拉深变形力理论计算模型研究

基于对冲压成形加工中拉深工序变形区材料的应力、应变特点的分析, 针对现有拉深力理论计算公式中忽略了材料厚度变化及加工硬化两个因素的影响的问题, 利用金属塑性成形理论中的主应力法, 考虑这两个影响因素,建立和提出了描述拉深力理论计算的一个新的数学模型, 并用铝板材料的拉深试验进行了验证.     

拉深变形力理论计算模型研究

基于对冲压成形加工中拉深工序变形区材料的应力、应变特点的分析, 针对现有拉深力理论计算公式中忽略了材料厚度变化及加工硬化两个因素的影响的问题, 利用金属塑性成形理论中的主应力法, 考虑这两个影响因素,建立和提出了描述拉深力理论计算的一个新的数学模型, 并用铝板材料的拉深试验进行了验证。
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非回转对称拉深中法兰材料变形规律的研究

非回转对称拉深成形过程中 ,压料面上法兰材料是变形的主体 ,直接影响到拉深成形性。在大量试验及测量计算的基础上 ,分析了矩形盒件拉深过程中压料面上法兰各部分材料的变形规律 ;指出法兰曲边材料向直边流入所带来的变形缓和效应与应力分布及其应变成分比的共同作用 ,是使矩形盒局部拉深比显著增大的重要原因。     

螺旋台阶零件多步成形过程数值模拟

鉴于零件对材料增厚及表面质量没有严格要求,采用无压边拉深来完成零件螺旋台阶面的成形,不仅模具结构简单,而且材料利用率高.围绕零件成形难点部位,以特征点的形式详细分析了拉深成形过程中特征区域的应力、应变、厚度和成形极限等模拟结果.在分析拉深工序的基础上,进一步对零件进行多工步模拟分析.结合等效塑性应变、厚度分布及成形极限等信息分析了其它工步作用过程中的变形特点.通过数值模拟结果与实际冲压结果的对比,验证了多工步数值模拟结果的有效性.     

非回转对称拉深中法兰材料变形规律的研究

非回转对称拉深成形过程中，压料面上法兰材料是变形的主体，直接影响到拉深成形性。在大量试验及测量计算的基础上，分析了矩形盒件拉深过程中压料面上法兰各部分材料的变形规律；指出法兰曲边材料向直边流入所带来的变形缓和效应与应力分布及其应变成分比的共同作用，是使矩形盒局部拉深比显著增大的重要原因。     

非回转对称拉深成形的有限元模拟

阐述钣料拉深成形有限元模拟的基本理论及关键技术,对非回转对称拉深成形的典型零件—矩形盒进行了成形模拟,分析其材料流动规律和应力应变状态,并着重分析钣坯形状对矩形盒成形性的影响     

蠕变条件下梯度材料球罐应力应变行为分析

推导内外压载荷下梯度材料球罐与时间相关行为的解析公式,在此基础上分别分析弹性梯度分布和蠕变梯度分布对球罐蠕变应力应变的影响.计算结果表明弹性参量的梯度变化只对蠕变初始阶段应力分布有影响,当蠕变应力达到稳态值后,球罐中的应力水平将只取决于蠕变参量的梯度分布;而蠕变应变分布则同时与材料的弹性和蠕变两种梯度变化有关.就降低梯度材料球罐蠕变应力应变值进行探讨,为梯度材料球罐的结构设计和优化提供基本的理论依据.     

轿车发动机罩外板拉深成形数值模拟研究

通过对冲压成形过程进行数值模拟,可以预测成形过程中的材料流动趋势和应力应变分布,从而实现工艺参数的优化.基于数值模拟技术,对汽车发动机罩外板的拉深成形过程进行了研究.分别采用方板毛坯模型和剪角板毛坯模型对发动机罩外板的拉深成形过程进行分析,结合数值模拟结果和理论分析,得到了更为合理的板料尺寸,同时得出了相关的拉深成形工艺参数,该研究对实际生产具有一定的指导意义.     

金属板材拉深过程的数值模拟研究

针对金属板料拉深过程中材料变形十分复杂的问题,建立了适合钢板拉深过程的三维有限元模型,采用所建立的有限元模型对板料拉深过程进行了数值模拟研究,研究了板料拉深过程中的变形情况,并对拉深过程中冲压力和金属板料的应力分布进行了分析。数值模拟结果与实际拉深过程中材料的变形过程一致,验证了三维有限元模型的正确性。     

非回转对称拉深成形中压料面上摩擦的研究

在大量拉深试验的基础上,结合法兰、矩形盒底部产生的应力应变状态以及载荷的变化情况,分析了相对凸模半径较大的薄板非回转对称成形过程中,压料力对拉深载荷以致断裂载荷所产生的复杂影响。指出法兰曲边部的滑动摩擦因数对于成形过程中的压料力相当敏感,并且对法兰部和断裂危险部材料的应力应变状态产生直接影响。特别是在面压较高的成形后期,由于法兰部润滑效果恶化,导致拉深载荷增大、成形极限降低。     

The influence of plastic-strain-induced anisotropy modeled as combined isotropic-kinematic hardening in the tension-torsion straining problem (I)

