溶剂型丙烯酸酯压敏胶的流变性能研究

针对分子量不同的溶剂型丙烯酸酯共聚物压敏胶的流变性能进行研究,通过频率扫描、振幅扫描两种不同模式进行流变性能测试,并对其蠕变性能进行了测试,通过测试,分析了分子量对流变性能的影响。结果表明,分子量增大,区分频率值(f*)变小,零剪切黏度(η0)变大,样品的弹性变好;在振幅扫描模式下,随着分子量变大,样品的线性黏弹区域变大,弹性模量(G′)与黏性模量(G″)均变大,但弹性模量增大的幅度大于黏性模量,因此,随着分子量变大,样品逐渐从G′G″,样品由黏弹性液体流变行为逐渐向黏弹性固体流变行为转变;蠕变测试说明分子量增大,有利于改善样品的抗剪切变形能力与蠕变回复能力,蠕变回复时间也随之变大。     

双稳态复合材料层合结构的黏弹性模型

为探明双稳态复合材料层合结构在复杂环境条件下的应用,对双稳态复合材料层合结构的黏弹性行为进行了研究。首先,将纤维简化为弹性材料,考虑基底材料的黏弹性行为。然后,根据纤维和基底的材料属性,通过理论分析得到了双稳态复合材料层合结构的黏弹性材料属性;根据经典层合板理论、最小应变能原理和Maxwell黏弹性模型建立了双稳态复合材料层合结构的黏弹性模型,通过理论分析得到其第二稳态主曲率与扭曲率随加载时间和温度的变化关系。同时,利用有限元软件ABAQUS及其子程序UMAT建立了相应的有限元模型,研究了加载时间和温度对层合结构第二稳态性能的影响。理论与模拟结果均表明:层合结构第二稳态主曲率随加载时间的延长和温度的升高而增大;扭曲率随加载时间的延长而减小,一般情况下随温度的升高而增大,但在加载时间较长且温度较高时,可能会出现扭曲率随温度升高而减小的情况。理论计算结果与有限元模拟结果的比较显示两者吻合较好,可以通过有限元模拟对双稳态复合材料层合结构的黏弹性行为进行研究。      

基于分数阶黏弹性模型的木塑复合材料蠕变/回复性能分析

木塑复合材料(WPC)是一种木质纤维增强聚合物的新型环保复合材料,为分析WPC在非恒定荷载下的变形行为,进行结构的长期变形设计,对WPC的蠕变/回复变形进行计算分析。采用叠加原理对比分析既有蠕变计算模型对WPC蠕变/回复的整体预测效果。结果表明,现有模型均不能良好预测其蠕变/回复行为。采用基于分数阶微积分的黏弹性模型对其蠕变/回复行为进行预测,提出一种双参数法的修正分数阶黏弹性模型。通过与已有实测数据对比表明,该模型能够准确反映WPC的静态黏弹性行为。结合实验数据,给出了不同WPC蠕变/回复模型的参数取值。      

基于Burgers模型对缓冲材料EPE压缩蠕变行为的分析

目的 为解决缓冲材料发泡聚乙烯因蠕变引起保护失效的问题,基于Burgers模型,分析载荷、应力保持时间对EPE压缩蠕变行为的影响。方法 根据不同应力下的不同保持时长压缩蠕变试验结果,拟合EPE不同应力下的压缩蠕变试验数据,分析不同应力、应力保持时间下的EPE蠕变过程中蠕变总量、弹性应变、黏弹性应变和黏性应变的变化规律。结果 Burgers四元件力学模型对EPE不同应力下的压缩蠕变实验数据拟合度为0.992 4～0.998 9。在同一应力保持时间下,随着应力从3.3 kPa增加到5.3 kPa,弹性模量E₁、弹性模量E₂、黏度系数η₂、黏度系数η1都逐渐减小,蠕变总量、黏性应变呈非线性显著增加,弹性应变、粘弹性应变呈线性微量增加;在同一应力下,随着应力保持时间从20 d增加到120 d,弹性应变一直保持不变,占蠕变总量的比例降低,粘弹性应变先微量增加后保持不变,占蠕变总量的比例降低,黏性应变增加,占蠕变总量的比例增加。结论 Burgers模型可较准确地模拟EPE不稳定蠕变阶段和稳定蠕变阶段的压缩蠕变行为;应力的增加导致EP...     

