The current study has portrayed the synthetic mixtures of Themeda quadrivalvis using gas chromatography–mass spectrometry (GCMS), the combination of green silver nanoparticles (AgNPs) formed with macrolide antimicrobials. The counter microbial effects were investigated with various concentrates of plant compounds, AgNPs, and macrolide-formed AgNPs against respiratory microorganisms. GCMS examination has shown the presence of various substances that intensifies the chloroform concentrate of T. quadrivalvis. A total of 51 mixtures were distinguished, and furthermore, the most severe zone of restraint was found in chloroform removal and against Klebsiella sp. (18 ± 4.7 mm). It has been demonstrated that the green mixture of AgNPs containing macrolide anti-toxins, such as azithromycin, erythromycin, and clarithromycin, demonstrates extensive antibacterial activities against a wide range of microorganisms. In contrast, the green union of AgNPs also demonstrates their efficacy against a wide range of respiratory microbes. The particles containing numerous relatively small fragments that were observed in the scanning electron microscopy analysis were found to be 20 nm in size. Previous studies have focused on phytochemicals and green amalgamations of AgNPs, but not much detail has been provided on T. quadrivalvis. It has been reported that the two concentrates (a plant concentrate in combination with consolidated green nanoparticle macrolide anti-toxins). The present study aims to treat respiratory microorganisms with a green methodology approach using nanotechnology; this analysis primarily focuses on offering creative approaches to make drugs against respiratory microbes.
Basalt fiber (BF) is a kind of high-performance fiber rising rapidly in recent years. BF is typically used in the field of structure engineering because of its high strength and high modulus. The preparation of BF-based composites first requires surface modification of BF to improve the interfacial bonding between BF and the resin matrix. With the continuous deepening of the research on BF surface modification, researchers have found that special surface modification can obtain BF-based functionalized composites, and this field has received extensive attention in recent years. In this article, research work on BF-based functional composites in recent years are summarized and reviewed from the aspects of electromagnetic shielding, water treatment, catalytic function and fire insulation. Finally, this article summarizes the BF surface modification methods, and proposes the development trends and direction of BF-based functional composites.
In recent years, calcium peroxide (CaO2) has attracted widespread attention in the medical community due to its excellent antitumor and antibacterial properties, and has gradually become a hot research topic in the biomedical field. CaO2 reacts with water (H2O) to produce calcium ion (Ca2+), oxygen (O2), and hydrogen peroxide (H2O2), where Ca2+ is suitable for calcium death caused by calcium overload, O2 is suitable for O2-dependent anticancer therapy, and H2O2 is suitable for H2O2-dependent anticancer therapy. In addition, H2O2 can also be used in the antibacterial field to treat bacterial infections. All these make the CaO2 to become a kind of excellent antitumor and antibacterial drug. This study mainly reviews the preparation and surface modification of CaO2, probes into the latest progress about CaO2 nanoparticles in the field of tumor treatment and antimicrobial therapy. Finally, the challenges that CaO2 still faces in the future research field are clarified, and its prospects are forecasted.
State-of-the-art treatment of such orthopedic diseases as fracture and femoral head necrosis implies the installation of prosthesis or fixed equipment into patients’ injured parts using bone drilling. This study proposes an ultrasonic longitudinal torsion-assisted drilling (ULTAD) technique for biotic bone drilling. A comparative experiment was carried out between conventional drilling and ULTAD drilling in biotic bone, namely porcine femur. These tests proved that under the same drilling parameters, the ultrasonic component in bone drilling could reduce the drilling temperature and forces, improve the material removal by chip breaking, shorten the length of bone debris, and facilitate their discharge. Moreover, the proposed ULTAD technique reduced the number, length, and width of microcracks in the borehole wall, thus protecting the drilled biotic bone from internal damage.
For the sustainability of the construction industry, geopolymers (GPM) are playing an important role compared with Portland cement due to their improved mechanical properties, enhanced durability, and outstanding performance in alkali and acidic conditions. Most of the previous review investigations explored the general behavior of GPM developed with kaolin, silica fume, rice husk ash, ground granulated blast furnace slag, fly ash, etc., but the comprehensive review study on the industrial by-products including granite waste powder (GWP) and bauxite residue (BR) is required to investigate their suitability in the construction industry. The current investigation aims to present a detailed review of the fresh, mechanical, durability, and microstructural behavior of the GPM paste produced using BR and GWP from the literature. The effect of different ingredients and testing conditions are evaluated for the fresh, mechanical, durability, thermal, and microstructural performance of the GPM paste. The results indicate that the pure BR having a lower ratio of SiO2 to Al2O3 reacts poorly, therefore, it should be blended with other aluminosilicates comprising a higher ratio of SiO2 to Al2O3 for better geopolymerization. Pre-activation approach of BR including three-hour calcination at 800 oC, one-hour thermal pretreatment of alkali with solid activators at 800 oC, mechanical co-grinding, and pulverization presented the improved strength and microstructural properties of GPM. When mixing GWP in large quantities, heat curing is preferred for 8 hours at 60 to 80 oC for better behavior of GPM. Incorporating the nanomaterials into GWP-based GPM showed a significant impact on initial compressive and tensile strengths. Further studies on the synergistic use of GWP with aluminosilicate products and BR with silica-rich pozzolanic ingredients for GPM are required. Improved physio-chemical features of BR-GPM and GWP-GPM are the potential research areas that can be addressed by incorporating raw materials for enhancing the internal matrix, such as nanoparticles, bio-additives, micro-fibers, etc. that have been observed to be effective for the GPM pastes.
More than 2 billion people around the world still use raw earth architecture, in countries like Nepal, India, and Iran. In China, the proportion of people living in earthen structures rose to 36%, some of them in western Sichuan. Minority dwellings in western Sichuan, China, use local stone and yellow mud as building materials and have been used for thousands of years. Because yellow mud is a brittle material with poor mechanical properties, and because the region is prone to earthquakes, the walls are highly susceptible to damage under seismic action. To improve the mechanical properties of yellow mud, the yellow mud of Taoping Qiang Village in western Sichuan was studied and modified. Uniaxial compressive tests were conducted on the modified specimens, and the existing ontogenetic equations of raw soil-based materials were analyzed and optimized. Finally, we developed the constitutive models for yellow clay and modified yellow clay in the western Sichuan area, which can be used for different kinds of modified materials through the variation of parameters. The results show that the compressive strength of yellow clay is improved by adding the modified materials. The optimized constitutive model can better fit the test curves, which can provide a basis for theoretical calculations and seismic mitigation of minority residential structures in western Sichuan or similar structural systems.
