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Akash VermaCMCShape Memory AlloysOutline2/15Introduction to SMAA Brief HistorySolid Stable states of SMAShape memory EffectPsuedoelastic effectApplications of SMALimitations of SMA

2SMA Introduction3/15Shape Memory Alloys (SMAs) are a class of metal alloys that can recover apparent permanent strains when they are heated above a certain temperature.The most effective and widely used alloys are NiTi, CuZnAl, and CuAlNiSMAs have two stable phases - the high-temperature phase, called austenite and the low-temperature phase, called martensiteThe shape change involves a solid state phase change involving a molecular rearrangement between Martensite and AusteniteSMA also exhibits superelastic (pseudoelastic) behavior

1.smart material that returns to its Normal shape and size after something like heat has manipulated it

3A BRIEF HISTORY4/151932 - A. lander discovers 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 (Nickel Titanium Naval Ordance Laboratory), which proved to be a major breakthrough in the field of shape memory alloys.1970-1980 First reports of nickel-titanium implants being used in medical applications.Mid-1990s Memory metals start to become widespread in medicine and soon move to other applications.4Solid stable states of SMA5/15SMAs have two stable phases : the high-temperature phase, called austenite and the low-temperature phase, called martensite. the martensite can be in one of two forms:twinned detwinnedA phase transformation which occurs between these two phases upon heating/cooling is the basis for the unique properties of the SMAs

Shape memory alloys display two distinct crystal structures or phases. Temperature and internal stresses (which play a part in super-elasticity) determine the phase that the SMA will be at.SMAs are said to exhibit a crystallographically reversible martensitic transformation. At high temperatures, the SMA exists as an austenite phase (the parent or memory phase) with long range order. On cooling below the transformation temperature, the austenite transforms to a thermoelastic martensite whose structure has many variants, typically sheared platelets. Because the martensitic structure is self-accommodating, the deformation on transformation to martensite is zero. The martensite deforms by a twinning mechanism that transforms the different variants to the variant that can accommodate the maximum elongation in the direction of the applied force. The interfaces between platelet The interfaces between platelets in the martensite phase slip very readily and the material is deformed at low applied stresse.twinin a crystalline solid occurs between two adjacent regions of the same crystal lattice, where one of the regions is related to the other by a simple shear. At a microscopic level, a twin appears as depicted in Figu5Thermally Induced Phase Transformation in SMAs6/15MfMsAsAfAusteniteMartensiteTEMPERATUREMfMsAsAfAusteniteMartensiteTEMPERATURE(twinned)(twinned)Characteristic temperatures:Mf=Martensitic FinishMs=Martensitic StartAs=Austenitic StartAf=Austenitic FinishShape memory effect7/15If mechanical load is applied to the material in the state of twinned martensite (at low temperature) it is possible to detwin the martensite. Upon releasing of the load, the material remains deformed. A subsequent heating of the material to a temperature above the austenite finish temperature (Af) will result in reverse phase transformation (martensite to austenite) and will lead to complete shape recovery.

7The Shape Memory Effect8/15seTCoolingDetwinningHeating/Recovery5/18/20158PSEUDOELASTIC BEHAVIOR9/15Occurs when an alloy is completely in the Austenite phaseIs not dependent on temperatureWhen the load is increased to a point, the alloy transitions from the Austenite phase to the detwinned Martensite phaseOnce the load is removed, the alloy returns to the it original Austenite shapeRubber like effect

STRESSTEMPERATUREMfMsAsAffssfAusteniteDetwinned Martensite(stressed)These unique alloys also show a Superelastic behavior if deformed at a temperature which is slightly above their transformation temperatures. This effect is caused by the stress-induced formation of some martensite above its normal temperature. Because it has been formed above its normal temperature, the martensite reverts immediately to undeformed austenite as soon as the stress is removed. This process provides a very springy, "rubberlike" elasticity in these alloys.9Applications of superelastic behavior10/15Orthodontal bracesFrames for eyeglassesAntennas for cellular phonesApplicationsApplications of Shape memory effectSelf-expandable cardiovascular stentBlood clot filtersEnginesActuators for smart systemsFlaps that change direction of airflow depending upon temperature (for air conditioners)Couplings

SMAs are useful for such things as actuators which are materials that "change shape, stiffness, position, natural frequency, and other mechanical characteristics in response to temperature or electromagnetic fields"10SMA Application:Coupling for Tubing

Use of memory alloys for coupling tubing:

A memory alloy coupling is expanded so it fits over the tubing (b) When the coupling reheated, it shrinks back to its original diameter(c) squeezing the tubing for a tight fit11/15The first industrial application occurred in 1969 when SMA couplings joined hydraulic pipes in the F-14 aircraft.11SMA Application: The Smart Wing Shape memory alloys to Change the Shape of the Wing of a Plane to make it more maneuverable. This is done by simply sending a electric current throw the part of the plane to heat it to the desired temperature. This changes the shape of the wing making the Plane more maneuverable. This was previously done with a heavy Hydraulic system, thus significantly reducing the weight of the plane.

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SMA Application: Robotic MusclesIt is difficult to simulation of our muscle and basic movements. Things like holding a pen or a pencil, feeling/touch, or just moving a finger are great challenges for Robotics. When the heat of a wire changes the shape and move ability of the metal. This is similar to a muscle as a nerve send a pulse to the muscle the size doesnt change, however it does weaken or strengthen to accommodate the need of the movement.

13/15Advantages and Limitations14/15Most SMA's have poor fatigue propertiesRelatively expensive to manufacture and machineHeat Dissipation

Shape memory effectPsuedo-elasticityHigh corrosion resistanceLight weightGood Bio Compatibility

AdvantagesLimitations15/15

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