Journal of Central South University最新文献

Mill vibration is a common problem in rolling production, which directly affects the thickness accuracy of the strip and may even lead to strip fracture accidents in serious cases. The existing vibration prediction models do not consider the features contained in the data, resulting in limited improvement of model accuracy. To address these challenges, this paper proposes a multi-dimensional multi-modal cold rolling vibration time series prediction model (MDMMVPM) based on the deep fusion of multi-level networks. In the model, the long-term and short-term modal features of multi-dimensional data are considered, and the appropriate prediction algorithms are selected for different data features. Based on the established prediction model, the effects of tension and rolling force on mill vibration are analyzed. Taking the 5th stand of a cold mill in a steel mill as the research object, the innovative model is applied to predict the mill vibration for the first time. The experimental results show that the correlation coefficient (R²) of the model proposed in this paper is 92.5%, and the root-mean-square error (RMSE) is 0.0011, which significantly improves the modeling accuracy compared with the existing models. The proposed model is also suitable for the hot rolling process, which provides a new method for the prediction of strip rolling vibration.

The modification behavior of different Er contents on the microstructures and properties of as-cast 8030 aluminum alloy was investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), hardness test, electrical conductivity test and tensile property test. The results show that the addition of Er can refine the grains of as-cast alloy, which mainly promotes the nucleation of α -Al by causing constitutional supercooling and forming the Al₃Er nanoparticles as a heterogeneous nucleation core. Er can change the morphology of Al-Al₆Fe eutectic structure of the alloy, furthermore, Er can adsorb on the surface of the Al₆Fe phase to refine the Al₆Fe phase at eutectic structure. Er can improve the tensile properties, especially the elongation of as-cast 8030 aluminum alloy, which is attributed to the modification of Al-Al₆Fe eutectic and Al₆Fe phase.

Machine-learning methodologies have increasingly been embraced in landslide susceptibility assessment. However, the considerable time and financial burdens of landslide inventories often result in persistent data scarcity, which frequently impedes the generation of accurate and informative landslide susceptibility maps. Addressing this challenge, this study compiled a nationwide dataset and developed a transfer learning-based model to evaluate landslide susceptibility in the Chongqing region specifically. Notably, the proposed model, calibrated with the warmup-cosine annealing (WCA) learning rate strategy, demonstrated remarkable predictive capabilities, particularly in scenarios marked by data limitations and when training data were normalized using parameters from the source region. This is evidenced by the area under the receiver operating characteristic curve (AUC) values, which exhibited significant improvements of 51.00%, 24.40% and 2.15%, respectively, compared to a deep learning model, in contexts where only 1%, 5% and 10% of data from the target region were used for retraining. Simultaneously, there were reductions in loss of 16.12%, 27.61% and 15.44%, respectively, in these instances.

The breakage and bending of ducts result in a difficulty to cope with ventilation issues in bi-directional excavation tunnels with a long inclined shaft using a single ventilation method based on ducts. To discuss the hybrid ventilation system applied in bi-directional excavation tunnels with a long inclined shaft, this study has established a full-scale computational fluid dynamics model based on field tests, the Poly-Hexcore method, and the sliding mesh technique. The distribution of wind speed, temperature field, and CO in the tunnel are taken as indices to compare the ventilation efficiency of three ventilation systems (duct, duct-ventilation shaft, duct–ventilated shaft-axial fan). The results show that the hybrid ventilation scheme based on duct-ventilation shaft–axial fan performs the best among the three ventilation systems. Compared to the duct, the wind speed and cooling rate in the tunnel are enhanced by 7.5%–30.6% and 14.1%–17.7%, respectively, for the duct-vent shaft-axial fan condition, and the volume fractions of CO are reduced by 26.9%–73.9%. This contributes to the effective design of combined ventilation for bidirectional excavation tunnels with an inclined shaft, ultimately improving the air quality within the tunnel.

Rocks will suffer different degree of damage under FT (freeze-thaw) cycles, which seriously threatens the long-term stability of rock engineering in cold regions. In order to study the mechanism of rock FT damage, energy calculation method and energy self-inhibition model are introduced to explore their energy characteristics in this paper. The applicability of the energy self-inhibition model was verified by combining the data of FT cycles and uniaxial compression tests of intact and pre-cracked sandstone samples, as well as published reference data. In addition, the energy evolution characteristics of FT damaged rocks were discussed accordingly. The results indicate that the energy self-inhibition model perfectly characterizes the energy accumulation characteristics of FT damaged rocks under uniaxial compression before the peak strength and the energy dissipation characteristics before microcrack unstable growth stage. Taking the FT damaged cyan sandstone sample as an example, it has gone through two stages dominated by energy dissipation mechanism and energy accumulation mechanism, and the energy rate curve of the pre-cracked sample shows a fall-rise phenomenon when approaching failure. Based on published reference data, it was found that the peak total input energy and energy storage limit conform to an exponential FT decay model, with corresponding decay constants ranging from 0.0021 to 0.1370 and 0.0018 to 0.1945, respectively. Finally, a linear energy storage equation for FT damaged rocks was proposed, and its high reliability and applicability were verified by combining published reference data,the energy storage coefficient of different types of rocks ranged from 0.823 to 0.992, showing a negative exponential relationship with the initial UCS (uniaxial compressive strength). In summary, the mechanism by which FT weakens the mechanical properties of rocks has been revealed from an energy perspective in this paper, which can provide reference for related issues in cold regions.

