振动时效对NiTi记忆合金回复特性与相变行为的影响

研究了振动时效对约束态下NiTi形状记忆合金的力学性能与相变行为的影响,用自制的拉伸机测试了振动与未振动NiTi合金在自由加热过程中的回复应变,用万能拉伸实验机测试了NiTi合金的力学性能,用DSC测试了NiTi合金的相变行为.结果表明,随着振动幅度的增加,NiTi合金丝在自由加热过程中输出的两段回复应变减小;随着振动时间的延长,NiTi合金输出的回复力减小,最多约80MPa.DSC结果表明约束态振动后再变行马氏体逆相变温度升高,相变潜热减小,而继承变形马氏体和热诱发马氏体相变潜热增加.所有结果均直接或间接表明,振动时效降低了NiTi形状记忆合金产生的回复力.这可能是由于振动在NiTi合金中产生了微观塑性变形,降低了回复力.     

多孔NiTi形状记忆合金研究进展

评述了近10年来国内外在多孔NiTi形状记忆合金研究和应用方面的最新进展,主要内容包括:(1)近年来多孔镍钛(NiTi)形状记忆合金的发展、微观结构特点、力学性能和功能性;(2)当前制备多孔NiTi形状记忆合金的主要方法以及优缺点;(3)多孔NiTi形状记忆合金的相变和超弹性行为,以及与致密合金的比较.最后,简要介绍了多孔NiTi形状记忆合金在生物医学领域作为人体硬组织植入和修复材料,以及智能结构和阻尼器件等方面的研究和应用前景,探讨了今后多孔NiTi形状记忆合金的研究重点.     

NiTi形状记忆合金疲劳行为的研究现状

NiTi形状记忆合金具有比其它同类合金更优良的力学性能、形状记忆效应、超弹性、阻尼特性和生物相容性等特点,广泛应用于工程、民用和医学领域.综述了NiTi形状记忆合金疲劳行为的研究现状;对其疲劳行为及其机制的研究,有助于进一步提高NiTi形状记忆合金的性能并延长它的寿命.     

高温热变形条件下Ni-Ti形状记忆合金的微结构演变

采用真空感应法炼制了不同氧、碳含量的NiTi和NiTiNb形状记忆合金 .分析研究了合金的微观组织、相结构以及高温热变形对合金微观组织的影响 ,重点研究和探讨了合金微观结构在高温热变形过程中的演变规律 .确定了合金组织中TiNi基体相、Nb相及在晶界形成的氧化物和碳化物的形变特点 .结果表明 ,合金中C、O含量决定其组织中碳化物和氧化物的形态和含量 ,高温热变形时 ,TiNi基体相和Nb相粒子均产生较大塑性变形 .当合金中氧和碳含量较高时 ,氧化物和碳化物在变形时碎裂 ,在组织中的分布比铸态更均匀 .在本文研究的氧、碳含量的范围内 ,氧化物和碳化物的存在对合金的力学性能 ,如拉伸强度、延伸率等影响不大 .     

多孔NiTi形状记忆合金的制备及性能

采用球磨后的NiTi合金粉末为原料,添加尿素作为造孔剂,利用粉末烧结法制备多孔NiTi形状记忆合金.研究烧结温度、保温时间和预成型压力等条件对制备的多孔NiTi合金组织结构和力学性能的影响.结果表明:相对于传统的Ni粉和Ti粉近等原子比混合烧结方法,此方法制备的多孔NiTi合金的相组成更加纯净.且随烧结温度升高,多孔N...     

Ti-18Nb-4Sn形状记忆合金在0.05%HCl溶液中的腐蚀行为

TiNi形状记忆合金用于人体内,长时间金属元素会不可避免地释放出来,Ni元素可能有致癌作用.因此,人们希望采用无Ni的Ti基形状记忆合金.Ti-Nb-Sn合金系的研究表明,该合金系在包括室温在内的较宽的温度范围内具有良好形状记忆效应;在通常温度下比NiTi合金具有更优异的变形能力;而且Nb和Sn元素对生物体没有不良影响.日本学者研究了Ti-18Nb-4Sn合金表面离子的释放量,并与纯Ti、NiTi合金进行了比较.     

NiTi纤维增强粘弹性基体与弹性基体复合材料的力学特性

借助Voigt混合律,针对马氏体逆相变过程,建立了NiTi纤维增强Kelvin粘弹性基体与弹性基体两种复合材料的应力-应变关系.在同样的升温过程及应力作用下,对两种复合材料的变形(应变)、约束态NiTi纤维逆相变开始温度进行了分析对比;升温、加载经历一段时间后,限制两种复合材料的应变为固定值,分析其受力特征.分析有助于了解NiTi纤维增强粘弹性基体与弹性基体复合材料的力学性能.     

