Superhydrophobic surfaces have attracted considerable interest due to their various functions and wide applications. Most of the existing methods for preparing superhydrophobic surfaces are only applicable to one or several specific substrate materials, which have the disadvantage of substrate-dependent. Here, an approach for the fabrication of substrate-independent superhydrophobic surfaces based on femtosecond laser-chemical hybrid processing is proposed. Micro/nanostructures are constructed on substrates via femtosecond laser direct writing technology, followed by modification with stearic acid. The laser-treated samples coated with stearic acid (LTx-SA, x presents different samples) surfaces have excellent superhydrophobic and self-cleaning properties. Moreover, it is worth noting that the LTx-SA surfaces remain stable superhydrophobicity after heating substrate from 20 °C to 100 °C, washing substrate 10 times, and exposing substrate to air for 60 days. This work provides an efficient and facile strategy for achieving substrate-independent superhydrophobic surfaces.
The effect of aging on the mechanical properties of the 2195-T34 Al−Li alloy at different stress levels was investigated. When the stress was below the high-temperature yield strength (YS), the YS and elongation (EL) of the low-stress aged (LSA) and stress-free aged (SFA) specimens were similar. When the stress exceeded the high-temperature YS, the ultimate tensile stress (UTS) and EL of the specimens (HSA specimens) decreased significantly. This decrease suggested that an increase in stress reduced the damage resistance of the material. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observations showed that variations in the effect of stress on the material properties were attributed to the combined effect of internal precipitate characteristics and Cu-rich precipitates at the grain boundary. The increase in stress induced the segregation of Cu atoms at the grain boundaries to form Cu-rich precipitates, facilitating the formation of precipitation-free zones (PFZ) at the grain boundaries. In addition, Cu-rich precipitates could act as damage nucleation sites, reducing the ductility of the material.
The effect of solid solution parameter and quenching cooling rate on the microstructure and properties of the 7055 aluminum alloy was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and hardness, electrical conductivity, immersion corrosion test methods. The results show that there is obvious coarse phase aggregation in the as-extruded alloy, with an area fraction of 23.8%; after single-stage solid solution at 450 °C/1 h, the coarse phase redissolves obviously, with an area fraction of 7.6%; the coarse phase is further reduced after the double-stage solution at 450 °C/1 h+475 °C/1 h, and the area fraction is reduced to 4.3%. When the second stage solution temperature is increased to 490 °C, the alloy is overburnt. The hardness and electrical conductivity of the alloy decrease after different solid solution treatments, and then increase significantly after aging treatment at 160 °/6 h. The quenching cooling rate has a significant effect on exsolution and corrosion resistance. The alloys with cooling rates of less than 30 °C/min have obvious exsolution of η phase and S phase, which reduce the driving force of subsequent aging precipitation. The quenching sensitive temperature range of the alloy is around 375–200 °C, and the exsolution during cooling can be significantly suppressed by passing through the quenching sensitive temperature range with cooling rates of not less than 60 °/min.
In this work, the interface morphology and element distribution of the TC1/AA1060/AA6061 composite plate were studied. The grain information was investigated by electron backscattered diffraction and interface temperature was obtained by numerical simulation to explain the grain information. The experimental samples were tested by mechanical methods. The results show that the TC1/AA1060/AA6061 composite plate has better welding quality by observing interface morphology and testing mechanical properties. The morphology of the two interfaces was consistent with the simulation results, and the interface temperature can be explained by the grain information at interfaces and vortex regions. The diffusion width of elements at the TC1/AA1060 interface was 12.3 µm and no intermetallic compounds were detected; Only Al and O element were detected in two vortex regions. In addition, nanoindentation test was performed at different regions and the results were discussed.