Ship–bridge collision is a common type of accident in bridge engineering which could cause heavy casualties and economic losses. To ensure the safety of both the ships and bridges during collision, a novel steel box-soft body combination was proposed in this work. The time history curves of the impact force of three downscaled facility specimens were obtained through the horizontal impact test. The influence of the steel box web spacing and the existence of the anti-collision facilities on the ship collision force reduction rate was investigated. The collision failure modes of ship bow and the anti-collision facilities, as well as the energy absorption behavior of the facility were analyzed. Based on ANSYS/LS-DYNA finite element (FE) analysis software, the nonlinear numerical models of the anti-collision facilities were generated. The analysis results show that the proposed anti-collision facility can not only greatly reduce the ship impact force, but the bow damage as well. The densified steel box web can improve the anti-collision performance of the whole anti-collision facilities to a certain extent. Compared with the direct impact on the steel plate, the maximum reduction rate of peak force of the proposed facility can be achieved to be 31.07%. The anti-collision facilities deformation energy absorption accounts for more than 70% of the total energy, which shows that the facility is able to absorb most of the energy and protect the bow. The FE simulation results coincide with the experimental outcomes, indicating the acceptable accuracy of the FE models.
The development of hybrid composite materials using honeycomb structure, typically a lightweight material, is commonly used in aircraft structures. However, the use of honeycomb with natural or synthetic composite remains unexplored in the literature. Therefore, this study aims to partially replace synthetic fiber, woven glass with a natural fiber of woven kenaf and honeycomb core. An experimental analysis investigated the mechanical strength of three different compositions using glass, kenaf, and honeycomb materials for structural application purposes. The properties of the sample were evaluated through the tensile, flexural, and impact strength, and the morphological damage was observed using scanning electron microscopy. The results showed that the composition of GKGKG laminate composite is the highest in tensile strength (147.64 MPa) and modulus (3.9 GPa), while the GKHKG composite was good in flexural strength (219.03 MPa) and modulus (11.47 GPa). In terms of impact properties, there was a slight difference in energy level (20–30 J) by GKGKG and GKHKG, showing the optimal hybrid configuration of composite for the newly developed material. In conclusion, the application of the new hybrid of GKHKG composite is promising in semi-structural and structural light-weight applications.
Thermal modification is an environment-friendly technology for improving various wood properties, especially the dimensional stability, decay resistance, and color homogeneity. In this work, four tropical wood species (African padauk, merbau, mahogany, and iroko) were thermally modified by the ThermoWood process. The influence of heat treatment on the color and chemical changes of wood was studied by spectrophotometry, Fourier transform infrared (FTIR) spectroscopy, and wet chemistry methods. As the temperature increased, a decrease in lightness (L*) and a simultaneous decrease in chromatic values (a*, b*) were observed, indicating darkening and browning of the wood surface. As a result of the heat treatment, the relative content of hemicelluloses decreased the most in merbau and mahogany, while the thermal stability of iroko and African padauk was higher. All examined wood species showed a strong correlation between the lightness difference value (ΔL*) and the content of hemicelluloses (r = 0.88-0.96). The FTIR spectroscopy showed that the breakdown of C]O and C]C bonds in hemicelluloses and lignin plays an important role in the formation of chromophoric structures responsible for the color changes in the wood.
Magnesium hybrid composites are a new class of lightweight metal matrix composites having excellent physical, mechanical, wear and corrosive properties. Hybrid magnesium matrix composites are fabricated using different combinations of reinforcements having basics properties like wear resistance and high strength of ceramics, self-lubricating of graphite, MoS 2 , CNT, and graphene, high thermal conductivity of carbon, diamond, and cubic boron nitride, and low cost of fly ash. This article presents an overview of different combinations of reinforcements used for fabrication of hybrid magnesium matrix composites and their effects on the mechanical and tribological properties of the hybrid materials. The major issues like agglomeration, interfacial phenomena, reinforcement–matrix bonding, and problems related to uniform distribution of particles are discussed in this article. Magnesium hybrid composites have the potential of satisfying the recent demands of aerospace, automobile, biomedical, defense, marine, and electronics industries. The future directions and potential research areas in the field of magnesium hybrid composites are also highlighted.
Tissue engineering is an enabling technology that can be used to repair, replace, and regenerate different types of biological tissues and holds great potential in various biomedical applications. As the first line of defense for the human body, the skin has a complex structure. When skin is injured by trauma or disease, the skin tissues may regenerate under natural conditions, though often resulting in irreversible and aesthetically unpleasant scarring. The development of skin tissue engineering strategies was reviewed. Although the traditional approaches to skin tissue engineering have made good progress, they are still unable to effectively deal with large-area injuries or produce full-thickness grafts. In vitro three-dimensional (3D) skin constructs are good skin equivalent substitutes and they have promoted many major innovative discoveries in biology and medicine. 3D skin manufacturing technology can be divided into two categories: scaffold-free and scaffold-based. The representatives of traditional scaffold-free approaches are transwell/Boyden chamber approach and organotypic 3D skin culture. Because of its low cost and high repeatability, the scaffold-free 3D skin model is currently commonly used for cytotoxicity analysis, cell biochemical analysis, and high-throughput cell function. At present, many drug experiments use artificial skin developed by traditional approaches to replace animal models. 3D bioprinting technology is a scaffold-based approach. As a novel tissue manufacturing technology, it can quickly design and build a multi-functional human skin model. This technology offers new opportunities to build tissues and organs layer by layer, and it is now used in regenerative medicine to meet the increasing need for tissues and organs suitable for transplantation. 3D bioprinting can generate skin substitutes with improved quality and high complexity for wound healing and in vitro disease modeling. In this review, we analyze different types of conventional techniques to engineer skin and compare them with 3D bioprinting. We also summarized different types of equipment, bioinks, and scaffolds used in 3D skin engineering. In these skin culture techniques, we focus on 3D skin bioprinting technology. While 3D bioprinting technology is still maturing and improvements to the techniques and protocols are required, this technology holds great promise in skin-related applications.
Graphite-carbon nitride (g-C 3 N 4 ) was prepared by thermocondensation, and g-C 3 N 4 /BiVO 4 material (GCB) and g-C 3 N 4 /CNTs composite material (GCC) were prepared by doping different contents of BiVO 4 and carbon nanotubes (CNTs) with g-C 3 N 4 samples, respectively. Then, BiVO 4 , CNTs, and g-C 3 N 4 samples with different contents were doped to prepare ternary composite material (GCBC). In the performance experiment, Sulfamethoxazole (SMZ) was used as degradation material to evaluate the photocatalytic performance of the prepared samples, and the degradation reaction kinetics equation, quadric cycle stability experiment, free radical capture, and intermediates identification were studied. The intermediates of photocatalytic degradation of SMZ were analyzed by high-performance liquid chromatography-mass spectrometry. From the experimental data, it can be seen that for SMZ solution, when the reaction time T = 0 min and retention time rt = 7.53 min, there is a peak corresponding to the substance with m / z [M + H] ⁺ of 254, which is judged as SMZ. At 20, 40, and 60 min, rt was 2.00, 7.06, and 9.57 min, indicating the presence of intermediates in the photocatalytic process. Experimental analysis shows that there are three intermediates of SMZ degradation by composite sample GCBC. In this work, three kinds of composite materials were successfully prepared, and a variety of characterization, SMZ as pollutants, test the photocatalytic performance of composite materials (GCB, GCC, and GCBC) samples, and elucidated the cyclic stability of the material, active species capture, and photocatalytic degradation mechanism.
