微平面模型与经典混凝土理论模型的比较

针对在混凝土非线性分析时所采用的宏观本构模型中,没有考虑混凝土软化阶段或考虑不当,以及在多轴受力情况下宏观模型不能很好地模拟混凝土受力状态的问题,基于微平面理论,利用MATLAB编写混凝土材料的非线性本构关系程序,从理论和计算结果两方面与经典的基于应力张量及其不变量的本构模型进行比较.比较结果表明,在弹性变形阶段,经典理论模型和微平面模型计算结果与试验结果无明显区别;在非弹性变形阶段,经典理论模型与微平面模型有较大的差异,后者与试验结果吻合较好.微平面理论在混凝土三向受力和软化阶段更能准确地描述混凝土材料本构关系,且本构关系更简单、清晰.     

基于SiPESC平台用户材料子程序的UMAT实现

针对复杂环境和加载条件下的材料本构模型,参照Abaqus所提供的用户材料子程序UMAT接口,实现基于SiPESC平台弹塑性分析功能的UMAT本构模型插件封装及调用.采用Ｃ++面向对象程序设计方法编制inp文件读取功能插件,实现Abaqus计算模型向SiPESC平台数据库的导入.将不同UMAT单独编译成动态库,同时利用工厂设计模式,实现不同材料本构模型的动态替换和调用.该设计模式可方便添加本构模型,具有一定的通用性、开放性和可扩展性.数值算例的验证表明基于SiPESC平台的UMAT的有效性.     

用自适应变步长BP神经网络求高分子材料的本构关系

本文阐述了人工神经网络基本原理,研究分析了BP神经网络模型的缺陷并提出了优化策略。建立了求高分子材料本构关系的三层前馈反向传播神经网络模型,并作了多次不同的泛化性测试。实例分析表明,自适应变步长BP神经网络在收敛速度及稳定性方面都有很好的效果,可应用于求高分子材料本构关系。     

通用转子材料的弹塑-损伤力学耦合数值建模

依据国产通用转子钢材料30Cr2MoV的力学试验及疲劳试验数据,依托大型非线性有限元软件MSC Marc,利用该软件的用户自定义接口,以混和强化理论为基础建立该材料的弹塑性-损伤力学耦合本构关系模型,最后采用增量有限元数值方法予以实现.     

弹塑性梁系统的动力学特性研究

研究了弹塑性梁系统的动力学特性.从弹塑性梁的非线性本构关系出发,同时考虑几何非线性,用虚功原理建立单个梁的动力学变分方程,利用假设模态法离散.在此基础上引入运动学约束关系,建立了弹塑性梁系统的刚-柔耦合动力学方程.对重力作用下的柔性单摆和双摆数值仿真结果表明,塑性应变引起横向变形绝对值增大和横向振动振幅衰减,在角加速度突变时塑性效应最为显著.     

计算资源受限MEC中任务卸载与资源分配方法

移动边缘计算(MEC)通过将计算中心下沉至网络边缘,可以有效服务于任务计算.然而,MEC拥有的计算资源并不是无限的,这带来了诸多问题.文章针对计算资源有限MEC系统中的计算卸载,分析了最大化MEC总收益的卸载与资源分配联合优化问题.首先通过Stackelberg模型来描述MEC与用户之间的交互,使用差异化定价策略增加对卸载的约束,然后将卸载问题转化为二元背包问题,最后,通过改进模拟退火算法分配计算资源,并迭代得到最优方案.仿真结果表明,所提方案可以最大程度提高用户卸载数量,并有效地提高了MEC系统的收益.     

形变体仿真中材质本构模型的应用与设计综述

本构模型是形变体仿真中最重要的因素之一,现有的基本的本构模型的应力应变关系具有一定的局限性,形变行为比较单一.近年来,很多研究工作探讨如何设计更加复杂并满足设计师需求的材质模型.本文将材质模型分为三类,传统的具有单一材质属性的均质材质、具有复合结构的非均质材质以及根据基本材质模型通过编辑材质参数和结构以及编辑形变行为的材质模型.此外,我们梳理近年来材质本构模型方面的研究成果,分类总结相关技术及其优缺点,最后讨论并指出形变体仿真中本构模型应用与设计领域主要的技术挑战和需要进一步探索的方向.     

