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MSE PhD Prospectus Defense: Jairaj Narendran

TITLE: Coupling Nonlinearities to Engineer Functional Mechanical Metamaterials

ADVISOR: Douglas Holmes ME, MSE

COMMITTEE: James Bird ME, MSE; Abigail Plummer ME, MSE; Tommaso Ranzani ME, MSE, BME

ABSTRACT: Nonlinearities emerge when the output of a mechanical system (e.g. stress) is not proportional to the input (e.g. strain) and cannot be predicted by linear relations. They occur in the presence of large deformations which result in large displacements, changes in material properties, or changes in boundary conditions. By adding intentional discontinuities or defects in otherwise continuous structures, we can elicit multiple nonlinearities which can interact to create new functional behavior. We study how introducing granular media to elastic shells can affect shell buckling phenomena. Shell structures are characterized by buckling nonlinearities when subject to large loads. Enclosed grains exhibit jamming behavior when introduced to sufficient external stimuli. When these two nonlinearities are coupled through the creation of an elastogranular shell, controlling the jamming behavior allows us to finely tune its stiffness and buckling behavior. Better understanding the elastogranular shell model allows us to utilize buckling behavior in potential applications for creating compliance-switching structures in soft robotics. Kirigami cuts and origami folds are discontinuities that have opposite effects on the structure to which they are applied. Cuts increase a structure's degrees of freedom and, when applied to a thin shell, result in nonlinear behavior in the form of a buckling instability. Folds decrease a structure's degrees of freedom, but when coupled with cuts on a thin shell, a new snapping instability emerges. In the kiri-origami shell work, we explore how various cut and fold parameters affect snapping behavior, but more fundamentally, the mechanics behind cut and fold interactions. Thin shells with kirigami cuts are capable of large deformations that are utilized for grasping behavior. However, the functional deformations caused by cut defects are accompanied by unwanted bending and material nonlinearities such as fracture. In the reinforced kirigami work, we enhance the functionality of the large deformations by changing design parameters of the kirigami shell while minimizing unwanted characteristics by reinforcing specific regions. These improvements give the gripper more robust functionality and open the door for further applications in industry and consumer settings.