Abstract: Fire-protective super thermal insulator is an inorganic material with a nanopore structure and super-low thermal conductivity. It can be classified as either a sol-gel aerogel-based composite or a fumed oxide-based composite. The matrix oxides are investigated from SiO2 to oxides with higher melting temperatures, including Al2O3 or ZrO2. It was found that the complex component oxides with the appropriate ratios exhibit better thermal stability than single oxide when exposed to fire. The infrared opacifier is a key component to this material that can significantly reduce its high-temperature thermal conductivity. The appropriate selection of opacifiers becomes possible by determining the specific infrared extinction coefficient and performing a numerical calculation based on Mie scattering theory. This fire protection material has high fireproof efficiency while also being very thin and is rated as having high fire resistance. With the development of ambient pressure drying for aerogel-based composite from supercritical drying, this fire protection material can be manufactured at low overall cost and will play an important role in passive fire protection systems in urban underground spaces.
Abstract: The performance of combustion of ventilation air methane (VAM) over transition metal oxide oxygen carriers was studied through experiments with using tube reactors. The results show that the activity of activated oxygen carriers in converting CH4 to CO2 is as follows:CuO60/γ-Al2O3 > NiO60/γ-Al2O3 > Fe2O360/γ-Al2O3. CH4 conversion based on CuO60/γ-Al2O3 decreases with increasing gas hourly space velocity, but increases with increasing bed temperature and CuO loading. The lower the initial CH4 concentration of ventilation air methane, the lower is the temperature for the CH4 conversion of 90%. There are catalytic combustion mechanisms and chemical-looping combustion mechanisms for CH4 combustion over both CuO60/γ-Al2O3, for which dispersion of the active component is low but loading is high, and CuO5.5/γ-Al2O3, for which dispersion of the active component is high but loading is low. There exists a maximum for CH 4 conversion based on the catalytic combustion mechanism at some temperatures, and when the bed temperature is higher than this temperature, the contribution of chemical-looping combustion is greater than that of catalytic combustion. The initial activity of CuO5.5/γ-Al2O3 is higher than that of CuO60/γ-Al2O3, while the stability of CuO60/γ-Al2O3 activity is better than that of CuO5.5/γ-Al2O3 activity under the same conditions.
Abstract: Two kinds of magnetite concentrates from Pilbara in Australia and an area in the northeast in China were used to explore the effect of wettability, which depends on particle size, on ballability. Capillary osmosis equipment of a horizontal plate was constructed based on the equation Washburn. To investigate the effect of particle size and wettability of ultrafine magnetite concentrates on ballability, ballability, balling test, and performance test were performed. The results suggest that ultrafine particle size and wettability strongly affect ballability. Its better wettability on account of particle ultrafine size characteristic is beneficial to improve its compressive strength. However, a narrow ultrafine particle-size distribution will limit the improvements in ballability, because it affects the capillary radius.
Abstract: The solidified iron layer in blast furnace (BF) hearth was estimated based on the blast furnace damage. The phase compositions of the solidified iron layer were studied using scanning electron microscope and energy dispersive spectrometer. The temperature and proportions of graphite precipitation were calculated by using the Thermol-calc software and the TCFE8 database. Finally, the formation of the solidified iron layer was examined. The results suggest that the solidified iron comprises iron and graphite. The temperature of the graphite precipitation is affected by the composition of the hot metal, and it is much higher than the solidification temperature of the hot metal. The proportions of precipitated graphite are affected by the C and Si in the hot metal, whereas the precipitated graphite increases the viscosity of the hot metal by 11.9%. The graphite precipitates at the interface with the Fe-refractory at lower temperature than that of the graphite saturation, which allows the C migration from the hot metal to the refractory interface.
Abstract: The influences of rare earth (RE) and Ti-RE complex treatment on the microstructures and toughness in the coarse grain heat-affected zone (CGHAZ) of C-Mn steel were investigated using a Gleeble-1500D thermal simulator with input heat energy of 65 kJ·cm-1. The inclusions and impact fracture morphology were observed and analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX), and the microstructure was characterized using an optical microscope (OM). The results show that the microstructures in the CGHAZs of RE-and Ti-RE-treated samples are mainly grain boundary ferrite (GBF) + polygonal ferrite (PF) + intragranular acicular ferrite (IAF) and grain boundary ferrite + intragranular acicular ferrite, respectively. Inclusions in the RE-treated specimen are La2O2S + Mn-Al-Si-O + MnS, while those in the Ti-RE-treated specimen are La2O2S + TiOx + Mn-Al-Si-O + MnS. The complex inclusions in Ti-RE-treated steel are smaller than those in RE-treated steel, and the size of IAF in Ti-RE-treated steel is smaller. The impact properties of the CGHAZ in Ti-RE-treated C-Mn steel is improved significantly, and the material is tougher than RE-treated steel.
