基于滑移线理论计算板料弯曲变形力

板料弯曲变形力一般都是根据材料力学方法计算,而滑移线法常用作分析理想刚塑性材料平面变形问题。通过对板料弯曲变形区应力状态分析,利用滑移线理论建立滑移线场,并根据滑移线场推导变形区的应力分布方程。基于变形区应力分布方程计算板料弯曲变形力,进一步对变形力进行修正,修正后的计算结果与根据弯矩求得的结果吻合较好。     

粗糙平板间平面镦粗的滑移线场的建立——用数学解析法和计算机辅助设计

通过分析粗糙平板间平面镦粗时金属的流动规律，用数学解析法和计算机辅助设计相结合，确定该塑性变形体内各点最大剪应力的轨迹，即建立滑移线场。     

滑移线速度场的分析及切削模型的建立

本文分析了滑移线速度场速度方程的三种不同表示方法：直角坐标法、极坐标法和滑移线法．并运用滑移线的理论，建立带限制前刀面刀具切削时滑移线场的切削模型，推导出其速度方程．     

粗糙平板间平面镦粗的移线场的建立：用数学解析法和计算机辅助设计

通过分析粗糙平板间平面镦粗时金属的流动规律，用数学解析法和计算机辅助设计相结合，确定该塑性变形体内各点最大剪应力的轨迹，即建立滑移线场。     

柱塞体变形模式转换的成形工艺分析与研究

在柱塞体复合挤压成形过程中,金属的流动方式为过渡方式,其金属的流动规律非常复杂,对柱塞体零件成形的三种不同工艺方案进行了数值模拟分析.并运用滑移线场理论对其流动规律进行了讨论,给出了塑性变形的滑移线场和速端图,预测了金属的流动方向、流动速度等.指出了成形工艺缺陷产生的原因,确定了正确的工艺方案.     

切削过程绝热剪切带的滑移线场研究

根据滑移线场理论,对于切削过程绝热剪切带内的塑性变形,提出了一种四边界五区域滑移线场模型,并给出了相应的速矢图。定义了包括刀屑摩擦接触边界、刚塑性边界、准刚塑性边界和准自由边界的绝热剪切带滑移线场边界。根据不同的应力边界条件、绝热剪切带内滑移线场应力变化趋势和滑移线场几何形状分析,将绝热剪切带滑移线场划分为五个区域。采用矩阵算子法确定了滑移线场模型的几何参量,给出了求解绝热剪切带内应力分布的方法。采用提出的绝热剪切带滑移线场模型,对于正交切削FV520(B)不锈钢材料,分析计算了由于绝热剪切引起的导裂角随刀具前角和切削速度的变化规律。通过已加工表面几何形貌实验观察,印证了导裂角与已加工表面质量的相关性。     

体心立方近β钛合金循环形变中的平面滑移行为

对单相体心立方近β钛合金在不同加载应力以及循环周次下进行压缩疲劳试验,对循环过程中的范性应变机制进行分析,通过研究滑移模式、显微组织演化等对早期微裂纹萌生的影响以及观察疲劳前后位错组态的演化,分析了循环形变特征与表面滑移模式之间的内在联系。结果表明:单相近β钛合金经纯压缩循环形变后出现出典型的平面滑移特征以及表面应力集中现象,循环形变后的位错湮灭、退孪晶和孪晶界结构简化造成的局部应力改变是导致应力集中滑移带出现以及平面滑移机制的重要因素。     

应变强化对022Cr17Ni12Mo2奥氏体不锈钢显微组织和力学行为的影响

采用电液伺服万能试验机、X射线衍射仪、金相显微镜和透射电子显微镜,研究了应变强化对022Cr17Ni12Mo2奥氏体不锈钢微观组织和力学行为的影响。结果表明：前期预应变强化过程中,材料没有发生相变,形变孪晶数量的增加使材料的屈服强度和硬度得到大幅提高,但塑性有所降低,发生形变孪晶诱发强度效应。随着预应变量的增大,应变强化能力减弱,瞬变应变有所降低,位错的滑移模式发生转变,从单系滑移和平面滑移向多系滑移和交滑移转变。     

