Lattice structures are widely used in the aerospace and biomedical fields, due to their lightweight, high specific strength, large specific surface area, good biocompatibility, etc. However, the balancing of the weight and the mechanical properties remains a challenge in designing lattice structures. Combining experiments and simulations, the present work first designs and evaluates the mechanical properties of uniform and gradient topology-optimized Ti-6Al-4V lattices with the same overall porosity of 84.27%, employing finite element simulations. Then, laser powder bed fusion technology is used to fabricate the uniform and gradient Ti-6Al-4V lattices, and their compressive performance is tested. The results indicate that, under longitudinal compression, the gradient lattice structure exhibits good layer-by-layer collapse deformation behavior, achieving better comprehensive performance than the uniform lattice structure. While under horizontal compression, the deformation behavior of the gradient lattice structure is similar to that of the uniform lattice structure, and the deformation is mostly randomly distributed. The cumulative energy absorption of the gradient lattice structure increased by approximately 20% compared with that of the uniform lattice structure. The results provide a technical basis for the integrated design of structural and functional components for aerospace applications.
This study established a thermal-mechanical coupling numerical simulation model for linear friction welding of GH4169 superalloy blisks using ABAQUS/Explicit and FRANC3D. A systematic analysis was conducted of the evolution laws of the temperature and residual stress fields under different process parameters during the welding process. Additionally, the effect of crack parameters on crack propagation and fatigue life under multi-axial loading was simulated. The results show that the peak temperature at the center of the friction interface is approximately 1300 °C. The stress distribution within the joint demonstrates periodic fluctuations. Axially, the friction interface experiences the maximum compressive stress. The crack parameters had a substantial effect on crack propagation characteristics. As the initial crack size increases from 0.6 mm to 1.0 mm, there is a concomitant 40.4 % reduction in fatigue life, from 75,089 cycles to 44,767 cycles. Moreover, crack propagation is highly sensitive to the crack orientation. As the crack width increases from 0.375 mm to 1 mm, the fatigue life decreased by approximately 28.2 %.
AbstractSemi-mobile in-pit crushing and conveying (IPCC) systems can help reduce truck haulage in open-pit mines by bringing the crusher closer to the excavation areas. Optimizing a production schedule with semi-mobile IPCC requires integrating extraction sequence, destination policy, crusher relocation, conveyor layout, and truck fleet investment decisions. A mining complex with multiple mines and IPCC systems should be optimized simultaneously to find an optimal schedule for the entire value chain. An integrated stochastic optimization framework is proposed to produce long-term production schedules for mining complexes using multiple semi-mobile IPCC systems. The optimization model has flexibility to select the crusher locations and conveyor routes from anywhere inside the pits. The framework uses simulated orebody realizations to consider multi-element grade uncertainty and manage associated risk. A hybrid metaheuristic solution approach based on simulated annealing and evolutionary algorithms is implemented. The method is demonstrated using an iron ore mining complex.
The acceleration of the energy transition is driven by current geopolitical conflicts and climate and environmental challenges. It is crucial for China to construct a new energy system adapting to these changing circumstances for the sustainability, security, and stability of the energy supply system. At present, fossil fuels still dominate the China’s energy demand. There are energy security issues due to lacking oil and gas resources, and new energy technologies. China will still maintain a high dependence on coal energy in short term, consequently, prompting the clean and efficient conversion of coal is vital for developing a new energy system. In this paper, the specific connotations and develop direction of the new energy system are identified, and then the development status, opportunities and challenges of the China’s coal chemical industry in the new era are presented, also the suggestions for improving the technology of clean and efficient coal conversion and the future development of coal chemical industry are put forward. The new era has endowed the new energy system with more connotations, that is the future energy system should be characterized by “safe and efficient, clean and low-carbon, diverse and synergistic, and intelligent and accessible”. In addition, the new era will put forward higher requirements for the clean and efficient development of the coal industry.Although China has made significant achievements in the clean and efficient conversion of coal, the key technologies still need some breakthroughs.Combining the systematic understanding of the relationship between the transformation and development of the coal industry and the “dual carbon” goals, and in the context of the construction of a new energy system, the promotion of clean and efficient coal conversion is of great significance for social and economic development and helping to achieve the “dual carbon” goals. The key lies in strengthening the basic research of relevant disciplines and specialties in this field, as well as the innovative development of clean and efficient coal conversion technologies.
