TiNi相变悬臂梁的横向冲击特性实验研究

利用改装的霍普金森压杆装置对TiNi形状记忆合金圆截面悬臂梁进行了横向冲击实验研究,并与45#钢悬臂梁的实验结果进行了对比,目的是探索相变对结构动态响应的影响。结果表明:在同样冲击条件下,TiNi悬臂梁的吸能效率优于钢悬臂梁;发现冲击过程中,TiNi试件根部内侧可能形成局部相变铰,使阻力曲线的斜率发生变化;卸载后相变铰消失,TiNi悬臂梁试件基本回复原状,钢试件则留下显著的残余变形。TiNi悬臂梁的冲击特性受热弹性马氏体相变和逆相变的支配,不同于传统的弹塑性机制。     

伪弹性TiNi合金圆薄板的准静态力学行为实验研究

采用阴影云纹和应变片方法对伪弹性TiNi合金圆板在固支条件下的准静态力学行为进行了实验研究,得到了载荷位移曲线、全场离面位移和局部应变等数据.载荷位移曲线呈现非线性、滞回耗能和无残余变形的特性,表明试样已经发生马氏体相变.应变测量显示,相变局限于加载中心较小区域,相变区内,环向应变大于径向应变,且拉伸侧应变大于压缩侧的应变.有限元模拟揭示出相变区内两侧表层的相变范围、相变铰区和马氏体相含量的不对称分布规律.     

横向冲击载荷下伪弹性TiNi合金矩形悬臂梁结构响应的实验研究

利用改装的霍普金森压杆装置对伪弹性TiNi合金矩形截面悬臂梁进行了横向冲击实验研究.结果表明:冲击自由端时,只在根部附近产生一个相变铰,冲击梁中间某位置时,则可能在多处形成相变铰;相变铰形成时拉伸和压缩两侧应变存在一定的不对称性,但是差别并不明显;相变铰的形成与发展过程中,应变并不是单调增加的,而是带有波动性;卸载后相变铰消失,TiNi悬臂梁形状完全回复;自由振动前期,应变的平衡位置与挠度的平衡位置有一定偏离,并且这种偏离随着梁的振动逐渐减小直至消失.TiNi悬臂梁的冲击特性受热弹性马氏体相变和逆相变的支配,不同于传统的弹塑性机制.     

耐磨TiNi形状记忆合金设计准则的有限元研究

采用有限元方法模拟微突体在TiNi形状记忆合金表面的压入过程，研究了伪弹性应变、伪弹性模量和相变启动应力等参数对TiNi合金抗磨性能的影响，并初步确立了TiNi形状记忆合金耐磨材料设计准则．结果表明：伪弹性应变对TiNi形状记忆合金摩擦学性能的影响最显著；就TiNi形状记忆合金耐磨材料的设计而言，应当强调提高伪弹性应变、降低伪弹性模量、增加相变启动应力；同时满足上述3方面要求的TiNi形状记忆合金的耐磨特性最优．     

圆柱薄壳的动相变屈曲行为

利用MTS809材料试验机对TiNi圆柱薄壳进行了轴向动渐进相变屈曲实验,对轴向冲击下处于伪弹性状态的TiNi合金柱壳的动相变屈曲行为进行了数值模拟研究。结果表明,不同的加载强度将会激发出柱壳不同的动屈曲响应模态。当冲击速度较高时,柱壳两端首先形成轴对称环形相变屈曲波纹,并产生应力平台;随着马氏体含量不断增加,环形相变屈曲波纹逐渐贯穿整个壳体,名义应力缓慢抬升;当名义应变超过一定阈值时,对称环形屈曲模态突变为非轴对称块状屈曲模态,名义应力大幅下降。撞击速度为40 m/s的算例（含10％随机缺陷）与S.Nemat-Nasser等的实验结果很好吻合,说明本文中计算模型、方法和结果的有效性经过了实验的考核。结果还表明,相变耗能是TiNi柱壳吸收冲击能量的主要机制,适合制作可重复使用的高效吸能元件,并给出了相应的理想厚径比。     

TiNi合金圆柱薄壳静压屈曲失稳特性的实验研究

对马氏体相变支配的伪弹性TiNi合金圆柱薄壳进行了准静态屈曲实验研究和分析,结果表明,TiNi柱壳的屈曲模态以非轴对称钻石型为主,卸载时可恢复,与马氏体相变和相变铰的行为相关,明显不同于传统弹塑性柱壳。还讨论了长径比和边界条件对屈曲模态、比能、临界失稳阈值等的影响。研究发现：随着长径比和边界条件的变化,TiNi圆柱薄壳呈现出多样化的屈曲模态发展。相同长径比下,两端简支的TiNi圆柱薄壳比能Se较大;随着长径比增大,边界条件的影响有逐步弱化趋势。相同边界条件下,长径比较小的TiNi圆柱薄壳比能较大。     

