Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Investment casting process is an important way to get complex parts of titanium alloy. However there are few research on the interfacial heat transfer coefficient (h) between casting and shell thus the temperature simulation of investment casting process of titanium alloy is often inaccurate. In order to get a relatively accurate h, a one-dimensional mathematical model for the reverse calculation of h between casting and shell in investment casting process of Ti6Al4V alloy was built and the analytic relationship between temperature and time/heat flux was established. Considering the calculated h is significantly affected by the error of parameters such as the specific heat capacity and thermal diffusivity of shell and position of thermocouples, research on the error of these parameters is essential. The relationship between the error of these parameters and the temperatures in the casting and shell was studied and it was found that the effect of different kind of error on the temperature field was obviously different. An experiment based on the one-dimensional mathematical model was done and temperatures of different positions were measured. Based on the effect of different kind of error and the difference between the calculate temperature field and the measured temperatures, the proportion of effect of each kind of error was assessed. These errors were revised on the basis of the assessment, thus a relatively accurate h between the casting and shell was obtained. The relationships between h and thickness of the solidified layer on the casting/temperature at the surface of casting can be divided into 4 stages: (1) Metal was liquid and h kept about 440 W/(m2稫); (2) Solid layer appeared on the surface, and h declined nearly 60%; (3) Solid layer grew up before metal became completely solid and h declined nearly 20% of its maximum; (4) After metal solidified, h declined slowly as temperature on the surface of casting dropped. These relationships were applied in a three-dimensional model for numerical simulation of the temperature field. Temperatures of different positions in casting and shell were calculated and calculated temperatures agreed with measured ones well. Thus the accuracy of h was identified and it can help solve problems in the production in investment casting process of Ti6Al4V alloy.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： A 2D axial symmetrical mathematical model was developed for stationary keyholing plasma arc welding (PAW), to describe the transport process in coupled high-temperature flow arc and molten pool in the workpiece. The evolutions of electric, magnetic, velocity and temperature fields were simulated. The simulated fusion line of the weld bead is in quite good agreement with the experimental results, validating the mathematical model. It turns out that, both the current density and the temperature reach the maximum values near the tip of the tungsten cathode. The arc displays a typical bell-shape above the workpiece, but becomes slim cone-shape near the central axis as the arc enters the keyhole. The argon plasma slows down sharply when it strikes the inner wall of the keyhole, so high pressure appears in the keyhole and some argon plasma flows back. The combination of fluid flow and heat transfer contributes to the reversed bugle shaped fusion line. The simulation of orthogonal test was further conducted to study the effects of operational and structural parameters of the weld torch. The range analysis shows that the structural parameters of weld torch are more influential than the operational parameters. That is, more attention should be paid to control the gap between two electrodes, the electrode shrinkage and the nozzle diameter to guarantee the welding quality.
Subjects: Psychology >> Applied Psychology submitted time 2021-03-25
Abstract： " " " " " " " " "
Peer Review Status:
Awaiting Review
Subjects: Biology >> Ecology submitted time 2018-05-18 Cooperative journals: 《生态学报》
Abstract：应用高通量测序技术对西北干旱区两种盐生植物黑果枸杞和里海盐爪爪根际土壤细菌的多样性和群落结构进行研究，旨在揭示两种耐盐植物根际土壤细菌之间以及根际与非根际细菌群落结构间的差异，为深入研究盐生植物根际土壤微生物与耐盐性之间的关系提供理论基础。结果表明：黑果枸杞、里海盐爪爪根际细菌多样性丰度高于非根际土，黑果枸杞根际土壤细菌多样性丰度高于里海盐爪爪。根际和非根际土壤细菌群落的组成和丰度存在差异，从黑果枸杞和里海盐爪爪根际土壤中分别检测出细菌21门289属和22门304属，而从非根际土壤中分别检测出28门285属和24门336属；在两种盐生植物根际土壤中，变形菌门和厚壁菌门均为优势门；拟杆菌门、放线菌门、蓝细菌门及浮霉菌门在根际土壤中的丰度显著高于非根际土壤，而厚壁菌门在根际土壤中的丰度低于非根际土壤。两种植物根际土壤中的细菌优势门和优势属的数量均高于非根际土壤，在黑果枸杞和里海盐爪爪的根际土壤中的细菌优势属分别有10个和9个，而二者非根际土壤中的细菌优势属各有4个，其中假单胞菌属是根际和非根际土壤中的共有优势属。黑果枸杞和里海盐爪爪根系细菌群落组成和丰度存在差异，只有假单胞菌属和盐单胞菌属是两种植物根际土壤中的共有优势属。Unifrac分析和聚类分析表明，两种盐生植物根际土壤细菌之间的相似性大于根际和非根际细菌群落间的相似性。细菌多样性与土壤有机碳、有机质、总氮正相关，与pH、电导率负相关，电导率和pH，有机碳和总氮分别是非根际土，根际土壤细菌群落物种组成的主要影响因素。
Subjects: Biology >> Ecology submitted time 2018-05-18 Cooperative journals: 《生态学报》
Abstract：以独山子区3种优势草本植物的根际与非根际土壤为研究对象，采用Biolog-ECO微平板法对土壤微生物功能多样性进行了研究。结果表明：3种不同植物根际与非根际土壤微生物代谢活性（AWCD）、丰富度指数Shannon（H）和均匀度指数McIntosh（U）均存在不同差异，且博乐蒿根际土壤微生物功能多样性均优于非根际土壤及其他两种植物；根际土壤微生物对糖类、脂类、酸类和胺类碳源物质比较敏感，非根际土壤微生物敏感于酸类、氨基酸类以及糖类碳源，根际土壤微生物对碳源的利用能力更强，且不同植物根际环境微生物碳源利用特征不同；微生物活性、丰富度指数和微生物均匀度指数与土壤pH值、SOM、AP和NO3--N存在显著正相关（P < 0.05）；博乐蒿根际土壤养分含量与微生物活性均较高，对环境的适应性更强，在独山子区生态环境管理与建设中可对其进行关注。
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