ObjectiveThis study aims to determine the relationship between multi-scale fracture characteristics and the mechanical behavior of deep coals, thereby helping gain further insights into the mechanisms behind the macro-mesoscopic damage and failure of the coals and providing a scientific basis for the stability assessment and mechanical modeling of deep coalbed methane (CBM) reservoirs. To this end, it is necessary to examine the differences in the coals’ mechanical properties under varying scales. MethodsThis study conducted uniaxial and triaxial mechanical tests, nanoindentation experiments, and CT scanning of the No. 8 coal seam in the Benxi Formation within the Ordos Basin. Based on the differences in fracture density and modulus of elasticity across varying scales, this study developed an upscaling model through fitting. Then, it investigated the influence of confining pressure on the mechanical parameters of fractures using this model. Results and Conclusions The structurally intact coal samples exhibited a fracture network formed by the dense interactions between cleats on the end faces and inside. The end faces had a face cleat density of 6–12 per 5 cm and a butt cleat density of 9–16 per 5 cm. CT scanning-based statistics reveal an internal cleat density of approximately 10 per 5 cm. At the microscale, fracture widths ranged from 0.52 μm to 13.41 μm. The presence of fractures significantly reduced the macroscopic modulus of elasticity of the coal samples, with values obtained from triaxial tests proving about 21% lower than those from nanoindentation experiments. As confining pressure increased, fractures gradually closed, leading to nonlinear increases in both the peak strength and modulus of elasticity of the coal samples. Correspondingly, the failure mode transitioned from tensile splitting to shear failure. The fitted model indicates that normal stiffness increased nonlinearly with confining pressure, with the increasing rate gradually slowing down. This model can be used to predict the law of changes in the macroscopic modulus of elasticity of coals under varying confining pressures. The results of this study provide an experimental basis for the multi-scale refined characterization and parameter prediction of the mechanical behavior of the coal reservoirs in the Benxi Formation within the Ordos Basin.
Objective Seismic-while-mining (SWM) data are usually acquired using multiple stations, each of which is equipped with multiple data acquisition traces. However, the SWM data received by these stations exhibit time differences due to the lack of GPS signals underground and the fact that current network synchronization technologies are confined by network delays underground. Given that the time synchronization accuracy directly affects the quality of data processing and imaging, the time difference correction of real-time SWM data is essential for accurate SWM detection. Methods Since current high-precision timing systems on the surface suffer from signal loss underground, this study proposed an adaptive time difference correction method based on SWM data. First, using an adaptive velocity analysis method characterized by separate scanning and combined analysis of data from various stations, the impacts of time differences between the stations on the velocity analysis were eliminated. Then, the model seismic traces of various stations were established based on the velocity analysis results. Accordingly, the time differences between the stations were derived, thereby achieving the automatic correction of time differences between SWM data. Results and ConclusionsThe testing results of a theoretical model indicate that the time differences obtained using the new method were highly accurate and scarcely affected by noise. This method was applied to the measured coherent single-shot SWM records of a coal mine’s working face. The application results reveal that the time differences of corrected SWM records between the stations were eliminated. Furthermore, the correction of time differences between various seismic traces with low signal-to-noise ratios was free from noise, demonstrating high adaptability. The travel time of seismic waves is a key attribute in SWM records. The accurate correction of time differences ensures the temporal consistency of the SWM data recorded by various stations, significantly enhancing the data accuracy.
Kržanović Daniel, Gomilanović Miljan, Jovanović Milenko
et al.
The disposal of mining waste is an indispensable technological operation during the exploitation of mineral raw materials and mining activity. A new technological approach to the disposal of mining waste, which is presented in this paper, predicts that all mining waste generated during the excavation and processing of ore in open pit mines and in flotation is disposed of in integrated tailings dumps. In this way, the construction of a flotation tailings pond is eliminated, i.e., the permanent risk that may arise due to an accident situation for the environment, facilities and population located downstream of the originally planned location of the flotation tailings pond is eliminated
Mining engineering. Metallurgy, Mineral industries. Metal trade
Taking the surrounding rock control of the abandoned roadway under the geological conditions of the compound area of Yuchang Coal Mine as the engineering background, aiming at the problem of difficulty in breaking and supporting the surrounding rock in the area where the abandoned roadway intersects, the surrounding rock control technology scheme and parameters of the crushing section of the mining roadway were studied. The theoretical width of the coal pillar stability of the mining roadway is obtained by theoretical calculation, it is necessary to use the support method of shed to maintain the roadway stability when the width of the elastic core area of the coal pillar in the triangular area of the cross roadway is less than 2 m by numerical calculation. Through the theoretical calculation and numerical simulation analysis of the stress and deformation of the surrounding rock of the roadway during excavation and mining, a reasonable scaffolding support area and support scheme were determined. Field measurement shows that the joint support method of anchor mesh cable and I-beam shed can effectively control the deformation of the roadway.
