Consideration of geometric nonlinearity in rigid-plastic finite element formulation of continuum elements for large deformation

A rigid—plastic finite element formulation for the continuum elements employing the geometric nonlinearity during an incremental time step is presented. In sheet metal deformation, the displacement for each step is considerably large even though the effective strain increment is very small. For such large displacement problems, geometric nonlinearity must be considered. In the elastic—plastic finite element using continuum elements, general incremental formulations to include the geometric nonlinearity are available. However, in the conventional rigid—plastic finite element analysis using continuum, elements, the geometric nonlinearity has not been considered properly during an incremental time step. In this paper, in order to incorporate geometric nonlinearity to rigid—plastic continuum elements during a step, the convected coordinate system is introduced. To show the stability of strain distributions by the effect of geometric nonlinearity according to incremental step size, two sheet metal forming processes, stretching and deep drawing process, are analysed with various step sizes. Then the computed results using the derived equation are compared with those obtained without considering geometric nonlinearity.     

利用反演技术求解消声器内部结构参数

应用流体动力学理论研究消声器内部流场,建立消声器有限元模型,确定给定结构参数求解出口气流流速的正问题;在正问题基础上,将出口气流速度作为消声器结构参数变化时的响应,运用反演技术求解消声器内部结构参数,并将反演问题转化为最优问题,采用遗传算法和梯度法相结合的混合优化算法进行优化,得到了较理想的仿真实验结果,验证了反演技术应用于消声器设计的可行性.     

Computational characterization of micro- to mesoscopic deformation behavior of semicrystalline polymers

In the present study, we clarify the micro- to mesoscopic deformation behavior of semicrystalline polymers by the finite element homogenization method. The crystalline plasticity theory using a penalty method for the inextensibility constraint in the chain direction and the nonaffine molecular chain network theory were used to the representation of the deformation behavior of crystalline and amorphous phases, respectively, in the composite microstructure of a semicrystalline polymer. Various directional tensions are applied to the two-dimensional plane-strain unit cell model of a composite microstructure. The results reveal a highly anisotropic deformation behavior caused by the rotation of the chain direction and lamella interface, which depends on tensile direction and manifests as substantial hardening/softening in the early stage of deformation. The mesoscopic structure of a semicrystalline polymer was modeled using a voronoi polygon comprised of composite microstructures with different lamella interface directions. The initial isotropy of the response of the mesoscopic scale was verified. Due to their interaction with the surrounding grains, the individual grains of the mesoscopic scale show a conservative response as compared with that of the unit cell, and a very nonuniform response depending on the location of the respective grain is observed; these are typical of the mesoscopic response of semicrystalline polymers.     

液动压悬浮抛光中磨粒与工件表面作用的数值模拟研究

针对液动压悬浮抛光固-液两相流中固相磨粒与工件表面撞击的过程中,对磨粒以不同的速度和不同的角度撞击工件表面后残余应力沿工件深度方向的分布规律进行了研究,利用ABAQUS软件建立了单颗磨粒撞击工件表面的三维有限元模型。对磨粒流撞击工件表面时的速度场进行了输出,利用PFC/3D软件建立了磨粒流撞击工件表面的三维离散元模型。研究结果表明:随着撞击角度和速度的增大,在工件表层形成的压应力场会增大,沿深度方向残余应力值急剧下降,磨粒流中磨粒间的撞击对磨粒撞击工件表面的速度场影响不大。     

晶须长径比对树脂基复合材料力学行为影响的数值模拟

在单向晶须增强树脂基复合材料的轴对称模型和已有研究成果基础上,利用有限元分析方法,研究该类复合材料中晶须长径比的变化对材料整体力学行为的影响.结果表明:晶须长径比对晶须应力作用明显大于对基体的影响;晶须的长径比h/r≤30时,随着晶须长径比的增大,发生在晶须端部处的集中应力急剧增加;但当长径比h/r＞30时,长径比的进一步增加对集中应力影响不大;随着晶须长径比的增大,界面剪切应力减小,分布曲线下移;但当长径比h/r＞30时,长径比的进一步增加对剪切应力影响不大;随着晶须长径比的增加,复合材料的拉伸强度逐渐增大.     

