The permeability of coal reservoirs is affected by its inherent properties, temperature, stress state, etc. Taking the 13-1 coal seam of Huainan Liuzhuang Coal Mine as the research object, the variation of CH4 permeability under the coupling of volume stress, temperature and gas pressure, and under cyclic confining pressure were studied based on the CH4 permeability test. The results show that the CH4 permeability of coal affected by the coupling of volume stress and gas pressure mainly controlled by the effective stress, and the greater the effective stress is, the lower the permeability is. The effect of gas pressure on CH4 permeability is limited by volume stress, but gas pressure has a greater effect on CH4 permeability than volume stress. The influence of temperature and gas pressure coupling on CH4 permeability is dominated by gas pressure. Permeability decreases with the increase of gas pressure showing a type of “U slide”, and the “slide” change is more obvious than the “U” change. The influence of gas pressure on CH4 permeability is greater than that of temperature, and the increasing gas pressure will reduce the influence of temperature on permeability. The cyclic confining pressure will cause irreversible plastic deformation of the pore fractures, which reduces effective seepage channels in the coal and decreases CH4 permeability. The plastic deformation produced by the first cyclic confining pressure is the largest, and the amount of plastic deformation gradually decreases with the increase of the number of cycles.
Coalfield spontaneous combustion causes problems such as wastage of coal resources, environmental pollution, casualties, and economic losses. In order to further promote attention to environmental issues during the process of coalfield spontaneous combustion, this paper analyzes the impact of coalfield spontaneous combustion on the environment through literature review and field geological investigation, compares and analyzes greenhouse gas assessment methods, introduces the effects of toxic and harmful gases (SOx, NOx, organic matter, Hg, HF) and aerosols on fire areas and surrounding environment, analyzes the damage caused by coal fires to land resources and surface vegetation, explores the impact of coal self-ignition on water quality, and analyzes from a geological perspective the geological disasters caused by coal fires and changes in geological conditions induced by burnt rocks. Combining with the development trend of safe, green, intelligent mining of coal and clean, efficient, low-carbon intensive utilization, the next step is to propose work prospects for reducing greenhouse gas and toxic and harmful gas emissions, evaluating soil and water pollutants, predicting and forecasting geological disasters, and characterizing burnt rocks to save water resources.
Rolling contact fatigue (RCF) of vacuum induction melted–vacuum arc remelted (VIM-VAR) M50 bearing steel under high loads was carried out, using a three-ball-rod RCF tester. Dark etching regions (DER) and butterflies were found in the subsurface region below the raceway of the RCF-tested sample. The DER appeared in the region of maximum shear stress located at a depth of 30 μm to 170 μm below the raceway. Carbon atoms migrated through high-density dislocations, and part of the martensite plates was transformed into cellular ferrites, due to the redistribution of dislocations during the deformation of martensite under the action of cyclic shear stress. Butterflies appeared in the region of maximum shear stress located at a depth of 20 μm to 314 μm below the raceway. Butterflies were initiated in the primary carbides, with length values ranging from 5 μm to 15 μm. The plate martensite in the butterfly wings was transformed into nanocrystalline ferrites, due to the increase in the dislocation density and rearrangement of dislocations during the extension of fatigue cracks from the primary carbides to the matrix under cyclic shear stress.
Jonathan D. Aubertin, Matthias Wimmer, Masoud Sedghi
An experimental method is proposed to assess blasting requirements based on in-situ cratering behavior. The method relies on single hole blast (SHB) tests to derive burden-dependent relationships. A non-linear crater model of the form [Formula: see text] is calibrated from SHB test results to describe the cratering behavior. Parameters [Formula: see text] and [Formula: see text] represent characteristic blastability index parameters that depend on geomechanical and operational conditions. A series of experimental SHB tests were conducted at three hard rock mines. The craters were mapped to capture the breakout profile and calibrate the model. Results showed that coefficient [Formula: see text] presents an inverse linear correlation with burden [Formula: see text], while exponent s is approximately constant for a considerable range of burden values. Experimental results are used to define burden dependent relationship for bench blast designs and blasthole placement in underground development rounds. A complementary analysis addresses the prevalence of multiple cratering mechanisms according to geology and burden dimension.
