hypothetical queston about drive shafts

kpoindex08

Registered User
Let's ponder about the strength of a drive shaft and the material it is constructed of. I see a lot of people swapping out there steel drive shafts for aluminum ones. I question if it is the right choice for a high torque application. What if the torque output of a said engine was 1000 ft lbs, there was no clutch slip, no tire spin, no transmission gears on the track, all axles held, no u join breakage Nothing to fail except for drive shafts. Steel VS aluminum. What material would be best?
 
i would think the aluminum would be stronger in the long run..imo i think the steel one is prone to weathering and steel cracks. and if im correct alumnum respond less to temp fluctations...
 
I dont know if this will help your comparison between steel and aluminum but the semi I drive has a dd15 (detroit) that on a daily basis pulls around 80, 000lbs. Its just shy of 500 hp and just south of 2000 lbf of torque which it will generate in about 1.5 seconds from idle. First gear is 14.80, seventh is 2.45,;), and thats a mild 10 spd. Some L or LL trans get into the 20.oo. It has an aluminum drive shaft. Most semis do now.
I did drop one about a month ago, in my yard, backing into my parking spot at the end of the day. It failed at the u/joint on the diff end. Its about as thick as my thigh and you could easily carry it with one arm, so there is major weight savings to be had with aluminum.

I guess this doesnt apply to a sc application but if only to shed some light on how durable aluminum is. Our 2013 trucks, some delivered in 2014, are quickly approaching half a million miles, most over 400, 000 already. They run two shifts day and night by multiple drivers on the worst roads in some of the heaviest traffic in the country. They are dependable, but they are also not aftermarket produced or enginered.
That being said they do fail, they are designed to do so at certain parameters.
https://youtu.be/IEH-xRUaAos

Money no object?
Could always go carbon fiber?
 
Using this hypothetical it seems like the aluminum drive shaft would break before the steel axles :p.

-Tim
 
The last time I was at the drag strip in 2nd round time trial I ran a faster El Camino and just before he crossed the finish line his steel driveshaft broke in two. I got a ringside seat as it came out from under his car and fortunately bounced away from mine. Aluminum driveshafts are built for specific maximum torque and are spec'ed that way. I've been running one for years.
 
Let's ponder about the strength of a drive shaft and the material it is constructed of. I see a lot of people swapping out there steel drive shafts for aluminum ones. I question if it is the right choice for a high torque application. What if the torque output of a said engine was 1000 ft lbs, there was no clutch slip, no tire spin, no transmission gears on the track, all axles held, no u join breakage Nothing to fail except for drive shafts. Steel VS aluminum. What material would be best?

I'm using a 3.5" aluminum drive shaft in my 93 SC that has a race weight of 4250 lbs and launches like this. In addition to strength, there is also the matter of harmonics and max shaft speeds.

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David
 
Let's ponder about the strength of a drive shaft and the material it is constructed of. I see a lot of people swapping out there steel drive shafts for aluminum ones. I question if it is the right choice for a high torque application. What if the torque output of a said engine was 1000 ft lbs, there was no clutch slip, no tire spin, no transmission gears on the track, all axles held, no u join breakage Nothing to fail except for drive shafts. Steel VS aluminum. What material would be best?

It's not that simple and you really shouldn't be asking an open forum this type of question because none of us have the engineering qualifications to answer that question. Call several specialists who make driveshafts for high HP applications and let them guide you. Get more than one opinion.


There are many things to consider when thinking about a driveshaft - shaft length, material and design harmonics, intended shaft rpm, and of course torque (HP is irrelevant to the driveshaft) and other consideration. But again, talk to an expert, don't rely on internet opinions.
 
...and wall thickness, diameter...


As far as the stock driveshaft goes, it's not a particularly stellar piece. It's a 2-piece crimped steel shaft that was designed for a chassis/drivetrain setup that was pushing a whole 315 ft-lb of torque at the time. The aftermarket aluminum shafts that many of us run far surpass the abilities of the stock driveshaft.
 
