Letter 11042

Yield strength of metals 

I need to weld a plate in a "T" shape, one piece is 6"x8" the other is 6"x6" this plate is welded to the 6x8 piece. I need to know how thick the material should be wether it is stainless steel or mild steel or hardened steel to have a yield strength of 55,000 psi. Also could you give me a formula to use to figure it out, thank you.

The 6x8 would be mounted to a surface with 2 anchors the 6x6 is mounted on center with a 2" hole on center, the force would be up and out.

THANKS AGAIN.

John G
- Ramsey, MN, USA

John:

Your terminology is wrong. 'psi' is a measure of the stress on, or strength of, a material per unit area.Are you trying to say that the load on this weldment is 55,000 lbs. tension? Engineers ALWAYS apply a 'factor of safety' as well, they never design to the yield strength of a material.This weldment will likely fail at the welds rather than within a member anyway, and designing tension welds is a very tricky business indeed. In fact, it is prohibited to design many structures (like cranes) with tension welds. There are other factors to consider like L/r ratio as well. Call in a local engineer: it is illegal to do engineering without a license, and for an engineer to try to do it by 'remote control' over the internet would be just as bad and probably just as illegal :-)

Ted Mooney, P.E.  finishing.com Brick, New Jersey

I'm designing a rectangle frame made from 1/4" x 2" angle iron. The dimension of the frame is 34"w x 30"l and the angle iron joints meet at a 45 deg angle and they have a 1/4 weld joint on each side. I have 4 - 1" x .045" square tubing that will set inside the frame and will welded to the frame equally spaced out. A 3/4" piece of plywood sits on top that acts as a base. How much weight can this hold?

Thanks,

HARRY S
- Spring, TX, US of A

I realize that skilled mechanics sometimes just piece things together non critical weldments based on experience and judgement, Harry, and I'd be wasting my breath trying to condemn something that is so widely practiced. But you simply can't proceed to engineer a load-carrying device via internet advice. It's no different than asking for internet advice on how long to make the incision for an appendectomy. An engineer or architect spends 2 years in engineering school just in "analyzing the forces" before he can take his first beginning course in structures or design of machine elements. Even in a simple device there are many potential modes of mechanical failure, just as there are many ways the patient can die during or because of an operation :-)

Ted Mooney finishing.com Brick, New Jersey

Post a question on a different subject.

 

Answer or follow-up on this subject (in non-commercial fashion).