6 ms·

Plastics under load have a lower Tg.

by brovonov 10mo ago

hatsunearu 10mo 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 10mo ago
  It kind of is, a better metric is HDT (Heat Deflection Temperature), and it is based on curve usually load over temp.
  - gpm 10mo ago
    And a datasheet for a (not necessarily the same) CF-ABS filament claims a HDT at 1.82 MPa of 93C: https://um-support-files.ultimaker.com/materials/1.75mm/tds/Method-ABS-CF/UltiMaker-Method-ABS-CF-TDS-v1.00.pdf https://um-support-files.ultimaker.com/materials/1.75mm/tds/... Something funny is going on with this material given the report is saying they measured a glass transition temperature of ~50C.
    - ggreer 10mo ago
      I doubt there is any form of ABS filament with such a low glass transition temperature. As the original poster said, it was probably PLA. I find it odd that the report didn't name the manufacturer of the part, and that the part was not listed on the LAA modification form. There can't be many people selling such parts at airshows, so you'd think the investigators would have been able to find out who made it. Now I wonder if the previous owner (who installed the new fuel system) printed the part himself, then claimed he bought it overseas to avoid blame.
Kirby64 10mo 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).
CarVac 10mo ago
Tg changes? Or do you mean they deflect sooner under more load?
- deleted 10mo ago
  [deleted]
- nomel 10mo 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/ https://pmc.ncbi.nlm.nih.gov/articles/PMC6403934/

Plastics under load have a lower Tg.

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 10mo ago
It kind of is, a better metric is HDT (Heat Deflection Temperature), and it is based on curve usually load over temp.
- gpm 10mo ago
  And a datasheet for a (not necessarily the same) CF-ABS filament claims a HDT at 1.82 MPa of 93C: https://um-support-files.ultimaker.com/materials/1.75mm/tds/Method-ABS-CF/UltiMaker-Method-ABS-CF-TDS-v1.00.pdf https://um-support-files.ultimaker.com/materials/1.75mm/tds/... Something funny is going on with this material given the report is saying they measured a glass transition temperature of ~50C.
  - ggreer 10mo ago
    I doubt there is any form of ABS filament with such a low glass transition temperature. As the original poster said, it was probably PLA. I find it odd that the report didn't name the manufacturer of the part, and that the part was not listed on the LAA modification form. There can't be many people selling such parts at airshows, so you'd think the investigators would have been able to find out who made it. Now I wonder if the previous owner (who installed the new fuel system) printed the part himself, then claimed he bought it overseas to avoid blame.

Kirby64 10mo 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).

CarVac 10mo ago

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

deleted 10mo ago
[deleted]
nomel 10mo 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/ https://pmc.ncbi.nlm.nih.gov/articles/PMC6403934/