In this paper, the strengthening mechanism of different Sm content on extruded Mg-6Al-2Sr alloy was studied. The microstructure was observed by metallographic experiment, X-ray diffraction, scanning electron microscopy and transmission electron microscopy, and the effect of Sm content on the microstructure of the alloy was analyzed by EBSD. The main experiment in this paper is the extrusion experiment of Mg-6Al-2Sr cast alloy with different Sm content. The results show that with the increase of Sm content, the generated Al2Sm phase is broken under the action of extrusion, and uniformly dispersed at the grain boundary along the extrusion direction, which hinders the grain growth. However, with the increase of Sm content, the Al2Sm phase increases and aggregates at the grain boundary, which has an adverse effect on the mechanical properties of the alloy. When the Sm content is 1.5 wt%, the average grain size of the alloy is the finest, and its tensile strength, yield strength and elongation reach 297.9 MPa, 257.8 MPa and 21.3%, respectively. The hardness reaches HV78.9, which is 15.6% higher than that of the alloy with 0 wt% Sm content. The yield strength increased by 34.6% and the elongation increased by 34.8%.
Lean duplex stainless steel 2101 (LDX 2101) is a promising material to replace 304 austenitic stainless steel in nuclear power plant in the future and it has been widely studied for its good economy, mechanical properties and corrosion resistance. Aiming at the underwater maintenance of nuclear power, the microstructure and texture evolution of laser wire direct energy deposition in underwater environment were studied by means of optical microscope and electron backscatter diffraction. The results show that the rapid cooling effect of underwater environment on the molten pool inhibits the transformation from ferrite to austenite. Since ferrites have the lowest surface energy, most of them were precipitated along the dense-packed (111)α and (110)α planes. The deposition structure shows typical cube texture and Goss texture. Although the texture of austenite is not as strong as that of ferrite passing through the deposition layer, the results show that the austenite phase was formed with a close Kurdjumov-Sachsorientation orientation relationship with respect to the ferrite phase. It is also found that the cyclic reheating effect of laser wire direct energy deposition not only changes the microstructure and texture, but also affects the grain size and the proportion of special grain boundaries. Improving the content and distribution uniformity of Σ3 grain boundary in the deposition structure is beneficial to improve the corrosion resistance.
With high-energy wet ball milling M2 high-speed steel (HSS) powder and ferrovanadium alloy, an in-situ synthesized core-shell MC carbides reinforced M2 HSS was prepared via vacuum sintering. The phase, morphology and composition distribution of the milled composite powders, and the evolution of the sintered microstructure with the temperature and the associated mechanical properties before and after heat treatment were investigated. The ground powders were fully refined into lamellae and aggregates with V-element evenly distributed inside. Almost full densification (∼99.2% relative density) of the modified M2 steel was achieved at 1180 °C by supersolidus liquid phase sintering. Near-spherical MC carbides and irregular M6C carbides were dispersed within the HSS matrix, and the MC developed a core-shell structure due to the solidification of the sintering liquid. Both the matrix grains and carbides of the sintered alloy had been refined by heat treatment, reaching satisfactory bending strength of 3580 MPa and hardness of HRC58, and enhancing the scratch resistance significantly.
In this paper, SiCf/SiC composites with three kinds of preform structures, namely 2D multilayered, 3D angle-interlock and multiaxis 3D braided, were prepared by chemical vapor infiltration. The influences of preform structure on mechanical and thermal properties of SiCf/SiC composites were discussed in detail, on the basis of comprehensive analyses of fiber arrangement, SiC matrix and pore distribution, and so on. The results show that the mechanical properties and thermal conductivity are comprehensively affected by the fiber arrangement and the density of composites, while the coefficient of thermal expansion is mainly influenced by the fiber arrangement. In addition, the thermal conductivity of 2D multilayered, 3D angle-interlock and multiaxis 3D braided composites could be explained by series model and parallel model, respectively. The continuous three-dimensional network structure of SiC matrix layer inside multiaxis 3D braided composites could be regarded as a fast channel for heat flow, resulting in a higher thermal conductivity. As the temperature increases, the scattering between phonons gradually increases and becomes the main factor affecting the thermal conductivity. In this case, the role of the SiC matrix layer as a fast channel for phonon propagation in multiaxis 3D braided composites gradually weakens.
