Abstract: The welding performance of steel structures such as offshore platforms, ships, bridges, buildings, and oil and gas pipelines directly determines the service life and safety of the structure, the importance of which cannot be minimized. In welding-related research, the toughness of the welding heat-affected zone is a key issue. This zone experiences temperatures as high as 1400℃, thereby causing the formation of coarse austenite grains. If the welding parameters are improperly controlled, microstructure refinement cannot be achieved by subsequent phase transformation, which results in decreased impact toughness. Multi-pass welding is even more complex, with the secondary heat input affecting the coarse-grain zone formed during the previous pass. This results in the formation of necklace-type M-A constituents, which also lead to deterioration in toughness. In this paper, the relevant research results were summarized with regarding the welding heat-affected zone and it was discuss that the composition of the parent material, the second phase, the welding process, and other factors effect the microstructures and properties of the heat-affected zone. This paper also offers ideas for improving the welding performance of large steel structures in low-temperature service circumstances.
Abstract: To solve the difficult problem of ultrasonic signal acquisition with respect to real-time tiny terrain detection in the deep-sea mining environment, an experimental ultrasonic detection system was designed and built that can simulate the real deep-sea mining reverberation environment. Using a simplified structure for the spiral mining head as a basis, Fluent software was used to simulate the impact of a spiral mining head and a multiple-impeller on the underwater flow field. A comparison of the results shows that the impeller model can realistically reflect the mining environment. Then, based on the impeller model, the vertical distribution of the sediment volume fractions is experimentally determined and the correctness of the design model is verified. Finally, an ultrasonic detection experiment is conducted and the results show that suspended sediment can generate viscosity and absorb sound waves, thereby causing serious reverberation interference. By implementing time-gain compensation in the ultrasonic detection system, the reverberation interference can be effectively suppressed and the probability of target detection increases. The results of this study provide a basis for studying ultrasonic microtopography detection in the deep sea mining reverberation environment.
Abstract: Rheological characteristics are fundamental to pipeline system design. Rheological tests were conducted to obtain the yield stress and viscosity index at different mass fractions. Slump tests were conducted to investigate the mobility of tailings slurry. Results show that the yield stress increases with the increase of mass fraction, especially when mass fraction is greater than 70%. After stirring in a high-speed activation stirrer, the yield stress in 70% mass fraction is decreased by 40.9%. When the mass fractions are lower than 74%, high slump values are obtained. Based on the basic parameters obtained in the rheological tests, the key parameters of the pipeline system were calculated, including the critical flow rate and frictional resistance loss. These analyses results could serve as references for pipeline system design.
Abstract: The transport of E.coli in reclaimed water in floatation system was investigated through simulate flotation, adsorption experiment and desorption experiments. The results show that E.coli in reclaimed water is rapidly adsorbed by ore particles, while tailing waste water can be reused to floatation safely. However, concentrates, middlings and tailings can pose health risks under certain exposure conditions. The transport of E.coli in flotation processes is dominated by the attachment of E.coli onto ore particles. Removal and adsorption rates decrease as the concentrations of E.coli increase. Meanwhile, E.coli adsorption on ore particles is sensitive to the changes of solution pH, and decreases as the solution pH increases. The attachment of E.coli onto mineral particles increases significantly at the presence of collector kerosene, PJ053, and the pH-adjusting agents CaO.
Abstract: To study the effect of carbonaceous matter on gold recovery in bio-pretreatment followed by a cyanide leaching process, the carbonaceous matter was characterized in high-sulfur Carlin-type gold flotation concentrate by gas chromatography-mass spectrometry (GC-MS), Raman spectroscopy, Preg-robbing index tests, and gold loading tests. The results indicate the presence of kerogen in the concentrate, which interferes with the gold extraction due to its strong gold adsorption. Both the Raman and PRI tests show a strong preg-robbing capacity of the carbonaceous matter in the samples. In addition, activated carbon in the cyanidation process of the bio-oxidized product could decrease by approximately 10.14% the adsorption of exposed gold by the carbonaceous matter. A final gold recovery rate is 80.17%.
Abstract: The conducted roasting tests were studied which pellets were made from blends of Western Australia ultrafine (WAU) magnetite concentrate and domestic magnetite concentrate or Brazilian hematite concentrate. The results show that the pellets made from 100% WAU magnetite concentrate exhibit inferior preheating and roasting performance under the following conditions:preheating at 1050℃ for 20 min and roasting at 1300℃ for 40 min, with compressive strengths of the preheated and fired pellets of each pellet 502 N and 2313 N, respectively. When blended 40% domestic magnetite concentrate or 20% Brazilian hematite concentrate with 60% or 80% WAU magnetite concentrate, the appropriate preheating and firing temperatures of the pellets are reduced from 1050℃ to 950℃ and 975℃, and from 1300℃ to 1250℃ and 1280℃, respectively. Moreover, the compressive strength of the fired pellets obviously improves to more than each pellet 2500 N. The microstructure of fired pellets made from WAU and domestic magnetite concentrate is characterized by fully grown Fe2O3 grains and close interlinkages among the hematite grains, which leads to low porosity and strong consolidation. In contrast, 20% Brazilian hematite concentrate blended with WAU magnetite concentrate yields nearly grown Fe2O3 grains in the fired pellets and only relatively close interlinkages between the hematite grains. The preheating and roasting performance of WAU magnetite concentrate pellets can be improved by optimizing the ore matching.
