Date of Award

5-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Committee Member

Oliver Myers, Committee Chair

Committee Member

Georges Fadel

Committee Member

Suyi Li

Abstract

Bistability is exhibited by a composite laminate when it rests in two stable equilibrium states. Certain composite laminates exhibit bistability by having two stable curvatures of opposite sign with the two axes of curvature perpendicular to each other. These laminates can be actuated from one state to the other. The actuation from the original post-cure shape to the second shape is called as ‘snap-through’ and the reverse actuation is called as ‘snap-back’. This phenomenon can be used in applications for morphing structures, energy harvesting, and other applications where there is a conflicting requirement of a structure that is load-carrying, light, and shape-adaptable. A number of researchers have tried to identify the key parameters affecting the behavior of such laminates. Geometric parameters such as stacking sequence, fiber orientation, cure cycle, boundary conditions, and force of actuation, have all been investigated. The objective of this research is to define relationships between the length, width and thickness of square and rectangular laminates required to achieve bistability. Using these relations, multiple bistable laminates up to 36 by 36 inch2 are fabricated with varying thickness up to 30 CFRP layers. Further, for laminates that are bistable, it is necessary to be able to predict the curvature and force required for actuation. Therefore, a method is developed which allows us to predict the curvature of both stable shapes, as well as the force of actuation of laminates for which the thickness and dimensions are known. Finite Element Analysis is used to carry out the numerical calculations, which are validated by fabricating laminates. The curvature of these laminates is measured using a profilometer and the force of actuation is recorded using a universal test set-up.

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