伪弹性形状记忆合金杆屈曲行为研究

对不同长细比伪弹性TiNi合金矩形截面杆进行了压缩试验,通过应变片和热电偶来捕捉杆中间截面表层材料的相变演化,采用热电偶测量杆中间截面受拉侧的温度,分析了长细比和材料相变对杆件承载能力的影响。结果表明:加载和卸载阶段,两端夹支TiNi杆的载荷-应变曲线随着长细比的改变发生明显的变化,对于短杆,相变会提高其承载能力;对于长杆,其极限承载能力取决于长细比,相变的影响集中在后屈曲阶段;对于低长细比杆件,加载阶段温度持续升高,而高长细比构件,应变达到最大值时温度已开始下降,所有杆件在卸载结束时的温度均低于加载初始时刻。     

超弹性镍钛形状记忆合金单轴相变棘轮行为的宏观唯象本构模型

超弹性镍钛形状记忆合金因其良好的力学性能以及独特的超弹性和形状记忆效应已广泛应用于土木工程、航空航天和生物医疗等多个领域,在实际服役环境中超弹性镍钛合金元件不可避免地会承受不同应力水平的循环载荷作用,亟待建立描述相变棘轮行为(即峰值应变和谷值应变随着正相变和逆相变循环的进行不断累积)的循环本构模型.为此,基于已有的超弹性镍钛形状记忆合金在不同峰值应力下的单轴相变棘轮行为实验研究结果,在广义黏塑性框架下,对Graesser等提出的通过背应力非线性演化方程反映超弹性镍钛形状记忆合金超弹性行为的一维宏观唯像本构模型进行了拓展,考虑了正相变和逆相变过程中特征变量的差异及其随循环的演化,以非弹性应变的累积量为内变量引入了正相变开始应力、逆相变开始应力、相变应变和残余应变的演化方程,同时通过峰值应力与正相变完成应力的比值来确定演化方程中的相关系数,建立了描述超弹性镍钛合金单轴相变棘轮行为的本构模型.将模拟结果与对应的实验结果进行对比发现,建立的宏观唯像本构模型能够合理地描述超弹性镍钛形状记忆合金的单轴相变棘轮行为及其峰值应力依赖性,模型的预测结果和实验结果吻合得很好.     

NiTi形状记忆合金动态压缩力学行为的实验研究

采用材料试验机和SHPB实验技术,对在不同初始温度(298～873K)和应变率(5×10-4、～2.3×103s-1)下的NiTi形状记忆合金的压缩力学行为进行了实验研究。结果表明:马氏体状态下的NiTi合金的力学行为对应变率的变化敏感,位错屈服段的硬化模量、相屈服段的硬化模量及马氏体重取向前的弹性模量对应变率的变化不敏感,而位错塑性变形前的弹性模量随应变率的提高迅速增大;奥氏体状态下的NiTi合金随着实验温度升高,无论是应力诱发马氏体相变应力还是奥氏体相屈服应力都逐渐下降,材料表现出温度软化效应。从超弹性温度范围内的卸载曲线中观察到了应力诱发马氏体到奥氏体的逆转变。     

TiNi相变圆柱壳的径向压缩特性实验研究

对不同几何尺寸和边界约束条件的TiNi合金圆柱壳进行了准静态径向压缩实验研究,利用数字摄像和图像处理技术得到了不同位置柱壳的变形特征和应变分布,结果表明,在柱壳表面受压处先出现相变铰,随着名义应变的增大,相变铰将发展成相变铰区;在柱壳表面受拉处出现相变铰,但此处材料先进入马氏体相.当径厚比和边界约束不变时,随着名义应变的增大,柱壳的耗能率和比能不断增加.当名义应变不变时,柱壳的耗能率和比能随边界约束个数的增多而增加,吸能效果更好,随径厚比的增加而减小,吸能效率下降.     

铈γ→α相变的室温动态特性

通过试样组件尺寸匹配设计的被动围压SHPB实验,获得了99.8%纯铈在1.7GPa静水压内的、包含γ?α相变和逆相变过渡区的室温动态静水压-体应变连续曲线。研究显示:室温铈γ→α相变是具有明显滞后现象的一级相变,而非以往研究认为的体积跃变的一级相变;相变过渡区的静水压范围是0.8~1.3GPa。逆相变过渡区的静水压范围是0.6~1.1GPa;逆相变过渡区的静水压-体应变曲线滞后于相变过渡区的静水压-体应变曲线0.15GPa静水压;在相变和逆相变过渡区内,静水压-体应变曲线按照约4.2GPa体积模量的线性关系演化;演化机制为γ和α两相均匀混合、静水压驱动两相组份转化。基于该演化机制,构建了描述相变前后和相变过程的静水压-体应变响应的三段线性模型。     

Equations of heterophase equilibrium of a biomembrane

Summary Phase transitions in a shell are considered within the frame example work of a biomembrane of a general shape divided into parts containing different phases. The configuration of a boundary separating these phases is determined by the condition of minimum of the total membrane free energy with respect to its position. Equations of equilibrium for both the membrane phases and the phase boundary are deduced. They allow to describe the heterophase state of the biomembrane. Received 11 December 1997; accepted for publication 31 July 1998     