Carbon nanotubes (CNTs) have garnered significant attention in the fields of science, engineering, and medicine due to their numerous advantages. The initial step towards harnessing the potential of CNTs involves their macroscopic assembly. The present study employed a gentle and direct self-assembly technique, wherein controlled growth of CNT sheaths occurred on the metal wire’s surface, followed by etching of the remaining metal to obtain the hollow tubes composed of CNTs. By controlling the growth time and temperature, it is possible to alter the thickness of the CNTs sheath. After immersing in a solution containing 1 g/L of CNTs at 60 °C for 24 h, the resulting CNTs layer achieved a thickness of up to 60 µm. These hollow CNTs tubes with varying inner diameters were prepared through surface reinforcement using polymers and sacrificing metal wires, thereby exhibiting exceptional attributes such as robustness, flexibility, air tightness, and high adsorption capacity that effectively capture CO₂ from the gas mixture.

In this study, the cooling rate was manipulated by quenching with water of different temperatures (30, 60 and 100 °C). Surface and internal residual stresses in the quenched 6061 aluminum alloy samples were measured using hole-drilling and crack compliance methods, respectively. Then, the processability of the quenched samples was evaluated at cryogenic temperatures. The mechanical properties of the as-aged samples were assessed, and microstructure evolution was analyzed. The surface residual stresses of samples W30°C, W60°C and W100°C is −178.7, −161.7 and −117.2 MPa, respectively along x-direction, respectively; and −191.2, −172.1 and −126.2 MPa, respectively along y-direction. The sample quenched in boiling water displaying the lowest residual stress (∼34 % and ∼60% reduction in the surface and core). The generation and distribution of quenching residual stress could be attributed to the lattice distortion gradient. Desirable plasticity was also exhibited in the samples with relatively low quenching cooling rates at cryogenic temperatures. The strengthes of the as-aged samples are 291.2 to 270.1 MPa as the quenching water temperature increase from 30 °C to 100 °C. Fine and homogeneous β″ phases were observed in the as-aged sample quenched with boiling water due to the clusters and Guinier-Preston zones (GP zones) premature precipitated during quenching process.

Aqueous zinc ion hybrid capacitors (ZIHCs) are considered one of the most promising electrochemical energy storage systems due to their high safety, environmental friendliness, low cost, and high power density. However, the low energy density and the lack of sustainable design strategies for the cathodes hinder the practical application of ZIHCs. Herein, we design the N and O co-doped porous carbon cathode by annealing metal-organic framework (ZIF-8). ZIF-8 retains the original dodecahedral structure with a high specific surface (2814.67 m²/g) and I_G/I_D ratio of 1.0 during carbonization and achieves self-doping of N and O heteroatoms. Abundant defect sites are introduced into the porous carbon to provide additional active sites for ion adsorption after the activation of carbonized ZIF-8 by KOH treatment. The ZIHCs assembled with modified ZIF-8 as the cathode and commercial zinc foil as the anode show an energy density of 125 W · h/kg and a power density of 79 W/kg. In addition, this ZIHCs device achieves capacity retention of 77.8% after 9000 electrochemical cycles, which is attributed to the diverse pore structure and plentiful defect sites of ZIF-8-800(KOH). The proposed strategy may be useful in developing high-performance metal-ion hybrid capacitors for large-scale energy storage.

Bedding structural planes significantly influence the mechanical properties and stability of engineering rock masses. This study conducts uniaxial compression tests on layered sandstone with various bedding angles (0°, 15°, 30°, 45°, 60°, 75° and 90°) to explore the impact of bedding angle on the deformational mechanical response, failure mode, and damage evolution processes of rocks. It develops a damage model based on the Logistic equation derived from the modulus’s degradation considering the combined effect of the sandstone bedding dip angle and load. This model is employed to study the damage accumulation state and its evolution within the layered rock mass. This research also introduces a piecewise constitutive model that considers the initial compaction characteristics to simulate the whole deformation process of layered sandstone under uniaxial compression. The results revealed that as the bedding angle increases from 0° to 90°, the uniaxial compressive strength and elastic modulus of layered sandstone significantly decrease, slightly increase, and then decline again. The corresponding failure modes transition from splitting tensile failure to slipping shear failure and back to splitting tensile failure. As indicated by the modulus’s degradation, the damage characteristics can be categorized into four stages: initial no damage, damage initiation, damage acceleration, and damage deceleration termination. The theoretical damage model based on the Logistic equation effectively simulates and predicts the entire damage evolution process. Moreover, the theoretical constitutive model curves closely align with the actual stress – strain curves of layered sandstone under uniaxial compression. The introduced constitutive model is concise, with fewer parameters, a straightforward parameter determination process, and a clear physical interpretation. This study offers valuable insights into the theory of layered rock mechanics and holds implications for ensuring the safety of rock engineering.

Non-pillar mining technology with automatically formed roadway is a new mining method without coal pillar reservation and roadway excavation. The stability control of automatically formed roadway is the key to the successful application of the new method. In order to realize the stability control of the roadway surrounding rock, the mechanical model of the roof and rib support structure is established, and the influence mechanism of the automatically formed roadway parameters on the compound force is revealed. On this basis, the roof and rib support structure technology of confined lightweight concrete is proposed, and its mechanical tests under different eccentricity are carried out. The results show that the bearing capacity of confined lightweight concrete specimens is basically the same as that of ordinary confined concrete specimens. The bearing capacity of confined lightweight concrete specimens under different eccentricities is 1.95 times higher than those of U-shaped steel specimens. By comparing the test results with the theoretical calculated results of the confined concrete, the calculation method of the bearing capacity for the confined lightweight concrete structure is selected. The design method of confined lightweight concrete support structure is established, and is successfully applied in the extra-large mine, Ningtiaota Coal Mine, China.