Traditional manufacturing processes for lightweight curved profiles are often associated with lengthy procedures, high costs, low efficiency, and high energy consumption. In order to solve this problem, a new staggered extrusion (SE) process was used to form the curved profile of AZ31 magnesium alloy in this paper. The study investigates the mapping relationship between the curvature, microstructure, and mechanical properties of the formed profiles by using different eccentricities of the die. Scanning electron microscopy (SEM) and electron backscatter diffraction techniques are employed to examine the effects of different eccentricity values (e) on grain morphology, recrystallization mechanisms, texture, and Schmid factors of the products. The results demonstrate that the staggered extrusion method promotes the deep refinement of grain size in the extruded products, with an average grain size of only 15% of the original billet, reaching 12.28 µm. The tensile strength and elongation of the curved profiles after extrusion under the eccentricity value of 10 mm, 20 mm and 30 mm are significantly higher than those of the billet, with the tensile strength is increased to 250, 270, 235 MPa, and the engineering strain elongation increased to 10.5%, 12.1%, 15.9%. This indicates that staggered extrusion enables curvature control of the profiles while improving their strength.
Selective laser melting (SLM) is a cost-effective 3D metal additive manufacturing (AM) process. However, AM 316L SS has different surface and microstructure properties as compared to conventional ones. Boriding process is one of the ways to modify and increase the surface properties. The aim of this study is to predict and understand the growth kinetic of iron boride layers on AM 316L SS. In this study, for the first time, the growth kinetic mechanism was evaluated for AM 316L SS. Pack boriding was applied at 850, 900 and 950 °C, each for 2, 4 and 6 h. The thickness of the boride layers ranged from (1.8±0.3) µm to (27.7±2.2) µm. A diffusion model based on error function solutions in Fick’s second law was proposed to quantitatively predict and elucidate the growth rate of FeB and Fe2B phase layers. The activation energy (Q) values for boron diffusion in FeB layer, Fe2B layer, and dual FeB+Fe2B layer were found to be 256.56, 161.61 and 209.014 kJ/mol, respectively, which was higher than the conventional 316L SS. The findings might provide and open new directions and approaches for applications of additively manufactured steels.
In this study, samples obtained from 1.3343 high-speed steel punches with TiN coatings were tested. The samples were subjected to heat treatment at different cryogenic temperatures (<196 °C) and durations (12, 24 and 36 h), followed by tempering at two different temperatures (200, 500 °C). For performance testing, a ball-on-disk wear test setup was utilized and a total of 6 groups of samples were examined. The effects of cryo-treatment and tempering on microstructure were revealed through microstructural analysis with scanning electron microscopy (SEM), X-ray (XRD diffraction), and Rietveld analysis. Additionally, the hardness of the punches was measured with microhardness measurements. The optimal wear resistance was observed in the 36 h deep cryo-treated and 200 °C tempered samples. The characterization study indicates that by cryogenic treatment a significant portion of the retained austenite transformed into martensite and secondary carbides formed, resulting in improved wear resistance and a slight increase in hardness.
The melt stirring in a large copper smelting oxygen bottom-blown furnace is caused by the large amount of gas movement blown in by two rows of oxygen lances. At present, the two rows of oxygen lances provide oxygen of equal strength, and the stirring in the central area of the melt is insufficient, which restricts the efficient progress of the smelting reaction. This study proposes a strong-weak coupling oxygen supply method and establishes an equivalent model based on a large bottom-blown furnace (LBBF) of an enterprise to simulate the bubble characteristics and flow characteristics of the molten pool. The results show that adjusting the flow ratio between the two rows of oxygen lances can create a “strong” and a “weak” coexisting source of disturbance in an LBBF. It is worth noting that when the flow rate ratio of the two rows of oxygen lances is 1.6, the peak velocity generated by the “strong” disturbance source in the molten pool increases by 18.92%, and the disturbance range increases. This method effectively strengthens the stirring in the central area of the molten pool, improves smelting efficiency, and does not produce harmful melt splashes. It provides important guidance for optimizing production practice.
