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变形—损伤耦合的超塑性恒压轴对称充模胀形的有限元模拟 总被引:1,自引:0,他引:1
采用大变形刚粘塑性有限元法模拟超塑性恒压轴对称充模胀形过程,分析了模具几何参数及材料参数对胀形过程中材料的流变行为、胀形制件厚度分布和成形时间的影响规律,给出了质点的流动轨迹,不同时刻制件的剖面形状及应力、应变分布;基于修正的Gurson粘塑性势推导了内部空洞体积分数累积增大模型并据此进行了变形-损伤耦合计算。 相似文献
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杆柱在水平圆孔中的稳定性分析 总被引:9,自引:0,他引:9
本文通过建立和求解杆、管柱在水平圆孔中的屈曲方程,分析了不同边界约束条件下杆柱临界失稳载荷因子β_0和杆柱长度因子α_0之间的关系,并讨论中间铰支座(扶正器或稳定器)对杆柱稳定性的影响。 相似文献
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本文利用Eulerian坐标系下弹塑性大变形基本公式及分叉屈曲的理论,采用有限元数值法,探索平面应变条件下具有幂硬化弹塑性材料,在不同位移加载参数及不同原始孔洞体积百分数下,材料内部空洞的长大、剪切分叉以及材料宏观力学行为.计算结果表明,宏观材料的软化、塑性可膨胀性、内部损伤的发展以及剪切分叉的临界应变值等,都与加载参数α、原始空洞尺度有着密切的关系. 相似文献
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尽管超塑胀形作为一种金属成形方法正日渐受到世界各国的普遍关注,但对超塑约束胀形理论的研究报道却还很少,尤其对胀形过程的有限元模拟研究就更为罕见。针对这种情况,采用大变形刚粘塑性有限元法模拟了轴对称零件向圆筒形凹模内超塑约束胀形的变形过程,着重研究了工具工件之界面摩擦对胀形件厚度分布不均匀性和胀形板料向凹模角部充填性的影响.结果表明,随着摩擦的降低,胀形件的侧向较厚部分能有所减薄,可以改善整个胀形件的厚度均匀性,但当摩擦因子Am≤0.2(相当于摩擦系数μ≤0.12)时,胀形件极顶部分的减薄过大;摩擦较小时,胀形板料向凹模角部的充填性较好;在考虑到极点附近厚度适度减薄和胀形板料对凹模角部充填性好的前提下,工艺上应当适当减小摩擦,其最佳状态是μ值约为0.3.为了检验所用刚粘塑性有限元法模拟的可靠性,将计算结果与试验结果作了对比,发现两者相当吻合。 相似文献
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挤出平缝口模通常用于加工膜和片材,对产品厚度的一致性有很高要求。本文给出了结合聚合物成型模拟技术、设计灵敏度分析和数值优化技术的口模形状优化设计方法。以最小压力降为目标函数,口模出口处任意点的速率与出口已知速率相对误差的平方和小于容许误差为约束函数,口模形状参数为优化设计变量,给出了目标函数的表达式,推导了日标函数、约束函数对优化设计变量的灵敏度公式。利用灵敏度分析和基于梯度的优化算法即序列二次规划算法(SQP法)求解最优设计参数。通过算例表明,应用该法进行口模优化设计可以减小压力降和口模出口速率变化率。 相似文献
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Using elastic crystalline viscoplastic finite element (FE) annlysis, the formability of BCC steel sheets was assessed. An
orientation probability assignment method in the FE modeling procedure, which can be categorized as an inhomogenized material
modeling, was newly proposed. In the study, the crystal orientations of three materials, mild steel, dual phase steel and
the high strength steel, were obtained by X-ray diffraction and orientation distribution function (ODF) analyses. The measured
ODF results have revealed clearly different textures in the sheets, featured by orientation fibers, skeleton lines and selected
orientations in Euler angle space, which are closely related to the plastic anisotropy. Then, the crystal orientations were
assigned to FE integration points by using this ODF data, individually. The FE analyses of the standard limiting dome height(LDH)
test show how the fiber textures affect the extent of strain localization in the forming processes. It was confirmed by comparison
with experimental results that this FE code could predict the extreme strain localization and assess the sheet formability.