Abstract: After effectively controlling the desulfurization of sintering flue gas, steel companies are now putting denitration on their agendas. In the absence of an economically viable and efficient end-of-pipe de-NOx system, it is necessary to control the sintering process to reduce NOx emissions. In this study, the influence of raw material and process condition parameters on NOx emissions was statistically analyzed with data from Baosteel's sintering production during 2013-2014. The results indicate that NOx emission levels associated with the sintering process can be lowered by decreasing the percentage of hematite, raising sintering fines and the return fines ratios, and enhancing the cold-air permeability, calcium ratio, and sintering bed depth.
Abstract: The thermodynamic diagram of calcium-aluminum-oxygen ternary system was determined through thermodynamic equilibrium calculation of liquid steel deoxidation. Based on this thermodynamic diagram and assuming 100% yield of Ca addition, the evolution mechanisms of inclusions with three different deoxidation schemes were predicted, including M kg addition of mCa/mAl=5 alloy, M kg addition of mCa/mAl=0.2 alloy and 0.2M kg addition of mCa/mAl=0.2 alloy. The calculated results show that the evolution history of inclusion is affected by both the addition quantity and Ca/Al mass ratio of Al-Ca deoxidizer. The optimal deoxidation scheme is that the Ca/Al mass ratio is 5 and addition quantity is M kg, which makes the initial[Ca] content of 0.01% and initial[Al] content of 0.002% in liquid steel. Under such a condition, the evolution history of inclusions is 12CaO·7Al2O3(l)/CaO·Al2O3(l)→CaO(s)→12CaO·7Al2O3(l)/CaO·Al2O3(l)→CaO(s)→ 12CaO·7Al2O3(l)/CaO·Al2O3(l), and the desirable alternative formations of solid and liquid inclusions can be realized during LF refining, which can greatly enhance the effective collision and promote the floating up of inclusions. The results can be applied in industry for steel deoxidizer selection and deoxidation operation.
Abstract: The phase transformations and precipitation behavior were investigated by using Thermo-Calc software in the Fe-(18-21)Cr-(3-5)Al-(0-0.03)C-(0-0.2)Si-(0-0.2)Mn multicomponent system relevant to FeCrAl stainless steel during solidification. The vertical sections of this system were calculated by using the TCFE7 database. Based on these vertical sections, the influence of different elements was analyzed in the phase transformations during solidification and a diagram of the phase-transformation path of FeCrAl stainless steel was obtained during equilibrium solidification. The results indicate that the full-phase transformation path of FeCrAl stainless steel during the cooling process from 1600℃ to 300℃ is as follows:L→AlN+αδFe→AlN+αδFe+Cr7C3→AlN+αδFe+Cr7C3+Cr23C6→AlN+αδFe+Cr23C6→AlN+αδFe+Cr23C6+σ→AlN+αδFe+Cr23C6+σ+α'→AlN+αδFe+Cr23C6+α'. The precipitation of Cr7C3 and σ, during the solidification process mainly depends on the carbon and silicon contents in the system, respectively. Increasing the aluminum content can enlarge the stable region of αδFe+Cr7C3, lower the precipitation temperature of α', and restrain σ precipitation. Increasing the chromium content can reduce the stable region of αδFe+Cr7C3 and enlarge the stable region of σ and α'.
