Hasil untuk "Materials of engineering and construction. Mechanics of materials"

CHEN Haoran, FAN Qixiang, WU Zhenghuan, HAO Xuehui, WANG Tiegang, LIU Yanmei, CAO Fengting

N2 flow rate is an important preparation parameter in the deposition process of nitride coatings.To investigate its effect on the microstructure， mechanical properties， and wear resistance of AlCrTiCN coatings， a combination of pulsed direct current magnetron sputtering and radio frequency magnetron sputtering was employed.Five different AlCrTiCN coatings were prepared by controlling various N2 flow rates (0，5，10， 15， 20 mL/min).The results showed that when the N2 flow rate was 0 mL/min and 5 mL/min， the AlCrTiCN coatings mainly consisted of pure metals and their carbide phases.As the N2 flow rate increased， the degree of amorphization in the coatings increased， the coating thickness gradually decreased， and the surface quality significantly improved.The hardness and elastic modulus of the coatings initially increased and then decreased， with the maximum values (23.1 GPa and 622.3 GPa) achieved at an N2 flow rate of 10 mL/min.The coating-substrate adhesion strength increased with the N2 flow rate and reached its maximum value of 30.8 N at an N2 flow rate of 20 mL/min.Due to the improvement in mechanical properties and the combined effect of the nanocrystalline-amorphous structure， the coating prepared at an N2 flow rate of 10 mL/min exhibited the lowest wear rate of 5.7×10-6 mm3/(N·m)， showing optimal wear resistance.The main wear mechanisms of the coatings prepared at different N2 flow rates were different.Adhesive wear was dominant in coatings prepared at N2 flow rates of 0， 15， 20 mL/min， while abrasive wear was dominant at 5 mL/min and 10 mL/min.In conclusion， N2 flow rate significantly affected the microstructure and overall performance of AlCrTiCN coatings.The coatings prepared at 10 mL/min exhibited the best mechanical and wear resistance properties.This study provided a reference for the design and optimization of high-performance multi-component coatings.

Viswanathan S. Saji

Plasma electrolytic oxidation (PEO) is a pivotal method to create a thick and adherent protective oxide layer on magnesium (Mg) alloys, significantly enhancing their wear and corrosion resistance. The functional oxide layers fabricated via PEO have diverse potential applications, including automobile, aerospace, machinery, biomedical, thermal protection, catalysis, and energy materials. The type and nature of the electrolyte and electrolyte additives used in PEO play a decisive role in shaping the morphology, compactness, porosity, composition, thickness, wear/corrosion resistance, mechanical properties, and other functionalities of the resulting layer. The in-situ integration of chemicals/particles into the PEO layer, facilitated by optimized electrolyte additives, is a well-established method for producing enhanced composite oxide layers. This potential for creating enhanced composite PEO oxide layers is a promising aspect of PEO technology, and this review explores the latest strategies in optimizing electrolyte and electrolyte additives for superior PEO layers in various applications.

Umar Muhammad, Qian Hui, Almujibah Hamad et al.

Renhao Wu, Soung Yeoul Ahn, Yeon Taek Choi et al.

This study delves into effects of deep cryogenic treatment (DCT) on enhancing the hydrogen embrittlement resistance of CoCrFeMnNi high-entropy alloy fabricated via laser powder-bed-fusion (L-PBF). Comparatively assessing as-print, conventional heat treatment, and DCT, we uncover how nanotwin formation within matrix serves as a critical mechanism to combat adverse effects of hydrogen embrittlement. This work reveals that DCT not only mitigates inherent residual stresses from L-PBF, thereby fostering dislocation redistribution and microstructural stabilization, but also synergizes with high-density dislocation cells. Our findings articulate a nuanced understanding of microstructural evolution in response to post-treatments and consequential enhancement of hydrogen embrittlement resistance.Highlights Laser-based additively manufactured CoCrFeMnNi undergoes post heat treatment and deep cryogenic treatment to tailor dislocations and residual stress.The inherent residual stress acts as the driving force for the redistribution of dislocations, leading to the development of a stable microstructure after deep cryogenic treatment.High-density dislocation cells and hydrogen collaborate to lower the local stacking fault energy, triggering gradient nanotwins.Nanotwin-ability effects by deep cryogenic treatment (77 K × 36 h) on the hydrogen embrittlement resistance of CoCrFeMnNi with interior defects are verified.

CHEN Xin, YU Jie, LI Yongguo et al.

