基于电子器件失效分析流程对失效LED分析方法的研究

结合一般电子器件失效分析方法,系统地设计了针对已失效LED器件的分析流程,并从封装结构和光、热特性几个方面比较了LED与一般器件失效分析方法的不同之处。通过分析发现了一般分析难以检测到的表面污染物污染、内部芯片断层等失效模式。实验证明,此方法对判断LED失效模式、推测失效机理更加准确,并可以有效地避免一般分析方法中过早的破坏性分析引入的损伤,以及将光电检测中电流和温度应力导致的损伤误判为器件原有失效因素。     

失效分析的任务、方法及其展望

概述了失效与失效分析的概念,以及失效分析的意义、作用和任务;以防止失效为出发点,论述了失效分析的工作思路、程序和辩证方法;展望了失效分析的未来。     

重大机械装备失效分析与预防

失效分析与预防是一门综合性的边缘学科,它是推动科学技术进步,促进国民经济发展的一个重要手段,是提高机械装备质量和延长使用寿命的重要途径。 长期以来由于种种原因,我国现有设备如发电设备、石化装备及交通运输工具等重大机械设备超期服役、带“病”运行相当普遍,有相当多的设备存在着各种结构缺陷、焊接缺陷、制造缺陷、材料缺陷和使用不当产生的裂纹或损伤、腐蚀介质的影响或长期超载运行等隐患;以及管理不善。一些设备盲目使用,不注意维修、保养和缺乏必要的监控和预防措旋,也加剧了事故的发生。     

断裂失效分析

机械产品的失效一般可分为非断裂失效与断裂失效两大类。非断裂失效一般包括磨损失效、腐蚀失效、变形失效及功能退化失效等。     

预应力混凝土梁桥系统失效树分析

针对预应力混凝土梁桥,采用失效树的方法进行系统可靠性分析。运用全局临界强度分枝-约界准则识别结构系统主要失效模式,以JC法计算各主要失效模式的可靠指标,采用Ditlevsen上下界公式分析结构体系的失效概率。以某汉江公路大桥为例,分析了失效树图形,研究了主要失效模式的可靠指标、失效概率及桥梁结构体系可靠性。与实桥运营状态的对比分析表明,上述理论分析较好地预测了实际的结构行为,能用于桥梁结构安全性及可靠性分析评估。     

平面杆系结构的失效包络图及失效评估

定义了平面杆系中的失效评估杆元、以及该杆元的正则杆端弯矩和正则杆端曲率,据此引入了杆件失效包络图、工作状态图、以及杆件失效指标,进而定义了平面杆系结构失效包络图、结构工作状态图。又据该图中反映杆元状态的点群的分布情况,分别从概率分布、加权平均和取最大值的角度定义了三种结构整体失效指标。利用杆元和结构失效指标可简明直观地进行结构失效评估,成为与通常基于结构物理性能改变的结构损伤评估不同的另一种几何评估模式。利用本方法分析了一个三跨六层框架,计算了该框架在多种荷载、梁柱线刚度比、以及失效评估杆元划分密度下的各种失效指标。     

失效分析中的模式思维方法

对事故模式和失效模式的归纳总结,从中引伸出预防事故或失效的新认识或新概念.     

直齿轮闭挤式精冲模具的失效分析

目的探索闭挤式精冲模具的失效情况及有效的防止措施。方法根据模具的受力特点,分析了闭挤式精冲模具的主要失效形式。通过实验、检测和金相分析,研究了模具失效的主要原理。结果总结出了防止模具失效、延长模具使用寿命的一些有效方法。结论闭挤式精冲凸模和主凹模失效主要发生在模具刃口处,改进模具结构,优化工艺参数,能减小模具受力,同时选择优质的模具材料也能减少失效。     

铁路装备的机械失效分析与预防

总结铁路装备的选材、制造工艺、产品质量特点,铁路装备产品总体上为价廉、制造冶金缺陷要求不严;介绍了主要部件失效的类型、形态特征和机理,大部分失效与冶金质量有关;阐述了铁路装备机械失效分析与预防的现状,提出了失效分析与预防紧密结合发展的几点方向.     

实例推理技术在航空部件失效分析中的应用

介绍了实例推理的基本原理,根据失效分析工作的特点,给出了部件失效分析的实例推理系统框架,并对存在的问题和今后的工作进行了探讨.     

