高精度应变式引伸计的研究

大量程引伸计的弹性元件处于大变形工伯状态，引伸计的非线性矛盾较突出。实验研究表明，某些结构的弹性元件，其线性度与结构的组合尺寸有关，存在着最佳线性条件，根据最佳条件和对夹持机构的考虑，设计了两种新型高精度引伸计。     

新型三向力传感器弹性元件的设计

应用弹性力学理论,对一种新型三向力传感器的弹性元件进行分析和探讨,给出了设计板柱式弹性元件各参数的通用方法及计算公式     

电子秤中平行梁弹性元件的性能分析

本文对电子秤中平行梁弹性元件的性能用有限元方法和测试技术进行了计算和分析，得到了满意的结果     

电子秤中平行梁弹性元件的性能分析

本文对电子秤中平行梁弹性元件的性能用有限元方法和测试技术进行了计算和分析，得到了满意的结果     

正弦波纹扁球壳的非线性强迫振动

波纹壳是传感器弹性元件的一类重要形式,也是精密仪器仪表弹性元件中的一类重要形式。由于波纹壳形状复杂、参数众多、厚度薄,对其进行非线性分析非常重要同时也是十分困难的。本文考虑一种在传感器弹性元件中有重要应用价值的正弦波纹浅球壳体,将这种壳体视为结构上的圆柱正交异性扁球壳,根据Andryewa的思想,分别得到了正弦波纹壳径向、环向在拉伸、弯曲下的等价的四个各向异性参数;建立了正弦波纹扁球壳的非线性强迫振动微分方程;得到了正弦波纹扁球壳非线性强迫振动的共振周期解及幅频特性曲线。     

橡胶弹性支座动态承载特性及其影响因素分析

基于复刚度理论,采用正交实验法,对风力发电机橡胶弹性支座进行动态性能实验,研究载荷频率、载荷幅值、预载荷诸因素对弹性支座动态性能的影响规律. 实验结果表明,橡胶材料的动态性能与载荷频率和幅值具有显著的相关性. 频率增加,橡胶弹性元件的弹性刚度和阻尼因子明显增大;幅值增加,弹性刚度减小,阻尼因子却逐渐增大. 对实验数据进行方差分析,表明载荷频率对动态性能的影响最大,其次是载荷幅值,预加载因素影响非常有限.     

磁流变弹性体自调谐式吸振器及其优化控制

本文研制了一种基于磁流变弹性体的自调谐式吸振器,它利用磁流变弹性体这种新型智能材料作为吸振器的弹性元件和阻尼元件,通过外加磁场控制磁流变弹性体的剪切模量来改变吸振器的固有频率,实现吸振器的移频.并将遗传算法改进移植到吸振器,对其进行优化控制.实验结果表明,这种遗传算法具有全局搜索和快速收敛的特点,它能使吸振器快速找到吸振器减振效果最佳点,并且经过优化控制的磁流变弹性体自调谐式吸振器在移频范围内具有很好的减振效果,减振效果最高可达25dB.     

波纹圆板的特征关系式

波纹圆板在精密仪器的灵敏弹性元件中起着很重要的作用。然而,这种弹性元件的理论研究至今还很不充分。造成这种状况的主要原因是波纹圆板本身形状复杂,参数很多,特别是大挠度非线性微分方程组在数学上求解极困难。以往的理论计算大致可分为两类。一类是采用壳体的大挠度方程来求解,如文献[1]用方法求得了浅正弦     

工程中一类非线性弹性元件--碟形弹簧和膜片弹簧的研究进展

本文较详尽地论述了工程中广泛应用的一类非线性弹性元件--碟形弹簧(Belleville 弹簧)和膜片弹簧的研究概况,力学理论在此类问题中的应用现状,并指出了今后有待进一步研究的方向与领域....     

