Q235覆管对AA5052铝合金基管颗粒介质胀形行为的影响

采用AA5052铝合金挤压管作内层基管、Q235碳素结构钢卷焊管作外层覆管的钢铝复合管对复合管颗粒介质胀形行为进行研究。通过塑性理论分析胀形过程中管间切向摩擦力及法向压力对基管应力大小的影响;利用数值模拟分析管间摩擦因数和覆管各向异性对基管的应变成形极限的综合影响,并给出单管、复合管胀形时的壁厚减薄情况和基管的应力、应变分布;通过管材颗粒介质内高压胀形试验,对比单管和复合管胀形条件下铝合金管的极限胀形比,分析复合管的变形协调性。结果表明：通过施加Q235碳素结构钢覆管,减小了AA5052基管胀形区中间截面处的双向拉应力,基管胀形区壁厚减薄变小,胀形比提高了22%,复合管下基管最大减薄率为17.5 %,成形性能显著提高。     

铝合金球壳液压胀形试验研究

研究了板厚1.5mm的3A21O铝合金板材和焊接接头的塑性成形能力,进行了铝合金球壳的整体液压胀形实验。实验结果表明:在保证焊接质量的前提下,铝合金球壳的胀形过程能够顺利进行。分析了壳体胀形过程中的变形和应力分布规律,从理论上给出了球壳的胀形屈服应力和开裂应力,最后采用动态显式有限元分析软件LS-DYNA给出了壳体的壁厚分布。     

基于成形应力极限的管材液压成形缺陷预测

基于塑性应力应变关系及Hill79屈服准则,推导出极限应力与极限应变间转化关系,进而建立2008T4铝合金的成形应力极限图(Forming limit stress diagram,FLSD)。采用LS-DYNA软件对三通管液压胀形过程进行模拟,应用FLSD预测胀形过程中破裂的发生及成形压力极限,并与传统成形极限图(Forming limit diagram,FLD)结果进行了对比。研究表明,FLD与FLSD预测结果中破裂缺陷位置相同,但极限内压力值存在很大差别,而FLSD预测结果与物理试验结果较吻合。考虑到FLD受应变路径影响显著的因素,将FLSD作为管材液压成形等复杂应变路径下的成形极限的判据更加方便可靠。     

汽车桥壳液压胀形极限成形系数及胀裂判据

利用研制的集增压器、冲液器、滑动胀形模具于一体的超高压液压胀形装置,在普通液压机上进行汽车桥壳样件的液压胀形胀裂试验,绘制出液体胀形压力与管坯压缩量不同的匹配关系时(即不同加载路径)的胀形极限图,揭示出极限胀形系数与管坯轴向应变存在线性关系kr=1 δ5-1.72εz,并与材料断后伸长率δ5有关.给出管坯胀裂时的应变判据|εn|=δ5及应力判据δθ=2σb,即胀裂时管坯壁厚方向的应变等于材料的延伸率,环向应力等于材料拉伸强度的2倍.研究成果能为理论研究及工程应用提供依据.     

基于三维成形极限应力图的AA6061挤压管材成形性能分析

为解决AA6061挤压管材成形性能极差的问题,建立了“固溶水淬+颗粒介质胀形+人工时效”的铝合金管件成形工艺流程。研究了固溶水淬和人工时效工艺参数对材料性能影响规律,并建立了考虑厚向应力的三维成形极限应力图;建立了管件颗粒介质胀形有限元仿真模型,分析管件变形特征质点的运动轨迹和应力应变状态,并应用理论成形极限图对管件破裂失稳点和胀形极限进行分析和预判。四方截面管件胀形工艺试验结果表明,颗粒介质胀形工艺与合适的热处理工艺相结合能够有效地解决AA6061挤压管材的成形问题;考虑厚向应力的三维成形极限应力图可作为铝合金管件胀形工艺方案制定的破裂失稳判据。     

小型桥壳液压胀形初始变形条件分析及成形试验

介绍了小型汽车桥壳的液压胀形工艺,提出了初始胀形内压的表达式,预测了初始胀形内压与轴向推力的匹配关系（即经向应力比的大小）对预胀形时各部分变形顺序的影响。在普通液压机上进行了两种加载路径下的液压胀形试验,在初始经向应力比小于零并保持恒内压的条件下,预胀形管坯先变形成两侧高、中部低的双鼓形,经增压后将中部胀起;在初始经向应力比大于零且内压恒定的条件下,预胀形管坯中部沿轴向胀裂;两种加载路径下,管坯扁锥体凸起与胀形区之间均产生了明显内凹缺陷。理论分析与试验结果均表明,初始变形条件对小型桥壳的预胀形有重要影响。     

