Ermittlung von Verfahrensgrenzen für das Fügen durch Knickbauchen anhand des Werkstoffes E235+N

Through a systematic approach and the consistent comparison of the results between experimental and numerical investigations, a deep understanding of the bulging mechanisms has been first developed. From these investigations process limitations were derived and presented in the form of a working diagram for the material E235+N. With regard to a wide industrial use of upset bulging as a joining technology, a technologically, productively as well as economically appropriate method could be developed and validated by means of practical and numerical experiments.     

大拉深比薄壁筒形件充液成形过程数值模拟

目的利用充液成形工艺成形普通拉深工艺难成形的大拉深比筒形件。方法通过理论公式计算了冷冲压工艺成形该制件的道次,利用有限元软件Dynaform对充液成形过程进行了3个步骤模拟,并研究了第1步拉深时初始反胀高度对成形制件减薄率的影响规律。结果利用理论公式计算,传统冲压方法成形拉深比为3.2的筒形件至少需要5个道次,而采用被动式充液成形方法只需要3个道次。每个道次的最大减薄率都在8%以内,最后得到拉深制件的最大减薄率为8.53%,在安全范围以内;第1步充液拉深时,反胀高度分别为1.75,2.75,3.75,4.75,5.75 mm时,得到制件的最大减薄率分别为5.28%,5.08%,4.8%,5.03%,5.03%。结论充液成形工艺较传统冲压工艺可以大大提高板料的成形极限,减少成形道次,成形制件质量好;合适的初始反胀高度,可以减小成形制件壁厚的最大减薄率。     

连续管现场快速修复技术

连续管作业时会出现压扁、折弯和局部破损等问题,在现场需要安全快速切断连续管损坏部位,并实施管-管对接焊修复工程。为此,研制了便携式和全位置连续管校直机、旋转锥套式胀圆器、管口开坡口机以及6个自由度对中机构等成套修复设备。在采油井口连续管作业现场,运用这些修复设备和试验制定的修复工艺,在很短时间内就可以高质量地修复损坏的连续管。修复后连续管接头的疲劳循环次数达到母材管的61%。应用连续管快速修复技术可大大提高连续管井下作业效率,保证作业的安全性。     

红砂岩地区某加筋土挡土墙凸形拐角鼓胀病害分析

对某红砂岩地区加筋土挡土墙鼓胀病害实例进行介绍和分析。首先介绍加筋土挡土墙的原设计情况,然后介绍该挡土墙凸形拐角处发生的上部面板鼓胀现象及变形量测结果。紧扣加筋土挡墙凸角区特点,分析凸角区鼓胀变形的原因:第一,在分析凸角锚固区筋带拉力增长系数与凸角长度关系的基础上,认为锚固区筋带作用合力增大是鼓胀变形的主要原因;第二,通过分析筋-土锚固特点,认为凸角区因筋带重叠导致筋带间土体水平位移增大、筋带自由段长度增大,导致筋带变形增大是鼓胀原因之二;第三,认为凸角段地形为边坡稳定不利地段,是凸角段挡墙面板容易产生鼓胀的原因。     

工业牌号铝合金的超塑性能及微观组织演化特征

采用实验方法研究国外广泛用于汽车车身板件冷冲压成形的工业牌号铝合金板材AA5182和6016的超塑性能,以及超塑变形中微观组织的演化特征。通过超塑性单向拉伸试验、材料变形前后的微观组织观察和自由胀形试验,揭示出铝合金AA5182具有一定的超塑性能,而铝合金6016的超塑性能很低。铝合金AA5182在温度为375℃、应变速率为1.67×10-3/s时,材料的延伸率达到210%,m值达到0.25;在温度为500℃、应变速率为1.67×10-2/s时,材料延伸率达到225%,m值达到0.35。     

AZ31 镁合金板材气体胀形的模拟及成形极限的预测

建立了300℃下AZ31镁合金板材气体胀形实验方法的有限元模型,并对板材胀形过程进行了仿真分析。基于板材应变历史分析,以二阶主应变转折点作为判别准则,预测了板材成形极限应变。通过模拟结果与实验结果的对比,分析解释了不同尺寸试样的变形情况。     

Error evaluation on experimental stress–strain curve obtained from tube bulging test

To get precise material data for advanced numerical modelling of tube hydroforming process, the tube bulging test is recommended. Stresses and strains in the tube cannot be evaluated easily and several approaches have been proposed. A review is proposed and points out their advantages and drawbacks.     

超塑胀形过程中空洞损伤演变的数值模拟

利用刚粘塑性有限元技术采用连续损伤力学导出的空洞损伤演变模型对超塑胀形的空洞损伤演变过程进行了数值模拟。以半球壳和圆筒形零件为例 ,给出了自由胀形和充模胀形件内部空洞体积分布状况 ,指出了空洞损伤对变形的影响 ,并对计算结果进行了分析讨论。计算得出了自由胀形极点处空洞体积分数发展曲线 ,与实验结果十分吻合。计算模型可推广至其他超塑成形问题     

Superplasticity and superplastic bulging behavior of ZrO<Subscript>2</Subscript>/Ni nanocomposite

ZrO2/Ni nanocomposite was produced by pulse electrodeposition and its superplastic properties were investigated by the tensile and bulging tests. The as-deposited nickel matrix has a narrow grain size distribution with a mean grain size of 45 nm. A maximum elongation of 605% was observed at 723 K and a strain rate of 1.67×10-3s-1 by tensile test. Superplastic bulging tests were subsequently performed using dies with diameters of 1 mm and 5 mm respectively based on the optimal superplastic forming temperature. The effects of forming temperature and gas pressure on bulging process were experimentally investigated. The results indicated that ZrO2/Ni nanocomposite samples can be readily bulged at 723 K with H/d value (defined as dome apex height over the die diameter) larger than 0.5, indicating that the nanocomposite has good bulging ability. SEM and TEM were used to examine the microstructure of the as-deposited and bulged samples. The observations showed that significant grain coarsening occurs during superplastic bulging, and the microstructure is found to depend on the forming temperature.     

基于改进应变楔模型的固体-散体串联组合桩鼓胀变形及沉降分析

针对传统碎石桩易在桩顶1~3倍桩径的深度范围内发生鼓胀破坏的现象,首先,在现有工艺的基础上提出一种固体（混凝土）-散体（碎石散体材料）串联组合桩,并简要阐述其承载特性、施工工艺及破坏模式;其次,建立了串联组合桩鼓胀变形的计算模型,探讨串联组合桩的鼓胀变形机理;然后,对应变楔模型进行修正,并结合广义胡克定律,计算固体-散体串联组合桩的鼓胀变形值及桩身沉降值;最后,通过传统碎石桩及筋箍碎石桩鼓胀变形及沉降试验验证所提理论方法的合理性,结果表明：理论计算值与试验结果吻合较好,可为碎石桩复合地基设计提供一定的参考,具有理论及工程应用价值。