磁流变弹性体自调谐式吸振器及其优化控制

本文研制了一种基于磁流变弹性体的自调谐式吸振器，它利用磁流变弹性体这种新型智能材料作为吸振器的弹性元件和阻尼元件，通过外加磁场控制磁流变弹性体的剪切模量来改变吸振器的固有频率，实现吸振器的移频。并将遗传算法改进移植到吸振器，对其进行优化控制。实验结果表明，这种遗传算法具有全局搜索和快速收敛的特点，它能使吸振器快速找到吸振器减振效果最佳点，并且经过优化控制的磁流变弹性体自调谐式吸振器在移频范围内具有很好的减振效果，减振效果最高可达25dB。     

Non-linear and failure behaviour of spotwelds: a “global” finite element and experiments in pure and mixed modes I/II

The paper deals with joint element model used in crashworthiness simulations. The first part of the paper is dedicated to the formulation of a new “global” finite element for spotweld modelling. The mechanical behaviour of the joint is elastic–plastic type and damage is taken into account to model the failure of the welded area. The second part of the paper concerns a new experimental procedure for joint strength analysis in pure and mixed modes I/II and for joint model characterisation. Experiment is based on Arcan principle and results are compared to open literature. In the last part of the paper, the parameters of the new joint model are identified using experiments and used for several shapes of spot-welded specimens. The model predicts reasonably the elastic–plastic part of the response but is unable to predict the post-peak response observed especially in the case of pure shear.     

弹塑性问题参数二次规划分析的隐式算法

传统的二次规划算法求解弹塑性问题时一般要经过对问题的线性化,如对屈服条件的一阶近似展开等,这在一定程度上会造成数值解的误差。为此,本文提出一种改进的策略,引入迭代与规划算法相结合的技术对问题进行处理,算法收敛平稳迅速,在大步长荷载增量下使算法的精度大大提高。由于本文的算法属于隐式算法,因而也就弥补了原二次规划算法求解弹塑性问题时只有显式算法的不足,从而达到了对原算法的进一步完善。     

Surface Impedance Tensor and Green’s Function for Weakly Anisotropic Elastic Materials

Recently Fu and Mielke uncovered a new identity that the surface impedance tensor of any anisotropic elastic material has to satisfy. By solving algebraically a matrix equation that follows from the new identity, we derive an explicit expression for the surface impedance tensor, which is correct up to terms linear in the components of the anisotropic part of the elasticity tensor of the material in question. From the well-known relationship between the surface impedance tensor and the Green’s function for infinite space, we obtain an explicit expression for the Green’s function, which is correct up to terms linear in the components of the anisotropic part of the elasticity tensor.      

Determining the rubber-cord moduli under plane stress conditions

A numerical-experimental approach to determine the elastic rubber-cord properties under plane stress conditions is described. The experimental part of this approach consists of uniaxial tension tests performed with two-ply rubber-cord samples; these experiments allow one to obtain the effective longitudinal Young’s moduli for various cord angles. Such samples correspond to a breaker that forms the basis of the running part of a radial tire. The numerical part of this approach consists of the following two stages: (i) determining the averaged in-plane elastic moduli and (ii) solving the corresponding inverse problem to determine the rubber and cord elastic moduli. The approach is illustrated by several examples. All computations were performed in the framework of the linear elasticity theory; the effects of nonlinearity and viscosity are not taken into account, which is reasonable for the operating range of tire deformations.     

Partial Uniqueness and Obstruction to Uniqueness in Inverse Problems for Anisotropic Elastic Media

We consider the inverse problem of identifying the density and elastic moduli for three-dimensional anisotropic elastic bodies, given displacement and traction measurements made at their surface. These surface measurements are modelled by the dynamic Dirichlet-to-Neumann map on a finite time interval. For linear or nonlinear anisotropic hyperelastic bodies we show that the displacement-to-traction surface measurements do not change when the density and elasticity tensor in the interior are transformed tensorially by a change of coordinates fixing the surface of the body to first order. Our main tool, a new approach in inverse problems for elastic media, is the representation of the equations of motion in a covariant form (following Marsden and Hughes, 1983) that preserves the underlying physics.In the case of classical linear elastodynamics we then investigate how the type of anisotropy changes under coordinate transformations. That is, we analyze the orbits of general linear, anisotropic elasticity tensors under the action by pull-back of diffeomorphisms that fix the surface of the elastic body to first order, and derive a pointwise characterization of parts of the orbits under this action. For example, we show that the orbit of isotropic elastic media, at any point in the body, consists of some transversely isotropic and some orthotropic elastic media. We then derive the first uniqueness result in the inverse problem for anisotropic media using surface displacement-traction data: uniqueness of three elastic moduli for tensors in the orbit of isotropic elasticity tensors. ^†Partially supported by an MSRI Postdoctoral Fellowship. Research at MSRI is supported in part by NSF grant DMS-9850361. This work was conducted while the first author was a Gibbs Instructor at Yale University. ^‡Partially supported by an MSRI Postdoctoral Fellowship, and by NSF grant DMS-9801664 (9996350).     