摩擦约束不完全变分不等原理及其微粒群优化解法

利用不完全变分不等原理,将摩擦约束纳入问题的能量泛函,同时放松体积不可压缩的约束条件ii=0,用罚因子处理体积应变。实际算例表明,不完全变分不等原理不但能计算速度场,而且能直接计算变形力,且所得到的变形力比滑移线场结合极值方法获得的解析解更接近试验结果。在有限变形情况下,仍能得到变形力的理想结果。同时,利用微粒群优化方法,直接求解变分问题的能量泛函,避开了变分不等式的求解困难问题。针对优化求解过程中出现解的随机性,利用求平均值方法,使求解过程稳定,有效地改善了求解结果,并由此扩展了微粒群算法的应用领域。     

锥形凸台成形的一种叠加滑移线场力学模型

分析了锥形凸台在不同体积成形工艺中的成形机理，基于模块化思想将锥形凸台的成形过程划分为挤压成形与角部充满两个特征时段；将上述两个特征时段的滑移线场力学模型有机联结，构建了锥形凸台成形过程的一种叠加滑移线场力学模型；介绍了叠加滑移线场力学模型的应力场与变形力的求解方法。该模型丰富了金属体积成形过程的特征单元库，可套用于局部成形的应力场与变形力求解，实现局部成形的模具优化设计。     

Fully plastic analyses of unequally notched specimens in bending

This paper proposes slip line fields for bending of unequally notched specimens in plane strain, that have a sharp crack in one side and a sharp V-notch in the other side. Depending on the back angle, two slip line fields are proposed, from which the limit moment and crack tip stress fields are obtained as a function of the back angle. Excellent agreement between slip line field solutions with those from detailed finite element limit analysis based on non-hardening plasticity provides confidence in the proposed slip line fields. One interesting point is that, for the unequally notched specimen, the difference between the crack tip triaxial stress for tension and that for bending increases significantly with the increase in the back angle. This suggests that such a specimen could be potentially useful to investigate the crack tip constraint effect on fracture toughness of materials. In this respect, the possibility of designing a new toughness testing specimen with varying crack tip constraint is discussed.     

光弹性贴片中用宽条带法分离主应变的研究

在光弹性贴片法中，通常利用剪应力差法和斜射法来分离主应变。对于应变梯度不大的平面可以采用条带法来分离主应变，但其应用性较差。本文研究用宽条带法来分离主应变，使条带法得到了进一步的推广和应用，从而为解决复合材料、陶瓷材料等新型材料的表面应力测定问题提供了一种新的研究方法。     

Plastic deformation analysis of strain-rate sensitive materials under plane strain conditions

The two-dimensional plane strain equation of plastic flow in accordance with the Levy-Mises constitutive relation is expressed in terms of stream functions of complex variables. Expressions for the stress, strain-rate and velocity are derived, assuming the stream function in the forms of both the summation and product of conjugate flow functions, for plastic flow in a nonlinear viscous (strain-rate sensitive) medium. The plastic states are also derived using a mixed mode solution expressed in terms of non-separable, independent conjugate complex variables. Application of the summation form solution is illustrated through the block indentation problem. Calculations are made on the effect of variation of the strain-rate sensitivity exponent on the contact stress. The predicted behavior of the contact stress suggests the possibility of the development of a specially instrumented plane strain block indentation test for the rapid determination of the strain-rate sensitivity of real materials. By reducing the results of the indentation of a perfectly plastic material it is found that the contact stress is uniform and the external load is constant. The stress on the contact surface obtained using the present analysis is identical to that available from a slip line solution to the problem.     

Modelling the plane strain compression test to obtain constitutive equations of aluminium alloys

Hot plane strain compression tests on 1050, 1198, 3003 and 3004 aluminium alloys have been conducted. Based on these experiments and on a set of internal type constitutive equations for hot working, the values of the parameters in the constitutive functions are determined. The constitutive equations proposed here, with the constitutive functions and material parameters associated, accurately reproduce the basic tests. The procedure used to fit the material parameters is improved, in comparison with classical slip line analysis, by using a finite element modelling of the plane strain compression test. It is demonstrated that accurate plane strain or three-dimensional large strain finite element analysis can be used to correct the friction and lateral spread effects. Furthermore, it is demonstrated from comparison with the experimental observations that microstructural parameters can be accurately determined from numerical modelling. The constitutive equations and finite element procedure proposed here can be useful for obtaining an improved analysis of hot rolling of aluminium alloys.     

