Continuous FEM simulation of multi-pass plate hot rolling suitable for plate shape analysis

In order to continuously simulate multi-pass plate rolling process, a 3-D elastic hollow-roll model was proposed and an auto mesh-refining module with data passing was developed and integrated with FE software, Marc. The hollow-roll model has equivalent stiffness of bending resistance and deformation to the real solid and much less meshes, so the computational time is greatly reduced. Based on these, the factors influencing plate profile, such as the roll-bending force, initial crown, thermal crown and heat transfer during rolling and inter-pass cooling can be taken into account in the simulation. The auto mesh-refining module with data passing can automatically refine and re-number elements and transfer the nodal and elemental results to the new meshes. Furthermore, the 3-D modeling routine is parametrically developed and can be run independently of Marc pre-processing program. A seven-pass industrial hot rolling process was continuously simulated to validate the accuracy of model. By comparison of the calculated results with the industrial measured data, the rolling force, temperature and plate profile are in good accordance with the measured ones.     

P-RE-Sr复合变质对A390合金组织的影响

通过加入P＋RE＋Sr对A390合金进行复合变质处理,并探讨了不同变质剂的不同变质工艺对该合金显微组织的影响.研究结果表明：当变质剂加入顺序采用先加P,变质温度为825℃,变质时间20min,接着加入RE,变质温度为825℃,变质时间10 min,再后加入Sr,变质温度为760℃,变质时间为30min,所得初晶硅尺寸为...     

实现大学生思政工作科学化与精细化的新策略

在科学发展观统领下,实现大学生思政工作科学化与精细化的新策略是：及时更新工作观念,在思政工作中不断改造主客观世界;切实把握内在规律,在理性支配下卓有成效地开展工作;务求做到以人为本,针对具体的对象灵活选择教育方法;建构新型工作队伍,持续提升思政工作人员的职业素养;不断实现有效创新,努力建构科学化精细化的长效机制。     

一种无背景知识的多关系频繁模式发现算法研究

在无背景知识的面向数据的频繁模式发现研究中按照关系数据库概念重新定义了面向数据的多关系频繁模式发现任务和搜索空间.同时,使用了一个优化的精化算子构建搜索空间,这一精化算子一方面有效地利用了关系数据库隐含的数据模式特征,从而能够自然地构建有趣形态的模式,另一方面能够在不过度限制搜索空间的情况下避免等价模式的产生.建立了一个候选模式评估共享计算策略,从而降低了方法评估阶段的时间复杂性.实验表明,所提出的MRFP-DA算法整体上具有良好的效率和可扩展性.     

Numerical Investigation of Lid-Driven Deep Cavity with Local Grid Refinement of MRT-LBM

In the case of lid-driven deep cavity flow, the effects of different resolutions of local grid refinement have been studied in the frame of multiple relaxation times (MRT) lattice Boltzmann method (LBM). In all the cases, the aspect ratio and Reynolds number are set as 1.5 and 3.200, respectively. First, the applied method is validated by comparing it with two reported works, with which agreements are reached. Then, six separate degrees of local grid refinement at the upper left corner, i.e. purely coarse grid, including 1/64, 1/32, 1/16, 1/8, 1/4 refinements of the lattice number in the width direction have been studied in detail. The results give the following indications:① The refinement degrees lower than 1/8 produce similar results; ② For single corner refinement, 1/4 refinement is adequate for clearing the noises in the singularity zone to a large extent;③ New noise around the interface between coarse and fine zones are introduced by local grid refinement. Finally, refinement of entire subzone neighboring the lid is examined to avoid introducing new noises and it has been found effective.     

Preparation and properties of AlON powders

Aluminum oxynitride (AlON) powders were synthesized using the raw materials of γ-Al₂O₃ and carbon black through the carbothermal reduction and nitridation process. The carbon content in the γ-Al₂O₃/C mixture and heating temperature were investigated. The AlON powders were synthesized by calcination for 2 h at 1750 °C when the carbon content in the γ-Al₂O₃/C mixture was 5.8 wt%. The particle size of powder is important to the transparency of ceramics, but the size of the synthesized powder was large. Therefore, a few methods, such as freeze-drying, ultrasonic dispersion, and liquid nitrogen ball milling, were used to reduce the particle size of powders. Among the three methods, liquid nitrogen milling had the best results.     