Abstract: Optical microscopy (OM), scanning electron microscopy (SEM), and electron microprobe analysis (EMPA) were used to determine the nature of carbonitrides decomposition in H13 hot work die steel under high temperature, including its morphology, size and composition. Most of the original carbonitrides are long strip (Vx,Mo1-x)(Cy,N1-y) ranging between 10~30 μm with a few square (Tix,V1-x)(Cy,N1-y). The result shows that the edge of the carbonitrides becomes saw-toothed after holding at 1200℃ for 2.5 h, and fine decomposed particles are formed. The average length of carbonitrides, mainly (Tix,V1-x)(Cy,N1-y), is reduced to 12.9 μm as increasing the holding time for 10 h. When the steel is held at 1250℃ for 5 h, about 87% of the carbonitrides disintegrate, especially (Vx,Mo1-x)(Cy,N1-y) dissolving and disappearing, and the carbonitrides size is less than 20 μm. When holding at 1250℃ for 10 h, all the carbonitrides remained are (Tix,V1-x)(Cy,N1-y), of which 70% are square and 93% decompose to fine particles, and can be controlled to size below 10 μm. It is deduced that (Tix,V1-x)(Cy,N1-y) decomposition is related to Fe diffusion by EMPA analysis and that the Fe content in (Tix,V1-x)(Cy,N1-y) gradually enhances while Ti and V contents decline. The carbonitrides reliably decompose at the position of small curvature radius and defect position, forming fine particles of 0.1~1 μm. The original carbonitrides disappear by zone dissolution from outer to inner. The equilibrium temperature of carbonitrides dissolution has a relationship with its constituents based on the two-sublattice model, and dissolution temperature for most (Tix,V1-x)(Cy,N1-y) in sample is between 1200℃ and 1246℃, which fits well with the experimental results.
Abstract: An environment with a weak corrosion tendency was used to promote the production of a limited metastable pitting distribution in 20CrMnTi steel. The law of metastable pitting initiation was investigated by using electrochemical noise. Using the ANSYS finite element method, the stress distribution and crack initiation risk of holes were analyzed and compared under different corrosion conditions. The results indicate that the pitting sensitivity of 20CrMnTi steel is high. The initiation of metastable pitting is preferentially concentrated at the edge of the impurity phase. The pitting induction period is obviously shortened and the pitting sensitivity increases with an increase in the Cl- concentration. The increase in the nucleation rate induced by different Cl- concentrations reduces the distance between pitting occurrences. Thus, surface microcracks readily connect and propagate pitting, thereby enhancing the risk of crack initiation.
Abstract: The corrosion behavior of low-carbon steel was investigated in a simulated hot and humid industrial-marine atmosphere by X-ray powder diffraction (XRD), scanning electron microscopy with X-ray microanalysis (SEM-EDS), mass loss, and a wet/dry alternate immersion corrosion test using a 0.1 mol·L-1 NaCl+0.01 mol·L-1 NaHSO3 solution. The results indicate that the corrosion processes of the experimental steels agree well with the d=Atn power function, with different steels having different values of A and n. The corrosion products are mainly in the amorphous phase and contain a small amount of Fe3O4, α-FeOOH, β-FeOOH, and γ-FeOOH crystals. It can be found that the rust layers have two parts-the body of the rust layer and a loose interface band. The Fe and O content gradients in the rust layer, from inner to outer, change very little. It can be concluded that the long-term interaction of Cl-, SO2 and H2O will lead to the deterioration of the inner structure. However, the addition of elements with high stability or corrosion resistance can improve the stability and density of the rust layer, and thereby enhance the corrosion resistance of the steels.
Abstract: To achieve better performance in finished cold-pilger rolled stainless steel tubes, it is critical to select an appropriate feed range. In this study, cold-rolling 304 stainless steel tube was used as the research object to simulate the entire cold-pilgering process at different feed ranges. Using finite element software, it was comparatively analyzed that the feed range effects on the metal flow rate, rolling force, equivalent stress, residual stress, and piping spring-back. The results indicate that the metal flow rate increases with an increased feed range in the groove bottom and the contact of the groove flank with the roll. In addition, the rolling force, equivalent stress and residual stress increase with increases in the feed range, increments of which will increase the spring-back of the piping. Rolling tests at different feed ranges were performed with the help of experimental rolling mill and it is found that test results are roughly identical to the simulation results. experimental test results regarding the dimensions and residual stress of the piping provide evidence for optimizing the selection of the feed range in pilger rolling.
Abstract: To optimize combustion efficiency, the structural characteristics of the zoned and staged double P-type gas-fired radiant tube were improved. The corresponding experimental and numerical studies were performed on the new radiant tube and the results show that deviations in the monitoring parameters are less than 1%, except for a NOx concentration of 11.6%, which proves the reliability of the model. On this basis, the gas and wall temperatures were compared by changing the nozzle position and structure parameters of main and branch pipes. The results show that as the nozzle position moves outward, the highest value of the surface temperature of the radiant tube gradually decreases and the minimum value of the wall temperature gradually increases. When the nozzle of the branch pipe locates at the intersection of the tee and branch pipes, it helps to reduce the impact of the high temperature gas on the pipe wall, improve the uniformity of the branch radial temperature, and prolong the service life of the radiation tube. When the nozzle is fully premixed, the temperature difference is minimized. When the pipe nozzle is asymmetric, the difference in the wall temperatures is minimized and the thermal combustion efficiency is the highest.
