Fe-Mn-Si-Cr-Ni-C系形状记忆合金中一种新的热机械循环训练机制

研究了热机械循环训练对Fe-Mn-Si-Cr-Ni-C系合金形状记忆效应的影响.结果表明对于不同碳含量的3种合金,只要中间退火温度选择适当,热机械循环训练都可显著提高合金的形状记忆效应.合金的最佳中间退火温度随碳含量的增加而升高.含碳最低(＜0.02%)合金的最佳中间退火温度为550℃,而含碳0.18%舍金的最佳退火温度高达1050℃.经TEM分析,发现对于低含碳量(≤0.12%)的两种合金,热机械循环训练提高合金形状记忆效应的机制是层错增加机制;而对于含碳量0.18%的合金,其机制是第二相的析出作用.     

Transformation characteristics of shape memory alloys in a thermal cycle

This paper presents a systematic study on the transformation characteristics of shape memory alloys in a thermal cycle with/without a load. The methods to determine some key material properties are proposed. The expressions for estimating the hysteresis and transformation interval under different types of loads are obtained. The influential factors in real experiments are identified and discussed.     

NiTiHf-based shape memory alloys

Abstract

NiTiHf-based shape memory alloys have been receiving considerable attention for high temperature, high strength and two-way shape memory applications since they could have transformation temperatures above 100°C, shape memory effect under high stress (above 500 MPa) and superelasticity above 100°C. Moreover, their shape memory properties can be tailored by microstructural engineering. However, NiTiHf-based alloys have some drawbacks such as low ductility and high slope in stress induced martensite transformation region. In order to overcome these limitations, studies have been focused on microstructural engineering by aging, alloying and processing. It has been revealed that microstructural control is crucial to govern the shape memory properties (e.g. transformation temperatures, matrix strength, shape recovery strain, twinning type, etc.) of NiTiHf-based alloys. A summary of the most recent improvements on selected NiTiHf-based systems is presented to point out their significant shape memory properties, effects of alloying, aging and microstructure of transforming phases and precipitates.     

Thermodynamic constitutive model for load-biased thermal cycling test of shape memory alloy

This paper presents a three-dimensional calculation model for martensitic phase transformation of shape memory alloy. Constitutive model based on thermodynamic theory was provided. The average behavior was accounted for by considering the volume fraction of each martensitic variant in the material. Evolution of the volume fraction of each variant was determined by a rate-dependent kinetic equation. We assumed that nucleation rate is faster for the self-accommodation than for the stress-induced variants. Three-dimensional finite element analysis was conducted and the results were compared with the experimental data of Ti–44.5Ni–5Cu–0.5 V (at.%) alloy under bias loading.     

Investigation on ferromagnetic shape memory alloys

Ferromagnetic shape memory alloys, exhibiting large recoverable strain and rapid frequency response, appear to be promising shape memory actuator material. These materials exhibit large shape memory effect associating with martensitic transformation, and magnetic-field-induced strain in the martensite state. The recent development in researches on NiMnGa, NiFeGa, and CoNiGa in our group is briefly reviewed. The perspectives of the ferromagnetic shape memory alloy are also described.     

A multi-dimensional constitutive model for shape memory alloys

This paper presents a multi-dimensional thermomechanical constitutive model for shape memory alloys (SMAs). This constitutive relation is based upon a combination of both micromechanics and macromechanics. The martensite fraction is introduced as a variable in this model to reflect the martensitic transformation that determines the unique characteristics of shape memory alloys. This constitutive relation can be used to study the complex behavior associated with 2-D and 3-D SMA structures. A simple example using this constitutive model is also presented, which reveals a new and interesting phenomenon of 3-D SMA structures.     

Calorimetric techniques for the evaluation of thermal efficiencies of shape memory alloys

The latent heat and entropy changes of NiTi shape memory effect (SME) alloys have been evaluated by three different calorimetric techniques; adiabatic calorimetry, differential scanning calorimetry and a Clapeyron analysis of isothermal stress-strain data. It is found that these techniques provide consistent estimates for the enthalpy and entropy to within 20% for NiTi and noble metal SME alloys. From published thermodynamic data for SME alloys, thermal efficiencies were calculated based on an ideal SME heat engine cycle. It was found that NiTi provides the maximum thermal efficiency with the highest temperature transformation range.     