In this study, Schwertmannite, Akaganéite and Ammoniojarosite were biosynthesized by different bacteria and characterized. Our results showed that bacteria are critical in mediating the mineral formation process: the morphology, crystallinity, grain size and specific surface area of each mineral varied upon different bacteria and culturing conditions. In addition, the formed minerals’ elemental composition and group disparity lead to different morphology, crystallinity and subsequent adsorption performance. In particular, adsorption difference existed in iron minerals biosynthesized by different bacteria. The maximal adsorption capacity of Akaganéite, Schwertmannite and Ammoniojarosite were 26.6 mg/g, 17.5 mg/g and 3.90 mg/g respectively. Our results also suggest that Cr(VI) adsorption on iron-minerals involves hydrogen bonding, electrostatic interaction, and ligand exchange. The adsorption only occurred on the surface of Ammoniojarosite, while for Akaganéite and Schwertmannite, the tunnel structure greatly facilitated the adsorption process and improved adsorption capacity. Thus, we conclude that the molecular structure is the primary determining factor for adsorption performance. Collectively, our results can provide useful information in selecting suitable bacteria for synthesizing heavy-metal scavenging minerals according to different environmental conditions.h
The high-carbon ferrochrome is an essential raw material for producing stainless steel, and the demand of it increases with the increase of stainless steel. So increasing Cr recovery rate from chromite is essential for lower costs and higher economic benefits in high-carbon ferrochrome production process. This study calculated the activity of CrOx in slag and investigated the distribution behavior of Cr between slag and alloy. The ω(MgO)/ω(Al2O3) was 1.0, and the w(CaO)/w(SiO2) was from 0.2 to 0.6 in this study. The calculation and experimental results showed that the main phases of the slag were chrome-containing spinel, magnesium-aluminum spinel, olivine and melilite. The content of spinel in slag decreased with the increasing w(CaO)/w(SiO2), and the w(CrOx) in spinel also reduced, but the content of melilite increased. The distribution ratio of Cr between slag and alloy decreased with the increase of slag basicity at 1600 °C, meansning that increasing the w(CaO)/w(SiO2) of slag can improve the recovery of Cr in chromite smelting process.
Identifying potential hazards is crucial for maintaining the structural stability of opencast mining area. To address the limitations of irregular structure and sparse microseismic events in opencast mining monitoring, this paper proposes an active-source imaging method for identifying potential hazards precisely based on velocity structure. This method innovatively divides the irregular structure into unstructured grids and introduces a damping and smoothing regularization operator into the inversion process, mitigating the ill-posedness caused by the sparse distribution of events and rays. Numerical and laboratory experiments were conducted to verify the reliability and effectiveness of the proposed method. The results demonstrate the competitive performance of the method in identifying hazard areas of varying sizes and numbers. The proposed method shows potential for meeting hazard identification requirements in the complex opencast mining structure. Furthermore, field experiments were conducted on an rare earth mine slope. It confirms that the proposed method provides a more concrete and intuitive scheme for stability monitoring for the microseismic monitoring system. This paper not only demonstrates the application of acoustic structure velocity imaging technology in detecting unstructured potential hazard regions but also provides valuable insights into the construction and maintenance of stable opencast mining area.
Recently, foamed polymers have been widely used in the repair of underground engineering disasters by grouting (trenchless technology) due to controllable gelation time and self-expansion. However, the grouting process becomes more complicated due to the complex geological conditions and the self-expansion of slurry. Therefore, this paper adopts a self-made visual experimental device with peripheral pressure and water plugging rate (WPR) monitoring functions to study the influence of main influencing parameters (particle size distribution, grouting amount and dynamic water pump pressure (DWPP)) on the spatiotemporal distribution of slurry WPR and diffusion dynamic response (peripheral pressure). The results show that: When grouting amount is 563 g and DWPP is 0.013 MPa, the expansion force of the slurry in the diffusion process is dominant and can significantly change the local sand and gravel skeleton structure. When grouting amount is 563 g, DWPP is 0.013 MPa, and particle size distribution type is III, the flow time of the polymer is shortened, the pores of the gravel are rapidly blocked. Then, the peripheral pressure decreases rapidly with the increase of the distance, and the time to reach the inflection point WPR is shortened. The instantaneous blockage of the pores leads to the delayed transmission of flow field blockage information.
