树脂基搭接碳纤维智能层的力阻特性

提出一种具有局部搭接结构的树脂基碳纤维智能层, 将其敷设于结构表面以检测结构受载时的变形, 实现对结构大范围监测。基于该智能层, 采用单轴拉伸和三点弯曲的加载方式, 对构件进行应变和位移检测。实验发现, 碳纤维局部搭接结构是引起力阻效应的主要因素, 其单位应变的电阻率变化的灵敏度达到104, 相当于非搭接连续碳纤维复合材料力阻效应灵敏度的34倍。实验结果还进一步表明, 树脂基搭接碳纤维智能层力阻曲线光滑稳定, 其传感极限约为8500 με。建立了树脂基搭接碳纤维复合材料的电学模型, 揭示了这种力阻效应主要来源于搭接界面处层间电阻的变化, 并从纤维轴向力、搭接面积和层间剪应变三个方面解释了这种层间电阻变化的机制。      

多层碳纤维毡复合材料的电磁屏蔽性能研究

通过对多层碳纤维毡(CFF)/环氧树脂(EP)复合材料的厚度、碳毡含量以及碳黑填充的设计，制备了多种多层结构碳纤维毡复合材料，研究了多层碳纤维毡复合材料的屏蔽性能。结果表明：随着厚度的增加，多层结构复合材料的屏蔽效能呈增高趋势；随碳毡含量的升高，多层结构复合材料的单位厚度屏蔽效能逐渐增高；碳黑(CB)的添加能进一步提升材料的屏蔽效能，碳黑填充位置的不同对多层结构复合材料的屏蔽效能影响较大；在4.00 GHz时，CFF-CB-GFF结构的屏蔽效能可达到约71 dB,可作为优良的结构功能一体化屏蔽材料。     

CFRP的剪切力阻效应

自制装置构造构件的平面纯剪切变形,将薄层状的树脂基碳纤维复合材料(CFRP)粘贴在构件的纯剪切区域表面,在弹性范围内分析了CFRP的电阻对平面纯剪切变形的响应。实验结果表明,剪应变导致单向连续碳纤维增强的CFRP的纵向电阻变化不明显,其剪切力阻效应灵敏度约为0.16;碳纤维毡增强的CFRP具有显著的剪切力阻效应,其电阻表现出随剪应变线性的可恢复的增加,其剪切力阻效应灵敏度约为2.58。结合线应变致力阻效应产生机制,并通过CFRP细观结构的分析得出,纤维的随机乱向分布及纤维搭接形态的多样性是碳纤维毡增强的CFRP存在剪切力阻效应的主要原因。     

基于电阻信号的CFRP纤维断裂识别实验及理论模型

碳纤维是决定CFRP复合材料性能的主要因素之一,因此为保证复合材料结构的健康状态、识别纤维的损伤与断裂就显得至为关键。文中通过加载电流并采集电阻信号的方式来识别CFRP复合材料中碳纤维的健康状态,通过实验和理论分析的方法进行了深入研究。实验针对2种不同铺层的试件进行测量:单向层合板[0]8和正交层合板[0/90]4。对试件端部进行了粘接铜箔处理以使试件稳定导电,使用KEITULEY2700数据采集仪测量试件电阻。实验内容包括静态电阻测量、拉伸受力状态下材料的电阻特性分析,并建立和推导了电阻-应变理论分析模型,进行了通电疲劳实验。研究结果表明,碳纤维的铺层角度对CFRP结构电阻有较大影响,[0]8铺层材料电导率和破坏强度约为[0/90]4铺层材料的2倍;CFRP材料受外载荷作用时,损伤程度与其电阻变化有对应的关系,其电阻信号变化可以作为反映材料损伤情况和识别纤维断裂的主要参数;实验结果与所建立的电阻-应变模型拟合结果吻合较好。文中研究的CFRP纤维断裂识别和航空复合材料结构健康监控及实时监测具有重要的意义。     

碳纤维织物增强水泥基复合材料拉拔过程力阻响应和等效分层破坏模型

碳纤维织物增强水泥基复合材料(CFRCM)被广泛研究并应用于混凝土结构加固和性能自监测,但目前碳纤维的力阻响应机制尚不明确。本文通过CFRCM纤维束的拉拔试验发现其荷载-位移曲线符合典型的粘结滑移三阶段特征,拉拔过程中的电阻变化也呈现出波动缓慢上升-快速增长-缓慢增长的三阶段特征,碳纤维束脱粘阶段的电阻增长率与极限拉拔力呈现中高度的正相关性。进一步基于拉拔过程碳纤维束的力阻响应建立了纤维等效分层破坏模型及计算方法,为电阻信息与受荷状态的相互转化提供了新思路。     

