一种陶瓷脆性材料动态本构参数的计算反求方法

提出了一种利用反射波和透射波响应反求陶瓷脆性材料动态材料本构参数的方法.通过数值模拟分析哑铃形试件在加载和测试中能有效地消除动态应力波的应力集中,从而得到有效的动态压缩强度,因此该文利用哑铃形得到的可靠反射波和透射波响应做反求输入信息.应用遗传算法,根据反射波和透射波响应反求材料本构参数,避免了应力波效应和应变率效应解耦的问题,不必分离结构响应和材料响应,从而快速地获取参数.     

一种脆性材料动态本构损伤参数的计算反求方法

提出一种利用平板撞击的瞬态速度剖面响应反求陶瓷脆性材料的动态本构损伤参数的方法.通过数值模拟再现平板撞击试验中的正平面波在飞片、样品和窗口材料中的传播情况,分析了"样品/窗口"界面瞬态速度剖面响应与材料参数之间的映射关系,进而建立了用响应反求本构参数的反问题,且通过一些数值试验验证该反问题是适定的.基于平板撞击速度剖面响应反求的方法,为快速地获得高应变率下一些传统方法难以测定出的本构参数提供新途径.     

确定地基固结过程中材料参数的反分析法

结合有限单元法和数学规划法提出一确定地基固结过程中材料参数的反分析法。该法可以根据固结过程中的位移值和孔隙水压力值反算地基土的弹性系数、泊松比以及渗透系数。文中通过一些算例对该法进行了验证。     

JC本构参数反求中的自适应微型遗传算法

提出自适应微型遗传算法,使种群的交叉和变异概率可以根据适应度的大小自我调节,该算法经过了测试函数的测试。本文以JC(Johnson-Cook)本构模型描述的高导无氧铜材料为例,集成运用该算法和有限元方法来反求JC动态本构参数。结果表明,该方法提高了收敛速度和搜索效率,能够快速地获取参数。     

混凝土材料动态本构参数的分阶段计算反求技术

基于不同应变率下的分离式Hopkinson压杆实验,提出了一种混凝土材料动态本构参数的分阶段反求方法。该分阶段反求方法中,结合不同的实验模型对未知参数进行敏感性分析,并依据敏感程度对参数进行分类,每类参数对应于1组实验,再利用反求方法分阶段确定各类参数,在每一类参数反求时均将上一次反求结果作为已知条件。结果表明,该分阶段反求方法充分利用所有实验的测量响应信息,能快速获取混凝土本构中较难确定的关键参数,为参数的确定提供了一种有效的途径。     

基于反求的医疗辅助弹性护具应变能的计算

提出了基于反求工程的医疗辅助弹性护具的设计方法,推导出弹性护具应变能的计算公式. 设计中应用网格简化技术减少扫描数据以及参数化技术将三维转化为二维进行计算,减少了网格点应变能的计算量,提高了设计效率. 应用应变能密度函数建立起弹性护具几何尺寸与应变能之间的关系,为医生或患者科学地选择医疗护具提供了依据.     

Johnson-Cook材料模型参数的实验测定

介绍一种通过Hopkinson拉伸实验、圆筒爆炸试验和计算机仿真来确定Johnson-Cook材料模型中相关常数的方法．     

基于最小二乘的工程结构边界载荷反求误差消减方法

机械装备工程结构强度计算和疲劳寿命预测等都需要准确获知结构的工作或边界载荷。然而,由于土壤和砂石等工作介质的切削及铲运等精确阻力模型难以建立,以及机械装备动力传动过程中的摩擦等损耗难以精确计算,导致准确获得装备工作结构的边界载荷非常困难。依据圣维南原理,采用有限元法建立复杂结构中局部结构应变与其边界载荷的关系,对边界载荷反求过程中误差来源和范围进行了分析和估计,提出了基于最小二乘法的复杂结构局部边界载荷误差消减方法。对推耙机横梁结构的边界载荷进行分析,验证了该误差消减方法的有效性。     