Additive manufacturing enables the development of high-performance materials by in-situ alloying of multiple components. In this study, Inconel 718-based composite, reinforced with tungsten carbide (WC), was synthesized on a 316L stainless steel substrate using laser directed energy deposition (DED). The microstructural evolution, distribution density of WC particles, and strengthening mechanisms of the DED-processed metal matrix composite (MMC) with different WC particle sizes and ratios are systematically investigated. It illustrated that increasing laser power enables the microstructure transforming from equiaxed to dendritic, which is attributed to the different cooling rates and temperature gradients. In addition, the morphology of the 60% WC ratio of the particle composite shows macrocracks. The incorporation of different sized WC affects retained WC distribution density and tailors a gradient layer around the edge of the WC particle. The in-situ WC-W2C phases precipitated in the deposited layer and the evenly distributed high level of ex-situ retained WC particles induce solid solution strengthening and dispersion strengthening, respectively. As a result, the optimal size of the 90 μm WC/Inconel 718 shows the highest wear resistance. The underlying strengthening mechanisms are elucidated. Consequently, the wear mechanism of Inconel 718-based composite reveals the typical abrasive wear characteristics in the presence of WC particles.
In this work, high chromium cast irons (HCCIs) reinforced by TiC particles are designed and fabricated to improve the erosion–corrosion and wear resistances of materials for the pumping and handling applications. The TiC particles are formed by the in situ solidification method. The experimental results show that the hardness of as-cast HCCIs is improved significantly with TiC volume fraction. It can be as high as 63 HRC when the TiC volume fraction is 9.8%. The introduction of TiC increases the abrasive wear resistance of the HCCIs in both as-cast and heat-treated states. However, it is unexpected to find that the presence of TiC significantly reduces the erosion–corrosion performance. It suggests that corrosion-enhanced erosion is the dominant mechanism that controls the mass loss of the TiC-strengthened HCCIs.
The surface species transformation of oxidized carrollite processing with NaHS and KBX was investigated. Flotation and contact angle tests indicate that the combination of NaHS and KBX takes a better flotation performance than adding NaHS or KBX alone. Thermodynamic analysis, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) results confirm the stronger chemisorption of KBX occurs on the oxidized carrollite surface with NaHS, which is beneficial to remove the cobalt oxides, thus contributing to the superior floatability. Interestingly, less elemental sulfur was observed on the carrollite surface as the interaction of NaHS and KBX than adding NaHS alone. It suggests that elemental sulfur is not the main contributor to the restored floatability of oxidized carrollite through sulfidisation. This study provided a new perspective to correlate the surface species with xanthate adsorption and oxidized carrollite flotation through determining the various intermediate products.
An optimum route to fabricate the Ni-based superalloy with homogeneous dispersion of Y2O3 particles is investigated. Ni-based ODS powder was prepared by high-energy ball milling of gas-atomized alloy powders and Y2O3 particles treated with a high-pressure homogenizer. Decrease in particle size and improvement of dispersion stability were observed by high-pressure homogenization of as-received Y2O3 particles, presumably by the powerful cavitation forces and by collisions of the particles. Microstructural analysis for the ball-milled powder mixtures reveal that Ni-based ODS powders prepared from high-pressure homogenization of Y2O3 particles exhibited more fine and uniform distribution of Ni and Y elements compared to the as-received powder. These results suggested that high-pressure homogenization process is useful for producing Ni-based superalloy with homogeneously dispersed oxide particles.
Mining engineering. Metallurgy, Materials of engineering and construction. Mechanics of materials
Zhicheng Zhang, James Femi-Oyetoro, Ismail Fidan
et al.
Additive manufacturing (AM) is a layer-by-layer manufacturing process. However, its broad adoption is still hindered by limited material options, different fabrication defects, and inconsistent part quality. Material extrusion (ME) is one of the most widely used AM technologies, and, hence, is adopted in this research. Low-cost metal ME is a new AM technology used to fabricate metal composite parts using sintered metal infused filament material. Since the involved materials and process are relatively new, there is a need to investigate the dimensional accuracy of ME fabricated metal parts for real-world applications. Each step of the manufacturing process, from the material extrusion to sintering, might significantly affect the dimensional accuracy. This research provides a comprehensive analysis of dimensional changes of metal samples fabricated by the ME and sintering process, using statistical and machine learning algorithms. Machine learning (ML) methods can be used to assist researchers in sophisticated pre-manufacturing planning and product quality assessment and control. This study compares linear regression to neural networks in assessing and predicting the dimensional changes of ME-made components after 3D printing and sintering process. In this research, the ML algorithms present a significantly high coefficient of determination (i.e., 0.999) and a very low mean square error (i.e., 0.0000878). The prediction outcomes using a neural network approach have the smallest mean square error among all ML algorithms and it has quite small p-values. So, in this research, the neural network algorithm has the highest accuracy. The findings of this study can help researchers and engineers to predict the dimensional variations and optimize the printing and sintering process parameters to obtain high quality metal parts fabricated by the low-cost ME process.