Abstract: The mechanical properties and strengthening mechanism of Fe-24Mn-3Si-3Al TWIP steels were investigated as a function of annealing process. The microstructures of the samples were analyzed by transmission electron microscopy, scanning electron microscopy, energy disperse spectroscopy. The experimental results indicate that as the annealing temperature and the holding time change, the mechanical properties of TWIP steel do not rise or fall monotonously, as would be conventionally. The mechanical properties change in the annealing processes of annealing temperature 800℃ for 10 min and 900℃ for 20 min. The strengthening mechanism is mainly dispersion strengthening in the case of annealing process of 800℃ annealing temperature for 10 min, and an increase in the precipitation of (Fe, Mn)23C6 leads to better mechanical properties. However, in the case of annealing process of 900℃ for 20 min, the precipitation of (Fe, Mn)23C6 does not change obviously, but many twinning systems are initiated and secondary twin and twin delivery are observed, which result in an increase in the ultimate tensile strength.
Abstract: The microstructure of Nb-Ti micro-alloy hot stamping steels was observed and investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The toughness and tear properties were investigated by Kahn tear test. The thermodynamic software Thermo-Calc was used to calculate and analyze the behavior and composition of precipitates. The results show that Nb-Ti micro-alloy hot stamping steels with mass fraction 0.13% C are composed of martensite. Compared with traditional hot stamping steel (22MnB5), the Nb-Ti micro-alloy steel has finer prior austenite grains, martensite packets, and martensite laths. The tensile strength is more than 1500 MPa, tear strength is 1878 MPa, and the unit propagation energy is 436 kN·m-1. Nearly all Nb——Ti elements exist as precipitates during austenization at 950℃ and they can hinder the growth of austenite grains effectively. Two types of precipitates of different sizes are dispersed in the martensite matrix. The sizes of Ti(C, N) precipitates range from 100 nm to 200 nm, and their quantity is low. The nanometer-sized precipitates are carbides or nitrides of Ti and Nb, which can strengthen the martensite matrix and improve the intensity.
Abstract: The effects of texture and precipitates on the plane anisotropy of Cu-Ni-Si alloy under different solid-solution temperature conditions were investigated by X-ray diffraction, electron backscattered diffraction, and transmission electron microscopy. The results show that strength and elongation first increase and then decrease with increasing solid-solution temperature, exhibiting apparently anisotropy. After 800℃ solid solution, the Cu' and S' are mainly texture and the alloy has weak anisotropic properties, which correlates with the coexistence of Brass, Goss, and {011}〈511〉orientation owing to deformed grains. Complete recrystallization can be obtained at high temperature solution (≥ 850℃), the Cu' and S' texture intensity increases, whereas the Brass texture weakens and disappears and the anisotropy increases. δ-Ni2Si precipitation is observed after 850℃ solution and subsequent aging, and the crystal orientation between the matrix and precipitates is [001]Cu//[110]δ and (010)Cu//(001)δ. The fraction of nanosize precipitates decreases significantly with increasing temperature and this improves the anisotropy.
Abstract: The effects of cooling velocity on the multiaxial fatigue properties of A319 alloy under circular loading conditions was studied by using the MTS809 servo-hydraulic testing system and scanning electron microscopy. The results indicate that the solidification cooling velocity of 10℃·s-1 leads to decrease in the size of microstructures, such as second dendrite arming space, Si particle, and void compared. Hysteresis loops with smaller second dendrite arming space show that there is almost no phase angle between strain and stress along the axial direction. Furthermore, the decrease in second dendrite arming space size manifests as a more remarkable additional hardening effect compared to that of the sample with a cooling velocity of 0.1℃·s-1. The local regions of crack initiation are completely different. The cracks in samples solidified at a cooling velocity of 10℃·s-1 initiate and propagate from large Si particulars, in contrast to the cracks in samples solidified at a cooling velocity of 0.1℃·s-1, which initiate from pores. It is also found the A319 samples under the two different cooling velocities show initial cyclic hardening followed by cyclic softening in the axial direction and initial cyclic hardening followed by stable tendency in the shear direction.
Abstract: The effects of fluoride ions on the corrosion resistance of 304, 2507, and 904L stainless steels in high-temperature concentrated sulfuric acid were investigated by immersion and electrochemical tests as well as scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses. The results show that the corrosion resistances of these three stainless steels improve when fluoride ions are added in high-temperature concentrated sulfuric acid. Of the three, the corrosion resistance of 904L is more stable and reliable. The nickel sulfide formed in sulfuric acid, which is thermodynamically unstable, causes active-passive transition. The corrosion resistance of stainless steel increases upon the addition of fluorine ions because the nickel and fluorine ions form a more stable compound to replace nickel sulfide.
