Modeling and Prediction of Thermal Cycle Induced Failure in Epoxy-Silica Composites

Epoxy resins filled with dielectric mineral particles are frequently used as insulating materials in power industry applications. Due to their excellent dielectric properties and relatively good thermal performance (resistance, ageing and conductivity) their usability is common and extensive. However, the mechanical performance of the resins is influenced by several factors such as resistance to crack propagation, especially in low temperature applications. This phenomenon is normally linked with appearance of two phase systems where particle filled epoxy material interacts with metallic inserts having significantly different thermal expansion coefficients. This kind of epoxy-metal interface can produce relatively high stresses in the product structure during thermal cycle loading. The paper deals with mechanical problems of power industry products and introduces the methodology for numerical modeling of failure in silica filled epoxy systems subjected to severe temperature gradients. Various aspects of material behavior modeling are covered in this article, including polymerization process, viscoelastic stress relaxation as well as stochastic cracking.     

热震中7YSZ热障涂层结构演变

采用低温超音速等离子喷涂(LT-HVOF)在镍基高温合金基体上制备了NiCoCrAlYTa粘结层, 使用大气等离子喷涂(APS)在粘结层上`制备了7wt%Y₂O₃-ZrO₂ (7YSZ) 陶瓷层。基于动态试验即热震实验研究了粘结层的扩散氧化机制, 探讨了陶瓷层的烧结及相变过程并观察了涂层的结构演变。实验结果表明: 动态热循环下随着热震次数的增加, 粘结层组元扩散氧化形成热生长氧化物(TGO)且厚度逐渐增加。此外, 粘结层组元在温度梯度下沿陶瓷层内部裂纹向高温区扩散, 最终在陶瓷层表面裂纹区域出现大量的金属氧化物, 同时粘结层组元的扩散有助于陶瓷层的烧结, 导致其显微硬度逐渐增大, 而粘结层由于Kirkendall效应, 其内部出现大量的孔洞导致其显微硬度逐渐降低。另外, 陶瓷层在相变及热循环应力的作用下表面出现了大尺度的宏观裂纹。     

Failure Analysis of a Threaded Pipe Ruptured During Hydraulic Testing

In the present case study, failure analysis of a piping system that ruptured during hydraulic testing has been carried out to find the root cause and determine the mode and mechanism of failure. Chemical composition of the pipe was found to be in compliance with the standard composition of AISI4130. The failure cause of the pipe has been investigated through visual examination, microstructural observation, hardenability analysis, and fractography. Threaded grooves were produced through machining after heat treatment. Variation in hardness and strength through thickness (from case to core) was evaluated using standard hardenability graph. Hardenability analysis showed that the strength of the pipe after machining was still well above the calculated maximum stress at any point of piping system. This finding was further supported by the microstructural study. The actual cause of pipe failure during hydraulic test was found to be due to the stress concentration factor being developed by some notch from improper thread machining which lead brittle failure and was also revealed by fractography analysis.     

Optical Emission Study of RF Thermal Plasma During Fullerene Synthesis

Results on studies of molecular spectra emitted in the initial stages of fullerene synthesis during processing of graphite powder in RF thermal plasma conditions are presented in this work. CN—usually present in carbon plasmas—and C₂ were found as dominant molecular species. The role of CN radicals on the fullerene formation was discussed in detail. Intensities of CN and C₂ lines were studied against the composition of gas phase and the feed rate of graphite powder. The rotational-vibrational temperatures of CN species were calculated by fitting the experimental spectra to the simulated ones. It was concluded that in the plasma region CN radicals could be formed by the reaction of C₂ with atomic nitrogen at smaller loads. This reaction lowered the yield of fullerenes. At larger loads, C₂ formation was decreased due to lower temperature of the particles compared to smaller load. The CN radicals were produced by the surface reaction of the hot carbon particles with nitrogen atoms. Results confirmed that for effective fullerene synthesis, the nitrogen content of the precursors and the plasma gases should be minimized.     