基于变形场测量数据主元压缩的模型参量反求方法

利用主元分析法对数字图像相关技术所测结构变形信息进行数据压缩,并进一步用于力学模型未知参量的反求计算。首先,为降低数字图像相关技术所测庞大数据的应用成本,提出利用主元分析法对结构表面变形场数据进行压缩,实现在保留结构表面变形信息主要特征的前提下显著降低数据量的目的;其次,针对压缩后的数据建立了基于最小二乘法的力学模型参量反求模型,并利用高斯牛顿法进行求解;最后,以具体算例从计算精度、收敛速度和抗噪性等方面验证了数据压缩对模型参量反求的效果。研究结果表明,所提方法在显著降低使用数据量的前提下,能够有效提高力学模型参量反求计算的收敛速度,特别是对于包含多个模型参数的反求问题,具有较高的精度和较好的稳定性。     

一种基于特征值反求的复合材料层合板波动特性的近似修改方法

采用一种特征值反求形式的方法用来近似层状复合板的波动特性修改。通过敏感度分析,确定层合板中能最显著地改变结构波动特性的结构参数为设计变量。采用二阶泰勒展式近似特征值和特征频率相对于设计变量的改变率。计算了不同结构变化时的色散特性,并与精确计算结果进行了比较。结果证明本方法对于层状复合板波动特性修改的近似是可行并且有效的。     

任意边界形状的二维刚塑性成形过程的无网格分析方法

将无网格伽辽金方法引入到塑性成形过程模拟,结合刚塑性材料假设,提出了基于刚塑性理论的无网格伽辽金方法,推导了其刚度矩阵方程和求解列式,给出了模具形状任意的二维塑性成形问题摩擦力边界条件的施加方法以及无网格方法应用于任意边界形状的塑性成形问题时的坐标转换关系,建立了无网格方法模拟任意边界形状的塑性成形问题的步骤,并编写了相应的计算程序。应用建立的方法对典型塑性成形过程进行了无网格方法分析,通过与刚塑性有限元方法分析结果的比较,验证了本文所建立方法的可行性。     

金属板料成形的快速有限元分析

研究了基于形变理论的金属板形成快速有限元分析的方法－反向方法,并实现了计算程序。通过实例的计算结果和实验以及增量方法进行了比较,表明此方法能够定性地分析成形工件中的变形情况。由于计算速度快、建立分析模模型简单,此方法可用于设计早期估计零件的可成形性,以及部分工艺参数对形的影响。     

Investigation of advanced strain-path dependent material models for sheet metal forming simulations

Sheet metal forming processes often involve complex loading sequences. To improve the prediction of some undesirable phenomena, such as springback, physical behavior models should be considered. This paper investigates springback behavior predicted by advanced elastoplastic hardening models which combine isotropic and kinematic hardening and take strain-path changes into account. A dislocation-based microstructural hardening model formulated from physical observations and the more classical cyclic model of Chaboche have been considered in this work. Numerical implementation was carried out in the ABAQUS software using a return mapping algorithm with a combined backward Euler and semi-analytical integration scheme of the constitutive equations. The capability of each model to reproduce transient hardening phenomena at abrupt strain-path changes has been shown via simulations of sequential rheological tests. A springback analysis of strip drawing tests was performed in order to emphasize the impact of several influential parameters, namely: process, numerical and behavior parameters. The effect of the two hardening models with respect to the process parameters has been specifically highlighted.     

A Newton type iterative inverse method for heat-conduction problems

An inverse problem for identification of the coefficient in heat-conduction equation is considered. After reducing the problem to a nonlinear ill-posed operator equation, Newton type iterative methods are considered. The implicit iterative method is applied to the linearized Newton equation, and the key step in the process is that a new reasonable a posteriori stopping rule for the inner iteration is presented. Numerical experiments for the new method as well as for Tikhonov method and Bakushikskii method are given, and these results show the obvious advantages of the new method over the other ones.     

A Newton type iterative method for heat-conduction inverse problems

An inverse problem for identification of the coefficient in heat-conduction equation is considered. After reducing the problem to a nonlinear ill-posed operator equation, Newton type iterative methods are considered. The implicit iterative method is applied to the linearized Newton equation, and the key step in the process is that a new reasonable a posteriori stopping rule for the inner iteration is presented. Numerical experiments for the new method as well as for Tikhonov method and Bakushikskii method are given, and these results show the obvious advantages of the new method over the other ones.     