The closed-cycle process will generate a large number of radioactive aerosols, and its high humidity, high acidity, and high radioactivity lead to rapid failure and high replacement frequency of glass fiber high-efficiency filters. In order to solve the above problems, hydrophobic modification of the traditional glass fiber filter material was proposed to improve its tolerance to severe conditions. The low surface energy modifier (polydimethylsiloxane) was used to realize the chemical hydrophobicity of filter material. The microstructure was constructed by introducing SiO2 nanoparticles to further improve hydrophobicity. The modification effect was analyzed by means of SEM, FTIR and contact angle measuring instrument, and the filtration performance of the modified filter material was further studied. The research results show that the modification can effectively improve the hydrophobicity of the glass fiber filter material and improve its moisture resistance. The static contact angle of the simply chemically modified filter material can reach 146°, and the modified filter material after the introduction of SiO2 nanoparticles exhibit an angle of more than 150°. When the mass fraction of polydimethylsiloxane and SiO2 nanoparticles is 2.0% and 0.5%, respectively, the corresponding filter material GF-PS-0.5 shows the best acid resistance, which is mainly due to the synergy of chemical hydrophobicity and microstructural hydrophobicity. The hydrophobicity of GF-PS-0.5 remains stable after a sufficient amount of γ-irradiation, indicating its good radiation resistance. The modified filter material maintains excellent filtration performance, and the filtration efficiency exceeds 99.99%. The modification process can improve the tolerance of the glass fiber filter material without influencing the filtration performance, showing a good application prospect.

Bo Fu, Huanxing Zhou, Fei Ye et al.

The crystalline blockage of tunnel drainage pipes poses a common challenge to tunnel engineering, particularly in regions with abundant groundwater and severe ion erosion. Based on the design of concrete mix proportion, this paper improves the calcium ion erosion resistance of shotcrete by adding permeable crystalline sodium methyl silicate waterproofing agent and silane waterproofing agent. Concurrently, the mechanical properties and microscopic characterization of waterproofing agent concrete are carried to determine the optimal dosage for practical engineering applications. The experimental results reveal that the sodium methyl silicate waterproofing agent has minimal impact on the calcium ion dissolution resistance of shotcrete. In contrast, the silane waterproofing agent significantly enhances the calcium dissolution performance of shotcrete, and the optimum dosage is identified as 0.4%. During long-term maintenance, the silane waterproofing agent proves more effective in improving the compressive strength of shotcrete compared to the sodium methyl silicate waterproofing agent, showing an increase rate exceeding 20%. Both waterproofing agents contribute to the enhancement of the tensile strength of shotcrete, and the enhancement effect is consistent with the compressive strength. The permeable crystalline waterproofing agent expedites the cement hydration process, resulting in the formation of higher-density calcium silicate hydrates (C-S-H) gel and ettringite (AFt). These substances fill the pores of shotcrete leading to a more compact internal structure. The calcium ion dissolution and mechanical strength test results collectively validate the superior effectiveness crystallization prevention of aterproofing agents . This research provides valuable insights for addressing the tunnel crystallization phenomenon caused by the calcium dissolution.

Christopher Leow, Peter B. Kreider, Silvano Sommacal et al.

Abstract Graphene enhanced thermoplastic composites offer the possibility of conductive aerospace structures suitable for applications from electrostatic dissipation, to lightning strike protection and heat dissipation. Spray deposition of liquid phase exfoliated (LPE) aqueous graphene suspensions are highly scalable rapid manufacturing methods suitable to automated manufacturing processes. The effects of residual surfactant and water from LPE on thin films for interlaminar prepreg composite enhancement remain unknown. This work investigates the effect of heat treatment on graphene thin films spray deposited onto carbon fibre/polyether ether ketone (CF/PEEK) composites for reduced void content. Graphene thin films deposited onto CF/PEEK prepreg tapes had an RMS roughness of 1.99 μm and an average contact angle of 11°. After heat treatment the roughness increased to 2.52 μm with an average contact angle of 82°. The SEM images, contact angle, and surface roughness measurements correlated suggesting successful removal of excess surfactant and moisture with heat treatment. Raman spectroscopy was used to characterise the chemical quality of the consolidated graphene interlayer. Spectral data concluded the graphene was 3–4 layered with predominantly edge defects suggesting high quality graphene suitable for electrical enhancement. Conductive-AFM measurements observed an increase in conductive network density in the interlaminar region after the removal of surfactant from the thin film. Heat treatment of the Control sample successfully reduced void content from 4.2 vol% to 0.4 vol%, resulting in a 149% increase in compressive shear strength. Comparatively, heat treatment of graphene enhanced samples (~ 1 wt%) reduced void content from 5.1 vol% to 2.8 vol%. Although a 25% reduction in shear strength was measured, the improved electrical conductivity of the interlaminar region extends the potential applications of fibre reinforced thermoplastic composites. The heat treatment process proves effective in reducing surfactant and thus void content while improving electrical conductivity of the interlayer in a scalable manner. Further investigations into graphene loading effects on conductive enhancement, and void formation is needed.

