Journal of Central South University最新文献

Rice husk ash (RHA) is currently utilized as a supplementary cementitious material in cement products due to its pozzolanic properties. This study aims to investigate the pozzolanic effect (PE) and filler effect (FE) of RHA on the mechanical properties and microstructure of cemented paste backfill (CPB). The effects of RHA content, cement-to-tailings ratio, and mass concentration on the unconfined compressive strength (UCS) of the CPB were investigated. The proportion of UCS that could be attributed to the PE was 67.30%–87.92% higher than the FE in CPB with RHA contents ranging from 10% to 20%. The FE of RHA exerted stronger influence at lower curing times, but the PE played more crucial roles at curing times of more than 3 d. These results provide new insights into the potential use of RHA as a cementitious material for use in backfilling during mining operations.

Manganese dioxide (MnO₂) is considered one of the most promising cathode materials for aqueous zinc-ion batteries because of its high theoretical capacity, high working voltage, and environmental friendliness. However, its severe capacity fading is caused by unstable crystal structure and manganese dissolution during discharge. Based on these reasons, dicyandiamide (DCDA) was used to coat α-MnO₂ and the effect mechanism of DCDA on the electrochemical performance of α-MnO₂@DCDA was systematically investigated. The results indicate that the physical confinement function of the DCDA not only improves significantly the structural stability of α-MnO₂ but also inhibits dissolution of manganese during discharge. More importantly, electrostatic interaction between nitrogen atoms in DCDA and cations in electrolyte can inhibit Mn²⁺ dissolution during discharge and promote Mn²⁺ deposition during charging, effectively inhibiting the loss of manganese active material. Compared with unmodified α-MnO₂ cathodes, α-MnO₂@DCDA cathodes exhibit significantly improved cycling stability, with a stable capacity of 102.6 mA·h/g after 1500 cycles at a high current density of 3 A/g, with a capacity retention rate exceeding 60%. This work provides an effective way to achieve stable cycling of MnO₂-based zinc-ion batteries.

The three-dimensional (3D) fractal contact model of the interaction between gear teeth is established considering the actual surface morphology of gear teeth. The time-varying meshing stiffness (TVMS) model of spur gear pair is established and verified by finite element (FE) method based on the loaded tooth contact analysis (LTCA) method and considering the influence of friction between the gear teeth. The meshing characteristics and wear depth under tooth surface wear fault condition are analyzed by incorporating the Archard’s wear model, considering the effects of tooth roughness and friction. The effects of friction and fractal parameters on TVMS and wear depth are analyzed. Friction causes the TVMS at the pitch line position to mutate. The increase in friction coefficient and decrease in fractal dimension result in the increase in wear depth and the decrease in TVMS within the region where two pairs of gear teeth engage in meshing. TVMS shows partial linearity with the change of fractal dimension. The influence of fractal dimension on TVMS and wear depth becomes increasingly prominent with the progression of wear cycles, surpassing the influence of friction coefficient.

In this investigation, the high-velocity oxygen fuel (HVOF) deposition technique was implemented to administer vanadium carbide (VC) and cupronickel-chromium (CuNiCr) composite coatings onto SS316 stainless steel. The significance of this research lies in its direct relevance to addressing corrosion-related challenges in marine environments. Preceding and subsequent to the execution of electrochemical corrosion examinations within a 3.5% sodium chloride (NaCl) medium at ambient temperature, a comprehensive scrutiny of the surface topographies of both the coated and uncoated specimens was conducted through scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The outcomes manifest that the intermetallic binder composed of copper (Cu), nickel (Ni), and chromium (Cr) within the coatings undergoes deterioration under the influence of the NaCl medium, thereby inducing localized pitting corrosion phenomena across the substrate. Intriguingly, the incorporation of VC within the coating formulation conspicuously amplifies the corrosion resistance attributes of the treated surface, thereby ameliorating the occurrence of confined corrosive pits. Amidst the assortment of coatings subjected to scrutiny, the VC imbued surface attains the most favorable outcome, showcasing minimal corrosion rate of 72.38×10⁻³ mm/a. In contrast, the SS316 base substrate exhibits the most escalated corrosion rate calculated at 783.82×10⁻³ mm/a.

In order to solve the formation of brittle compounds in brazed joints, an innovative rare earth modified reduced graphene oxide reinforced AgCuTi composite brazing filler was designed to achieve brazed joints with Ag-Cu eutectic as the main organization almost free of brittle compounds, and at the same time, the dispersion of graphene in the joint interfaces was improved. Microanalysis and discussion of the brazing fillers with and without Ce modification showed that the Ce modified reduced graphene oxide was more uniformly dispersed in the brazing fillers. The interfacial microstructures of C/C composites-C/C composites joints with and without Ce modified brazing fillers were compared, and the effect of graphene content on the organization and properties of the joints was investigated. The results showed that the shear strength of the joints was significantly enhanced by using Ce modified brazing fillers. When the graphene content was 0.5 wt.%, the average shear strength of the brazed joints obtained by using Ce modified brazing fillers was 31.82 MPa, increased by 50%.

