Quote:
Originally Posted by The Badger
Reinforcements in the casing wouldnt help once the bonding starts to fall apart .
Mike ..... what temp can a gearbox get to , and whats the breakdown temp of carbon fibre ? Are you aware of any system of NDT that works in this day and age for CF . As far as I know , it doesnt exist ?
Also , any fatigue crack would quickly become contaminated with hot oil and detereiorate even quicker , breaking down the CF faster .
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The easiest way to test that the manufactured component has reached desired thermal properties would be to take a trimmed off section, and test for the Tg.. hell, even catching the dust off a drilled hole and you can do that!
A common misconception is that it's the carbon that will degrade, it isn't, it's the resin matrix that holds the fibres together, certainly in this instant.
Most epoxy resins (assuming it's an epoxy based pre-preg used... although it could be something else with higher temperature properties.) tend to degrade badly around 200°C, although the Tg tends to be a lot lower, around 120-160°C. Tg is the glass transition, the point which resin goes from being a nice hard stiff substance (glassy, geddit!) to much more flexible.
There's two ways to measure the Tg; Heat flow (DSC - Differential scanning calorimetery) and mechanically (DMA - Dynamic Mechanical analysis). Genereally DMA needs a decent size sample, as it relys on loading a specimen repeatedly during a set temperature cycle. When the tg is reached, the properties change. Ok, it's not quite so simple, but gives an idea
DSC on the other hand works by measuring the heat flow between two small samples, so only requires around 14mg of material...
Other NDT methods for carbon components include ultrasounding (checking for voids in laminates), as well as mechanically testing off-cut panels... whether there's enough material to do so from a gearbox casing though, no idea!
(I work within R&D of composite components, so a know a little
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