Engineering aspects of shape memory alloys pdf

 

    of civil engineering structures, considering both passive and semi-active devices. • It discusses some aspects related to the processing of the shape memory. Engineering Aspects of Shape Memory Alloys provides an understanding of shape memory by defining terms, properties, and applications. It includes tutorials. Shape Memory Alloys (SMAs) have been on the forefront of research for the . engineering effects, and applications of shape memory alloys, including the.

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    Engineering Aspects Of Shape Memory Alloys Pdf

    Download Citation on ResearchGate | On Jan 1, , T.W. Duerig and others published Engineering Aspects of Shape Memory Alloys. Darel E. Hodgson, Shape Memory Applications, Inc., Ming H. Wu, Memry Corporation, c memory. Although a relatively wide variety of alloys are known to exhibit the shape memory effect Proceedings of Engineering Aspects of. Shape. shape memory and superelastic properties. Shape loys or alloy compositions, but to a family of alloys .. Duering and G.R. Zadno, Engineering Aspects of.

    Correspondence and Footnotes Abstract Shape memory alloys SMA are materials that have the ability to return to a former shape when subjected to an appropriate thermomechanical procedure. Pseudoelastic and shape memory effects are some of the behaviors presented by these alloys. The unique properties concerning these alloys have encouraged many investigators to look for applications of SMA in different fields of human knowledge. The purpose of this review article is to present a brief discussion of the thermomechanical behavior of SMA and to describe their most promising applications in the biomedical area. These include cardiovascular and orthopedic uses, and surgical instruments. Key words: Shape memory alloys, Biomaterials Introduction Shape memory alloys SMA constitute a group of metallic materials with the ability to recover a previously defined length or a shape when subjected to an appropriate thermomechanical load 1. When there is a limitation of shape recovery, these alloys promote high restitution forces. Because of these properties, there is a great technological interest in the use of SMA for different applications. Although a relatively wide variety of alloys present the shape memory effect, only those that can recover from a large amount of strain or generate an expressive restitution force are of commercial interest. SMA based on Ni-Ti are the alloys most frequently used in commercial applications because they combine good mechanical properties with shape memory. The remarkable properties of SMA have been known since the 's.

    Similar results have been obtained by Infrared IR thermography. In addition, displacement and strain fields in near crack tip regions have been analyzed by DIC. The knowledge of the effective SIF is of great importance since it allows defining both fast fracture conditions and stable fatigue crack growth. In fact, fracture mechanics based approaches have been largely used for fatigue investigations, i.

    Finally, more recently, crack tip transformation mechanisms have been analyzed by local mechanical measurements based on instrumented indentation In particular, stress-induced martensitic transformations have been captured by the indentation response and the effects of the testing temperature have been also analyzed. All these experimental studies, have confirmed that highly localized stresses arising in the crack tip region cause local stress-induced texture evolutions, leading to the formation of detwinned martensite at the very crack tip.

    Applications of Shape Memory Alloys for Neurology and Neuromuscular Rehabilitation

    These phase transitions play a significant role on crack evolution mechanisms under both static and fatigue loading conditions. To better understand the effects crack tip texture evolutions on fracture and fatigue properties of SMAs, numerical and analytical studies have been carried out.

    In particular, the Finite Element FE method, with special constitutive models for SMAs, has been used to analyze the near crack tip stresses and transformation mechanisms 25 , 26 , 27 , 28 , 29 , 30 , 31 , In addition, some analytical models have been developed 33 , 34 , 35 , 36 , 37 , 38 , 39 , which are mainly based on modified linear elastic fracture mechanics LEFM concepts.

    In particular, a novel analytical method has been developed in ref. This method allows predicting the extent of crack tip transformation region as well as the resulting stress distribution.

    Furthermore, based on this model fracture control parameters for SMAs have been proposed 39 , i. However, despite the large number of research reports on fracture of NiTi SMAs, much effort should be paid for an effective understanding of the role of phase transformations on the crack formation and propagation mechanisms. Within this context, systematic experiments and theoretical studies were carried out in this investigation with the aim of capturing the actual stress-strain distribution at the crack tip.

    The effects of temperature on fracture properties of SMAs, within the pseudoelastic regime of the alloys, were also analyzed. In particular, temperature controlled fracture tests were carried out, by using single edge crack specimens made of a commercial pseudoelastic NiTi alloy. A satisfactory balance between these properties gives the SMA materials the right characteristics to be employed in a number of different fields and, in particular, those related to physical rehabilitation.