This work summarizes the different natural lighting systems applied for pollutant treatment systems using photocatalysis. The principles and fundamentals of the technologies used are revisited and examples of technologies most used for treatment either at the laboratory or at the pilot plant level are disclosed. This unveils a general panorama of treatment technologies via photocatalysis, using natural sunlight as an illumination source. Aside from these concentrated solar power systems that are inviable for photocatalytic aqueous treatments, reported scientific works are shown about heliostats, parabolic troughs, Fresnel lenses, and direct illuminated systems. As a valuable result of this review, the power used in photocatalytic systems requires higher attention not only in these systems but in laboratories and prototypes. Photocatalysts and their countless configuration variants are limited due to the potential barriers in particle borders, interfaces, and surfaces to cause redox reactions in water and pollutant target molecules. These factors reduce photocatalyst efficiencies for converting light energy to useful electron pair charge carriers for water treatments. The use of solar concentration systems applied to photocatalytic treatment systems can generate enough charge carriers, improving the efficiency of the systems, and making it feasible to scale up various configurations of this treatment pathway. Subsequently, the photocatalyst material and light are both important.
The solidification property and mechanism of soft soil based on the industrial waste residue was studied systematically. First, the properties of soft soil solidified by single blast furnace slag, phosphogypsum and cement were carried out, and the solidification effect of Portland cement was better compared with blast furnace slag and phosphogypsum. Second, the composite solidification agent formula with excellent solidification performance was developed, and the mass ratio of Portland cement, blast furnace slag and phosphogypsum was 1:2.3:0.8. At this time, compressive strength was up to 8845.1 kPa. Finally, the composition and microstructure of the solidification soft soil was studied by X-ray diffractometer and scanning electron microscope. Calcium hydroxide formed by the hydration of Portland cement and calcium sulfate in phosphogypsum were used as activators for hydration reaction of blast furnace slag, and more hydration products under the synergistic action of Portland cement hydration and blast furnace slag hydration were formed. Hydrated calcium silicate colloid and Ettringite crystal played an important role in skeleton and filling, and the structure of soft soil solidified by composite solidification agent was the most compact.
Carbon/carbon (C/C) composites have received considerable attention for one of the most promising materials in thermal-structural applications owing to their low density, excellent mechanical strength at high temperature, and superior thermal shock resistance. However, C/C composites are susceptible to destructive oxidation in atmospheric environment at high temperature. Matrix modification by adding ultra-high-temperature ceramics (UHTCs) into carbon substrate has been proved to be a favorable route to achieve the improved ablation resistance of C/C composites. In this work, the main fabrication approaches of UHTCs-modified C/C composites were summarized, including chemical vapor infiltration/deposition, precursor infiltration and pyrolysis, reactive melt infiltration, and slurry infiltration, and the advantages and drawbacks of each process were also briefly analyzed. In addition, anti-ablation properties of UHTCs-modified C/C composites under different ablation tests with different shape specimens were introduced. Finally, some likely future challenges and research directions in the development and application of these materials were presented.
The main aim of the current work is to investigate the effect of equal channel angular pressing (ECAP) processing parameters, namely, number of passes, ECAP die angle, route type, and processing temperature on the mechanical and electrical properties of pure copper (Cu). The finite element method was used to simulate the homogeneity of stress and plastic strain distribution during ECAP processing. The response surface methodology (RSM) was used to identify the optimum ECAP processing parameters by analyzing the impact of ECAP conditions on responses. A second-order regression model and analysis of variance were created to analyze the ECAP condition of optimum responses. A genetic algorithm (GA) was also applied to optimize the ECAP condition. Finally, a hybrid RSM-GA was created to improve the optimization of ECAP responses and corresponding conditions evaluated using GA. The developed models were validated and compared with the experimental findings to prove that they are reliable as predictive tools. The optimization findings revealed that route Bc was more effective in improving the hardness, yield stress, ductility, and impact energy whereas route A was more effective in improving the ultimate tensile strength and the electrical conductivity of the Cu billets. Furthermore, the optimum die angle, number of passes, and processing temperature for the mechanical and electrical properties were also identified individually.
Limitation in practical applications of biopolymer–fiber composite is mainly at higher temperatures. Thus, this study highlights the effects of fiber orientation on the durability of polylactic acid (PLA) reinforced with unidirectional (UD) continuous kenaf fibers at elevated temperatures. PLA and long kenaf fiber were fabricated using the hot-pressing method and stacked at fiber orientations of 0°, 45°, or 90°, relative to the tensile force. Dynamic mechanical analysis of the composites shows excellent anti-shock and temperature-resistant properties of the composite. UD PLA–kenaf composites with a 0° fiber orientation showed an ultimate tensile of ∼190 MPa and a flexural strength of ∼235 MPa, and the strength of the composite was able to retain up to 120°C temperature. The debonding behavior of the fiber from the matrix (fiber pull-out) supported by microscopy proved that interfacial failure occurs from the local strains, which initiate cracking. Interfacial failure and stress transfer have caused a remarkable reduction in composite strength when fibers were oriented at 90°. Hence, this current improvement in the performance of the UD PLA–kenaf fiber composite may potentially replace conventional synthetic fibers, especially for structural automotive applications.
Nonoxide ceramics excel among the reinforcements used for aluminum matrix composites due to their variety of morphologies and mechanical properties. Among these reinforcements are carbides (SiC, B4C, and WC); carbon materials (graphite, carbon fibers, carbon nanotubes, and graphene); nitrides (silicon nitride [Si3N4] and BN); and hollow Fe spheres. Although the effect of adding different percentages of reinforcements has been widely studied for Al matrices, matrix–reinforcement interactions need more attention. The consequences of these interactions can include interface formation, loss of alloying elements, reinforcement deterioration, modifications in the matrix microstructure, different precipitation sequences and kinetics, and interfacial diffusion of elements. These interactions may be significantly modified by the alloying elements, needing more in-depth analyses for a correct selection of the matrix–reinforcement system. Al matrices with Si, Cu, and Mg outstand, and the focus of the present work is their reciprocal interactions with nonoxide reinforcements. The novelty of this review consists of the analysis and discussion of these interactions, emphasizing the modifications originated by each one of these alloying elements, and the conditions needed to increase or avoid their effects on the composite. Besides, an analysis of the crystallography of the generated interfaces is presented, including their impact on mechanical properties. This could be helpful for a better understanding and selection of the matrix–reinforcement system, also serving as a benchmark study.