原位内生NiTi合金复合材料的温度记忆效应(英文)

对NiTi形状记忆合金在冷轧变形后的不完全相变特征进行了研究.通过设计试样原始表面形状的方法,将具有不同位错密度的宏观区域引入形状记忆合金内部,使整个材料获得了复合材料的特征.结果表明,由于位错织构和马氏体变体界面的作用,使逆转变温度扩展到一个较大的温度范围,这将会进一步增加温度记忆效应的潜在应用价值.     

形状记忆合金纤维混杂正交对称铺层板的固有频率

形状记忆合金（SMA）混杂复合材料板是将有预应变的SMA纤维与普通纤维混杂单层内构成的。基于主动应变能调节（ASET）的概念,可实现对板的固有频率的调整。本文采用Galerkin法导出形状记忆合金（SAM）纤维混杂对称正交智能复合材料铺层板自由振动的频率的分析表达式。数值结果表明,SMA纤维的相变激发温度、体积含量、分布方式及其预应变对固有频率均有的影响,尤其是温度、SAM含量及其分布的作用更为显著,是结构振动控制的重要设计参数。     

Mg/NiTi复合材料的制备及阻尼性能

采用Mg粉的无压熔渗法制备Mg/NiTi复合材料以提高多孔NiTi合金的强度和阻尼性能。通过OM、SEM、EDS和XRD分析Mg/NiTi复合材料的显微组织结构,采用压缩实验分析其抗压强度、吸能能力,采用热机械分析仪分析其内耗和存储模量。结果表明:经Mg粉无压熔渗后,多孔NiTi合金的孔隙被Mg填充,其孔隙率由原来的50.38%下降至5.6%,且Mg与NiTi合金的界面结合良好。多孔NiTi合金主要由B2奥氏体相和B19'马氏体相及少量Ni₃Ti相和NiTi₂相组成;Mg/NiTi复合材料除增加了熔渗的Mg相外,还新生成了Mg₂Ni相。Mg的渗入未改变多孔NiTi合金相变行为,但提高了相变温度。Mg/NiTi复合材料的抗压强度可达554 MPa,较多孔NiTi合金提高了61%,压缩断裂方式也由多孔NiTi合金的孔壁崩塌断裂转变为Mg/NiTi复合材料的剪切断裂。Mg/NiTi复合材料的吸能较多孔NiTi合金有大幅提高。同时,Mg/NiTi复合材料的内耗值有所增加,而存储模量大幅提高,整体呈现出更佳的阻尼性能。      

SMA杂交复合材料板低速冲击响应研究

本应用有限单元法，研究了形状记忆合金(SMA)对复合材料板低速冲击响应性能的影响。研究中，通过分析对比不同SMA体积含量复合材料板的低速冲击响应，得出SMA能的效地改善复合材料板低速冲击响应性能的结论，其中，SMA体积含量为0．3的复合材料板的最大挠度大约减少了30％。     

形状记忆合金纤维正交各向异性层合矩形板的非线性弯曲振动

研究了形状记忆合金(SMA)纤维混杂复合材料大挠度层合板的非线性自由与受迫振动特性。基于描述SMA力学行为的Brinson理论以及层合板材料性能预测的混合率, 建立了SMA纤维混杂复合材料大挠度层合板的本构方程, 基于对称层合各向异性弹性板的非线性理论, 建立了以横向挠度和应力函数表示的板的横向振动方程和相容方程。采用Galerkin近似解法将振动方程化为时间变量的含有三次非线性项的Duffing型常微分方程, 采用谐波平衡法(HBM)获得系统的固有频率方程和强迫振动稳态频率响应方程。数值计算表明: 非线性板自由振动频率比与激励温度的关系具有与线性板相同的特征, 马氏体相向奥氏体相转变阶段温度对板的振动频响特性曲线的影响最显著, 同时也讨论了SMA纤维含量、 板的纵横比以及自由振动幅值对板的非线性频率比的影响。      

Adaptability of hybrid smart composite plate under low velocity impact

Present study deals with an approach to the detection of the strains and optimization of shape memory alloys (SMA) under low velocity impact. It is assumed that the sensor is mounted on the opposite side of the impact process, and SMA fibers are embedded within the layers of a composite plate. Modeling the SMA fibers constitutive has been derived as the one-dimensional equations. With different skew angles of the piezoelectric sensor, we can illustrate that the measured charge manifests the strain components induced by the impact. By changing the SMA volume fractions and the temperature increments, we can significantly reduce the deflections. It can be shown that the application of piezoelectric sensors is effective in the monitoring of the transient strain. In addition, the optimization of the distribution of volume fraction of SMA fibers provides further benefits in reducing the deflection of the plate.     

