Superelastic Shape Memory Elements Using Intrinsic Sensor Effects

2011 ◽  
Author(s):  
Alexander Czechowicz ◽  
Sven Langbein
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Elastic Deformation ◽  
Elastic Element ◽  
Medical Applications ◽  
Resistance Change ◽  
Ambient Temperatures ◽  
Superelastic Effect ◽  
Elastic Elements ◽  
Elastic Characteristics

The superelastic effect of shape memory alloys (SMA) allows reversible material deformations of up to 8% of an element’s length. Although such SMA elements are commonly used for medical applications, only a few utilizations are used in the field of industrial automation. An often disregarded advantage of superelastic elements is the option to replace a conventional elastic element with a smart element including elastic characteristics as well as a deformation sensor. The resistance change of pseudoplastic and superelastic alloys in dependency of varying ambient temperatures, their characteristics during deformation and concepts for different elastic elements with intrinsic sensor functions are the topics of the paper at hand. Additionally, this paper offers an overview over possible combinations of both alloy types utilized as sensing elements. A demonstrator device, capable of elastic-deformation and sensor-feedback signals is presented at the end of this publication.

Adaptive Elastic SMA Elements for Damping Applications

2013 ◽  
Author(s):  
Alexander Czechowicz ◽  
Peter Dültgen ◽  
Sven Langbein
Keyword(s):  
Boundary Conditions ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Smart Materials ◽  
Electrical Resistance ◽  
Thermal Activation ◽  
Hysteretic Behavior ◽  
Damping Function ◽  
Actual Shape ◽  
Elastic Elements

Shape memory alloys (SMA) are smart materials, which have two technical usable effects: While pseudoplastic SMA have the ability to change into a previously imprinted actual shape through the means of thermal activation, pseudoelastic SMA show a reversible mechanical elongation up to 8% at constant temperature. The transformation between the two possible material phases (austenite and martensite) shows a hysteretic behavior. As a result of these properties, SMA can be used as elastic elements with intrinsic damping function. Additionally the electrical resistance changes remarkably during the material deformation. These effects are presented in the publication in combination with potential for applications in different branches at varying boundary conditions. The focus of the presented research is concentrated on the application of elastic elements with adaptive damping function. As a proof for the potential considerations, an application example sums up this presentation.

Laser welding of shape memory alloys for medical applications

2008 ◽  
Author(s):  
Ronny Pfeifer ◽  
Dirk Herzog ◽  
Oliver Meier ◽  
Andreas Ostendorf ◽  
Heinz Haferkamp ◽  
...  
Keyword(s):  
Laser Welding ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Medical Applications

Recent Developments in High Temperature Shape Memory Alloys

1994 ◽  
Vol 360 ◽  
Author(s):  
Jeno Beyer ◽  
Jan.H. Mulder
Keyword(s):  
High Temperature ◽  
Research And Development ◽  
Shape Memory Alloys ◽  
Time Dependence ◽  
Shape Memory ◽  
Medical Applications ◽  
Space Technology ◽  
Shape Memory Properties ◽  
Recent Developments ◽  
Number Of Cycles

AbstractThe functional properties of Shape Memory Alloys (SMA's) are used succesfully at present in a variety of industrial and medical applications. The use of these materials in smart structures is now emerging in the field of aeronautic/space technology. Many applications require higher operating temperatures than available to date, or higher cooling rates and/or a higher number of cycles. For this purpose the properties and fabricability of commercial alloys as Ni-Ti-(X), Cu-Al-Ni or Cu-Zn-Al are being adjusted and improved. Other feasible alloys are being developed. The research and development is directed towards the control of the stress, strain, temperature and time dependence of shape memory properties for a stable in-service behaviour. In this paper the various approaches taken up in recent years by academic and industrial laboratories for developing high temperature SMA's are reviewed.

