Research Progress and Aerospace Applications of Shape Memory Alloys

As one of the newly developing intelligent/smart materials,shape memory alloys(SMAs)have become an important material and have broad application prospects.With smart structures,the integration of SMAs as actuators and sensors in structural components,has drawn significant attention and interest in the aerospace field.In this paper,the research status of SMAs at home and abroad in recent years was reviewed,including the characteristics,classification,investigation progress and applications in the aerospace field.Finally,the development trend prospects for SMAs was also presented.

Improvement of Concrete Shear Wall Structures by Smart Materials

Smart materials have found numerous applications in many areas in civil engineering recently. One class of these materials is shape memory alloy (SMA) which exhibits several unique characteristics such as superelasticity and shape memory effect. Due to these characteristics, research efforts have been extended to use SMA in controlling civil structures. This paper investigates the effectiveness of SMA reinforcements in enhancing the behavior of shear walls, especially when subjected to seismic excitations. Two ordinary and coupled shear walls were introduced as reference structures and were modeled by ABAQUS software. For improving the seismic response of the shear walls, vertical SMA reinforcing bars were proposed to be implemented like conventional steel reinforcements, throughout the height of the structures and in every connecting beam in the coupled shear wall system. The one dimensional superelastic model of SMA material was implemented in the computer software using FORTRAN code. The dynamic response of the shear walls subjected to seismic loading was investigated through time history analyses under El-centro and Koyna records. The results showed that using superelastic SMA material instead of steel bars caused remarkable reduction in residual displacement for both ordinary and coupled shear walls. In addition, SMA reinforcements could significantly decrease the maximum deflection of the coupled shear wall system.

Two-Way 4D Printing： A Review on the Reversibility of 3D-Printed Shape Memory Materials

The rapid development of additive manufacturing and advances in shape memory materials have fueled the progress of four-dimensional （4D） printing. With the right external stimulus, the need for human interaction, sensors, and batteries will be eliminated, and by using additive manufacturing, more complex devices and parts can be produced. With the current understanding of shape memory mechanisms and with improved design for additive manufacturing, reversibility in 4D printing has recently been proven to be feasible. Conventional one-way 4D printing requires human interaction in the programming （or shapesetting） phase, but reversible 4D printing, or two-way 4D printing, will fully eliminate the need for human interference, as the programming stage is replaced with another stimulus. This allows reversible 4D printed parts to be fully dependent on external stimuli; parts can also be potentially reused after every recovery, or even used in continuous cycles-an aspect that carries industrial appeal. This paper presents a review on the mechanisms of shape memory materials that have led to 4D printing, current findings regarding 4D printing in alloys and polymers, and their respective limitations. The reversibility of shape memory materials and their feasibility to be fabricated using three-dimensional （3D） printing are summarized and critically analyzed. For reversible 4D printing, the methods of 3D printing, mechanisms used for actuation, and strategies to achieve reversibility are also highlighted. Finally, prospective future research directions in reversible 4D printing are suggested.

An investigation on multilayer shape memory polymers under finite bending through nonlinear thermo-visco-hyperelasticity

This study presents a semi-analytical solution to describe the behavior of shape memory polymers(SMPs) based on the nonlinear thermo-visco-hyperelasticity which originates from the concepts of internal state variables and rational thermodynamics.This method is developed for the finite bending of multilayers in a dual-shape memory effect(SME) cycle.The layer number and layering order are investigated for two different SMPs and a hyperelastic material.In addition to the semi-analytical solution,the finite element simulation is performed to verify the predicted results,where the outcomes demonstrate the excellent accuracy of the proposed solution for predicting the behavior of the multilayer SMPs.Since this method has a much lower computational cost than the finite element method(FEM),it can be used as an effective tool to analyze the SMP behavior under different conditions,including different materials,different geometries,different layer numbers,and different layer arrangements.

The Parameters Selection of SMA Optically Activated and Its Application

Shape Memory Alloy (SMA) optically activated is the key technology of optical SMA activator.According to the shape memory mechanism of SMA,researches are done on the activating response time and light wavelength of activating source etc of SMA optically activated to approach the parameters selection of optical activation.SMA has the optimum efficiency in the range of 13 seconds to 27 seconds when SMA is illuminated continuously by wavelength of 675nm;The power of light wave has a low effect on SMA;The longer the activating wavelength,the quicker the response time of SMA activated.If the proper activating time and activating wavelength are adopted, and the structure deformation of composite material of SMA imbedded may be actively controlled,an ideal effect will be gotten.The research provides an evidence for the design of optical SMA activator and is of great significance to its application.The research on smart structure has a wide application prospect.

