汽车薄钢板不均匀拉伸皱曲行为研究

为了掌握汽车薄钢板在不均匀拉伸状态下的起皱行为,以确定临界皱曲指标、评价板材抗皱性能,建立了不均匀拉伸起皱试验硬件与软件系统,实现了试件中心皱高△h、载荷F、标距处应变λ140的计算机连续测量,得出了△h-F、F-△L、△h-λ140的关系曲线,分析了皱曲的发生和发展过程.研究结果表明,整个皱曲过程经历了加载初期的面内变形、临界变形、后屈曲突变、后屈曲平稳变形、皱曲变陡载荷下降及皱曲连续变陡等阶段.     

带孔方板对角拉伸的起皱失稳特性测试与分析

传统方板对角拉伸试验(Yoshida buckling test,YBT)方法在测量板料起皱性能时,能够得到的应力状态有限,不能全面评估板料在复杂工况下抵抗失稳起皱的能力.本工作提出一种带内孔YBT试样单向拉伸的板料起皱性能测试方法,利用数值模拟与实验研究了带不同大小圆孔YBT试样拉伸过程的受力与变形特征,探讨了内孔对试样应力分布及起皱行为的影响.研究表明,内孔改变了YBT试样平面内的应力分布,且内孔轴向两端存在压应力,横向两侧存在拉应力;随着孔径增大,横、轴向应力比增大,最大压应力位置应力状态发生改变,由横向受压、轴向受拉转为双向受压;孔径较大时,内孔侧边区域会出现二次起皱现象.     

弹塑性弯曲所致残余应力及其对板料拉伸屈服强度的影响

应用弹塑性工程理论,分析了板材弯曲后残余应力的成因及表达式.进一步分析了由于这种宏观残余应力的存在,使得其在拉伸载荷下提早屈服,使板材屈服强度降低的主要原因,是由于拉伸过程中截面上应变不同步、不协调所致.     

一种冲压皱曲缺陷的仿真分析方法

针对金属薄板冲压成形中的皱曲缺陷,提出一种基于有限元环境的冲压皱曲缺陷仿真分析方法。该方法根据工程实际应用经验将仿真环境中的冲压件皱曲进行了量化评估,通过对应变调节方向和应变调节量的分析,掌握起皱区域的成形性状态,为金属流动调节提供支持。本文以NumiSheet 2002的标准件作为应用实例,对其皱曲缺陷进行了仿真分析,结果表明该方法对皱曲缺陷分析有效、可行,可以提高金属薄板冲压成形仿真分析的效率,节约仿真成本。     

双相钢激光拼焊板温拉伸流变应力模型研究

在通过温拉伸实验获得的真实应力-应变曲线的基础上,采用Zener-Hollomon参数的双曲正弦形式来建立双相钢激光拼焊板温拉伸条件下的流变应力模型,方程中材料参数通过最小二乘法线性回归获得,并将其表示成应变的多项式形式,从而使此模型适用于整个应变过程中.流变应力的预测值与实验值吻合较好,预测的最大相对误差为6.27%,最大均方差为8.718MPa,从而验证了双相钢激光拼焊板温拉伸流变应力模型的准确性.     

板面弹性压板力对提升板料失稳临界应力 的作用及其应用

从分析矩形薄板的受压失稳临界应力人手,提出在冲压成形板料的上下面设置弹性压板力,从而提升板料的失稳临界应力,减少板料的受压屈曲与起皱.根据这个原理设计的新型冲压模具可有效地控制板料的起皱,同时具有"一模多用"的作用.试验也表明,具有板面多点压板功能的冲压模具,可以显著地提升 l板料的失稳临界应力,减少板料的起皱.     

薄板剪应力起皱研究

以Hill关于弹塑性失稳理论为基础,建立了剪应力起皱失稳的速度场分布,给出了临界起皱剪应力理论计算结果,分析了板料屈服强度、硬化指数、板厚方向性指数及板料厚度对临界剪应力的影响,并与实验和数值模拟结果进行了对比。研究表明:薄板在剪应力作用下可以产生起皱,临界剪应力理论计算、实验及数值模拟结果基本相符,临界剪应力随屈服强度σs减小、硬化指数n值的增大、板厚方向性指数r值的增大、板料厚度t的增大而增大。     

双向等轴拉伸载荷下二维编织陶瓷基复合材料的应力-应变行为预测

将二维编织结构简化为(0°/90°)s正交铺层结构。采用含损伤变量的剪滞分析理论,解得双向等轴拉伸载荷下,0°层和90°层开裂后各层的应力分布;基于随机基体裂纹演化理论,随机纤维损伤和最终失效理论,确定了0°层和90°层沿纤维方向的应力-应变关系,以及切线拉伸模量与施加载荷之间的关系;然后,将切线拉伸模量代入正交铺层结构的剪滞分析中,进而预测出二维编织陶瓷基复合材料在双向等轴拉伸载荷下的应力-应变关系。预测结果表明:在双向等轴拉伸载荷下,二维编织陶瓷基复合材料的横向和纵向应力-应变曲线基本相同,与单向加载时的应力-应变曲线相近。     

纵向拉伸对尼龙帘线-橡胶复合材料横向拉伸力学性能影响的实验研究

采用十字形试件,在双轴拉伸条件下研究了尼龙帘线-橡胶复合材料单层板纵向定载荷对横向力学性能的影响和横向定载荷对纵向力学性能的影响。实验结果表明:纵向拉伸载荷对尼龙帘线-橡胶复合材料的横向拉伸力学性能有很大的影响。随着纵向拉伸载荷的增加,横向应力应变关系发生了很大的变化;横向拉伸强度先上升然后又下降;而其断裂变形和变形能却逐渐减小。横向拉伸载荷对尼龙帘线-橡胶复合材料的纵向拉伸力学性能影响却很小。这可能与材料纵向和横线拉伸性能差异太大有关。     

考虑纤维随机分布的复合材料热残余应力分析及其对横向力学性能的影响

建立了考虑纤维随机分布并包含界面的复合材料微观力学数值模型,模拟玻璃纤维/环氧复合材料固化过程中的热残余应力。通过与纤维周期性分布模型的计算结果进行对比,发现纤维分布形式会对复合材料的热残余应力产生重要影响,纤维随机分布情况下的最大热残余应力明显大于纤维周期性分布的情况下。研究了含热残余应力的复合材料在横向拉伸与压缩载荷下的损伤和破坏过程,结果表明:热残余应力的存在显著影响了复合材料的损伤起始位置和扩展路径,削弱了复合材料的横向拉伸和压缩强度。在横向拉伸载荷下,考虑热残余应力后,复合材料的强度有所下降,断裂应变显著降低;在横向压缩载荷下,考虑热残余应力后,复合材料的强度略有下降,但失效应变基本保持不变。由于热残余应力的影响,复合材料的横向拉伸和压缩强度分别下降了10.5%和5.2%。      

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.     

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.     

新闻(英文)

正China and Greece Sign the Standardization Cooperation Agreement Witnessed by Chinese Premier Li Keqiang and Greek Prime Minister Antonis Samaras,AQSIQ Minister Zhi Shuping and ELOT Chairman and Executive Director Angelos Tolkas signed the SAC-ELOT Standardization Cooperation Agreement.The Agreement is one of the critical cooperation documents signed during Li Keqiang’s visit in Greece,encouraging China and Greece to