This vid is interesting ... 7 materials compression tested, carbon fiber and titanium among them

Slide to 4 mins and 11.52 mins

https://youtu.be/PlvyZ1r1DCM

The video doesn't mention anything about what type of carbon fibre was used.

Was it standard Intermediate or High Modulus?

What was the resin system used was it wet layup which cures at room temperture which is weaker or Aero quality Pre Impregnated which is stored in a freezer and needs to be cooked under vacum at 90-180 Deg C?

Was it baked in Autoclave up to 4 bar pressure to compact layup considerably more or just vacum bagged?

We can see it used woven cloth which doesn't keep fibres aligned with load paths it loses considerable strength with crimp on the weave pattern. Unidirectional fibres are straight can be tailored to load paths resulting in a much stronger product.

That test with short lengths that would be used in SFA applications doesn't give the full story.

Wall buckling causes columns or tubes to fail in compression this is a bigger factor over Ultimate compressive strength when designing tubes loaded in compression.
Take a plastic straw push down on it in compression the wall will buckle then it doesn't hold anything after that. Cut the straw in half it can handle far more load. Halve it again it will hold even more.
Slenderness ratio is important here the shorter the tube the stronger it is for same diameter which they refer to as moment of inertia
https://www.engineeringtoolbox.com/euler-column-formula-d_1813.html

So all that video showed me was Carbon Fibre is far lighter than metals, by using a really short length it favoured the metals because it minimised wall buckling failure.

Those who use that for the recent sub case are thinking maybe some bodyparts could have been removed from crushed spam can.

Formula One shows the failure mode with CF is excellent a front on impact is compression load. With impacts over 85 G you start extruding your brain through your ears. They have crash test requirement with 55G maximum peak the carbon structure can hold that without peaking higher.
Not many deaths in F1 since they stopped using metal chassis and embraced carbon fibre.

The HANS device stopped basal skull fractures which killed Ratzenberger and a few others. Basal skull fracture is the bottom f your skull braking away from your neck.

The sub that imploded had a factor of safety of 2.25 which is way too low. It did 21 dives before it imploded. Anything with a factor of safety that low isn't going to last.

Atmospheric pressure test - watch all 2mins 30 secs

https://youtu.be/JsoE4F2Pb20?t=140

Bias_2012 wrote on Jul 3^rd, 2023 at 11:08pm:

Atmospheric pressure test - watch all 2mins 30 secs https://youtu.be/JsoE4F2Pb20?t=140

Atmospheric pressure is 14.7 PSI

I doubt they had anywhere near a vacum in the barrel so crushing pressure was way less than 14.7 PSI

14.7 PSI = 0.10 Mega pascals
Ultimate compressive strength with mild steel around 250 Mpa.

Wall buckling under compression is a far bigger factor to deal with compared to UCS.