Abstract: Aluminum-based coatings were prepared by flame spraying. After remelting and diffusion treatment, the phase, composition, friction and corrosion resistance were analyzed experimentally by using scanning electron microscopy, X-ray diffraction, energy dispersive spectrometer, wear tester. The results indicate that the surface phase consists of Al and FeAl3, inner layer phase mainly contains FeAl 3 and Fe2 Al5. The coating has higher micro-hardness than the underlying material, with a maximum of up to HV 950. In an experiment of high-temperature oxidation at 800℃ and 900℃, the spray-aluminized samples show almost no weight gain, and the antioxidant properties of cast iron improve substantially (by dozens of times). In addition, the samples show excellent wear and corrosion resistance.
Abstract: Al2O3, SiO2 and ZnO were coated around nano-sized BaTiO3 particles by means of aqueous chemical coating. Then, BaTiO 3 -based energy storage ceramic material with average grain size of 120 nm was fabricated by the two-step sintering method. The coating layer can restrain grain growth and abnormal grain growth, and can enhance significantly the AC breakdown strength of the material to over 150 kV·cm-1, while providing energy density of 0.829 J·cm-3. Energy-dispersive spectroscopy proves the gathering of doping elements near grain boundaries, thus indicating the existence of a core-shell structure. High-temperature impedance spectroscopy and fitting results further explain that the energy storage properties were improved. Although the energy density of this ultrafinecrystalline ceramic material is moderate, the advantages of fine grains and low sintering temperature make it possible for the material to be used in multilayer ceramic capacitors, which can increase energy storage by orders of magnitude. This improvement is impossible to achieve with conventional energy storage ceramics.
Abstract: Electron irradiation and simultaneous pulsed-laser and electron dual-beam irradiation were performed using laser high voltage electronic microscopy (HVEM) at 500℃, and the void-denuded zone (VDZ) and radiation-induced segregation (RIS) near the random grain boundary were observed and analyzed after irradiation. Compared to electron irradiation, the effect of simultaneous pulsed-laser and electron dual-beam irradiation on vacancy diffusion was investigated. The results show that the width of VDZ after simultaneous pulsed-laser and electron dual-beam irradiation is 48 ±16 nm which is smaller than the VDZ width of 71 ±27 nm after electron irradiation. Both the magnitude and width of Cr and Ni segregation under simultaneous pulsed-laser and electron dual-beam irradiation are lower than those under electron irradiation. The ratio of vacancy flux of simultaneous pulsed-laser and electron dual-beam irradiation to that of electron irradiation is 45.7%. Compared to electron irradiation, the vacancy flux flowing into point defect sinks is lower owing to enhanced recombination between vacancies and interstitial spaces under simultaneous pulsed-laser and electron dualbeam irradiation. This has the effect of suppressing RIS and void swelling. Therefore, simultaneous pulsed-laser and electron dualbeam irradiation is expected to provide new insights into the suppression of void swelling.
Abstract: Periodical impulses in vibration signals are key features in rolling element bearing fault diagnosis. Based on an overcomplete dictionary composed of different morphological atoms, morphological component analysis can be used to extract the signal components of different types of morphologies. A new morphological component analysis method based on a novel over-completed dictionary was proposed herein. According to morphological differences between components in rolling element bearing fault vibration signal, the method after improved dictionary could more targeted to extract impulse components containing fault feature. Then through envelope spectrum analysis, the fault characteristic frequency was extracted accurately, and rolling element bearing local faults were diagnosed. Compared with the Fast Kurtogram method for bearing fault diagnosis, the new method could avoid non-accuracy and non-optimality problems caused by artificial choice of resonance band, and improve the effectiveness of fault diagnosis. By analyzing both the simulation signal and the experimental dataset of rolling element bearing faults, the proposed method is validated.
Abstract: Due to the low efficiency of the thin-walled hole measurements and the shortcomings relating to the position of the hole and the radius measurement, a method based on T-scan measurements was proposed to reconstruct the characteristics of the hole of thin-walled sheet metal parts. Firstly, point cloud data of a thin-walled hole were obtained with a T-scan, then were sorted into scan line data in accordance with the Euler distance of the successive points in the point cloud data. The points of the plane and the edge points of the thin-walled hole were subsequently gained by processing the scan line point cloud data with an algorithm. Finally, the plane parameters were obtained by applying the robust eigenvalue plane fitting method, which managed the points of the plane, and the hole center coordinates and pore sizes were obtained with the use of the least square circle fitting space. Ultimately, the features of the thin-walled hole were reconstructed. Through measuring and processing test pieces and thin-walled sheet metal parts, this experiment demonstrates that the algorithm can be well applied in practice and that the accuracy meets the requirements of the actual measurement accuracy of sheet metal parts.
