镍钛形状记忆合金冲蚀磨损研究进展

介绍了材料的冲蚀磨损理论,主要包括微切削理论、薄片剥落磨损理论、变形磨损理论和二次冲蚀理论,分析了冲蚀磨损的影响因素。在综述N iTi合金冲蚀性能研究现状的基础上,对N iTi合金的冲蚀机制进行了分析,认为超弹性及超塑性(形状记忆效应)起到了决定性的作用,除此之外,加工硬化性能、耐疲劳性、马氏体变体的择优取向及自适应性对N iTi合金的冲蚀性能也起到了很大作用。总结了N iTi合金作为耐冲蚀材料在实际应用中存在的问题,为N iTi合金冲蚀性能的研究方向提出了建议。     

Modelling and simulation of the superelastic behaviour of shape memory alloys using the element-free Galerkin method

This paper is concerned with the application of the element-free Galerkin method to simulate the superelastic behaviour of shape memory alloys (SMA). The meshfree shape functions are derived from a moving least-squares interpolation scheme. A thermomechanical SMA constitutive law is used to describe the superelastic effect. The incremental displacement-based formulation for large deformation is developed by employing the meshfree shape functions and the continuum tangent stiffness tensor in the weak form of the equilibrium equations. By eliminating the unknown constrained nodal variables from the discrete equations, an effective approach is developed for the imposition of the essential boundary conditions. The numerical tests show that the proposed meshfree scheme can successfully reproduce the superelastic behaviour of shape memory alloys.     

SMA柔性扭转驱动器的结构设计与优化研究

设计了一种基于柔性结构的SMA扭转驱动器,通过加热SMA丝收缩带动柔性结构变形从而实现驱动器的扭转输出。柔性结构在SMA丝拉力作用下的变形情况对驱动器的转角输出有很大的影响,为获得最大的输出转角,需对柔性结构的形状和SMA丝的作用点位置进行优化设计。采用三次B样条曲线描述柔性结构的形状,通过有限元法分析柔性结构的变形,并应用遗传算法进行柔性结构的形状优化和SMA丝作用点位置优化。实际算例表明,利用优化方法可快速有效地获得使SMA柔性扭转驱动器输出转角最大的柔性结构形状与SMA丝作用点位置。     

A mathematical model for smart functionally graded beam integrated with shape memory alloy actuators

This paper presents a theoretical study of the thermally driven behavior of a shape memory alloy (SMA)/FGM actuator under arbitrary loading and boundary conditions by developing an integrated mathematical model. The model studied is established on the geometric parameters of the three-dimensional laminated composite box beam as an actuator that consists of a functionally graded core integrated with SMA actuator layers with a uniform rectangular cross section. The constitutive equation and linear phase transformation kinetics relations of SMA layers based on Tanaka and Nagaki model are coupled with the governing equation of the actuator to predict the stress history and to model the thermo-mechanical behavior of the smart shape memory alloy/FGM beam. Based on the classical laminated beam theory, the explicit solution to the structural response of the structure, including axial and lateral deflections of the structure, is investigated. As an example, a cantilever box beam subjected to a transverse concentrated load is solved numerically. It is found that the changes in the actuator’s responses during the phase transformation due to the strain recovery are significant.     

板材热连轧过程的计算机仿真

利用热力耦合大变形有限元理论对热轧过程中金属的变形、温度及其影响因素,连轧温降等方面进行深入的研究,并在不同的轧制条件下,对热轧变形过程的温度场、变形情况及金属流动等进行了实测,将实测结果与计算机模拟结果进行对比,二者吻合良好。     

非稳态轧制过程的热力耦合刚塑性有限元模拟

采用三维大变形热力耦合刚塑性有限元法对平板轧制咬入阶段进行仿真,仿真条件与实际轧制过程一致。将仿真结果与实际生产数据进行比较,结果表明采用该方法对非稳态轧制过程进行仿真是可行并且可靠的。研究了非稳态阶段的轧制力分布特点和轧件的变形特点,分析了轧件表面温度对头部厚跃现象的影响规律。
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作大运动的空间桁架结构动力有限元分析

作大运动的空间桁架,由于运动和变形的耦合将产生动力刚化现象,传统的动力学难以及这种影响,在有限元方法中首次引入单元耦合形函数（阵）将单元弹性位移表示成为单元结点位称的二阶小量形式,利用几何非线性应变－位移关系式,在小变形假设条件下确定单元耦合形函数。根据Ｋａｎｅ方程,运用模态坐标压缩,并通过适当的线性处理,得到了一致线性化的动力学方程,编制空间桁架结构动力刚度有限元分析程序。仿真算例证明理论和算法     

形状记忆合金驱动梁的变形分析及试验研究

将预拉伸的形状记忆合金 (Shapememoryalloy ,简称SMA)薄片作为驱动器 ,粘贴在构件表面。加热SMA ,当其发生相变时 ,会产生很大的恢复力 ,驱动构件发生变形。建立了粘有SMA薄条应变驱动器的简化机翼—梁的力学模型 ,分析了单边粘贴SMA梁的压弯复合变形 ,给出了其应变分布及弯曲变形的解析表达式。同时通过试验对理论结果进行了验证。     

复合材料细观几何结构对有效模量的影响

基于平均值坐标插值的多边形有限元方法--重心有限元,以代表性单胞为计算模型,讨论增强相的细观几何特征对纤维增强复合材料有效模量的影响.通过改变增强相的尺寸、形状和方位等几何特征后得到的计算结果表明,增强相尺寸是影响有效模量的最基本的因素.除此之外,方位的影响较之形状的影响要更加显著.     

