Bullet proof (literally) driveshaft

Ok, so we had a little off-road event here last weekend. My front drive shaft drive shaft ripped it's self into multiple pieces when i landed on a large rock. When i got home i started looking for drive shaft making stuff. What I came up with was a length of case hardened 4140 1.5" dia. bar stock. I'm hoping it will end any future disagreements with wayward boulders. It should have a tensile strength right around 150,000psi and a shear modulus of 11600ksi. and will not dent. Has anybody ever tried this before? how did it work?

 

All I have to add is....



that's some stout stock to use! 'spensive too!

 

Heavy, too. What's it weigh? Wondering if the inertial energy acts like a flywheel?

 

It weighs about 30 lbs. As far as the inertial energy, i'm sure there is some of that but it's somewhat not noticable

 

There is a young fellow around here who races off road. He got tired of making drive shafts out of sqaure tube and made one from 4140 bar stock. It works VERY well.

 

glad to hear it!

 

No real reason it shouldn't work that I can see. We use that stuff at work for industrial drive shafts on metal processing equipment. As already mentioned, it's heavy and expensive. It should be balanced and the welds NDT tested too if you were using it at any speed other than crawling.

 

As far as balance. it's made from a rod ground to within .0001 +/- so i know it just doesn't get any better than that. i did machine and align the knuckles to within .001 +/-. The only thing in question would be the welds and i don't believe that'll make much difference for this application. As far as NDT testing, that's not a bad idea considering the properties of a higher carbon chrome moly. I'll have a buddy who is a weld x-ray guy for a pipe fitting outfit check it out for inclusions. I'll probably magnaflux it myself to see if there is any micro stress cracking. Rest assured, this jeep is off-road only and never gets above 10 mph.

 

Total weight matters little. It's the distance from the axis that has the greatest effect. Since the shaft is an inch and a half diameter, 3/4" isn't going to have any noticeable effect. Take the same thirty pounds and spin it like a prop, with a decent pivot bearing, the shaft would spin for an hour and trying to stop it with your hand would be a really bad idea.