טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAvraham Dekel
SubjectSelf-Propagating Miniature Device Based on Shape
Memory Alloy
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Doron Shilo
Full Thesis textFull thesis text - English Version


Abstract

In recent years, there has been a growing amount of research in the field of self-propagating mechanical devices. Many concepts of propagation mechanisms were investigated, aiming to mimic animal locomotion. Existing propagating devices range over many sizes. However, miniaturization is typically restricted by the size of the electrical and mechanical components required for autonomic motion. Micronized device can't be seen by the human eye which makes it suitable for military and intelligence agency applications.

In this work we present a novel terrestrial self-propagating device based on an active element of shape memory alloy (SMA).

The device is composed of only two simple mechanical components: an active SMA NiTi wire, and a rapid manufactured titanium alloy ring that serves as a restoring elastic spring. Both parts are assembled in series forming an SMA-spring actuator that performs periodic elongation and contraction displacements under repeated changes in the ambient temperature. Planar propagation is achieved thanks to the special design of the device's small legs and their penetration into the ground surface, which results in an asymmetric cyclic deformation of the metallic ring.

An analytical mechanical analysis of both the cyclic deformations and the planar propagation is formulated, which leads to the necessary conditions for both types of motion. This analysis provides design rules, according to which several devices are manufactured. A dedicated experimental setup is build and allows testing the performance of the devices. It is shown that the formulated design rules are valid and accurately predict the conditions required for planar propagation under periodic temperature changes.

In addition, a general analytical model for the stress - strain - temperature relations in an SMA-spring actuator is formulated and is validated using the experimental results. Finally, the feasibility of scaling down the mm-sized device presented in this work to the micron-scale is performed, and its expected performances are exhibited.