טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentVollach Shahaf
SubjectThe Mechanical Response of Shape Memory Alloys under
a Rapid Heating Pulse
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Doron Shilo
Full Thesis textFull thesis text - English Version


Abstract

Shape Memory Alloy, (SMA), is a novel actuation method which has a huge potential in small scale actuators.  The SMA actuation is based on a solid state phase transformation between its hot and cold phases. SMAs can recover from almost any deformed shape in the cold phase to a trained predefined geometrical shape in the hot phase. The shape recovery usually boasts extra-ordinary large deformations, up to 10% strain, and may exert large stresses as well, even above 500 MPa. Both merits can improve performance and/or reduce dimensions when manifested in small scale actuators. The SMA’s typical work/volume and typical actuation strain, have figures that far surpasses any other common actuation method, albeit, usually achieved at a slow operational rate in the range of 1-100 Hz. All present actuators are not limited by their phase change rate but by their heating rate. This research addresses the operational rate by applying a single energetic rapid heating electrical pulse to a contracting SMA element that pulls a weight. The electrical pulse heats the SMA in a manner of several microseconds, which is faster than the phase change (i.e. SMA reaction is observed long after the electrical pulse has diminished). This is in-fact the first time a heated SMA actuator is observed to be limited by its phase change kinetics. The SMA reaction is being studied to extract the actuation performance of the SMA: the actuation stroke, velocity, acceleration, force and kinetic energy values are obtained. Those are later compared with other fast industrial actuators. Since the phase transformation is the limiting mechanism of the SMA response, the reaction is also utilized to glance at the phase change kinetic properties such as stress-strain plots and nucleation time analysis. Both studies shed positive light over the possible operational rate using small scale SMA actuators.