Thermomechanical cycling, two way memory and concomitant effects in Cu-Zn-Al alloys

Amplifying and Leveraging Generated Force Upon Heating and Cooling in SMA Knitted Actuators

This work reexamines traditional shape memory alloy (SMA) loading paths commonly used in SMA-based actuator applications and presents a novel, superimposed condition in which SMA generates substantial forces upon heating and cooling. This atypical effect, which is investigated with a textile-based actuator, was found to be prominent at the completion of material phase transformation, at which point thermal expansion/contraction became the dominant force-generating mechanism. We demonstrate that amplification of generated forces can be accomplished by varying the applied thermal load, applied structural strain, as well as actuator architecture. Specifically, we present SMA knitted actuators as an actuator architecture that increases the effect by aggregating SMA wires within a complex strain profile-effectively providing a larger operational window for the effect to propagate. The amplification of blocking forces through this novel operational procedure suggests reconsidering traditional blocking force design paradigms and opens untapped actuator application spaces, such as the highlighted medical and aerospace wearable technologies.

Observation of the two-way shape memory effect in an atomistic model of martensitic transformation

We study a system of classical particles in two dimensions interacting through an isotropic pair potential that displays a martensitic phase transition between a triangular and a rhomboidal structure upon the change of a single parameter. Previously it was shown that this potential is able to reproduce the shape memory effect and super-elasticity, among other well known features of the phenomenology of martensites. Here we extend those previous studies and describe the development of the more subtle two-way shape memory effect. We show that in a poly-crystalline sample, the effect is mostly due to the existence of retained martensite within the austenite phase. We also study the case of a single crystal sample where the effect is associated to particular orientations of the dislocations, either induced by training or by an ad hoc construction of a starting sample. Received: 16 January 2017,  Accepted: 23 March 2017; Edited by: L. Viña ; Reviewed by: J. Pons, Universitat de les Illes Balears, Palma  de Mallorca, Spain; DOI: http://dx.doi.org/10.4279/PIP.090004 Cite as: E. A. Jagla, Papers in Physics 9, 090004 (2017) This paper, by E. A Jagla, is licensed under the Creative Commons Attribution License 3.0.  

Modelling of Adaptive Composite Materials with Embedded Shape Memory Alloy Wires

Various models and calculation methods for the description of shape memory behaviour have been developed in recent years by different research groups. Some of the models have already been extended towards the thermomechanical and functional behaviour of matrix materials with embedded SMA-wires. The basic concepts of a thermomechanical model which has found widespread use in the literature on smart materials, are critically reviewed.

A recently developed model based on a generalised thermodynamic analysis of the underlying martensitic transformation is discussed more into detail. Experimental verifications indicate that this thermodynamic model can be developed to an effective tool for the materials design of matrix materials with embedded SMA-wires.

Shape memory alloys for medical applications

The shape memory alloys exhibit a number of remarkable properties, which open new possibilities in engineering and more specifically in biomedical engineering. The most important alloy used in biomedical applications is NiTi. This alloy combines the characteristics of the shape memory effect and superelasticity with excellent corrosion resistance, wear characteristics, mechanical properties and a good biocompatibility. These properties make it an ideal biological engineering material, especially in orthopaedic surgery and orthodontics. In this work the basis of the memory effect lies in the fact that the materials exhibiting such a property undergo a thermoelastic martensitic transformation. In order to understand even the most elementary engineering aspects of the shape memory effect it is necessary to review some basic principles of the formation and the characteristics of the martensitic phase. The different properties of shape memory, superelasticity, two-way shape memory, rubber-like behaviour and a high damping capacity are reviewed. Some applications proposed in recent years are described and classified according to different medical fields.