降温速率对低压ZnO压敏电阻性能的影响

采用低压ZnO压敏电阻配方,利用正电子湮没寿命谱(PAS)及SEM,对试样微结构进行了分析.结果表明,急冷能使低压ZnO压敏电阻的微空洞尺寸增大,缺陷浓度降低.通过分析PAS参数与电性能参数的关系,对急冷能明显降低电压梯度提出了新的解释.     

化学沉淀法的醇水比对氧化锌压敏电阻性能的影响研究

通过化学沉淀法制备得到ZnO压敏电阻样品并分析研究了样品的显微结构特性、宏观电学参量和介电响应特性,包括阻抗谱和介电损耗谱。采用XRD和SEM观测分析了ZnO压敏电阻的物相组成和微观结构。电学参数测试结果表明,当化学沉淀法的醇水比为2∶1时,ZnO压敏电阻表现出的各项电性能均比较好：电压梯度为584.01 V/mm,非线性系数为73.43,泄漏电流为0.13μA/cm²。该结果表明化学沉淀法可以作为制造高性能ZnO压敏电阻的有效途径。另外,通过介电谱的测试结果可以看出,介电损耗峰的峰值能体现出ZnO压敏陶瓷中缺陷的浓度,改变化学共沉淀法中的醇水比能够相应地改变ZnO压敏陶瓷中本征点缺陷的浓度。     

Bi掺杂对直流ZnO电阻片缺陷结构和电性能的影响

普遍认为,Bi2O3是ZnO电阻片形成晶界势垒及非线性伏安特性的基础,然而Bi元素对构成势垒的缺陷结构的作用机制仍不清楚.基于一种优化的介电谱,笔者研究了Bi2O3含量对现代直流ZnO电阻片本征点缺陷锌填隙和氧空位、非本征缺陷晶间相结构和界面态的作用机制.实验结果表明,Bi掺杂使得晶界势垒结构发育完善,所以掺入Bi元素...     

Co_2O_3对ZnO晶粒电阻率的影响

研究(1-x)ZnO+xCo_2O_3一元掺杂ZnO陶瓷系统,通过测定瓷体中ZnO晶粒的自由电子浓度和晶粒电阻率,并利用扫描电镜分析ZnO晶粒本身的缺陷结构,就Co_2O_3对ZnO晶粒电阻率的影响进行了研究。     

双列球型轮毂轴承单元耐久性寿命计算分析

对于双列球型轮毂轴承单元数学模型,采用模拟试验载荷谱进行轮毂轴承单元耐久性寿命计算,并分析预紧载荷、侧向加速度和受载偏心距等对球型轮毂轴承单元耐久性寿命的影响。分析结果表明:适当的轴向预紧可提高轮毂轴承单元的刚性以及左右两列轴承的载荷分布均匀性,当轴向预紧量为0.02 mm时,轮毂轴承单元的寿命达到最大值;受载偏心距的影响,使得车辆左右两侧轮毂轴承单元的寿命存在差异,一般驾驶室左侧轴承单元寿命稍高;轮胎半径的大小会同时影响轮毂轴承单元的旋转速度和加载力矩,当轮胎半径取200 mm时轴承单元寿命最长。     

钡、镁、铝添加剂对氧化锌电阻片稳定性的影响

以 BaO、MgO、Al_2O_3为添加剂的 ZnO 电阻片,由于杂质在晶界处偏析和晶粒中对 Zn 原子作等价或不等价的取代,当含量和比例适当时,可使小电流和大电流性能同时得到改善;填隙 Zn 离子数的减少,晶界结构的稳定都极大地改进了长期工作的稳定性。按本文配方和工艺制备的 ZnO 电阻片,当荷电率提高到0.75及以上时,具有所需求的长期使用寿命。     

Gd2O3掺杂对ZnO压敏电阻片电气性能的影响

研究了不同掺杂含量的Gd2O3对氧化锌(ZnO)压敏电阻片的电气性能、微观特性、物相特性和介电特性的影响.研究表明,掺杂Gd2O3对ZnO敏电阻片的电气性能具有重要影响,掺杂过量的Gd2O3对ZnO敏电阻片的晶粒生长具有抑制作用,锌填隙浓度提升,具体表现在电位梯度、泄漏电流提升而非线性系数大大减小.而掺杂少量的Gd2O3提升氧空位浓度,减小锌填隙浓度,进而抑制泄漏电流.此时掺杂量在0.5％(摩尔分数)Gd2O3电气参数分别为526 V/mm、15 μA/cm2、非线性系数28.该研究可帮助氧化锌压敏电阻优化配方,增强电气性能,改善电力系统的安全稳定性.     

钇掺杂对ZnO电阻片微观结构和电性能的影响

研究了在ZnO-Bi2O3-Sb2O3系ZnO电阻片中添加少量硼酸和掺杂0.2%～0.8%(摩尔分数)的氧化钇(Y2O3),其显微结构和电性能的变化情况。结果表明,随Y2O3掺杂量的增加,ZnO压敏电阻片的电位梯度从210V/mm提高到422.5V/mm;当掺杂量为0.6%(摩尔分数)时,电性能达到最佳,即残压比最小,为1.12;漏电流最小,为353.0μA。掺杂Y2O3使ZnO晶粒周围除了形成Zn7Sb2O12尖晶石外,还形成了具有细微颗粒的含钇相(Zn-Sb-Y-O)和含铋相(Bi-Sb-O),尖晶石相、含钇相和含铋相的同时存在更加有效地抑制了ZnO晶粒的长大。添加硼酸和增加含钇相在很大程度上改善了ZnO电阻片的电性能。     