This study examines the cyclic pullout behavior of two types of cold-drawn NiTi shape memory alloy fibers, such as paddled and crimped fibers. For this, two diameters of 1.0 and 0.7 mm are considered. The experimental cyclic pullout results show that the deep crimped fibers produce a higher maximum pullout resistance than the shallow crimped fibers. When heated, the shallow crimped fiber increases the diameter more significantly than the deep crimped fiber, whereas the fiber wave depth decreases more than the deep crimped fiber. Thus, the maximum pullout resistance increases for the heated shallow crimped fiber and decreases for the heated deep crimped fiber. The displacement recovery ratio (DRR) reduction with an increasing slip is significant for the fiber with a low anchoring bond. The high anchoring bond fiber also introduces a higher average DRR than the fiber with a relatively low anchoring bond. Under heating treatment, the average DRR increases due to the prestressing in the fiber due to the shape memory effect. However, the anchoring bond of the fiber is enough to produce prestressing in the fiber. The anchoring bond of the fiber and the prestressing also influence the energy dissipation (ED). The higher anchoring bond results in a higher ED value, and the prestressing in the fiber contributes more to the increased ED values.
After tin–lead solders are banned, the widely used electronic packaging interconnect materials are tin–silver, tin–copper, and other alloy solders. With the application of high-power devices, traditional solders can no longer meet the new requirements. Nano-silver (Ag) paste, as a new solder substitute, exhibits excellent properties, such as excellent thermal and electrical conductivity, sintering at lower temperatures, and service at high temperatures. However, many organic devices still cannot withstand this temperature, and are often not suitable for the connection of nano-Ag paste packaging materials, therefore, it is very urgent to further reduce the sintering temperature of nano-silver paste. Based on the transient liquid phase sintering technology, by doping the nano-Ag paste with the nano-tin paste with a lower melting point to make the two uniformly mix, pressureless sintering at low temperature can be realized, and a sintered joint with a connection strength greater than 20 MPa can be formed. Considering that tin is easy to be oxidized, and the core–shell material can prevent the oxidation of tin, and at the same time ensure the uniform distribution of tin in silver, the doping scheme of the core–shell structure is determined. Heterogeneous flocculation method refers to the particles with different properties of charges which attract each other and agglomerate. It is a continuous reduction method for preparing core–shell materials. This method has the advantages of mild reaction conditions and less equipment investment, so the heterogeneous flocculation method is selected to prepare Sn@Ag core–shell nano paste. And research its sintering performance and strengthening mechanism.
Glass fiber-reinforced polymer (GFRP) composite materials are widely used in many manufacturing industries due to their low density and high strength properties, and consequently, the need for precision machining of such composites has significantly increased. Since composite materials have an anisotropic and heterogeneous structure, the machinability of composite materials is quite different from conventional materials. In the machining of GFRP composite pipes, tool wear, cracks or delamination, a rough surface, etc., many unwanted problems may occur. Therefore, GFRP composite pipes are difficult to process. To prevent such problems, it is very crucial to select suitable process parameters, thereby achieving the maximum performance for the desired dimensional integrity. In this study, through turning of GFRP composites with different orientation angles (30°, 60°, and 90°), the effects of cutting speed (50, 100, and 150 m·min−1), feed rate (0.1, 0.2, and 03 mm·rev−1), and depth of cut (1, 2, and 3 mm) on cutting force and surface roughness were determined. Then, with the use of these machining parameters, a model of the system for determining cutting force and surface roughness was established with artificial neural networks (ANNs). The ANN was trained using Levenberg–Marquardt backpropagation algorithm. It has been observed that the results obtained with the ANN model are very close to the data found in experimental studies. In both experimental and model-based analysis, minimum cutting force (44 N) and surface roughness (2.22 µm) were achieved at low fiber orientation angle (30°), low feed rate (0.1 mm·rev−1), and depth of cut (1 mm) at high cutting speeds (150 m·min−1).
In this study, different input parameters for electric discharge machining (EDM) are examined in order to revise the distinctiveness of EDM for machining aluminum-based hybrid metal matrix composites (MMCs). The versatility of hybrid aluminum MMCs makes them very popular and sought after in the automotive, aerospace, marine, and space industries. In this article, an optimized process parameter setting for hybrid MCCs machining with an EDM machine is determined that have silicon carbide (SiCp) and graphite (Grp) particles added as reinforcement materials in varying amounts (Al–0.7Fe–0.6Si–0.375Cr–0.25Zn/10 wt%SiC/3 wt%Gr–MMC, Al–0.7Fe–0.6Si–0.375Cr–0.25Zn/15 wt%SiC/5 wt%Gr–MMC, and Al–0.7Fe–0.6Si–0.373Cr–0.25Zn/20 wt%SiC/8 wt%Gr–MMC). The stir casting method was used to prepare these hybrid aluminum MMCs (3 samples). A study of surface roughness (SR) and material removal rate (MRR) was conducted to examine the effects of dominant parameters. An experiment is planned using a central composite rotatable design (CCRD) of response surface methodology (RSM). It is possible to predict MRR and SR with 95% degree of accuracy by utilizing the quadratic model. Non-dominating Sorting Genetic Algorithm-II was employed to solve “mathematical models” for multi-objective optimization of output response characteristics. The scanning electron microscope (SEM) images of the tool and workpiece materials show that the recast layer has been formed on the tool face and the surface of the machined work-piece. Based on the results, it was determined that an optimal value of MRR (2.97 g·min−1) was obtained at 90 µs, 30 µs, 7.0 V, and 14 A as P
off, gap voltage, and peak current, respectively. As a result of the findings, the SR is reciprocally proportional to P
on, and the SR is commensurate with P
off. It was determined that the optimal value of SR (2.41 µm) could be attained at 30 µs, 52 µs, 6.0 V, and 12 A as the P
off, gap voltage, and peak current, respectively. For an optimal set of response variables, P
on can be specified as 30 µs, P
off as 30 µs, gap voltage as 6 V, and peak current as 14 A as process parameters for MRR and SR. The SEM images of the tool material and the workpiece material clearly demonstrate a recast layer formed on the tool face and the machined surface of the workpiece. The optical microscopy analysis reveals a uniform distribution of SiCp and Grp particles in the Al–0.7Fe–0.6Si–0.375Cr–0.25Zn matrix. In addition to recast layers and machined surfaces, EDS analysis reveals the deposition of tool material on the surface of the workpiece. The composites fabricated may replace materials in many of these applications where “friction” is a significant factor.
Today, the growth of the cosmetic industry and dramatic technological advances have led to the creation of functional cosmetical products that enhance beauty and health. Such products can be defined as topical cosmetic drugs to improve health and beauty functions or benefits. Implementing nanotechnology and advanced engineering in these products has enabled innovative product formulations and solutions. The search included organic molecules used as cosmeceuticals and nanoparticles (NPs) used in that field. As a result, this document analyses the use of organic and inorganic particles, metals, metal-oxides, and carbon-based particles. Additionally, this document includes lipid and nanoparticles solid lipid systems. In conclusion, using NPs as vehicles of active substances is a potential tool for transporting active ingredients. Finally, this review includes the nanoparticles used in cosmeceuticals while presenting the progress made and highlighting the hidden challenges associated with nanocosmeceuticals.