    Among the several properties of SMA, pseudoelasticity and the shape memory effect SME are the most useful in neurology and neuromuscular rehabilitation applications: in particular, stable quasi constant stress levels and long large deformability ranges plateaux and also the possibility to modify those parameters with thermomechanical treatments can be exploited in designing a variety of devices and solutions for rehabilitation; because, in addition, these same materials also display interesting internal friction and mechanical hysteresis characteristics, the peculiarities of SMA could be of help in applications that possess dynamic characteristics.

    There are a number of groups who have been developing ideas and devices exploiting SMA for imparting forces on or producing movements of body parts, especially with the aim of assisting or replacing lost functions. The most relevant experiences address biomedical problems, such as the mobilization of paralyzed hands, fingers e. The corpus of published literature highlights the promising aspects of SMA technology [ 17 ] and also describes the limitations connected with those materials.

    Shape memory alloys: Properties and biomedical applications

    Considering the designs based on the shape memory effect, most papers mention the compactness and the possibility to develop flexible technologies as valuable aspects of SMA actuation, while the trade-off between torque or force output and actuation speed appears to be the main issue in rehabilitation applications.

    The question of actuator control, which is also one of great consequence, is approached by various authors in different ways, depending on the final aim: the literature on rehabilitation applications of SMA describes open-loop strategies directed at simply triggering the start or pacing the repetition of actuation cycles [ 10 , 11 ]; open-loop methods are also proposed to obtain specified movement trajectories [ 8 , 9 ]; alternatively, more sophisticated closed-loop strategies are reported to provide very precise control of actuation timing and output parameters [ 18 , 19 ].

    The use of pseudoelasticity is proposed in different papers tackling, in particular, limb positioning and gait rehabilitation [ 14 , 15 , 16 ]. In those works, the deformability, adaptability and the nonlinear mechanical properties of SMA are considered as a resource for obtaining compliant and biomechanically-sound solutions to the clinical problems connected with spasticity and paresis.

    An additional review of prior results can be found in [ 20 ]. Results and Discussion of Selected Rehabilitation Applications In relation to the characteristics discussed above, some applications of SMA in the field of neuromuscular rehabilitation will be reported and described, with the aim of demonstrating the feasibility and relevant outcomes and showing how the different functionalities of this class of materials can be applied. Portable Devices for Passive and Aided Exercise The physical rehabilitation of patients that suffer from paresis as a consequence of a neurological insult generally includes active exercise, which is often segmental at an initial stage and becomes increasingly functional as motor recovery proceeds.

    Although it is recognized that active exercise is extremely important for the re-acquisition of motor skills, passive mobilization of the limbs is also a standard part of physical treatment, because it can help safeguard the viscoelastic properties of tissues in otherwise disused muscles and joints.

    This approach is particularly important in the sub-acute period after the neural trauma, because in that phase, paresis itself precludes the active work-out of the patient. In addition to this, it can be imagined that a repetitive mobilization of the affected segments could help maintain viable a network of neuronal circuitry that is involved in movement planning and execution, at least by continually providing proprioceptive information and avoiding deafferentation.

    In keeping with this latter consideration, our group created a portable mobiliser for the ankle joint, described in [ 21 ].

    Engineering Aspects of Shape Memory Alloys

    Portability was the fundamental requirement in order to make this device truly available to patients in the acute phase, because they are often bedridden and sometimes cannot even sit upright. Therefore, it was decided that the system should be suitable to be utilized by patients sitting on or lying in bed. This characteristic differentiates the present device from other ones able to produce passive movements of the tibiotarsal joint.

    The concept was implemented using SMA actuation, because it allows compactness and low weight. For reasons related to the possibility of assessing the central effects of the therapy administered through this device, it was also of interest that the actuator should emit limited electromagnetic noise, in order not to affect electroencephalographic EEG measurements.

    This is also possible using SMA-based technology. Finally, Part V deals with superelasticity, with an introductory paper and then several specific examples of product engineering. We are always looking for ways to improve customer experience on Elsevier. We would like to ask you for a moment of your time to fill in a short questionnaire, at the end of your visit. If you decide to participate, a new browser tab will open so you can complete the survey after you have completed your visit to this website.

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