SUBJECT: Ph.D. Dissertation Defense
BY: William Johnson
TIME: Thursday, August 13, 2020, 11:00 a.m.
PLACE: Online, Online
TITLE: Metamaterial Applications for Vibration and Wave Propagation in 1D Elastic Rods
COMMITTEE: Dr. Massimo Ruzzene, Co-Chair (ME)
Dr. Michael Leamy, Co-Chair (ME)
Dr. Karim Sabra (ME)
Dr. Aldo Ferri (ME)
Dr. Claudio Di Leo (AE)


This dissertation is focused on the application of phononic materials to problems encountered in industry. Three main problems are addressed: vibration mitigation for a large electrical generator; the modeling of impact and bouncing of electrodes within circuit breakers; and pulse shaping using phononic materials for Hopkinson bar tests. Previous research in the field of elastic metamaterials has focused on introducing band gaps to block the propagation of waves at particular frequencies. Through various techniques wave directionality, focusing, or topological modes can be introduced into a structure. A large variety of phononic material concepts and analysis techniques are available in the literature, but so far a limited number of practical applications for these materials have been developed. Because of the wide variety of ideas from which to draw, this field is beginning to reach a level of maturity where applications can be developed. In addressing the problems described above, this dissertation expands the practical application of phononic materials. To this end, this dissertation discusses the modeling of waves created by impact, phononic material techniques to mitigate vibration, modeling techniques to obtain dispersion relationships and predict wave shapes, and techniques to obtain geometry optimized for dispersion. For vibration mitigation grounding springs were considered as a possible solution to create a mechanical high pass filter. For the circuit breaker electrodes, a new model clarified the role that various parameters such as wave speed, spring stiffness, and electrode length played in determining the length of the bounce. Finally, pulse shaping using phononic materials was explored for use in Hopkinson bar tests. The results demonstrate that for a known input pulse traveling in a 1D elastic waveguide, that pulse can be shaped using a phononic material to create a desired output pulse shape. The particular geometric parameters were found and pulse shaping concept validated using an optimization routine in Abaqus.