Enhanced thermal stability of (NaCe)‐multidoped CaBi2Nb2O9 by A‐site vacancies‐induced pseudo‐tetragonal distortion

Although A‐site codoping of alkali metal and rare‐earth elements are known to effectively promote the d₃₃ of CaBi₂Nb₂O₉ (CBN), its thermal depoling behavior cannot be well promised. In this work, piezoelectricity of CBN was effectively promoted by (NaCe) modification, and its thermal instability was caused by the lattice evolution from orthorhombic structure to pseudo‐tetragonal structure during thermal depoling process. A‐site vacancies could induce pseudo‐tetragonal distortion in Ca_0.92(Na_0.5Ce_0.5)_0.08Bi₂Nb₂O₉ ceramic, which obviously enhanced the thermal stability of lattice by reducing the rotation of the Nb–O octahedron during the thermal depoling process, as compared with orthorhombic structure, thereby weakening the swing of spontaneous polarization (P_s) and promoting the thermal depoling performance. Consequently, good thermal stability was obtained (remained 92% of initial d₃₃ after depoling at 600°C). Moreover, dominant role of oxygen vacancies in the electrical conduction and relaxation process promised that the introduction of small amount of A‐site vacancies would not influence the electrical properties obviously.     

奥氏体晶粒细化的研究

在Gleeble1500热模拟机上以SS400钢为研究对象，用冷加工 回火再结晶和冷加工 a→γ逆相变等工艺，研究了冷变形对马氏体(铁素体)再结晶行为的影响以及奥氏体晶粒细化的方法。结果表明：低温变形对板条马氏体的再结晶行为有一定影响，并且由于低温变形后快速升温的铁素体回复、再结晶与奥氏体(铁素体)相变等相继发生，从而得到比较细小的奥氏体晶粒。     

Effects of ZrO2-La2O3 co-addition on the microstructural and optical properties of transparent Y2O3 ceramics

Commercial Y₂O₃ powder was used to fabricate Y₂O₃ ceramics sintered at 1600 °C and 1800 °C with concurrent addition of ZrO₂ and La₂O₃ as sintering aids. One group with different contents of La₂O₃ (0–10 mol%) with a fixed amount of 1 mol% ZrO₂ and another group with various contents of ZrO₂ (0–7 mol%) with a fixed amount of 10 mol% La₂O₃ were compared to investigate the effects of co-doping on the microstructural and optical properties of Y₂O₃ ceramics. At low sintering temperature of 1600 °C, the sample single doped with 10 mol% La₂O₃ exhibits much denser microstructure with a few small intragranular pores while the samples with ZrO₂ and La₂O₃ co-doping features a lot of large intergranular pores leading to lower density. When the sintering temperature increases to 1800 °C, samples using composite sintering aids exhibit finer microstructures and better optical properties than those of both ZrO₂ and La₂O₃ single-doped samples. It was proved that the grain growth suppression caused by ZrO₂ overwhelms the acceleration by La₂O₃. Meanwhile, 1 mol% ZrO₂ acts as a very important inflection point with regard to the influence of additive concentration on the transmittance, pore structure and grain size. The highest in-line transmittance of Y₂O₃ ceramic (1.2 mm in thickness) with 3 mol% of ZrO₂ and 10 mol% of La₂O₃ sintered at 1800 °C for 16 h is 81.9% at a wavelength of 1100 nm, with an average grain size of 11.2 µm.     

Cation-substitution induced stable GGAG:Ce3+ ceramics with improved optical and scintillation properties

Among the aluminate garnet materials, cerium doped gadolinium gallium aluminum garnet ceramics (GGAG:Ce) have shown great performance advantages, which suggests their promising applications in medical imaging, high energy rays detection and high power LED lighting. The goal of this work is to raise the thermostability of GGAG:Ce by means of partial Y³⁺ substitution, and to find out the relationship between the crystal structure and the optical properties. GGAG:Ce³⁺,xY³⁺ ceramics were prepared via chemical precipitation, and a combination of sintering in oxygen atmosphere and hot isostatic pressing. In order to identify the detailed crystal structure information, Rietveld refinements were first taken on the XRD patterns. Crystal structure refinements verify the ability of mutual substitution of Y and Ga atoms between the dodecahedron and octahedral sites. The optical, luminescent and scintillation properties have been investigated. Results show that the transmittance of the sample can reach 77% at the emission peak wavelength, while the spectrally corrected light yield value reaches 61,000 ± 1200 photons/MeV.