共查询到18条相似文献,搜索用时 78 毫秒
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应用适用于板料轴对称成形过程的应力平衡方程对薄壁圆筒工件抛物面型缩口成形中的应力进行了分析,得出了薄壁圆筒工件抛物面型缩口成形时的经向应力与各种参数之间的关系及缩口力的计算公式,从而为工艺设计人员制定此类缩口工艺提供了方便. 相似文献
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通过对原球头成形生产过程中存在的产品质量问题--二次缩口后外球壳表面出现筋条,并导致球头不圆,提出了改进生产工艺及模具结构等措施,以保证球头的表面质量. 相似文献
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目的主要研究厚壁管两端同时温、热锥形缩口工艺的特点,以及缩口过程不同工艺参数对壁厚增厚的影响。方法通过选择合理的材料模型与热力耦合等温度场模拟参数,建立了有限元模型,使用DEFORM体积成形软件对厚壁管两端同时温热缩口工艺进行了分析,探究了温、热缩口两种条件下应力应变分布特点。结果模拟实验获得了管材缩口系数、模具半锥角、t/d0值、摩擦因子、成形温度等工艺参数,在温、热两种条件下对壁厚增厚量的影响曲线。结论管材缩口过程具有典型的变形阶段:入锥弯曲阶段、反弯曲阶段和缩口稳定阶段;管材高温下缩口变形特点为周向、轴向的压缩变形和径向的增厚变形;厚壁管缩口的增厚变形量随着模具半锥角的增大和缩口系数的减小而增大,同时受摩擦因子、成形温度、管材壁厚的影响较大。研究结果为管材缩口壁厚增厚工艺提供了基础技术数据。 相似文献
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广州白云国际会议中心景观桥采用缩口钢承板作为组合桥面结构板,这在桥梁建造上是较罕见的。本文介绍了缩口钢承板在桥梁使用上的特点、安装过程,开创了材料使用新思路,为桥梁工程提供了经验。 相似文献
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目的 探究大型锥筒件内凸缘缩口成形的最佳工艺参数。方法 首先,根据内凸缘缩口成形的工艺原理,使用三维软件构建内凸缘缩口成形的仿真模型,并用Deform进行仿真成形。在此基础上,以缩口件高度和成形载荷作为内凸缘成形质量的判断依据,基于响应面法得到关于缩口件高度和成形载荷的回归预测模型。分析不同的摩擦因数、挤压速度和凹模锥度对内凸缘成形质量的影响,优化得到最佳的成形工艺参数,最后进行物理试验验证。结果 通过响应面法拟合得到了缩口件高度和成形载荷关于3因素的多元非线性模型,模型通过F检验得出的显著性概率P值均小于0.000 1,失拟项值均大于0.05,且模型预测值与试验模拟值的关系接近直线,充分说明了该数学模型的合理性。当摩擦因数为0.3、挤压速度为3 mm/s、凹模锥度为9°时,毛坯的成形载荷最小,为90 k N,缩口件高度最低,为1 350 mm,与模型预测相比,误差均小于10%。结论 优化后的工艺参数使内凸缘成形质量高、表面光滑无缺陷、成形载荷小,为大型锥筒的内凸缘成形工艺提供了参考。 相似文献
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针对各向同性均质弹塑性材料圆棒试样单向拉伸试验,分别从理论上以及采用有限元法分析了变形特性与应力应变本构关系的相关性,探讨了形成颈缩的必要条件及实际颈缩形貌的形成过程。结果表明,等效塑性应变εp达到一定临界值后,流变应力σ0不再随等效塑性应变εp的增大而增大的材料的应力应变本构特性,以及试样为非理想圆柱体是产生颈缩的必要条件,颈缩后期内部形成断裂是导致颈缩区最小截面位置弧形轮廓线曲率半径较小的原因。 相似文献
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真应力-应变曲线的一种图解求法--缩颈过程分析 总被引:1,自引:0,他引:1
为求缩颈阶段的真应力,分析了试样缩颈过程。结果表明,最小缩颈截面运动的轨迹是一个锥面外凹的虚拟圆锥体,它与缩颈体是完全不同的两个体,应该用前者而非后者的截面积(半径)去求真应力。推导证明,缩颈半径点(缩颈最小横截面与缩颈最上端母线的交点)的轨迹线是一条向上凹、严格单调减及导数逐渐减小的曲线,提出了一种轨迹线方程的图解求法。由此指出,计算缩颈阶段真应变时,应以参与缩颈的长度而非试样的标距为初始长度。 相似文献
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Márquez-Lucero A Gomez JA Caudillo R Miki-Yoshida M José-Yacaman M 《Small (Weinheim an der Bergstrasse, Germany)》2005,1(6):640-644
A method is introduced to assess the tensile strength of carbon nanofibers, carbon nanotubes (CNTs), and linear chains of carbon atoms (C-chains) obtained from thin amorphous carbon films by electron irradiation. Transmission electron microscopy images show that the nanofibers undergo a radiation-induced necking process, characterized by CNT formation and often followed by the formation of a C-chain. Simulations of the necking process are carried out to determine the tensile stress supported by the nanofiber and CNT neck. 相似文献
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P. Wriggers C. Miehe M. Kleiber J. C. Simo 《International journal for numerical methods in engineering》1992,33(4):869-883
The necking process of a bar in an uniaxial tension test is influenced by the heat production due to inelastic deformations. Thus, for an analysis of this problem the thermomechanical coupling has to be considered. A finite element model and an associated algorithm are developed for this purpose. This computational tool allows the study of adiabatic processes as well as processes with heat flux. The analysis of the necking process of a perfectly cylindrical specimen shows that, in contrast to isothermal and adiabatic cases, no bifurcation occurs in the case where heat flux is considered. 相似文献
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A new mechanistic approach is used to characterize resistance of polyethylene to deformation and fracture in double-edge-notched tensile test. The new approach considers all three mechanisms involved in the fracture process, i.e. for fracture surface formation, shear plastic deformation, and necking, and can be used to determine values of specific energy consumption for each mechanism. This is different from the conventional approach, known as essential work of fracture (EWF), which does not consider the difference between shear plastic deformation and necking. Results from the new approach for a polyethylene copolymer show that specific energy density for fracture surface formation is about half of that determined from the EWF approach, and specific energy density for necking is very close to that determined from simple tensile test. The latter provides some support for validity of the new approach in characterizing fracture behaviour of polyethylene when accompanied by large deformation and necking. The paper also points out crack growth conditions that have to be met for valid application of the EWF approach and shows that such conditions are not met when deformation and necking occur in polyethylene. 相似文献