Strength theory is the basic theory for calculating and designing the strength of engineering materials in civil, hydraulic, mechanical, aerospace, military, and other engineering disciplines. Therefore, the comprehensive study of the generalized nonlinear strength theory (GNST) of geomaterials has significance for the construction of engineering rock strength. This paper reviews the GNST of geomaterials to demonstrate the research status of nonlinear strength characteristics of geomaterials under complex stress paths. First, it systematically summarizes the research progress of GNST (classical and empirical criteria). Then, the latest research the authors conducted over the past five years on the GNST is introduced, and a generalized three-dimensional (3D) nonlinear Hoek–Brown (HB) criterion (NGHB criterion) is proposed for practical applications. This criterion can be degenerated into the existing three modified HB criteria and has a better prediction performance. The strength prediction errors for six rocks and two in-situ rock masses are 2.0724%–3.5091% and 1.0144%–3.2321%, respectively. Finally, the development and outlook of the GNST are expounded, and a new topic about the building strength index of rock mass and determining the strength of in-situ engineering rock mass is proposed. The summarization of the GNST provides theoretical traceability and optimization for constructing in-situ engineering rock mass strength.
In blasting engineering, the location and number of detonation points, to a certain degree, regulate the propagation direction of the explosion stress wave and blasting effect. Herein, we examine the explosion wave field and rock breaking effect in terms of shock wave collision, stress change of the blast hole wall in the collision zone, and crack propagation in the collision zone. The produced shock wave on the collision surface has an intensity surpassing the sum of the intensities of the two colliding explosion shock waves. At the collision location, the kinetic energy is transformed into potential energy with a reduction in particle velocity at the wave front and the wave front pressure increases. The expansion form of the superposed shock wave is dumbbell-shaped, the shock wave velocity in the collision area is greater than the radial shock wave velocity, and the average propagation angle of the explosion shock waves is approximately 60°. Accordingly, a fitted relationship between blast hole wall stress and explosion wave propagation angle in the superposition area is plotted. Under the experimental conditions, the superimposed explosion wave stress of the blast hole wall is approximately 1.73 times the singleexplosion wave incident stress. The results of the model test and numerical simulations reveal that large-scale radial fracture cracks were generated on the blast hole wall in the superimposed area, and the width of the crack increased. The width of the large-scale radial fracture cracks formed by a strong impact is approximately 5% of the blast hole length. According to the characteristics of blast hole wall compression, the mean peak pressures of the strongly superimposed area are approximately 1.48 and 1.84 times those of the weakly superimposed and nonsuperimposed areas, respectively.
The deformation and fracture evolution mechanisms of the strata overlying mines mined using sublevel caving were studied via numerical simulations. Moreover, an expression for the normal force acting on the side face of a steeply dipping superimposed cantilever beam in the surrounding rock was deduced based on limit equilibrium theory. The results show the following: (1) surface displacement above metal mines with steeply dipping discontinuities shows significant step characteristics, and (2) the behavior of the strata as they fail exhibits superimposition characteristics. Generally, failure first occurs in certain superimposed strata slightly far from the goaf. Subsequently, with the constant downward excavation of the orebody, the superimposed strata become damaged both upwards away from and downwards toward the goaf. This process continues until the deep part of the steeply dipping superimposed strata forms a large-scale deep fracture plane that connects with the goaf. The deep fracture plane generally makes an angle of 12°–20° with the normal to the steeply dipping discontinuities. The effect of the constant outward transfer of strata movement due to the constant outward failure of the superimposed strata in the metal mines with steeply dipping discontinuities causes the scope of the strata movement in these mines to be larger than expected. The strata in the metal mines with steeply dipping discontinuities mainly show flexural toppling failure. However, the steeply dipping structural strata near the goaf mainly exhibit shear slipping failure, in which case the mechanical model used to describe them can be simplified by treating them as steeply dipping superimposed cantilever beams. By taking the steeply dipping superimposed cantilever beam that first experiences failure as the key stratum, the failure scope of the strata (and criteria for the stability of metal mines with steeply dipping discontinuities mined using sublevel caving) can be obtained via iterative computations from the key stratum, moving downward toward and upwards away from the goaf.
During flotation, the features of the froth image are highly correlated with the concentrate grade and the corresponding working conditions. The static features such as color and size of the bubbles and the dynamic features such as velocity have obvious differences between different working conditions. The extraction of these features is typically relied on the outcomes of image segmentation at the froth edge, making the segmentation of froth image the basis for studying its visual information. Meanwhile, the absence of scientifically reliable training data with label and the necessity to manually construct dataset and label make the study difficult in the mineral flotation. To solve this problem, this paper constructs a tungsten concentrate froth image dataset, and proposes a data augmentation network based on Conditional Generative Adversarial Nets (cGAN) and a U-Net++-based edge segmentation network. The performance of this algorithm is also evaluated and contrasted with other algorithms in this paper. On the results of semantic segmentation, a phase-correlation-based velocity extraction method is finally suggested.