The third author is indebted to the National Natural Science Foundation of China for financial support (Grant No. 59875025)
to the research cooperation with OIT, Japan. 相似文献
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《International Journal of Plasticity》2004,20(11):1953-1981
A combined necking and shear localization analysis is adopted to model the failures of two aluminum sheets, AA5754 and AA6111, under biaxial stretching conditions. The approach is based on the assumption that the reduction of thickness or the necking mode is modeled by a plane stress formulation and the final failure mode of shear localization is modeled by a generalized plane strain formulation. The sheet material is modeled by an elastic-viscoplastic constitutive relation that accounts for the potential surface curvature, material plastic anisotropy, material rate sensitivity, and the softening due to the nucleation, growth, and coalescence of microvoids. Specifically, the necking/shear failure of the aluminum sheets is modeled under uniaxial tension, plane strain tension and equal biaxial tension. The results based on the mechanics model presented in this paper are in agreement with those based on the forming limit diagrams (FLDs) and tensile tests. When the necking mode is suppressed, the failure strains are also determined under plane strain conditions. These failure strains can be used as guidances for estimation of the surface failure strains on the stretching sides of the aluminum sheets under plane strain bending conditions. The estimated surface failure strains are higher than the failure strains of the forming limit diagrams under plane strain stretching conditions. The results are consistent with experimental observations where the surface failure strains of the aluminum sheets increase significantly on the stretching sides of the sheets under bending conditions. The results also indicate that when a considerable amount of necking is observed for a sheet metal under stretching conditions, the surface failure strains on the stretching sides of the sheet metal under bending conditions can be significantly higher. 相似文献
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Christian F. Niordson Pia Redanz 《Journal of the mechanics and physics of solids》2004,52(11):2431-2454
A finite strain generalization of the strain gradient plasticity theory by Fleck and Hutchinson (J. Mech. Phys. Solids 49 (2001a) 2245) is proposed and used to study size effects in plane strain necking of thin sheets using the finite element method. Both sheets with rigid grips at the ends and specimens with shear free ends are analyzed. The strain gradient plasticity theory predicts delayed onset of localization when compared to conventional theory, and it depresses deformation localization in the neck. The sensitivity to imperfections is analyzed as well as differently hardening materials. 相似文献
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采用Tersoff势对含Stone-Wales(SW)拓扑缺陷的单层石墨烯薄膜的单向拉伸力学性能进行了分子动力学模拟,分别研究了SW拓扑缺陷对扶手椅型和锯齿型石墨烯拉伸力学性能及变形机制的影响.研究结果表明,单个SW缺陷对两种手性石墨烯薄膜的杨氏模量几乎无影响,而对薄膜的强度、应变等力学性能和变形破坏机制的影响与手性有关.对于扶手椅型石墨烯薄膜,单个SW缺陷降低了薄膜的拉伸强度和拉伸极限应变,降低幅度分别为5.04%和7.07%.在外载作用下,新的缺陷的萌生位置出现在SW缺陷附近;而对于锯齿型石墨烯薄膜,单个SW缺陷基本不影响薄膜的力学性能和变形破坏机制. 相似文献
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Tension and compression experiments on magnesium rolled sheets and extruded products of AZ31 (Mg?+?3%Al?+?1%Zn) and ZE10 (Mg?+?1%Zn?+?0.3%Ce based misc metal) were performed at room temperature. The tests were conducted along the longitudinal and the transverse direction to quantify the in-plane anisotropy. Samples built from adhesively-bonded layers of sheets were used for in-plane as well as through-thickness compression testing. It was verified that this simple testing method leads to identical results as using comb-like dies and equi-biaxial bulge testing, respectively. In the case of uniaxial loading, the longitudinal and transverse strain components were measured using independent extensometers. R-values were calculated from these signals. The mechanical responses were correlated to the microstructure and the texture. The recorded differences between tensile and compressive response reveal the strength differential effect of the materials. The distortional character of the plastic behaviour is evidenced through their responses to equi-biaxial tensile loading. Significant differences in the compressive responses of the two alloys were identified by comparing the respective hardening rates. 相似文献
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W. Johnson 《Applied Scientific Research》1959,8(1):228-236
Summary Expressions are obtained for a best upper bound to the load necessary to cause extrusion through square dies, under conditions of plane strain, using a punch face which is inclined to the axis of the extrusion container. The results are interpreted to suggest how for a given reduction that angle of punch face may be chosen which delays the onset of cavity deformation. The modes of deformation considered suggest the mechanism, whereby the oxide layers on the rear of a billet may become entrained down the centre of an extruded product. 相似文献
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Toshihiko Kuwabara Yutaka Kumano Jindra Ziegelheim Ikuya Kurosaki 《International Journal of Plasticity》2009,25(9):1759-1776
In-plane tension and compression experiments on copper alloy sheets (phosphor bronze) and 6000 series aluminum alloy sheets (AA6016-T4) were conducted using a specially designed testing apparatus. The apparatus is equipped with comb-type dies so that stress–strain curves of a sheet specimen subjected to tension followed by compression, and vice versa, can be measured without buckling of the specimen, as well as those for monotonic tension and compression. A difference was observed in the flow stresses between tension and compression for the as-received copper alloy, but not for the aluminum alloy. Moreover, stress reversal tests, such as tension followed by compression and compression followed by tension, were carried out in order to measure the Bauschinger effect. In the second part of the experiment, bending moment–curvature diagrams were measured for the as-received and pre-stretched specimens. The bending moment–curvature diagrams were compared with those calculated using the stress–strain curves obtained from the tension–compression tests, and were in good agreement with those calculated with the tension–compression asymmetry and the Bauschinger effect correctly reproduced. 相似文献