带有形状记忆致动器的自适应机翼

 在由EU(European Union)通过TMR(Training and Mobility of Researchers)进行“晶状固体中的相变”项目规划中，柏林工业大学热动力学专业开发了一种自适应机翼样品．它由一个可弯曲的基板和一个空气动力外壳组成．该自适应机翼的重要组成部分是集成到结构中的传感器和致动器．在这种情况下，电阻应变片用于测量机翼的形状，而由形状记忆线材制成的致动器组件则起调节结构的“金属肌肉”作用．利用相应的调整算法，可以获得大量不同要求的形状．     

Applications of titanium-nickel shape memory alloys

The shape memory alloy based on the TiNi phase has given rise to a wide range of commercially viable products. Two applications are described which illustrate the different ways in which shape memory can be used in an industrial product. In one of these, the change in shape is prevented so that the shape memory tubular element can be used as a mechanical coupling to join two pipes together securely. Such couplings have replaced welding in hydraulic lines in aircraft and ships and in the repair of undersea pipe lines.The other application demonstrates the use of a tubular shape memory element in torsion to operate a boom latch and release mechanism for the deployment of the booms on a space satellite. It is shown that a shape memory alloy can satisfy a tight and exacting specification in operating as an actuator.     

A robust model of pseudoelasticity in shape memory alloys

A model of pseudoelasticity in shape memory alloys is developed within the incremental energy minimization framework. Three constitutive functions are involved: the Helmholtz free energy and rate‐independent dissipation that enter incrementally the minimized energy function, and the constraint function that defines the limit transformation strains. The proposed implementation is based on a unified augmented Lagrangian treatment of both the constitutive constraints and nonsmooth dissipation function. A methodology for easy reformulation of the model from the small‐strain to finite‐deformation regime is presented. Finite element computations demonstrate robustness of the finite‐strain version of the model and illustrate the effects of tension–compression asymmetry and transversal isotropy of the surface of limit transformation strains. Copyright © 2012 John Wiley & Sons, Ltd.     

形状记忆合金驱动的微执行器

以TiNi基为代表的形状记忆合金（SMA）具有做功密度大、可恢复应变应力大、驱动电压低、良好生物相容性等优点，在微执行器领域具有极为广阔应用前景。本文主要总结了TiNi基SMA丝、薄带、薄膜在微执行器方面的国内外研究应用现状，并对目前SMA在微驱动领域应用所存在的问题及其未来的发展趋势进行了分析讨论。     

A numerical study on bolted end-plate connection using shape memory alloys

Superelastic shape memory alloys (SMAs) have the ability to recover their original shape after experiencing large strains. A new beam-to-column connection incorporating long shank SMA bolts is presented in this paper. By using the unique characteristics of SMAs, the connection possesses self-centering abilities. The 3D connection model is created using the software ANSYS, and Auricchio’s model is used to simulate the superelastic behavior of the SMA bolts. With cyclic loads applied on the beam ends, the behavior of the connection is studied. The results show the semi-rigid and moderate energy dissipation characteristics of the connection. Since the moment-carrying capacity of bolt cluster controlled below the elastic flexural capacity of connecting beam, a superelastic hinge forms just at the beam-to-column interface. The inelastic interstory drift angle of the connection reaches 0.035 rad, and 94% of the total rotations are recoverable upon unloading.     

Transformation behaviour and one-way shape memory effect in Fe-Mn-Si shape memory alloys

Humboldt-Fellow, on leave from Centro Atomico Bariloche, 8400 Bariloche, and CRUB, Universidad National del Comahue, Argentina.     

Repeatable temperature memory effect of TiNi shape memory alloys

An incomplete transformation cycle induces a kinetic stop in the following complete transformation cycle in TiNi shape memory alloys. The kinetic stop can be regarded as a memory of the previous interruption temperature. This memory was generally believed to be a one-time phenomenon. Herein, we show that the temperature memory effect is actually a long-lasting phenomenon. Experimental results show that a repeatable temperature memory effect can be introduced into a TiNi alloy by a deformation lager than 12%. Deformation induced dislocations are considered a main factor to the persistence of the memory. The memory becomes more distinct with increasing numbers of the incomplete thermal cycle, but the memory becomes less distinct with increasing numbers of subsequent complete transformation cycling.     

Influence of thermal cycling on the martensitic transformation and shape memory effect of a Fe－16Mn－

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Martensitic transformation and shape memory properties of Ti-Ta-Sn high temperature shape memory alloys

The effects of Ta and Sn contents on the martensitic transformation temperature, crystal structure and thermal stability of Ti-Ta-Sn alloys are investigated in order to develop novel high temperature shape memory alloys. The martensitic transformation temperature significantly decreases by aging or thermal cycling due to the formation of ω phase in the Ti-Ta binary alloys. The addition of Sn is effective for suppressing the formation of ω phase and improves stability of shape memory effect during thermal cycling. The amount of Sn content necessary for suppressing aging effect increases with decreasing Ta content. High martensitic transformation temperature with good thermal stability can be achieved by adjustment of the Ta and Sn contents. Furthermore, the addition of Sn as a substitute of Ta with keeping the transformation temperature same increases the transformation strain in the Ti-Ta-Sn alloys. A Ti-20Ta-3.5Sn alloy reveals stable shape memory effect with a martensitic transformation start temperature about 440 K and a larger recovery strain when compared with a Ti-Ta binary alloy showing similar martensitic transformation temperature.