利用SMA的SME特性改善复合材料板低速冲击响应性能的研究

本文将具有一定塑性应变的形状记忆合金(SMA)纤维埋设在复合材料板中，利用其形状记忆功能(SME)改善复合材料板的低速冲击响应性能。研究中，应用有限元法对SMA杂交复合材料板的低速冲击响应进行了分析，其中，SMA中产生的恢复应力通过实验得出的应力-温度关系确定，冲击接触力通过修正的Hertzian接触定律求得；研究结果表明具有形状记忆功能的SMA能有效地改善复合材料的低速冲击响应性能。     

Free vibration of buckled SMA reinforced composite laminates

The effect of shape memory alloys (SMA) on the free vibration behavior of buckled cross-ply and angle-ply laminates by varying the SMA fiber spacing was investigated using the finite element method. The formulation of the location-dependent linear, nonlinear stiffness and mass matrices due to non-homogeneous material properties and the temperature-dependent recovery stress stiffness matrix were derived. Numerical results show that the increase of SMA fiber volume fraction and prestrain may generate more recovery stress, and increase the stiffness of SMA reinforced composite laminates. Therefore, the postbuckling deflections of the plate will be decreased considerably and the natural frequencies of the plate may be modified significantly. The buckling mode and fundamental natural mode are dependent on the graphite fiber orientation of the SMA reinforced angle-ply laminates. The relationship between the buckling mode and fundamental natural mode is clearly displayed and studied in detail.     

Thermal post-buckling and flutter characteristics of composite plates embedded with shape memory alloy fibers

It is investigated that the composite plate embedded with shape memory alloy (SMA) fibers is subject to the aerodynamic and thermal loading in the supersonic region. The nonlinear finite element equations based on the first-order shear deformation plate theory (FSDT) are formulated for the laminated composite plate embedded with SMA fibers (SMA composite plate). The von Karman strain–displacement relation is used to account for the large deflection. The incremental method considering the influence of the initial deflections and initial stresses is adopted for the temperature-dependent material properties of SMA fibers and composite matrix. The first-order piston theory is used for modeling aerodynamic loads. This study shows the effect of the SMA on the critical temperature, thermal post-buckling deflection, natural frequency and critical dynamic pressure of the SMA composite plate.     

Knowledge and Method Base for Shape Memory Alloys

It is often impossible for design engineers to decide whether it is possible to use shape memory alloys (SMA) for a particular task. In case of a decision to use SMA for product development, design engineers normally do not know in detail how to proceed in a correct and beneficial way. In order to support design engineers who have no previous knowledge about SMA and to assist in the transfer of results from basic research to industrial practice, an essential knowledge and method base has been developed. Through carefully conducted literature studies and patent analysis material and design information could be collected. All information is implemented into a computer supported knowledge and method base that provides design information with a particular focus on the conceptual and embodiment design phase. The knowledge and method base contains solution principles and data about effects, material and manufacturing as well as design guidelines and calculation methods for dimensioning and optimization. A browser‐based user interface ensures that design engineers have immediate access to the latest version of the knowledge and method base. In order to ensure a user friendly application, an evaluation with several test users has been carried out. Reactions of design engineers from the industrial sector underline the need for support related to knowledge on SMA.     

Micromechanical Modelling of Shape Memory Alloy Composites

An isothermal finite element method (FEM) model has been applied to study the behavior of two kinds of shape memory alloy (SMA) composites. For SMA‐fiber reinforced normal metal composites, the FEM analysis shows that the mechanical behavior of the composites depends on the SMA volume fraction. For normal metal‐fiber reinforced SMA matrix composites, the SMA phase transformation is affected by the increasing Young’s modulus of the metal fiber. The phase transformation was also treated using a simple numerical analysis, which assumes that there are uniform stresses and strains distributions in the fiber and the matrix respectively. It is found that there is an obvious difference between the FEM analysis and the simple numerical assessment. Only FEM can provide reasonable predictions of phase transformations in SMA/normal metal composites.     

Bending of shape-memory alloy-reinforced composite beam

Based on the one-dimensional thermo-mechanical constitutive relation of a shape-memory alloy (SMA) in which the dependence of the elastic modulus of SMA upon the martensite fraction is considered, a constitutive relation for the bending of a composite beam with eccentrically embedded SMA wires has been developed. The deflection-temperature relation upon heating and cooling has been analysed for the SMA-reinforced composite beam.