Implementation and Investigation of a Compact, Powerful System for Diagnosis and Control of Shape Memory Alloys in Technical Applications

2019 ◽  
Author(s):  
Max Kaiser ◽  
Nils Neblung ◽  
Martin Gurka
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Electrical Resistance ◽  
Control Strategies ◽  
Memory Systems ◽  
Constant Load ◽  
Resistance Change ◽  
Model Based ◽  
And Control

Abstract In this paper we present the development, implementation and testing of a compact system for diagnosis and control of actuators based on metallic shape memory alloys (SMA). Using NiTi-SMA, very compact, cost-effective and lightweight actuation systems can be realized. In applications where the SMA is activated by internal Joule heating or its condition is diagnosed by the self-sensing of its electrical resistance, an electrical system capable of reliably measuring very small resistance changes (< 1 ohm) without affecting the phase-state of the SMA is required. In addition, the system must offer the possibility to evaluate the nonlinear, hysteresis-afflicted behavior of the SMA and to handle this difficulty, e.g. utilizing a model-based control. This paper presents a simple compact and adaptive system based on a microcontroller that meets these requirements. Detailed functional tests were carried out with the system to establish a correlation between the change in electrical resistance in the range < 200 mOhm and the current strain state of the actuator. For this purpose, a first series of tests was performed, with the SMA wires working against a constant load. In a second tests series, the SMA wires worked against springs of different stiffness. The use of a microcontroller enables simple implementation of different control strategies. The control system for the non-linear resistance change utilizes a fuzzy logic which divides the control algorithm into three regimes. In the regime of the martensitic phase transformation a PI-controller is used. The state of actuators with an absolute electrical resistance < 1 Ohm and a resistance change < 200 mohm associated with the phase transformation can be precisely measured and controlled with an accuracy < 10 mohm. The system can be configured with little effort for different tasks and shape memory systems of different sizes. Furthermore, it is possible to implement more complex control algorithms up to model-based controllers.

scholarly journals SMA Wire Characterization for 3D Steerable Active Devices

2018 ◽  
Author(s):  
Saeed Karimi ◽  
Bardia Konh ◽  
Hashem Ashrafiuon
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Smart Materials ◽  
Loading Condition ◽  
Memory Effects ◽  
Medical Applications ◽  
Temperature Changes ◽  
Active Devices ◽  
Shape Memory Effects ◽  
Biomedical Fields

Shape Memory Alloys (SMAs) are a unique class of smart materials that recover their deformed shapes, caused by a loading condition, through temperature changes [1]. SMAs are employed in a variety of areas including aerospace, automotive, and biomedical fields. Their Pseudoelastic characteristics, shape memory effects, and biocompatibility make them particularly suitable for medical applications.

Thermomechanical modeling and experimental investigation of transformation-induced creep and stress relaxation in shape memory alloy wires

2016 ◽  
Vol 28 (7) ◽  
pp. 923-933 ◽  
Author(s):  
Fateme Zare ◽  
Mohammad Jannesari ◽  
Mahmoud Kadkhodaei ◽  
Peiman Mosaddegh
Keyword(s):  
Stress Relaxation ◽  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Reverse Transformation ◽  
Creep Recovery ◽  
Thermomechanical Model ◽  
Ambient Temperatures ◽  
Relaxation Responses ◽  
Creep And Stress Relaxation

Creep and relaxation phenomena are being observed in shape memory alloys, not only at high temperatures but also at room temperature, due to their martensitic transformation. Transformation-induced creep and stress relaxation in shape memory alloys occur due to temperature variations during loading and unloading cycles. In this work, a one-dimensional fully coupled thermomechanical model was employed to develop a continuum framework for studying these behaviors in shape memory alloy wires. A decrease or increase in stress was observed during forward or reverse transformation at a constant amount of strain, showing the stress relaxation and stress recovery, respectively. Similarly, the model predicts that strain increases or decreases when stress is held fixed in the course of forward or reverse transformation, meaning the phenomena of creep and creep recovery, respectively. This model provides the ability of investigating the effects of different ambient temperatures, strain rates, applied stresses and strains, and wire radii on the creep and relaxation responses of shape memory alloys. Relaxation and creep experiments at different ambient temperatures and loading or unloading rates were also done on NiTi wires, and the theoretical predictions were shown to be in a good agreement with the empirical observations.

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