The application of lightweight and high-strength Al alloys are crucial to reduce energy consumption and emissions in today's world. The lightweight and high strength 7 series aluminum alloy is widely used in aerospace, but its poor welding performance has been a bottleneck restricting the further lightweight of structural parts. In this work, a lightweight and high-strength Al joint with a tensile strength of ∼400 MPa was successfully prepared by single mode laser beam welding using non-weldable 7075 aluminum alloy as the experimental mode. The superfine laser beam reduces the volume of molten pool and increases the solidification rate of molten pool, which significantly inhibits the growth behavior of each microstructure, thus refining the microstructure. The geometrically necessary dislocations (GND) density of each microstructure of 7075 joint after tensile test was: 1.32 × 1014 m−1 for EZ, 1.21 × 1014 m−1 for CLZ, HAZ is 1.17 × 1014 m−1 for HAZ. The synergistic effect of heterogeneous microstructure and work hardening enhanced the tensile strength of 7075 joint. Furthermore, TEM, FIB and EBSD were used to characterize the fracture behavior of the 7075 joint in detail. TEM images showed that the discordant interface between α-Al grain boundary and SiO2 particle was the potential source of crack initiation. The microstructure refinement design and technical selection strategy of the work provide a new insight for laser welding of lightweight and high strength 2xxx/7xxx aluminum alloy.
In order to solve the problems that restrict the efficient development of coalbed methane resources under the conditions of soft and low permeability outburst coal seams in Huainan Mining Area, such as complex coal seam structure, multi-source gas emission, rapid decline of drainage flow, high rock roadway and drilling costs, and low (ultra-low) concentration coalbed methane utilization rate, six key technologies suitable for the coordinated development mode of coal and coalbed methane under the condition of coal seam group mining in Huainan mining area are put forward, namely: coalbed methane extraction technology of ground level staged fracturing wells, shield rapid construction technology of coalbed methane extraction roadways, enhanced extraction technology of underground soft coalbed methane, coalbed methane extraction technology of pressure relief in ground mining area, the construction technology of "replacing roadways with holes", and cascade utilization technology of low concentration coalbed methane. The application of supporting key technologies shows that staged fracturing technology and refined drainage and production technology of roof horizontal wells in broken and soft coal seam have effectively improved the pre pumping production of coalbed methane; The full face hard rock roadheader in deep coal mine roadway greatly improves the roadway excavation efficiency, realizing the automation and less humanization of hard rock excavation; Sand adding of hydraulic fracturing and ultra-high hydraulic slotting have realized pressure relief and permeability enhancement in large areas underground coal mine; Type III and IV surface mining area wells can replace the roof high drainage roadway in the treatment of pressure relief gas in coal seam group mining, and reduce the coalbed methane drainage intensity of other measures; The technology of "replacing roadways with holes" has significantly improved the quality of successful directional drilling at middle and high levels in complex roof; Cascade utilization technology of low concentration coalbed methane has greatly reduced the emission of coalbed methane. The six key technologies have guaranteed the safe production in Huainan mining area, and comprehensively improved the output of coal and coalbed methane and the utilization level of coalbed methane. Six key technologies ensure the safe production in Huainan mining area, and comprehensively improved the output of coal and coalbed methane and the utilization level of coalbed methane. Finally, in view of the problems such as high operation cost, low production, small scope of hydraulic fracturing coal reservoir reconstruction technology for surface horizontal wells, and the risk of breakage of mining wells, and small scale of cascade utilization of ultra-low concentration coalbed methane, the development direction of deep CBM precise geological guidance, super large scale efficient reservoir volume transformation, pumping effect evaluation technology, stable and continuous pumping technology of surface wells in mining areas, underground large area intelligent hydraulic enhanced permeability technology, "one well with multiple uses" collaborative pumping CBM technology, and full concentration CBM comprehensive utilization technology are proposed.
In order to modify the room-temperature plasticity of TiAl-based alloy, grain boundary character distribution (GBCD) in TiAl-based alloy was tuned through multidirectional isothermal forging (MDIF) combined with annealing. The experimental results showed that MDIF provided appropriate driving force for the regeneration of the coincidence site lattice (CSL) boundaries through recovery and recrystallization process. Combination of MDIF and annealing at 1100 °C for 90 min promoted the formation of a large number of annealing twins and increased the fraction of low-ΣCSL boundaries to 65.88% and the ratio of (Σ9+Σ27)/Σ3 to 15.12%, which contributed to the disruption of random boundary networks and enhanced the room-temperature plasticity of the TiAl-based alloy.
T.L. Ajeesha, Ayyar Manikandan, Ashwini Anantharaman
et al.