An inverse problem formulation of the immersed-boundary method

We formulate the immersed-boundary method (IBM) as an inverse problem. A control variable is introduced on the boundary of a larger domain that encompasses the target domain. The optimal control is the one that minimizes the mismatch between the state and the desired boundary value along the immersed target-domain boundary. We begin by investigating a naïve problem formulation that we show is ill-posed: in the case of the Laplace equation, we prove that the solution is unique, but it fails to depend continuously on the data; for the linear advection equation, even solution uniqueness fails to hold. These issues are addressed by two complimentary strategies. The first strategy is to ensure that the enclosing domain tends to the true domain, as the mesh is refined. The second strategy is to include a specialized parameter-free regularization that is based on penalizing the difference between the control and the state on the boundary. The proposed inverse IBM is applied to the diffusion, advection, and advection-diffusion equations using a high-order discontinuous Galerkin discretization. The numerical experiments demonstrate that the regularized scheme achieves optimal rates of convergence and that the reduced Hessian of the optimization problem has a bounded condition number, as the mesh is refined.     

覆盖件冲压仿真中的网格形态优化技术

覆盖件冲压仿真计算模型中网格密度分布的合理性与网格单元形态的优劣,对仿真结果的准确性有很大的影响.提出了一种改进的全四边形网格细分方法,使网格的密度分布适于覆盖件冲压分析计算要求,可保证细分后网格的协调性,并将算法推广以处理非结构化四边形网格和三角形四边形混合网格的细分.提出的网格细分策略,有助于提高细分后网格的质量.提出了适用于细分后四边形网格和非结构四边形网格的拓扑形态优化操作,可有效的提高网格模型的形态质量.     

爆轰产物状态方程的水下爆炸反演理论研究

由于水下爆炸过程中爆轰产物的信息以水中压缩波形式向外传递,本文旨在探讨如何利用水下爆炸试验数据确定爆轰产物的状态方程。相较于常规圆筒试验,水下爆炸试验具有装置简单成本低、装药尺寸限制少、测定压力范围更广的特点,更适用于大药量或非理想炸药的现场测试。本文从水中冲击波轨迹和波后压力时程曲线出发,发展了由冲击波及其波后流场还原水气界面的逆特征线算法,以及根据水气界面确定爆轰产物状态方程的遗传算法。与水下爆炸正演结果对比,发现逆特征线法可以较准确地还原水气界面的位置和压力参数,有效压力下限可达2 MPa,远低于圆筒试验的测试下限0.1GPa。根据水气界面的反演结果,遗传算法也能稳定地优化JWL方程参数,8种常用炸药的等熵衰减压力误差在爆压至0.01 GPa的区间内都小于3%。结果表明,利用本文的逆特征线算法和遗传算法,理论上可以反演出压力范围较宽、准确性较高的爆轰产物状态方程。     

Numerical study for influences of material parameters on hydrostatic bulging of metal sheet

In this paper, the influences of various material parameters, the hardening exponent (n), the rate sensitivity (m). the thickness anisotropy parameter (R) and the index M in the Hosford and Hill yield function, on the hydrostatic bulging of a circular clamped sheet of ductile metal materials are analysed by introducting a rigid-viscoplastic finite element method. By numerical studies, an empirical relationship within the average limit thickness strain – ₃ ^* and the material parameters (n andm) is obtained. Besides, it has been found that the influences of surface shapes of the yield function on the average limit thickness strain can be reflected by the Barlat'sP value which represents the effects ofR andM values.This work is supported by the National Natural Science Foundation and Natural Science Foundation of the Youth of China.     

基于有限元分析的特征值反问题求解的逆摄动方法

本文研究特征值反问题的求解方法,根据广义特征值反问题理论和有限元法的特点,以转子系统平面梁单元有限元模型结构分析的特征值反问题求解为例,给出一种新的逆摄动方法,给出了本逆摄动法较完整的理论基础,给出了其逆摄动参数的显式计算公式及相应的取值方法,本逆摄动法也可推广到其他单元类型的有限元模型特征值反问题的求解。