Date of Award

8-2016

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Committee Member

Dr. Oliver Myers, Committee Chair

Committee Member

Dr. Georges Fadel, Committee Co-Chair

Committee Member

Dr. Srikanth Pilla

Abstract

Composite materials, specifically Laminated Fibre Reinforced Polymers / Plastics (FRP), are versatile material systems which have become a part of everyday life. These are no longer considered “space age” materials, but are also being used in aircraft/military, automotive/transportation and construction/civil infrastructure applications. The major reasons behind these materials gaining prominence are that they are light weight, they have high strength to weight ratio and tailored properties. In the recent past, 35 years back, an entirely new research area in the field of composite materials had begun called “Bistable Composites”. These composites, as the name suggests, have two stable shapes and a snap through / snap back phenomenon between these two shapes, which makes them suitable materials for use in “Adaptive Structures”. Bistable composites are unsymmetric laminated FRPs that exhibit bistability because of the unsymmetric laminate stacking sequence about the middle surface. In this research, the possibility of obtaining desired shapes in both stable states of any given geometry is explored using Finite Element (FE) simulations and experimental validation. The methodology followed is as follows: the given geometry is tessellated and several iterations are carried out to find the combination of symmetric and unsymmetric laminates for which the desired shapes are achievable. To decide on the proper tessellation and carry out the iterations efficiently, two major topics are addressed initially. They are the behavior of individual unsymmetric laminates and the behavior of the combination of symmetric and unsymmetric laminates. In the individual unsymmetric laminates, the effects of geometry and fibre orientation on the snap through and snap back loads are studied, to identify the parameters that controls the critical load at which the shape changes. In the combination of symmetric and unsymmetric laminates, various standard geometries are split into smaller geometries, each of those are made into symmetric or unsymmetric laminates and different combinations of those symmetric and unsymmetric laminates are studied to find the various bistable shapes that are possible in each standard geometry. An experimental setup is built to measure the snap through and snap back loads of the individual rectangular unsymmetric laminates. The simulation results obtained are validated by fabricating those laminates and conducting experiments to confirm the data obtained numerically.

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