Zeyu Wang, Xinran Song, Hui Huang et al.

Abstract Artificial enzymes featuring the desirable catalytic activity built on nanomaterials are known as nanozymes. Compared with the natural counterparts, nanozymes have demonstrated distinct characteristics including cost‐effectiveness, ease of preparation, high stability, and excellent recycling efficiency. With the rapid innovation of nanoscience and technology, a growing number of nanozymes have been deeply applied in disease prevention, diagnosis, and treatment. In addition, a multimodal platform for effectively interacting with complicated biologic settings has also been achieved by the inherent nanomaterial and dynamic features of nanozymes, which goes beyond simply serving as an enzyme substitute. In this review, we systematically discuss and highlight the classification and catalytic mechanism of nanozymes, regulation of nanozyme activity as well as the research progresses of nanozyme‐enabled/augmented enzyodynamic therapy in treating cancer based on producing and eliminating reactive oxygen species, bacterial infection, inflammation, neurodegeneration, and radiation‐induced tissue damage. Furthermore, the current challenges and future development direction of nanozymes in enzyodynamic disease therapy have been outlined and outlooked. It is highly anticipated that this review will be of guiding significance for better understanding the physiochemical properties and biological effect of nanozymes and the corresponding emerging enzyodynamic disease therapeutics.

Fazle Rabbi, Amna Nisar, Noor Ul Ain Nawaz et al.

Abstract In the current study, a novel method was used to synthesize silver nanoparticles (AgNPs) by utilizing Quercus baloot aqueous extract as a reducing agent. The biosynthesized AgNPs were then subjected to various physicochemical characterizations to assess their effectiveness against microbial familiarity. The characterization techniques included ultraviolet‐visible spectro‐photometry (UV‐Vis), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffractometer (XRD), and Fourier‐transform infrared spectroscopy (FTIR). The UV‐Vis analysis revealed a distinctive spectral peak at 420 nm, indicating the presence of silver nanoparticles. SEM imaging displayed the nanoparticle size range of about 100 nm at a magnification of 30,000x, while TEM demonstrated that the nanoparticles had a spherical morphology with a size of approximately 100 nm. Moreover, the crystalline structure of the silver nanoparticles was confirmed by XRD analysis, further validating their successful synthesis. Additionally, FTIR analysis provided evidence of the presence of phytochemicals involved in synthesizing the AgNPs. the biosynthesized silver nanoparticles (AgNPs) were evaluated for antibacterial and antifungal activities. The AgNPs displayed substantial efficacy against common bacterial strains, including Staphylococcus aureus (71%), Escherichia coli (59%), and Klebsiella pneumoniae (64%). Furthermore, they demonstrated significant antifungal activity against plant pathogenic fungi, namely Aspergillus niger (65%), Aspergillus flavus (70%) and Fusarium oxysporum (61%).

Yuxuan MA, Lunjing YAN, Meijun WANG et al.

Carbon foam catalysts (CF1, CF2, CF3) were prepared by spontaneous foaming method using Liulin coal (LL) as raw materials, and the pyrolysis experiments of Xinjiang Naomaohu long-flame coal (NMH) and Inner Mongolia Shengli lignite coal (SL) were performed by Py-GC/MS at 700 ℃. The effects of carbon foam catalysts with different pore structure on the distribution of gaseous tar products were investigated. The results show that compared with normal semicoke catalyst (SC), carbon foam catalysts have more significant advantages in improving the quality of tar from coal pyrolysis. The catalytic performance of carbon foam catalysts is closely related to its pore structure and chemical character. After the action of CF1, the total amount of tar during pyrolysis of NMH and SL is significantly increased (the increase rates are 10.26% and 31.31%, respectively), which is related to its suitable specific surface area (281.14 m2/g), rich micropore structure (microporous area accounts for 88.96% of the total specific surface area), and appropriate reactivity. CF2 and CF3 with rich hierarchical pore structure and higher reactivity make the total amount of NMH and SL tar decrease. In addition, the relative content of light aromatic hydrocarbons in gaseous tar of coal pyrolysis increases and the relative content of compounds containing O, N and S decreases by CF catalysts. These results indicate that these CF catalysts can significantly promote catalytic cracking, deoxidation, aromatization, and other reactions during the pyrolysis of NMH and SL, and can directionally control the distribution of gaseous tar from coal pyrolysis.