The aggregation of low-dimensional nanofillers in the host ceramic matrix significantly discounted their reinforcing efficiency. Herein, employing two-dimensional graphene (G) and one-dimensional SiC nanowire (SiCnw), WC-G-SiCnw ceramic composites were prepared through spark plasma sintering. The effects of sintering temperature, soaking time and pressure on the mechanical properties of the WC-based composites were reported. The influence of graphene and SiCnw on the densification, microstructure and mechanical properties of the ceramic composites were investigated. The experimental results demonstrated that excellent mechanical properties were achieved for WC-0.15 wt.% G–0.45 wt.% SiCnw prepared through sintering at 1900 °C for 15 min holding time and 60 MPa pressure, with a hardness of 25.6 GPa, a flexural strength of 1499 MPa and a fracture toughness of 11.6 MPa·m1/2. The toughening mechanisms were mainly the combination of G and SiCnw induced crack deflection, bridging and pullout. This study provided a simple toughening method in developing high-performance ceramic composites.
Heterocoagulation between fine particles can interfere with the flotation separation of different minerals. Therefore, the study of particle heterocoagulation is significant. This study found that fine calcite affected galena flotation and examined the interactions between galena and fine calcite particles in suspension pulp. The best flotation behaviour was observed for pure galena minerals at pH 9; however, the flotation separation of galena and fine calcite yielded unsatisfactory results under these conditions. The results of zeta potential measurement, scanning electron microscopy, and X-ray photoelectron spectroscopy indicate that heterocoagulation occurred between the calcite and galena particles at pH 9. The interaction mechanism shows that dissolved hydroxy calcium could be absorbed on the surface of galena and render a positive charge, causing coagulation between the calcite and galena particles due to electrostatic attraction. This new discovery provides a reference for the pre-inhibition of gangue minerals and adjustment of the chemical ratio during the flotation process.
In order to efficiently remove 4-nitrophenol (4-NP) and 2,4-dinitrophenol (2,4-DNP), 4-NP and 2,4-DNP were used as template molecules and double-template magnetic molecularly imprinted polymers (D-MIPs) were prepared by surface molecular imprinting technology using itaconic acid as functional monomer, Fe3O4@SiO2 as carrier, ethylene glycol dimethacrylate as crosslinking agent and azodiisobutyronitrile as initiator. The morphology of D-MIPs was characterized using FT-IR and SEM. The adsorption specificity, regenerability, and applicability of D-MIPs were studied in detail. The results show that D-MIPs successfully coated the surface of the Fe3O4@SiO2 carrier and had a good polymerization effect, specific recognition sites, and good imprinting performance, with a diameter of 90 nm and homogeneous shape. The theoretical adsorption capacities of 4-NP-MIPs, 2, 4-DNP-MIPs, and D-MIPs for target molecules were 103.97, 73.14 and 123.99 mg/g, respectively. There were many adsorption sites with different adsorption energies. D-MIPs reached the optimal adsorption equilibrium state in 30 min. The best fitting models for the MIPs were the Freundlich adsorption and pseudo-second-order kinetic models, indicating that adsorption of MIPs occurred via a chemical adsorption process. Test results show that MIPs had highly specific recognition and selective adsorption capacity in different water samples. After eight regeneration cycles, the adsorption capacity of D-MIPs decreased by 7.51%, confirming that MIPs had excellent regeneration.