The mechanical parameters and failure characteristics of sandstone under compressive-shear stress states provide crucial theoretical references for underground engineering construction. In this study, a series of varied angle shear tests (VASTs) were designed using acoustic emission (AE) detection and digital image correlation technologies to evaluate the mechanical behaviors of typical red sandstone. AE signal parameters revealed differences in the number and intensity of microcracks within the sandstone, with a test angle (α) of 50° identified as a significant turning point for its failure properties. When α≥50°, microcrack activity intensified, and the proportion of tensile cracks increased. As α increased, the number of fragments generated after failure decreased, fragment sizes became smaller, and the crack network simplified. Cracks extended from the two cut slits at the ends of the rock, gradually penetrating along the centerline towards the central location, as observed from the evolution of the strain concentration field. Both cohesion (c) and internal friction angle (ϕ) measured in VAST were lower than those measured under conventional triaxial compression.
The stress gradient of surrounding rock and reasonable prestress of support are the keys to ensuring the stability of roadways. The elastic-plastic analytical solution for surrounding rock was derived based on unified strength theory. A model for solving the stress gradient of the surrounding rock with the intermediate principal stress parameter b was established. The correctness and applicability of the solution for the stress gradient in the roadway surrounding rock was verified via multiple methods. Furthermore, the laws of stress, displacement, and the plastic zone of the surrounding rock with different b values and prestresses were revealed. As b increases, the stress gradient in the plastic zone increases, and the displacement and plastic zone radius decrease. As the prestress increases, the peak stress shifts toward the sidewalls, and the stress and stress gradient increments decrease. In addition, the displacement increment and plastic zone increment were proposed to characterize the support effect. The balance point of the plastic zone area appears before that of the displacement zone. The relationship between the stress gradient compensation coefficient and the prestress is obtained. This study provides a research method and idea for determining the reasonable prestress of support in roadways.
Femtosecond laser processing is an important machining method for micro-optical components such as Fresnel zone plate (FZP). However, the low processing efficiency of the femtosecond laser restricts its application. Here, a femtosecond laser Bessel beam is proposed to process micro-FZP, which is modulated from a Gaussian beam to a Bessel annular beam. The processing time for FZP with an outer diameter of 60 µm is reduced from 30 min to 1.5 min on an important semiconductor material gallium arsenide (GaAs), which significantly improves the processing efficiency. In the modulation process, a central ablation hole that has an adverse effect on the diffraction performance is produced, and the adverse effect is eliminated by superimposing the blazed grating hologram. Meanwhile, the FZP machined by spatial light modulator (SLM) has good morphology and higher diffraction efficiency, which provides a strong guarantee for the application of micro-FZP in computed tomography and solar photovoltaic cells.
hRed-green-blue (RGB) beam combiners are widely used in scenarios such as augmented reality/virtual reality (AR/VR), laser projection, biochemical detection, and other fields. Optical waveguide combiners have attracted extensive attention due to their advantages of small size, high multiplexing efficiency, convenient mass production, and low cost. An RGB beam combiner based on directional couplers is designed, with a core-cladding relative refractive index difference of 0.75%. The RGB beam combiner is optimized from the perspective of parameter optimization. Using the beam propagation method (BPM), the relationship between the performance of the RGB beam combiner and individual parameters is studied, achieving preliminary optimization of the device’s performance. The key parameters of the RGB beam combiner are optimized using the entropy weight-technique for order preference by similarity to an ideal solution TOPSIS method, establishing the optimal parameter scheme and further improving the device’s performance indicators. The results show that after optimization, the multiplexing efficiencies for red, green, and blue lights, as well as the average multiplexing efficiency, reached 99.17%, 99.76%, 96.63% and 98.52%, respectively. The size of the RGB beam combiner is 4.768 mm×0.062 mm.
The worm wheel whose undercutting characteristic is researched is a member of offsetting normal arc-toothed cylindrical worm drive. The tooth profile of the worm in its offsetting normal section is a circular arc. The normal vector used to calculate the first-type limit function is determined in the natural frame without the aid of the curvature parameter of worm helicoid. The first-type limit line is ascertained via solving the nonlinear equations iteratively. It is discovered that one first-type limit line exists on the tooth surface of worm wheel by numerical simulation, and such a line is normally located out of the meshing zone. Only one intersection point exists between the first and second-types of limit lines, and this point is a lubrication weak point. The undercutting mechanism is essentially that a part of the meshing zone near the conjugated line of worm tooth crest will come into the undercutting area and will be cut off during machining the worm wheel. The machining simulation verifies the correctness of undercutting mechanism. Moreover, a convenient and practical characteristic quantity is proposed to judge whether the undercutting exists in the whole meshing zone via computing the first-type limit function values on the worm tooth crest.