Vanadium and its derivatives are used in various industries, including steel, metallurgy, pharmaceuticals, and aerospace engineering. Although China has massive reserves of stone coal resources, these resources have low grades. Therefore, the effective extraction and recovery of metallic vanadium from stone coal is an important way to realize the efficient resource utilization of stone coal vanadium ore. Herein, Bacillus mucilaginosus was selected as the leaching strain. The vanadium leaching rate reached 35.5% after 20 d of bioleaching under optimal operating conditions. The cumulative vanadium leaching rate in the contact group reached 35.5%, which was higher than that in the noncontact group (9.3%). The metabolites of B. mucilaginosus, such as oxalic, tartaric, citric, and malic acids, dominated in bioleaching, accounting for 73.8% of the vanadium leaching rate. Interestingly, during leaching, the presence of stone coal stimulated the expression of carbonic anhydrase in bacterial cells, and enzyme activity increased by 1.335–1.905 U. Enzyme activity positively promoted the production of metabolite organic acids, and total organic acid content increased by 39.31 mg·L−1, resulting in a reduction of 2.51 in the pH of the leaching system with stone coal. This effect favored the leaching of vanadium from stone coal. Atomic force microscopy illustrated that bacterial leaching exacerbated corrosion on the surface of stone coal beyond 10 nm. Our study provides a clear and promising strategy for exploring the bioleaching mechanism from the perspective of microbial enzyme activity and metabolites.
High-temperature oxidation behavior of ferrovanadium (FeV2O4) and ferrochrome (FeCr2O4) spinels is crucial for the application of spinel as an energy material, as well as for the clean usage of high-chromium vanadium slag. Herein, the nonisothermal oxidation behavior of FeV2O4 and FeCr2O4 prepared by high-temperature solid-state reaction was examined by thermogravimetry and X-ray diffraction (XRD) at heating rates of 5, 10, and 15 K/min. The apparent activation energy was determined by the Kissinger–Akahira–Sunose (KAS) method, whereas the mechanism function was elucidated by the Malek method. Moreover, in-situ XRD was conducted to deduce the phase transformation of the oxidation mechanism for FeV2O4 and FeCr2O4. The results reveal a gradual increase in the overall apparent activation energies for FeV2O4 and FeCr2O4 during oxidation. Four stages of the oxidation process are observed based on the oxidation conversion rate of each compound. The oxidation mechanisms of FeV2O4 and FeCr2O4 are complex and have distinct mechanisms. In particular, the chemical reaction controls the entire oxidation process for FeV2O4, whereas that for FeCr2O4 transitions from a three-dimensional diffusion model to a chemical reaction model. According to the in-situ XRD results, numerous intermediate products are observed during the oxidation process of both compounds, eventually resulting in the final products FeVO4 and V2O5 for FeV2O4 and Fe2O3 and Cr2O3 for FeCr2O4, respectively.
Te treatment is an effective method for modifying sulfide inclusions, and MnTe precipitation has an important effect on thermal brittleness and steel corrosion resistance. In most actual industrial applications of Te treatment, MnTe precipitation is unexpected. The critical precipitation behavior of MnTe inclusions was investigated through scanning electron microscopy, transmission electron microscopy, machine learning, and first-principles calculation. MnTe preferentially precipitated at the container mouth for sphere-like sulfides and at the interface between MnS grain boundaries and steel matrix for rod-like sulfides. The MnS/MnTe interface was semicoherent. A composition transition zone with a rock-salt structure exhibiting periodic changes existed to maintain the semicoherent interface. The critical precipitation behavior of MnTe inclusions in resulfurized steels involved three stages at varying temperatures. First, Mn(S,Te) precipitated during solidification. Second, MnTe with a rock-salt structure precipitated from Mn(S,Te). Third, MnTe with a hexagonal NiAs structure transformed from the rock-salt structure. The solubility of Te in MnS decreased with decreasing temperature. The critical precipitation behavior of MnTe inclusions in resulfurized steels was related to the MnS precipitation temperature. With the increase in MnS precipitation temperature, the critical Te/S weight ratio decreased. In consideration of the cost-effectiveness of Te addition for industrial production, the Te content in resulfurized steels should be controlled in accordance with MnS precipitation temperature and S content.