Influence of surface roughness on the bonding quality in twin-roll cast clad strip

Manufacturing of aluminum-steel clad strips by means of twin-roll casting is of great interest due to a shorter production chain in comparison with convenient technologies. Experiments on twin-roll casting of clad strips of pure aluminum and an austenitic stainless steel of 2.5?mm total thickness with the inline abrasive cleaning of a steel substrate’s surface performed. The corresponding device for the inline surface preparation is designed. The influence of surface roughness of the substrate’s surface on the bonding strength between strip layers is analyzed. The mechanism of intermetallic bonding on the roughened surfaces is discussed. It is shown that surface roughness of steel substrate up to 4.2?µm provides bonding strength above 100?MPa.     

Central Venous Catheter Associated Infections Pathophysiology,Incidence, Clinical Diagnosis,and Prevention – A Review

The incidence of catheter related bloodstream infections poses a substantial burden on patient’s life’s and well‐being. Estimated 2 – 6 % of patients suffer from catheter associated bloodstream infections (BSI). Reports on mortality of these patients are up to 30 % in addition to a substantial prolongation of hospital days. The estimated cost of therapy of a BSI is approximately 10 000 € per patient. There is a definitive need for antimicrobially active medical devices for prophylaxis. Endowment of catheters with antibiotics and desinfectants have substantial limitations regarding spectrum of activity, duration of activity and clinical efficacy. The oligodynamic activity of silver has the greatest potential for prevention of catheter related infections. Various technologies in particular surface coating of these medical devices have been advocated previously with limited success. A new technology with impregnation of the entire catheter matrix with billions of nanoparticles of silver⁰ which results in a surface of 2000 cm²/g polyurethane (PU) has been developed. Central venous catheters manufactured according to the technology of the first and second generation have been investigated with good results of antimicrobial activity and biocompatibility. Favorable results in experimental investigations and good clinical results in controlled prospective, randomized, investigator blinded studies of the first generation silver catheter have been obtained. In 660 patients in an overall reduction of BSI of 66 % was observed. Favorable results in a postmarketing surveillance with 3000 patients were seen. The premarketing surveillance of the second generation silver‐catheter indicated an even greater reduction of catheter related BSI. In 204 patients with a mean duration of catheter placement of 9.2 days only one catheter related BSI was diagnosed. The rate of catheter colonization was <10 %. The catheter was well tolerated. A further improvement with increased antimicrobial activity was achieved by activation of silver nanoparticles in the third generation catheter: The superior results of in vitro tests and excellent biocompatibility lets us expect an additional improvement of preventive measures. The duration of antimicrobial activity has been investigated and lasts at least 370 days. The concept of impregnation of a polymer matrix and silicone can be extended to various other clinical applications e.g. Sheldon, Hickman and urologic catheters. Substantial savings in the cost of patient care through prevention of complications can be expected which is of particular importance with the disease oriented (DRG) remuneration system.     

Energy and exergy analysis of single effect and series flow double effect water–lithium bromide absorption refrigeration systems

In this paper, the energy and exergy analysis of single effect and series flow double effect water–lithium bromide absorption systems is presented. A computational model has been developed for the parametric investigation of these systems. Newly developed computationally efficient property equations of water–lithium bromide solution have been used in the computer code. The analysis involves the determination of effects of generator, absorber and evaporator temperatures on the energetic and exergetic performance of these systems. The effects of pressure drop between evaporator and absorber, and effectiveness of heat exchangers are also investigated. The performance parameters computed are coefficient of performance, exergy destruction, efficiency defects and exergetic efficiency. The results indicate that coefficient of performance of the single effect system lies in range of 0.6–0.75 and the corresponding value of coefficient of performance for the series flow double effect system lies in the range of 1–1.28. The effect of parameters such as temperature difference between heat source and generator and evaporator and cold room have also been investigated. Irreversibility is highest in the absorber in both systems when compared to other system components.     

Thermal conductivity of composites

A general expression for the effective thermal conductivity of inhomogeneous media in terms of the Fourier components of the spatial variation of the conductivity is applied to composites consisting of inclusions in a continuous matrix. It is reformulated in terms of the mean square fluctuations of the conductivity. Specific cases treated are spherical inclusions and long cylinders, both random and with preferred directions. The results hold provided the difference in thermal conductivities is small or provided the concentration of inclusions is not too large. The theory fails if the thermal conductivity of the matrix is much smaller than that of the inclusions. The same considerations also apply to electrical conductivity.     

