Date of Award

2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Kelkar, Dr. Ajit

Abstract

The ability to predict failure of composite laminates due to delaminations is critical because of its subsurface nature. Traditional strengthening methods such as stitching and Z-pinning, while improving interlaminar properties in woven composites, lead to a reduction of the in-plane properties. Electrospun non-woven sheets of nanofibrous mat applied at interfacial regions offer an option to traditional treatments. Applications where protrusion energy must be dissipated completely would benefit the most from the use of the electrospinning treatment. Examples are bullet proof vests and vehicle armor. Penetration of a projectile through a composite material may be avoided by creating more energy absorbent crack surfaces. The objective of the present study was to increase the energy absorption capability of a composite laminate subjected to an impact of a projectile. The use of Tetra Ethyl Orthosilicate (TEOS) chemically engineered glass nanofibers manufactured with the electrospinning technique in woven glass fiber resin pre-impregnated composite laminates was investigated for their potential to improve the interlaminar properties. Electrospun glass fiber mats were produced using a computer controlled collector plate in conjunction with a high voltage power supply and a syringe injection pump. Electrospun glass nanofibers pre-impregnated woven mats were manufactured using a vacuum bag method and cured in a computer controlled oven. The interlaminar properties of the nano engineered hybrid composites were obtained using low velocity impact tests and were compared with those without the presence of electrospun nanofiber layers. Impacted specimens were examined using C-scan analysis to determine impact damage dimensions. Compression-After-Impact (CAI) coupons were obtained from the impact tested specimen and were further tested for residual strength. Microscopic examinations were performed to study the progressive failure mechanism. A decrease of 27% residual compression strength was observed when electrospinning nanofibers were added to the lamina interfaces. The study indicated that the electrospun fiber embedded coupons had higher damage areas compared to those without electrospun fiber layers, indicating more impact energy absorption capability in the electrospun fiber-embedded coupons.

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