The synthesis of carbide coatings on graphite substrates using molten salt synthesis (MSS), has garnered significant interest due to its cost-effective nature. This study investigates the reaction process and growth kinetics involved in MSS, shedding light on key aspects of the process. The involvement of Ti powder through liquid-phase mass transfer is revealed, where the diffusion distance and quantity of Ti powder play a crucial role in determining the reaction rate by influencing the C content gradient on both sides of the carbide. Furthermore, the growth kinetics of the carbide coating are predominantly governed by the diffusion behavior of C within the carbide layer, rather than the chemical reaction rate. To analyze the kinetics, the thickness of the carbide layer is measured with respect to heat treatment time and temperature, unveiling a parabolic relationship within the temperature range of 700–1300°C. The estimated activation energy for the reaction is determined to be 179283 J·mol−1. These findings offer valuable insights into the synthesis of carbide coatings via MSS, facilitating their optimization and enhancing our understanding of their growth mechanisms and properties for various applications.
This work investigated the effect of Cr and Si on the mechanical properties and oxidation resistance of press hardened steel. Results indicated that the microstructure of the Cr–Si micro-alloyed press hardened steel consisted of lath martensite, M23C6 carbides, and retained austenite. The retained austenite and carbides are responsible for the increase in elongation of the micro-alloyed steel. In addition, after oxidation at 930°C for 5 min, the thickness of the oxide scales on the Cr–Si micro-alloyed press hardened steel is less than 5 µm, much thinner than 45.50 µm-thick oxide scales on 22MnB5. The oxide scales of the Cr–Si micro-alloyed steel are composed of Fe2O3, Fe3O4, mixed spinel oxide (FeCr2O4 and Fe2SiO4), and amorphous SiO2. Adding Cr and Si significantly reduces the thickness of the oxide scales and prevents the generation of the FeO phase. Due to the increase of spinel FeCr2O4 and Fe2SiO4 phase in the inner oxide scale and the amorphous SiO2 close to the substrate, the oxidation resistance of the Cr–Si micro-alloyed press hardened steel is improved.
We discussed the decrease in residual stress, precipitation evolution, and mechanical properties of GH4151 alloy in different annealing temperatures, which were studied by the scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), and electron backscatter diffraction (EBSD). The findings reveal that annealing processing has a significant impact on diminishing residual stresses. As the annealing temperature rose from 950 to 1150°C, the majority of the residual stresses were relieved from 60.1 MPa down to 10.9 MPa. Moreover, the stress relaxation mechanism transitioned from being mainly controlled by dislocation slip to a combination of dislocation slip and grain boundary migration. Meanwhile, the annealing treatment promotes the decomposition of the Laves, accompanied by the precipitation of μ-(Mo6Co7) starting at 950°C and reaching a maximum value at 1050°C. The tensile strength and plasticity of the annealing alloy at 1150°C reached the maximum (1394 MPa, 56.1%) which was 131%, 200% fold than those of the as-cast alloy (1060 MPa, 26.6%), but the oxidation process in the alloy was accelerated at 1150°C. The enhancement in durability and flexibility is primarily due to the dissolution of the brittle phase, along with the shape and dispersal of the γ′ phase.
This work aims to investigate the mechanical properties and interfacial characteristics of 6061 Al alloy plates fabricated by hot-roll bonding (HRB) based on friction stir welding. The results showed that ultimate tensile strength and total elongation of the hot-rolled and aged joints increased with the packaging vacuum, and the tensile specimens fractured at the matrix after exceeding 1 Pa. Non-equilibrium grain boundaries were formed at the hot-rolled interface, and a large amount of Mg2Si particles were linearly precipitated along the interfacial grain boundaries (IGBs). During subsequent heat treatment, Mg2Si particles dissolved back into the matrix, and Al2O3 film remaining at the interface eventually evolved into MgO. In addition, the local IGBs underwent staged elimination during HRB, which facilitated the interface healing due to the fusion of grains at the interface. This process was achieved by the dissociation, emission, and annihilation of dislocations on the IGBs.
