Fracture properties of epoxy/poly(styrene‐co‐allylalcohol) blends

The epoxy/polystyrene system is characterized by a poor adhesion between the constituent phases, which determines its mechanical properties. The adhesion can be improved via blends based on epoxy resin and random copolymers, poly(styrene‐co‐allylalcohol) (PS‐co‐PA). In this work, the influence of PS‐co‐PA content and the good adhesion between the phases on the tensile properties and the fracture toughness achieved through instrumented Charpy tests have been investigated. The tensile strength and the deformation at break showed an increase in the PS‐co‐PA content while the Young's modulus remained the same. The tensile fracture surfaces revealed that the improvement of these magnitudes was mainly due to a crack deflection mechanism. Also, the fracture toughness of the blends was superior to that of the pure epoxy resin. The main operating toughening mechanism was crack deflection. The fractographic analysis showed that ～ 80% of the particles were broken, and the crack tended to divert from its original path through the broken PS‐co‐PA particles. The remaining particles were detached from the epoxy resin, and the holes left suffered plastic deformation. Analytical models were used to predict successfully the toughness due to these mechanisms. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Toughness Optimization of SBR Elastomers – Use of Fracture Mechanics Methods for Characterization

Elastomer materials are used in a wide application range and subjected to different loading from which failure of the material results. Because this failure is caused by initiation and propagation of cracks, the application of fracture mechanics methods for the assessment of the material is obvious. A short summary of the methods of technical fracture mechanics including possibilities of determination of crack resistance curves is given. Vulcanizates on the basis of SBR 1500 with various sulfur and carbon black contents were investigated. For describing the crack initiation and crack propagation behavior, several fracture mechanics examination methods were applied. Tear‐analyzer results were used to assess the crack propagation behavior under fatigue‐like loading conditions. Furthermore, for the characterization of the crack resistance of the materials under impact‐like loading conditions, instrumented tensile‐impact tests were performed. To obtain information about the initiation and propagation of a stable crack, quasi‐static fracture mechanics tests were applied. The results of the several tests are discussed in dependence on sulfur and carbon black contents. We found a non‐monotonous behavior of the toughness as a function of carbon black loading. An explanation is given in connection with a percolation‐like transition in filler morphology on larger length scales.

Schematic crack propagation curve for characterizing the fatigue behavior of the vulcanizates recorded in a TFA test.     

短纤维/橡胶发泡复合材料的微观结构及拉伸破坏机理

对锦纶短纤维增强的NR发泡材料的微观结构及拉伸破坏行为进行了研究，并分析了其破坏机理。采用未处理短纤维增强的NR发泡材料中短纤维成为泡孔的成核点，并大部分悬空在泡孔中，拉伸破坏时泡壁与短纤维结合处容易出现应力集中，成为裂纹的起始点，失效时短纤维大部分被抽出；预处理短纤维能与橡胶基体之间产生良好的粘合，从而处于橡胶基体中。其短纤维增强的NR发泡体拉伸产生的裂纹扩展时遇到纤维，纤维能起到承载应力、使应力转向、阻止裂纹扩展的作用，一定程度上改善了复合材料的拉伸强度等物理性。     

Toughened electrospun nanofibers from crosslinked elastomer‐thermoplastic blends

A crosslink‐able elastomeric polyester urethane (PEU) was blended with a thermoplastic, polyacrylonitrile (PAN), and electrospun into nanofibers. The effects of the PEU/PAN ratio and the crosslinking reaction on the morphology and the tensile properties of the as‐spun fiber mats were investigated. With the same overall polymer concentration (9 wt %), the nanofiber containing higher composition of PEU shows a slight decrease in the average fiber diameter, but the tensile strength, the elongation at break and tensile modulus of the nanofiber mats are all improved. These tensile properties are further enhanced by slight crosslinking of the PEU component within the nanofibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

供电企业配电线路故障及策略

通过分析供电线路安全运行的影响因素,提出了防范故障的策略,希望能够对配电线路的安全运行提供帮助。     

电力工程自动化系统故障分析的方法

由于电力工程自动化系统的操作程序不断复杂化,故障的出现频率也随之增加。因此,必须建立完善的故障分析和解决方案,方能保证电力工程的正常、顺利推进。在此基础上,就电力工程自动化系统故障分析方法进行分析、探讨。     

基于广义Hoek-Brown准则的节理岩体力学参数折剪计算

节理化岩体力学参数是矿山工程地质和稳定性分析的重要基础数据,一般在实验室通过单轴、三轴试验只能得到岩石的力学参数,无法得到岩体的力学参数。目前,利用岩石力学参数确定岩体力学参数的方法较多,但都过于烦琐或准确度不高,急需一种新的简易确定方法。因此,通过利用基于广义Hoek-Brown准则的地质强度指标（GSI法）,并结合相应的岩土分析软件,强度折剪岩石力学参数值,从而得到岩体的力学参数。通过将该方法应用于赤峰中色白音诺尔矿业有限公司岩体力学参数的计算中,证明采用该方法考虑岩体的结构面和完整性,可较为准确地反映节理化岩体的力学特性,且方便可行,具有工程实用价值。?     

电力线路施工中的关键问题分析

通过分析电力线路施工中的关键问题,提出了一些与电力线路施工相关的建议,以期为电力施工向更加优化的方向发展作出贡献。     

减少220 kV主变压器故障冲击技术措施

由于220 kV主变压器中压侧所配的过流保护需要与下级110 kV主变压器保护相配合,导致主变高、中压侧过流保护动作时间整定过长。在110 kV系统发生短路故障时,如果相关保护、开关不能正确动作,则主变压器将承受大电流、长时间的冲击,极有可能损伤变压器。