This work presents the design and application of a low-cycle reciprocating loading test on 23 recycled aggregate concrete-filled steel tube columns and 3 ordinary concrete-filled steel tube columns. Additionally, a systematic study on the influence of various parameters (e.g., slenderness ratio, axial compression ratio, etc.) was conducted on the seismic performance of the specimens. The results show that all the specimens have good hysteresis performance and a similar development trend of skeleton curve. The influence of slenderness ratio on the seismic index of the specimens is more significant than that of the axial compression ratio and the steel pipe wall thickness. Furthermore, artificial intelligence was applied to estimate the influence of parameter variation on the seismic performance of concrete columns. Specifically, Random Forest with hyperparameters tuned by Firefly Algorithm was chosen. The high correlation coefficients ( R ) and low root mean square error values from the prediction results showed acceptable accuracy. In addition, sensitivity analysis was applied to rank the influence of the aforementioned input variables on the seismic performance of the specimens. The research results can provide experimental reference for the application of steel tube recycled concrete in earthquake areas.
This research focuses on the addition of low-cost rare earth metals (REMs) to improve the comprehensive properties of hyper duplex stainless steels (DSSs). The effects of REM on the microstructure, mechanical properties, and pitting corrosion of hyper DSSs were analyzed by optical/scanning electron microscope metallographic examination, X-ray diffraction analysis, tensile test, impact test, and potentiodynamic polarization test. With the addition of REM, micro/nanoscale REM inclusions were formed, and the microstructure of the alloy was refined. With the increasing content of REM, the average diameter and area of inclusions in the alloy decreased at first and then increased. While the mechanical properties showed a trend of first increasing and then decreasing. An appropriate amount of stable REM inclusions could reduce the susceptibility of pitting corrosion and improve the pitting corrosion resistance of the alloy. The hyper DSSs with REM content in the range of 0.018–0.031 wt% have excellent mechanical properties and pitting resistance.
Acoustic black holes have good application prospects in the field of vibration and noise reduction. Based on engineering practice, this study proposes a systematic process method for the application of acoustic black hole structure in raft structure, which provides new ideas and references for improving the vibration isolation performance of floating raft system and reducing the level of ship vibration and noise. The influence law of each parameter on structural vibration and the recommended value range of each parameter are given, which provides support for the systematic method and process of the application of acoustic black holes in the raft structure. Then, the acoustic black hole process is applied to a floating raft system. According to the characteristics of the raft structure, an application scheme of the acoustic black hole in the raft structure is formed, and the vibration level drop of the floating raft vibration isolation system before and after the acoustic black hole is embedded, calculated, and analyzed. The changes further improve the vibration reduction and isolation performance of the raft system and effectively reduced the mechanical noise level of the ship’s cabin.
Fused deposition modelling is known for its ability to customise materials at peak performance for instant use but lacks in terms of interfacial adhesion of layup sequences. Hence, the mechanism of acquiring excellent interfacial adhesion, mainly via dried-up printed sample, has been discovered, resulting in the proper bonding formation upon layers. Result reveals that the flexural strength increased by 23% under 70°C drying conditions (5 h) and the impact strength increased by 240% compared to pure polyamide. This mechanism resists the deformation growth between the layers and enhances the mechanical strength at the highest level.
Sublimation growth of cubic silicon carbide (3C–SiC) with diameters of 50 and 100 mm was performed on freestanding homoepitaxial grown seeds. For both seeds and sublimation grown crystals, two different relaxation axes with varying curvature could be observed with the higher bent axis aligned perpendicular to the original wafer flat. A general reduction in the wafer bow independent of the starting curvature and size of the seeds could be observed. Using the X-ray imaging, we could observe in situ that the bow reduction is linked to the growth of new material and cannot be initiated by heat up or cool down processes alone. Raman spectroscopy of the grown crystals revealed that the observed flattening goes along with a tensing of the seeding layers while the surface of the crystals remains free of a stress gradient. A slight concave bending of lattice planes along the main relaxation axis could be observed by high-resolution XRD rocking curve measurements while for the lower bent axis, no lattice plane bending occurred. Full width half maximum values of the (002) reflection showed values as low as 67 arcseconds proofing the possibility to grow large-area, high-quality 3C–SiC using sublimation growth.
The large-scale application of phenolic aerogel is limited by its complex and lengthy production process as well as its expensive cost. Herein a simultaneous drying-curing method for phenolic aerogels was designed based on the sol–gel process, and a series of phenolic aerogels with different hexamethylenetetramine (HMTA) contents were prepared. The material parameters such as microstructure, pore structure, mechanical properties, shrinkage, and density of the aerogel were characterized. The results show that compared with the conventional full-sealing method, the simultaneous drying-curing method shortens the preparation time of aerogels by nearly half and improves the safety of the preparation process. The prepared phenolic aerogels still maintain the nanoporous microscopic morphology. When the HMTA content is 1/6 of the phenolic mass, the linear shrinkage rates of the aerogels prepared by this method and the conventional full-sealing method are 9.8 and 9.4%, respectively. The densities are 0.25 and 0.22 g·cm−3, and the BET specific surface areas are 54.42 and 54.31 m2·g−1, and the compressive yield strengths are 1.76 and 1.16 MPa. At the same time, the thermal conductivity of the phenolic aerogels prepared by the simultaneous drying-curing method is less than 0.06 W·(m·K)–1 at room temperature. These results indicate that the properties of the aerogels prepared by the simultaneous drying-curing method are close to those prepared by the conventional method, which proves that this method has guiding significance for the large-scale, low-cost, and rapid production of nanoporous phenolic aerogels.
To achieve better mechanical properties and higher scour resistance of yellow mud in Qiang Village, this study investigated how to improve yellow mud by single factors of straw, starch, cement, and epoxy resin. First, the effect of each material on the shear strength of yellow mud was analyzed through the direct shear test, and the effect of the respective material on the scour resistance of yellow mud was examined using a self-made spray device. Subsequently, combined with the results of the two experiments, the improvement effect of the material was comprehensively studied, and the optimal dosage of the respective material was determined. Lastly, an electron microscope was used to observe the microscopic morphology of the samples, and the improvement mechanism of each material was discussed from qualitative and quantitative perspectives. As revealed by the results, straw, starch, cement, and epoxy resin improved the shear strength and scour resistance of yellow mud. Peaks of straw, starch, and epoxy resin were found in their corresponding properties-dosage curves, corresponding to the optimal dosage in the experimental range. The corresponding performance curve of cement showed a unidirectional change, which was found with a significant improvement effect.
