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Advanced Engineering Science

Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-12-01-2022-113
Total View : 71

Abstract :

Surface quenching of the rail steel using the laminar plasma jet can increase its service life, but the treatment parameters can only be determined by the experimental methods currently, which is time-consuming and laborious. If a simulation model for the surface quenching process can be established to quickly predict the variation of the temperature field in the surface quenching process and the hardness distribution within the hardened zone, the optimal treatment parameters can then be obtained rapidly. A numerical simulation model was firstly established by the finite element method to obtain the temperature distribution. Then the limit value of the carbon diffusion was determined by the hardness distribution obtained from the surface quenching experiment. After that, the Austenite transformation rate at each heating rate was determined using JMATPRO. Finally, a model for predicting the metallographic structure was proposed. With the numerical simulation model, the variation of the temperature field during the surface quenching process could be obtained. By selecting the nodes greater than the phase transition temperature (for example, 745 ℃ for the U75V rail steel), the width and depth of the hardened zone could be predicted. The prediction error was found to be within 8% errors compared with experimental results. By extracting the temperature change curve of the nodes in the hardening zone and substituting into the metallographic structure prediction model, the transformation of the austenite and martensite at each node position in the hardening zone could be calculated, and the hardness at the hardening zone could be predicted. A series of surface quenching experiments with different surface quenching parameters, e.g. including arc current, anode diameter, scanning speed, etc., were carried out. It was found that the hardness predicted by the proposed simulation model was in good agreement with the actual hardness, which verified the effectiveness of the proposed simulation model for the laminar plasma jet surface quenching of rail steel.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-12-01-2022-112
Total View : 13

Abstract :

Transition metal Fe2+ is the most economical, effective and environmentally friendly PS activation substance, but Fe2+ is prone to be oxidized and loses its activation ability, resulting in poor continuous effect of the Fe2+/PS system. In order to improve the efficiency of the Fe2+/PS system in oxidizing and degrading organic pollutants, iohexol, a commonly used iodinated X–ray contrast media in medical field, was taken as the target pollutant,and its degradation in four advanced oxidation proeesses such as UV/PS,Fe(C2O4)3 3–/PS,UV/Fe(C2O4)3 3–/PS and Fe2+/PS was studid. The effects of Fe(C2O4)3 3– concentration, ultraviolet light intensity and pH on the degradation of iohexol and PS decomposition in UV/Fe(C2O4)3 3–/PS system were examined, and then the Fe2+ concentration change and its conversion rate in the system were analyzed. The results verified that the oxidation decomposition rates of iohexol in the four advanced oxidation systems were 83.8%, 7.0%, 98.8%, and 69.9% respectively, among which the UV/Fe(C2O4)3 3–/PS system could promote the reduction of ferrous irons through ultraviolet light, Fe2+ that activates PS in the solution was gradually released, and the degradation of iohexol was the most efficient and complete. As the concentration of Fe(C2O4)3 3– increased, the decomposition rate of PS in the UV/Fe(C2O4)3 3–/PS system increased, while the degradation rate of iohexol first increases and then decreases. Under four different initial Fe(C2O4)3 3– concentrations (20, 50, 100, 200 μmol/L), the degradation rate of iohexol is in the order of 100>200>50>20 μmol/L. In the UV/Fe(C2O4)3 3–/PS system, the Fe2+ concentration first increases rapidly and then slowly decreases, the degradation rate of iohexol, the decomposition rate of PS and the highest conversion rate of Fe2+ are all positively correlated with ultraviolet light intensity and negatively correlated with pH. Therefore, the use of ultraviolet light to reduce iron ions can greatly improve the Fe2+ activation efficiency, and the system has strong adaptability to influencing factors such as light intensity and pH, and has great application prospects in the field of advanced oxidation in water treatment.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-12-01-2022-111
Total View : 11

Abstract :

