistical analysis was performed on the dielectric property of nanofluid samples for better breakdown accuracy. The maximum enhancement at specific nanoparticle concentrations was shown by each nanofluid. The results show that under the S–S electrode configuration, the greatest overall enhancement was observed for Fe₃P in mineral oil, with an enhancement of 70.05%, and Fe₃O₄ in synthetic ester oil, with an enhancement of 46.29%.

Machine learning-driven automated replication micrographs analysis makes possible rapid and unbiased damage assessment of in-service steel components. Although micrographs captured by scanning electron microscopy (SEM) have been analyzed at depth using machine learning, there is no literature available on the technique being attempted on optical replication micrographs. This paper presents a machine-learning approach to segment and quantify carbide precipitates in thermally exposed HP40-Nb stainless-steel microstructures from batches of low-resolution optical images obtained by replication metallography. A dataset of nine micrographs was used to develop a random forest classification model to segment precipitates within the matrix (intragranular) and at grain boundaries (intergranular). The micrographs were preprocessed using background subtraction, denoising, and sharpening to improve quality. The method achieves high segmentation accuracy (91% intergranular, 97% intragranular) compared to human expert classification. Furthermore, segmented micrographs were quantified to obtain carbide size, shape, and density distribution. The correlations in the quantified data aligned with expected carbide evolution mechanisms. Results from this study are promising but necessitate validation of the method on a larger dataset representative of evolution of thermal degradation in steel, given that characterization of the evolution of microstructure components, such as precipitates, applies to broad applications across diverse alloy systems, particularly in extreme service.

As the global agenda turns more towards the so-called challenge of climate change and lowering carbon emissions, research into green, renewable energy sources becoming nowadays more and more popular. Offshore wind power, produced by FOWTs (i.e., Floating Offshore Wind Turbines), is one such substitute. It is a significant industrial part of the contemporary offshore wind energy industry and produces clean, renewable electricity. Accurate operational lifetime assessment for FOWTs is an important technical safety issue, as environmental in situ loads can lead to fatigue damage as well as extreme structural dynamics, which can cause structural damage. In this study, in situ environmental hydro and aerodynamic environmental loads, that act on FOWT, given actual local sea conditions have been numerically assessed, using the FAST coupled nonlinear aero-hydro-servo-elastic software package. FAST combines aerodynamics and hydrodynamics models for FOWTs, control and electrical system dynamics models, along with structural dynamics models, enabling coupled nonlinear MC simulation in the real time. The FAST software tool enables analysis of a range of FOWT configurations, including 2- or 3-bladed horizontal-axis rotor, pitch and stall regulation, rigid and teetering hub, upwind and downwind rotors. FAST relies on advanced engineering models—derived from the fundamental laws, however with appropriate assumptions and simplifications, supplemented where applicable with experimental data. Recently developed Gaidai reliability lifetime assessment method, being well suitable for risks evaluation of a variety of sustainable energy systems, experiencing nonlinear, potentially extreme in situ environmental loads, throughout their designed service life. The main advantage of the advocated Gaidai risks evaluation methodology being its ability to tackle simultaneously a large number of dynamic systems' degrees of freedom, corresponding to the system's critical components.

La_1-xCa_x(B1,B2,B3)O₃ perovskite powders doped with calcium were synthesized and sintered. Calcium doping modified the A-site of the perovskite structure, while the B-site was composed of three cations in equal atomic amounts. Cations on the B-site included cobalt, chromium, iron, manganese, and nickel. Sintering temperature varied from 1200 to 1400 °C in air. Density measurements and microstructure imaging determined effect of composition on sintering. Electrical conductivity of sintered compacts was measured using the four-wire measurement method at temperatures of 300 to 900 °C in air. Electrical properties as a function of composition indicate the effect of calcium doping in combination with varied B-site substitution increases electrical conductivity and improves sintering.

Enabling gears to withstand loss of lubrication in gearboxes without secondary oil supply systems can reduce weight and space demand and thus fuel consumption. This study investigates the potential of surface and material technologies on the loss of lubrication performance of gears. Thereby, superfinished, coated, and nitrided gears are compared to ground gears. Systematic experiments under loss of lubrication are performed at a back-to-back gear test rig with circumferential speeds of up to 20 m/s and Hertzian pressures in the pitch point of up to 1723 N/mm². Torque loss, pinion bulk temperatures, and tooth flank surface are analyzed. The results show that surface and material technologies can greatly influence frictional behavior and damage initiation of gears operating under loss of lubrication. With the materials and conditions tested, superfinishing yields to accelerated rise of frictional losses and thus scuffing. Coatings lead to significantly enhanced service life under loss of lubrication by friction reduction and scuffing avoidance.