聚对苯二甲酸乙二醇酯熔体等温结晶的焓松弛

利用微分扫描热分析（DSC）获得了聚对苯二甲酸乙二醇酯（PET）熔体等温结晶过程焓松弛速率曲线,并对结晶焓松弛速率曲线进行微分从而获得等温结晶焓松弛加速度曲线。文中通过定义相对结晶速率R和相对结晶加速度A,确定了相对结晶速率R和相对结晶加速度A与结晶焓松弛速率和结晶焓松弛加速度之间对应相差的一个常数值,然而其所对应的变...     

7050铝合金时效成形中应力松弛行为与回弹方程

通过自主设计的单向拉伸应力松弛装置研究7050铝合金时效成形过程中的应力松弛行为和回弹方程。结果表明:时效温度范围内7050铝合金的应力松弛曲线表现为典型的对数衰减曲线。该松弛过程可以分为应力快速下降,应力缓慢衰减和应力保持相对恒定3个阶段。随着温度的升高应力松弛极限逐渐降低。由于7050铝合金时效析出与应力松弛中位错蠕变的共同作用引起了松弛过程槛应力现象。通过解析7050铝合金应力松弛行为的特征和松弛曲线的泰勒方程得到该合金在时效温度范围内的应力松弛经验公式,以此获得该合金时效成形过程中的应力松弛方程,并利用该经验公式较好地预测时效成形后试样的回弹率。     

生物可降解材料PLGA的应力松弛性能

针对基于生物可降解材料聚乳酸-羟基乙酸共聚物(PLGA)的热压成型工艺仿真研究中,粘弹性材料模型参数缺乏的问题,通过单轴拉伸应力松弛试验,研究了生物可降解材料PLGA在5种温度状态下的应力松弛性能。基于时间-温度等效原理,平移得到60℃的松弛模量主曲线,并采用广义Maxwell模型对此主曲线进行拟合。结果表明:随着温度的升高,PLGA材料的松弛时间明显缩短,且拟合曲线与原数据误差较小,说明广义Maxwell模型能较理想地模拟PLGA材料的应力松弛行为。这些数据的获得为后续仿真研究提供了参考。     

一种新的聚合物基复合材料应力松弛经验模型

视黏弹性元件弹簧和粘壶的特性参数为时间的函数,建立双变参Maxwell模型,求解其本构方程及松弛函数,探讨了其松弛函数与经验KWW函数的关系,提出了一种新的应力松弛经验模型。运用最小二乘原理,建立该模型参数的确定方法。开展了玻璃纤维增强聚合物(GFRP)复合材料的长期应力松弛实验,并通过实验数据的分析验证了该模型的正确性。研究表明,新应力松弛经验模型拟合曲线与实测曲线吻合较好,相关系数达到96%以上,说明了该模型适合描述GFRP复合材料的黏弹性松弛特性。     

聚苯乙烯泡沫(EPS)蠕变松弛实验研究

室温下,对3种密度的聚苯乙烯泡沫(Expanded polystyrene,简称EPS)进行了一系列单轴拉伸蠕变实验和单轴压缩松弛实验.实验表明:在本实验范围内,任何一条蠕变曲线都可分为3个阶段,即瞬时弹性段、过渡蠕变段和稳态蠕变段;同时表明同密度的EPS其蠕变量值随着应力水平的增大而增大,同应力水平下的EPS其蠕变量值随着密度的增大而减小.并认真分析了一系列松弛实验曲线,建立了包含密度影响的EPS松弛模型并对该模型进行了验证.     

聚丙烯/尼龙6共混物熔体的松弛时间

用扫描电镜对聚丙烯(PP)/尼龙6(PA6)共混物断面形貌进行了表征,用旋转流变仪小振幅剪切模式测试了PP/PA6共混物的动态模量,并采用广义Maxwell模型对于损耗模量-角频率曲线进行了拟合。扫描电镜结果表明,聚丙烯接枝马来酸酐(PP-g-MAH)有效提高了PP和PA6之间的相容性,使得分散相PA6粒径尺寸减小。广义Maxwell模型中,当松弛模数为N=5和6时,拟合曲线与实验数据在低频下存在明显的偏差,而松弛模数为N=7时,广义Maxwell模型能够较好地拟合实验曲线。固定PP/PP-g-MAH质量比为90/6时,随着PA6含量的增加,共混物PP/PP-g-MAH/PA6的松弛时间延长,松弛时间谱曲线以短时区为轴心逆时针旋转,向长时区偏移。     

基于LM算法的粘弹性材料剪切松弛模量的拟合

在对粘弹性材料进行有限元计算时,需要材料的剪切松弛模量,必须对经验公式或实验数据进行转换。根据KWW经验公式与广义Maxwell剪切松弛函数的对应关系,列出了求解松弛时间与剪切松弛模量的超定非线性方程组,用LM优化算法得到了方程组的最优解。初步讨论了初值的选取方法。根据此方法得到的松弛时间与剪切松弛模量的拟合曲线的拟合度达到了0.99以上。所提出的方法也适用于用实验数据(随时间变化的应力应变)求解材料的剪切松弛模量。     

尼龙11的力学松弛与结构变化

在 - 18 0℃～ + 180℃的范围内测试了尼龙 11的动态力学性能 ,讨论了拉伸和退火处理对尼龙11力学松弛过程的影响。α松弛峰表征尼龙 11非晶区中链段的松弛运动 ,样品结晶度的增加使模量 E′降低 ;β松弛峰与羰基的运动有关 ,经过干燥的样品 ,β峰几乎消失 ;γ松弛峰是分子链中亚甲基协同运动引起的。尼龙 11的弹性模量随温度升高而下降 ,但由于氢键的作用 ,尼龙 11在低于 180℃时仍具有较好的热态力学性能。     

尼龙11的力学松弛与结构变化EI

在 - 18 0℃～ + 180℃的范围内测试了尼龙 11的动态力学性能 ,讨论了拉伸和退火处理对尼龙11力学松弛过程的影响。α松弛峰表征尼龙 11非晶区中链段的松弛运动 ,样品结晶度的增加使模量 E′降低 ;β松弛峰与羰基的运动有关 ,经过干燥的样品 ,β峰几乎消失 ;γ松弛峰是分子链中亚甲基协同运动引起的。尼龙 11的弹性模量随温度升高而下降 ,但由于氢键的作用 ,尼龙 11在低于 180℃时仍具有较好的热态力学性能。     

介电弹性体力学松弛的试验与理论研究

针对介电弹性体的粘弹性应力松弛现象,通过单轴拉伸的应力松弛试验研究了材料应力在不同预拉伸率下的时变特征,建立了材料基于Prony级数的准线性粘弹性模型。研究结果表明:通过理论计算和实验结果的对比验证了模型的准确性,预拉伸率是影响介电弹性体薄膜应力松弛曲线的重要因素,基于二阶Prony级数的准线性粘弹性模型能够有效模拟介电弹性体薄膜预拉伸率在[2,6]区间内的非线性力学松弛特性,而且与实验值拟合度较高;在预拉伸率为4,400s条件下,介电弹性体薄膜的应力达到0.126MPa。     

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.……     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

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.     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

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 ...