The corrosion behavior and corrosion mechanism of the Pb-rich phase and Cu-rich structure of the Sn–Pb bronze alloy in a high-chloride and high-humidity environment were studied. The phase composition of the bronze alloy was analyzed by observing the metallographic and EPMA element distribution, the potential of the microstructure was characterized by SKPFM. The corrosion products and morphology results after electrochemical and neutral salt spray tests were analyzed. The results showed that the matrix structure of bronze material was composed of Pb-rich phase and Cu-rich structure (α(I) phase and (δ+α(II)) eutectoid). During the corrosion process, the rich Pb phase preferentially corroded as the anode and diffused towards the surroundings, while the rich Cu structure served as the cathode. In the rich-Cu structure, compared with δ, the α phase was used as the anode. The corrosion products on the alloy surface mainly included Cu2O, PbCO3, and Cu2(OH)3Cl. As the corrosion gradually deepened along the depth of α phase, the galvanic couple effect between α phase and δ phase and the “oxygen concentration cell” effect gradually increased.
A novel mechanical attachment for conducting in-plane biaxial tensile test is provided in this paper. In this attachment, the conversion of force from an external actuator into two pairs of orthogonal forces is achieved by specially designed trapezoidal blocks. By using trapezoidal blocks with different inclination angles, biaxial tensile tests of six different tensile ratios can be performed. A heating device is designed for the attachment to conduct thermal biaxial tensile tests. The heating device adopts a combination of the induction heating technology and the conduction heating method. With the developed mechanical attachment and the heating device, the forming limit curves (FLC) of DP590 sheets at ambient temperature, 300 °C, 400 °C and 500 °C are determined using biaxial tensile tests. A classical Nakazima test procedure at ambient temperature is carried out to establish a reference FLC for the material, and the reference FLC is further used to evaluate the results from biaxial tensile tests. Furthermore, an anisotropic GTN model based on Yld2000-3d yield criterion is calibrated by inverse identification procedures and applied to predict the localized necking and fracture for DP590 sheets under biaxial tensions.
Philipp Leerhoff, Johannes C. Brouwer, Amir Mohseni Armaki
et al.
In the pre-reduction cyclone of the HIsarna process, both thermal decomposition and gas reduction of the injected iron ores occur simultaneously at gas temperatures of 1723–1773 K. In this study, the kinetics of the thermal decomposition of three iron ores (namely OreA, OreB and OreC) for HIsarna ironmaking were analysed as an isolated process with a symmetrical thermogravimetric analyser (TGA) under an inert atmosphere. Using various methods, the chemical and mineralogical composition, particle size distribution, morphology and phase distribution of the ores were analysed. The ores differ in their mineralogy and morphology, where OreA only contains hematite as iron-bearing phase and OreB and OreC include goethite and hematite. To obtain the kinetic parameters in non-isothermal conditions, the Coats–Redfern Integral Method was applied for heating rates of 1, 2 and 5 K/min and a maximum temperature of 1773 K. The TGA results indicate that goethite and hematite decomposition occur as a two-stage process in an inert atmosphere of Ar. The proposed reaction mechanism for the first stage of goethite decomposition is chemical reaction with an activation energy ranging from 46.55 to 60.38 kJ/mol for OreB and from 69.90 to 134.47 kJ/mol for OreC. The proposed reaction mechanism for the second stage of goethite decomposition is diffusion, showing an activation energy ranging between 24.43 and 44.76 kJ/mol for OreB and between 3.32 and 23.29 kJ/mol for OreC. In terms of hematite decomposition, only the first stage was analysed. The proposed reaction mechanism is chemical reaction control. OreA shows an activation energy of 545.47 to 670.50 kJ/mol, OreB one of 587.68 to 831.54 kJ/mol and OreC one of 424.31 to 592.32 kJ/mol.
