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brovonov | 2 months ago

Plastics under load have a lower Tg.

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Kirby64|2 months ago

Tg does not change with load.

HDT does, kind of, but that’s already covered by the load being defined for the various conditions. HDT is always defined at a specific load so it also does not change with load (since load is fixed).

hatsunearu|2 months ago

Isn't Tg a poorly defined metric? It seems like thermoplastics will lose their strength as temperature goes up and there's no abrupt transition where there's a near step-change in behavior

brovonov|2 months ago

It kind of is, a better metric is HDT (Heat Deflection Temperature), and it is based on curve usually load over temp.

CarVac|2 months ago

Tg changes? Or do you mean they deflect sooner under more load?

nomel|2 months ago

Maybe "load" includes the heat that comes from the changes forces from the vibrations? But even then, that would be additional heat sources, rather than a change in the temperature where it happens.

Polycarbonate shows little change vs pressure [1]:

[1] https://pmc.ncbi.nlm.nih.gov/articles/PMC6403934/