SMA 增强含损伤智能结构的失效研究

从细观角度出发, 运用变分原理着重对形状记忆合金(Shape Memory Alloy, SMA) 增强含损伤智能结构的热、力学行为进行了分析, 给出了含损伤典型单元体的细观位移场、应力应变场的数学描述, 建立了SMA增强智能结构界面的失效判据, 并通过算例对失效判据进行了直观的几何描述。本文的结果为进一步研究智能结构的完整性提供了相应的理论支持。     

含椭球夹杂耐热梯度功能材料细观结构优化应力方程

梯度功能材料具有复杂的细观结构组合方式,对其进行细观力学的研究是当前的主要发展方向。本文作者对非均质、耐热、含椭球夹杂梯度功能材料的细观结构与性能进行了分析,研究其细观力学建模和在机械/热载荷下的损伤演化和破坏。结果可应用于多相夹杂梯度功能材料的细观应力分析和细观性能预测,并均以显式给出,以便于工程应用。     

基于Preisach理论的形状记忆合金温度-位移迟滞仿真研究

摘 要：智能材料如形状记忆合金(Shape Memory Alloy,SMA)已经广泛应用于驱动器和传感器的设计,实现定位和主动控制目的。然而,受迟滞影响,SMA驱动器的工作精度大大降低,限制了其应用。多数智能材料中,选择Preisach理论成为迟滞建模工具,近年来,也涉及到SMA材料系统。本文,讨论运用Preisach模型描述SMA驱动器系统的迟滞行为,尤其针对驱动器系统的模型建立过程,修正经典Preisach模型的几何解释和数值实现方法。最后,引入Gobert给出的Preisach平面的辨识函数执行仿真计算,数值结果表明该模型能够很好地描述SMA驱动器的迟滞行为。     

空间网架结构形状记忆合金隔震研究

利用形状记忆合金(Shape Memory Alloy,SMA)的独特性能研制合适的隔震装置是SMA在隔震领域应用的关键之一。该文设计了一种超弹性SMA隔震支座;推导了该支座的理论力学模型,建立了它的有限元模型,运用理论模型进行数值模拟并与有限元结果进行了对比;针对所设计的SMA隔震支座,提出了简易的SMA隔震设计方法,对某空间网架结构进行了隔震设计与分析。结果表明,该文设计的SMA隔震支座能有效降低网架结构地震响应。该文的研究为控制空间网架结构的地震响应提供了可行的方法。     

考虑磁场影响的磁性形状记忆合金分段线性化超弹性本构模型研究

磁性形状记忆合金(Magnetic Shape Memory Alloy,MSMA)作为一种新型智能材料,同传统温控形状记忆合金一样具有形状记忆效应和超弹性效应。现有的MSMA本构模型大多存在理论性强、形式繁杂、参数较多等问题,不利于实际工程应用。为此,该文借助线性化方法,建立了超弹性MSMA分段线性化应力-应变关系;引入应力择优取向马氏体变体体积分数作为内变量,基于塑性理论框架,构建了MSMA分段线性化超弹性本构模型;提出了描述临界应力与环境磁场关系的Logistic关系函数,并基于试验数据拟合了关键参数;利用所建立的本构模型对考虑磁场影响下的MSMA超弹性进行了数值模拟,并从滞回曲线形状和滞回耗能两个方面与试验结果对比。结果表明:所提出的临界应力与环境磁场关系函数拟合优度可达0.993;材料本构模型预测曲线与试验结果较为接近,理论耗能能力与试验结果误差平均为11.9%。因此,模型能够较为准确地模拟MSMA的超弹性变形过程和耗能能力,为预测考虑磁场影响的MSMA超弹性特性提供了一种简便方法。     

单自由度SMA阻尼结构在高斯白噪声激励下的平稳随机振动分析

设计了一种超弹性形状记忆合金(Shape Memory Alloy, SMA)阻尼器。在SMA丝的Graesser本构模型基础上, 建立了SMA阻尼器的常规力学模型, 进而提出了其简化力学模型。采用随机等价线性化法建立了单自由度SMA阻尼结构在高斯白噪声激励下的平稳随机振动分析公式。算例比较了随机等价线性化法和蒙特卡罗(Monte Carlo)模拟法计算的结构振动响应, 证明了随机等价线性化法的有效性;比较了无控结构和SMA阻尼结构的动力特性和振动响应, 说明了SMA阻尼器能增加结构的刚度和阻尼比, 因而可有效抑制结构的振动。     

NiTi形状记忆合金的性能测试与表征

从NiTi形状记忆合金(Shape Memory Alloy，SMA)性能评价和智能结构研究的角度出发，分析了SMA的应力、应变、温度、电阻以及相变之间的关系。通过分阶段和不同变量组合，对SMA的力学、热学和电学特性进行了实验研究。建立了拉伸状态下形状各异的应力一应变曲线通用物理模型，并进行了数值模拟。结果表明：SMA在马氏体相变，特别是R相变时出现一系列物理、力学性质的异常变化，其本构关系呈现高度非线性；数值模拟结果与实验结果较好地吻合；采用应力、应变、电阻、温度四坐标同步测量是对SMA性能评价的重要方法和有效手段。     

