The focus of the research is to develop a consistent and repeatable method to
evaluate the coefficient of thermal expansion (CTE) of carbon fibers at high
temperatures. Accurate measurement of the CTE of carbon fibers is essential to
understand and develop optimal processing procedures as well as computational
simulations to predict properties and allowables for fiber-reinforced composites. The
mismatch between the coefficient of thermal expansion of the fiber and the matrix has a
profound impact on the development of residual stresses and the subsequent damage
initiation and progression, potentially diminishing the performance of composite
structures.
In situ transmission electron microscopy (TEM) is selected to perform the
experimental work on account of the high resolution and the capability of evaluating
both the longitudinal and transverse CTE. The orthotropy in the CTE is tested by
rotating the fibers through 45° about their axis. The method is validated by testing
standard tungsten filaments of known CTE. Additionally, the microstructure of the fibers
is studied in a field emission scanning electron microscope as well as through selected
area diffraction patterns in a TEM to observe presence of any potential orthotropy. The
pitch based P55 fiber revealed a cylindrically orthotropic microstructure, but the PAN
based IM7 and T1000 fibers did not reveal any orthotropy. Finite element models of
hexagonally arranged IM7 fibers in a 977 epoxy matrix are developed using PATRAN
and analyzed using the commercial FEA code ABAQUS 6.4. The fiber properties were
considered temperature independent where as the matrix properties were varied linearly
with temperature. The lamina properties evaluated from the finite element modeling are
in agreement with the experimental results in literature within 10% in the temperature
range of room temperature to the stress free temperature of the epoxy, however at
cryogenic temperatures the difference is greater. The residual stresses developed during
processing of the composite indicated a potential location for fiber matrix debonding to
be in the matrix dominant regions.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3073 |
| Date | 12 April 2006 |
| Creators | Kulkarni, Raghav Shrikant |
| Contributors | Ochoa, Ozden |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 4847202 bytes, electronic, application/pdf, born digital |
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