斜纹编织碳纤维/环氧树脂复合材料II型分层性能及损伤演化表征

为研究编织复合材料在静载及疲劳载荷下的分层特性及损伤演化模式,对斜纹编织CF3052/3238A碳纤维/环氧树脂复合材料II型静开裂及疲劳开裂性能进行了测试。结果表明:斜纹编织CF3052/3238A碳纤维/环氧树脂复合材料裂纹扩展行为受纬向纤维影响存在周期性局部受阻现象,分层破坏模式除层间开裂外还存在纬向纤维脱粘;斜纹编织CF3052/3238A碳纤维/环氧树脂复合材料裂纹扩展速率符合Paris公式,不同加载控制模式下编织复合材料疲劳驱动力增长规律存在本质区别:恒幅疲劳载荷下斜纹编织复合材料疲劳驱动力呈抛物线型单调增长;而恒幅疲劳位移下复合材料疲劳驱动力随分层长度呈波峰型分布;采用基于载荷控制模式和位移控制模式下的疲劳驱动力模型,可对斜纹编织CF3052/3238A碳纤维/环氧树脂复合材料进行损伤演化表征,其表征效果良好,具有工程参考价值。      

编织结构复合材料动态特性的实验模态分析

利用实验模态分析方法对碳纤维/环氧树脂编织结构增强复合材料的动态力学特性进行了实验研究, 确定了编织复合材料梁、管的振动模态参数与传递函数, 并与钢质梁、管的动态性能相比较。结果表明: 在冲击脉冲载荷作用下, 先进编织结构复合材料与传统金属材料相比具有较高的固有频率、阻尼比, 以及比刚度大、稳定性好、对冲击脉冲载荷作用的减震效果等良好的综合动力学特性。      

碳纤维单丝偏轴拉伸力阻效应实验与理论分析

碳纤维在复合材料基体中的分布较大程度地影响了碳纤维智能材料的感知特性,故需在微米尺度下研究多角度偏轴拉伸下的碳纤维单丝的力电功能响应。测试了不同角度拉伸环境下碳纤维单丝的电阻变化,并对其电阻的变化情况进行了分析。结果表明碳纤维单丝在外载荷偏轴拉伸作用下电阻变化与拉伸角度间存在非线性关系。外载荷在纤维方向产生的应变对电阻变化率的作用强于垂直纤维方向应变对电阻变化率的作用,62°拉伸角为正负力阻效应的临界角度。     

碳纤维/环氧树脂复合材料缠绕接头拉伸失效机制

通过试验及数值模拟对碳纤维/环氧树脂复合材料缠绕接头轴向拉伸失效机制进行研究。基于ABAQUS有限元软件,通过连续介质损伤模型及内聚区模型,分别对碳纤维/环氧树脂复合材料缠绕接头各部件及界面进行模拟,编写用户自定义材料子程序(UMAT),建立复合材料的渐进损伤模型,最终得到碳纤维/环氧树脂复合材料缠绕接头的应力分布和载荷-位移曲线,并与试验结果对比确定结构的失效机制。结果表明:有限元分析所得碳纤维/环氧树脂复合材料缠绕接头损伤部位及失效模式与试验吻合,失效载荷与试验值相差较小,证明仿真分析方法的有效性。通过对比失效模式发现,拉伸载荷作用下,链环是主承力部件,其弧形端部是应力集中处,纤维断裂即从此处开始发生并向外扩展,导致链环断裂及整体结构破坏。      

化学镀镍碳纤维/环氧树脂复合材料电磁屏蔽性能

采用化学镀方法对碳纤维进行表面镀镍, 采用SEM、 EDX、 XRD分析了镀镍碳纤维的微观形貌、 镀层成分和镀层结构, 通过电阻测试研究了镀镍碳纤维的导电性。将体积分数为2.5%、 5%、 7.5%、 10%的镀镍碳纤维作为导电填料制备镀镍碳纤维/环氧树脂复合材料, 并用屏蔽室法测试了不同频段复合材料的屏蔽效能。结果表明: 碳纤维化学镀镍后, 表面形成了一层均匀的复合镀层, 镀层中镍的质量分数高达94%, 镀镍碳纤维的电阻值仅为碳纤维原丝的1/54。镀镍碳纤维/环氧树脂复合材料的电磁屏蔽能力较碳纤维原丝有所提高。复合材料的屏蔽效能随镀镍碳纤维添加量的增加而升高。在低频频段(kHz频段), 复合材料的屏蔽能力主要决定于材料的本征参数, 不同镀镍碳纤维含量的镀镍碳纤维/环氧树脂复合材料的屏蔽能力相差不大; 在中高频频段(MHz、 GHz频段), 镀镍碳纤维/环氧树脂复合材料屏蔽效能主要决定于材料的电阻率。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.