Gear flank modification is essential to reduce the noise generated in the gear meshing process, improve the gear transmission performance, and reduce the meshing impact. Aiming at the problem of solving the additional motions of each axis in the higher-order topology modification technique and how to accurately add the different movements expressed in the form of higher-order polynomials to the corresponding motion axes of the machine tool, a flexible higher-order gear topology modification technique based on an electronic gearbox is proposed. Firstly, a two-parameter topology gear surface equation and a grinding model of wheel grinding gears are established, and the axial feed and tangential feed are expressed in a fifth-order polynomial formula. Secondly, the polynomial coefficients are solved according to the characteristics of the point contact when grinding gears. Finally, an improved electronic gearbox model is constructed by combining the polynomial interpolation function to achieve gear topology modification. The validity and feasibility of the modification method based on the electronic gearbox are verified by experimental examples, which is of great significance for the machining of modification gears based on the continuous generative grinding method of the worm grinding wheel.
On-machine measurement (OMM) stands out as a pivotal technology in complex curved surface adaptive machining. However, the complex structure inherent in workpieces poses a significant challenge as the stylus orientation frequently shifts during the measurement process. Consequently, a substantial amount of time is allocated to calibrating pre-travel error and probe movement. Furthermore, the frequent movement of machine tools also increases the influence of machine errors. To enhance both accuracy and efficiency, an optimization strategy for the OMM process is proposed. Based on the kinematic chain of the machine tools, the relationship between the angle combination of rotary axes, the stylus orientation, and the calibration position of pre-travel error is disclosed. Additionally, an OMM efficiency optimization model for complex curved surfaces is developed. This model is solved to produce the optimal efficiency angle combinations for each to-be-measured point. Within each angle combination, the effects of positioning errors on measurement results are addressed by coordinate system offset and measurement result compensation method. Finally, the experiments on an impeller are used to demonstrate the practical utility of the proposed method.
hThe gears of new energy vehicles are required to withstand higher rotational speeds and greater loads, which puts forward higher precision essentials for gear manufacturing. However, machining process parameters can cause changes in cutting force/heat, resulting in affecting gear machining precision. Therefore, this paper studies the effect of different process parameters on gear machining precision. A multi-objective optimization model is established for the relationship between process parameters and tooth surface deviations, tooth profile deviations, and tooth lead deviations through the cutting speed, feed rate, and cutting depth of the worm wheel gear grinding machine. The response surface method (RSM) is used for experimental design, and the corresponding experimental results and optimal process parameters are obtained. Subsequently, gray relational analysis-principal component analysis (GRA-PCA), particle swarm optimization (PSO), and genetic algorithm-particle swarm optimization (GA-PSO) methods are used to analyze the experimental results and obtain different optimal process parameters. The results show that optimal process parameters obtained by the GRA-PCA, PSO, and GA-PSO methods improve the gear machining precision. Moreover, the gear machining precision obtained by GA-PSO is superior to other methods.
In this study, a series of triaxial tests are conducted on sandstone specimens to investigate the evolution of their mechanics and permeability characteristics under the combined action of immersion corrosion and seepage of different chemical solutions. It is observed that with the increase of confining pressure, the peak stress, dilatancy stress, dilatancy stress ratio, peak strain, and elastic modulus of the sandstone increase while the Poisson ratio decreases and less secondary cracks are produced when the samples are broken. The pore pressure and confining pressure have opposite influences on the mechanical properties. With the increase of the applied axial stress, three stages are clearly identified in the permeability evolution curves: initial compaction stage, linear elasticity stage and plastic deformation stage. The permeability reaches the maximum value when the highest volumetric dilatancy is obtained. In addition, the hydrochemical action of salt solution with pH=7 and 4 has an obvious deteriorating effect on the mechanical properties and induces the increase of permeability. The obtained results will be useful in engineering to understand the mechanical and seepage properties of sandstone under the coupled chemical-seepage-stress multiple fields.
