نگهداری فضاهای زیرزمینی یکی از مهمترین مقولههای مهندسی معدن و عمران است که کابلهای کششی بهعنوان یکی از رایجترین ابزارهای نگهداری در این فضاها بهکار میروند. در این پژوهش، در محیطی پیوسته، با استفاده از نرمافزار FLAC3D، الگوهای مختلف کابل کششی شامل آرایشهای مرسوم، کوتاه–بلند، و پیچشی در شرایط تودهسنگ بسیار ضعیف مدلسازی شده تا اثر آنها بر پایداری تونل بررسی شود. هدف این مطالعه، تعیین الگوی بهینه کابل کششی برای کاهش مصرف مصالح و دستیابی به حداکثر پایداری است. نتایج نشان داد که الگوی کوتاه–بلند با طولهای 5 و 5/7 متر و فاصلهگذاری 5/1 × 2/2 متر، جابجایی تونل را از 7 سانتیمتر (حد مجاز ساکورایی) به 5/5 سانتیمتر کاهش میدهد. همچنین، این الگو مصرف کابل کششی را تا 10 درصد (معادل 175 متر در 28 متر طول تونل) نسبت به الگوی مرسوم کاهش داد. الگوی پیچشی با طول 5/7 متر نیز کمترین جابجایی (5/3 سانتیمتر) را به همراه داشت، اما الگوی کوتاه-بلند به دلیل سهولت اجرا و صرفهجویی اقتصادی بهعنوان الگوی بهینه پیشنهاد شد.
After being self-ion implanted at 400 °C and 550 °C, the microstructure and irradiation hardness of kilogram-scale V-4Cr-4Ti alloys were studied using a transmission electron microscope (TEM) and nano-indentation test technology. Irradiation was performed using self-ions (V<sup>2+</sup>) at 2.5 MeV with design influences of 1.15 × 10<sup>15</sup> ions cm<sup>−2</sup>, 4.59 × 10<sup>15</sup> ions cm<sup>−2</sup>, and 9.17 × 10<sup>15</sup> ions cm<sup>−2</sup>, so that the peak damages of V-4Cr-4Ti alloys are 1, 4, and 8 dpa, respectively. Compared with the 400 °C samples, the 550 °C samples exhibited a higher-density number of dislocation loops and increased hardness and reached saturation at lower irradiation doses. The irradiation temperature was mainly responsible for these differences, and the potential mechanism for its effect on the irradiation behavior was discussed.
The economic viability of open-pit mining declines as open-pit mines deepen because of the rising costs. To extract the deep portion of the mineral reserves, the costs in open-pit mining should be reduced, or open-pit mining should be switched to underground mining. One of the important challenges for transitioning from open-pit to underground mining is determining the Optimal Transition Depth. In this paper, a scenario-based model without the limitations of previous models is presented to determine the Optimal Transition Depth. Given that the nature of the transition problem is production planning, price and operating cost uncertainties effectively determine the Optimal Transition Depth. In this study, the pyramid method is used to simultaneously quantify price and operating cost uncertainty. The Choghart iron mine is used as a case study to evaluate the proposed model. The optimal transition depth and transition zone for this mine have been calculated in a 3D block model using the proposed method. Unlike previous scenario-based models, the suggested model considers all transmission depth options. Using the proposed model, the optimal transition depth in the Choghart mine is 26 m above the ultimate pit limit. The transition from open-pit to underground at the Optimal Transition Depth obtained increases 2.06% of the net present value (NPV) of the mine compared to the initial state. Additionally, a sensitivity analysis was conducted for four parameters: Base price, base costs, annual discount rate, and price volatility. The results show that the base price is the most influential parameter on the value of NPV at the optimal depth of transition, while the price volatility parameter exhibits a non-linear relationship with the value of NPV.
