Date of Award

12-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Committee Member

Dr. Oliver J. Myers, Committee Chair

Committee Member

Dr. Suyi Li

Committee Member

Dr. Georges Fadel

Abstract

Until recently, Carbon Fiber was considered to be a space-age material because of its applications. However, due to the advancements in the synthesis of these materials and manufacturing carbon fiber on a large scale, it has now become possible to use carbon fiber in day-to-day applications. Components which were traditionally being made out of steel or aluminum are now being redesigned and made using carbon fiber composites. The Boeing 787 Dreamliner fuselage is an excellent example where carbon fiber has been used as the major component. This is due to the fact that carbon fiber components are much lighter and have a higher strength to weight ratio. Moreover, carbon fiber can be synthesized according to the requirements of the application for possessing any custom-tailored properties. In the 1980’s, an important phenomenon termed as Bistability in composites was observed in unsymmetric CFRP laminates.[1] Bistability in composites is the existence of two stable states in the same composite structure. It is possible to transition between these two stable states by a snap-through or a snap-back process. The composite samples experience a large deformation while snapping-through or snapping-back and thus, a bistable composite can find an application as a part of an Adaptive Structure. The phenomenon of Bistability is observed due to the unsymmetric stacking sequence of the laminates and the thermal stresses developed during the curing process of these composite laminates. While a lot of work has been done on Bistable composites, this research aims at combining the concept of Kirigami with Bistable Composite structures. According to this method, the Bistable laminates are fabricated in a Kirigami pattern. The concept of Kirigami is very similar to Origami. The only difference is that Kirigami allows cutting in addition to folding along the creases of a 2-dimensional pattern. This results in the creation of complex 3-dimensional structures. Thus, the Kirigami pattern is used to lay the individual laminae in such a way that individually bistable laminates are connected to each other with the help of a tab. In this research, the curing process and the snap-through and the snap-back processes of a Kirigami unit cell are simulated using ABAQUS™. Further, the same tests are recreated using a Universal Testing Machine setup for qualitative validation of the FEA model. A separate testing procedure has also been developed to investigate the strength and the snapping phenomenon due to the presence of the tab in the structure. This procedure is again used to validate the FEA results obtained from ABAQUS™. In doing so, this research aims to answer some of the questions concerned with the snapping behavior and stiffness of Kirigami composites.

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