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针对传统弯曲起皱理论模型忽略管材周向波形特性造成预测精度不高的难题,基于理论推导和参数拟合建立了管材起皱周向波形函数,结合管材弯曲应力特性建立了其成形起皱机理模型,采用有限元仿真以及实验方法验证了该理论模型的正确性。研究结果表明:新建理论模型的管材起皱预测准确度达到了94.5%,较传统模型提高了12%,改善了传统模型预测精度不高的难题;弯曲半径越小,管材越易起皱。工程中为避免起皱,临界弯曲成形半径不应小于1.89倍管道直径。 相似文献
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薄壁抛物线形壳体成形过程为拉深和胀形两种变形模式的复合,极易发生起皱和破裂。固体颗粒介质成形是采用固体颗粒代替刚性凸模或凹模(或弹性体、液体)对板料进行成形的工艺。板材在颗粒介质内压的作用下成形,可以有效防止抛物线形件拉深成形过程中侧壁的起皱;由于颗粒内压是非均匀分布的,故可以有效控制抛物线形件成形过程中的破裂,提高板材的成形极限。根据固体颗粒介质成形工艺的特点,提出了两次成形薄壁深壳体零件的工艺,建立了数值分析模型,通过数值模拟和试验对该成形过程和工艺参数进行了分析。结果表明,采用固体颗粒介质成形工艺过程简单、成形工件壁厚分布均匀、表面质量好、回弹小。 相似文献
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不均匀压下面内弯曲成形过程的有限元模拟研究 总被引:2,自引:0,他引:2
金属板带不均匀压下面内弯曲成形,能够发展成为一种利用材料塑性变形不均匀、可充分挖掘材料成形潜力的先进塑性加工方法。然而,这方面的研究还不深入,在国内尚属开创性工作。对锥辊实现的这一成形过程,建立了刚塑性有限元模型,对模拟中需要解决的关键问题提出了算法或处理技术;在此基础上,开发了相应的模拟系统并用试验验证了其可靠性。结果表明,所开发的模拟系统可靠,从而为深入系统研究这一过程的变形机理与成形规律提供了一种有效的先进手段。 相似文献
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管材流体高压成形起皱行为与皱纹控制研究进展 总被引:2,自引:0,他引:2
管材的起皱行为及其控制方法是目前流体高压成形领域的研究热点,对汽车、航空航天等重要领域高性能轻质整体复杂薄壁零件的成形制造具有重要意义.针对流体高压成形中薄壁管材受载复杂而易发生失稳起皱的问题,首先综述了管材在轴压或轴压与内压联合作用下的塑性失稳及起皱行为,讨论常用的管材轴向临界起皱应力模型及在流体高压成形中的应用,并发现通过预制有益皱纹可预先在变形区聚集材料从而显著提高管材成形极限.此外,重点介绍管材流体高压成形过程中起皱行为的控制方法,对管材起皱过程的应力分布、皱纹几何形状的演变规律进行了分析.提出可将三维应力状态和非均匀温度场作用下管材起皱行为作为重点研究方向,这不仅有助于构建复杂受载、非均质管壳的失稳起皱理论体系,而且可提高难变形材料大膨胀率管件的成形制造能力. 相似文献
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汽车覆盖件在成型过程中易出现拉裂、起皱等现象,应用冲压成形CAE技术,可以模拟仿真成形过程中材料的流动,预测破裂、起皱、回弹等缺陷。本文以汽车左车门内板为研究对象,应用AutoForm软件进行了成形仿真与分析,研究了压边力、摩擦系数、拉延筋参数对对成形的影响,通过正交法获得了最优化工艺方案。 相似文献
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管材弯曲成形的国内外研究现状及发展趋势 总被引:19,自引:0,他引:19
总结了近年来国内外学者和工程技术人员从理论分析、实验研究、有限元数值模拟方面着手对管材弯曲成形开展的大量研究工作和取得的研究进展 ,包括管材弯曲过程中的起皱和破裂分析、横截面变形以及卸载后的回弹分析和预测等 ,并阐述了管材弯曲成形研究的发展趋势。 相似文献
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《机械工程学报》2019,(18)
在对金属管材的热态内压成形加工过程中,由于镁合金相对于传统钢材体现出更为复杂的材料特性,使其在生产工艺和数值模拟等方面的研究更具有挑战性,其中破裂失效成为制约其产品质量的重要因素。通过对AZ31B镁合金的热态内压试验和有限元模拟分析,微观结构观察和相关材料常数测定,可以有效地对其材料损伤演化规律及破坏形式进行预测,预判裂纹产生的危险区域及扩展方式。研究表明,从室温过渡到300℃的范围内,AZ31B镁合金管材的成形性能随着温度提高而显著提升。为了避免在塑性成形的过程中出现弯曲起皱现象,并进一步提高成形件的尺寸精度,应该使其初始轴向进给保持在较低的状态,然后使其随着内压的增长而同步提升,并在轴向进给结束后,进一步小幅增加内压并保持。以连续损伤力学为基础,通过建立各向异性损伤的材料模型并与相关试验相互验证,能够有效地描述AZ31B镁合金的力学行为,并对其成形过程中相关的工艺参数提供依据。 相似文献
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进行了核电站90°弯管在内压和面内弯曲载荷作用下的棘轮效应试验,并采用数值方法研究了90°弯管的极限载荷、安定载荷和棘轮边界。利用理想弹塑性有限元分析,基于两倍弹性斜率准则和切线相交准则分别确定了90°弯管单独承受内压和弯曲载荷的极限载荷;利用线性匹配方法确定了90°弯管在单独内压和弯曲载荷以及两者共同作用下的极限载荷和安定载荷;利用Ohno-Wang模型,结合C-TDF弹塑性有限元分析方法和线性匹配方法分别确定了90°弯管的棘轮边界;最后,对弹塑性有限元方法和线性匹配法确定的棘轮边界进行了比较。结果表明:两倍弹性斜率准则、切线相交准则和线性匹配方法确定的极限载荷误差为10.78%,其中弹性迭代的线性匹配法能高效、快速地进行计算。比较C-TDF法和线性匹配法确定的棘轮边界,结果发现:当内压在20~35 MPa之间时,两种方法确定的棘轮边界吻合很好;当内压小于20 MPa时,两种方法的预测结果呈现不同的趋势。 相似文献
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F. I. Ruzanov 《Journal of Machinery Manufacture and Reliability》2008,37(6):572-577