Magnetic and optical properties of copper doped spinel calcium ferrite (Ca1-xCuxFe2O4; x = 0, 0.2, 0.4, 0.6, 0.8, 1) nanoparticles (NPs) have fascinated the attention of researchers. Spinel Ca1-xCuxFe2O4 NPs were prepared by co-precipiation technique. The as prepared compositions were subjected to structural, magnetic, electrical and optical properties. Cubic spinel phase was observed through powder X-ray diffraction (PXRD) studies and the lattice constant increased with increase in calcium concentration and the average crystallite size in the range 32–19 nm. Transmission Electron microscope (TEM) technique provided information on the morphology of the synthesized ferrites. FT-IR spectral bands observed at 579, 480 and 514 cm−1 confirmed the M−O vibration for Ca–O, Fe–O and Cu–O bands responsible for the formation of spinel. Magnetization, coercivity and retentivity were calculated from vibrating sample magnetometer (VSM) studies. Hysteresis loops revealed the magnetic behavior of the prepared Ca1-xCuxFe2O4 NPs. The adsorption and desorption measurement were achieved from Brunauer–Emmett–Teller (BET) analysis. Band gap of the prepared spinel ferrites were found to be 1.8–2.5 eV revealing semiconducting behaviour of the nanocatalysts. Frequency dependent dielectric studies revealed that at high frequency both dielectric constant and dielectric loss were decreased. The photocatalytic degradation (PCD) of the synthesized spinel ferrites with methylene blue (MB) as organic pollutant and their antibacterial activity was also studied. Ca0.2Cu0.8Fe2O4 (CCFO-5) nanocatalyst exhibited 96% degradation in 180 min with methylene blue dye.
Mihaela Botea, Ioana Pintilie, Vasile-Adrian Surdu
et al.
Graded structures with different architectures were obtained by spark plasma sintering from (Ba1-xSrx)TiO3 (BST, x = 0.10; 0.20; 0.30) powders. The presence of the composition gradient was confirmed by structural and compositional investigations using X-ray diffraction and electron microscopy combined with energy dispersive X-ray spectroscopy. The concentration gradient was either asymmetric (3 layers, starting with x = 0.10 and ending with x = 0.30) or symmetric (5 or 6 layers, starting and ending with x = 0.10, and with a single or double x = 0.30 layer in the middle, respectively). Electrical measurements reveal a decrease of the dielectric constant with increasing the number of the layers. It was found that the symmetric graded structure with 6 layers has the best thermal stability of both, the dielectric constant (variation of only 8% between zero and 100 °C) and the pyroelectric coefficient (6% variation between zero and 80 °C). In addition, an enhancement of the pyroelectric signal for frequencies above 100 Hz is obtained in symmetric structures, an effect that is attributed to the additive contributions of the signals originated from the layers with different Sr content.
In view of the problems of large dip angle of coal seam and soft broken coal seam of 32# coal seam in the construction of long borehole along the coal seam in the 313 working face of Qinan Coal Mine, using double power head rig and auxiliary drilling tools, the research on drill pipe and casing double pipe directional drilling technology is carried out; through the selection of key equipment, selection of drill pipe and drill pipe bit, selection of casing and casing bit, optimization of pneumatic directional drilling process parameters, and the proposed drilling pipe in the casing of large diameter screen hole protection methods and tests, all theses effectively improve the depth of drilling along the coal seam, realize the control of the long drilling path along the coal seam, and improve the adaptability of the formation.
When using near-infrared reflectance spectrum to identify coal gangue, the change of detection distance between spectrum acquisition device and working face and dust interference will affect near-infrared reflectance spectrum. In order to select the best pre-processing method for near infrared reflectance spectrum for coal gangue, samples of anthracite and gangue with similar appearance are collected. A spectrum acquisition device consisting of near infrared spectrometer, collimator and halogen lamp is set up in the laboratory to acquire near infrared reflectance spectrum of coal gangue at different detection distances (1.2,1.5,1.8 m) and dust concentrations (200, 500, 800 mg/m3). Through the analysis of near-infrared reflectance spectrum characteristics of coal gangue, it is found that the detection distance and dust concentration change have no obvious impact on the waveform of near-infrared reflectance spectrum curve and the position of absorption valley of coal gangue. The absorption wavelength point of spectral characteristics will not be changed. However, the reflectance of near-infrared reflectance spectrum of coal gangue will be significantly affected. The spectral reflectance will decrease with the increase of detection distance and dust concentration, which will cause near-infrared reflectance spectrum drift of coal gangue. In order to enhance the absorption characteristics of near-infrared reflectance spectrum of coal gangue, the spectrum data are preprocessed by differential, standard normal variable transformation and polynomial smoothing methods. The preprocessed near-infrared reflectance spectrum data of coal gangue are input to the particle swarm optimization BP neural network model for coal gangue identification. The experimental results show that the differential preprocessing method has the best optimization effect on the near-infrared reflectance spectrum data of coal gangue collected under the change of detection distance and dust concentration, and can eliminate the impact of detection distance and dust concentration on the spectral reflectance effectively.
