Date of Award

2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Shivakumar, Kunigal

Abstract

The objective of this research was to assess the effect of polymer nanofiber interleaving on the onset of edge delamination and propagation under both static and cyclic loading conditions. The material selected was AS4/3501-6 carbon fiber/epoxy laminate, an aerospace grade autoclave processed composite. The interleaving fabric was Nylon-66 produced by an electrospinning process. The equivalent thickness was 0.82 u­m, average areal density was 0.93 g/m2, and diameter range was 75 - 200 nm. The stacking sequence selected was the (0n/90n)s laminate with n = 2 and 6 which possess high interlaminar transverse and normal stresses at the edges. Both non-interleaved (base) and interleaved specimens were fabricated and tested under tensile static and cyclic loading. The cracking and delamination behavior was observed in-situ using high speed photography. Static tension test results showed that the interleaved (02/902)s laminates had an increased delamination onset strength of 7% over that of the base laminate with the same stacking. The crack initiation stress was 15% higher and the crack density at saturation was 14% higher for the interleaved laminates. The interleaved (06/906)s laminates had enhanced delamination onset strength of 11%. Crack initiation stress and crack density at saturation increased by 11% and 23%, respectively. The tension-tension fatigue tests for the (02/902)s laminates revealed increased delamination onset life by 10 times for the interleaved laminates. Delamination onset life increased by 15 times at the 0.95 stress level, 3 times at the 0.85 stress level, and 11 times at the 0.75 stress level. At the 0.95 stress level, the (06/906)s laminates with interleaving had delamination onset life increase by 10 times. There were delamination onset life increases by 6 times at the 0.85 stress level and 7 times at the 0.75 stress level.

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