共查询到17条相似文献,搜索用时 234 毫秒
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提出了一种改进的反向模拟法,以最终构型为研究对象,采用Euler坐标系,基于虚功原理获得有限元列式. 改进的反向模拟法采用了一种基于塑性流动理论的本构方程,可以充分考虑应变历史对塑性变形的影响. 为了避免流动理论应力更新算法过程中关于未知量\Delta\lambda 的非线性方程的求解,引入等效应力思想,无需Newton-Raphson迭代直接计算未知量\Delta \lambda . 盒形件的拉深实例中,传统的基于塑性形变本构方程的反向模拟法和改进的基于塑性流动本构方程的反向模拟法计算结果,分别与基于增量有限元法的正向数值模拟求解器LS-DYNA计算结果进行对比. 通过获得的坯料轮廓、成形极限图、等效应变分布、计算效率等的比较,验证了所提出的基于塑性流动理论本构模型的应力更新算法的有效性. 相似文献
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鉴于有限元算法不能有效地模拟侵彻过程所产生的金属碎片, 本文中基于三维自适应FE-SPH耦合算法的基本理论, 自主开发了模拟多层间隔金属靶侵彻问题的三维FE-SPH耦合计算程序。该程序采用四面体单元对多层间隔金属靶侵彻模型进行初始离散, 计算过程中, 当四面体单元等效塑性应变超过某一设定值时, 单元自动转化为SPH粒子, 并引入有限单元-粒子接触算法和耦合算法, 实现大变形和破碎区域采用SPH方法计算, 克服有限元法单元畸变存在的问题。多层间隔靶侵彻算例分析表明, 三维FE-SPH耦合计算程序采用等效塑性应变作为转化判据计算结果较稳定, 并且能够有效地再现侵彻过程中所产生的碎片, 能够模拟侵彻碎片对后层靶的毁伤效应。 相似文献
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板材多点成形过程的有限元分析 总被引:8,自引:0,他引:8
多点成形过程采用静力隐式格式进行数值模拟是比较合适的。本文建立了用于多点成形过程分析的静力隐式弹塑性大变形有限元方法 ,给出了对稳定迭代收敛过程效果较好的板壳有限单元模型、处理多点不连续接触边界的接触单元方法以及增量变形过程中应力及塑性应变计算的多步回映计算方法。基于这些方法编制了计算软件 ,应用该软件进行了矩形板的液压胀形过程及球形模具拉伸成形过程的有限元分析 ,数值计算结果与典型的实验结果及计算结果吻合很好。最后给出了球形、圆柱形目标形状的实际多点成形过程的数值模拟结果。 相似文献
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三维非均匀介质中弹性波传播的数值模拟 总被引:5,自引:1,他引:4
提出了一种三维非均匀介质中弹性波传播数值模拟的方法,文中称为三维格子法。该算法是二维格子法(一种二维非均匀介质中P-SV波传播的数值模拟算法)向三维非均匀介质情况的推广。在空间离散上该文方法与有限元方法类似,容许根据连续体的形状和介质分界面任意剖面网格,且自然满足自由表面边界条件。不同于常规有限差分法在各个节点上满足动力学微分方程,该算法通过满足各节点周围格子的整体平衡(积分平衡方程)来对问题进行求解,三维格子法所需的计算机内存及计算耗时与同阶精度的规则网格有限差分法相当。算例表明,该文提出的三维格子法具有较高的精度且可很好地模拟三维复杂形状地表对弹性波的反射和绕射。 相似文献
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提出了一种计算二维有限变形弹塑性摩擦接触问题形状设计灵敏度的算法. 采用主动
集策略和mortar方法处理接触边线上的约束条件. 在mortar接触边线的切线和法线方向上
采用相同的名义罚函数,提出基于名义罚函数的移动摩擦锥算法来正则化接触约束条件,发
展了一种新的二维多体有限变形摩擦接触算法. 在此基础上, 通过将离散形式的摩擦接触问题
控制方程对形状设计变量微分,得到了该路径相关问题的直接微分法解析设计灵敏度
计算格式, 其节点位移灵敏度方程在每个增量步不用迭代、直接求解. 与国际上现有
的二维多体有限变形摩擦接触问题的解析设计灵敏度算法相比,本算法不需分
解为法向和切向推导,表达式较简洁,便于编程实现. 数值算例验证了算法的精度
和有效性. 相似文献
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A quasi-three-dimensional shell element model, which can be effectively used to simulate the flanging and spring-back deformation,
is introduced into the independently developed CAE software, KMAS. In this model, a double surface contact algorithm, which
allows the gap between punch and die to change, and a spring-back treatment scheme based on finite element meshing are described.
And then the flanging and spring-back deformations of the retractor's kickstand of a railcar made of stamped thick metal plate
are numerically simulated. The simulation results of flanging deformation are compared with those of international commercial
software, PAM-STAMP, and experimental ones. Finally, a predicting scheme of spring-back quantily for this problem is given.