超弹性形状记忆合金丝(NiTi)力学性能的试验研究

从土木工程振动控制的角度出发 ,通过NiTi形状记忆合金丝处于超弹性状态下的力学性能试验 ,研究温度、加载速率、应变幅值、循环次数等加载工况对形状记忆合金的相变应力、耗能能力、变形模量及残余应变等力学性能参数的影响规律 ,并给出了各力学性能参数与主要影响它的加载工况之间的关系。试验和分析结果表明 ,处于超弹性状态下的形状记忆合金具有良好的耗能阻尼性能、较大的可恢复变形能力和很高的结构驱动能力 ,可满足土木工程结构振动控制的需要。

形状记忆合金对混凝土梁驱动效应分析

着重研究形状记忆合金偏心埋置于混凝土梁后 ,合金在逆相变过程中对梁变形的驱动效应。研究了合金预应变值、配置量及直径粗细、混凝土龄期、通电激励模式、试件养护方法及截面尺寸等因素对于梁变形性能(合金驱动效应 )的影响规律。试验结果表明 :合金在逆相变过程中能对混凝土梁产生很大的驱动力 ,使得对梁挠度值的主动控制与调整成为可能 ;可以按需要增加预应力值 ,以补偿预应力损失等 ;合金的预应变值、配置量、通电激励模式、直径粗细等因素对于合金的驱动效应有较大影响。

基于SMA的智能预应力梁主动控制试验研究

在工程结构的长期使用过程中,随着外部荷载及温度、湿度等环境条件的变化,材料与结构性能会发生退化,这就要求结构具有一定的智能特性以适应上述变化。针对这一问题,提出一种新型智能预应力结构——形状记忆合金智能预应力梁,将形状记忆合金以体外预应力筋的形式布置在钢筋混凝土梁体外,利用形状记忆合金在相变过程中产生的回复力对梁施加驱动力。进行2根形状记忆合金智能预应力梁的主动控制试验。试验结果表明,通过控制形状记忆合金的温度,可以有效地实现对混凝土梁的变形和裂缝的主动控制。当形状记忆合金的温度分别达到56℃、81℃时,梁的跨中挠度恢复百分比分别为17.3%、8.5%,曲率恢复率分别为11.8%、4.8%,最大裂缝宽度分别减小了14.3%、15.8%。此外,还进行了形状记忆合金智能预应力梁的非线性有限元分析,计算值与试验结果吻合良好。

功能梯度形状记忆合金梁纯弯曲的理论分析

功能梯度形状记忆合金(Functionally graded shape memory alloy,FG-SMA)是一种兼备功能梯度材料(Functionally gradedmaterial,FGM)和形状记忆合金(Shape memory alloy,SMA)特性的新型功能材料。根据复合材料力学和已有的SMA本构关系,通过充分考虑组分材料的应力应变关系,建立一个描述FG-SMA力学性能的宏观本构模型。应用该模型,对由弹性材料A和SMA组成的FG-SMA梁在纯弯曲载荷下的力学行为进行研究,详细讨论加载过程的弹性阶段和相变阶段,并给出相应的解析解。通过算例,对截面的应力分布、中性轴的位置和弯矩与曲率的关系进行详细讨论。结果表明,与普通FGM相比,FG-SMA可显著减小载荷作用下的最大应力,避免材料由于应力过大而导致的破坏。研究结果可为FG-SMA材料的设计和进一步研究提供一定的依据。

含形状记忆合金的智能材料结构的应用

在介绍形状记忆合金几种重要特性的基础上,讨论了含形状记忆合金的智能材料结构的应用,并就该研究领域的发展方向提出了几点建议。

基于智能材料的液晶显示器主动拆卸结构设计方法研究

将形状记忆材料作为液晶显示器支架之间的主动拆卸单元,运用ADSM方法对液晶显示器支架进行了重新设计。提出了液晶显示器支架主动拆卸设计原则,建立了主动拆卸单元的力学分析模型,利用ABAQUS优化了主动拆卸单元在液晶显示器支架上的布置位置,确定了主动拆卸结构的最优尺寸及其在支架结构中的布置位置,通过实验对液晶显示器支架主动拆卸结构的尺寸、位置及拆卸效果进行了验证。