Accurate assessment of coal brittleness is crucial in the design of coal seam drilling and underground coal mining operations. This study proposes a method for evaluating the brittleness of gas-bearing coal based on a statistical damage constitutive model and energy evolution mechanisms. Initially, integrating the principle of effective stress and the Hoek-Brown criterion, a statistical damage constitutive model for gas-bearing coal is established and validated through triaxial compression tests under different gas pressures to verify its accuracy and applicability. Subsequently, employing energy evolution mechanism, two energy characteristic parameters (elastic energy proportion and dissipated energy proportion) are analyzed. Based on the damage stress thresholds, the damage evolution characteristics of gas-bearing coal were explored. Finally, by integrating energy characteristic parameters with damage parameters, a novel brittleness index is proposed. The results demonstrate that the theoretical curves derived from the statistical damage constitutive model closely align with the test curves, accurately reflecting the stress-strain characteristics of gas-bearing coal and revealing the stress drop and softening characteristics of coal in the post-peak stage. The shape parameter and scale parameter represent the brittleness and macroscopic strength of the coal, respectively. As gas pressure increases from 1 to 5 MPa, the shape parameter and the scale parameter decrease by 22.18% and 60.45%, respectively, indicating a reduction in both brittleness and strength of the coal. Parameters such as maximum damage rate and peak elastic energy storage limit positively correlate with coal brittleness. The brittleness index effectively captures the brittleness characteristics and reveals a decrease in brittleness and an increase in sensitivity to plastic deformation under higher gas pressure conditions.
As a typical sedimentary soft rock, mudstone has the characteristics of being easily softened and disintegrated under the effect of wetting and drying (WD). The first cycle of WD plays an important role in the entire WD cycles. X-ray micro-computed tomography (micro-CT) was used as a non-destructive tool to quantitatively analyze microstructural changes of the mudstone due to the first cycle of WD. The test results show that WD leads to an increase of pore volume and pore connectivity in the mudstone. The porosity and fractal dimension of each slice of mudstone not only increase in value, but also in fluctuation amplitude. The pattern of variation in the frequency distribution of the equivalent radii of connected, isolated pores and pore throats in mudstone under WD effect satisfies the Gaussian distribution. Under the effect of WD, pores and pore throats with relatively small sizes increase the most. The sphericity of the pores in mudstones is positively correlated with the pore radius. The WD effect transforms the originally angular and flat pores into round and regular pores. This paper can provide a reference for the study of the deterioration and catastrophic mechanisms of mudstone under wetting and drying cycles.
This study was designed to enhance the soft clayey soil treatment effects using an innovative mechanochemically activated geopolymer (GP) through the optimized inclusion of nano-metakaolin (NM) and polypropylene fiber. The study also investigated the possible improvements in the binding ability of GP stabilization under different curing regimes. To this end, binders including lime alone, LG (slag-based geopolymer), LGNM (nanomodified LG with NM) and LGNMF (LGNM/fiber) mixture were separately added to soft soil samples. The fabricated composites were then subjected to a set of macro and micro level tests. The results indicated that, adding LG binary with a 20% NM replacement can lead to a significant increase (by nearly 21 times) in soil strength and a remarkable decline (about 70%) in the compression index. In fact, NM can play a great role in accelerating the rate of hydration reactions and forming a densely packed fabric, which staggeringly improve the soil hydromechanical attributes. It was also observed that raising the curing temperature will effectively augment the polymerization kinetics, leading to a substantial increase (∼2 times) in the soil solidification process. However, the stabilized composites containing NM may reveal a brittle nature under more intense stress. Such a potential drawback seems to be resolved by the integration of fibers within the matrix. LGNM combined with fiber would boost (≥10 times) the energy absorption capacity of the soil, notably enhancing its residual strength. Overall, LGNMF may not only feature a broader range of benefits (inc. economic, technical, environmental) compared to traditional binders but also promote the ductility of the GP materials.
To understand the specific behaviors of coastal coral sand slope foundations, discrete element method (DEM) was employed to examine the effect of breakable particle corners on the performance of coral sand slope foundations under a strip footing, from macro to micro scales. The results demonstrate that the bearing characteristics of coral sand slope foundations can be successfully modeled by utilizing breakable corner particles in simulations. The dual effects of interlocking and breakage of corners well explained the specific shallower load transmission and narrower shear stress zones in breakable corner particle slopes. Additionally, the study revealed the significant influence of breakable corners on soil behaviors on slopes. Furthermore, progressive corner breakage within slip bands was successfully identified as the underling mechanism in determining the unique bearing characteristics and the distinct failure patterns of breakable corner particle slopes. This study provides a new perspective to clarify the behaviors of slope foundations composed of breakable corner particle materials.