Abstract: The flexible hinge is one of the most important components in lamina emergent mechanisms (LEMs), so the design of a new type of lamina emergent torsional (LET) joint can play a key role in its movement performance. This paper presents double- and triple-series LET flexure hinges, designs the structure of the two hinges, and derives the calculation formula for their bending equivalent stiffnesses. Through theoretical and finite element analyses of the design example, verifies the correctness of the calculation formula for equivalent stiffness. By comparing the bending, tension, and compression performances of the double-and triple-series LET flexure hinges with those of the outside LET flexure hinge, which shares the same outline dimensions of the former, it can be concluded that the triple-series LET flexure hinge can greatly enhance bending performance without any obvious decrease in its tension and compression performances.
Abstract: The vibration signals of planetary gearboxes are composed of complex frequency components and interfering noises, and their spectra have intricate sidebands, which cause difficulty in and even misleading fault identification. In different fault cases, the vibration signatures in multiple domains typically differ from normal states with different discrepancies. Based on this hypothesis, time and frequency domain features are extracted for the purposes of fault identification. The vibration signal is adaptively decomposed into a set of mono-components, and the instantaneous energy of each mono-component is calculated in time-frequency domain by exploiting the merits of local mean decomposition, including its better robustness to noise and freedom from pseudo-mode and negative frequency problems. Manifold learning is utilized to tackle the high-dimensionality and non-linearity aspects of multiple-domain feature space construction. A new method is proposed for estimating the intrinsic dimension and selecting the k-nearest neighborhood based on the improved pseudo-nearest neighbor. In addition, isometric feature mapping (ISOMAP) is utilized to reduce the dimensions of the multiple-domain feature space. The proposed method is validated by analyzing the planetary gearbox lab experimental dataset. Based on the clustering analysis results of the extracted manifold features, the localized faults on the sun, planet, and ring gears are successfully identified.
Abstract: The dynamic topology of a mobile ad hoc network poses a real challenge when designing the routing protocol, especially in high-dynamic environments. In this paper, a new routing protocol was proposed that is based on on-demand and greedy forwarding. This protocol proposes three opinions to RGR, i.e., through scoped flooding to decrease control overhead in route discovery phrase, through mobility prediction to monitor the condition of the reactive path and help nodes choose the proper next-hop in the GGF phrase and through delayed route requests to reduce unnecessary waste of network resources. In contrast to RGR, AODV, Modified-RGR, and Optimized-RGR simulation, the results show the improved RGR not only has a high packet acceptance ratio, but has a low normalized routing overhead and an average end-to-end delay.
Abstract: Based on the similarity simulation theory, a parallel-tunnel model test system was constructed that consists of a test bench design, a monitoring system design, a loading system design, and the construction of a rock mass model. The models were monitored in key positions of displacement, stress changes, and destruction of the tunnel walls. It is found that the experimental observation and numerical simulation results based on the Mohr-Coulomb model exhibit relatively large disparities. However, based on the Plastic-Hardening model, the yield states and variation laws of the rock and soil were obtained by numerical simulation and these results are in good agreement with the experimental results. If all aspects of research results is integrated, the Plastic-Hardening model accurately reflects real changes in the states of the rock and soil in actual engineering applications and tests and can provide an important reference for double parallel-tunnel construction and maintenance under similar geological conditions.
Abstract: The process of diagnosing tunnel health as a fuzzy system has the characteristics of randomness and fuzziness. Traditional risk assessment methodologies do not account for the fuzziness and randomness of risk. Therefore, using cloud theory, a new comprehensive risk assessment model was proposed for shield tunnels aimed at the fuzziness and randomness of health diagnosis system of shield tunnel structure. Firstly, the normal cloud model of evaluation terms is constructed, which reflects the health status of the tunnel structure. Then, the normalized value of monitoring data of tunnel structural health status index is transformed into membership cloud model by the principle of the reverse cloud generator. And the importance linguistic value of the health status index is transformed into the weight of the cloud which is used for characterization importance of health index. Finally, the cloud theory computing method is used to diagnose the health status of the tunnel structure, and the cloud model of health status is obtained. The improved method of cloud model was applied to diagnose the structural health status of shield tunnel of Metro Line 2, and this method greatly improves the visualization and robustness of the diagnosis results.
Abstract: The torsional tuned liquid column damper (TTLCD) is a cost-effective passive device for reducing the torsional response of a plan-asymmetric building under wind or seismic load. In this paper, the equations of relative liquid motion in three kinds of TTLCDs, as well as the control forces with the reference point and various inclined angles of the upright columns were derived. The optimal TTLCD control parameters were given through transforming method of the TTLCD-structure equivalent to a TTMD-structure system using Den Hartog or Ikeda formulas. Finally, the TTLCD design method was evaluated and the TTLCD design process was described. The numerical results of a four-storey plan-asymmetric structure show that TTLCDs can effectively mitigate earthquake-induced coupled flexural torsional responses and that the proposed method is feasible.
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
