RV5-SMA ppt.pptx shaoe memory alloys kkfkfkfkf
- 2. ⦁ A shape-memory alloy is an alloy that "remembers" its original shape ⦁ SMA, smart metal, memory metal, memory alloy, muscle wire, smart alloy ⦁ An alloy after deformation returns to its pre-deformed shape when heated. ⦁ An alloy that undergoes large strain & capable of recovering the initial configuration ⦁ At the end of deformation process spontaneously or by heating.
- 4. ◦ 1932 - A. Ölander discovered the pseudoelastic properties of Au-Cd alloy. ◦ 1949 - Memory effect of Au-Cd reported by Kurdjumov & Kandros. ◦ 1967 –At Naval Ordance Laboratory, Beuhler discovers shape memory effect in nickel titanium alloy, Nitinol, which proved to be a major breakthrough in the field of shape memory alloys. ◦ 1970-1980 –First reports of nickel-titanium implants were used in medical applications. ◦ Mid- 1990s –Memory metals start to become widespread in medicine and soon move to other applications. 🞂
- 5. ⦁ SMAs are typically made by casting, using vacuum arc melting or induction melting. ⦁ These special techniques help to keep impurities in the alloy to a minimum and ensure the well mixing of the metals. ⦁ The ingot is then hot rolled into longer sections and then drawn into wire. ⦁ The way in which the alloys are "trained" depends on the properties wanted. ⦁ The "training" dictates the shape that the alloy will remember when it is heated. ⦁ This occurs by heating the alloy so that the dislocations re-order into stable positions, but not so hot that the material recrystallizes. ⦁ They are heated to between 400 °C and 500 °C for 30 minutes, shaped while hot, and then are cooled rapidly by quenching in water or by cooling with air. ⦁ Shape-memory polymers have also been developed, and became commercially available in the late 1990s
- 6. ⦁ The yield strength is lesser than conventional steel, but some SMAs have a higher yield strength than plastic or aluminum ⦁ The yield stress for Ni Ti can reach 500 MPa. ⦁ Exhibit the super elastic properties ⦁ High level of recoverable plastic strain can be induced. ⦁ The maximum recoverable strain SMAs can hold without permanent damage is up to 8 % for some alloys. ( For conventional steels it is only 0.5 % only) ⦁ The cost of the metals are high & therefore effective processing is required ⦁ The processing is difficult and expensive to implement SMAs into a design.
- 8. ⦁ Ag-Cd 44/49 wt.% Cd ⦁ Au-Cd 46.5/50 at.% Cd ⦁ Cu-Sn approx. 15 at% Sn ⦁ Cu-Zn 38.5/41.5 wt.% Zn ⦁ Cu-Zn-X (X = Si, Al, Sn) ⦁ Fe-Pt approx. 25 at.% Pt ⦁ Mn-Cu 5/35 at% Cu ⦁ Fe-Mn-Si ⦁ Co-Ni-Al ⦁ Co-Ni-Ga ⦁ Ni-Fe-Ga ⦁ Ti-Nb ⦁ Ni-Ti approx. 55–60 wt% Ni ⦁ Ni-Ti-Hf ⦁ Ni-Ti-Pd ⦁ Ni-Mn-Ga ⦁ Cu-Al-Ni 14/14.5 wt% Al and 3/4.5 wt% Ni Wt % Extensive properties Actuator applications At% Intensive properties Energy applications Ex: 2 metals A,B form an alloy Wt % of A= mA/(mA+mB) Wt % of B= mB /(mA+mB) A A B at % of A= N /(N +N ) at % of B= NB /(NA+NB)
- 12. Austenite Martensite High Temperature state Hard, firm Symmetric Inelastic Resembles titanium Simple FCC structure Thermal/Mechanical deformation Low temperature state Soft Less Symmetric Elastic Complex structure Twinned& un twinned Heat/stress induced transformation
- 16. Mf < As < Ms < A f Ms: T at which austenite starts to transform to martensite upon cooling Mf: T at which transformation of austenite to martensite is complete upon cooling As: T at which martensite begins to transform to austenite upon heating Af : T at which transformation of martensite to austenite is complete upon heating
- 17. Advantages of SMA • High strength • Super elasticity • Fatigue resistance • Wear resistance • Easy fabrication • High power/weight ratio • Light weight • Bio compatibility • Shape memory property Disadvantages of SMA • Initial investment • Sensitive fabrication • Residual stress • Lower max freq of actuators • Non-linear actuation force
- 18. ⦁ When a SMA is in its cold state (below As), the metal can be bent or stretched and will hold this shape until heated above the transition T. ⦁ Upon heating, the shape changes to its original. ⦁ When the metal cools again, it will remain in the hot shape until deformed again. ⦁ In this case, cooling from high Tdoes not cause macroscopic shape change.
- 19. ⦁ The material remembers two shapes: one at high T & the other at low T. ⦁ Shows shape memory effect during both cooling and heating. ⦁ The metal can be trained to leave some reminders of the deformed low temp condition in the high temperature phases. ⦁ Above a certain T, the metal loses the 2 way memory effect. This is called “amnesia”