Ali Mokhtar, Ali Saifullah, Andinusa Rahmandhika

The increasing number of motorized vehicles has a direct impact on exhaust gas air pollution. The air pollution in urban areas is dominated by motorized vehicle emissions, along with pollution problems. This study aims to reduce motor vehicle emissions by using a catalytic converter design made from a brass plate catalyst in the shape of a honeycomb. Honeycomb-shaped brass is suitable for catalysts in the catalytic converter. Besides being easy to obtain and cheap in price, the catalyst can reduce and oxidize exhaust gases well, making it suitable as a catalyst material. The method used in this research is the experimental method. It is started from the design of the catalytic converter house and determining the type of catalyst to the process of making the catalytic converter with a honeycomb-shaped brass plate. Then, testing to determine the emission of exhaust gases produced is required. The last step is to compare it without using a catalytic converter or standard conditions. From the results of the emission test, it was found that the use of a catalytic converter made from a brass plate catalyst in the shape of a honeycomb can reduce HC and CO emissions, while CO2 emissions have increased. A decrease in HC gas emissions by 19.1% for a single catalytic converter and 33.7% for a dual catalytic converter is better compared to without using a catalytic converter or standard conditions. Reduced CO gas emissions by 23.8% for a single catalytic converter and 43.1% for a dual catalytic converter are compared to without using a catalytic converter. Meanwhile, CO2 gas emissions increased by 60.7% for a single catalytic converter, and 81.6% for multiple catalytic converters are compared without using a catalytic converter. This is a result of the addition of oxygen to the oxidation process that running smoothly.

C. Suresh, Y.S. Vidya, H. Nagabhushana et al.

Novel and highly effective red emitting phosphor Pr3+ doped (1–11 mol %) Lanthanum Oxyfluoride (LaOF) nanoparticles were synthesized as part of solid state white light emitting diodes by a low temperature solution combustion method using Centella asiatica leaf extract as a reducing agent. The structural and optical characterization of the nanophosphor is described. The nanophosphor shows a prominent emission in the red region. The concentration dependence of the Pr3+ luminescence is investigated. The Photoluminescence analysis, CIE and CCT coordinates suggest that phosphors derived from LaOF: Pr3+might a probable application for white LEDs. In addition, the effect of cation substitution on the strength of luminescence is further elucidated. The Judd-Ofelt theory was used to analyze various radiative properties. Finger Prints dusted by LaOF: Pr3+(5 mol %) NPs exhibit clear and bright images under UV 254 nm light and are helpful for identification of individuals.

Alexander Belostotsky, Nikita Britikov, Oleg Goryachevsky

The article compares the requirements for calculating the snow load on the coatings of buildings and structures in accordance with the regulations of technically developed countries and associations – Russia, the European Union, Canada and the United States. It was revealed that in these norms the general approaches, the subtleties of calculating the coefficients, the set of standard coatings and the schemes of the form coefficient proposed for them differ significantly. This situation reflects the general problem of determining snow loads – at the moment there is no recognized unified scientifically grounded approach to determining snow loads on coatings of even the simplest form. The difference in the normative schemes of snow loads is clearly demonstrated by the example of a three-level roof.

L.R. Jaidev, Kaushik Chatterjee

Three-dimensional (3D) printing by material extrusion is being widely explored to prepare patient-specific scaffolds from biodegradable polyesters such as poly(lactic acid) (PLA). Although they provide the desired mechanical support, PLA scaffolds lack bioactivity to promote bone regeneration. The aim of this work was to develop a surface engineering approach for enhancing the osteogenic activity of 3D printed PLA scaffolds. Macro-porous PLA scaffolds were prepared by material extrusion with 70.2% porosity. Polyethyleneimine was chemically conjugated to the alkali-treated PLA scaffolds followed by conjugation of citric acid. These polymer-grafted scaffolds were immersed in the simulated body fluid to yield scaffolds coated with calcium-deficient hydroxyapatite (PLA-HaP). Surface roughness and water wettability were enhanced after surface modification. PLA-HaP scaffolds exhibited a steady release of calcium ions in an aqueous medium for 10 days. The adhesion and proliferation of human mesenchymal stem cells (hMSCs) on PLA-HaP was ~50% higher than on PLA. Mineral deposition resulting from hMSC osteogenesis on PLA-HaP scaffolds was nearly twice that on PLA scaffolds. This was corroborated by the increase in alkaline phosphatase activity and expression of several osteogenic genes. Thus, this work presents a surface modification strategy to enhance the bioactivity of 3D printed scaffolds for bone tissue regeneration. Keywords: 3D printing, Tissue scaffold, Surface engineering, Hydroxyapatite, Stem cells

Takashi Kato, Takuya Matsumoto, Chizuru Hongo et al.