It's not that simple and you really shouldn't be asking an open forum this type of question because none of us have the engineering qualifications to answer that question. Call several specialists who make driveshafts for high HP applications and let them guide you. Get more than one opinion.


There are many things to consider when thinking about a driveshaft - shaft length, material and design harmonics, intended shaft rpm, and of course torque (HP is irrelevant to the driveshaft) and other consideration. But again, talk to an expert, don't rely on internet opinions.


I assume he meant for use on an MN12, but after re-reading all the qualifiers, maybe not.

David
 
I assume he meant for use on an MN12, but after re-reading all the qualifiers, maybe not.

David

Regardless of vehicle, no one here is qualified to answer his questions. A simple call to couple custom driveshaft manufacturers will answer his question much better than any of us could.
 
If mass is maintained Aluminum
If Diameter is maintained Steel

This assumes length doesn't change.

Since this boils done to torsion, and Steel has basically 3x the strength of Aluminum in this respect but here's the kicker Aluminum is 3x lighter. One more monkey wrench is Aluminum has a finite fatigue life, so given an infinite time the Aluminum will fail, where as the Steel one will not assuming it is protected from rust.

Now the harmonics is beyond me.

Semis have a capped max weight so they are made as light as possible so more load can me carried.
 
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If you are pushing 1000 lb-ft of torque, and putting all that to the ground, then you clearly have spent a ton of money on that setup, and at that point, what's another $1500, might as well spring for carbon fiber driveshaft.
 
Chickencoupe,
I am a PM inspector for Waste Management. We just got a new truck with an aluminum shaft in it and all our Macks have steel shafts. So natrualy this got me thinking about its longevity.

XR7 Dave,
I relize this may be too technical for most but I still have faith in some intelligent replys. I chose to post here because I believe there should never be an unturned rock in the field of information.

David Neibert,
I did intend this hypothetical situation to revolve around the MN12. The hypothetical part is the power applied. As your pictures show an aluminum drive shaft works well for your application. I do ponder its fatigue point.

racecougar,
I shound have been a little more precise. Mostly I see people ditching the factory unit for an aluminum unit. Why do they choose aluminum over steel? I would guess weight but is the weight saving/longevity to cost ratio better for steel or aluminm?

bowez,
You toutch on the point I think is the critical point in my question. The fatigue rate of aluminum. In my materal science class in high school we tested several materals of the same length and diamiter. We bent it 90* as many times as it took to brake the materal. Glass of course broke instantly. Lead on the other hand took alot more bending but was easy to bend. If memory servers corectly we called it malleability? The aluminum rod easy to bend but quick to brake was less malleable. I am not by any means an engineer or a scientist. But being under these trucks and seeing how a drive shaft acts in extreem conditions I don't see an aluminum shaft lasting as long as a steel shaft under all the same conditions.

I do not fully understand the harminics either. I do understand a driveshaft under load is constantly changing.

Man I cant seem to get the hang of how to reply with mutiple quotes! I wish I was more tablet savy. Sorry such a long reply but I wanted a address as many points as possible. Thank you for your time fellas. I enjoy the MN 12 world and like interacting on as many levels as I can.
 
The last time I was at the drag strip in 2nd round time trial I ran a faster El Camino and just before he crossed the finish line his steel driveshaft broke in two. I got a ringside seat as it came out from under his car and fortunately bounced away from mine. Aluminum driveshafts are built for specific maximum torque and are spec'ed that way. I've been running one for years.

Whoa--that's crazy! The knock on aluminum driveshafts though, is that when they do break, it's not a clean break that falls on the road, the resulting breakage will shred the transmission tunnel with its sharp edges. That's a scary proposition. The other knock on aluminum driveshafts is that while they do save rotational weight, the weight that they save is not far enough away in diameter to have much of an effect, performance wise. The idea is that with lighter wheels, they save rotational weight that is much further away from the axle (center of rotation).
 
Not really malleability but elasticity. Steel can be bend forever as long as you stay in the elastic zone, Aluminum is not so. For a driveshaft its a moot point, but in structural application its a very important consideration--IMO why Ford has kept the frames of the F150 steel.
 
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