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 Greg ----- Original Message ----- From: rowr To: swiftsolo@xxxxxxxxxxxx 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
|
