非平底凹模铝板/塑料复合成形中铝板大塑性变形分析

在注塑机上利用非平底凹模制备了形状较复杂的铝板/聚丙烯复合结构件,实现了将金属板料成形、塑料注射成形融为一体的复合成形的新工艺.利用弹塑性大变形更新的Lagrange有限元法对于复合成形中铝板成形过程进行了数值模拟.成形铝板的实验测试厚度与有限元模拟值具有良好的相符性.铝板成形中形成3个板厚减薄较严重的区域.板厚减薄严重的Ⅱ区,发生了胀形变形和剧烈的塑性剪切变形.Ⅰ区和Ⅳ区之间的大塑性变形区分为B区和C区2个部分,B区内绝对值最大的主塑性应变为负,C区内绝对值最大的主塑性应变为正.Ⅲ区与Ⅳ区之间的D区绝对值最大的主塑性应变为负.     

铝合金矩形截面内高压成形塑性变形规律(英文)

采用实验和固体元数值模拟研究了铝合金矩形截面内高压成形过程塑性变形的发生与发展规律,给出了主应力三维图形可视化表征及在屈服柱面上的应力轨迹,分析了典型点应力及应变状态。结果表明:在矩形截面内高压成形过程中,圆角区外层首先发生屈服,圆角区内层两端部分各约1/4区域最后进入塑性变形。圆角区应变状态为沿着厚向缩短和环向伸长的趋势变化,过渡点最先发生塑性变形并且等效应变始终最大。在变形过程中随着内压的增大,过渡点的轴向应力始终为拉应力。     

不同应力状态下St14-T冷轧薄板本构关系研究

采用液压胀形试验分析了双向拉伸变形过程板材的应力梯度和应变分布 ,确定了双向拉伸变形状态下板材的应力应变关系曲线 ,探讨了不同应力状态下板材的本构关系。研究结果表明 ,不同应力状态下板材的本构方程存在一定的差异 ,双向拉伸变形条件更有利于发挥材料塑性变形的潜力。与单向拉伸相比 ,双向拉伸变形更有助于板料变形的均匀化 ,并抑制颈缩的产生和进一步扩展     

从力学角度浅谈冲裁间隙对冲裁件质量的影响

<正> 冲裁过程分为弹性变形、塑性变形和断裂三个阶段。当凸模接触板料后,对板料施加压力使之产生弹性压缩和弯曲变形;凸模继续对板料施加压力,刃口切入板料内并把一部分金属材料挤入凹模型腔,刃口区的金属产生塑性剪切变形,同时还伴有金属纤维的弯曲和拉伸变形。随着塑性变形的进行刃口附近的材料内的应力不断增大并产生应力     

数字图像相关法在薄板成形极限测定中的应用

成形极限曲线可展现板料在塑性失稳前所能达到的最大变形程度,是板料成形分析中的重要判据。为获得准确的试验成形极限曲线,该文通过刚性半球凸模胀形试验、采用数字散斑图像相关方法对AA6061铝板的成形极限曲线进行测定,得出了成形极限试验测定和极限应变提取的方法;通过对AA6061铝板进行盒形件拉深试验,建立拉深过程的有限元模型,比较了数值模拟和试验测定的极限拉深深度。比较结果表明,数字图像相关方法能够有效获取变形过程中的全场应变信息、搜索临界破裂状态,且能采用曲线拟合方式计算极限应变,避免了人为误差,提高了测量精度。拉深试验表明,所测成形极限曲线对拉深极限具有较高的预测精度。     

工业纯铝板料渐进成形极限图研究

板料渐进成形极限图和传统成形极限图有显著不同,到目前为止尚未有统一的测试方法.提出了一种测试板料渐进成形极限图的方法,成形工具分别沿往复圆弧和交替往复圆弧轨迹运动,对0.9mm工业纯铝板进行渐进成形.板料破裂后,获得了主应变和次应变,建立了该种板料渐进成形极限图.通过板料渐进成形分别成形了一些零件,测量了零件的主应变和次应变并绘制了它的渐进成形极限图.结果表明,所获得的工业纯铝渐进成形极限图能较为准确地预测渐进成形中板料的破裂,测试方法适用于渐进成形极限图的建立.     