Einfluss der Werkstoffzähigkeit auf das Festigkeitsverhalten unter mehrachsiger Beanspruchung am Beispiel von Schweißverbindungen aus Stahl und Aluminium

Influence of Ductility on the Multiaxial Fatigue Behaviour by the Example of Welded Joints of Steel and Aluminium The multiaxial fatigue behaviour of materials with different ductility under constant and changing principal stress directions is also applicable to welded joints of different materials. For this, welded flange tube connections of the fine grained steel StE 460 and the artificially aged aluminium alloy AlSi1MgMn T6 were investigated under constant amplitude combined bending and torsion. Out‐of‐phase loading, i. e. changing principal stress directions, of the steel joints led to a decrease of fatigue life, which is observed at ductile material states. However, for the aluminium joints out‐of‐phase loading resulted same behaviour as in‐phase loading, which indicates a semi‐ductile material behaviour. The results for the welded steel joints were evaluated on basis of local stresses by the integral hypothesis of the Effective Equivalent Stress EES (WVS). This hypothesis for ductile material states takes into account the life decreasing influence of out‐of‐phase loading by considering the interaction of the shear stresses on different planes. The fatigue behaviour of the aluminium welds is described by the critical plane based combination of shear and normal stresses (KoNoS), which is valid for semi‐ductile material states.     

Surface State Control by Ultrasonic Plastic Deformation at the Final Machining Stage

Basic results of research into the process of the surface geometry formation during ultrasonic plastic deformation of metallic materials are presented. The results of mathematical modeling of the microgeometry and surface undulation formation in the machining of materials of different hardness are also presented. Experimental validation of the adequacy of the proposed models is provided.     

Multiple-jet electrospinning methods for nanofiber processing: A review

Electrospinning is a versatile method of producing continuous nanofibers through the application of an electric field. The simplest and earliest form of electrospinning involves the use of a single-needle spinneret to draw the solution out and form fibers. The process, however, is very time consuming, limiting the potential wide-scale application of electrospun nanofibers. Many multiple-jet electrospinning methods have been proposed to overcome the problem of low productivity, but the generation of multiple jets brought about other problems such as jet repulsion, lower process controllability, and deterioration of fiber quality. Thus, continuous development is necessary for the optimization of the process. The aim of this review is to provide an overview of the recent electrospinning technologies reported in the literature, particularly on various multiple-jet electrospinning methods from both nozzles and free surfaces. The general principle underlying the electrospinning process, as well as important parameters involved are also presented in this paper.     

Certified reference materials of trace elements in water

Measurement of trace elements is playing a vital role in industries and various sectors of science and technology including semiconductors, food, health and environmental sectors. In most of the cases a small error in measurement can vitiate all the measures taken for quality control and management. Many decisions regarding the suitability of material/products are based on the analysis. To reduce or eliminate the rejection rate of the products, accurate and reliable measurements are needed which can be achieved by the use of certified reference materials (CRMs). Their use in calibration of analytical equipments and validation of test methods ensures high quality in measurements and it provides traceability to the measurement data with national/international measurement systems (SI unit) also. In the present scenario of globalization of economy, use of certified reference materials (CRMs) in measurements is essential for global acceptance of products and test reports. Their use fulfil a mandatory requirement of international quality systems (ISO 9000, ISO/IEC standard 17025) including our national accreditation body, National Accreditation Board for Testing and Calibration Laboratories (NABL), World Trade Organization (WTO) etc. International manufacturers of CRMs are meeting most of the requirement of CRMs of the country. To meet the demand of CRMs indigenously, the National Physical Laboratory, India initiated a national programme on preparation and dissemination of certified reference materials.     

The Study of Low Surface Energy Fluorocarbon Coatings with Fluor Content Being Lower

A kind of low surface energy fluorocarbon coatings from the synthesized fluoro-acrylic resin was developed.The molecule orientation principle of nonpolar and polar functional groups in the coatings was analyzed. The contact angles of pure water drops on the surfaces of various fluoro-monomer homopolymers and interpolymers were measured. The relation of coatings' fluoro-content with the surface energy was determined. The distribution of fluoric functional groups in the coatings was investigated. The test results show that though the total content of fluor of the fluorocarbon coatings is relative few, their surface energy is really low due to the enrichment of fluoro-chains on the surfaces.