ZnO电阻片寿命内冲击老化的研究

分析了冲击电流对ZnO电阻片的老化影响。通过试验研究放电电流的幅值大小、波形、放电次数以及环境温度四个因素对老化的影响,并推导基本规律;结合标准对非线性金属氧化物电阻片性能要求的规定,提出能够一定程度上反映ZnO电阻片剩余寿命的参数,给带间隙线路避雷器提供了一种新的在线监测方法。相关的产品已经研发出来,现场应用效果良好。     

锈蚀RC梁持荷作用后的疲劳寿命预测模型

为探究锈蚀混凝土梁在持荷损伤后的疲劳寿命规律，文中通过引入锈蚀作用修正系数，建立损伤混凝土梁的疲劳寿命预测模型；根据线弹性断裂力学基本理论，考虑钢筋等效初始缺陷尺寸，建立基于EIFS的疲劳寿命预测模型。并根据S-N曲线方程分析损伤混凝土梁剩余疲劳寿命随着钢筋临界锈蚀率的变化规律，研究表明当钢筋锈蚀率超过7.5%时，损伤混凝土梁的疲劳寿命不足50%。疲劳寿命预测模型与结果可为混凝土结构疲劳性能分析提供参考。     

Correlation between standards and the lifetime commissioning

This paper reviews the applicability and drawbacks of available European and international standards related to lifetime commissioning, by structuring them into Norwegian commissioning procedures. The work describes research on lifetime commissioning that proposes a generic framework on building performances. The generic framework describes a component in HVAC system by performances. The results of the standard review show that there is a need for measurement and testing standards in hydronic systems. In addition, there is no generic framework on the definition of energy-efficiency measure in the reviewed standards. Findings on a case study, where lifetime commissioning procedures were tested, are presented. After the performances of the case study were defined by the generic framework, it was found that 20% of all the performances can be monitored by a building energy management system. Due to good operation, the building managed to achieve 3% lower energy consumption than design a year after the building was taken in use. In addition, results show that energy signature curves can be used only in a modified way to predict heating consumption, while electricity consumption cannot be described in that way.     

基于寿命函数的斜拉索系统维修更换策略研究

展开寿命周期内拉索劣化规律和维修更换策略的研究,获得桥梁结构的最优成本-效益比,是缆索桥梁养护维修的重要研究内容之一。根据拉索寿命函数和拉索系统的串并联模型,研究斜拉桥拉索系统失效概率变化即结构劣化的规律,分析全寿命周期内不同维修更换措施对结构失效概率的影响。运用周期成本理论,进一步分析不同维修更换时间和更换策略的经济性。结合一斜拉桥模型,验证了模型的适用性,并且以延长使用寿命和累积维修费用最低为目标,获得该桥的最优维修策略。研究表明,寿命函数和周期成本理结合是确定斜拉桥拉索更换优化策略的有效途径,为工程拉索更换策略提供有益的参考。     

服务面对用户诉求,提供终身解决方案

行胜于言——用户对服务诉求,重在结果的有效程度,用户需要满意的服务,企业需要有效的劳动。随着工程机械市场发展,产能大幅提升已超出想象,工程机械产品技术的同质化导致服务质量优     

桥梁缆索用HDPE寿命研究现状

分析了HDPE材料的脆性与延性开裂各自的特点,阐述了应力开裂的微观和宏观机理和应力开裂寿命的实验方法,高温环境实验获得的寿命数据需要外推至常温,为此分析了三种外推方法的优缺点,对大气老化对材料劣化的影响机制和相关数值模型也作了介绍。     

提高混凝土泵眼镜板使用寿命的研究

分析了混凝土泵眼镜板的工作条件、失效形式及性能要求。针对目前眼镜板在材料、结构上存在的问题，提出了选用新材料、新工艺制作眼镜板的方法。使用该方法制造的眼镜板耐磨性高，外形美观精致，使用寿命最高可提高近一倍。     

Extending the lifetime of steel truss bridges by cost-efficient strengthening interventions

Abstract

The large number of existing bridges and viaducts all around the country has become a major problem for bridge owners. In the specific case of steel truss bridges, a reasonable method to extend the lifetime of existing structures is represented by the introduction of new deck systems combined with diffused strengthening interventions. In this study, a stepwise approach considering different loading conditions is presented (historical and Eurocode loads). The structural analysis has been performed on a case study bridge with a finite element model (FEM) calibrated on load tests. It was found that the predicted deformation agreed reasonably with the experimental results. Different strengthening alternatives were analysed and discussed: the introduction of orthotropic deck; the construction of composite deck with differentiating thickness and ordinary concrete strength; the construction of composite deck with differentiating thickness and high concrete strength; in some cases, also steel-to-steel interventions on the bridge are provided. It has been found that the best structural strengthening alternative lies in the construction of a composite concrete or of an ultra high-performance concrete (UHPC) or an ultra high-performance fibre-reinforced concrete (UHPFRC) deck with a reduced thickness (compared with traditional interventions) resting on the existing steel structure combined with steel-to-steel interventions.     

The use of stress-density functions for lifetime predictions of brittle structures

The tools necessary to perform a lifetime analysis for a brittle structure are presented. The paper explains methods for measuring the relevant material properties, such as Weibull modulus m, normalization strength σ₀, and subcritical crack growth parameter n, and for combining them with suitable statistics, stress analysis, and linear-elastic fracture mechanics, in order to arrive at strength-probability-time (SPT) diagrams for a particular structure. Moreover, it will be shown, how mathematical difficulties arising during the statistical analysis can be overcome by making use of the so-called stress-density functions, which were recently introduced by Nadler [1].     

对灭火系统控制器寿命的认识和理解

从产品的系统应用及电子产品特点的角度,提出对自动灭火系统控制器寿命的理解和认识。