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SHAPE MEMORY ALLOYS
| Date post: | 17-Sep-2015 |
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SHAPE MEMORY ALLOYS
Acknowledgement
Information and pictorial illustrations to create this work have been drawn from class notes, prescribed text books and various internet resources. The author gratefully acknowledges the same. Any objections to the use of internet resources may please be indicated to [email protected] so that the same can be removed from the illustrations used in this file.
This presentation is created with the sole intention of benefitting a large number of student community. This may not be used for any commercial purpose.
AGENDA
Introduction
Characteristics of Shape Memory Alloys
Applications of Shape Memory Alloys
INTRODUCTION
Shape memory alloys are a class of metal alloys that can recover apparent strains when they are heated above a certain temperature.
Shape Memory Alloys are lightweight and a solid state alternative to conventional actuators such as hydraulic pneumatic and motor based systems.
Shape memory alloys have different shape memory effects. Two common effects are one way and two way shape memory.
Characteristics of Shape Memory Alloys
Shape Recovery Stress
Fe-SMAs are usually applied as jointing goods.
Such application using the Fe-SMAs is more in need of the recovery stress rather than the recovery strain.
Solid line and broken lines indicate the behavior of
the recovery stress with and without training, respectively.
The behavior of the above material is shown below.
Shape recovery strain
Shape recovery strain depends on the initial strain and the number of cycles of training.
Training treatment consists of repetitive processing of proper deformation and heating.
The recovery strain shows a maximum value with 5~8% initial strain and higher strain deteriorates its value.
On the other hand, the results of the shape recovery ratio show that training treatment is imperative to obtain perfect shape recovery, not to mention that the initial strain is restricted to the region of low strain (less than 2%).
Super elasticity-
SMAs also display super elasticity, which is characterized by recovery of unusually large strains.
As a result, these materials can reversibly deform to very high strains up to 8 percent.
Applications of Shape Memory Alloys
Aircrafts and Spacecrafts
SMAs are being explored as vibration dampers for launch vehicles and commercial jet engines.
Automotive Industry
The automotive valve used to control low pressure pneumatic bladders in a car seat that adjust the contour of the lumbar support / bolsters makes use of SMAs.
Other targeted applications include electric generators to generate electricity from exhaust heat and on-demand air dams to optimize aerodynamics at various speeds.
Robotics
There are studies on using SMAs in robotics in order to create very light weight robots.
Civil Structures-
The Intelligent Reinforced Concrete (IRC) incorporates SMA wires embedded within the concrete as they can sense cracks and contract to heal macro-sized cracks.
Telecommunication
The autofocus actuator for smart phones and optical image stabilisation modules are driven by SMA wires.
Medicine
Used as fixation devices in orthopaedic surgery and dental braces to exert constant tooth-moving forces on the teeth.
The self expanding properties of Nitinol alloys manufactured to Body Temperature Response provides an alternative to balloon expandable devices in stent grafts.
This gives the ability to adapt to the shape of certain blood vessels when exposed to body temperature.
Optometry
The eyeglasses made of shape-memory alloys are more robust against being accidentally damaged.
Dentistry
Dental braces using SMA technology exert constant tooth-moving forces on the teeth.
The nitinol archwire developed in 1972 by orthodontist George Andreasen revolutionized clinical orthodontics.
Andreasen's alloy has a patterned shape memory which expands and contracts within the given temperature ranges due to its geometric programming.
Engines
Experimental solid state heat engines have been developed since the 1970s which includes the Banks Engine, developed by Ridgway Banks.
They operate from relatively small temperature differences in cold and hot water reservoirs.
Crafts
Sold in small round lengths for use in affixment-free bracelets.
Thank You !
Compiled by :
Sudarshan.S.K
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