This study aims to simulate pulsatile blood flow in the carotid artery with different stenosis severities and pulse rates. The effects of different severities of stenosis, pulse rates, and arterial wall properties on the surrounding fluid are investigated by using fluid-structure interaction (FSI) and arbitrary Lagrangian-Eulerian (ALE) methods. Carreau-Yasuda non-Newtonian and modified Mooney-Rivin hyperelastic models are applied for blood with non-Newtonian behavior and hyperelastic blood vessel’s wall, respectively. Results are presented in terms of wall radial displacement, pressure distribution, the axial velocity profile, and wall shear stress for blood. By increasing the stenosis severities, there would be a change in several parameters. Axial velocity, variation of blood pressure, the maximum wall shear stress, and wall radial displacement experience a growth. Furthermore, when the pulse rate grows in the stenosis severity of 75%, the maximum flow rate moments, maximum values for wall radial displacement, pressure, axial velocity, and wall shear stress increase as well. Using a hyperelastic model for the arterial wall, as opposed to elastic and rigid models, and treating the surrounding fluid as non-Newtonian and unsteady, allows us to achieve a more realistic simulation. In the stenosis having up to 50% of severity, red blood cells are under the enforcement of insignificant damage, while hemolysis is observed in the severe stenosis of 75%. By improving atherosclerosis, which leads to the development of elastic modulus from 500 kPa to 2 MPa, the 65% growth of the maximum value of shear stress at 60 bpm pulse rate and in the stenosis with 75% severity has been noticed. It can be demonstrated that hyperelastic models of the arterial walls lead to lower axial velocity, lower blood pressure, lower shear stress, and higher radial displacement, as opposed to rigid and elastic arterial walls.
To study the effect of liquid cooling, including acid cooling and water cooling, on the microscopic characteristics of high-temperature granite, scanning electron microscopy and energy spectroscopy analysis tests (SEM-EDS) as well as mercury injection experiments were carried out on liquid-cooled granite. The SEM-EDS results show that the elemental composition is barely affected by water cooling, while acid cooling causes reductions in O, Si, and metallic elements. The pores and cracks were observed in both cases. Moreover, a more non-flat, loose, and rough surface is created under acid cooling conditions compared to water cooling. Mercury injection tests show an increase in porosity, pore volume, and specific surface area in liquid-cooled granite samples, while their fractal dimensions show an opposite trend. Acid cooling leads to significantly greater property changes than water cooling, owing to the dissolution effects of mud acid. The results demonstrate that the acid cooling process results in greater capacity of pore generation and expansion, as well as lower pore structure complexity, compared to water cooling.
To investigate the mechanism of water’s effect on the pore structure of rocks, this study relies on the sandstone formation in Wanfu Coal Mine, Shandong, China. Scanning electron microscopy (SEM), nitrogen adsorption-desorption, and high-pressure mercury intrusion combined with pore structure testing experiments were conducted on sandstone samples subjected to different immersion times. The aim was to analyze the variations in the pore structure of micropores (<2 nm), mesopores (2–50 nm), and macropores (>50 nm). The results indicate that the pore structure of the sandstone consists mainly of narrow and wedge-shaped structures. The pores have the ability to connect and form fissures. During the water absorption process, the porosity of the sandstone initially decreases and then increases. The proportion of micropores decreases initially and then increases, while the proportion of mesopores and macropores increases initially and then decreases. According to the quantitative assessment of pore structure using generalized fractal dimension and spectral width, it is found that there is a positive correlation between pore structure and pore quality. That is, as the difference in fractal dimension and spectral width increases, the pore structure becomes more complex. There is a negative correlation between pore structure and porosity, that is, larger porosity corresponds to smaller differences in fractal dimension and spectral width.
In this study, a series of coal measures mudstone specimens containing a prefabricated flaw were subjected to true triaxial test (TTT), namely, specimens of the intermediate principal stress (σ 2) parallel to prefabricated flaw (TTT-Flaw-2) and specimens of the minimum principal stress (σ 3) parallel to prefabricated flaw (TTT-Flaw-3). The main objective of this study was to investigate the effects of the loading direction of σ 2 and the position of prefabricated flaw on the strength and failure modes of specimens. The results showed that the peak strength of intact and flawed specimens first increased and then decreased with increasing σ 2, which could be fitted by the Mogi-Coulomb criterion. Under the same loading stresses, the strength of intact specimen was larger than that of flawed specimens, and specimens TTT-Flaw-2 had the lowest strength. The X-ray computerized tomography scanning results revealed that fractures were not always observed to form along the prefabricated flaw tips but were distributed randomly inside the specimen under conventional triaxial test conditions. Under TTT conditions, anti-wing cracks initiated from the vicinity of the prefabricated flaw tip and were observed in σ 2-drrection for specimens TTT-Flaw-2. While for specimens TTT-Flaw-3, shear cracks appeared in σ 2-direction, and few anti-wing cracks were observed in σ 3-direction.
