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Chad Stapleton
Joined: 19 Jul 2001
Posts: 4403
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 Posted: Tue Oct 25, 2005 6:28 am Post subject: |
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| Kevin Willmorth wrote: | The Youngs Modulus of steels (ferrite materials) varies based on composition as follows (in GPa - or gigapascals):
Iron (Fe) 196
Low Alloy Steels 200 - 207
High Alloy Steels 190 - 200
Irons 170 - 190
This indicates a range in modulus from 170 through 207 based on alloy alone. However, this is just a measure of the bulk properties of the metal, and not of its actual strength as a final component. |
Nobody makes axles from pure iron, nor i doubt, from high alloy... so the "E " range is more like 200 to 207... not a great difference.
| Kevin Willmorth wrote: |
Axles are not subjected to pulling (streching) forces against the raw material, they are subject to the bending forces placed on the tubular structure, which is more plastic than elastic in dynamic..... |
....That is several times people have suggested that these axles are operating in the "plastic" mode. By definition, a plastic deformation is PERMANENT... and only occures when you exceed the elastic limit...IE when you BEND your axle.
Axles are flexing in the ELASTIC range of their strain curve..as do ALL spring systems
| Kevin Willmorth wrote: | | We are not talking simple hardness or stiffness of the raw materials here, we are talking about strength, or the resistance the axle has to bending and flexing. . |
If the GEOMETRY of the component is the same, and the "flexing " does not exceed the ELASTIC LIMIT of the material, (ie- it returns to its original shape) then im afraid the "resistance the axle has to flexing" is solely dependant on Youngs Modulous ... which as stated above will vary by less tha 4% for the materials likely to be used. However, "Bending" will be a function of the steels UTS ( which does vary hugely from steel to steel).
| Kevin Willmorth wrote: | | .....Using the stiffneess formula alone, and assuming all steels have the same yeild strength ..... |
WHOOOAAHHH...... totally incorrect. Yeild strength is no way the same for all steels. Go check your info .
| Kevin Willmorth wrote: | ...
The difference has more to do with the strength of materials based on alloy and heat treatment- which is how bicycles are designed. Alloy steels are not just steel, they have other materials alloyed into them, to begin with. Further, the addition of heat treating, which acts on both the core steel AND the alloys contained, changes the stenght of the tube... |
Yes, heat treatment will change the STRENGTH of the steel, but it will not significantly change its YM value. Remember ..strength is determined by the GEOMETRY and the UTS, and since the shape is not changing and we are not going anywhere near the UTS range ( elastic range only until you permanently bend the axle).. then you should forget this STRENGTH issue and return to the STIFFNESS or ELASTIC DEFLECTION which is what is happening.
| Kevin Willmorth wrote: | | ...Add to this the affect of axle diamter, and we have a range of stiffnesses. The original question of the advantages on a 50mm over a 40mm axle is somewhat complex and does include some level of marketing hype. Differences do exist between the two in terms of flex resistance - specifically at both ends of the range (40mm soft as the most flexible, and 50mm hard as the least felxible.) In te middle of the range, I suggest that neither the 40 or 50mm axles has any advantage over the other, as they can both produce very similar characteristics.. |
You are missing a very simple advantage...... WEIGHT.
For any given "stiffness" a 50m axle will be significantly lighter than a 40mm axle. Or to be more precise , for a given weight, the 50mm axle will be much stiffer. That is why they were intoduced in European CIK karts .
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Chad
"Those of you who think you know everything are annoying to those of us who do !!" |
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Andrew (AJ) Weber
Joined: 18 Mar 2003
Posts: 599
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| Posted: Tue Oct 25, 2005 9:12 am Post subject: |
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| Chad Stapleton wrote: |
....That is several times people have suggested that these axles are operating in the "plastic" mode. By definition, a plastic deformation is PERMANENT... and only occures when you exceed the elastic limit...IE when you BEND your axle.