Project supported by the National Natural Science Foundation of China (No. 19832020) and the Ministry of Education of China. 相似文献
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A numerical approach to spherical indentation techniques for material property evaluation 总被引:1,自引:0,他引:1
In this work, some inaccuracies and limitations of prior indentation theories, which are based on experimental observations and the deformation theory of plasticity, are investigated. Effects of major material properties on the indentation load-deflection curve are examined via finite element (FE) analyses based on incremental plasticity theory. It is confirmed that subindenter deformation and stress-strain distribution from deformation plasticity theory are quite dissimilar to those obtained from incremental plasticity theory. We suggest an optimal data acquisition location, where the strain gradient is the least and the effect of friction is negligible. A new numerical approach to indentation techniques is then proposed by examining the FE solutions at the optimal point. Numerical regressions of obtained data exhibit that the strain-hardening exponent and yield strain are the two key parameters which govern the subindenter deformation characteristics. The new indentation theory successfully provides a stress-strain curve and material properties with an average error of less than 3%. 相似文献
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在粉末打印骨支架的工艺中,粘结剂的性质是影响骨支架质量的关键因素。采用分子动力学的模拟方法对三种常用高分子粘结剂的体系进行了构建和模拟,从微观分子层面研究了聚合物粘结剂PVP,PAM和PVA的部分性质,比如密度、内聚能及力学性能,并对三种粘结剂的性能参数进行了比较,对其内在关系进行了揭示。此外,还通过建立粘结剂与羟基磷灰石的界面相互作用模型,对三种粘结剂与羟基磷灰石的界面结合能进行了计算和比较,分析了影响高聚物粘结特性的根本原因。这一工作不仅对常用粘结剂的基本性质进行了预估,而且对骨支架粉末粘结工艺中粘结剂的选择提供了理论依据。 相似文献
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《International Journal of Plasticity》1999,15(7):687-720
A multiphase material is considered, which consists of a homogeneous elastic-plastic matrix containing a homogeneous statistically uniform random set of ellipsoidal elastic-plastic inclusions. The elastic properties of the matrix and the inclusions are the same, but the so-called “stress-free strains”, i.e. the strain contributions due to temperature loading, phase transformations, and the plastic strains, fluctuate. A general theory of the yielding for arbitrary loading (by the stress and by the temperature) is employed. The realization of an incremental plasticity scheme is based on averaging over each component of the nonlinear yield criterion. Usually, averaged stresses are used inside each component for this purpose. In distinction from this usual practice physically consistent assumptions about the dependence of these functions on the component's values of the second stress moments are applied. The application of the proposed theory to the prediction of the thermomechanical deformation behavior of a model material is shown. 相似文献
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《International Journal of Solids and Structures》2002,39(3):709-723
The problem of a tube under pure bending is first solved as a generalised plane strain problem. This then provides the prebifurcation solution, which is uniform along the length of the tube. The onset of wrinkling is then predicted by introducing buckling modes involving a sinusoidal variation of the displacements along the length of the tube. Both the prebuckling analysis and the bifurcation check require only a two-dimensional finite element discretisation of the cross-section with special elements. The formulation does not rely on any of the approximations of a shell theory, or small strains. The same elements can be used for pure bending and local buckling a prismatic beam of arbitrary cross-section. Here the flow theory of plasticity with isotropic hardening is used for the prebuckling solution, but the bifurcation check is based on the incremental moduli of a finite strain deformation theory of plasticity.For tubes under pure bending, the results for limit point collapse (due to ovalisation) and bifurcation buckling (wrinkling) are compared to existing analysis and test results, to see whether removing the approximations of a shell theory and small strains (used in the existing analyses) leads to a better prediction of the experimental results. The small strain analysis results depend on whether the true or nominal stress–strain curve is used. By comparing small and finite strain analysis results it is found that the small strain approximation is good if one uses (a) the nominal stress–strain curve in compression to predict bifurcation buckling (wrinkling), and (b) the true stress–strain curve to calculate the limit point collapse curvature.In regard to the shell theory approximations, it is found that the three-dimensional continuum theory predicts slightly shorter critical wrinkling wavelengths, especially for lower diameter-to-wall-thickness (D/t) ratios. However this difference is not sufficient to account for the significantly lower wavelengths observed in the tests. 相似文献
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基于非经典塑性理论和连续介质损伤力学,利用在一个特殊坐标系下基于椭球形孔洞模型得到的可考虑孔洞形状变化混合强化材料的损伤演化率得到了铁素体相的损伤本构方程,通过混合物理论利用铁素体和渗碳体相各自本构关系并考虑其几何特征得到了珠光体团的损伤本构模型。进而采用Hill自洽方法,得到了珠光体材料的宏观损伤本构描述,发展了相应的数值方法与程序。讨论了孔洞形状对材料损伤的影响,并对典型珠光体双相材料BS11在非对称循环加载史下的弹塑性响应特性进行了分析,得到了与实验较为一致的结果。 相似文献
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Experimental data from combined tension-torsion of thin walled tubes of annealed polycrystalline copper subjected to various non-proportionate loading, unloading and reverse loading paths are presented. The measurements are compared with predicted values from classical incremental theory of plasticity in terms of true stress and true strain and a recently developed incremental theory of plasticity by Bell in terms of nominal stress and nominal strain. These experimental data reveal that the plastic strain produced by the various proportionate and non-proportionate loading, unloading and reverse loading paths are in better agreement with Bell's incremental theory of plasticity as compared to classical incremental theory. 相似文献