In order to understand the diffusion behavior of polyurethane (PU) in asphalt and the adhesion between modified asphalt and aggregate, the diffusion system of PU-modified asphalt was studied by molecular dynamics simulation software. Asphalt molecular model, PU molecular model, and PU-modified asphalt molecular model were established, respectively, and were geometrically optimized. The interface model between original asphalt molecule and aggregate, modified asphalt molecule and aggregate, PU molecule and asphalt molecule are established. The diffusion coefficient is calculated from the mean square displacement curve of asphalt and PU, so as to characterize the diffusion ability of asphalt and PU. The adhesion between modified asphalt and aggregate is characterized the interface energy between modified asphalt and aggregate. The results show that the molecular movement of the two substances is relatively active, and the micro-holes in the system structure can be filled in a short time. The interface energy between PU-modified asphalt and aggregate is more significant than that between original asphalt and aggregate. PU-modified asphalt has good diffusion ability and better adhesion with aggregate.
Elastic modulus plays a key role in the application of porous metallic materials. However, to the best of our knowledge, few attempts have been made to model the simultaneous dependence of elastic modulus on temperature and porosity for metallic materials. The present article contributes to a rational temperature-porosity-dependent elastic modulus model for metallic materials with all parameters having definite physical significance. The model can well predict the elastic moduli of porous metallic materials, from extremely low temperature to ultrahigh temperature, and from dense material to about 0.9 porosity, with reference to an easy-to-access elastic modulus. In a special case, when intrinsic elastic modulus [M] = 2 and critical porosity P
C = 1, a phenomenological parameter-free predictive model can be obtained. The model can be applied when the matrix Poisson ratio is 0.1 < v < 0.4 for Young’s modulus and 0.17 < v < 0.27 for shear modulus, which covers most metallic porous materials.
In the course of the construction of deep foundation pits during the winter in seasonally frozen areas, the pit wall soil is often unstable due to frost heave and thawing settlement, which leads to hidden safety hazards in engineering construction. Based on the analysis of the deformation data of a pile-anchor supporting a deep foundation pit in Harbin obtained from monitoring during the winter, the influence of freezing and thawing cycles was investigated. The results show that the horizontal displacement in the middle of the shallow layer of the foundation pit is significantly larger than that on both sides during the freeze–thaw cycles, and the spatial effect becomes noticeable. The stress concentration at the external corner of the foundation pit, coupled with the effects of atmospheric precipitation and freeze–thaw cycles, led to the maximum growth rate of horizontal displacement up to 1.40 mm·day ⁻¹ . The external corner effect is evident from 1 m in the shallow layer of the pit to the depth H/2 of the foundation pit. The support scheme is generally feasible, and we can appropriately enhance the support of the shallow layer of the foundation pit during the freeze–thaw cycles. For similar projects experiencing freeze–thaw cycles, the safety reserve can be appropriately enhanced when carrying out support design.
Numerous researches have been directed toward enzyme-free biosensors to alleviate the shortcomings encountered with enzymatic biosensors, in particular the intricate enzyme immobilization procedure. Herein, Co3O4/electrospun carbon nanofiber (ECNF) nanocomposites are successfully prepared to be employed as enzyme-free biosensors for diagnosis of glucose. Two parameters including the carbonization time and the amount of Cobalt(ii) acetate tetrahydrate precursor are optimized, which are 5 h and 0.5 g, respectively. The 0.5 Co3O4/ECNF-5 h nanocomposite delivers superior sensitivity (475.72 μA·mM−1·cm−2), broad linear range (2–10 mM), and detection limit (LOD) less than 1 mM (0.82 Mm). In addition, the electrode shows excellent selectivity. The chronoamperometric analysis of 0.5 Co3O4/ECNF-5 h nanocomposite is performed by adding successively glucose analyte and interfering agents to the 0.1 M sodium hydroxide solution. No significant amperometric signal to the interfering agents including uric acid, ascorbic acid, and dopamine is delivered by this electrode, testifying the great selectivity of the electrode toward the diagnosis of target analyte (glucose) in spite of the existence of interfering species. Taking the aforementioned explanations into account, it can be concluded that the Co3O4/ECNF nanocomposite can be an appropriate free-stand electrode for high-performance enzyme-free glucose biosensor.
A series of titanium dioxide (TiO2) modified with 3-aminopropyltriethoxysilane (APTES) was prepared by high-temperature calcination in an argon atmosphere in the temperature range from 800 to 1,000°C. The properties of the obtained samples were compared with those of pure TiO2 annealed under the same conditions. Examining electron paramagnetic resonance (EPR) parameters at room temperature for APTES–TiO2 showed an intense resonance line from defects related to conducting electrons with g
eff from 2.0028 to 2.0026 and 1.9052 for temperatures 800, 900, and 1,000°C, respectively, while for pure calcined TiO2, these ERP lines were not observed. With the increase in the calcination temperature to 900°C for APTES–TiO2 samples, the EPR increases linearly. This has been combined with a relatively high anatase content and small crystallites. The EPR line intensity at RT calculated for 1 g of sample showed an almost linear relationship with the photoactivity in removing ORANGE II dyes from water.
This study first tried to fabricate AA1060/Al 2 O 3 composites via the stir casting and accumulative roll bonding process. Then, the effect of nano Al 2 O 3 Vol% on mechanical, wear, and microstructural properties of these kinds of composites have been investigated. An excellent particle distribution through the aluminum matrix has been achieved after the fourth cycle. Then, mechanical properties, wear resistance, and microstructural properties have been investigated. The results showed that the strength of these composites was enhanced and the elongation of samples decreased by higher alumina Vol% contents. Also, there is a significant increase in wear resistance by increasing alumina content in the Al matrix through the stir casting process.
The flexspline (FS) of the harmonic drive (HD) is subjected to thermal load and force load during operation, leading to the deformation difference between the inner and outer surfaces of the FS. As a result, the transmission performance of the HD assembly decreases. To overcome this problem, the thermal–mechanical coupling deformation mechanism of the FS is analyzed, and then the influence of the deformation difference on the transmission accuracy of the HD is studied in this article. On this basis, the structural parameters of the wave generator are optimized to eliminate actual backlash and to improve the actual transmission accuracy. Finally, the effectiveness of the calculation method proposed in this article was proved by the prototype test.
Freeze–thaw damage and the lack of aggregate resources have become two major problems facing the construction industry. The use of recycled aggregate to produce recycled concrete has good social and economic value. In this study, the author used recycled coarse aggregate as a substitute for stone to mix recycled concrete. In order to enhance the performance of concrete, a microwave heating modification process was introduced and 0.10% volume fraction of polypropylene fiber (PPF) was added. The effect of microwave heating modification on the frost resistance of fiber-reinforced self-compacting recycled concrete was studied. The results show that with the increase in the number of freeze–thaw cycles, the degree of denudation and deterioration of the three groups of concrete surfaces becomes more and more serious, the number of surface cracks gradually increases after the concrete is damaged, and the plastic deformation becomes more and more serious, W
n gradually increases, E
n gradually increases, D
n gradually increases, σ
0 gradually decreases, ε
0 gradually increases, ε
u gradually increases, E
c gradually decreases, and μ gradually decreases. Under the same number of freeze–thaw cycles, the frost resistance of the three groups of concrete is A > C > B. Microwave heating modification improved the frost resistance of group C concrete compared to that of group B concrete. Due to the incorporation of PPF into the concrete, the load did not drop sharply when the load acting on the concrete reached the failure load. The prediction results of the established constitutive model are in good agreement with the experimental results.
