What's Shaped Memory Alloys? Shape Memory MAs) are novel materials that 罪· trength and can retain. However. when the material is heated above its crystal structure, which causes it to return to its original shape Shaped Memory Effect Definition of a Shape Memory Alloy At a low temperature, a SMa can be seemingly "plastically Shape Memory Alloys (SMAs)are a unique el covered by metal alloys that can recover apparent permanet temperature. This is called the Shap strains when they are heated above a certain Memory Effect SME). At a high temperature, a large temperature. deformation can be recovered simply by releasing the Ankerite applied force. This behavior is k High teeprmare phare Cubit Cryatal truetime 说括 Wannsee L4 temperarure ph在 Meeoclzc Cr时a5pme a) Shape Memory Effect and (b)Superelasticity Definition of a Shape Memory Alloy Typical CsCl structure ne of the rectangles The SMAs have two stable phases. the highrtemperatu The size of the spheres dition. the mar indicates depth is for the u properties of the SMAs. The key effects of SMAs associated with the phase transformation are Series of stacked planes pseudoelasticity and shape memory effect. ng in the absence of applied I transforms from austenite into twinned (selfaccommodated) transformation takes place and as a result the material of the planes that leads to changes in the atomie transforms to austenite positions during the phase (A-M)transition.7 Despair Cool weather Warm weather What¢s Shaped Memory Alloys? Shape Memory Alloys (SMA's) are novel materials that have the ability to return to a predetermined shape when heated. When a SMA is cold, or below its transformation temperature, it has a very low yield strength and can be deformed quite easily into any new shape-which it will retain. However, when the material is heated above its transformation temperature it undergoes a change in crystal structure, which causes it to return to its original shape. Shaped Memory Effect At a low temperature, a SMA can be seemingly “plastically” deformed, but this “plastic” strain can be recovered by increasing the temperature. This is called the Shape Memory Effect (SME). At a high temperature, a large deformation can be recovered simply by releasing the applied force. This behavior is known as Superelasticity (SE). (a) Shape Memory Effect and (b) Superelasticity Definition of a Shape Memory Alloy Shape Memory Alloys (SMAs) are a unique class of metal alloys that can recover apparent permanent strains when they are heated above a certain temperature. Different phases of SMA The SMAs have two stable phases - the high-temperature phase, called austenite and the low-temperature phase, called martensite. In addition, the martensite can be in one of two forms: twinned and detwinned. A phase transformation which occurs between these two phases upon heating/cooling is the basis for the unique properties of the SMAs. The key effects of SMAs associated with the phase transformation are pseudoelasticity and shape memory effect. Upon cooling in the absence of applied load the material transforms from austenite into twinned (self-accommodated) martensite. As a result of this phase transformation no observable macroscopic shape change occurs. Upon heating the material in the martensitic phase, a reverse phase transformation takes place and as a result the material transforms to austenite. Definition of a Shape Memory Alloy Typical CsCl structure The size of the spheres indicates depth. 2D projections of one of the rectangles. Series of stacked planes The arrows indicate one component of the sliding of the planes that leads to changes in the atomic positions during the phase (A®M) transition