The novel CO2 static blasting method offered good prospects for application as it was more effective than mechanical rock breaking, less vibratory, less dusty and quieter than the traditional drill and blast method. We carried out both true triaxial CO2 static blasting fracturing experiments and rock-breaking site vibration monitoring experiments to extract vibration signal characteristics, focusing on slope safety. The results show that: 1) the peak vibration velocity of CO2 static blasting decayed rapidly and dropped below 30 mm/s at 6 m; 2) the principal frequency of the vibration waveform spectrum caused by CO2 static blasting was higher than that of the drill-and-blast method; 3) the vibration velocity prediction formula used in the drill-and-blast method was applicable to CO2 static blasting, and the prediction formula with elevation was more accurate. An HIG fracturing model for CO2 static blasting is proposed, which provides a basic framework for research of new rock-breaking techniques. The vibration displacement of the slope under CO2 static blasting is minimal, and more attention should be paid to the exothermic and temperature measurement of the polyenergy agent in the future.
The engineering optimization of ultra-high strength concrete (UHPC) requires urgent exploration of the strengthening mechanism of steel fiber in UHPC and the establishment of an effective simulation model. In this study, we propose a new fracture phase field model that considers the fracture energy of the interface between steel fiber and UHPC matrix. The model is utilized to conduct uniaxial tensile numerical simulations of 3D UHPC incorporating steel fibers, and a comparative experiment is conducted to validate the proposed model. The results display a notable agreement between the simulation and experiment. It is found that the tensile strength and residual strength of UHPC increase with steel fiber volume content and decrease with steel fiber diameter. The inclusion of steel fibers in UHPC results in more intricate crack patterns during the fracture process. The above results can be attributed to the debonding occurring at the interface between the steel fiber and the UHPC matrix which dissipates additional energy and thus enhances the UHPC. This work establishes a theoretical foundation for UHPC performance design and the development of effective simulation methods.
The silt in the Yellow River flood field exhibits strong water sensitivity and unique mechanical properties, which makes it vulnerable to vibration load. This study investigates the dynamic elastic modulus and damping ratio characteristics of the silt by considering the influence of confining pressure and saturation through dynamic triaxial tests. Test results indicate that the backbone curves of the silt are consistent with a typical hyperbolic relationship. The dynamic elastic modulus sharply decreases and eventually tends to stabilize with increasing dynamic strain. Furthermore, the dynamic elastic modulus gradually increases with an increment in confining pressure and decrement in saturation, while the damping ratio simultaneously decreases. A binary linear equation can conveniently estimate the dynamic elastic modulus at a small strain. Based on quantitative analyses, a modified Hardin-Drnevich model is preliminarily proposed to calculate the dynamic elastic modulus and damping ratio of the silt. This investigation supplies a theoretical reference for the engineering construction of the Yellow River basin.