车载抬头显示光学系统塑料元件反射膜的研制

为了提高抬头显示系统中投影镜和反射镜的耐环境性和光学性能,以聚碳酸酯(PC)作为基底,采用电子束蒸发技术,使用过渡层和连接层技术以及渐增式离子源工艺,解决了薄膜与基底的附着力问题;利用真空退火,改善了环境测试过程中薄膜的膜裂现象;通过调节最外层SiO₂的离子源工艺,改善了水煮测试过程中薄膜因水汽渗透而导致的反射率下降的问题。制备了耐环境性能强的平均反射率大于95%的金属-介质结构的高反射膜。实际样品满足抬头显示系统的要求,并通过了多项环境测试。     

Failure Analysis of Swelling in Prismatic Lithium-Ion Batteries During Their Cycle Life After Long-Term Storage

This paper details the failure analysis of swelling in prismatic lithium-ion batteries (LIBs) after undergoing several charge–recharge cycles subsequent to long-term storage. The methods of analysis are nondestructive and mainly involve the use of computed tomography (CT) and cell disassembly. Two situations are compared. The first cell is examined after long-term storage, in which case a void space, presumably a gas bubble, is observed around the Ni tap in the cell, and traces of side reactants are found around the center of the anode electrode. This cell is compared with a swollen cell examined after undergoing several cycles after long-term storage, in which, according to the CT results before and after gas removal, gas is detected inside the jelly roll and inside the space between the can body and the jelly roll. Moreover, side reactants are identified near the center of the anode electrode, causing the color of the anode electrode to become irregular. The results show the gas bubbles and side reactants generated as a result of long-term storage are determined to be responsible for the swelling in the cell due to prolonged cycling.     

抛物面型X射线组合折射透镜光学性能分析

抛物面型X射线组合折射透镜是一种适用于硬X射线波段的新型光学元件.由于采用抛物面型,可以消除球差,因而能够产生亚微米尺度焦斑并具有更好的成像性能.本文给出了旋转轴对称抛物面型X射线组合透镜的理论研究成果.首先,利用矩阵光学方法,推导了其精确的焦距公式,得到了薄透镜判定准则;其次,根据衍射理论,推导出焦点处的光强分布,得到其极限焦斑大小.最后,本文还给出了透过率和有效孔径的理论公式.针对用Al、Be、PMMA三种材料制作的抛物面型X射线组合折射透镜,本文给出了各个光学性能指标的数值计算沣结果.     

头戴式虚拟现实设备的热舒适研究

目的了解头戴式虚拟现实设备的热特性,以及用户的主观热舒适感受。方法让被试者使用头戴设备45min,过程中采用温度记录器记录数据,最后用主观量表获取热舒适评分。获得的数据用SPSS进行方差分析,并结合设备的物理属性进一步进行主观热舒适影响因素分析。结果三款头戴设备的平均微环境温度在使用时间内共上升了8.11℃,主观热不适程度随使用时间的增加而增强。数据统计结果表明,三款设备间的微环境温度和主观热舒适数据差异显著(p0.05)。结论头戴式虚拟现实设备在使用时间内的微环境温度变化会对用户造成"轻微不适"的热感受,在提升产品热舒适方面可以从显示器的发热性和目镜的散热性入手。用户更青睐透气性强、且对面部相对不造成压力的S款设计。     

Glare Characteristics of Lenses and Optical Instruments in the Visible Region

An automatic laboratory glare photometer has been constructed and used to measure the glare characteristics of some typical lenses, and a focal systems by the elementary source method. From the glare distributions produced by the instrument, the concept of a glare spread function (g.s.f.) has been developed and it has been shown that the use of g.s.f.'s permits the glare characteristics of an optical system to be expressed in a manner more basic than has hitherto been possible. The numerical values of the g.s.f. depend only on the system under test and not on the geometry of the test equipment. Glare spread functions can be useful in several contexts. They can be used as procurement standards prior to design or manufacture and the measured g.s.f.'s of existing instruments can be used to calculate glare distributions in particular situations, different from the one actually used for the measurement.     

Methods of Checking the Optical Characteristics of Soft Contact Lenses

A new classification is proposed for contact lenses based on standard specimens (tolerance monitoring). The best wavelengths have been determined for measuring the spectral transmission coefficients of the standard specimens, and realistic bounds have been defined for the tolerance fields for the most common colors of these lenses.     