Axles are flexing in the ELASTIC range of their strain curve..as do ALL spring systems
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Yes it is permanent, but there is also that transition zone between where 100% elasticity
ends and the yield point (where stress/strain starts going backwards). There is still
permanent deformation here, but if we are just touching into that region on very high
load corners, while the axle is rotating, it could straighten back out on exit. Maybe.
I do sometimes come off the track with slightly bent soft axles after not hitting even a
curb. I then do another session and it is straight again. I know that one particular
CRG shifter tuner avoids the S20 because his drivers bend the thing on fresh YHBs
without hitting a thing. That tells me that we are certainly not 'safely' (as in anywhere
near an aerospace 1.5 or civil 15.0 factor of safety) in the elastic region.
What I am fairly certain of is that Young's modulus variation is NOT a differentiating
factor for axles. I am also very certain that axles of the exact same dimensions do
behave differently. How? Slightly going past pure elastic deformation is one
(admittedly distasteful) possible explanation.
Another possible explanation is that it is not just the elastic (Young's) modulus at
play. Actually, I am pretty sure that the elastic modulus would apply to the axle
wall flexing at the top and bottom, but it would be the shear modulus at play on the
sides of the axle. Which is all rotating of course. I forgot whether or not there is a
shear modulus correlation with 'hardness' in steel. Does anyone here know? |
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Bob Baldwin
Joined: 23 Nov 2002
Posts: 231
Location: United States, CA, Chino Hills
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| Posted: Tue Oct 25, 2005 10:34 am Post subject: |
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WOW
I have a hard enough time just trying to figure out what tire pressures to use.  |
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Kevin Willmorth
Joined: 17 Oct 2004
Posts: 1160
Location: United States, Wisconsin,
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| Posted: Tue Oct 25, 2005 6:00 pm Post subject: |
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[quote="Chad Stapleton"] | Kevin Willmorth wrote: | | You are missing a very simple advantage...... WEIGHT. For any given "stiffness" a 50m axle will be significantly lighter than a 40mm axle.... |
Not sure what's going on here anymore. Reading the poss here it would appear that what is being suggested is that all 50mm axles are the same, and all 40mm axles are the same just because they are made from steel.
They are not, so want to explain that?
As far as the 50mm axles weighing less than the 40mm? Sorry, just ain't so. Not only is the 50mm x 2.5mm axle is heavier than the 40mm x 3mm axle (more material, since its larger diameter is not compensated for by a corolary reduction in wall thickness - PLUS the 50mm bearing set (with carriers) are heavier than the smaller diameter 40mm bearings and carriers. Hubs are also heavier, as well as sprocket carriers. I have both for the same kart, the 50mm assembly is simply heavier - by a bit.
I'm not a 40mm axle proponent. I am simply saying that there is not a significant difference between the two sizes. The original question was whether a significant advantage exists - I suggest that no, not really. You can get both to produce the desired stiffness for a given chassis - with the exception of the extremes in stiff or soft setups.
The rest was an acedemic exploration I am not prepared to take further, as I am not a metalurgist - just a geek who likes to talk about techy crap most of don;t know jack about. I'll leave that to those who are, and avoid going any further down that road.  |
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joseph hollinger
Joined: 12 Sep 2002
Posts: 9483
Location: United States, California, san francisco
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| Posted: Tue Oct 25, 2005 6:25 pm Post subject: |
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| Kevin Willmorth wrote: |
As far as the 50mm axles weighing less than the 40mm? Sorry, just ain't so. Not only is the 50mm x 2.5mm axle is heavier than the 40mm x 3mm axle (more material, since its larger diameter is not compensated for by a corolary reduction in wall thickness ... |
I think you missed the part where Chad said: "For any given stiffness"
A 50x2.5 is significantly (about 75%) stiffer than a 40x3. |
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Mike Goebel
Joined: 28 Jul 2001
Posts: 5766
Location: United States, California, Winnetka
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| Posted: Tue Oct 25, 2005 6:48 pm Post subject: |
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| joseph hollinger wrote: |
I think you missed the part where Chad said: "For any given stiffness"
A 50x2.5 is significantly (about 75%) stiffer than a 40x3. |
Yeah but the 50mm 2.5 wall weighs way more 5% more 
Mike G.