双层管液压胀合的判据准则及分析比较

双层管液压胀合的成形质量取决于胀合液压力的大小，因此准确确定胀合液压力的范围对胀合质量起着决定性的作用。文中通过对双层管液压胀合过程中五种情况的受力分析，讨论内管及外管的应力应变关系。利用内外管之间的变形协调条件，得出液压胀合的适用条件以及胀合液压力pi的工作范围。通过与已有文献的比较，得出的结论同时适用于内层管为薄壁管和厚壁管的情况。     

直径400mm铝合金球壳的整体液压成形

本文介绍了直径400mm铝合金球壳的整体液压胀形过程,测定了壳体胀形过程中球壳板的小心挠度变化和板面应变分布,并对板面的应力应变分布规律及壳体的变形特点进行了分析。     

高温超塑胀形实验装置

超塑变形具有很强的结构敏感性，其变形规律与应力状态和变形路径有关，因此在处理二维胀形问题时，不能直接引用一维拉伸的实验数据，胀形实验装置便成为理论研究和制定工艺方案的重要手段。设计了高温超塑胀形实验装置，并针对实验装置进行了程序设计。该实验装置具有氩气净化、炉外加热、温度和压力闭环控制，能同时施加正压、背压并按设定的恒压、恒极点胀形速度和应变速率进行实验，同时可以无接触地记录胀形件极点高度与时间的关系，并观察其形貌变化过程。     

双层管液压胀合的原理及力学分析

详细阐述双层管的液压胀合原理。根据对双层管分析的基本假设,研究双层管液压胀合过程中的受力状态。采用弹塑性理论,对双层管内管及外管的应力应变关系进行讨论,并利用内外管周向应变的变形协调条件,得出液压胀合的适用条件以及胀合液压力Pi与残余接触压力P^＊间的计算关联式。     

Effects of process parameters on electromagnetic forming of AZ31 magnesium alloy sheets at room temperature

In this work, the effects of process parameters on AZ31 magnesium alloy sheets were investigated by electromagnetic bulging experiments. The bulging height increases with increasing discharging energy, which is adjusted by tuning discharge voltage and capacitance. The limit dome height of electromagnetic forming is markedly improved as compared to quasi-static forming. In order to improve the efficiency of the energy, 0.5- and 1-mm thick Al driver sheet were used to accelerate the magnesium alloy sheets. For rupturing the AZ31 sheet, the discharging energy can be reduced from a maximum value of 4.356 kJ (no driver) to 2.304 kJ (with1-mm Al driver sheet). The numerical simulation for the electromagnetic forming of AZ31 sheet is performed by means of ANSYS FEA software. The change of velocity, strain rate, and plastic strain energy were analyzed by simulation. Compared with quasi-static forming limit results, increases in the major and minor principal strains of approximately 68 and 72 % were achieved, respectively.     

Analysis of the bulging process of an AZ31B magnesium alloy sheet with a uniform pressure coil

As the lightest metal material, magnesium alloy is widely used in the aerospace, automobile, and consumer electronic industries. However, magnesium alloy sheet has poor formability at room temperature. Electromagnetic forming is a high velocity forming technique that can promote the formability of low ductility materials, improve the strain distribution of workpieces, and reduce their wrinkling and springback. In this work, a uniform pressure coil was used to bulge AZ31B magnesium alloy sheets. The finite element method was then used to analyze this bulging process. The bulging contours and displacements of AZ31B magnesium alloy sheets were consistent with the experiment results. The distribution of the magnetic field intensity and magnetic field forces were found to be better than using a flat spiral coil. The deformation rule of AZ31B magnesium alloy sheet using the uniform pressure coil differed from that using the flat spiral coil. The largest strain occurred at the center of the sheet.     

0Cr18Ni9Ti不锈钢材料单轴应力塑性变形研究

对0Cr18Ni9Ti不锈钢材料进行单轴塑性变形试验,建立应力-应变曲线关系,讨论循环加载和含蠕变循环加载对0Cr18Ni9Ti材料塑性变形的影响,得出其在试验加载条件下的塑性变形规律。     

Multiple necks around biaxially loaded holes in sheets

Experiments are described in which holes in sheets of 3 and 4 mm thick half-hard commercially pure aluminium are equibiaxially expanded by hydraulic bulging using an undersheet of 1 mm thick mild steel. Discrete radial necks are formed within the annulus (not at the bore), the number of which depends on the initial hole diameter/sheet thickness ratio. Prediction of the amount of deformation at the onset of neck formation requires the deformation history of elements to be followed. The number of necks depends approximately linearly on the ratio of the initial diameter of the hole to the sheet thickness. Further loading produces radial cracks within some (but not all) of the thinning necks.     