In order to express the plastic-strain-induced anisotropy at finite deformation of ductile metals, a combined isotropic-kinematic hardening model which is a particular form of anisotropic hardening, is an appropriate model because of its simple and convenient mathematical formulation. This paper examines the applicability of the model in the computation of general straining problems by performing a numerical tension-torsion test. The anisotropy generated by plastic flow is expressed by back stress. The evolution equation contains form invariant isotropic functions of plastic strain rate and back stress and also involves the spin associated with induced anisotropy. A numerical fitting procedure allowed us to show that circules modeled as combined isotropic-kinematic hardening around the loading nose are in good agreement with the experimental yield loci taken from the nonproportional straining. The measure of checking the applicability of combined isotropic-kinematic hardening by analyzing the total stress history has also been demonstrated by simulating an extrusion process using the finite-element method. From the computed results. the angle variations between the principal stress direction and the material direction, initially axial, were observed if they are small enough in the active plastic deformation region to ensure that the stress point will move along the part of the yield locus exhibiting nearly uniform curvature. This indicated that stress and deformation can be predicted with combined isotropic-kinematic hardening as long as the loading is not reversed.     

材料参数对汽车覆盖件冲压成形性能影响的数值模拟

使用基于动力显示算法的板料成形非线性有限元分析软件eta/DYANFORM对一个典型的汽车覆盖件零件冲压成形过程进行了数值模拟,从大量的计算结果中,研究三个重要的材料力学性能参数即屈服强度σs、应变强化指数n和厚向异性系数r对最终零件冲压成形性能的影响。在分析软件的后处理器中观察板料的厚度变化、总拉深力、板料的最大变形位移和沿冲压方向的最大应力,并作出了相应的曲线,最后根据所作曲线的变化得到了材料性能参数影响板料冲压成形性能的有关结论。     

Radial flow simulation of drawing and extrusion of rigid/hardening materials

A combination of rigorous relations (drawn from continuum plasticity) with pragmatic engineering arguments, leads to new approximate formulae for the stress fields and velocity profiles in some basic steady forming processes. The latter include drawing and extrusion in two (plane strain) and three (axisymmetric) dimensions.The theory derived here accuonts for wall friction and, more important, is not restricted by any particular choice of the strain hardening function. The applicability of the present analysis is limited, though, to dies of sufficiently small angles, taper and wall friction.Confidence in our results is gained by comparing them with a few consistent approximations obtained from available exact solutions in theoretical plasticity.The simplicity and usefulness of the new formulae is demonstrated by specifying the results for rigid/power-hardening materials, and evaluating the drawing limits associated with the occurrence of necking and separation at the exit of the die.It is also shown that the present approximate solution can be used for rapid evaluation of the stress field in drawing of rigid/perfectly-plastic composite (bimetallic) sheets and tubes.     

Influence of hardening rule on prediction of cyclic plasticity in pressurized thin tubes subjected to cyclic push-pull

The paper considers the cyclic plastic behaviour of a thin-walled tube subjected to steady internal pressure and cyclic reversed axial push-pull. Tubes under such a loading combination are known to exhibit continued strain growth in the hoop direction. The steady-state behaviour of the tube is investigated using a number of hardening rules within the framework of time-independent plasticity theory. Isotropic hardening and Prager kinematic hardening are considered first and shown to yield no strain growth at the steady state. When a kinematically hardened yield surface is assumed to translate in the direction of the stress rate vector, considerable steady-state strain growth is predicted in the hoop direction. Consideration of two-surface plasticity theory yields also large steady-state strain growth. Closed-form analytical expressions are derived for growth rates and ranges of cyclic plasticity for all hardening rules considered. Contours of strain growth are plotted for practical ranges of primary and secondary stresses using representative material properties. Comparison with limited test data indicate that the predicted steady growth rate is larger than about four times observed rate.     

液压扭矩板手的复杂三维问题的数值分析

运用三维非线性有限元分析方法，分析了一种液压扳手的三维应力和应变，得到了应力应变精确的数值解，发现了该结构的应力分布水平有较明显的不均匀，并探讨了圆角对扳手强度的影响，为进一步的优化设计提供了理论依据。     

An elastoplastic analysis of flange wrinkling in deep drawing process

The onset of flange wrinkling of a deep drawing cup is analyzed as an elastoplastic bifurcation problem. The flange is modeled as an elastoplastic annular plate subject to axisymmetric radial tension along its inner edge. As observed in the laboratory as well as practical industrial applications, aluminum alloy sheets usually wrinkle in the plastic range. Therefore, the critical condition governing the onset of elastoplastic wrinkling is formulated within the context of the general bifurcation theory. A closed-form solution for the critical drawing stress is developed based on an assumed nonlinear plastic stress field and the deformation theory of plasticity. The theory properly accounts for the plastic anisotropy of the aluminum sheets and the critical drawing stress at the onset of wrinkling is also compared against the one employing the flow theory of plasticity. The predicted critical bifurcation stress and the wave numbers are compared to those obtained by Senior's one-dimensional theory. It is demonstrated that there is a strong dependency of the critical bifurcated stress at the onset of wrinkling on the shear stress induced on the flange. The effects of flange width, drawing ratios, material properties, strain hardening on the onset of wrinkling are investigated. The differences between the present theoretical approach and Senior's theory are emphasized.     

Deep drawing of a thin-walled hemisphere

A model of deep drawing of a thin-walled hemisphere with a flat bottom from a plane blank by a rigid punch, considering the work hardening and wall thickness variation is developed. Elastic bending and von Mises membrane rigid-plastic strain with different friction coefficients at the punch and die contact boundaries are considered. The computational model determines the distribution of the wall thickness and the material work hardening along the shell generatrix, the drawing force versus punch displacement relation, and the critical parameters of the process in which some defects are probable.