弹性有限元应力线性化及迭加原理

介绍了弹性实体有限元应力线性化处理方法,并在此基础上举例说明应力分量迭加原理。     

油压机盖板结构设计及优化分析

基于力学模型初步确定盖板结构几何参数,建立三维模型导入有限元软件HYPERMESH进行静载荷应力分析。对于结构应力集中处引发的应力奇异问题,结合弹性理论分析应力奇异产生的原因,提出减小圆环压板厚度、设置肋板圆角过渡及增加撑脚等措施来优化分析模型。优化结果显示应力集中程度减弱,最大等效应力减小,压力传递均匀,整体重量降低9.5%。实际使用过程中满足要求,验证了理论分析的正确性,为肋板焊接类结构设计及分析提供参考。     

Computational evaluation of strain-rate-dependent deformation behavior of rubber and carbon-black-filled rubber under monotonic and cyclic straining

The molecular chain network model for elastic deformation behavior and the reptation theory for viscoelastic deformation behavior are used to derive a constitutive equation for rubber. The new eight-chain-like model contains eight standard models consisting of Langevin springs and dashpot to account for the interaction of chains with their surroundings. Monotonic and cyclic deformation behavior of rubber with relaxation under different strain rates have been examined. The results reveal the roles of the individual springs and dashpot, and the strain rate dependence of materials in the monotonic and cyclic deformation behaviors, particularly softening and hysteresis loss, that is, the Mullins effect, occurring in stress-stretch curves under cyclic deformation processes. The validity of the results is checked through comparison with experimental results. The deformation behaviors of a plane strain rubber unit cell containing carbon-black (CB) under monotonic and cyclic straining are investigated by computational simulation using the proposed constitutive equation and homogenization method. The results reveal the substantial enhancement of the resistance of CB-filled rubber to macroscopic deformation, which is caused by the marked orientation hardening due to the highly localized deformation of rubber. The role of strain rate sensitivity on such characteristic deformation behaviors as increases in the resistance to deformation, hysteresis loss, and the effects of the distribution morphology and the volume fraction of CB on the deformation behavior is clarified. The increases in the volume fraction and in the aggregation of the distribution of CB substantially raise the resistance to deformation and hysteresis loss.     

切削加工表面残余应力的理论预测

对零件已加工表面的形成过程进行分析，提出表面分离法的分析模型；自行研制了求解在移动载荷作用下的二维热弹塑性力学问题的有限计算软件－ＭＴＰｌａｓｔ；对切削的已加工表面残余应力进行理论预测，并与试验结果相比较，探讨残余应力的形成机理，为控制已加工表面的残余应力提供了理论依据。     

应用ABAQUS的膜式空气弹簧弹性特性仿真研究

以某乘用车悬架膜式空气弹簧为研究对象,建立空气弹簧的有限元分析模型。应用有限元分析软件ABAQUS对其垂向静态力学特性进行仿真分析。有限元数值计算结果与空气弹簧的垂向静态力学特性试验结果吻合度较高,证明了有限元数值计算方法的正确性。对膜式空气弹簧结构设计参数进行灵敏度分析,得出的结论是:气囊内压与帘线角是膜式空气弹簧静态力学特性的最敏感参数。     

冲压座椅强度与疲劳有限元仿真

结合力学基本概念,对某冲压座椅的失效原因进行了仿真分析。首先应用圣维南原理等力学概念对冲压座椅几何模型进行简化,然后结合计算力学理论采用商业软件对座椅进行底板强度和靠背疲劳仿真分析。仿真结果表明,冲压座椅装配孔的改进改善了局部区域的应力分布。     

硬化深度对港口起重机车轮接触应力的影响

在建立港口起重机轮轨接触的三维实体模型的基础上，通过商业软件ANSYS建立了车轮材料不做硬化、硬化10mm、硬化25mm、全部硬化4种有限元模型；计算了这4种模型点接触和线接触2种轮轨接触模型的接触应力和接触面积，并与相应的赫兹理论值对比。通过对不同车轮硬化处理方式的接触应力和接触面积的比较，分析硬化处理对车轮接触的影响。     