基于SMA主动阻尼的桅杆振动控制的研究

将SMA(Shape Memory Alloy, 形状记忆合金)丝作为桅杆结构的纤绳或纤绳的一部分,把它和PSD光电位置传感器、数据采集板、计算机、恒流源组成控制系统,以对桅杆的振动进行控制。对桅杆结构的振动控制试验表明,处于超弹性状态的SMA纤绳,可以成为性能优异的主动阻尼器,并有效地使结构振动得到抑制。     

具有中等组分不同网状结构功能梯度构件的三维动力特性分析

功能梯度材料具有复杂的细部结构,其内部构造远比匀质材料复杂,因此其构件动力分析很难求得其解析解。该文建议一种新颖的功能梯度构件动力分析的细观元法。细观力学研究的目的在于建立材料的宏观性能同其组分材料性能及细观结构之间的定量关系,它可揭示不同的材料组合具有不同的宏观性能的内在机制。此法可实现材料细观结构到构件宏观响应的直接过渡分析,而计算单元与自由度又等同一般常规有限元,却使得组成功能梯度材料构件的各种材料细观构造得到反映。通过细观元技术,对具有中等组分不同网状结构功能梯度构件进行三维动力特性分析,并给出其三维固有频率及振型的三维分布,特别是给出了不同网格结构功能梯度板件应力振型的平面等值线图差异。结果表明:不同细观网格结构对功能梯度材料结构三维动力响应有较明显影响。     

含界面相三维全五向编织复合材料拉伸行为模拟及失效机制研究

基于三维全五向（Q5D）编织复合材料的细观结构模型,通过引入界面相单元,建立了含界面相Q5D编织复合材料单轴拉伸损伤失效分析模型。应用Python语言实现对ABAQUS的二次开发,将Linde等提出的失效准则和Von-Mises应力准则分别用于纱线和基体的渐进损伤判断,并确定材料的整体失效模式;对于界面相,采用Quads准则进行损伤判断。利用周期性位移边界条件,对含界面相Q5D编织复合材料的纵向拉伸应力-应变行为进行了渐进损伤数值模拟,详细讨论了在纵向拉伸载荷作用下材料的细观损伤起始、扩展和最终失效的演化过程,分析了材料的细观损伤失效机制,预测了材料的极限破坏强度,并研究了界面相性能对材料整体力学行为的影响规律。研究结果表明,数值模拟结果与实验值吻合较好,验证了渐进损伤模型的有效性,为该类材料的力学分析和优化设计奠定了基础。     

Theoretical analysis of a functionally graded shape memory alloy plate under graded temperature loading

As a new kind of functional material, functionally graded shape memory alloy (FG-SMA) possesses the excellent properties of both shape memory alloy (SMA) and functionally graded material (FGM). By combining the heat conduction theory with the theory of the mechanics of composite materials, a macro constitutive model, which can be used to describe the mechanical behavior of FG-SMA under graded temperature loading, is established. With this macro constitutive model, the thermo-mechanical properties of an FG-SMA plate, which is composed by ceramic and SMA and subjected to different surface temperature loads, are investigated. The theoretical results show good agreement with the existing data, which indicates that the macro constitutive model provided here is valid. The obtained results show that the martensite transformation does not always happen first at the top or bottom of the plate, and it is dependent on the surface temperatures. It can also be found that the stress decreases markedly due to the martensite transformation. This research can provide a basis for the design and in-depth investigation of FG-SMA material.     

SMA新型阻尼器在RAC框架上的减震性能分析

对所选SMA(形状记忆合金)丝材进行了应力-应变关系测定试验,并基于SMA丝材试验结果及相变伪弹性理论,设计一种新型SMA合页型阻尼器,并将其应用于所选RAC混凝土三层框架模型之中。通过ANSYS有限元软件对其进行的地震作用下的结构时程响应分析。结果表明：新型SMA阻尼器是一种较为理想的被动耗能装置,能够有效的减小结构的位移、速度及加速度响应,减震效果明显。     

A thermo-micro-mechanical modeling for smart shape memory alloy woven composite under in-plane biaxial deformation

This paper presents a theoretical study of the in-plane behavior of Smart Shape Memory Alloy Woven Composites (SSMAWC) under biaxial loading by developing an integrated micromechanical constitutive model. The model studied in this research is established on the geometric parameters of fibers, metal layers, unit cell, the material constants of composite constituents, and the orientation of fibers, in which the fibers in one direction are SMA ones. The Helmholtz free energy of a Shape Memory Alloy, in 3-Dimensional and 1-Dimensional applications is derived. Using mechanical energy of matrix and elastic yarns, the constitutive relations are developed with the use of strain energy approach and energy variation theorem. The kinetic relations of SMA depicted by Brinson is coupled with the final governing equation of the composite to predict the stress history in smart shape memory alloy woven composites. The deflection of the structure, subjected to uniform biaxial loading is studied numerically. It is found that the effect of Shape Memory Effect (SME) of the SMA wires on the behavior of plain woven flexible fabric composite is significant.     

