4130 in torsion application.

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Hi All,I'm working on a project to shore up the rear beam axle in a front wheel drive vehicle, and we're working on some designs that have been promising thus far.  The current design we are using requires a round tube, two machined fittings that attach the tube to the beam axle and potentially a pair of blade style arms out to the lower shock mounting bolt.  The design as it stands uses a pair of 1018 Cold Rolled and machined end caps that attach the tube to the car.  They are cylindrical and the tube interfaces with them on center at a 90 degree angle.  The caps are 1.125" diameter, the tube is 1" x .109 Wall.  Our prototype system used hot rolled electric welded 1" x .083 wall tubing and performed very well.  We were considering two things:  first, an alloy change for the tube from the hot rolled 1010 to something like a cold drawn DOM 1020 in 1 x .109 wall or going up to the same dimensions in a 4130; second: potentially adding a pair of blade style arms that interface with the shock mount bolts.  In either option we would be doing a ~1200F stress relieving heat treat of the parts at minimum. The questions we have are thus:1.  If we do a blade style arm off of the tube (round hole through the blade which the tube passes through and is welded to), are we best off to do a full circumference weld on both sides of the arm or is there a benefit to stitch welding such a small tube?  2.  Material-wise, what considerations do we need to make in choosing our fitting (arms and caps) alloy to match the 4130?  We're pretty sure that the 1020 will be a good match if we stuck with 1018 arms/caps.  But not so sure about the compatibility with 4130.3.  We have two options:  1018 to 1020 and 1018 to 4130.  What rod would be best in each of these situations?  We're not very familiar with working with 4130 but its properties are prime for this application.  Our concerns are mainly that we have a product in hot rolled that seems to work well...and we'd like to improve its longevity and improve its torsional capacity to some extent, but if complications may arise due to the use of 4130 we may benefit from just running the DOM 1020 instead.  But if there's not enough concern against the 4130, it is certainly the prime material for the application.Jason
Reply:That's roughly what we're talking about.  Weld joint at the coped connection and at the tube-arm connections.
Reply:I'm guessing this is a torsion bar thing, so......If you have Solid Works for your modeling then possibly you will have Cosmos.  You can run this thru Cosmos and come up with stress and deflection per stress.I did this exact same exercise for my 41 Willys Pro street.  I needed a very short stiff rear anti roll bar.  There wasn't anything available so I did the cad and analysis and came up with an 1 1/4 dia .120 wall tube 18 inches long.  Believe me it is stiff but works very well. I have 18k miles on it and and it still has not taken a set.  (permanenly twisted)If you have a Roarks book os stress and strain there is a section on beams in torsion.  Mine is in storage since I'm now retired.All steel have the same modlus of elasticity so for a given length,dia and wall they will deflect the same for a given load.....up to the yield point.  This is why spring steel  can survive twisting much farther and still come back.  It's yield is much higher than mild steel.  180 ksi vs. 30-40 ksi  4130 yield is about 70 ksi. I would do your project with 4130 because it is about the same cost for material and TIG welds very easily.  I would not bother stress relieving unless you have good heat treating facilities available.I welded one bar all the way around but tossed it in favor of a bolted on arm.  Purely for servicability.  I drilled a hole thru the tube and welded a tube in this with the id size for the bolt.  I made a mating sleeve welded to the arms with a tube/hole also.  If you want to weld the arms on,  I would go all the way around.  No undercut permitted.  I assume you some adjustable links to connect the arms.My bar is mounted on the rear end and the links go up to the chassis.  The bar adds to unsprung weight but it was the only way I could mount it.
Reply:Man, you guys get all technical and serious with this mumbo jumbo stuff........  I like these guys' way of thinking...My favorite sceens in the video are at  0:48 and 4:25!  Classic "Craftsman wrench" steering fabrication!  You guys know that I'm just kidding with ya'll, right?  Lincoln Power Mig 216Lincoln AC/DC-225/125Miller  625 X-Treme PlasmaMiller 211 Forney 95FI-A 301HF 91110Victor Journeyman O/PMilwaukee DaytonMakita  Baileigh NRA Life Member
Reply:We just built some 4130 sway bars with welded features... Used 4130 rod and had them normalized afterwards. I am guessing you are an engineer/engineering student Griffith?