基于有限元法的半轴强度和疲劳寿命计算

传统的根据经验公式校核半轴强度的方法存在计算时间长、计算精度低等缺点,利用有限元法可方便的在半轴三维建模、有限元网格划分的基础上进行半轴强度分析,同时可在强度分析的基础上进行半轴寿命的计算.通过建立半轴的三维模型,划分网格,在有限元的理论基础上对半轴进行强度校核,同时结合有限疲劳寿命设计理论进行疲劳寿命的计算,得出汽车半轴的应力和使用疲劳寿命.     

焊接接头残余应力的计算机模拟

应用有限元方法，采用有限元分析软件ANSYS，用计算机模拟了焊接接头残余应力的大小和分布，模拟结果和实验结果比较吻合，证明了这种方法具有重要的实用价值。     

基于相变与收缩耦合的1Cr12焊缝冷却动态力学行为

建立了相变体积应变与混合相力学性能的固态相变模型,同时考虑随动硬化与相变塑性的影响,研究了各因素对1 Cr12钢焊缝冷却动态力学行为的影响规律.在此基础上,开展了焊接试验件纵向残余应力的验证试验,试验结果与模拟结果吻合良好.研究结果表明:马氏体相变的体积膨胀、力学性能变化以及塑性机制均对焊缝收缩的动态力学行为有一定的影...     

Numerical simulation of mold filling and deformation behavior in rheology forming process

Rheology forming is a novel semi-solid processing method, which is different from traditional mold forging and conventional casting processes. The rheological behavior of metallic alloys containing both solid and liquid phases investigated the low and high solid fraction ranges. Rheology forming has several obvious advantages including its excellent forming ability resulting in the easier production of complex work pieces, more flexibility in shaping pieces, and more compact inner quality because of its high pressure. This research paper presents the theory of the rheology forming process and the results of a finite element simulation of rheology forming for aluminum alloys. The algorithms for both a single- and two-phase flow model, developed for this study, gives the die filling patterns, velocities, temperatures and solid fractions of the rheology material during the rheology process. To calculate the velocity and temperature fields, the respective governing equations corresponding to the liquid and solid regions were used. Therefore, the respective numerical models that take the co-existing solid and liquid phases within the rheology material into consideration have been developed to predict the defects of parts manufactured by the rheology process. This study compares of the velocity, temperature, and solid fraction between the single- and two-phase flow models. And, to predict the liquid segregation in the parts, the deviation of velocity between the liquid and solid regions in the two-phase flow model was analyzed.     

螺纹计算中有限元与经典力学的联合应用

针对某受力螺栓,先建立整个结构的有限元模型,用有限元方法计算出螺栓所受的外力,然后用该计算结果和螺栓的已知条件,通过经典力学对其强度进行校核。通过有限元与经典力学的联合应用,得到了该螺栓较为精确的强度校核结果。     

大型封头热拉深力学机理及仿真研究

研究了大型封头热拉深过程中的有限元仿真方法及其力学机理。结合宏观塑性理论中的能量法建立了大型封头热拉深过程中的拉深力计算理论模型,建立了大型封头热拉深过程的有限元模型,通过与某大型封头的实际测试结果的比较,验证了所建立的理论模型与有限元模型的准确性,从而为研究大型封头热拉深过程中有效的工艺控制提供了方法和理论依据。     

轮轨接触应力数值计算方法

为了得到轮轨接触应力较精确的数值解,分别采用Hertz接触理论模型、传统有限元模型及改进有限元模型求解轮轨接触应力,并从计算精度和计算时间方面对3种模型进行了比较.结果表明,有限元模型较Hertz接触理论模型更能反映轮轨接触的实际情况,改进的有限元模型在允许的计算精度范围内可以大大提高计算效率;轮轨最大接触应力发生在轮轨表面以下约2.5 mm的位置,呈弧形分布,并随轴重的增加而增大,高应力区宽度增大,离初始接触位置一定距离处的钢轨表面出现高应力区.