Carbon nanotube forest growth on NiTi shape memory alloy thin films for thermal actuation

Actuation frequencies in thermally triggered Shape Memory Alloy (SMA) thin films are limited by the slow heat transport into/out of the films. Carbon Nanotubes (CNTs) are known to exhibit an exceptionally high thermal conductivity. Thus, we propose to thermally contact SMA films with CNTs to increase SMA actuation frequencies by enhanced heat transport through the CNTs. The basic requirement for this envisaged nanotube application is to obtain CNT forest growth on a SMA material while retaining a reversible martensitic transformation, as required for Shape Memory Effect exploitation. We show how such growth can be achieved on thin films of the SMA material NiTi. Future work is needed to measure thermal properties and obtainable cycling frequencies of CNT-SMA structures.     

Concept of a start-up clutch with nickel-titanium shape memory alloys

The ability of Shape Memory Alloys (SMA) to remind two different macroscopic shapes and to alter between these shapes by changing their temperature, leads to innovative approaches within drive technology. Especially Nickel-Titanium (NiTi) Shape Memory Alloys offer high actuating forces and adjustment travel in combination with high cycle stability. The shape memory effect is based on the transformation between martensitic and austenitic microstructure depending on the temperature of the actuators. The transformation temperatures in the range of 20°C to 100°C make NiTi SMA attractive for engineering applications. This paper investigates the technical use of NiTi SMA as actuators within a start-up clutch. The start-up of a drive train demands a higher torque, caused by the acceleration of the masses, than during the nominal speed. This demand can be realized with NiTi-Shape Memory Alloys (NiTi-SMA) without increasing the nominal size of the clutch appreciable.     

Numerical Modelling of the Activation Behaviour of SMA‐Actuator Wires – Application in an Innovative Drive System

The activation behaviour of Shape‐Memory‐Alloy actuators (SMA) (and more specifically their dynamic properties) is characterised by the rate of heating and cooling. This paper deals with the development, the validation and the application of a numerical model that simulates the activation behaviour of straight SMA‐wires depending on their geometry, the loading condition and an arbitrary time variant heating current. Taking changing thermal, electrical, geometric and mechanical boundary conditions into consideration, the model supports the design layout process of technical solutions with SMA‐wires. Based on this numerical model for dimensioning and conditioning of SMA‐actuators, an innovative rotatory drive system powered by straight SMA‐wires is presented.     

利用SMA进行桅杆振动控制的研究

提出了一种利用形状记忆合金(SMA)控制桅杆结构振动的新方法，即将SMA丝作为桅杆结构的纤绳或纤绳的一部分，把它和PSD传感器、数据采集板、计算机、恒流源组成控制系统，利用恒流源输出电流加热SMA丝，使其处于超弹性状态，变成性能优异的主动阻尼器，进而对桅杆结构的振动进行控制。对桅杆结构的振动主动控制试验表明，处于主动阻尼状态的SMA纤绳可以有效抑制结构振动。     

应用SMA智能阻尼器的结构模糊控制

利用形状记忆合金(SMA)的弹性模量随温度变化的特性和SMA超弹滞回耗能特性,设计提出一种新型SMA智能阻尼器。采用模糊控制器确定SMA智能阻尼器的SMA丝工作组数,从而瞬时准确地确定SMA智能阻尼器的刚度和阻尼的档位,并有效降低受控结构地震反应。利用MATLAB提供的模糊控制工具箱和Simulink模块建立仿真模型,数值分析某三层框架结构在无控、主动控制和模糊控制三种情况下的地震反应。仿真结果表明:在模糊控制情况下框架结构底层位移和加速度反应幅值分别降低了41%和48%,控制效果显著,接近主动控制的效果,从而验证了所设计提出的SMA智能阻尼器及其模糊控制的有效性与可靠性。     

形状记忆合金超弹性阻尼特性及工程应用

从工程中一种常见机器隔振模型出发,推导出了系统传递功率流表达式.计算模拟形状记忆合金的超弹性循环曲线并计算了TiNi形状记忆合金丝加卸载循环时的超弹性等效阻尼,并据此将合金丝作为一种等效阻尼材料应用到隔振模型中.通过计算机仿真,得出在此模型中使用记忆合金丝作为阻尼材料时不同的环境温度和系统振幅对模型隔振效果的影响.