The problem of curved strip pure bending under a two-dimensional stress has been considered. The values of stresses, the bending moment, and the curvature radius of the stress rupture surface have been obtained. Hoopential uniform compressive stresses causing the loss of the plane form equilibrium stability of the deformable strip act in the region adjacent to its internal surface. The problem has been solved using the principle of virtual work and the variational equation representing a sum of the work of external and internal forces delivered on the strip deflection variations. When the deflection takes place, ring-type fibers of the strip extend. This leads to additional ring deformations and stresses opposite in sign to momentless deformations and stresses. It results in unloading. 相似文献
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The problem of inelastic bending and collapse of tubes in the presence of internal pressure is investigated using experiments and analyses. The experiments involve 1.5-inch diameter, D/t=52 stainless steel tubes bent to failure at fixed values of pressure. The moment-curvature response is governed by the inelastic characteristics of the material. Bending induces some ovalization to the tube cross section while, simultaneously, the internal pressure causes the circumference to grow. Following some inelastic deformation, small amplitude axial wrinkles appear on the compressed side of the tube, and their amplitude grows stably as bending progresses. Eventually, wrinkling localizes, causing catastrophic failure usually in the form of an outward bulge. Internal pressure stabilizes the structure, it increases the wavelength of the wrinkles and can increase significantly the curvature at collapse. The onset of wrinkling is established by a custom bifurcation buckling formulation. The evolution of wrinkling and its eventual localization are simulated successfully using a FE shell model. The material is represented as an anisotropic elastic-plastic solid using the flow theory, while the models are assigned initial geometric imperfections with the wavelength of the wrinkling bifurcation mode. It is demonstrated that successful prediction of collapse requires very accurate representation of the material inelastic properties including yield anisotropies, and that as expected, the collapse curvature is sensitive to the imperfection amplitude and wavelength imposed. 相似文献
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The prediction and prevention of wrinkling have been challenging issues in sheet metal forming processes. In an effort to provide the design and process engineers a reliable and efficient tool in assessing the onset of flange wrinkling, an analytical model, based on the wrinkling criterion proposed by Cao and Boyce [1], is presented here. The critical buckling stress and wavelength as functions of normal pressure are calculated using a combination of energy conservation and plastic bending theory. The present results are in excellent agreement with those obtained from Cao and Boyce’s numerical approach which has demonstrated its excellent predictive capability by comparing the experimental study of a conical cup [1] and a square cup forming [2]. Additionally, the effects of the tension in the plane of sheet and material properties on the initiation of flange wrinkling are investigated. 相似文献
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内压支撑下薄壁管弯曲变形力学分析 总被引:3,自引:0,他引:3