The durability of concrete structures is often reduced owing to the corrosion of reinforcement in an aggressive environment. Ordinary reinforcement methods, such as wrapping section steel or steel plate, are also vulnerable to corrosion. Using 6061-T6 aluminium alloy as near-surface reinforcement of the concrete structure is a feasible method. In this study, the corrosion resistance of 6061-T6 aluminium alloy bars was studied by simulating the coastal environment, atmospheric environment, and concrete internal environment with chloride solution, simulated acid rain solution, and saturated Ca(OH)2 solution. The corrosion rate of the 6061-T6 aluminium alloy in the above environments was tested using a weight loss method, and its corrosion resistance was evaluated using the metal corrosion resistance classification standard. Based on the electrochemical reaction mechanism, the polarisation properties and AC impedance spectra of steel and 6061-T6 aluminium alloy were compared, and the corrosion resistance mechanisms of steel and the 6061-T6 aluminium alloy in the above corrosive environments were obtained. The results show that the 6061-T6 aluminium alloy has better corrosion resistance than steel bars in chloride and atmospheric environments, with corrosion currents of 0.012 and 0.037 µA·cm−2, and 8-day corrosion rates of 0.051 and 0.031 mm·a−1, respectively. However, owing to the activity of the aluminium alloy, its corrosion resistance in an alkaline environment inside concrete is poor; the corrosion current is 0.22 µA·cm−2 and the 8-day corrosion rate is 16.166 mm·a−1. The research results can provide a reference for applying aluminium alloy bars as external prestressed concrete bars and near-surface steel bars.
In the present work, manganese cobaltite (MnCo2O4) spinel (MCO) was synthetized by Pechini and hydrothermal method, characterized and photocatalytically evaluated toward H2 production through water splitting under visible-light irradiation. Characterization consisted in Thermogravimetry analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy, scattering transmission electronic microscopy, BET surface area, UV-Vis spectroscopy, cyclic voltammetry, Hall effect, and photoluminescence. The MCO were evaluated as photocatalyst using an artificial visible light lamp and monitored by gas chromatography. XRD analysis found a pure spinel phase MCO. The surface area was ∼5 m2·g−1 for the MCO synthetized by Pechini and increased to 155 m2·g−1 with the hydrothermal method with acetates as precursors. The Pechini MCO showed higher carrier mobility but the fastest recombination. Photocatalytic evaluation of the MCOs showed that the highest photocatalytic activity generated was 12 μmol H2/gcat at 8 h with the MCO obtained by hydrothermal method with the acetates.
Aluminum alloy AA2020 has a greater demand for the high strength-to-weight ratio used in applications like aerospace, naval, and automotive applications because heat treatment produces high strength. Friction stir welding (FSW) is widely employed in forming butt joints of AA2020-T4 using a square profile tool. In this work, the wear characteristics and the corrosion behavior with and without age-hardened treatment are studied and compared. In this work, the wear characteristics and the corrosion behavior with and without age-hardened treatment (after a 1-hour solution treatment of AA2020 alloy at 505°C, quenched in water at ambient temperature) are studied and compared. Age-hardened models with a high aging duration (16–20 h) at 177°C showed a reduction in wear resistance for low spindle speed in contrast to the as-FSWed joints. In the corrosion medium, long aging time heat-treated FSWed joints showed high passivity in a 3.5 wt% NaCl solution. Intergranular and pitting types of corroded surfaces in as-FSWed joints were spotted. 20 h of age-hardened FSWed joints achieved the minimal corrosion rate (CR) and is suggested for moderate wear resistance and good CR. The speed appears to have a greater impact on wear rate than the weld speed and applied load. It is also worth noting that the CR increases by 5% with the increasing spindle speed and falls by 4% with the increasing weld speed.
The failure of rock mass is mainly due to the failure of the structural plane, which is an important factor to reduce the mechanical properties and stability of rock mass. The shear strength of rock mass is one of the parameters for the stability calculation of large-scale rock mass engineering. The shear strength of a rock structural plane is strongly influenced by surface morphology. Considerable research has been conducted regarding the correlation between two-dimensional structural plane morphology and shear strength. However, quantitative research on three-dimensional (3D) morphology is relatively limited. In this study, 3D printing technology was used to create molds. Using cement and sand as the main materials, additives such as early strength and water-reducing agents were added, and test samples of irregular surface topography were created. The 3D roughness was quantified by formula calculation. Using a ZScanner® 800 hand-held 3D laser scanner to perform scanning on the structural surface, the parameter curve was analysed by generating 3D coordinate information and a 3D image of the fracture surface, and the quantitative parameter M p 3 D describing the 3D morphology of the structural surface was constructed. The change rule of R p 3 D and joint roughness coefficient (JRC) were analysed under different scanning resolutions, Δ(r), the scanning precision was suggested, and the functional relationship between JRC and M p 3 D was established. Finally, a formula for shear strength parameters considering the 3D characteristics of a structural plane surface was established. The model validation results show that the experimental data were within the 95% confidence band of the model curve, the average error of the shear strength was 10.4%, the errors of friction angle and cohesion, C, were 3.4 and 9.4%, and the reliability was fine.
Recycled rubber particles can be produced by using waste tires. Adding recycled rubber particles to concrete can form rubber concrete (RC). RC can not only reduce the amount of natural sand and reduce the cost of concrete but also improve the static compressive toughness of concrete. Adding steel fiber into RC can improve the strength of concrete. In order to study the compressive toughness of steel fiber rubber concrete (SFRC), rubber particles washed with NaOH are added to steel fiber reinforced concrete. This can enhance the bonding performance between the recycled rubber particles and concrete. The volume ratio of recycled rubber is 5, 10, and 15%. Prismatic and cubic test blocks were prepared and their compressive tests were carried out. The results show that the stress interaction between the rubber particles and steel fiber in concrete significantly improves the compressive strength, elastic modulus, and stress–strain relationship of concrete. The compressive toughness and ductility of concrete are improved. When the content of rubber particles is 15–20%, the compressive toughness of SFRC is improved most obviously. Through experiments, the toughness index and specific toughness of rubber steel fiber reinforced concrete are calculated, which explores a new way and method for studying the compressive toughness of similar recycled material concrete.
