Axles, Drilled vs. No Drilled.

There's been some talk lately about whether a drilled axle is weaker or not. I model a 36 ford axle in Autodesk Inventor, then transfered it to Ansys 10 FEA software, and check them both with a 5000 pound load on them. Here's the results:

PS, this may answer some of the questions on this thread:
http://www.jalopyjournal.com/forum/showthread.php?t=102755

 

As you can see, not alot of difference between the two. All of my support conditions in the model very closely reflect a realistic condition.

Edited to say, they were 1" holes I put in the model. You can count them. I placed 2500 pounds on a split face over each spring perch hole, to model the load from a spring over axle. The axle is supported at each end in a fashion that closely matches a pair of spindles.

Edited again to say, I replied below with more details on how a came up with this ****...

 

Very nice, always good to have some science back up old fashioned know-how. Now for us science-ignorant, could explain what the graphs mean?

 

Von Mises stress in an equivalent stress contained in an element. Fea busts up the part into many thousands of elements, and finds the equivalent stress in each. The more elements you have in a mesh, the more accurate your result will be. I have a ****load of elements in these meshes, so they should be pretty accurate. If the equivalent stress exceed the yield strength of the material, you'll have problems. If these axles have a standard yield strength of 30kpsi, then you can see that this load could yield the axle if a bump was hit, or some other impact load. These axles were tempered though, so I'm sure their yield is much higher. I have no idea what it is though. 5000 pounds is a lot higher than they'd ever experience statically anyways....

 

Awesome post very interesting!

 

How did you apply the load? In the Z axis only? I would think the holes in the web would not affect it loaded in that direction, but maybe in the Y axis with the decrease in modulus in the drilled one? What about torsional loads? Can you twist it in that software? Very cool by the way. My experience is with RISA 3-D and Staad.

 

AW ****! I so wanted to be living on that edge that endangered the entire human race. Dammit Are you sure the sky isn't falling?

 

Great information, Thanks!

 

you are a mad scientist

 

thats all fine and dandy but thats a static load
what about a dynamic load?????
i think driving it would inflict more stress than that( like hitting that magical moving pothole)
just a thought
tom
by the way nice model

 

I'm no scientist, but wouldn't the critical question be strength under stress rather than static load. These are subject to much more than 5000 lb. when stressed.

 

So, light blue is bad?


Thanks for the info. That's one serious program.

 

and not to mention 70 year old cast steel which is prone to imperfections and stress cracking/relieving due to age, usage, improper storage and any possibly torching or realigning having been done on it in the past that may have increased the brittleness of the material due to improper heat transfer and quenching...

 

Aaron....I thought you were a scientist??? JK.

Matt

 

The problem with any FEA is to make sure your ***UMPTIONS are correct. Not saying what you have done is right or wrong it's just that you present your ***umptions as fact. For instance 5,000 lbs SOUNDS great but I have no idea if it's realistic or not. Might I ask how you came up with THAT particular number????

On the same token I have to wonder what forces are generated when we are going 60 or 80 mph and hit a 6" deep chuck hole??

Static loads are one thing dynamic loads quite again another.

Now don't get me wrong - drilling axles has been done for years with sucess I get that and maybe everything you've shown here is reasonable, but if you really want to present this as fact you need to show more of your process IMHO.

 

Just make sure you don't put your kid in the rumble seat.

 

another quick point that I'd like to make is that any item that has been cast or forged and has not been stress relieved in the factory (which I'm sure henry probably wasn't aware of) tends to keep it's stress within its original form, ie within the "skin" of its original casting/forging...any type of machining or grinding to that "skin", or any dents and dings can release that stress from the internal structure of the steel outwards...now while many times this has no adverse effect on things like this, it just may be that one strange instance where that rock that grandpa hit on the farm comes back to haunt you after you've relieved yet even more stress after drilling a bunch of holes in the axle and essentially started a chain reaction of internal structure decomposition...and add insult to injury if you happened to work harden a hole or two along the way on the drill press and forced your way through it...while it may be a long shot, I'd be willing to say that is where many axle failures start...oh, and when you were smoothing out your axle with the flap disc on the angle grinder, that's another way of removing that "skin"...chances are it's a HUGE what-if situation and shouldn't discourage anyone from modifying their axle, just take into consideration things like heat and structure before doing so...

 

You forget where your load IS on the axle...

 

Good to see some real science being brought into it. But let's hear some real-world experience, anyone ever seen a drilled axle fail? Some pictures and commentary would go a long way.

 

Isn't the axle forged steel?

The original ones are anyway.

 

I'd like to know this as well.

Theory aside, anyone know of actual instances of drilled axle failure?

 

Ahh that **** was funny!!! I drilled the hell out of mine and my dads.

 

My Coupe I had had a old original daga axle drilled with small 3/8 holes and at the spindle you could kick the tire and watch it move slightly. Kinda scary but it did make it just fine on the 2800 mile roadtrip to Paso last year. Freeked my dad out when I showed him at a gas station one day.

 

I REPEAT, DRILLED AXLES SEEM TO HAVE SOME PROBLEMS IN THE Y AXIS.

 

Okay, I added some more pictures. I added pictures of the loading conditions, should be pretty clear. What isn't clear on them is the support conditions at the spindle, so I will describe it. If you don't understand FEA modeling you prolly won't have a clue what I'm talking about. They are cylindrical supports, through the kingpin bores, and are radialy free, axially fixed, and tangentially free. This would allow for rotation about the kingpin, and allow the kingpin to move in any direction perpendicular to the axis of the kingpin, as in if the axle was bowing, the top of the spindle would move either in or out, you feelin me? The support is fixed axially because in real life the axle cannot travel down along the axis of the kingpin because the spindle and wheel/tire/ground would stop it. The loads shown above are parallel to the axis of each respective perch. Now, I understand that I did not compensate for a pair of bones, but comon you ****a's, what do you expect for me to do over just my lunch break. Sheesh...hehehe....

 

Oh yeah, to the guy who said I am stating all this as fact, I'm not. I could be wrong, this is just my take on it. And I am ABSOLUTELY sure that one could produce a more detailed model than this, I did this over my lunch break today, INCLUDING the model, so cut me some slack, I honestly didn't think it would get this much response. Though I must say I'm glad it is! Don't be so fukkinn touchy, hehehe...

 

So what's the short answer?

Holes don't make any difference?

 

welcome to the HAMB, where grown men complain just for the sake of being whiny *****es, "because he didnt take into account the twisting moment as applied through a 65 year old bias ply tire traveling down the road at 90 miles an hour simultanseously striking a ra**** with one wheel and sinking into a 4" pothole whilst swerving to dodge an endagered midget..."

great modeling.

(even though it isn't done to the appropiate level as to be posted here in the HAMB, next time if you arent going to do it 100% dont do it at all... )

 

Thanks! Thanks! Thanks! Nice bit of info

 

after further explination... you are still a mad scientist... I would like to see some photos of bent/broken axles, anyone got some?