The secondary fly ash problem in the application process of fly ash of municipal solid waste incineration (shorter form, fly ash) melting treatment technology has become a constraint. It is beneficial to the development of harmless and resource utilization technology of secondary fly ash by mastering the distribution law of salt in the gas phase product of fly ash melting, and it can be used as a reference for the design of tail gas purification equipment and operation. The fly ash released from one municipal solid wastes incineration plant in Jiangsu Province was adopted. The fly ash melting experiments were performed in a self-designed high-temperature pilot-scale plasma arc furnace system. The weight subtraction method, X–ray fluorescence spectroscopy, atomic absorption spectrometry and electrochemical process were used to analyze melting fly ash and slag during melting and to abtain gaseous phase migration rate of Na, K, Ca, Mg and Fe. The thermodynamic model was used to simulate the distribution rules of gaseous phase salts at 1000~1600 ℃, with 0~50% auxiliary material, at different atmosphere (without gas, nitrogen or air) and 0~12% water content of fly ash. The simulation results showed that NaCl, (NaCl)2, KCl, (KCl)2, CaCl2, KCaCl3, KMgCl3, FeCl2 etc. were main compositions of gaseous phase salts during fly ash melting. These compositions distribution was greatly effected by melting temperature and was little effected by melting atmosphere, auxiliary material amount and water content of fly ash. At atmosphere, there were new product Na2SO4 in gaseous phase salts. The simulation values and the experimental values of gaseous phase migration ratio of Na and K fitted well, and the simulation values were largely smaller than the experimental ones of Ca, Mg and Fe. It is suggested that the distribution law of gaseous product salt should be used to develop the technology of salt separation or chloride salt utilization, so as to realize the comprehensive utilization of secondary fly ash, change the current situation that the secondary fly ash is mainly landfill, and thoroughly realize the harmless and resource utilization of fly ash.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-12-01-2022-110
Total View : 11

Abstract :

High entropy alloys break through the traditional alloy design concept with one or two elements as basic elements, and have a simple phase structure and excellent comprehensive performance prepared by equimolar ratio or near equimolar ratio, which is expected to further expand the performance limit and application of metal materials. In order to study the effect of element doping on phase structure, microstructure and wear resistance, CoCrCuFeMn and CoCrCuFeMnZr high entropy alloys with equal molar ratio were prepared by vacuum melting method. The phase structure, microstructure, hardness and wear resistance of CoCrCuFeMn alloy before and after Zr addition were investigated by XRD, OM, SEM, EDS, microhardness tester and friction-wear tester. It was found that after Zr addition, the phase structure of CoCrCuFeMnZr alloy was changed from the original two FCC phases to two HCP phases, and the microstructure was obviously refined. The two alloys were typical dendrite structure. The friction curves of the two alloys showed a trend of first increasing, then decreasing, and then stabilizing. After Zr addition, the friction coefficient and mass loss rate decreased from 0.57 and 4.14% to 0.47 and 0.49% respectively, and the microhardness increased from 219.6 HV to 983.5 HV. The results showed that the HCP transformation of alloy phase structure was mainly related to the formation of a rough solid-liquid interface rich in Zr with large atomic radius and Z-shaped HCP orientation. The reason why Cu is enriched in the interdendrite region is that its melting point is the lowest, its electronegativity is the largest, its atomic radius is second only to Zr, and it has the corresponding largest positive mixing enthalpy with all alloy elements except Zr, so it is enriched in the interdendrite region with the latest solidification. Due to the fact that the melting point of Mn is only higher than that of Cu, Mn has the largest electronegativity difference except Zr, and there is a negative mixing enthalpy between Mn and Co or Zr and the largest positive mixing enthalpy between Mn and Cu, which is not conducive to its long-range diffusion and entering into the lattice site of the leading phase, the segregation coefficient of Mn is the smallest. The increase of hardness and wear resistance of the alloy with Zr element is due to fine grain strengthening, solid solution strengthening and phase structure transformation.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-12-01-2022-109
Total View : 9

Abstract :

Due to the weak integrity of the damaged masonry pagodas, it is easily to be destroyed heavily for the pagodas affected by earthquake again, even are collapsed. Using rigid hoops to restrain and strengthen the masonry can improve the mechanical properties of ancient masonry pagodas. To study the seismic performance of damaged masonry pagoda reinforced with rigid hoop, three sub-structure models of the masonry pagoda were designed and constructed, and the pseudo-static tests were carried out. The failure phenomena of seismic damaged specimens and the specimens restrained by angle steel hoops were observed, and the load-displacement curves of the restrained specimens were obtained. The numerical models were established to calculate the stress, strain and deformation of the ancient pagoda substructure, and the seismic performance indexes of the reinforced ancient pagoda substructure were obtained through comparative analysis with the test results. As results, the hoop device can effectively confine the horizontal deformation and the expansion of diagonal cracks, improve the ability of the ancient pagoda substructure to resist horizontal deformation, and delay the degradation of structural rigidity. The numerical model can reflect well to the damage of the structure and reinforcement device the characteristics of collaborative work with the structure of the pagoda, and the research results can provide references for the seismic reinforcement of ancient masonry pagoda.

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