光学传递函数双胶合标准镜头的比对

双胶合标准镜头是国际上具有代表性的光学传递函数标准镜头,本文所介绍的由中国计量科学研究院设计加工的双胶合标准镜头的计算程序比对和国内验证比对实验的情况.     

焦度计用柱镜度标准镜片的研究

在分析三种面形柱镜度标准镜片的矢高、球差等对焦度计测量柱镜度影响的基础上,优选球柱形镜片作为柱镜度标准镜片.进而讨论了其光学设计和不确定度分析.通过实验研究,表明球柱形柱镜度标准镜片可用于解决焦度计柱镜度示值的校准问题.     

光学设计软件中的汉字显示

本文讲述了利用文本、图形方式转换子程序SETMOD、显示汉字子程序DRAWCC来实现FORTRAN语言编写光学设计软件的汉字显示问題。     

纳米节能材料成型压缩变化及其绝热试验

以纳米SiO2粉末与高折射率矿物粉末、增强纤维及高温收缩抑制剂,经千法混合后压制成型,制备较大体积密度的纳米节能材料。通过压制试验,研究了原料混合粉末在模具内的体积变化,探讨了物料中的气体对体积收缩率的影响,得到了材料体积密度与成型压力的关系。通过背温试验,将体积密度450kg／m3的纳米节能材料与现有市场上的复合反射绝热材料的绝热效果进行对比。结果表明,对于同样20mm厚度的两种材料,纳米节能材料热面温度稳定在668℃时,其冷面温度只有140℃。而复合反射材料热面温度稳定在641℃时,冷面温度高达229℃。纳米节能材料的绝热效果明显优于复合反射材料。     

失效概率的Bayes估计及其应用

对无失效数据 (ti,ni) ,在时刻ti 的失效概率 pi =P{T 相似文献   

超精密光学镜片三维表面形貌参数评定方法研究

分析了当前超精密光学镜片表面评定方法及其存在的不足,提出引用ISO 25178-2中规范的部分表面3D参数来表征精密光学镜片三维表面,找出光学镜片表面形貌与对应的光学性能存在的关系,并实现ISO对超精密光学镜片三维表面的评定。仿真实验表明:当光学镜片表面的高度服从高斯分布时,其评价光学系统性能的传递函数随着均方值的减小而增大。用实例说明ISO的部分三维参数对光学镜片三维表面可以很好地区分,利用新的综合评价方法评定光学镜片表面形貌具有一定的可行性。     

双目光学透视式头盔显示器的实验研究

采用分立元件研制双目光学透视式头盔显示器,对双目透视式头盔显示中的关键问题进行实验研究.用偏振分光棱镜作为组合镜,通过理论分析,发现图像源和外界环境的亮度随偏振片方位角呈余弦变化规律,并通过调整偏振片使头盔显示器的图像与外界环境达到最佳融合状态.调查研究了头盔显示器双目重叠范围的改变对视觉效果的影响,数据结果显示,双目重叠范围为单目视场的33～50%时效果最佳.最后根据视差原理编程制作立体图像对,分别显示于头盔显示器的左右眼,实现立体显示.     

The Diffraction Theory of the Aberrations of Stigmatic Orthomorphic Optical or Electron Optical Systems Containing Toric Lenses or Quadrupoles

The diffraction theory of the aberrations of optical systems with an axis of rotational symmetry is now thoroughly established, and the extension to kindred electron optical systems is straightforward. In electron optics, however, certain types of systems containing quadrupoles are of importance, and such systems suffer from aberrations which affect only very oblique rays in axially symmetrical systems. The distortions of the wave surface which correspond to these new aberrations are listed in the present note, and Nijboer's expressions for the consequent disturbances in the image plane of a rotationally symmetrical system are supplemented accordingly. Only the special case—which is, nevertheless, an important one—of stigmatic systems, producing an image free of first-order distortion?, is considered. The analysis is applicable to electron optical orthogonal systems containing quadrupoles and optical systems containing parallel toric lenses alike.