Marine concrete is a kind of construction material which is seeking its growing application in marine engineering. However, the marine concrete structures are exposed to aggressive environment and harmful ions. Therefore, it is crucial to improve the durability of marine concrete. The concrete structure located in the tidal zone is subjected to the dry–wet cycles caused by tidal action, chloride ion (Cl ⁻ ) erosion in seawater, and CO 2 erosion in air. When these factors work together, they cause great damage to the marine concrete structure. In view of the three environmental factors, namely, Cl ⁻ erosion, carbonation, and dry–wet cycles, taking fly ash, fibers, and nanomaterials as examples, this article expounds the research status of durability of marine concrete, introduces the latest research progress, the addition of fibers, fly ash, and nanomaterials can improve the Cl ⁻ corrosion resistance and dry–wet cycles resistance of marine concrete, while the addition of fly ash is unfavorable for carbonation resistance. And the future development trend of marine concrete is prospected.
Rubber material is widely used in railway vehicles due to its superior damping performance. The testing methods, fatigue, and aging theories of rubber materials are of great significance to improve the design, manufacture, and application of rubber components for railway vehicles. This work systematically introduces the constitutive theory, mechanical testing standards, and testing methods of rubber materials. Then, the aging mechanism is described and the research progress of rubber fatigue properties is reviewed from the perspectives of fatigue crack initiation and fatigue crack propagation. Moreover, the reinforcement methods of rubber materials are presented. Finally, according to the working conditions of rubber components in railway vehicle, the technical difficulties and future research trends of fatigue characteristics analysis of rubber materials and components are pointed out.
The holes and defects in rock materials have a great impact on the mechanical properties and failure mechanism of rock, cracks often appear in the form of flat ellipses in natural rock mass, and the current research is still insufficient. For this purpose, based on the Particle Flow Code (PFC) of discrete element particle flow program, the numerical prefabricated fractured rock samples with the ratios of the long and short axes of the elliptical fractures being 5, 7.5, 10, 12.5, and 15 were simulated in order to obtain the strength and failure characteristics, stress concentration characteristics at tips of numerical rock samples in uniaxial compression test. The results of the numerical test simulation show that: (1) When the rock models with prefabricated elliptical crack were damaged, the initial cracks occurred at the end of the short axis of the elliptical crack, and penetrated up and down from the surface of the elliptical crack, the wing cracks occurred at both ends of the long axis, gradually formed a macro-crack, and the secondary cracks extended near the wing crack. (2) With the increase of the ratios a:b of long and short axes of the elliptical fracture, the strength and elastic modulus of the numerical rock samples gradually decreased, Poisson’s ratio gradually increased, and the total number of micro-cracks in the rock models decreased. (3) The numerical solutions of stress concentration factor k obtained by numerical simulations at the tip of the elliptical crack increased with the increase in the ratio of a:b; it was highly consistent with the variation law of the analytical solution of the stress concentration factor calculated by the theory of flat ellipse. The stress concentration is an important reason for failure of rock with elliptical cracks. Study on the crack tip will be very useful and significant.
Rice husk is considered as a waste product of farming. However, rice husk ash (RHA) has a good pozzolanic activity, which can be used in cement-based materials as a supplementary cementitious material (SCM), and it is also suitable for self-compacting concrete (SCC). This study reviews the physical and chemical properties of RHA and the properties of RHA–SCC mixtures such as fresh properties (crucial factors and evaluation methods of workability for fresh SCC), mechanical properties (compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity), and durability (water absorption and sorptivity, acid resistance, chloride penetration resistance, electrical resistivity, and alkali silica reaction). It was observed that the workability of SCC decreases with an increase in the incorporation rate of RHA. An incorporation rate of RHA in the range of approximately 15–20% enhances the mechanical properties and durability of SCC. The incorporation of RHA into SCC can reduce the environmental burden of rice husk treatment, and promote sustainable development of cement industries and reduce the cost of SCC.
Graphene oxide (GO) has been widely used to enhance the tensile/compressive strength of cement-based materials, whereas its shear reinforcing effect is still unknown. To verify the feasibility of GO as a shear reinforcement material, the shear reinforcing effect of GO on cement was experimentally investigated. The nanoscale Young’s modulus (E) of the GO-enhanced cement was measured with the peak force quantitative nanomechanical mapping method to clarify the enhancing mechanism. Results show that the addition of 0.02 and 0.04 wt% GO in cement could improve the shear strength by about 12 and 40%, respectively, which is mainly due to the enhanced cohesion, and at the nanoscale, the average E of the low-density hydration product increased by 1.6 and 13.2%, whereas that of high-density hydration product remains almost unchanged. There exist fewer nanoholes/cracks and unhydrated cement grains but more the high-density hydration product in GO-enhanced cement, implying a denser microstructure and higher hydration degree. GO can enhance the shear strength of cement because of its enhancing effects on the microstructure, nanoscale Young’s modulus of hydration products, as well as the hydration degree.
Aiming at the present situation that the effect of excitation type on typical ship grillage structure vibration is not fully revealed, different excitations are applied on typical ship grillage structure to study the effect of different excitation. Finite element method (FEM) is introduced to solve grillage vibration and sound radiation, and a test model is used to verify the effectiveness of the simulation method by comparing test results and simulation results. Mean square vibration velocity and acoustic power are compared to explore the effect of excitation type on grillage vibration. The research shows that the simulation method (FEM) is effective in grillage vibration and sound radiation; the peak frequency of acoustic power and mean square velocity of grillage structure under different excitation are basically the same; uniform distribution excitation is a better way to reduce structure vibration and noise.
Nano-modified multimodal and conventional Cr 3 C 2 –NiCr coatings were fabricated by high-velocity oxygen-fuel spraying deposited on CuCrZr substrates. Results showed that individual nano-modified multimodal Cr 3 C 2 –NiCr particles were composed of nano (25−180 nm), submicron (200 nm to 0.5 μm), and micron (2–4.5 μm) Cr 3 C 2 grains, NiCr binder phases, and a tiny amount of rare earth oxide additives. The nano-modified multimodal Cr 3 C 2 –NiCr coatings maintained a unique structure: submicron Cr 3 C 2 grains embedded in the voids formed by micron Cr 3 C 2 grains, NiCr binder phases and nano Cr 3 C 2 grains imbedded in the voids formed by submicron and micron Cr 3 C 2 grains, and nano Cr 3 C 2 grains are dispersed in NiCr metal binder phases. A few discontinuous elongated amorphous and nanocrystalline phases existed in them. The mechanical interlocking was the dominant bonding mechanism accompanied by local metallurgical bonds. Compared to the conventional coating, the multimodal coating was uniform and dense (porosity was 0.3 ± 0.12%) as well as not obvious lamellar structures, the adhesive strength was 75.32 ± 1.21 MPa, exhibiting a 65 pct increase, and the microhardness was increased by about 18%. The lower porosity and higher strength of nano-modified multimodal structure coating were mainly related to dispersion distribution and synergistic coupling effects of Cr 3 C 2 hard grains with different scales.