1. DIRECT
THERMAL
DIFFUSIVITY
MEASUREMENT
ALONG
THE
AXIAL
DIRECTION
OF
CARBON
FIBER
USING
LASER
FLASH:
SPECIMEN
PREPARATION
AND
RESULTS
Jordan
Burgess1,
Ma0hew
Weisenberger
1,
Sarah
Edrington1,
and
John
Craddock1
1
University
of
Kentucky
Center
for
Applied
Energy
Research,
Carbon
Materials
Group,
2540
Research
Park
Dr.,
Lexington,
KY
40511
Accurate
and
precise
on-‐axis
thermal
diffusivity
measurement
of
carbon
fiber
is
of
great
interest
for
numerous
applicaTons,
but
can
be
a
parTcularly
difficult
measurement.
In
parTcular,
sample
preparaTon
methodology
can
have
a
profound
influence
on
thermal
diffusivity
results.
Current
on-‐axis
fiber
thermal
conducTvity
measurements
are
oXen
performed
using
the
ASTM
(E1225)
Guarded
Hot-‐Plate
method,
which
requires
a
composite
specimen
of
resin
and
fibers
secToned
with
the
fibers
oriented
in
the
desired
direcTon.
While
the
isotropic
resin
thermal
conducTvity
is
well
known,
one
can
back
calculate
the
fiber
conducTvity
suspended
within
the
matrix.
This
requires
some
assumpTons
be
made
about
resin-‐fiber
thermal
interacTons.
Subsequently
the
thermal
diffusivity
can
be
calculated
with
known
density
and
heat
capacity.
Others
have
invesTgated
single-‐filament
thermal
tesTng
incorporaTng
the
3-‐
omega
method.
Yet
single
filaments
pose
significant
sample
preparaTon
challenges.
In
this
study,
we
develop
and
describe
a
sample
preparaTon
methodology
using
carefully
collimated
bundles
of
dry
carbon
fibers.
The
difficult-‐to-‐measure
axial-‐direcTon
thermal
diffusiviTes
were
obtained
and
the
results
are
presented.
Our
data,
obtained
using
this
preparaTon
methodology
and
laser
flash
analysis,
show
carbon
fiber
thermal
diffusiviTes
with
very
low
standard
deviaTons.
This
methodology
poses
a
challenge
to
current
on-‐axis
diffusivity
measurement
methods.
The
primary
advantages
of
this
method
are:
-‐Allows
direct,
on-‐axis
measurement
of
tows
of
fiber
-‐Well-‐aligned,
dry
fibers
-‐Does
not
assume
epoxy-‐fiber
interacTon
LFA
TesTng
The
chart
above
illustrates
thermal
diffusivity
measurements
obtained
by
LFA
at
25
oC
and
under
near
vacuum
pressure.
All
samples
were
run
under
vacuum
to
miTgate
any
thermal
losses.
The
fibers
are
from
a
broad
spectrum
of
high
and
low
thermal
diffusiviTes.
The
magnitude
of
the
values
reported
are
as
expected
for
the
respecTve
fiber
types
and
are
listed
in
order
of
descending
diffusivity;
K1100
(mesophase
pitch),
M55J
(high
modulus),
IM7
(intermediate
modulus),
PAN(CAER)
(in-‐house
modulus),
and
NARC
Rayon.
The
graph
to
the
leX
shows
a
shot
from
the
LFA
soXware
(blue)
fit
with
Cape
and
Lehman
model
(red).
From
the
Cape-‐Lehman
model,
the
LFA
soXware
calculates
the
half-‐
rise
Tme
and
subsequently
calculates
a
diffusivity
value.
The
Tght
fit
of
the
red
curve
is
evidence
that
the
values
reported
are
valid
and
the
sample
preparaTon
methodology
is
viable
for
direct,
on-‐axis
diffusivity
measurements
on
dry
fiber.