Permanent displacement occurs in strike-slip faults due to stick-slip action, causing significant damage and distinct partitioning features in tunnels intersecting these faults. To elucidate the longitudinal and cross-sectional partitioned failure mechanism of tunnels and provide seismic design support for tunnels intersecting active faults, we investigated several seismic damage examples to summarize three tunnel failure modes: circumferential cracks, inclined cracks, and longitudinal cracks. The key influencing factors, such as fault type, intersection angle, fault dislocation, and tunnel stiffness, were identified and discussed. The results show the following. 1) The mechanical response and safety of tunnels are primarily influenced by fault type, while dip angle has a minimal impact; 2) Tunnels subject to left-lateral strike-slip faulting can be longitudinally divided into bending-compression-shear (L-BCS) and bending-compression (L-BC) zones, while those subject to right-lateral strike-slip faulting can be divided into bending-tension-shear (L-BTS) and bending-tension (L-BT) zones; 3) The range of the L-BCS and L-BTS zones is 1.4D–1.7D (D is the tunnel diameter), whereas the range of the L-BC and L-BT zones varies with key influencing factors; 4) The cross section of tunnels can be divided into eccentric-compression (C-EC) and eccentric-tension (C-ET) zones, which are susceptible to eccentric compression or eccentric tension failure. The C-EC and C-ET zones are approximately 5D away from the fault plane; 5) The C-EC zone of tunnels that traverse left-lateral strike-slip faults includes the left hance of the hanging wall, right hance of the footwall, tunnel crown, and tunnel invert, while the C-ET zone includes the left hance of the hanging wall and right hance of the footwall. In addition, the cross-sectional partitioning of a tunnel crossing a right-lateral strike-slip fault is symmetrical to that of a left-lateral fault.
This paper presents a case study on the subgrade settlements of four national railway lines induced by twin shield tunnel excavations. The development characteristics of subgrade settlements can be divided into three stages. The monitoring data indicate that subgrade settlements increase gradually before the shield machine crossing the monitoring region, then increase sharply during the shield machine crossing, and finally approach to be stable after the shield machine crossing. Immediately splicing the segments into rings, implementing the compensation and secondary grouting facilitate the control of subgrade settlements. Operational parameters play a crucial role in controlling the subgrade settlements. The effects of the operational parameters of the shield machine on the subgrade settlements are analyzed. The investigation reveals that excessive shield driving velocity causes large subgrade settlements, accompanied by the sudden reduction of rotation torque and total thrust. The excavated earth volume affects the subgrade settlements insensitively because of its easily controlling. Synchronous grouting volume can rise the existing subgrade if not controlled appropriately. Great subgrade settlements cause large earth pressures to be exerted at the chamber. Some valuable references and guidance are given through this paper for the operational parameter setting of shield machines and deformation control of multiple railway lines due to the shield tunnel excavation beneath.
This paper proposes a gradient descent based restoration method of track irregularity. Based on the theory of asymmetric chord-reference method (CRM), the restoration of track irregularity is described as an optimization problem for an underdetermined linear system. Gradient descent method is employed to solve this optimization problem, where a quadratic cost function considering penalization is used. To evaluate the performance of the proposed method, an inspection trolley was setup and used in a field test on a scaled bridge model. Comparison between the proposed method and level measurement validates a good accuracy of gradient descent based restoration method. Compared with traditional method which needs a specially designed inverse filter, the proposed method has a clear physical meaning, which only needs configuration of asymmetric CRM and measured chord reference value to establish the optimization model. This suggests that gradient descent method has good operability in the field test. And the repeatability assessment reveals that the proposed method has a good track irregularity restoration reproduction capacity.
This study proposes an efficient parallel computation method based on Seed-preconditioned Conjugate Gradient (Seed-PCG) algorithm, to address the issue of computational inefficiency of random multi-sample in three-dimensional (3D) finite element (FE) model of train-track-soil. A 3D train-track-soil coupled random vibration analysis model is established using the finite element method (FEM) and the pseudo-excitation method (PEM) under track irregularity excitation. The Seed-PCG method is utilized to solve the system of linear equations with multiple right-hand sides arising from the random analysis of the vehicle-induced ground vibration. Furthermore, by projecting the Krylov subspace obtained from solving the seed system by the PCG method, the initial solution of the remaining linear equation systems and the corresponding initial residuals are improved, leading to an effective enhancement of the convergence speed of the PCG method. Finally, the parallel computing program is developed on a hybrid MATLAB-Compute Unified Device Architecture (CUDA) platform. Numerical examples demonstrate the effectiveness of the proposed method. It achieves 104.2 times acceleration compared with the multi-point synchronization algorithm (MPSA) proposed by author ZHU under the same computing platform. Moreover, compared with the PCG method, the number of iterations is reduced by 18 % and the acceleration is increased by 1.21 times.