The influence of powder characteristics on the sintering behaviour and impurity content of spark-plasma-sintered zirconium

At present, most zirconium products as well as its alloys are obtained by foundry methods. New technologies used to manufacture high-quality components, such as direct laser sintering or microwave sintering, require spherical powders of a narrow particle size distribution, as this affects the packing density and sintering mechanism. The powders also have to be chemically pure, as impurities such as H, O, C, N and S cause brittleness and problems with corrosion. Commercially procured, high purity zirconium powders from three different sources were characterised for their particle size and phase composition. Dilatometer studies have shown the effect of powder contamination at the beginning and at end of the sintering process. For powders of 99.9% purity, the start of sintering takes place at a temperature of about 700 °C. For powders of 98.8% purity, the sintering starts at 500 °C. In the studies presented in this paper, the SPS/FAST (Spark Plasma Sintering/Field Assisted Sintering Technique) method was chosen for densification processes. Sintered materials were characterised for their density using the Archimedes principle, relative density and Vickers hardness. A determination of the oxygen, nitrogen and hydrogen content in zirconium powders and sintered samples was carried out. The studies confirmed that SPS of zirconium powders in an argon atmosphere slightly decreases the content of oxygen and nitrogen. At 1000 °C, at pressure of 35 MPa, in argon, there is no decomposition of zirconium hydrides in sintered materials.     

[产品服务]产品服务系统工程特性最终重要度确定方法

提出了一种考虑产品与服务交互的产品服务系统（PSS）工程特性最终重要度确定方法。应用模糊软集合方法解决质量屋在传递信息过程中存在的模糊性和不确定性;利用客户需求改进比率和“买点”对需求基本重要度进行修正,确定需求最终重要度;在工程特性基本重要度的基础上,利用PSS工程特性之间的自相关矩阵、工程特性竞争优先度以及改进比率合成获得工程特性最终重要度。最后以某企业轮式装载机PSS设计为实例,验证了方法的有效性。     

汽车三级分段变刚度双质量飞轮非线性振动研究

分析了三级分段变刚度双质量飞轮（DMF）刚度随扭转角变化的特征,考虑刚度非线性因素建立了搭载DMF的汽车传动系非线性扭转振动模型和对应的微分方程,采用平均法和Runge-Kutta数值积分方法编制算法程序,推导和分析扭转角非线性频率特性近似解析解,并对不同转矩频率下的强迫振动响应进行仿真分析,以进一步探究三级分段变刚度DMF在传动系统中的非线性振动特性。     

气辅成型中成型工艺对制品翘曲的影响

对气辅成型制品翘曲缺陷采用正交实验方法和数值模拟方法进行了研究。研究了气体注射延迟时间与气体注射压力及气体注射时间与气体注射压力两对工艺参数的交互作用对制品翘曲缺陷的影响。结果表明,对制品翘曲影响最为严重的是气体注射时间与气体注射压力的交互作用。较长的延时可以减轻制品翘曲的程度,但气体无法穿透或穿透不足等问题也是延时过长会造成的,因此选择合适的气体注射时间与气体注射压力以及气体延时组合非常重要。     

基于FSM的电力远动规约设计

电力系统于1998年开始推行新的电力系统远动规约标准IEC60870-5-101,为了便于该规约的推广应用,编写较好的应用软件,引入有限状态机FSM(FiniteStateMachine)进行设计,并且基于面向对象技术提出一种高度结构化的有限状态机的实现框架。同时,应用有限状态机理论,抽象出链路层对象的有限状态机模型,并用状态图进行描述。有限状态机实现框架的引入,实现了灵活的复用机制,提高了系统的健壮性和可维护性。通信软件的开发,提供了一种比较便捷通用的开发模式,且现场实际运行良好。     

Cyclic grain boundary migration and sliding in pure aluminum

Reverse bending fatigue tests were conducted on high purity polycrystalline aluminum in the temperature range from 298 to 773 K. Observations show that the grain boundaries migrate and slide at temperatures above ≈500 K. The activation energy for migration is estimated as 76.1 ± 5.0 kJ mol⁻¹ and this is consistent with other measurements on high purity Al. Migration occurs cyclically but there is a small proportion of the boundaries, of the order of 10%, which are immobile and exhibit no measurable migration. Grain boundary sliding occurs at both the migrating and immobile boundaries, but at the migrating boundaries the total sliding offset, measured by a projection of interference fringes across the migrated region, tends to be small. Careful inspection shows that migration usually precedes sliding at the migrating boundaries, and the migration of triple junctions leads to the formation of very diffuse triple point folds.     

稀土萃取过程的广义预测解耦控制

考虑稀土萃取过程具有多变量、强耦合特性,提出一种基于广义预测解耦控制(GPDC)的稀土萃取过程控制方法.首先针对模型未知的强非线性稀土萃取过程,构建基于极限学习机的组分含量系统模型,并依据模型特点设计多个稀土萃取过程GPDC控制器;然后为降低各控制回路间的耦合性,在控制器的性能指标中引入校正策略,通过回路中模型预测值与...     

生态高校校园热微环境探讨

随着自然环境的破坏,高校校园生态化已经成为发展的必然,通过从外部环境、校园规划、建筑设计及建筑节能几方面探讨了相应的热微环境改善措施,以确保生态校园具有良好的热微环境。     

轨道-箱梁结构振动传递的模型试验研究

以京沪高铁常用的32 m无砟轨道箱梁结构为原型进行了模型试验,其中模型为轨道-箱梁结构.根据1/10的几何相似比,介绍了试验模型各结构的设计与制作过程,荷载激励由激振器施加.试验结果表明:轨道板振动在500-1024 Hz频段内衰减缓慢,底座板和顶板振动在0-1024 Hz频段内衰减较快;振动由顶板传递至翼缘板的过程中...