Date of Award

12-10-2021

Document Type

Dissertation - Open Access

Degree Name

Doctor of Philosophy in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Dr. Sirish Namilae

First Committee Member

Dr. Marwan Al-Haik

Second Committee Member

Dr. Daewon Kim

Third Committee Member

Dr. Alberto Mello

Fourth Committee Member

Dr. Eduardo Rojas

Abstract

The ubiquitous usage of polymer matrix composites in many applications demands a comprehensive understanding of composite interfaces and processing induced residual stresses, which critically affect both the manufacturing processes and the deformation mechanisms. Processing induced residual stresses are often responsible for causing warping, delamination, and dimensional instability in composite structures. This research includes new in-situ experimental approaches, cure cycle design, interface modification, and thermomechanical modeling for developing a fundamental understanding of the cure kinetics during composite manufacturing. Strains, ply-movement, and formation of defects are observed in-situ using digital image correlation (DIC) during the autoclave cure cycle for the first time. The processing-induced defects in the composite are further characterized by X-ray micro-computed tomography (micro-CT). A non-destructive method is developed to calculate residual stresses using DIC Strains in combination with temperature-dependent moduli obtained from Dynamic Mechanical Analysis (DMA) and Classical Laminate Theory (CLT). Cure cycle design with interrupted cure and interface modification with ZnO nanorods experiments are developed to reduce these processing- induced residual stresses and thereby increase laminate strength. The experimental results are validated through thermomechanical modeling of the composite cure process.

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