The purpose of this study is to investigate the effects of semi-angle and platinum tube wall thicknesses on the first-step drawing process of platinum-clad nickel bars using finite element simulation. Three different semi-angles of die (3°, 5°, 7°) and three different platinum tube wall thicknesses (0.275 mm, 0.3 mm, 0.325 mm) were selected in the study. The effects of semi-angle and platinum tube wall thicknesses on drawing force, equivalent stress, cladding behavior and damage coefficients during the first-step drawing process were discussed in detail. The simulated results of cladding condition and damage obtained from Deform 3D V11 software are validated with experimental results, and it was found that the results were in good agreement. The results of this study may provide a reference for the practical production of platinum-clad nickel wires.
The weakening of basal texture is beneficial to improve the formability and mechanical properties of deformed magnesium alloys. In this paper, the microstructure and texture evolution of single pass rolled Mg-1.1Mn-0.5Al alloys with various reduction of 10%–60% at 200 °C were observed to reveal twin variants selection and mediated dynamic recrystallization (DRX) mechanism. The results showed that the type and volume fraction of activated twins were strongly related to rolling reduction. Primary {101¯2} tensile twins (TTWs), which were mainly activated in the 10% reduction rolled alloys, were not sufficient to induce recrystallization due to the absence of cumulative dislocation and lower plastic strain energy. In contrast, {101¯1}/ {101¯3} compression twins (CTWs) and {101¯1}−{101¯2}/ {101¯3}−{101¯2} double twins (DTWs) were preferred for recrystallization because of higher dislocation accumulation and stored strain energy. The occurrence of DRX was beneficial to absorb stored energy, relax stress concentration and weaken basal texture in adjacent domains. Due to the sufficient stress provided by massive basal slip dislocations, the type I and type II DTWs were more commonly observed than the type III and type IV variants, which involved much more dissociations of the mixed <c+a> dislocations in deformed magnesium alloys.
In order to achieve the goal of lightening the braking system of urban rail trains, SiCp/ZL101 and ZL101 plates were welded by friction stir lap welding (FSLW) to prepare a new type of brake disc material. The friction and wear properties of the friction-stir-processed composite material were studied at different temperatures (30 °C, 100 °C, 150 °C, 200 °C, 250 °C, 300 °C) to provide a theoretical basis for the evaluation of braking performance. The experimental results showed that the sliding friction processes at each temperature were relatively stable, the friction coefficients did not vary much and the average friction coefficients changed slightly, stabilizing at about 0.4. The wear extent and the depth of wear scars increased with the increase in the temperature, reaching the highest at 150 °C and then began to decrease. At room temperature, the wear forms were mainly oxidative wear and abrasive wear; as the temperature rose, under the cyclic shearing action of the grinding ball, the abrasive debris fell off under the expansion of fatigue cracks and fatigue wear was the main form at this stage. When the temperature reached 200 °C, it began to show the characteristics of adhesive wear; after 250 °C, due to the gradual formation of a mechanical mixed layer containing more SiC particles and oxides on the wear surface, it exhibited high-temperature lubrication characteristics, and the wear extent was equivalent to 35% of the wear extent at normal temperature, indicating that the composite material had good high-temperature friction and wear properties.
In this paper, the hot workability of Mg-1Li-1Al (LA11) alloy is assessed through a uniaxial compression test in a temperature range from 200 to 400 °C and a strain rate, έ, of 1–0.01 s<sup>−1</sup>. The present study reveals that flow stress increases when the strain rate increases and deformation temperature decreases. Based on the hyperbolic sine equation, the flow stress constitutive equation of this alloy under high-temperature deformation is established. The average activation energy was 116.5 kJ/mol. Avrami equation was employed to investigate the dynamic recrystallization (DRX). The DRX mechanism affected by the deformation conditions and Zener–Hollomon parameters is revealed. Finally, the relationship between DRX volume fraction and deformation parameter is verified based on microstructure evolution, which is consistent with the theoretical prediction.