铝板数控单点渐进成形的成形极限曲线研究

对薄壁复杂构件进行数控单点渐进成形时,板料易发生破裂、起皱等缺陷,且材料变形机制演化复杂,对加载条件极为敏感,使得板料在数控单点渐进成形时的破裂预测和控制变得极难。为此,选取1060铝板作为研究材料,通过试验研究了数控单点渐进成形技术中板料的成形性能,以实现对破裂的预测和控制。利用拓印法将制件的空间变形问题转化为平面变形问题,采用数码显微镜对拓印的制件网格数据进行测量和提取,选用插值法和多项式拟合法对数据进行拟合处理,最终得到了1060铝板料在数控单点渐进成形技术下的成形极限曲线(FLC)。通过对FLC进行分析研究,得到了制件破裂区和安全区域的应变分布,实现了制件破裂的预测和控制。为进一步提高1060铝板的成形极限,将超声振动引入到单点渐进成形中,通过试验对比研究了超声振动辅助渐进成形的FLC和传统渐进成形的FLC,试验结果表明:当振动功率为120 W、振动频率为25 kHz时,1060铝板料的成形极限提高了11%。     

Effects of driver sheet on magnetic pulse forming of AZ31 magnesium alloy sheets

In this work, the formability of AZ31 magnesium alloy sheets was investigated by electromagnetic bulging experiments with driver sheet. Al (0.5 mm, 1 mm, and 2 mm thick) and Cu (1 mm thick) driver sheets were used to accelerate the AZ31 sheet in electromagnetic forming (viz magnetic pulse forming) process. In order to evaluate the effect of impact induced by driver sheet, the electromagnetic bulging experiments with gap between AZ31 sheet and driver sheet were investigated. Compared with quasi-static forming limit results, increases in the major and minor principal strains (with 0.5 mm, 1 mm driver sheet, and without driver sheet) of approximately 68 % and 72 % were achieved, respectively. However, the major and minor principal strains with 2 mm Al driver sheet increased about 148 % and 184 %. When the energy is up to 2.788 kJ after the first crack (with 1 mm Al driver sheet) producing, the major and minor strains increase about four times compared to the quasi-static condition.     

Study of the impact of riveting sequence, rivet pitch, and gap between sheets on the quality of riveted lap joints using finite element method

Sheet metal parts are widely used in the assembly of aircraft. The most common method of joining sheet metal parts is through riveting. There are many parameters associated with a riveting process that affect the quality of rivets and the integrity of the final assembled product. This paper presents a study on the effect of some controllable process parameters in riveting (i.e., the sequence of riveting, distance between rivets (pitch), and gap between sheets) on the quality of riveted lap joints and the formed rivets. The study is performed on a one eight-inch nominal diameter flat head Tinner rivet and 0.064-in.-thick aluminum sheet. Finite element simulation is used as a means of modeling and analysis of the riveting process. Statistical design of experiment is employed to analyze the simulation data. A good combination of riveting process parameters is found which minimizes the residual stress in sheets and rivets, bulging and material growth in sheets, and which reduces the chances of postriveting clearance in a riveted lap joint.     

0Cr17Mn17Mo3NiN奥氏体不锈钢的热变形行为及热加工图

采用Gleeble-3500热模拟试验机研究0Cr17Mn17Mo3NiN奥氏体不锈钢在950~1 100℃,0.01~1 s^-1条件下的热变形行为。依据热压缩过程中0Cr17Mn17Mo3NiN奥氏体不锈钢的真应变-真应力曲线,确定了其在该热变形参数下的高温本构方程,并根据动态材料模型建立热加工图。结果表明,在相同的应变速率下,流变应力随着温度的升高而降低;而在相同的变形温度下,流变应力随着应变速率的减小而降低。0Cr17Mn17Mo3NiN奥氏体不锈钢的热变形激活能为549 kJ/mol。在980~1 050℃范围内,真应变为0.4,应变速率为0.01~0.1 s^-1时,能量耗散效率η值为0.28~0.3,0Cr17Mn17Mo3NiN奥氏体不锈钢容易发生动态再结晶。因此,该温度区域是最优的热加工工艺窗口。