Variation of activation energy determined by a modified Arrhenius approach: Roles of dynamic recrystallization on the hot deformation of Ni-based superalloy

The hot deformation behaviors of Ni18Cr9Co9Fe5Nb3Mo superalloy were explored in the formation temperature range free ofγ'phase with various strain rates applied.The hot deformation behaviors are initially modeled with Arrhenius equation which gives an average activation energy of 581.1 kJ mol-1.A modified Arrhenius approach,including the updated Zener-Hollomon parameter is proposed to consider the change of activation energy under different deformation conditions which turns out a relatively accurate computation for activation energy of hot deformation,i.e.,the standard variance for modified model calculated in the covered deformation condition is just 35.4 ％ of that for Arrhenius equation.The modified model also proposes a map for activation energy which ranges from 571.5-589.0 kJ mol-1 for various deformation conditions.Microstructural features of the representative superalloy specimens were characterized by electron backscattered diffraction (EBSD) techniques in order to clarify the influence of activation energy on the microstructural formation.It is found that the Ni-based superalloy samples with higher activation energy are promoted by the degree of dynamic recrystallization which suggests that the rise in activation energy gives either a better recrystallization rate or finer grains.     

Mg-8.08Gd-2.41Sm-0.3Zr合金热压缩变形及热加工图

利用铸造法制备了Mg-8.08Gd-2.41Sm-0.3Zr合金,对该合金进行均匀化处理,然后进行热压缩实验,研究了Mg-8.08Gd-2.41Sm-0.3Zr合金在变形温度为350~500℃、应变速率为0.002s~(-1)、0.01s~(-1)、0.1s~(-1)和1s~(-1)及最大变形量为50%条件下的变形行为,计算了该合金的热变形激活能,构建了合金高温塑性变形的本构关系,建立了合金的热加工图。结果表明:Mg-8.08Gd-2.41Sm-0.3Zr合金的流变应力随着变形温度的升高或者应变速率的降低而显著降低,合金发生动态回复与再结晶,其热变形激活能为Q=213.693kJ/mol;合金高温变形时存在两个失稳区:T=430~500℃、ε=0.37~1s~(-1)以及T=350~390℃、ε=0.006~1s~(-1);合金的能量耗散率大于30%的区域有T=370~430℃、ε=0.37~1s~(-1),T=390~500℃、ε=0.006~0.37s~(-1)以及T=350~500℃、ε=0.002~0.006s~(-1),这些区域适合进行热加工。     

Flow behavior and processing map for hot deformation of ATI425 titanium alloy

Flow behavior and processing map play important roles in the hot deformation process of titanium alloys. In this research, compression Gleeble tests have been carried out to investigate the stress–strain relationship at temperatures ranging from 700 to 1000℃ and strain rates ranging from 0.001 to 1 s~(-1) for ATI 425 titanium alloy. Arrhenius type constitutive equation was obtained to describe the compressive flow behavior with modification of additional deformation dead zone, friction model, temperature model and strain rate. The introduction of novel calculation method for value in Arrhenius equation gives more accurate fitting than traditional one. Processing maps were drawn based on the distribution of dissipator co-content, and optimized deformation temperature and strain rate range obtained. It is proven to be accurate and effective through the experimental results. The microstructure analysis shows that more dynamic recrystallization can be achieved in the area with larger value on the processing map.     

A robust return‐map algorithm for general multisurface plasticity

Three new contributions to the field of multisurface plasticity are presented for general situations with an arbitrary number of nonlinear yield surfaces with hardening or softening. A method for handling linearly dependent flow directions is described. A residual that can be used in a line search is defined. An algorithm that has been implemented and comprehensively tested is discussed in detail. Examples are presented to illustrate the computational cost of various components of the algorithm. The overall result is that a single Newton‐Raphson iteration of the algorithm costs between 1.5 and 2 times that of an elastic calculation. Examples also illustrate the successful convergence of the algorithm in complicated situations. For example, without using the new contributions presented here, the algorithm fails to converge for approximately 50% of the trial stresses for a common geomechanical model of sedementary rocks, while the current algorithm results in complete success. Because it involves no approximations, the algorithm is used to quantify the accuracy of an efficient, pragmatic, but approximate, algorithm used for sedimentary‐rock plasticity in a commercial software package. The main weakness of the algorithm is identified as the difficulty of correctly choosing the set of initially active constraints in the general setting. Copyright © 2016 John Wiley & Sons, Ltd.     

Process optimisation and microstructural evolution of friction stir spot-welded Al6061 joints

The joint strength and subsequent microstructural evolution of a friction stir spot-welded AA6061-T6 alloy was investigated according to the process parameters: tool rotation speed, dwell time and pin angle of the tool. A maximum tensile shear load of 2.78?kN was obtained from the joints generated under a combination of process variables like 1000 and 1500?rev?min^?1, 5?s, 5°. Under a fixed pin angle of 5° and a rotational speed of 1000?rev?min^?1, an increase in dwell time from 1 to 5?s resulted in a considerable increase in tensile shear load. An empirical process map under a fixed tool design is proposed to determine a feasible range of process conditions.     

