Shape memory alloys


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Shape memory alloys

  1. 1. WELCOME Shape Memory Alloy 1
  3. 3. INTRODUCTION  Shape Memory Alloys are materials that “remember” their original shape.  If deformed, they recover their original shape upon heating.  They can take large stresses without undergoing permanent deformation.  They can be formed into various shapes like bars, wires, plates and rings thus serving various functions. Shape Memory Alloy 3
  4. 4. HISTORY  1938: Arne Olande observed shape and recovery ability of Au-Cd alloy.  1938: Greninger and Mooradian observed the formation and disappearance of martensitic phase by varying the temperature of a Cu-Zn alloy.  1962-63: Ni-Ti alloys were first developed by the United States NavalOrdnance Laboratory.  Nitinol – Nickel Titanium Naval Ordnance Laboratories. Shape Memory Alloy 4
  5. 5. PROPERTIES  SMA’s exhibit 2 important properties. 1. Shape Memory Effect 2. Pseudo-Elasticity Shape Memory Effect  Austenite and Martensite – Two phases exhibited by SMA’s in solid state.  SMA moulded into parent shape in austenite phase. Shape Memory Alloy 5
  6. 6. Shape Memory Alloy 6 What is shape memory effect (SME)?
  7. 7. Shape Memory Alloy 7
  8. 8.  If deformed in martensite phase, the parent shape is regained upon heating.  As and Af are the temperatures at which transformation from martensite to austenite starts and finishes.  Transition dependant on temperature and stress.  Repeated use of shape memory effect leads to functional fatigue. Shape Memory Alloy 8
  9. 9. Pseudo-Elasticity  Occurs without temperature change.  This property allows the SMA’s to bear large amounts of stress without undergoing permanent deformation.  Applications: Reading glasses. Shape Memory Alloy 9
  10. 10.  Temperature of SMA is maintained above transition temperature.  Load is increased until austenite transforms to martensite.  When loading is decreased, martensite transforms back of austenite.  SMA goes back to original shape as temperature is still above transition temperature. Shape Memory Alloy 10
  11. 11. WORKING OF SMA’S  A molecular rearrangement in the SMA’s austenite and martensite phase is responsible for its unique properties.  Martensite is relatively soft and occurs at lower temperatures.  Austenite occurs at higher temperatures.  The shape of austenite structure is cubic. Shape Memory Alloy 11
  12. 12.  The un-deformed Martensite phase is the same size and shape as the cubic Austenite phase on a macroscopic scale.  No change in size or shape is visible in shape memory alloys until the Martensite is deformed.  To fix the parent shape, the metal must be held in position and heated to about 500°C.  The high temperature causes the atoms to arrange themselves into the most compact and regular pattern possible resulting in a rigid cubic arrangement (austenite phase). Shape Memory Alloy 12
  13. 13. APPLICATIONS 1. Reinforcement  SMA’s are particularly beneficial for construction in seismic regions.  If SMA is used as reinforcement, it will yield when subjected to high seismic loads but will not retain significant permanent deformations.  The seismic performance of reinforced concrete and steel columns with SMA bars was investigated by Wang (2004). Shape Memory Alloy 13
  14. 14. 2. Bolted Joints  Beam-column and column-foundation joints are the weakest links in a structure during an earthquake.  SMA materials can be effectively employed in such joints to reduce their vulnerability by dissipating greater energy through large plastic deformation and then recovering it on removal of load. Shape Memory Alloy 14
  15. 15. 3. Prestressing  The benefits of employing SMAs in prestressing include: i. Active control on the amount of prestressing ii. No involvement of jacking or strand-cutting iii. No elastic shortening, friction, and anchorage losses ove time  SMA strands are used in pre tensioning and post tensioning. SMA’s in prestressing have the potential for creating smart structure. Shape Memory Alloy 15
  16. 16. 4. Restrainers  One of the main problems of bridges during earthquakes is their unseating because of excessive relative hinge opening and displacement  . Limitations of existing unseating-prevention devices include small elastic strain range, limited ductility, and no recentering capability.  These limitations can be overcome by introducing SMA restrainers as they have larger elastic strain range and can be brought back to its original position even after deformation Shape Memory Alloy 16
  17. 17. CONCLUSION  SMA’s have the potential to be used effectively in seismic regions.  The high cost of SMAs is a major limiting factor for its wider use in the construction industry.  Their capability to allow the development of smart structures with active control of strength and stiffness and ability of self-healing and self-repairing opens the door for exciting opportunities, making them the construction material of the future. Shape Memory Alloy 17
  18. 18. REFERENCE 1. K Otsuka, C M Wayman, Shape Memory Materials, Cambridge University press, 1999. 2. Kauffman, George and Isaac Mayo, (1996) The Story of Nitinol: The Serendipitous Discovery of the Memory Metal and Its Applications, The Chemical Educator, VOL. 2, pp1430-4171. 3. Peter Filip and Karel Mazanec, (1995) Influence of work hardening and heat treatment on the substructure and deformation behaviour of TiNi shape memory alloys, Scripta Metallurgica et Materiala, Volume 32, Issue 9, 1 May 1995, pp 1375-1380. 4. Rogers, Craig., (1995), Intelligent Materials, Scientific American Sept. 1995:, pp154-157. 5. Lin, Richard., Shape Memory Alloys And Their Applications, (Created: January 21, 1996. Last modified: February 22, 2008), <>, (July 17, 2011). Shape Memory Alloy 18
  19. 19. Thank You 19