In oil sands mining, bitumen and fines contents are used to predict ore processability. However, experimental results show that certain solid fractions known as Organic Rich Solids (ORS) negatively affect the overall bitumen recovery. A conceptual mine planning framework based on a goal programming model for oil sands production scheduling and waste management is presented. Bitumen recovery is additionally adjusted based on the ORS content. The model features automated production targeting (APT) and limited duration stockpiling constraints that optimize the annual production capacities. The model is implemented with two scenarios. Scenario 1 uses processing recovery calculated based on Alberta Energy Regulatory requirements while Scenario 2 uses processing recovery additionally adjusted based on ORS content. Results for Scenario 1 show a 3.46% overestimation of net present value compared to Scenario 2. The APT constraints provide planners a robust and efficient technique for determining annual production tonnages with minimum periodic variations.
One of the challenges of modern crystallography of complex systems (complex metallic alloys, proteins, aperiodic crystals and quasicrystals) is to properly describe the disorder in these systems and discuss correctly the refinement results in terms of the structural disorder. In this paper we briefly discuss a new approach to phasons and phonons in quasicrystals and focus on the new theory of phonons in these materials. A newly derived correction factor for phonons in the form of the Bessel function is the approximated way of describing optic modes in the phonon spectra of quasicrystals. It is applied to a real decagonal quasicrystal in the Al-Cu-Rh system with 56/38 atoms per thick/thin structural unit, based on 2092 unique reflections selected from the collected diffraction data, significantly improving the refinement results. The final R-factor value is 7.24%, which is over 0.5% better result comparing to originally reported. We believe our work will open a broader discussion on the disorder in quasicrystals (and other aperiodic systems) and motivate to develop new approaches to treat the diffraction data influenced by different types of disorder in the new way.
Mining engineering. Metallurgy, Materials of engineering and construction. Mechanics of materials
Working principle of hydraulic buffer system of hydraulic driven hoist and its main influencing factors were analyzed. System simulation model was established based on AMEsim, and influence law of overload valve diameter, overload valve opening pressure, engine swept volume, bucket weight and operating speed to bucket displacement and engine inlet pressure were simulated and analyzed. The analysis results can provide theoretical guidance for further optimization of design of the over-discharging buffer system.
Nasim Bakir, Antoni Artinov, Andrey Gumenyuk
et al.
One of the main factors affecting the use of lasers in the industry for welding thick structures is the process accompanying solidification cracks. These cracks mostly occurring along the welding direction in the welding center, and strongly affect the safety of the welded components. In the present study, to obtain a better understanding of the relation between the weld pool geometry, the stress distribution and the solidification cracking, a three-dimensional computational fluid dynamic (CFD) model was combined with a thermo-mechanical model. The CFD model was employed to analyze the flow of the molten metal in the weld pool during the laser beam welding process. The weld pool geometry estimated from the CFD model was used as a heat source in the thermal model to calculate the temperature field and the stress development and distributions. The CFD results showed a bulging region in the middle depth of the weld and two narrowing areas separating the bulging region from the top and bottom surface. The thermo-mechanical simulations showed a concentration of tension stresses, transversally and vertically, directly after the solidification during cooling in the region of the solidification cracking.
In view of problems of asynchrony of torque and speed existed in traditional synchronous control strategy of dual-motor drive based on current differential closed-loop as well as mechanical torsional vibration caused by load disturbance is not considered, a synchronous control strategy of dual-motor drive for mine-used belt conveyor based on speed differential closed loop was put forward taking dual-motor drive system of mine-used belt conveyor as research object. The current signals of dual-motors were compensated by using rotate speed error between dual motors, if the rotate speed error of dual motors was produced, the rotate speeds were adjusted by adjusting currents (torque) of dual motors, so as to keep the rotate speeds in synchronization. For torsional angle of mechanical axis caused by load disturbance, a torsional vibration suppression strategy was proposed: torsional angle equation was allocated rationally to attenuate the torsional angle rapidly, so as to achieve good suppression effect for torsional vibration. Matlab/Simulink simulation results demonstrate reliability of the control strategy.