一种强化孔翻边过程的方法

毛坯在拉应力作用下发生破裂,是板料上的孔在翻边时的主要限制因素。毛坯的变形部分处在平面应变(径向及切向拉应变)及体积应变状态。凹模边缘上的径向拉应力最人,并向孔的周边逐步降低。毛坯孔的外表端面层是处于线性应力状态条件下,因此,孔翻边时,切向纤维将发生拉伸,横向材料的厚度将减薄。孔的自由边由于切向变形达到最人值而发生     

铝板的成形极限数值模拟研究

通过系统地分析板料胀形成形机理，建立金属板料成形的有限元模型。分别设定不同类型和厚度的铝板及钣金尺寸，利用擅长在板料成形领域计算的LS-DYNA3D软件对板料胀形过程进行有限元模拟。并对不同型号，不同厚度铝板的成形极限图进行了分析，结合试验部分进行验证，确认3003铝合金板材的成形极限高于1060铝合金板材，且增加板厚可以提高材料的成型极限。     

基于Dynaform铝制错列锯齿翅片成形有限元模拟

使用有限元软件模拟了翅片成形与卸载回弹过程,研究了冲压压力对翅片成形过程的影响.结果表明:翅片成形过程中,板料变形主要集中在锯齿上.冲压压力为20 MPa时,成形较好;铝板的厚度变化较小,最小板厚是1.96 mm,减薄率是8％.错列锯齿翅片大多数区域的应力、应变分布均匀平稳,但在锯齿端部,铝板的应力、应变复杂,易产生缺陷,在成形过程中应采取必要的应对措施.     

天线面旋压成形焊缝撕裂的分析与控制

在大型抛物线旋转曲面的数控旋压精密成形加工时，需要先装厚度为2.5-3mm的LF21铝板拼接成大尺寸的毛坯。在旋压强力塑性变形过程中，成形后内、外曲面的焊缝常出现大量的微裂缝，热影响区出现撕裂开口等缺陷，严重影响曲面成形精度和天线反射面的使用寿命，有的甚至无法完全成形而报废。针对空心旋压成形过程铝板的变形特点，分析了天线曲面焊缝开裂原因，并对其氩弧焊接工艺控制过程积累的经验进行了总结。     

Influence of process parameters on hybrid forming of aluminum sheet

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复合金属板材曲面模具挤压的上限法分析

通过上限法分析了复合金属板材经反复曲面模具的挤压过程。变形材料可以分为双金属区和单金属区2个变形区域。每个区域材料的流变状态都设为平面应变状态。得到内能,剪切能和摩擦能的表达式,并应用到上限模型中。确定了铜包覆铝复合材料采用楔形模具和流线曲面模具的挤压力。通过有限元软件ABAQUS模拟得到2种模具的相应结果,并与上限法模型进行对比,比较结果表明,两者具有很好的一致性。     

A geometrical model of the kinematics of incremental sheet forming for the prediction of membrane strains and sheet thickness

The sine law is a simple geometrical model for incremental sheet metal forming (ISF). It is based on the assumption that the deformation is a projection of the undeformed sheet onto the surface of the final part. The sine law provides approximations of sheet thinning for shear spinning and ISF at negligible computational cost, but as a plane strain model it can be applied only when plane strain deformation prevails.     

一种建立板料成形极限应力图的新方法

基于塑性理论建立了比例加载条件下双向拉伸应力应变关系,结合Swift分散性失稳准则,提出了一种建立板料成形极限应力图的方法。分别应用Hill 48和Hosford屈服准则以及单向拉伸性能参数,建立了铝合金板(r<1)和薄钢板(r>1)两种材料的成形极限应力图(FLSD),分析表明,不同的屈服准则的选取对于成形极限应力曲线有不同的影响,对于不同类型的材料屈服准则的影响程度也不同。与由通常的成形极限图(FLD)转换所得到的成形极限应力图(FLSD)进行了对比分析,结果表明,所提出的方法计算过程更为简便,并能较为准确地建立成形极限应力图,可以作为复杂加载路径下的成形极限破裂判据。     

Finite element analysis of forming of sheet metal blank in manufacturing metal/polymer macro-composite components via injection moulding

A new approach to manufacture metal/polymer macro-composite components is presented, in which the injected polymer melt from the injection machine forces the sheet metal blank to deform according to the contour of the mould and the space between the formed sheet blank acts as the moulding cavity of the polymer melt. As the melt cools down, it adheres to the surface of the formed sheet blank. The mechanism of adhesion bonding between the polymer and the surface of the formed sheet blank is discussed briefly. The deformation characteristics and evolution of plastic strains of the sheet blank during the manufacturing process, the distribution of plastic strains and thickness of the formed sheet blank, and the effects of drawing-in of the flange on these have been analysed by the finite element method and experiment. According to deformation characteristics, the formed sheet blank can be divided into five regions. It is shown that deep drawing is the dominating process when the pressure increases from 0 to about 30 MPa; after this stage, stretch forming of the sheet blank that has already been in the mould cavity is the dominating process and two highly strained zones with severe thickness reduction are developed.     

