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对U型截面弯曲件失稳起皱问题进行了研究,通过板材成形性能实验及起皱模拟实验,对失稳起皱原因进行了分析,为类似的异型截面弯曲件起皱的预防提供了可行的实验分析方法。 相似文献
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本文通过实验和有限元模特怪圆板成对无液压胀形过程进行了研究。在有限元模拟中,分析了初始几何缺陷对壳体起皱的临界压力和起皱形态的影响。结果表明,有限元模拟的带初始缺陷的壳体胀形时的起皱临界压力和起皱形态与实验结果非常吻合,而完善壳体的起皱临界压力和起皱形态与实验结果则有较大差别。 相似文献
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某汽车后地板上横梁在拉延后,出现了严重的起皱缺陷。针对该问题,首先使用Auto Form软件模拟其拉延工序,分析起皱原因。由于拉延过程中板料中间的材料没有被充分拉延,导致在产品台阶圆角与侧壁交界处因剪应力造成起皱。其次,利用Auto Form软件对冲压工艺进行了优化。仿真实验结果表明,通过增大台阶面的过渡圆弧半径R可以减少起皱,当R值过大时,在后序翻边时会导致台阶边缘有开裂风险,当R为400 mm时,产品成形较好。最后,通过冲压试验验证该优化方案的有效性,起皱问题得到了有效控制,从而减少了模具开发成本,缩短了生产周期,保证了该产品按期交货。 相似文献
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本文通过实验和有限元模拟对圆板成对无模液压胀形过程进行了研究。在有限元模拟中,分析了初始几何缺陷对壳体起皱的临界压力和起皱形态的影响。结果表明,有限元模拟的带初始缺陷的壳体胀形时的起皱临界压力和起皱形态与实验结果非常吻合,而完善壳体的起皱临界压力和起皱形态与实验结果则有较大差别 相似文献
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钛合金马鞍形薄蒙皮零件采用一次热压偶合成形,容易产生起皱缺陷。以某机身TC4 0.8 mm马鞍形蒙皮为研究对象,运用成形理论和力学知识,分析起皱产生的原因及规律,提出了分型面多步热压成形工艺设计和模具压边结构设计两种控制起皱的方法。研究结果表明,受冲压成形过程中金属流动不均匀与悬空区板坯平面内压应力过大的影响,马鞍形蒙皮容易发生剪应力起皱,起皱部位一般发生在马鞍侧壁区域。采用分型面多步成形可降低零件工艺难度,优化设计模具压边结构有利于控制金属的流动趋势,从而抑制悬空侧壁区材料堆积起皱。最终,通过工艺试验,试制出表面质量完好的马鞍形蒙皮零件。 相似文献
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以某汽车前门内板拉延过程中出现的起皱缺陷为例,通过鱼骨分析法对起皱原因进行排查,并对前期工艺设计阶段的冲压仿真进行回顾,得出仿真与实际流入量情况基本一致。再通过起皱趋势、表面缺陷高度、过程分析以及成形性等冲压仿真的起皱评价指标对前门内板的拉延过程进行评估,发现以上起皱评价指标在产品平缓区域存在失效情况。针对此情况,引入起皱高度Δ,并将其与板料跟上模的接触距离关联起来,通过板料厚度的3%、5%和10%这3个阈值对冲压件的起皱进行量化分级,同时优化冲压成形仿真参数设置,提出了针对产品平缓区域的起皱评价指标及流程。最后,通过工程验证,该起皱评价指标及流程对产品平缓区域的起皱评估有效。 相似文献
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Wrinkling is one of the major defects in sheet metal products and may be also attributable to the wear of the tool. The initiation
and growth of wrinkles are influenced by many factors such as stress ratios, mechanical properties of the sheet material,
geometry of the workpiece, contact condition, etc. In the study, the bifurcation theory is introduced for the finite element
analysis of wrinkling initiation and growth. All the above mentioned factors are conveniently considered by the finite element
method. The wrinkling initiation is found by checking the determinent of the stiffness matrix at each iteration and the wrinkling
behavior is analyzed by successive iteration with the perturbed guess along the eigenvector. The effept of magnitude of perturbation
on the wrinkling behavior can be avoided by the Newton-type iteration method. The finite element formulation is based on the
incremental deformation theory and elastic-plastic material modeling. The finite element analysis is carried out using the
continuum-based resultant shell elements considering the planar anisotropy of the sheet metal. In order to investigate the
effects of geometry and stress state on the wrinkling initiation and growth, a modified Yoshida buckling test is proposed
as an effective buckling test. The finite element analysis are carried out for the modified Yoshida buckling test. The buckling
behavior of the sheet is analyzed for various modified dimensions. 相似文献
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承受非均匀拉伸矩形薄钢板的横向皱曲现象,既存在于汽车零件冲压成形制造中,也常见于薄带钢生产制造(尤其连续退火和热镀锌)中,是一个未完全解决的力学问题。文章认为矩形板宽度方向局部区域张力集中诱导生成的压应力是这一力学现象发生的主因,通过利用伽辽金变分与泛函分析原理给出了一种收敛性好、速度快的求解矩形方板弹塑性状态下应力场与屈曲临界应力的一种迭代算法,讨论了板的几何尺寸、拉伸非均匀度、材料性能对弹塑性状态前屈曲应力场的影响,根据临界载荷最小原则对皱曲区域进行了合理优化,同时结合有限元仿真和常温态非均匀拉伸实验,验证了解析计算模型的合理性。 相似文献
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Mohammad Amin ShafaatMahmoud Abbasi Mostafa Ketabchi 《Journal of Materials Processing Technology》2011,211(11):1783-1795
Wrinkling phenomenon has been one of the major limiting failure modes in sheet metal forming processes. Wrinkling phenomenon in sidewall area of the cup formed in the conical cup test was considered both experimentally and numerically. A new deflection function is developed in this research and the effects of material anisotropy on the onset of wrinkling are studied using Hosford and Hill-1948 yield criteria under isotropy, normal anisotropy and planar anisotropy conditions. It was observed that application of Hosford yield criterion resulted in better prediction of wrinkling onset. It was also found that as the effective stress increases, consistency between predicted results and experimental data at the onset of wrinkling improves. Also, a good agreement between experimental data and predictions using proposed deflection function is obtained. 相似文献