管件内压弯曲又称为管件充液弯曲,具有减小截面畸变,延缓薄壁管内侧失稳起皱,提高弯曲成形极限等优点。支撑内压在其中起到了关键性的作用,对于环向和轴向的应力应变分量具有重要影响。采用塑性理论,对内压和弯矩共同作用下的薄壁管弯曲变形进行理论分析。考虑内压对微元平衡方程的影响,建立一个新的理论分析模型,通过求解非线性方程组,得到薄壁管应力应变的分布规律,定量分析内压对薄壁管应力应变的影响趋势。同时通过将有限元分析得到的应力应变分量的信息,与理论解进行对比发现,理论预测和模拟结果相符合,验证所建立的理论分析模型的可靠性。结果表明,轴向和环向应力随内压升高均大大提高,环向应变随内压升高线性递增,而厚向应变线性减小。 相似文献
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EFFECT OF UNEQUAL DEFORMATION IN DEVELOPMENT OF ADVANCED PLASTIC PROCESSING TECHNOLOGIES 总被引:1,自引:0,他引:1
Yang He Xian Feijun College of Materials Science Engineering Northwestern Polytechnical University Xi''''an China 《机械工程学报(英文版)》2002,15(1):79-82
0 INTRODUCTION(Plastic processing technology can make materials shape and improve their properties. Under the situation of rise of international market competition, knowledge economy, and green manufacturing, plastic processing technology is faced with a challenge from mark, information, environment, and resources. Therefore, plastic processing technologies are required to develop towards the 21st century in order to produce parts with light weight, high strength, high precision, high effi… 相似文献
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H. Li H. Yang K. Liu 《The International Journal of Advanced Manufacturing Technology》2013,65(9-12):1303-1318
Bent tubular parts have attracted extensive applications in various industries due to high strength and light weight. However, tube bending (TB) is a strong knowledge-based tri-nonlinear physical process with multi-tool constrains, and minor inappropriate tooling design may induce several failures such as wrinkling, over thinning (even fracture), section distortion, and springback. In response to the urgent requirements of the tubular products with mass quantities and diverse specifications, we proposed an integrated methodology for robust and loop tooling design for TB by combining several technologies such as knowledge-based engineering, parametric CAD modeling, and parametric finite element modeling. Via the spreadsheet formatted rules extracted from different sources of knowledge, several sequences are automatically conducted to preliminarily avoid the wrinkling and section distortion, including the selection of tooling sets (bend die, clamp die, pressure die, wiper die, or mandrel die with flexible balls), the determination of die dimensions, 3D modeling of both external and internal tools, die assemble, and the selection of material type for each die. Then, by importing the feature parameters of tools into 3D-finite elements models, the bendability of tube under previously designed multi-tool constraints is quantitatively evaluated in terms of multi-defect, and the springback can be calculated to redesign the bending die by radius reduction. The design variables are only tube diameter, wall thickness, bending radius, bending angle, and material types. The tool design system is then implemented, and the reliability and efficiency of the system are experimentally verified in the aviation industries regarding several practical bending cases with different specifications and tubular materials. 相似文献