Date of Award

12-2021

Document Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Dr. Sirish Namilae

First Committee Member

Dr. Marwan Al-Haik

Second Committee Member

Dr. Mandar Kulkarni

Abstract

The formation of residual stresses during the processing of composite parts can lead to undesired defects such as delamination which can reduce the overall strength of a completed component. Furthermore, the addition of curvature to the part geometry tends to result in wrinkle formation which leads to stress concentrations developing throughout the curing process in the areas near these wrinkles. In this work, Digital Image Correlation (DIC) will be used to monitor the development of stresses throughout the cure cycle of carbon fiber prepreg in several different lay-ups and across tool plates with varying curvatures to determine what effect the curvature has on the formation of residual stresses. Four different layup configurations are used, with two using regular-thickness plies, [0/90]s and [45/-45]2, and two using thin plies, [0/90]3s and [45/-45]6. The strains that develop during the cure cycle are measured using the DIC and temperature dependent modulus data is obtained using Dynamic Mechanical Analysis (DMA). Utilizing these, the residual stresses are calculated using composite lamination theory (CLT), with a code developed in MATLAB. Results indicate that the cross-ply samples cured on the curved plates generated higher residual strains than those cured on the flat plate, while in the asymmetric tests, the residual strains which developed were nearly identical regardless of the tool plate geometry. The same trend could be seen in the residual stresses in each ply, and together this points to layups which would naturally warp based on their ply-angles having a lower effect from the introduction of tool-plate curvature. Recommendations for future investigations are discussed.

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