Date of Award

Spring 2023

Access Type

Thesis - Open Access

Degree Name

Master of Science in Aeronautical Engineering

Department

Aerospace Engineering

Committee Chair

Sirish Namilae

First Committee Member

David Sypeck

Second Committee Member

Fady Barsoum

Abstract

Composite laminates of unsymmetric layup families often exhibit twin stable shapes at room temperature, a phenomenon known as bistability. Unsymmetric bistable composite laminates have often been suggested for applications in aerospace morphing structures, damping, and energy storage, because of their ability to easily change their shape while being homogenized with the rest of the composite structure.

This study analyzes the mechanisms responsible for bistability in unsymmetrical [0/0/90/90] laminates through a combination of experiments and modeling. Several unsymmetrical laminates with different aspect ratios were fabricated using autoclave processing. Digital image correlation (DIC) is used to monitor laminate strains in situ during the processing of the composite and to correlate processing strains to the degree of bistable behavior in differently sized samples. Room-temperature curvatures were measured and compared with analytical and FEA models. Load responses to changes in the shape of the laminate were measured for each sample size to determine the effects of the size and aspect ratio for both as-fabricated and machined samples. It is shown that the “snap-through” load and curvatures of the laminates decrease as the length of one side of the sample decreases. It is also shown that the snap-through load of samples further machined with a water jet cutter post-cure decreased significantly, but possessed only slightly less curvature compared to identically sized samples that were not machined. The results show that there are significant limitations to the application of this type of laminate, but there is ample potential for property modification during processing, which can increase the size of the design space.

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