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Lihong Zhang Anne Marie Habraken Amine Ben Bettaieb Laurent Duchêne 《Journal of Materials Engineering and Performance》2013,22(9):2437-2445
This article presents an analytic model for the prediction of wrinkling occurring in metal/polymer coatings under particular conditions. Owing to different thermal expansion coefficients (TECs) of the substrate and the different coating layers, temperature variation can induce a compressive stress in the coating. The wrinkling is the material response to the instability caused by this compressive stress. In this study, a reference case was selected: a 0.27-mm-thick steel sheet with a 5-μm-thick polymer layer and, on top of it, a thin aluminum film of 50 nm in thickness. For this reference case, it was observed and predicted by the model that an increase in temperature yielded to the wrinkling of the thin aluminum film. The geometry of the multilayer coating and the properties of the constituent materials are factors able to promote or prevent the wrinkle. To better understand and predict their effects, a sensitivity analysis was carried out with the proposed analytic model. A special attention was devoted to the temperature when wrinkling occurs. The key parameters having a significant influence on the wrinkling temperature were identified. It is concluded that the elastic modulus of the thin aluminum film and that of the polymer, the TEC of the thin film, and the initial stress induced during the processing of the multilayer system all had a significant influence on the wrinkling temperature. 相似文献
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Accurate material characterisation of anisotropic yielding behaviour for modern sheet metal requires the testing under multiaxial stress conditions like in the shear test or plane strain test. While most approaches include time-consuming finite element simulations for evaluation of inhomogeneous stress distributions, this paper shows a new method to determine stress data based directly on digital image correlation data. This accurate and efficient semi-analytical method can be used in direct stress analysis or inverse material parameter identification schemes as well. The methodology will be described and exemplarily results of the plane strain test and the shear test will be discussed. 相似文献
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Ti-15-3钛合金橡皮成形凸弯边起皱预测 总被引:1,自引:0,他引:1
基于ABAQUS/Explicit对Ti-15-3钛合金室温锥杯成形实验中悬空侧壁起皱现象进行分析,通过对零件边缘的皱纹波长和峰高的定量研究,获取较适合Ti-15-3钛合金室温成形侧壁起皱的模拟参数。将Ti-15—3钛合金室温锥杯成形起皱获取的模拟参数,用于Ti-15-3钛合金凸弯边橡皮成形起皱的预测,通过定量比较凸弯边边缘的皱纹波长和峰高,分析不同硬度的橡皮对Ti-15-3钛合金凸弯边橡皮成形起皱的影响。经实验验证,有限元模拟对Ti-15—3钛合金凸弯边上皱纹的模拟与实验结果有很好的一致性。 相似文献
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在金属板料塑性成形加工中 ,起皱是常见的 ,它影响成形件质量 ,预测与防止起皱已成为人们长期以来关注的热点问题。起皱实质上是金属板料的一种压缩不稳定现象。本文把板料塑性屈曲前后的材质状态视为刚塑性 ,板材塑性皱曲时 ,所满足的全部方程 :平衡 ,机动 ,屈服及流动定律 ,归结为一个泛函的求极值问题 ,在这个泛函中 ,内力场与速度场是彼此独立的自变函数。用直接法可以方便地求得金属板料塑性屈曲问题的近似解析解。文中以环缺在边界纵向拉压力作用下的皱曲问题为例 ,具体地给出了皱曲载荷及板的内力及速度场形态 相似文献
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《Journal of Materials Processing Technology》2000,97(1-3):88-94
Surface distortions in the form of localized buckles and wrinkles are often observed in sheet metal forming process. In many cases the presence of wrinkles is unacceptable for the final product and the purposes of assembly. Because of the trend in recent years towards thinner gauges and higher strength, wrinkling is increasingly becoming a more common and troublesome mode of failure in sheet metal forming.In this study, a numerical analysis for evaluating a wrinkling limit diagram (WLD) for an anisotropic sheet subjected to biaxial plane-stress is presented. Here the scheme of plastic bifurcation theory for thin shells based on the Donnell–Mushtari–Vlasov shell theory is used. The effects of various material parameters — yield stress, strain-hardening coefficient and normal anisotropy — and geometrical parameters on the WLD are investigated numerically and compared with the results of the experiments of Kawai and Havranek. 相似文献