Cellulose nanofibers are green nanomaterials because of their biodegradability and sustainability, they are also attractive structural materials because of their high mechanical performance. For further expansion of their application and acquisition of their reliability, mechanical reinforcement and functionalization of cellulose nanofiber materials are required. In this work, we focused on the mechanical properties and thermal conductivities of composites of cellulose nanofibers and a nanodiamond (ND). Compared with graphene oxides, which are conventional two-dimensional nanocarbon fillers in aqueous media, natural diamond possesses a much larger modulus. It also has the highest thermal conductivity among all the elemental substances. The ND possesses hydrophilic oxygen functional groups at the surface, following a high dispersion in aqueous media and the rigid diamond structure at the core. In this work, the ND resulted in an increased mechanical reinforcement and enhancement of the thermal conductivity of the cellulose nanofiber, while keeping the high visible light transmittance originating from the latter. In particular, 2,2,6,6-tetramethylpiperidine 1-oxyl-oxidized cellulose nanofibers were reinforced more effectively than quaternary ammonium cellulose nanofibers because of the stronger interaction with the ND and higher dispersibility of the ND. Accordingly, it was proved that the cellulose nanofiber/ND composite was a promising high-strength and high-thermal-conductive material.

Pingping Qiu, Weibin Qiu, Zhili Lin et al.

Abstract A graphene-based on-chip plasmonic nanostructure composed of a plasmonic bus waveguide side-coupled with a U-shaped and a rectangular nanocavities has been proposed and modeled by using the finite element method in this paper. The dynamic tunability of the plasmon-induced transparency (PIT) windows has been investigated. The results reveal that the PIT effects can be tuned via modifying the chemical potential of the nanocavities and plasmonic bus waveguide or by varying the geometrical parameters including the location and width of the rectangular nanocavity. Further, the proposed plasmonic nanostructure can be used as a plasmonic refractive index sensor with a sensing sensibility of 333.3 nm/refractive index unit (RIU) at the the PIT transmission peak. Slow light effect is also realized in the PIT system. The proposed nanostructure may pave a new way towards the realization of graphene-based on-chip integrated nanophotonic devices.

Bo Li, Jianxun Liu, Feng Han et al.

Improving the compatibility between flame retardant and asphalt is a difficult task due to the complex nature of the materials. This study explores a low dosage compound flame retardant and seeks to improve the compatibility between flame retardants and asphalt. An orthogonal experiment was designed taking magnesium hydroxide, ammonium polyphosphate, and melamine as factors. The oil absorption and activation index were tested to determine the effect of titanate on the flame retardant additive. The pavement performance test was conducted to evaluate the effect of the flame retardant additive. Oxygen index test was conducted to confirm the effect of flame retardant on flame ability of asphalt binder. The results of this study showed that the new composite flame retardant is more effective in improving the compatibility between flame retardant and asphalt and reducing the limiting oxygen index of asphalt binder tested in this study.

Spěváček Jiří, Ilavský Michal

陈列, 佐辉, 苗红生 et al.

The φ110 mm bar products of steel 3Cr2W8V were forged from 740 kg ingot melted by 15 t EAF and re- fined by 25 t LF. At end of refining period,the oxygen content in steel was 29×10^-6and the liquid steel was treated by rare earth treatment with adding 0.048% RE alloy(21~24RE,44Si,3Mn,5Ca,3Ti,bal Fe). The yield of rare earth elements was 30.78%.The examination results showed that the rare earth treatment could be effciently to improve segregation of eutectic carbides in die steel 3Cr2W8V and obviously to decrease segregation of deleterious elements such as P,Pb, Sn,As,Sb at grain boundary.

陈慧琴, 刘建生, 郭会光

The retaining ring is an important component of turbogenerator. The high deformation stress-strain curves of three  kind  of  retaining  ring  steel-0.53C- 16.98Mn-3. 17Cr(1),0. 12C- 19.57Mn- 19.27Cr-0.60N(2)and  0.06C- 18.58Mn- 19. 15Cr-0.69N(3)and the high temperature plasticity- reduction of area of containing nitrogen retaining ring steel at temperature 800~1200 ℃ have been studied by Gleeble- 1500 thermal simulation machine. The results showed that with increasing nitrogen content in steel,the critical deformation value for dynamic recrystallization increased in order to gradually  increase corresponding deformation force; the maximum reduction of area of containing nitrogen steel was at 1050 ℃,and  the high plastic deformation region shrunk with increasing nitrogen content in steel. Therefore modifying deformation model to  increase process plasticity is an available way to increase the quality of retaining ring.