Abstract: A hyper-dexterous manipulator (HDM) cleaning device, mounted on an underwater adsorption robot, was designed to address the complications of cleaning the space structure surface on ship propellers. The HDM mechanical structure was constructed by exploiting the high degrees of freedom associated with skeleton-like biological muscle. Considering the characteristics of high-pressure water jet, Hooke's hinge was used to replace flexible components at joints. Kinematics and inverse kinematics modeling of the singleended manipulator was performed using the geometric analysis method wherein a manipulator model based on the assumption of equal arcs was obtained from a multi-joint connecting rod transformation. Then, a mapping relation between the multi-joint drive space and the operation space was derived. The comparison of simulated experiments to physical results reveals that the robot arm design achieves the desired operating position and robustness can be guaranteed during the loading experiment.
Abstract: To improve the performance of the speed servo system in the permanent magnet synchronous motor (PMSM) and to reduce the influence of disturbance in the control system, a sliding mode control method was proposed based on a novel reaching law and disturbance observer. A novel reaching law was presented to solve the contradiction between sliding mode surface reaching time and the system chattering in the regular reaching law, and which can simultaneously improve the system response speed. A sliding mode disturbance observer (SMDO) was employed to estimate the system's lumped disturbances, such as parameter variations and external disturbances. The estimated value was utilized as a feed-forward to compensate for the speed controller and to further increase the anti-disturbance ability of the system. The switching gain of SMDO was designed as a function of the observed error of disturbance to suppress chattering of the sliding mode estimated value. The simulation results demonstrate that the novel reaching law has an improved dynamic system response speed compared to the regular reaching law and that it can accurately and rapidly track the step speed signal. The SMDO accurately observes the varying system disturbance. When load disturbance is added to the system, the maximum speed fluctuation under PI control is 75 r·min-1, whereas the sliding mode control, which is based on the novel reaching law and disturbance observer, records a maximum speed fluctuation of 30 r·min-1 and guarantees better and more robust system performance. The experimental results demonstrate that the system that relied on the proposed sliding mode control method can rapidly track a speed command of 400 r·min-1 without overshoot. The regulation time is 0.12 s and the steady-state accuracy is ±4 r·min-1. The SMDO can accurately estimate the system disturbance without overshoot while also improving the system's anti-disturbance ability. When the motor is operating at a steady speed of 400 r·min-1 and then is added a 0.6 N·m load torque disturbance, the method based on the novel reaching law and disturbance observer gives a maximum speed fluctuation of 23 r·min-1. This speed fluctuation represents a reduction of 8% compared to that with PI control. The simulation and experimental results are in good agreement. These results indicate that the proposed control method can improve the dynamic and robust performance of the speed servo system and effectively alleviate the chattering of the sliding mode control system.
Abstract: The reasons for low-order harmonics in the input current of a 3-1 matrix converter (3-1MC) were analyzed, and the relationship of modulation function between the output side and power compensation side was derived. The single grid-side current feedback control strategy cannot be used to control the input current component without steady state error under unbalanced input. It was proposed that input current positive sequence and negative sequence dq axis decoupling for the inner loop, and output side and compensation voltage weighted synthesis for the outer loop in the double closed-loop decoupling control strategy. The experimental and simulation results show that the proposed scheme not only facilitates power compensation using a 3-1MC but also effectively suppresses low-order harmonics in the input current and the output voltage under unbalanced input. Moreover, the proposed strategy improves the practicality of 3-1MCs.
Abstract: Considering the multi-level distribution network has becoming more and more common, a two-echelon location routing problem (2E-LRP) model was established based on minimum total cost objective function. To solve the 2E-LRP model, a simulated annealing with large neighborhood search algorithm was developed. In the framework of the simulated annealing algorithm, a large neighborhood search process was embedded, which includes destroy-and-repair principles as well as some local search methods to further improve the range of the neighborhood search in the solution space. The proposed model and algorithm were tested by two-echelon benchmark instances and compared with the standard simulated annealing algorithm solutions and the internationally best known solutions. The results show the proposed model and algorithm to be correct and that the algorithm can obtain better solutions than standard simulated annealing when solving large-scale problems.
Abstract: A suitable energy management mechanism for a wireless network with intermittent connectivity was proposed to deal with unbalanced load and limited energy resources of nodes. According to the historical information, the active degree, residual energy and data forwarding rate of nodes were estimated in a distributed way. In addition, the node utility was effectively estimated by fully considering network features. Furthermore, the proposed mechanism employs the serviceability differences of nodes and the Pareto optimal theory to choose the best next-hop relay node adaptively. The data forwarding operation was executed. Thus the network performance degradation caused by selfish nodes was prevented effectively. The simulation results show that the proposed mechanism can not only balance the load on nodes and solve the problem of network "hotspots", but also prolong network lifetime and improve its delivery rate and delay performance greatly compared to other energy management mechanisms.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