形状记忆合金驱动薄壁圆管扭转变形分析 及试验研究

将预拉伸的形状记忆合金(Shap ememory alloy,简称SMA)丝作为驱动器,缠绕并粘贴在薄壁圆管表面。加热SMA,当其发生相变时,会产生很大的恢复力,驱动圆管发生扭转变形。建立了粘有SMA丝应变驱动器的薄壁圆管的力学模型,分析了一个温度循环中,薄壁圆管受SMA驱动发生的压扭复合变形,给出了薄壁圆管扭转角与激励温度之间的关系。同时通过试验对理论结果进行了验证。     

形状记忆合金梁的非线性弯曲变形

形状记忆合金(Shape memory alloy,SMA)梁作为一种新型智能元件,在工程领域的应用日益广泛。基于实测的形状记忆合金材料应力-应变关系曲线及梁的大变形理论,同时考虑SMA材料拉压力学性能的不对称性及简支端移动等因素,建立形状记忆合金梁非线性弯曲变形的控制方程,并采用打靶法、辛普森数值积分等方法对方程进行数值求解。通过梁在不同载荷条件下的挠曲线以及最大挠度—弯矩曲线,分析材料非线性、几何非线性及简支端移动3个因素对SMA超弹性梁弯曲变形的影响规律。结果表明:梁中性层位置随弯矩变化;弯矩较小时,材料性能是线性的,几何非线性及简支端移动对梁的弯曲变形几乎不产生影响;弯矩较大时,材料性能是非线性的,几何非线性及简支端移动对梁的弯曲变形产生明显影响。     

Finite element method for rigid-plastic analysis of metal forming—Formulation for finite deformation

For the finite element analysis of metal forming processes, a method based on the equilibrium of nodal forces is proposed by assuming the deforming metal to be a slightly compressible rigid-plastic material. As an extension of the method, a formulation for finite deformation is derived on the basis of the equilibrium of nodal forces at the end of incremental deformation. The effects of work-hardening and shape change of element during incremental deformation are incorporated. This formulation is more accurate than that of the simple extension of infinitesimal deformation when dealing with non-steady problems, and is particularly effective for the processes in which the mode of deformation is sensitively changed by the distribution of flow stress and variation of shape. The effectiveness of the method is demonstrated by the examples of a tension test on an axi-symmetric specimen and of the plane-strain compression of blocks.     

滑动接触中摩擦发热的数值分析

在滑动接触中，存在摩擦起热问题，运动机理对接触行为参数特性的影响不同于纯滚动接触，采用有限元方法，利用ANSYS软件，对2维滚滑模型进行分析，通过研究接触区的温度，接触应力和变形在运动学状态下的变化特性，可以看到接触状态的非稳定性必定会造成实际摩擦状态的不同，这也是形成接触表面不均匀磨损的原因之一。     

水工钢结构焊接残余应力有限元模拟分析

采用有限元数值计算方法模拟了钢结构在焊接过程中产生的残余应力和变形特性,采用了双线性弹性-塑性模型、Von Mises屈服准则,和增量原理处理焊接过程中的材料非线性问题,建立了热-结构耦合有限元模型和方法。数值仿真结果表明,采用单元生死处理方法对于模拟多道焊缝问题是有效的。     

铝热精轧轧制区温度场三维有限元模拟

根据某铝热连轧厂生产线实际结构参数和工艺参数,应用弹塑性有限元法,考虑轧件金属塑性变形热、摩擦热、界面接触热导等对轧件和轧辊传热的影响,运用大型通用有限元分析软件MSC.Marc建立了铝热连轧精轧机组F2机架的热力耦合三维有限元仿真模型.通过分析轧件温度场的分布规律,为更好地控制轧件的温度分布、提高产品的质量提供依据.     

确定结构极限载荷的有限元简化算法

基于线性硬化材料形变理论，本文提出了一种计算结构极限载荷的有限元简化算法。与传统的弹塑性增量有限元方法相比，本方法可以避免每一增量步的平衡迭代和在每个高斯点的本构方程的积分，同时该方法不仅理论简洁，而且易于编制成程序或耦合入其他有限元程序中。     

Development of a shape memory alloy multiple-point injector for chemotherapy

A medical needle is described that allows injection to take place at multiple sites through a single stab wound. This is achieved by extruding multiple, thin, and curved internal needles from a larger, straight, outer needle. The development and finite element modelling of the shape memory alloy (SMA) inner needles is presented in this paper. A non-linear elastic element model was used in this process to allow for the non-linear properties of the alloy and the large deformations that occur. The model provided maximum strain values and penetration forces for the inner needles. The deformation force on the tip of the needle was measured against displacement to confirm the predicted penetration force. Applications for the device include the treatment of liver cancer by direct injection of alcohol into the tumours.     

转子系统中形状记忆合金的非线性性能分析

选择形状记忆合金(shape memory alloy，SMA)制作的弹簧元件作为转子系统的弹性支承，研究对转子振动的主动控制。采用电流加热控制记忆合金元件的相变，进而控制转子的振动。讨论了记忆合金因受热而引起的热应力和热弹性的非线性耦合问题，用摄动法对非线性方程进行求解，避免直接假设线性化所引起的误差，提高了解的精度。仿真结果表明数值计算解与理论解符合的良好。     

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.     

计及非线性变形的空间自由旋转梁有限元模型

根据柔性梁的几何非线性变形理论,针对大范围运动的空间柔性梁,在考虑了弯曲和扭转的非线性因素对3个变形方向的影响的基础上,利用有限元方法进行离散,得到了较为精确的变形模式。利用Lagrange方程建立了非线性变形模式下的动力学方程,该方程包含了较为完全的刚度矩阵和各种耦合项。对一带有扭转弹簧的中心体-空间柔性梁结构进行仿真计算,说明变形耦合在横向变形中的作用不可忽视。