Lead Zirconium Titanate (PZT) is a potential piezoelectric material for sensor and transducer applications due to its outstanding piezoelectric coupling near the morphotropic phase boundary (MPB). This is because PZT can switch between tetragonal and rhombohedral phases. PZT is still considered to be one of the piezoelectric materials that has received the greatest amount of attention from researchers and is used the most frequently. Modification with Lithium will improve the piezoelectric properties. In this study, the structural properties and morphological studies of Lead zirconium titanate and Lead zirconium titanate with Lithium modification have been evaluated. Various Scherrer’s models and other models, such as the Williamson-Hall model and Size-strain plots model, were used to display the observed fluctuations in crystallite size. Morphological analysis was used to determine the particle size. Graphs showing the distribution of particle sizes were drawn.
Mining engineering. Metallurgy, Materials of engineering and construction. Mechanics of materials
This is an article in the field of mineral materials.While titanate coupling agent JN-114 and aluminate coupling agent DL-411 were used as modifiers, the surface of heavy calcium carbonate was modified by dry method. The effect of surface modification on heavy calcium carbonate was studied by means of activation index and contact angle. The mechanism of surface modification was analyzed with infrared spectrum analysis, and its filled PP composite was studied. The results show that the best modification process of JN-114 is as follows: reagent dosage 1.0%, modification temperature 70 ℃, modification time 30 min, modified heavy calcium carbonate activation index 99.21%, contact angle 114.34°. DL-411 modification best process: reagent dosage 1.0%, modification temperature 90 ℃, modification time 30 min, modified heavy calcium carbonate activation index 100.00%, contact angle 121.70°. Infrared spectrum analysis showed that JN-114 and DL-411 both acted on the surface of heavy calcium carbonate by chemical adsorption，heavy calcium carbonate changed fromhydrophobicity into hydrophobicity. The surface modification of JN-114 and DL-411 can effectively improve the impact strength of PP composite. When the modified heavy calcium carbonate filling content is 20%, the impact strength of the composite reaches the best, which is 38.87% and 41.97% higher than that of pure PP, respectively.
This paper presents a novel rock engineering system (RES) based method for estimating blast-induced vibration attenuation risk index and predicting peak particle velocity (PPV). The RES approach involves three key steps, which are the identification of influencing parameters, the construction of an interaction matrix and the rating of parameters based on their influence on ground vibration. The selected parameters are the scale distance (SD), the ratio of the scale distance to stemming divided by the burden (SD/TB), the distance of the monitoring station (D), the scale distance divided by the burden (SD/B), the ratio of the scale distance to powder factor (SD/PF) and the ratio of scale distance to spacing divided by the burden (SD/SB). The results indicated that all the six parameters considered have statistically significant influences on the constructed interaction matrix system, with the SD having the highest weighty factor (21.43%) while SD/TB is the lowest (14.29%). The maximum rating of the parameters is 5, 5, 4, 5, 5, 4 for SD, D, SD/B, SD/PF, SD/SB and SD/TB, respectively. The attenuation risk index ranges from 14.29 to 63.43, and the slope of the actual measured PPV against the calculated attenuation risk index is negative. The developed RES-based model demonstrated better performance and a reliable method for ground vibrations prediction with a higher degree of accuracy, considering its higher determination coefficient (R2 = 0.96) and smaller error (RMSE = 1.08, MAD = 0.79, MAPE = 9.95) compared to multiple regression, Langefors & Kihlstrom and Hudaverdi models.
This investigation aims to improve the ductility of ultrahigh strength (>2 GPa) press hardening steels (PHS) by exploiting the heterogeneous carbon distribution in lath martensite. The proposed strategy is demonstrated in a medium carbon PHS with a lath martensite microstructure produced by quenching austenite. It is found that by enhancing auto-tempering, the solute carbon content in the coarse laths formed earlier during martensitic transformation can be reduced, leading to the softening and ductilizing of these laths. The softened coarse laths of small volume fraction provide significant improvement in the post-uniform elongation (PUE) without compromising the ultrahigh strength of lath martensite. The remarkable improvement in the PUE of ultrastrong lath martensite achieved by exploiting heterogeneous carbon distribution is expected to be instructive for the development of ultrahigh strength PHS with good ductility and fracture toughness.