With the rapid development of the aerospace industry, there is an increasing demand for miniaturized parts made of Inconel 718 foils. However, the grain size effect on the plastic deformation behavior of thin sheets is significant, which considerably limits the fabrication and application of micro-components from Inconel 718. In this study, a series of uniaxial tensile tests and scanning electron microscopy experiments were conducted on Inconel 718 foils with different grain sizes to investigate the grain size effect on plastic deformation behavior. The grain size, orientation, and kernel average misorientation were characterized via electron backscatter diffraction to elucidate the deformation mechanism associated with the grain size effect. The results demonstrate that as the grain size increased, the number of grain orientations transforming into (< 2bar 32 >) gradually decreased owing to weakened grain rotation and coordination under tensile stress, leading to a significant reduction in yield strength and maximum tensile strength. Additionally, the plastic deformation within the grain interior diminished significantly, while grain boundary sliding became a prominent deformation mechanism during tension as grain size increased, resulting in decreased fracture strain and ductile fracture characteristics. Finally, a mixed material constitutive model incorporating grain size and strain was developed for microforming research on Inconel 718 foils.

Due to the increased service temperature of turbine blades, the high temperature conditions seriously deteriorate the mechanical properties of nickel-based superalloys, thus it is necessary to prepare the anti-oxidation coating. This research investigated the microstructure evolutions and oxidation behaviors of simple and silicon-modified aluminide coatings at 1000 °C for 200 h. After oxidation, serious spalling out and failure appeared due to spinal NiCr₂O₄ and volatile Cr₃O phase formation in the IN718 superalloy. For the aluminide coating, the formation of stable α-Al₂O₃ oxide film significantly improved the oxidation resistance, with a mass gain of only 0.1 mg/cm² during the oxidation of 100–200 h. The silicon-modified aluminide coating exhibited the lowest mass gain, rapidly formed stable SiO₂ oxide film due to the existence of the Cr_9.1Si_0.9 phase and maximum grain size in the external coating, and the internal Al₂O₃ oxide together with the coating formed the pinning effect, effectively preventing the delamination of the oxide film. However, the formation and growth of the Ni₃Si phase generated microcracks, leading to its rate of mass gain surpassing that of aluminide coating during oxidation of 100–200 h, which illustrates that effectively regulating the Si content is imperative to prolonging the service life of turbine blades.

Gravity anomalies generated by density non-uniformity are governed by the 3D Poisson equation. Most existing forward methods for such anomalies rely on integral techniques and cell-centered numerical approaches. Once the gravitational potential is calculated, these numerical schemes will inevitably lose high accuracy. To alleviate this problem, an accurate and efficient high-order vertex-centered finite-element scheme for simulating 3D gravity anomalies is presented. Firstly, the forward algorithm is formulated through the vertex-centered finite element with hexahedral meshes. The biconjugate gradient stabilized algorithm can solve the linear equation system combined with an incomplete LU factorization (ILU-BICSSTAB). Secondly, a high-degree Lagrange interpolating scheme is applied to achieve the first-derivate and second-derivate gravitational potential. Finally, a 3D cubic density model is used to test the accuracy of the vertex-centered finite-element algorithm, and thin vertical rectangular prisms and real example for flexibility. All numerical results indicate that our high-order vertex-centered finite-element method can provide an accurate approximation for the gravity field vector and the gravity gradient tensor. Meanwhile, compared to the cell-centered numerical algorithm, the high-order vertex-centered finite element scheme exhibits higher efficiency and accuracy in simulating 3D gravity anomalies.

Floating slab track is widely used in urban rail transit because of its proven vibration attenuation and isolation performance. To investigate the elastic wave propagation in floating slab structure, the characteristic equation for wave dispersion is obtained using generalized plane wave expansion. Double periodicities from unit slab and fastener spacing are considered simultaneously. The complex dispersion curve of the infinite periodic floating slab track is obtained. Eight band-gaps are found to exist in the range from 0 to 300 Hz, and the corresponding theoretical analysis on wave dispersion is provided. An impact test was conducted, which verifies the band-gaps blocking effect on elastic wave propagation. Based on the wave-mode properties, it is found that the band-gap formation mechanism of track structure with double periodicities is different from track structure with a single periodicity, i.e., the localized Bragg scattering or localized resonance modes cannot prevent the propagation of coupled elastic waves in the case of double periodicities. The results in the frequency-wave number domain demonstrate that anomalous Doppler effect occurs in the stopband range and the normal Doppler effect occurs in the passband range.

High-voltage electric pulse (HVEP) technology merits further investigation into its potential applications. The effectiveness of using HVEP to induce pre-damage and deteriorate hot dry rock (HDR) was investigated in this study. Different peak voltages of HVEP were applied to heated-granite flake specimens. Furthermore, the influence of temperature on HVEP stimulating granite was investigated. The results show that when the applied peak voltages exceeded 96 kV, through-fracture failure occurred in the heated-granite specimens, with higher voltages producing more complex through-fracture networks. The microcrack density of granite specimens increased from 8.63 mm/mm² to 13.26 mm/mm² when the applied voltage rose from 96 kV to 144 kV. Notably, the difficulty of granite electrical breakdown gradually decreased with the increasing temperature of thermal treatment. Through-fracture failures were observed in all granite specimens heated above 400 °C after three HVEP discharges at 120 kV. The maximum damage caused by HVEP was found within the temperature range of 300–400 °C. Additionally, an escalation in the development of internal pores and cracks as the granite specimen temperature increased was observed by using scanning electron microscopy (SEM), accompanied by an increase in pore size and crack width and depth.