Demands on Shape Memory Alloys from the Application Designer's Point of View

The use of Shape Memory Alloys in dampers devices able to reduce the wind, rain or traffic induced oscillations in stayed cables is well represented in the literature. An analysis realized on standard cables at existing facilities shows the reliable efficiency of the SMA wire in damping oscillations. Such studies also provide tools to build the SMA dampers and to account for the effects of the external temperature in the SMA. The particular study reported in this paper focuses on a critical discussion on the relation between the wire diameter and macroscopic behavior and external temperature effects. The damping requires the absorption of the mechanical energy and its conversion to heat via the action of hysteresis cycles. The study was realized on wires of different diameters. In particular, the study centers on wires of diameter 0.2, 0.5 and 2.46 mm. The flat cycles showed by the thin wires (i.e., diameter 0.2 and 0.5 mm) and the non-classical S-shaped cycles of wires of diameter 2.46 mm establish clear differences of the response under external summer-winter temperature actions. Depending of the room temperature and SMA composition, a complete flat transformation in thin wires requires stresses, in general, near 300-400 MPa. A complete transformation for an S-shaped cycle need stresses as higher as 600 MPa. The analysis of the behavior of these wires under the action of warm temperatures in summer and cold temperatures in winter, suggests that thin wires lose their pseudo-elastic state in winter. The S-shaped permits positive working in extended temperature domain and a supplementary investigation establishes that S-shaped can be increased by strain aging. The hysteretic behavior in S-shaped permits practical working under external temperatures as applications in bridges require. From a fundamental point of view, the flat cycles are coherent with the classical treatment of the SMA as a first order phase transition but the S-shaped can be considered associated to an anomaly in heat capacity.

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Application of Shape Memory Alloys in Locking Devices

Volume 2: Mechanics and Behavior of Active Materials; Integrated System Design and Implementation; Bio-Inspired Materials and Systems; Energy Harvesting ◽

10.1115/smasis2012-8155 ◽

2012 ◽

Author(s):

Ralf Theiß ◽

Daniel Lichte ◽

Kai-Dietrich Wolf

Keyword(s):

Shape Memory Alloys ◽

Shape Memory ◽

Conceptual Development ◽

Control Unit ◽

Point Of View ◽

Electric Motors ◽

Security Issues ◽

Translational Movement ◽

Alternative Approach ◽

And Control

Networked and automated locking systems are an easy to use and to administer solution for governmental and commercial use, especially in combination with advanced authentication technologies like RFID-based keys. Regardless of the advances of authentication technologies locking systems still use electric motor transmission units, which are controlled by an authentication and control unit. From an economic and an engineering point of view this approach has significant weaknesses. The main issue is the transformation of the rotational movement generated by the motor into a translational movement, which is necessary for locking applications. This leads to the implementation of a complex transmission and an inappropriate and inefficient mode of operation for the used electric motors, inflicting the reliability and increasing the overall cost as well as the required building space of the system. Consequently, there is a need to reduce the complexity and the cost of locking systems by optimizing the actuator and the mechanical components. An alternative approach for actuators is usable with Shape Memory Alloys (SMA) and the Shape Memory Effect. Components made from SMA can return after a deformation into a pre-trained shape under certain thermal and mechanical conditions. SMA-based components can provide mechanical work as well as high forces while returning to their previous shape. Common SMA-based actuators have the form wire and provide significant pull forces when activated thermally. So it becomes possible to replace conventional electric motors and the necessary transmission with SMA-based wire actuator. The article provides an overview of the requirements and restrictions for the application of SMA in locking systems, illustrating the issues of existing locking system designs and an approach to overcome their limitations with a system based on SMA. After a short introduction chapter two introduces SMA as an alternative approach for actuators. Chapter three focuses on the main issues of locking systems and explains the requirements for the development of new actuators for locking devices. Chapter 4 describes the conceptual development of an approach for a SMA-based locking system illustrating security issues. The article concludes with a summery and an outlook.

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Application of Electron Backscatter Diffraction to Shape Memory Alloys

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.521.255 ◽

2012 ◽

Vol 521 ◽

pp. 255-268 ◽

Cited By ~ 1

Author(s):

Paola Bassani

Keyword(s):

Shape Memory Alloys ◽

Shape Memory ◽

Electron Backscatter Diffraction ◽

Point Of View ◽

Theoretical Point ◽

Characterization Methods ◽

Research Areas ◽

Time Shape ◽

Electron Backscatter ◽

Backscatter Diffraction

This overview highlights very recent application of electron backscatter diffraction (EBSD) to shape memory alloys, as main investigation technique but also as ancillary technique for other characterization methods. Over the last two decades EBSD in the scanning electron microscope has become a powerful tool for the characterization of many materials and transformation. In the mean time, shape memory alloys (SMA) are continuously studied: from a theoretical point of view, in order to clarify unsolved fundamentals of their phase transformations and characterize or develop new SMA systems, and from an engineering point of view, to solve design and processing problems related to the continuously growing examples of applications. Application of EBSD to SMA, even if hindered by limitations generally found also in other metallic system when phase transformation and martensitic phases are involved, provided useful information for both research areas.

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Processing and Superelasticity of Ni-Ti Shape Memory Alloys

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.660.103 ◽

2015 ◽

Vol 660 ◽

pp. 103-107

Author(s):

Mircea Dobrescu ◽

Marius Vasilescu

Keyword(s):

Plastic Deformation ◽

Shape Memory Alloys ◽

Shape Memory ◽

Alloy Composition ◽

Martensitic Transformations ◽

Heat Treating ◽

Point Of View ◽

Stored Energy ◽

Influence Of Temperature ◽

Ti Alloys

In the paper is shown the study of super elasticity of Ni-Ti shape memory alloys from the point of view of stored energy, strain dependencies and martensitic transformations that influence superelasticity of Ni-Ti shape memory alloys [1]. We also present the influence of temperature and alloy composition on the properties of Ni-Ti alloys after plastic deformation and heat treating [2].

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