The main antioxidant compounds contained in cocoa are polyphenols, including flavonoids such as epicatechin, catechin, and procyanidin. This study aims to determine the antioxidant activity of three samples of cocoa powder using 1,1-diphenyl-2-picrylhydrazyl (DPPH) as a free radical by electroanalytical methods, namely cyclic voltammetry (CV) and differential pulse voltammetry (DPV). From the CV information obtained, the first anodic peak from DPPH appears at a potential of 0.33 V with an anodic current of 2.75 A/cm2, while the first anodic peak at DPPH after adding the chocolate sample which has the highest antioxidant activity appears at a potential of 0.43 V with an anodic current of 4.60 A/cm2. From the DPV information obtained, the anodic peak of DPPH appears at a potential of 0.19 V at an anodic current of 2.11 mA, while the anodic peak at DPPH after adding the chocolate sample which has the highest antioxidant activity appears at a potential of 0.02 V at an anodic current of 1.97 mA. The results show that the electroanalytical method has the potential to analyze the antioxidant activity of cocoa powder samples.
Viktor Alekseevich Kukartsev, Aleksandr Ivanovich Cherepanov, Vladislav Viktorovich Kukartsev
et al.
The efficiency of the production of foundry products depends on the reliable operation of the melting furnace including, therefore, the durability of its lining. The most common material adopted for the production of an acid furnace crucible lining is quartzite, in which during the pretreatment (heating to 800 °C followed by holding), a tridymite phase appears that maintains a constant volume at 840–1470 °C for a long time and provides high lining durability of 300–350 melts, but only when using melting temperature regimes not exceeding 1500 °C. However, the absence of iron scrap leads to the smelting of synthetic iron from only one steel scrap using higher melting temperatures (1550–1570 °C), which sharply reduces the lifetime of the lining to 220 melts. This work is devoted to research aimed at establishing technology for the pretreatment with the original quartzite, which ensures the formation of a phase state that successfully withstands elevated temperatures for a long time. The studies were carried out using a Bruker D8 ADVANCE diffractometer and a Shimadzu XRF-1800 X-ray wave-dispersive spectrometer. The work consisted of drying samples of the original quartzite at temperatures of 200 and 800 °C with subsequent exposure to temperatures of 200, 400, 600, 870, 1000, 1200, 1470 and 1550 °C. As a result, the conditions for pretreatment of quartzite were established, during which during its further use, a cristobalite phase can be obtained, which makes it possible manufacture a high-temperature lining that ensures its high durability. The introduction of this technology will ensure the efficiency of the production of foundry products for enterprises operating induction crucible furnaces at industrial frequency.
The influence of stress-controlled fatigue (SCF) damage on the fracture location shifting of welded joints for NiCrMoV steels in the corrosive solution of 3.5wt.% NaCl is systematically investigated by electrochemical measurements, immersion tests, slow strain rate tensile (SSRT) tests, and fractural morphology observations in the present work. The results show that both the yield strength (YS) and the ultimate tensile strength (UTS) of welded joints are increased after the SCF tests. The susceptibility of stress corrosion cracking (SCC) and galvanic corrosion of the SCF damaged welded joints are higher than that of the as-received specimens. In addition, the fracture locations of welded joints after SSRT tests in the corrosive solution are shifted with the degree of SCF damage. Different degrees of fatigue damage are accumulated in the three zones of welded joints during the cyclic deformation, which could change the competitive relation of the most susceptive SCC zone between the fusion zone and the middle of WM.
Dmitry Valeev, Andrei Shoppert, Alexandra Mikhailova
et al.
Sandy grade alumina is a valuable intermediate material that is mainly produced by the Bayer process and used for manufacturing primary metallic aluminum. Coal fly ash is generated in coal-fired power plants as a by-product of coal combustion that consists of submicron ash particles and is considered to be a potentially hazardous technogenic waste. The present paper demonstrates that the Al-chloride solution obtained by leaching coal fly ash can be further processed to obtain sandy grade alumina, which is essentially suitable for metallic aluminum production. The novel process developed in the present study involves the production of amorphous alumina via the calcination of aluminium chloride hexahydrate obtained by salting-out from acid Al-Cl liquor. Following this, alkaline treatment with further Al<sub>2</sub>O<sub>3</sub> dissolution and recrystallization as Al(OH)<sub>3</sub> particles is applied, and a final calcination step is employed to obtain sandy grade alumina with minimum impurities. The process does not require high-pressure equipment and reutilizes the alkaline liquor and gibbsite particles from the Bayer process, which allows the sandy grade alumina production costs to be to significantly reduced. The present article also discusses the main technological parameters of the acid treatment and the amounts of major impurities in the sandy grade alumina obtained by the different (acid and acid-alkali) methods.
