Beams as stiff as steel

mrehorstdmd

Yeah, stiff as steel until they leave them in a parked car...

kb58

They probably mix their units... like, "This PLA beam of size X is as stiff as a bar of steel of size Y."

Phaedrux

https://reprapltd.com/3d-printed-beam-that-is-as-stiff-as-steel/

o_lampe

@phaedrux
the most interesting info in this article was for me, that an infinite Z printer can do these struts without support. I haven't heard of this before. I always try to design things to avoid support, but they are often too chunky because of that.

deckingman

@mrehorstdmd said in Beams as stiff as steel:

Yeah, stiff as steel until they leave them in a parked car...

,.......or inside a heated printer enclosure.

achrn

@kb58 said in Beams as stiff as steel:

They probably mix their units... like, "This PLA beam of size X is as stiff as a bar of steel of size Y."

Actually, it's 'this PLA truss is the same stiffness as a steel section with a low stiffness per unit weight of the same weight'. So it's not completely irrelevant comparison.

They've demonstrated, mainly, that trusses are stiffer than solid square sections. If only someone had told Sir John Fowler, messrs Bailey, Pratt, Warren, Fink, ...

kb58

@achrn Haha, yeah. If they proving anything, it's that the cross sectional shape of materials matters for bending strength, and has little or nothing to do with the material itself.

bot

Stiffness != strength. Stiffness is just the slope of the stress/strain curve: ie, how resistant to bending it is.

This would fail at a much lower stress than the steel sample. It would simple resist bending to the same degree as the steel (before the PLA breaks). The steel would not break at anywhere near the stress levels the PLA would.

fcwilt

@bot said in Beams as stiff as steel:

Stiffness != strength. Stiffness is just the slope of the stress/strain curve: ie, how resistant to bending it is.

Can you explain "stress" and "strain"?

Frederick

dc42

@fcwilt said in Beams as stiff as steel:

Can you explain "stress" and "strain"?

Stress ~ applied load
Strain ~ movement (e.g. stretching or bending) resulting from applied load.

Footnote for pedants: it is sometimes said that person is "under strain" but this is technically incorrect. A person can be under stress or exhibiting strain.

achrn

@dc42 said in Beams as stiff as steel:

Footnote for pedants: it is sometimes said that person is "under strain" but this is technically incorrect. A person can be under stress or exhibiting strain.

In the good old days (before Amazon) I once tried to get a bookshop to order 'Roarks Formulas for Stress and Strain' (which is a standard structural engineering textbook) and the assistant outright refused to search for it under engineering, insisting on looking in psychology and psychiatry and related fields. They couldn't find it there in the catalogue so maintained they couldn't order it. I gave up, and found it on the shelf in a better bookshop in a more academic city.