Hot torsion tests were performed on the Al-7Mg alloy at the temperature ranging from 300 to 500°C and strain rates between 0.05 and 5 s−1 to explore the progressive dynamic recrystallization (DRX) and texture behaviors. The DRX behavior of the alloy manifested two distinct stages: Stage 1 at strain of ≤2 and Stage 2 at strains of ≥2. In Stage 1, there was a slight increase in the DRXed grain fraction (X DRX) with predominance of discontinuous DRX (DDRX), followed by a modest change in X DRX until the transition to Stage 2. Stage 2 was marked by an accelerated rate of DRX, culminating in a substantial final X DRX of ∼0.9. Electron backscattered diffraction (EBSD) analysis on a sample in Stage 2 revealed that continuous DRX (CDRX) predominantly occurred within the ( ) [001] grains, whereas the (111) [110] grains underwent a geometric DRX (GDRX) evolution without a noticeable sub-grain structure. Furthermore, a modified Avrami’s DRX kinetics model was utilized to predict the microstructural refinement in the Al-7Mg alloy during the DRX evolution. Although this kinetics model did not accurately capture the DDRX behavior in Stage 1, it effectively simulated the DRX rate in Stage 2. The texture index was employed to assess the evolution of the texture isotropy during hot-torsion test, demonstrating significant improvement (>75%) in texture randomness before the commencement of Stage 2. This initial texture evolution is attributed to the rotation of parent grains and the substructure evolution, rather than to an increase in X DRX.
Electronic devices have become ubiquitous in our daily lives, leading to a surge in the use of microwave absorbers and wearable sensor devices across various sectors. A prime example of this trend is the aramid nanofibers/polypyrrole/nickel (APN) aerogels, which serve dual roles as both microwave absorbers and pressure sensors. In this work, we focused on the preparation of aramid nanofibers/polypyrrole (AP15) aerogels, where the mass ratio of aramid nanofibers to pyrrole was 1:5. We employed the oxidative polymerization method for the preparation process. Following this, nickel was thermally evaporated onto the surface of the AP15 aerogels, resulting in the creation of an ultralight (9.35 mg·cm−3). This aerogel exhibited a porous structure. The introduction of nickel into the aerogel aimed to enhance magnetic loss and adjust impedance matching, thereby improving electromagnetic wave absorption performance. The minimum reflection loss value achieved was −48.7 dB, and the maximum effective absorption bandwidth spanned 8.42 GHz with a thickness of 2.9 mm. These impressive metrics can be attributed to the three-dimensional network porous structure of the aerogel and perfect impedance matching. Moreover, the use of aramid nanofibers and a three-dimensional hole structure endowed the APN aerogels with good insulation, flame-retardant properties, and compression resilience. Even under a compression strain of 50%, the aerogel maintained its resilience over 500 cycles. The incorporation of polypyrrole and nickel particles further enhanced the conductivity of the aerogel. Consequently, the final APN aerogel sensor demonstrated high sensitivity (10.78 kPa−1) and thermal stability. In conclusion, the APN aerogels hold significant promise as ultra-broadband microwave absorbers and pressure sensors.
The development of 3D structural composites with electromagnetic (EM) wave absorption could attenuate EM waves. Herein, magnetized flower-like Cu9S5/ZnFe2O4 composites were fabricated through a multistep hydrothermal method. The crystallographic and surface phase chemical information, morphological structure, and magnetic and EM parameters of the composites were analyzed. The prepared Cu9S5/ZnFe2O4 composites have multiple loss paths for EM waves and present an overall 3D flower-like structure. The Cu9S5/ZnFe2O4 composites exhibit a minimum reflection loss of −54.38 dB and a broad effective absorption bandwidth of 5.92 GHz. Through magnetization, ZnFe2O4 particles are self-assembled and grown on the surfaces of Cu9S5. Such a modification is conducive to the generation of additional cross-linking contact sites and the effective introduction of a large number of phase interfaces, crystalline defects, special three-dimensional flower-like structures, and magneto–electrical coupling loss effects. Moreover, the synergistic effect of multiple loss strategies effectively improves EM wave absorption by the material. This work can provide a strategy for the use of magnetization-modified sulfide composite functional materials in EM wave absorption.
A glass frit containing Li2O–MgO–ZnO–B2O3–SiO2 component was used to explore the low-temperature sintering behaviors and microwave dielectric characteristics of tri-rutile MgTa2O6 ceramics in this study. The good low-firing effects are presented due to the high matching relevance between Li2O–MgO–ZnO–B2O3–SiO2 glass and MgTa2O6 ceramics. The pure tri-rutile MgTa2O6 structure remains unchanged, and high sintering compactness can also be achieved at 1150°C. We found that the Li2O–MgO–ZnO–B2O3–SiO2 glass not only greatly improves the low-temperature sintering characteristics of MgTa2O6 ceramics but also maintains a high (quality factor (Q) × resonance frequency (f)) value while still improving the temperature stability. Typically, great microwave dielectric characteristics when added with 2wt% Li2O–MgO–ZnO–B2O3–SiO2 glass can be achieved at 1150°C: dielectric constant, ε r = 26.1; Q × f = 34267 GHz; temperature coefficient of resonance frequency, τ f = −8.7 × 10−6 /°C.