Antonio Rubio-Mateos, Asuncion Rivero, Eneko Ukar
et al.
In finishing processes, the quality of aluminum parts is mostly influenced by static and dynamic phenomena. Different solutions have been studied toward a stable milling process attainment. However, the improvements obtained with the tuning of process parameters are limited by the system stiffness and external dampers devices interfere with the machining process. To deal with this challenge, this work analyzes the suitability of elastomer layers as passive damping elements directly located under the part to be machined. Thus, exploiting the sealing properties of nitrile butadiene rubber (NBR), a suitable flexible vacuum fixture is developed, enabling a proper implementation in the manufacturing process. Two different compounds are characterized under axial compression and under finishing operations. The compression tests present the effect of the feed rate and the strain accumulative effect in the fixture compressive behavior. Despite the higher strain variability of the softer rubber, different milling process parameters, such as the tool feed rate, can lead to a similar compressive behavior of the fixture regardless the elastomer hardness. On the other hand, the characterization of these flexible fixtures is completed over AA2024 floor milling of rigid parts and compared with the use of a rigid part clamping. These results show that, as the cutting speed and the feed rate increases, due to the strain evolution of the rubber, the part quality obtained tend to equalize between the flexible and the rigid clamping of the workpiece. Due to the versatility of the NBR for clamping different part geometries without new fixture redesigns, this leads to a competitive advantage of these flexible solutions against the classic rigid vacuum fixtures. Finally, a model to predict the grooving forces with a bull-nose end mill regardless of the stiffness of the part support is proposed and validated for the working range.
Sung Woo Park, Hyunjong Lee, Byung Hoon Lee
et al.
Active brazing of zirconia with metallic alloys is a promising method for enhancing the mechanical property of zirconia. However, the brazing process of zirconia and metallic alloys has not been studied in detail because of a limitation in selection of materials and processing conditions. Here, we successfully brazed zirconia with Ti-3Al-2.5V alloy using amorphous Zr<sub>54</sub>Ti<sub>22</sub>Ni<sub>16</sub>Cu<sub>8</sub> active filler alloy. By manipulating the brazing temperature from 800 °C to 860 °C, a highest strength of ~186 MPa was achieved at 860 °C. Reduced brittle (Zr,Ti)<sub>2</sub>(Ni,Cu) intermetallic phases from formation of island-type (Zr,Ti) matrix, ZrO<sub>2-X</sub>, TiO, and TiO<sub>2</sub> interlayer play a key role in increasing the joint strength. Our findings will be helpful in developing brazing processes for zirconia and metallic alloys.
In the system Au(III)-HCl-A324H<sup>+</sup>Cl<sup>−</sup>, liquid-liquid extraction experiments were used to define the extraction equilibrium and the corresponding extraction constant; furthermore, the facilitated transport of this precious metal from HCl solutions across a flat-sheet supported liquid membrane was investigated using the same ionic liquid as a carrier, and as a function of different variables: hydrodynamic conditions, concentration of gold(III) (0.01−0.1 g/L), and HCl (0.5−6 M) in the feed phase, and carrier concentration (0.023−0.92 M) in the membrane. An uphill transport equation was derived considering aqueous feed boundary layer diffusion and membrane diffusion as controlling steps. The aqueous diffusional resistance (Δ<sub>f</sub>) and the membrane diffusional resistance (Δ<sub>m</sub>) were estimated from the proposed equation with values of 241 s/cm and 9730 s/cm, respectively. The performance of the present carrier was compared against results yielded by other ionic liquids, and the influence that other metals had on gold(III) transport from both binary or quaternary solutions was also investigated. Gold was finally recovered from receiving solutions as zero valent gold nanoparticles.