The special columnar jointed structure endows rocks with significant anisotropy, accurately grasping the strength and deformation properties of a columnar jointed rock mass (CJRM) under complex geological conditions is crucial for related engineering safety. Combined with the irregular jointed networks observed in the field, artificial irregular CJRM (ICJRM) samples with various inclination angles were prepared for triaxial tests. The results showed that the increase in confining pressure can enhance the ability of the ICJRM to resist deformation and failure, and reduce the deformation and strength anisotropic degrees. Considering the field stress situation, the engineering parts with an inclination angle of 30°–45° need to be taken seriously. Four typical failure modes were identified, and the sample with an inclination angle of 15° showed the same failure behavior as the field CJRM. Traditional and improved joint factor methods were used to establish empirical relationships for predicting the strength and deformation of CJRM under triaxial stress. Since the improved joint factor method can reflect the unique structure of CJRM, the predictive ability of the empirical relationship based on the improved method is better than that based on the traditional joint factor method.
The intersection is a widely used traffic line structure from the shallow tunnel to the deep roadway, and determining the subsidence hidden danger area of the roof is the key to its stability control. However, applying traditional maximum equivalent span beam (MESB) theory to determine deformation range, peak point, and angle influence poses a challenge. Considering the overall structure of the intersection roof, the maximum equivalent triangular plate (METP) theory is proposed, and its geometric parameter calculation formula and deflection calculation formula are obtained. The application of the two theories in 18 models with different intersection angles, roadway types, and surrounding rock lithology is verified by numerical analysis. The results show that: 1) The METP structure of the intersection roof established by the simulation results of each model successfully determined the location of the roof’s high displacement zone; 2) The area comparison method of the METP theory can be reasonably explained: ① The roof subsidence of the intersection decreases with the increase of the intersection angle; ② The roof subsidence at the intersection of different roadway types has a rectangular type > arch type > circular type; ③ The roof subsidence of the intersection with weak surrounding rock is significantly larger than that of the intersection with hard surrounding rock. According to the application results of the two theories, the four advantages of the METP theory are compared and clarified in the basic assumptions, mechanical models, main viewpoints, and mechanism analysis. The large deformation inducement of the intersection roof is then explored. The J2 peak area of the roof drives the large deformation of the area, the peak point of which is consistent with the center of gravity position of the METP. Furthermore, the change in the range of this peak is consistent with the change law of the METP’s area. Hence, this theory clarifies the large deformation area of the intersection roof, which provides a clear guiding basis for its initial support design, mid-term monitoring, and late local reinforcement.
In order to accommodate higher speeds, heavier axle weights, and vibration damping criteria, a new floating slab structure was proposed. The new type of floating slab track structure was composed of three prefabricated floating slabs longitudinally interconnected with magnesium ammonium phosphate concrete (MPC). This study investigated the dynamic performance of the structure. We constructd a full-scale indoor experimental model to scrutinize the disparities in the impact performance between a longitudinally connected floating slab track and its longitudinally disconnected counterpart. Additionally, a long-term fatigue experiment was conducted to assess the impact performance of longitudinally connected floating slab tracks under fatigue loading. The findings are described in the following. 1) The new structure effectively suppresses ground vibrations, exhibiting a well-balanced energy distribution profile. However, the imposition of fatigue loading leads to a reduction in the damping performance of the steel spring damping system, thereby reducing its capacity to attenuate structural vibrations and leading to an increase in ground vibration energy; 2) After 107 loading cycles, the attenuation rate of the vibration acceleration for the MPC increases by 171.9%. Conversely, at the corresponding disconnected location, the attenuation rate of ground vibration acceleration decreases by 65.6%. In conclusion, longitudinally connected floating slab tracks exhibit superior vibration reduction performance. While the vibration reduction performance of longitudinally connected floating slab tracks may diminish to some extent during long-term service, these tracks continue to meet specific vibration reduction requirements.