基于Abaqus的光学胶动态力学行为分析

黏胶的动态力学性能对终端产品可靠性的影响越来越重要.基于Abaqus的超弹性和黏弹性的本构模型定义光学胶的动态力学参数,用Abaqus/Explicit对静态压缩和落球试验进行仿真分析,通过与实际试验结果的对比验证仿真分析结果.结果表明,在准静态到高应变率的范围内,采用超弹性和黏弹性的本构模型可以准确描述光学胶的动态力学行为.     

LS-DYNA用户自定义材料模型开发与验证

当DYNA材料库中不包含所需要的材料模型时,用户可以自定义材料,生成新的DYNA求解器,进行问题的求解。其中需要采用数值算法求解本构方程组时,半隐式的图形返回算法体现了其良好的使用性。通过对一个简单的理想弹塑性模型的求解公式的推导,进一步阐述了这种方法以及编写材料程序的基本过程,并采用单单元模型验证了所编写程序的正确性。     

材料中应变率力学性能测试数据处理与表征方法

针对材料的中应变率力学性能测试数据,为数据处理与本构表征设计专用的分析软件。给出了载荷测量和应变测量方法,梳理了从测试数据到本构参数所历经的数据处理流程和方法,按照逻辑程序和功能模块化设计,基于MATLAB GUI平台编制了数据处理软件。利用该软件处理了S580B合金钢的测试数据,得到3种动态本构模型对应的应变强化参数和应变率敏感性参数,结果表明,Johnson-Cook模型相对于Cowper-Symonds模型和塑性随动模型更适合反映S580B合金钢的动态力学性能,拟合曲线和试验结果较为吻合。利用该专用软件,处理手段和过程完整可追溯,本构参数更容易获得,很大程度地提高了中应变率动态力学性能测试工作的效率和规范性,为冲击动力学数值仿真提供了重要的数据支持。     

一种快速构建/替换模型的通用实时仿真系统

提出一种综合运用实时工具箱(RTW)与Windows实时扩展子系统(RTX)构建实时仿真系统的方案。采用实时动态链接库(RtDll)形式封装由RTW生成的模型代码,实现由成熟软件快速建模并由自定义VC工程快速封装的模型。根据仿真过程设计可动态加/卸载仿真模型的仿真引擎,兼顾模型与引擎的解耦和实时交互,实现模型输入输出信息的及时传递和模型参数的在线调整。该系统在运行结果与Simulink一致的同时提高了仿真实时性,适用于快速建模与实时仿真实验。     

Experiment and hydro-mechanical coupling simulation study on the human periodontal ligament

In this paper, a new method involving an experiment in vivo and hydro-mechanical coupling simulations was proposed to investigate the biomechanical property of human periodontal ligament (PDL). Teeth were loaded and their displacements were measured in vivo. The finite element model of the experiment was built and hydro-mechanical coupling simulations were conducted to test some PDL's constitutive models. In the simulations, the linear elastic model, the hyperfoam model, and the Ogden model were assumed for the solid phase of the PDL coupled with a model of the fluid phase of the PDL. The displacements of the teeth derived from the simulations were compared with the experimental data to validate these constitutive models. The study shows that a proposed constitutive model of the PDL can be reliably tested by this method. Furthermore, the influence of species, areas, and the fluid volume ratio on PDL's mechanical property should be considered in the modeling and simulation of the mechanical property of the PDL.     

鸟体动力学本构模型参数反演的并行优化技术

研究鸟体本构模型的动力学过程,是飞行器抗鸟撞,保证飞行安全的重要问题。由于鸟体模型参数难确定,为得到准确而合理的鸟体参数,在已知鸟体本构模型的前提下,采用并行优化技术对本构参数进行反演。将鸟撞平板的试验结果与数值仿真结果的相对误差平方和最小作为目标函数,将待反演的鸟体参数作为设计变量,在同一撞击速度范围内,将鸟撞不同靶板分为不同工况构造并行优化反演模型。把反演得到的鸟体参数代回到鸟撞平板仿真模型中检验,经与试验结果对比,效果较好,表明采用的并行优化技术是有效的、可靠的。并行优化反演技术的实现为更准确的获取鸟体参数提供了新的思路和方法,也为提高飞行器抗鸟撞设计研究提供有益参考。     