Ductile fracture behavior of 5052 aluminum alloy sheet under cyclic plastic deformation at room temperature

Ductile fracture behavior of a 5052 aluminum alloy sheet undergoing cyclic plastic deformation is investigated in order to clarify the effect of cyclic plastic deformation on formability enhancement in incremental stretch sheet forming at room temperature. In the incremental forming, formability markedly increases owing to strain distribution and accumulation effects. The former effect is activated when the deformation region expands along tool paths. Thus, localization of deformation, which leads to necking or fracturing, can be prevented. On the other hand, local strain is accumulated without fracturing when a blank sheet is repeatedly subjected to out-of-plane deformation at the same position. In this paper, the effect of the strain accumulation due to cyclic deformation generated by bending and unbending is primarily focused on to discuss the effect on deformability. To apply cyclic plastic straining to the specimen, a cyclic stretch-bending test was adopted. A cyclic tensile test was also conducted for larger bending curvature. The experimental results show that cyclic bending–unbending affects the ductility of sheet metals. The fractography obtained by scanning electric microscopy also indicates that fewer and smaller voids are observed particularly on bending the inner side than on the outer side.     

2219铝合金薄壁曲面拉伸件的变形与强化规律

为了研究拉伸成形2219铝合金薄壁曲面件的变形与强度分布规律,通过网格应变法和单向拉伸试验对曲面件各个区域的应变与力学性能进行测试,得到全域范围内的变形与强度分布规律。结果表明:等效应变分布在1%~15%范围,但瓜瓣曲面件有效区域的等效应变在7%~12%,变形较为均匀;屈服强度为312.8~346.9 MPa,抗拉强度为421~442.2 MPa;强度与变形量之间成正比例关系,抗拉强度和硬度皆随变形量增加而增大。所有测试数据表明拉伸成形的2219铝合金薄壁曲面件满足火箭燃料贮箱箱底的力学性能要求。     

7075-T6铝合金板温热成形极限图实验

研究7075-T6铝合金板在温热状态下成形性能,采用电化学腐蚀网格法,利用热力耦合条件下的通用板材成形性能实验机和网格应变自动测量分析系统,获得了7075-T6铝合金板在温热状态下(室温~200℃)的成形极限图(FLD)。实验表明,7075-T6铝合金板的成形极限曲线受温度影响显著,并随温度的升高而上升。基于实验数据,建立了不同温度下7075-T6铝合金板成形极限图的计算模型。     

Prediction of forming limit curve for pure titanium sheet

Commercially pure titanium (CP Ti) has been actively used in the plate heat exchanger due to its light weight, high specific strength, and excellent corrosion resistance. However, researches for the plastic deformation characteristics and press formability of the CP Ti sheet are not much in comparison with automotive steels and aluminum alloys. The mechanical properties and hardening behavior evaluated in stress–strain relation of the CP Ti sheet are clarified in relation with press formability. The flow curve denoting true stress–true strain relation for CP Ti sheet is fitted well by the Kim–Tuan hardening equation rather than Voce and Swift models. The forming limit curve (FLC) of CP Ti sheet as a criterion for press formability was experimentally evaluated by punch stretching test and analytically predicted via Hora's modified maximum force criterion. The predicted FLC by adopting Kim–Tuan hardening model and appropriate yield function shows good correlation with the experimental results of punch stretching test.     

On the effects of predeformation on work hardening of ultra-low-carbon sheet steel

Predeformation affects the work-hardening behavior of sheet metals in sequential forming operations by producing various strain histories in different parts of the sheet. Several investigators have reported the effects of two-stage deformation on the behavior of sheet metals, particularly justification has been presented on face-centered cubic (fcc) alloys. However, the works on low-carbon ferritic steels are not conclusive. This article reports some new findings of the effects of two modes of predeformation on the subsequent stress-strain relationship in ultra-low-carbon sheet steels. The details of a laboratory test system are presented along with methods used to reduce the data. The effect of the stability ratio, a measure of the degree to which the interstitial atoms are free, on the hardening rate at second-stage of deformation was studied. For stabilized sheet steels, it was found that changes in strain path from equibiaxial stretching to uniaxial tension cause an increase in the flow stress relative to the flow stress at similar effective strain in continued monotonic. For unstabilized sheet steels, a significant increase in the flow stress was not observed with either equibiaxial prestraining or cold rolling and equibiaxial stretching.