EEG source localization using a sparsity prior based on Brodmann areas

Localizing the sources of electrical activity in the brain from electroencephalographic (EEG) data is an important tool for noninvasive study of brain dynamics. Generally, the source localization process involves a high‐dimensional inverse problem that has an infinite number of solutions and thus requires additional constraints to be considered to have a unique solution. In this article, we propose a novel method for EEG source localization. The proposed method is based on dividing the cerebral cortex of the brain into a finite number of “functional zones” which correspond to unitary functional areas in the brain. To specify the sparsity profile of human brain activity more concisely, the proposed approach considers grouping of the electrical current dipoles inside each of the functional zones. In this article, we investigate the use of Brodmann's areas as the functional zones while sparse Bayesian learning is used to perform sparse approximation. Numerical experiments are conducted on a realistic head model obtained from segmentation of MRI images of the head and includes four major compartments namely scalp, skull, cerebrospinal fluid (CSF), and brain with relative conductivity values. Three different electrode setups are tested in the numerical experiments. The results demonstrate that the proposed approach is quite promising in solving the EEG source localization problem. In a noiseless environment with 71 electrodes, the proposed method was found to accurately locate up to 6 simultaneously active sources with accuracy >70%.     

基于情境体验的移动室内地图需要与策略研究

目的研究基于情境体验的移动室内地图交互设计,提升用户体验。方法通过阐述情境体验定义及要素关系,分析其对室内地图交互设计的影响,根据室内地图的功能特点,归纳出产品的3种典型使用情境,具体分析了各典型情境中的情境影响因素。结论总结出了用户在特定情境下的关注点和需求,并提出了基于情境体验的移动室内地图产品交互设计策略,最终结合设计实践对理论可行性进行了验证。     

Overlapping Shadow Rendering for Outdoor Augmented Reality

Realism rendering methods of outdoor augmented reality (AR) is an interesting topic. Realism items in outdoor AR need advanced impacts like shadows, sunshine, and relations between unreal items. A few realistic rendering approaches were built to overcome this issue. Several of these approaches are not dealt with real-time rendering. However, the issue remains an active research topic, especially in outdoor rendering. This paper introduces a new approach to accomplish reality real-time outdoor rendering by considering the relation between items in AR regarding shadows in any place during daylight. The proposed method includes three principal stages that cover various outdoor AR rendering challenges. First, real shadow recognition was generated considering the sun’s location and the intensity of the shadow. The second step involves real shadow protection. Finally, we introduced a shadow production algorithm technique and shades through its impacts on unreal items in the AR. The selected approach’s target is providing a fast shadow recognition technique without affecting the system’s accuracy. It achieved an average accuracy of 95.1% and an area under the curve (AUC) of 92.5%. The outputs demonstrated that the proposed approach had enhanced the reality of outside AR rendering. The results of the proposed method outperformed other state-of-the-art rendering shadow techniques’ outcomes.     

针对全盲用户的导航软件信息无障碍设计

目的 研究影响全盲用户使用导航软件的因素,并基于信息无障碍设计,提出具体的设计策略和服务系统架构,为导航软件进一步服务全盲用户提供借鉴。方法 首先,提出信息无障碍设计中信息的等效替代、强固性、易用性及设计的通用性原则。其次,从生理、认知和行为习惯等方面分析全盲用户群特征,并通过实地访谈和观察实验的方法对全盲用户进行调查研究,构建人物角色模型,绘制用户旅程图,从而获知全盲用户使用导航软件的痛点和机会点。结论 研究表明当前导航软件的无障碍服务水平有待提升,存在缺少盲道指引、无障碍物提示、目的地定位不准确等问题,因此,在增加盲道指引,利用听觉感官给予交互反馈,提供实时路况这3个具体功能点的基础上,构建信息无障碍的服务系统架构。     

基于CSSCI数据库的中国传统村落研究知识图谱分析

目的 随着研究者们对中国传统村落的深透研究,涌现出了大量的相关研究文献,为了能够更好地把握其发展动向。方法 以信息可视化软件Citespace为研究工具,将1998年至2017年间 CSSCI数据库中有关传统村落研究的253条文献作为研究对象,制作并分析近20年间我国传统村落文献共被引图谱、期刊共被引图谱、作者共被引图谱以及关键词&主题词共现图谱。使用Citespace绘制出的图谱可以很明显地看出我国传统村落的研究前沿、与研究相关的范畴和重要文献、该领域具有影响力的作者及其研究的热门要点。结论 研究表明：在研究的方法和视角上包含多个学科交叉的特点,研究对象由单一转为多元化,更深入地挖掘和剖析了研究内容;在CSSCI数据库中对Citespace软件分析出的前5位高被引作者,以“传统村落”、“古村落”、“传统聚落”和“历史文化名村”为关键词进行检索、整理和分析,挖掘文章的优势,对文章中的不足进行剖析;“古村落的保护发展与传承”、“历史文化遗产的多重价值与可持续发展路径”、“景观规划和活化机理”等成为热点研究领域,以传统村落综述研究的角度与手法,对以后的研究人员更好地了解传统村落领域的前景有一定的参照、借鉴意义。