38MnB5热成形钢高温变形行为及本构方程

利用Gleeble-3500热模拟试验机对38MnB5热成形钢的高温变形行为进行研究, 分别在650~950℃温度区间内, 以0.01、0.1、1和10 s-1的应变速率对其进行等温单向拉伸测试, 并得到相应条件下的真应力-应变曲线.结果表明: 38MnB5热成形钢流变应力随着变形温度的升高而减小, 随着应变速率的增大而增大.当应变速率逐渐增加时, 热变形时发生的动态回复和动态再结晶效果并不显著, 而当温度逐渐升高时, 二者作用逐渐加强.考虑了温度、应变速率和应变的综合复杂影响, 建立38MnB5热成形钢高温下的本构方程.此本构方程通过对流变应力、应变、应变速率等实验数据的回归分析, 得到与变形温度、应变速率和应变相关的材料参数多项式.计算结果与实验结果对比发现, 通过本构方程所获得的计算值与试验值吻合良好.      

A strategy for defects healing in 3D printed ceramic compact via cold isostatic pressing: Sintering kinetic window and microstructure evolution

In this study, we developed a unique defect healing method for 3D printed ceramic compact via cold isostatic pressing (CIP) after debinding, and typical features of interlayer interface defects of 3D-printed zirconia compact were characterized and found to be reduced significantly. The characteristic sintering kinetics window and microstructure evolution of the healed sintered bodies were systematically investigated, which was found to be quite different from conventional shaping methods. The three sintering stages are probed by their feature microstructure details such as the mechanically flattening surface at the early sintering stage, the heterogeneous microstructure and high porosity in the interlayer interface region at the middle stage, and the slightly ripple-like structural features combined with the healed interlayer defects at the final stage. The evolution of the pore structure of the healed 3D printed bodies were traced and the mechanical properties such as the Young's modulus, hardness, and fracture toughness were measured to understand the significance of the heal effect.     

Size dependent phase transformation and mechanical behaviors in nanocrystalline Ta thin films

Nanocrystalline (NC) Ta thin films with various thicknesses (t = 600, 1200, and 2200 nm) were grown on Si (100) substrate by using magnetron sputtering system. A phase transformation from β-Ta to α-Ta was observed when the thickness reduced to 600 nm, which is rationalized by employing a thermodynamic model. It was interesting to find that the α-Ta phase exhibited tetrahedral pyramidal grain morphology, while the β-Ta had equiaxial grain. Hardness and strain rate sensitivity (SRS, m) were measured as a function of film thickness t. Compared with the reduction in SRS as the grain size decreased in the submicron bcc metals, the NC Ta thin films with average grain size smaller than ~72 nm showed an opposite trend, both in the α-Ta and in the β-Ta phase. Improved m was observed as the grain size reduced but the increasing trend was not continuous between different phases. This unusual variation trend of m in the NC Ta was explained by a model based on the traditional double-kink mechanism coupled with a GB-mediated dislocation process, which agrees well with the experiment results.     

Ultrafine-Grained Multiphase Steels with Different Microstructural Constitutions Fabricated Through Annealing of Tempered and Deformed Martensite

Ultrafine-grained (UFG) steels with different microstructural constitutions were fabricated through annealing of tempered and deformed martensite. Effects of various second phases on deformation behaviors and mechanical properties of UFG steels were investigated. In this study, it was shown that retained austenite is the most beneficial microstructure constitution for enhancing the ductility of low-alloyed UFG steels.     

Morphologies and Influential Factors of Forsterite Film in Grain-Oriented Silicon Steel

The product quality of grain-oriented silicon steel may be affected by each process because of its complicated production technology. Morphologies, compositions and structures of forsterite film formed in different conditions on the samples subjected to high temperature annealing were measured by using a scanning electron microscope, an energy disperse spectroscope, an X-ray diffractometer and Fourier transform infrared technique respectively. The morphologies and influential factors of forsterite film were investigated. The results showed that the major component of forsterite film composed of light-gray spherical particles was Mg₂SiO₄, and the minor was MgAl₂O₄. If the amount of MgO coated on the surface of the steel was less, bare holes or even large-scale bare grains for forsterite film appeared. The higher temperature of water bath during decarburization annealing led to gaps of strips in forsterite film. Moreover, MgO coating method had great influence on forsterite film. Roller coating method was beneficial to increase compactness and smoothness of forsterite film, but was disadvantageous to its thickness.     

Revisiting the weighting function for lightness in the CIEDE2000 colour-difference formula

We have used 13 experimental datasets (7420 colour pairs) to study the performance of the weighting function for lightness proposed by the CIEDE2000 colour-difference formula, because it has been suggested that this function can be improved by using the weighting function for lightness S_L = 1 adopted by the CIE94 colour-difference formula. Using the standardised residual sum of squares (STRESS) index, it was found that: (i) replacing the S_L in CIEDE2000 with S_L = 1 improved the results for 7/13 datasets considered, but the improvement was statistically significant only for 1/13 datasets; (ii) a Whittle-type lightness-difference formula can be used to replace the term ∆L*/S_L in CIEDE2000, which led to a new colour-difference formula with no statistically significant difference with respect to CIEDE2000 for any of the 13 experimental datasets. A modification of the CIEDE2000 formula using a Whittle-type lightness formula is proposed.     

基于工作流网的金融机具产品开发过程建模研究

为了精确、有效地量化分析和评估产品设计开发过程,提出了产品开发过程的多视图模型和基于任务结构的产品开发过程模型.应用工作流网与任务结构的相似性,结合产品功能实现的要求,对开发过程的任务结构图进行描述,实现了由产品开发过程的任务结构模型到工作流网的模型映射机制.针对金融机具纸币清分机的开发过程,进行了基于工作流网的设计过程验证,实现了产品设计开发过程中的任务分配和性能评估,以便对产品开发周期进行更量化、更精确的分析.     

A new cadmium-organic framework fluorescent sensor for Al3 + and Ca2 + ions in aqueous medium

A new metal-organic framework (MOF), [Cd₂(bptc)(HCOO)]·NH₂(CH₃)₂·3H₂O (1), where H₄bptc = 3,3′,5,5′-biphenyltetracarboxylic acid, was obtained by solvothermal reaction. The topology of MOF 1 is a (5,8)-connected net with {4¹⁶ · 5⁸ · 6⁴}{4⁴ · 5⁶}₂ point symbol. MOF 1 shows high stability in aqueous solution. Luminescence study indicates that MOF 1 possesses selective turn-on luminescent sensing functions towards Al^3 + and Ca^2 + ions in aqueous solutions.     

线上线下混合模式的实验课程改革——以数据结构课程为例

该文以数据结构课程为例,从课程性质和内容进行介绍,利用线上线下混合式教学,对实验实施改革。以数据分析作为基础进行方法总结,对实验课程内容进行全方位的改革和实施。     

离线式带钢双面翻转检查站方案设计及实践

针对某酸轧机组检查站穿带困难、检查效率低、产生废品多、故障率高的问题,开发了一种离线式带钢双面检查站。该检查站新增了带钢翻转装置,将在入口分切剪处完成定尺剪切的带钢试样由两侧压板夹紧,中间可升降皮带机落下,翻转装置将带钢试样张紧,并翻转90°或者180°,实现带钢的双面检查。皮带机两侧布置有可升降、可横移的活动操作平台,检测人员站在平台上对带钢进行打磨检查,可同时对带钢上下表面进行检测。由于缩短了带钢的传输距离,有效减少了其他擦划伤的影响,提高了带钢表面质量检测准确性。