A solution to plane strain extrusion by the upper bound approach and the weighted residuals method

The analysis of plane strain extrusion through wedge shaped dies is based in a general kinematically admissible velocity field coupled with the method of weighted residuals. The expressions of velocity and strain rate are derived analytically and the resulting fields for several extrusion ratios are obtained by minimizing the upper bound power with respect to free parameters introduced in the inlet and outlet boundaries. The stresses are calculated from a stress function, using the strain rate field and the boundary conditions, by the least squares method.The results are compared with the complete solution obtained by the slip line field.The technique is shown to give satisfactory results and can be applied to more complex metalforming processes, as it requires only modest computing time and resources.     

Force plane diagrams for slip line fields of indirect type for end-extrusion

The paper presents some force plane diagrams for slip line fields for end-extrusion through square dies with slipping friction on die and container faces. These diagrams are constructed using a computational procedure based on a nonlinear optimization technique. Diagrams are presented for different friction conditions on the die and the container faces and these are compared with the results from the slip line field analysis.     

双向载荷下威布尔应力参量的研究

以往对双轴断裂的研究多采用线弹性断裂力学参量且限于弹性材料，局部法理论提出了威布尔应力参量，威布尔应力作为度量脆性断裂概率的参量已广泛采用。为研究双向载荷对威布尔应力的影响，文中开发了威布尔应力计算程序并进行考核验证，以威布尔应力为参量，以ASTM A36钢中心裂纹板为研究对象，结合有限元分析方法，研究二维裂纹问题在不同双向载荷比下威布尔应力参量的变化规律，从而得到双向载荷对脆断概率的影响。计算结果表明，平面应力状态下，双向载荷对威布尔应力和脆断概率基本上没有影响；而在平面应变状态下，威布尔应力和脆性断裂概率随双向载荷比增大而增大。     

Precursors of Global Slip in a Longitudinal Line Contact Under Non-Uniform Normal Loading

This article describes the mechanism of precursor events; the mechanism was determined through an experiment and simulation by considering non-uniform normal loading. In the experiment, real-time observations of a contact zone were performed using a longitudinal line contact of PMMA specimens (i.e., a slider on a stationary base block) under a total normal load of 400 N. Partial propagations of the detachment front were considered as precursor events, and it was found that non-uniform normal loading influences the occurrence frequency of the precursor events and the increasing rate of the propagation length. In the simulation, the time evolution of a multi-degree-of-freedom system with Coulomb friction was studied. The model considered in the simulation comprised multiple masses serially connected by linear springs on a stationary rigid plane. By regarding the precursor in the experiment to correspond to a partial slip (i.e., simultaneous slip of some of the masses) in the simulation, the influence of non-uniform normal loading on the precursor events can be explained to a certain extent. Additionally, it was found that the apparent static friction coefficient (i.e., the ratio of the maximum tangential load to the total normal load) could be lesser than the real static friction coefficient due to the residual strain in the slider.     

Blank development and the prediction of earing in cup drawing

The article deals with the prediction of blank shapes using the method of plane strain characteristics. In one case the material is assumed to be an incompressible, non-hardening, isotropic solid, and ideal blank shapes are developed when deep drawing prismatic cups. The significance of the study is that the resulting slip line field pattern does not violate the Hencky equations. The earing behaviour when deep drawing cylindrical cups from circular disks has also been predicted based on a particular form of anisotropy which allows for four fold symmetrical earing. The technique permits the blank shape to be calculated throughout the entire drawing operation, and demonstrates how the ears develop.     

An approximate load estimation method for three dimensional metal forming problems

Slip line field solutions have been presented only for plane strain and axisymmetric problems in the literature. In fact due to the very nature of the differential equations for the slip line field theory, it has never been possible to apply the theory to three dimensional problems. In this paper a three dimensional solution is presented for metal forming processes using an approximate load estimation method based on the slip line field theory. This has been done by extending the axisymmetric solution and modifying it in order to apply it to the three dimensional case. Using the idea of stream lines and stream surfaces, the deforming region has been defined. A generic stream surface was developed which was a ruled surface with a three dimensional shape. The slip line field theory could only be applied to flat surfaces in the case of axisymmetric problem. Here using some assumptions an approximate load estimation method was developed so that it was applied to the three dimensional stream surfaces and hence to the deforming region under considerations. This method was applied to the forward extrusion of elliptical sections from round billets. Experiments were also carried out by authors to verify the theory. The results obtained from the new formulations were compared to the results obtained from other analytical, numerical and experimental methods. It was shown that there exist good agreements between these results.