Date of Award

Summer 2018

Document Type


Degree Name

Master of Science (MS)


Mechanical & Aerospace Engineering

Committee Director

Dipankar Ghosh

Committee Member

Oleksandr Kravchenko

Committee Member

Chauncey Wu


Automated Fiber Placement (AFP) technology shows great promise in manufacturing carbon fiber composite structures. However, intermittent defects occur in the process that can affect the overall mechanical performance of the structure. The aim of this work is to investigate the effects of deliberately placed principal defects (Gap, Overlap, and Fold) on the compressive response under quasistatic (strain rate ~10-3 s-1) and dynamic (strain rate ~103 s-1) loading conditions. The controlled defects were placed at the laminate level in different orientations and depths. High strain rate compression experiments were conducted using a split Hopkinson pressure bar (SHPB) set up, whereas an electrohydraulic testing machine was employed to perform quasistatic compression tests. Three 24 ply carbon fiber panel structures (quasi-isotropic, unidirectional, and quasi-isotropic with deliberately placed defects) were manufactured using AFP with IM7-8552 material, for testing and developing comparative baseline measurements. Results show that there is a significant effect of deliberately placed defects on the compressive strength of composites. Aside from the thickness orientation, the laminate directions along the side of the defect demonstrated a higher peak strength than in the traverse direction. The experimental results revealed a decrease in compressive strength; however, the defects along the fiber direction disturbed the laminate matrix, causing the cured resin in the fiber matrix to slightly strengthen the samples.


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