Impact Strength (mild steel tubing)

[Restomod]

I need to calculate what percentage increase in impact strength I will get by inserting a 1" OD round tube with .083 wall inside a square 1 3/4" width tube with a .059 wall. Both are mild steel, ERW tubing.

Can anyone help in how to go about this ?

Thx.

 

[MikeHalloran]

The small tube will just rattle around in there until the big tube buckles enough to load it.



Mike Halloran
Pembroke Pines, FL, USA

 

[metengr]

Restomod;
Impact strength is not a measurable or defined quantity. Are you attempting to increase stiffness under load or increase the ability to absorb energy from impact(dynamic) loading?

 

[Restomod]

I'm attempting to increase the ability to absorb energy from impact. To answer Mike's concern, the tubing will be welded in place. For example purposes let's say the round tube is centered inside the square tube.

I'm reinforcing the chassis of a 67 Mustang with a hidden roll cage within the skin. The square tubing represents the A pillar on the car. I can't fit more then a 1" tube in there and I also don't want to add too much weight to the car. If the .083 wall tubing will increase the absorption of a crash by at least 100% I'll probably stick with it. If not I'll probably go with a .120 wall.

 

[MikeHalloran]

The round tube, even if welded at the ends, won't be substantially loaded until it contacts the square tube in three places, e.g. after the square tube has buckled. Then, yes, it will help resist further deformation, but it's still a very small tube for use in a rollcage. I'd use the .120 wall, thicker if I could get it and fabricate it, larger in diameter if I could possibly squeeze it in.

I'd also take a serious look at stuffing the A-pillar with hardwood, e.g. oak or ash, instead of the steel tube, completely filling it and gluing the wood in for good measure. That would keep the pillar from buckling right away, and stiffen it up a bit.

Actual detailed analysis of either case would be a nightmare absent modern tools, which I don't have and probably couldn't use if I did.

If you want to be a little scientific about it, build a couple of analogs of the A-pillar, reinforce them in a couple of different ways, then fit a pressure gage to a hydraulic press and measure the force required to deflect the analog, say as a centrally loaded beam, keep going until it stops looking like an A-pillar, and integrate the forces over the total deflection to get a measure of the energy absorbed.



Mike Halloran
Pembroke Pines, FL, USA