Mechanical analysis of phase transition experiments of the bacterial flagellar filament

Bacterial flagellar filaments can undergo a polymorphic phase transition in both vitro and vivo environments. Each bacterial flagellar filament has 12 different helical forms which are macroscopically represented by different pitch lengths and helix radii. For external mechanical force induced filament phase transitions, there is so far only one experiment performed by Hotani in 1982, who showed a very beautiful cyclic phase transition phenomenon in his experiment on isolated flagellar filaments. In the present paper, we give a detailed mechanical analysis on Hotani＇s experiments. Through theoretical computations, we obtained a phase transition rule based on the phase transition mechanism. The theoretical analysis provides a foundation facilitating the establishment of phase transition theory for bacterial flagellar filaments.     

Equilibrium Configurations of an Inflated Cylindrical Membrane

We study the inflation of a cylindrical elastic membrane under conditions where more than one equilibrium radius is possible at the same pressure. In particular, we investigate the existence of solutions connecting two sections of different radii. The existence of such solutions is found to be linked to a Maxwell equal area rule.     

Constitutive Relations for a Viscoelastic Body under Crystallization Conditions

The problem of describing the thermomechanical behavior of viscoelastic polymer materials under conditions of their post-production cooling accompanied by crystallization is considered. A variant for constructing phenomenological constitutive relations, which continuously reflect the relation between the stress and strain tensors in a wide range of temperature variation, is suggested. The relations are based on representation of the medium in the form of a composition of a melted material and a completely crystallized material with allowance for the history of permanent incipience and deformation of the new phase in the interval of phase-transformation temperatures. To determine the material functions and constants, experiments are planned on specimens at temperatures corresponding to particular phase states. Results of experiments and numerical analysis of the fields of displacements generated by solidification of a circular polyethylene plate are given.__________Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 4, pp. 78–87, July–August, 2005.     

Numerical study of dynamic phase transitions in shock tube

Shock tube problem of a van der Waals fluid with a relaxation model was investigated.In the limit of relaxation parameter tending towards zero,this model yields a specific Riemann solver.Relaxing and relaxed schemes were derived.For an inci- dent shock in a fixed tube,numerical simulations show convergence toward the Riemann solution in one space dimension.Impact of parameters was studied theoretically and nu- merically.For certain initial shock profiles,nonclassical reflecting wave was observed.In two space dimensions,the effect of curved wave fronts was studied,and some interesting wave patterns were exposed.     

加载路径和温度对NiTi合金相变特性的影响

利用MTS装置,对NiTi形状记忆合金在不同加载路径(拉、压、扭以及拉/压-扭比例加载)和不同温度(28~150℃)下的准静态相变行为进行了较系统的实验研究。结果表明,材料呈现明显的伪弹性效应和拉压不对称性。随着温度的升高,相变起始应力逐渐增大,伪弹性效应和拉压不对称性逐渐减弱。当温度达到一定阈值时,拉压不对称性消失,材料基本呈现弹塑性状态。通过实验曲线确定了NiTi合金的相变临界参数,在σ-τ应力空间中对三种常用宏观相变临界准则进行了讨论,比较了它们各自的适用性。     

复正交矩阵区对角化条件及其对相变问题的应用

本文给出(2n×2n)复正交矩阵正交相似于(2×2)正交矩阵直接和的充分必要条件,作为实际例子,并讨论它对二维Ising模型相变问题的应用。     

Moving inelastic discontinuities and applications to martensitic phase transition

Summary In this work, equations of the kinetics and kinematics are developed for heterogeneous materials containing inelastic discontinuities with moving boundaries. From the derived free energy and the power of external forces one obtains the driving force acting on the moving boundary. Introducing the interface operators and some hypothesis on inelastic fields, one gets the driving force for the formation of an ellipsoidal domain. The theoretical model is illustrated by the derivation of nucleation and growth conditions of a martensitic plate inside an inhomogeneous plastic strain field. The obtained results are combined with a study of the kinetics and kinematics to derive the constitutive equation of an austenitic single crystal, from which the overall behavior of polycrystalline TRIP steels is deduced using the self-consistent scale-transition method. Comparison with experimental data shows a good agreement. Received 7 May 1999; accepted for publication 14 June 1999     

Evolution of a long-wave train in loss of stability of a phase interface in geothermal systems

The transition to instability of phase interfaces in geothermal systems when a water stratum overlies a steam stratum and the most unstable mode corresponds to zero wavenumber is considered. The nonlinear Kolmogorov-Petrovskii-Piskunov equation describing the evolution of a narrow strip of weakly unstable modes is obtained. This equation is an analog of the well-known Ginzburg-Landau equation corresponding to the case of destabilization of modes with finite wavenumbers. It is shown that in the neighborhood of the critical points there exist two locations of the plane phase interface which coincide at the instant at which the instability threshold is reached and then disappear.