Approximating thermo-viscoelastic heating of largely strained solid rubber components

Mechanically induced viscoelastic dissipation is difficult to compute when the constitutive model is defined by history integrals. The computation of the viscous energy dissipated is in the form of a double convolution integral. In this study, we present a method to approximate the dissipation for constitutive models in history integral form that represent Maxwell-like materials. The dissipation is obtained without directly computing the double convolution integral. The approximation requires that the total stress can be separated into elastic and viscous components, and that the relaxation form of the constitutive law is defined with a Prony series. A numerical approach often taken to approximate a history integral involves interpolating the history integral’s kernel across a time step. Integration then yields finite difference equations for the evolution of the viscous stresses in time. In the case when the material is modeled with a Prony series, the form of these finite difference equations is similar to the form of the finite difference equations for a Maxwell solid. Since the dissipation rate in a Maxwell solid can be easily computed from knowledge of its viscous stress and the Prony series constants (spring-dashpot constants), we computationally investigated employing a Maxwell solid’s dissipation function to couple thermal and large strain history integral based finite element models of solid rubber components. Numerical data is provided to support this analogy and to help understand its limitations. A rubber cylinder with an imbedded steel disk is dynamically loaded, and the non-uniform heating within the cylinder is computed.     

Tonpilz型压电陶瓷超声传感器的设计

超声传感器是一种电声转换器件,其敏感元件压电陶瓷控制传感器的主要性能。设计了一种谐振频率为140 kHz的Tonpilz型压电陶瓷超声传感器,从压电方程入手,建立了不同的理论模型,对等效网络法和有限元法2种不同的设计方法进行了比较。相应的试验表明:有限元法的分析结果直观明了、建模快捷、分析准确,其误差可控制在5%以内。设计研制的Tonpilz型传感器工艺简单、造价低廉、性能稳定。     

集成电路高层故障模型间关系分析方法

集成电路的测试变得日益重要,传统的门级测试虽然效果很好,但是随着电路规模的增大而面临着测试时间太长的困境．高层测试可以很好地缓解测试时间过长的问题,但最大的困难是缺少恰当的故障模型．通过对高层故障模型与门级固定型故障模型间关系可以建立高层故障模型的评估规则。在该规则下可以再对高层故障模型间关系进行分析,以确定彼此间的覆盖关系．归纳模型间的互相覆盖以确定彼此是否包含,这有助于对高层故障模型进行评估,寻找能够对应逼近门级固定型（stuck-at）故障模型的高层故障模型序列,该模型序列有望指导新的测试生成．最后,以对ITC99中标准时序电路的实验来说明该理论方法．     

Effect of load/unload process on friction/stiction and durability of head-disk interface

 Effect of various operating parameters viz. load/unload speed, disk speed, ramp height, and disk dynamics on load/unload performance, friction/stiction and durability of a head-disk interface (HDI) were studied. Load/unload performance was evaluated using acoustic emission signals and friction force measurements. The load/unload performance was found to be better for higher load/unload durations, lower disk speeds and higher ramp heights. The effect of ramp height was studied for two different slider suspension designs. A slider suspension with `A' type suspension design performed well for higher ramp heights. The slider with `B' suspension design was not affected by a change in ramp height. Disk dynamics studies indicated how strongly HDI can be affected by disk vibrations and supported the effect seen by varying ramp heights. Durability tests revealed that the HDI deteriorated faster for lower ramp heights for a slider with `A' type suspension design than for the slider with `B' type suspension design. Received: 22 February 2002/Accepted: 20 June 2002     

Concrete model with normality and sequential identification

To facilitate numerical finite element analysis, it is desirable to endow the constitutive model with normality, associatedness, continuity, convexity and absence of corners. Although these mathematical conditions represent only crude approximations of the actual behavior of concrete, it is of interest to find the best possible constitutive model which meets these conditons. This is one objective of the present paper. The second objective is to develop a model which permits a simple identification of material parameters from test data. The material parameters need not be obtained by simultaneous nonlinear optimization of the fits of all data. Rather, they are obtained in sequence through a precisely defined procedure which involves solving two systems of linear equations. The model describes not only hardening but also post-peak softening under various triaxial stress states. The model agrees well with the available basic test data from monotonic loading tests.