Fabulous practical
observation Roger, Thanks.
But, do you really mean Celsius not Fahrenheit? 120-130F is only
48.8-54.4C
Im guessing the bolt might need to
be quite a bit hotter than that. Im fairly confident that my black 49er
mast has been much hotter than that over a long period and many cycles
and its stiffness (which is obviously functionally measurable) has not
changed all that much. So Swift builders need not bee too anxious that
your new boat will melt if you spill a cuppa tea on the deck. I
regularly autoclave my epoxy containing instruments at work so I am
interested in this phenomenon from another angle.
The degradation in properties of
advanced composites, such as graphite/epoxy, by exposure to elevated
temperatures is a concern also of NASA.
Here is some info I dug up and I'm
selectively paraphrasing here -
Studies have shown that
Graphite/epoxy composite materials exposed to temperatures in the range
of 177 C to 232 C (350 F to 450 F) can affect the resin matrix
sufficiently to degrade the mechanical properties.
In the temperature range below about
177 C (350 F), the dynamic modulus, G*, as a function of strain
amplitude were seen to be within the viscoelastic range. Although there
is also some evidence of changes in the range of 50C to 177C, (chemical
changes that im sure cannot be reversible) extreme aging at temperature
(10,000 hours at 121 C) studies have shown mixed results with some
graphite/epoxy laminate schedules exhibiting sheer strength decreases
of up to 68% and yet other graphite/epoxy laminates increased in their
sheer strength(up to 32%).
References available if anyone is
interested.
Figure 6.
Interlaminar Shear Strength as a Function of Temperature and Exposure
Time
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Greg
----- Original Message -----
Sent:
Wednesday, February 02, 2005 9:03 AM
Subject:
Epoxy and bolts
If you inadvertently let some
epoxy get into a hole and then forgot to take the bolt or screw out,
chances are, the bolt is in there for good. Even an easy out will
battle to remove the bolt.
SO, by this stage, you have
already stripped the bolt head and cannot drill it out because then you
will drill into your T-nut which is already in your beautifully sealed
hull......
Here is a little tip for getting a
bolt out . Epoxy starts getting soft at about 120- 130F, so much so
that there is a large debate going on in the homebuilding aircraft
market about using epoxy on wings, then painting the aircraft black.
Some manufacturers are suggesting that they paint all aircraft a light
colour if they live in a hot zone of the world. The results of a black
aircraft sitting in the tropical sun and then taking off with gooey
wings could be ... interesting.
Anyway, back to getting the bolt
out. Take a very small size DULL drill bit and drill into the centre of
the bolt. This will heat the bolt up to such an extent that the epoxy
will soften enough to remove the bolt with a pair of pliers.
happy building
Roger
