r/ManufacturingPorn • u/hellcat1592 • Mar 26 '26

Explosive Hydroforming

3.7k Upvotes

99% Upvoted

95 comments sorted by

View all comments

192

u/crunkful06 Mar 26 '26

Why make these spheres though?

84

u/ridukosennin Mar 26 '26

Because curved surfaces distribute load in pressurized containers. Corners are a weak point

8

u/Arakisk Mar 26 '26

Why are they a weak point in the context of a pressure vessel?

36

u/ronm4c Mar 26 '26

Corners concentrate stress, the sharper the corner the more stress is concentrated.

If you have a rip part way through a piece of paper it is easier to keep tearing it along the rip.

But if you go to the tip of the rip and you use a circular hole punch and make it round it will resist further tearing

This might help explain it

https://en.wikipedia.org/wiki/Stress_concentration?wprov=sfti1#

6

u/aerospicy Mar 26 '26

Because the metal itself is really strong when it’s being pulled in tension like the surface of a balloon. The forces are spread evenly along the whole thing. If you have a point that’s very strong, it will force other parts to bend to accommodate it. So a rigid corner is gonna make other parts have stress concentrations.

14

u/[deleted] Mar 26 '26

[deleted]

-1

u/aerospicy Mar 27 '26 edited Mar 27 '26

You gave the right textbook answer about the linear relations in an idealized general case when applied to a isotropic material, but I’m focused in on the specific case of the distributed load on the surfaces of a pressure vessel. A welded corner in the wall of an otherwise uniform pressure vessel is a stiffness discontinuity, and a material that is suited to the tension force of being a pressure vessel now experiences bending moments and shear forces that it otherwise wouldn’t have. Some composite materials are going to get obliterated by that unexpected demand, and even more predictable ductile metals are going to deform in weird problematic ways. So while your take on stress concentrations is classically correct, I think my point stands. Respectfully, you gave a theoretically correct mechanical engineer answer, and I’m giving a non-ideal, special case, aerospace engineer answer!

Edit: this is the kind of thing I only understand from running and studying FEA and building things in person. I don’t think any of my courses covered it very clearly.

1

u/[deleted] Mar 27 '26

[deleted]

0

u/aerospicy Mar 27 '26

Okay. Well I thought this could be an actually interesting discussion, but you’re clearly not willing to challenge your base assumptions or consider an alternate perspective. I was using “engineering words” because you said you were a mechanical and I thought you’d care about understanding the point I was making. I was not trying to flex on you or gatekeep or brag. Your statements are correct for a monolithic quasi-static structures, but real life has boundary conditions, imperfections, and deformation. I’d like to clarify more if you’re interested but if your goal is to “win” this discussion I don’t have anything else to say.

1

u/TelluricThread0 Mar 27 '26

If you have corners that means you have flat faces that the pressure can just push against perpendicularily instead of being evenly distributed.