In order to deeply understand the influence of driving position of vibrating flip-flow screen on motion characteristic of main and floating screen frame, mechanical model and vibration differential equation of the vibrating flip-flow screen were established with consideration of the effect of damping.The formulas of amplitude and phase of main and floating screen frame were derived using complex number method under different forms, and the method of determining phase through quadrant was also proposed based on practical problems in Engineering.In addition, the feasibility of vibrating flip-flow screen driven by floating screen frame was also analyzed theoretically.The motion characteristics of main and floating screen frame of vibrating flip-flow screen driven by main screen frame and driven by floating screen frame were compared under the condition that only position of vibration exciter was changed while the first natural frequency and the second natural frequency remain unchanged.Eventually, characteristics of the floating driving flip-flow screen were obtained, such as, low resonance frequency, wide frequency modulation area and large amplitude of main and floating screen frame.
For optimizing control of ore preparation processes, a complex criterion “yield of productive class −2... +10 mm” adapted to the conditions of closed cycle crushing – screening was proposed, which reflects the efficiency of all the processes as a whole. The established dependences of yields of individual ore grain-size fractions and the proposed optimization criterion on the parameters of the crushing process show their relationship with energy intensity of the process. It was shown that increasing load on the screen causes decreasing screening efficiency and increasing mass fraction of +2 mm grain-size fraction in the circulating ore. Excessive increasing width of the crusher relieve slot causes increasing output of the circulating product and increasing energy consumption. Decreasing relieve slot below 7.5 mm leads to increasing yield of −2 mm fraction. Improved system and algorithm for visiometric analysis of ore grain-size were proposed and tested. Ore grain-size control sensors are located above the conveyors for transportation of the screening oversize and undersize. The visiometric analysis mode provides for consecutive switching on/off the feeding conveyors and crushers, which ensures the flow of crushed product from one crusher into the measurement zone. Total duration of the grain-size analysis for ores from 6 crushers amounts to 12 minutes that does not affect the final productivity. The developed algorithm application enables significant increasing accuracy of the crushed ore grain-size analysis and reducing energy consumption at the ore preparation stage.
To ease the imbalance between the supply and demand for iron ore in the ferrous industry of China, a low-temperature reduction process via an ore-coal composite method was developed to recover iron from low-grade iron-ore resources (about 30%). In addition, industrial tests on this new reduction process were performed using a rotary kiln (φ1.5 m×15 m). However, rings were formed in the rotary kiln after some days of operation, and these rings affected normal operation. Ring formation during rotary kiln reduction has become a restraining factor for development of coal direct reduction processes using rotary kilns. Previous studies have mainly focused on the reduction process of high-grade ore (> 60%) for direct-reduced iron production. The manner in which highgrade ore reduction differs from low-grade ore reduction is unclear. So, the characteristics of the ring samples need to be studied primarily. Then, the characteristics that affect the formation mechanisms of the rings need to be investigated. Accordingly, relative operation may be developed and ring formation may be prevented. In this paper, ring samples formed in a rotary kiln during a low-grade iron-ore reduction process were studied. The characteristics and formation mechanisms of the ring samples were investigated in detail. The characteristics for ring samples collected from different positions in the rotary kiln were analyzed from the aspects of macro morphological, physical, and chemical compositions, softening and melting properties, and microstructural properties. Thermodynamic phase diagrams, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray diffraction, and chemical phase analyses were applied to reveal the ring formation mechanism during the rotary kiln reduction process. Results show that rings mainly comprise pellets and molten wrappage surroundings. The amount of molten wrappages and the proportions of MFe and CaO increase in the ring samples that are next to the kiln wall. The results also show that the ring samples exhibit lower softening and melting temperatures at this location. The main reason of ring formation is found to be the low melting phases including fayalite formed by FeO and SiO2 in pelletizing powder and hedenbergite compounded by CaO (brought about by coal ash). Moreover, the existence of low melting point phases promotes the diffusion and migration of newly formed iron grains between metallized pellets, which exacerbates ring formation.