复合材料螺栓连接预紧力松弛的温度-时间依存行为

针对碳纤维增强环氧基复合材料机械连接结构耐久性设计中的2个关键问题:黏弹性预紧力松弛的温度-时间依赖行为及其长期性能预测方法进行研究。建立了以蠕变全应变理论为基础的预紧力松弛预测模型。36 h的恒温耐久试验表明:初始预紧力越大,温度越高,连接件预紧力松弛速率越快;复合材料连接件的松弛速率远大于金属连接件;预紧力松弛主要表现为材料蠕变过程。对比短期试验结果表明:本模型能较好地实现对不同温度、预紧力和连接材料的松弛预测,为确立试验数据的外推方法提供了依据。      

聚合物梯度材料黏弹性断裂的双控制参数

针对组分材料体积分数任意分布的聚合物功能梯度材料,研究其在蠕变加载条件下Ⅰ型裂纹应力强度因子（SIFs）和应变能释放率的时间相依特征。由Mori-Tanaka方法预测等效松弛模量,在Laplace变换域中采用梯度有限元法和虚拟裂纹闭合方法计算断裂参数,由数值逆变换得到物理空间的对应量。分析边裂纹平行于梯度方向的聚合物功能梯度板条,分别考虑均匀拉伸和三点弯曲蠕变加载。结果表明,聚合物梯度材料应变能释放率随时间增加,其增大的程度与黏弹性组分材料体积分数正相关;材料的非均匀黏弹性性质产生应力重新分布,导致裂纹尖端应力场强度随时间变化,当裂纹位于黏弹性材料含量较低的一边时,应力强度因子随时间增加,反之,随时间减小。而且,材料的应力强度因子与时间相依的变化范围和体积分数分布以及加载方式有关,当体积分数接近线性分布时,变化最明显,三点弯曲比均匀拉伸的变化大。SIFs随时间的延长增加或减小、加剧或减轻裂纹尖端部位的“衰坏”,表明黏弹性功能梯度裂纹体的延迟失稳需要联合采用应力强度因子与应变能释放率作为双控制参数。     

树盘干缩异向性引起应变的测算及分析

研究探讨了干燥过程中树盘受抑制干缩应变、自由干缩应变、弹性应变、黏弹性蠕变应变以及机械吸附蠕变的图像解析测算法;运用该方法测算了白桦树盘常规缓慢干燥(含水率分布均匀)过程中干缩异向性引起的弦向各应变,分析了干燥过程中不同含水率阶段的应力状态及应力与各应变的关系。结果表明:应变的图像解析测算法可满足精度要求;树盘干燥至fiber saturation point(FSP)以下,弦向首先受拉伸应力作用,随着干燥的进行,拉伸应力转变为压缩应力;应力方向与各应变对应关系不同,与黏弹性蠕变应变无明显对应关系,与机械吸附蠕变基本对应。     

重组竹顺纹受压蠕变性能及预测模型

为研究重组竹顺纹受压蠕变性能,对12个重组竹受压试件进行了蠕变试验,通过分析蠕变增长率和Burgers模型中各参数,得到重组竹受压试件受压蠕变变化规律。结果表明,重组竹在持续受压荷载作用下,应力水平较低时,蠕变变形发展稳定,不会发生承载力破坏;应力水平较大时(达到60%极限载荷水平),将会直接导致重组竹受压屈曲破坏,蠕变变形呈非稳定性增长;重组竹受压蠕变应变增长率随时间增加而逐渐增大,其增长速率则呈减速状态,受压蠕变的应变增长率随应力比增加而增大。基于试验结果,分析了重组竹受压蠕变试验的弹性变形、黏弹性变形和黏性变形的变化规律,对不同荷载水平的Burgers模型参数进行确定,并进一步推导了Burgers模型参数随应力水平的变化规律。基于此,建议考虑荷载水平的重组竹受压蠕变预测模型,模型预测结果与试验曲线一致。      

复合材料残余应力和固化变形数值模拟及本构模型评价

为了评价不同固化本构模型,建立了预测复合材料构件残余应力/应变和固化变形的三维数值模型。该模型由热化学分析模块和热力分析模块构成,考虑了热化学耦合、材料性能的各向异性、化学收缩及黏弹性等因素。基于线弹性、黏弹性和Path-dependent三种典型的本构模型,预测了构件的残余应力/应变及固化变形。通过与试验结果对比,验证了所建数值模型的有效性,并重点研究了不同本构模型的适用性。结果表明,黏弹性本构模型最佳,对构件的残余应力/应变及固化变形的预测结果均较好; Path-dependent本构模型次之,对构件的残余应变和固化变形的预测结果较好,但对构件的残余应力的预测结果稍差;线弹性本构模型最差,除了对构件的残余应变和较薄构件的固化变形的预测结果较好外,其他预测结果都较差。     

高阻尼黏弹性阻尼器性能与力学模型研究

对2个高阻尼黏弹性阻尼器进行不同应变幅值、加载频率下的力学性能试验和疲劳性能试验,研究试件在不同工况下的最大剪应力、存储剪切模量、损耗剪切模量和等效黏滞阻尼比等力学性能及其变化规律,提出五单元模型模拟黏弹性阻尼器的滞回性能。研究结果表明：黏弹性阻尼器滞回曲线饱满、稳定,具有较高的等效黏滞阻尼比,表现出良好的变形性能和耗能能力;黏弹性阻尼器力学性能与应变幅值的相关性明显,与加载频率相关性较小,抗疲劳性能较好;五单元模型模拟的滞回曲线与试验滞回曲线吻合良好。     

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.