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。

镍钛形状记忆合金丝的性能测试分析

从形状记忆合金（ Ｓ Ｍ Ａ）的性能测试和智能材料与结构研究的角度出发，论述了 Ｓ Ｍ Ａ 驱动元件的应力、应变、温度和相变之间的测试关系，并通过分阶段和不同的变量组合，对直径０．５ｍ ｍ 的 Ｎｉ Ｔｉ Ｓ Ｍ Ａ 丝（ Ｎｉ４９．２％ ａｔ Ｔｉ）的基本驱动特性进行了系统的测试分析，测试内容主要集中于相变温度、自由状态下的最大回复应变、约束状态下的回复应力等。结果表明， Ｎｉ Ｔｉ Ｓ Ｍ Ａ 丝的应力应变温度关系呈现出高度的非线性，环境温度和外加应力是影响 Ｎｉ Ｔｉ丝性能的主要因素，外载荷将使相变温度升高；约束回复中，随着约束应变量的增大和温度的升高， Ｎｉ Ｔｉ丝的回复应力也增大。该测试结果为更好地监测和控制 Ｎｉ Ｔｉ Ｓ Ｍ Ａ 的驱动行为、设计 Ｓ Ｍ Ａ 驱动元件提供了参考依据。

振动控制的发展及趋势

描述了振动控制的主要发展过程及最新发展动向 ,介绍了机敏材料与智能结构 ,主动与半主动振动控制和杂合技术 ,同时还指出新的研究方向 :形状记忆合金在振动控制研究的应用研究。

智能材料与结构及其在智能飞行器中的应用

为了满足民用和军事领域对智能飞行器日益增长的需求,在承载、连接等功能的基础上,具有自诊断、自适应、自控制、自修复等“智能功能”的智能结构应运而生。这一技术的出现显著地推动了航空领域的发展,如利用形状记忆合金作为驱动器驱动指定结构变形可以改变飞行器气动性能,而利用压电材料作为传感器和驱动器对结构进行健康监测和振动噪声控制是当前智能结构研究的重要方向。以此为背景,介绍了南京航空航天大学智能结构研究团队近十年来在智能结构方面的研究进展,以期为智能结构技术的发展与创新提供可以借鉴的思路。

非对称铺设SMA层的复合材料梁在热荷载作用下的变形分析

基于几何非线性理论,提出一类偏心铺设的形状记忆合金(SMA)复合材料梁的数学模型,建立梁在温度载荷作用下的非线性弯曲控制方程,应用打靶法进行数值求解,得到均匀加热下两端不可移简支SMA层合梁的热弯曲数值解.给出具体算例的平衡构形和平衡路径,并分析和讨论SMA的几何和物理参数对梁变形的影响.结果表明梁在升温的一开始就发生变形,升温过程中随着SMA的相变,变形趋势加剧,通过改变SMA的几何、物理参数可以调整梁的变形.

混凝土梁智能自修复试验与研究

利用形状记忆合金的形状记忆效应和受限回复产生较大驱动力的特性以及胶粘剂对裂缝的填充、修复特性,研究了一种智能自修复混凝土梁.通过试验验证了智能混凝土梁的自修复能力,并对智能混凝土梁的修复机理进行了分析.试验结果表明:裂缝产生后,胶粘剂从修复纤维管中渗入裂缝;通电加热改变形状记忆合金温度而使其对梁施加回复力,裂缝闭合.修复后的试样再次加载时,其开裂荷载提高,修复后的裂缝未再次开裂,而在试件中出现了新的裂缝.

形状记忆合金增强复合材料梁的弯曲

本文根据形状记忆合金的－维热－力学本构关系推导了形状记忆合金丝混杂的纤维增强复合材料梁的纯弯曲变形的本构关系，并对温度变化时梁的曲率变化问题作了分析。

智能材料结构的振动抑制

目前热门研究的智能材料结构是将材料构件与传感元件、致动元件结合成一个整体．传感元件作为信号传输与神经系统，使复合材料具有视觉和神经系统；致动元件作为局部或整体的致动器完成在役时的自适应功能。形状记忆合金是智能结构最先应用的驱动元件．本文就形状记忆合金作为分散致动器埋人或粘贴在结构上，利用其特殊的力学性能和物理性能，改变结构的自报频率，抑制结构振动的研究作了介绍．

不同材料模型的超弹TiNi合金法向接触的有限元分析

采用多线性弹性和双线性等向强化两种材料模型 ,对在法向力载荷作用下的TiNi形状记忆合金进行有限元模拟。结果表明 :多线性弹性模型不适合用来分析TiNi合金的超弹性 ;而通过用最大弹性变形量 (与屈服极限对应的极限应变值 )来模拟TiNi合金的超弹性 ,采用双线性等向强化模型可以描述TiNi合金的超弹性与产生的最大VonMises弹性应变及最大VonMises塑性应变之间的关系 ,能够为以TiNi合金作为机敏材料、耐磨材料及耐磨膜层材料设计提供依据。最后 ,在该材料模型下 ,将用有限元方法与用纳米力学探针得到的位移与载荷关系曲线进行对比 。