טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentBenichou Itamar
SubjectTheoretical and Experimental Study of Multi-Stable
Mechanisms
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Josef Givli
Full Thesis textFull thesis text - English Version


Abstract

Saw-tooth pattern appearing in a (generalized) force-displacement response is the fingerprint of transition processes involving discrete switching events between metastable states. This phenomenon, sometimes termed “discrete phase transformations” (DFT), is abundant in small scale systems and is the mechanism responsible for a large number of non-linear processes at the macro-scale.

Nature provides numerous examples for DFT, a wide range of biological molecules undergo phase transition through a series of individual unfolding/folding events as part of their normal functionality or as a result of external constraints. Other examples, from the perspective of material science, are observed when a mechanical load is applied on small samples of materials such as shape memory alloys and ferromagnetic shape memory alloys (FSMA).

Based on the model of a 1D chain composed of bistable elastic elements, we have developed a novel approach for modeling the behavior of such structures. This model enables separation between the elastic response and other non-linear features of the system, thus providing valuable information regarding intrinsic properties of the material. Further, we obtain explicit expressions for the energy barriers that separate between metastable states (configurations). Using these results we were able to provide insights into the function of the structural protein titin, and to the jerky motion of twin boundaries in the FSMA NiMnGa. Experiments have been performed in order to validate some of our theoretical predictions. Finally, we study the overdamped dynamics of bistable chains subjected to thermal fluctuations (random noise originating from nonzero temperature). We found a new non-dimensional quantity, similar in construction to the Boltzmann factor, which captures the intricate competition between rate, temperature, and energy barriers underlying the dynamics of such systems.