弹性结构横向弯曲振动传递率 1)

振动的传递是振动理论的重要组成部分。在振动力学的教材中,对于离散结构的积极隔振和消极隔振,振动的传递率已有明确的定义。由于弹性结构的振动不止通过一个点传递,尚需讨论如何定义传递率。通过两端弹性支撑梁,定义了弹性结构横向弯曲振动的各支撑端点的振动传递表达式,及支撑点合力的振动传递率表达式。结果显示三种传递率可能存在较大的差别。建议将这一基本振动理论问题收录于教材,并早日进人本科生和研究生的教学课堂。     

2D FE–DEM analysis of tractive performance of an elastic wheel for planetary rovers

We have been developing a simulation program for use with soil–wheel interaction problems by coupling Finite Element Method (FEM) and Discrete Element Method (DEM) for which a wheel is modeled by FEM and soil is expressed by DEM. Previous two-dimensional FE–DEM was updated to analyze the tractive performance of a flexible elastic wheel by introducing a new algorithm learned from the PID-controller model. In an elastic wheel model, four structural parts were defined using FEM: the wheel rim, intermediate part, surface layer, and wheel lugs. The wheel rigidity was controlled by varying the Young’s Modulus of the intermediate part. The tractive performance of two elastic wheels with lugs for planetary rovers of the European Space Agency was analyzed. Numerical results were compared with experimentally obtained results collected at DLR Bremen, Germany. The FE–DEM result was confirmed to depict similar behaviors of tractive performance such as gross tractive effort, net traction, running resistance, and wheel sinkage, as in the results of experiments. Moreover, the tractive performance of elastic wheels on Mars was predicted using FE–DEM. Results clarified that no significant difference of net traction exists between the two wheels.     

A thermomechanically coupled viscoelastic cohesive zone model at large deformation

A new viscoelastic cohesive zone model is formulated for large deformation conditions and within a fully coupled thermomechanical framework. The model is suitable for the simulation of a wide range of problems especially for polymeric materials. It can capture viscoelastic crack propagation as well as energy dissipation due to this process. Starting from the principles of thermodynamics, a 3D finite element formulation is derived for a fully coupled simultaneous solution of the thermal field and the deformation field. The viscoelastic model is constructed by extending an elastic exponential traction separation law using a simple rheology. The viscous part of the tractions is postulated to have the same characteristic length as the elastic part and that they are related by a single material parameter. A Newtonian dashpot is used to describe the evolution of the viscous separation. Furthermore, thermal effects are accounted for using temperature expressions in both the traction laws and the viscosity of the dashpot, and using a heat conduction law across the interface. The model is implemented within an implicit finite element code and the internal variable is calculated using an internal iteration. Different numerical examples are used to verify the model and a comparison with experimental data shows a satisfactory agreement.     

Finite multiplicative plasticity for small elastic strains with linear balance equations and grain boundary relaxation

This paper is concerned with the formulation of a phenomenological model of finite elasto-plasticity valid for small elastic strains for initially isotropic polycrystalline material. As a basic we assume the multiplicative split of the deformation gradient into elastic and plastic part. A key feature of the model is the introduction of an independent field of 'elastic' rotations which eliminate the remaining geometrical nonlinearities coming from finite elasticity in the presence of small elastic strains. In contrast to micro-polar theories an evolution equation for is presented which relates to making use of a new device found by the author to perform the polar decomposition asymptotically. The model is shown to be invariant under both change of frame and rotation of the so called intermediate configuration. The corresponding equilibrium equations at frozen plastic and viscoelastic configuration constitute then a linear, elliptic system with nonconstant coefficients which makes this model amenable to a rigorous mathematical analysis. The introduced hysteresis effects within the elastic region are related to viscous elastic rotations of the grains of the polycrystal due to internal friction at the grain boundaries and constitute as such a rate dependent transient texture effect. The inclusion of work hardening will be addressed in future work. Received March 07, 2002 / Published online February 17, 2003 RID="*" ID="*"Communicated by Kolumban Hutter, Darmstadt