The Black magic of axles raises it's ugly  head again.
Last edited by Mike Goebel on Tue Oct 25, 2005 8:02 pm, edited 1 time in total |
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Tim Doll
Joined: 18 Jul 2001
Posts: 2644
Location: United States, Washington,
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| Posted: Tue Oct 25, 2005 7:28 pm Post subject: |
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| Mike Goebel wrote: |
The Black magic of axles raises it's ugly :twisted:head again. |
Ah, come on.... I want to talk about torque vs. horsepower.
Tim
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Standard disclaimer - I'm FREE - No longer affiliated with any organization, I can say whatever I darn well please!.
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Erik Maxfield
Joined: 16 May 2004
Posts: 1069
Location: United States, California, Vacaville
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| Posted: Tue Oct 25, 2005 9:44 pm Post subject: |
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I just got home from work and checked my email really quickly before I went out to dinner with my wife. I got myself all torqued up to write a lengthly thesis about plastic deformation, elastic deformation, the flexure formula, some basics on applied metallurgy, and throw in a ton of formulas just so that I could justify my existence and all those years I wasted in college to myself (not to mention wow everybody with my total lack of anything more constructive to do on a Tuesday night).......then I read the rest of the posts....
Chad you stole my thunder. 
Now I would be interested in a discussion on axle stiffness vs. hub length....
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Erik
The early bird gets the worm.....
The second mouse gets the cheese....
Stock CR125.
Chassis-FrankenKART
Intrepid/ITAL combination |
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Chad Stapleton
Joined: 19 Jul 2001
Posts: 4403
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| Posted: Wed Oct 26, 2005 4:12 am Post subject: |
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| Andrew (AJ) Weber wrote: |
Yes it is permanent, but there is also that transition zone between where 100% elasticity
ends and the yield point (where stress/strain starts going backwards). There is still
permanent deformation here, but if we are just touching into that region on very high
load corners, while the axle is rotating, it could straighten back out on exit. Maybe. |
That "transition zone" ... where the Stress / strain curve starts to become non-linea, is the plastic deformation zone.
It would be a very brave designer to contemplate using a structural material in this area of its abilities, and a very clever one to sucessfully make it work.
work out the loadings ( its been done before on this forum) you will find the axles are no where near their elastic limit in any normal situation.
| Andrew (AJ) Weber wrote: | ....What I am fairly certain of is that Young's modulus variation is NOT a differentiating
factor for axles. I am also very certain that axles of the exact same dimensions do
behave differently. How? Slightly going past pure elastic deformation is one
(admittedly distasteful) possible explanation.
Another possible explanation is that it is not just the elastic (Young's) modulus at
play. Actually, I am pretty sure that the elastic modulus would apply to the axle
wall flexing at the top and bottom, but it would be the shear modulus at play on the
sides of the axle. Which is all rotating of course. I forgot whether or not there is a
shear modulus correlation with 'hardness' in steel. Does anyone here know? |
I fully agree, it is all still a mystery, but you cannot ignor the existing science and metalurgical facts. 
_________________
Chad
"Those of you who think you know everything are annoying to those of us who do !!" |
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Andrew (AJ) Weber
Joined: 18 Mar 2003
Posts: 599
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| Posted: Wed Oct 26, 2005 9:40 am Post subject: |
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| Chad Stapleton wrote: |
That "transition zone" ... where the Stress / strain curve starts to become non-linea, is the plastic deformation zone.
It would be a very brave designer to contemplate using a structural material in this area of its abilities, and a very clever one to sucessfully make it work.
work out the loadings ( its been done before on this forum) you will find the axles are no where near their elastic limit in any normal situation.
I fully agree, it is all still a mystery, but you cannot ignor the existing science and metalurgical facts. |
Yes, yes, I understand all of that, and I am not trying to ignore facts. I am trying to figure
out where we are mismodeling the system such that the facts don't fit the model.
I'll have to search for the worked out loadings. Hopefully, they are not just a simple
little cantelever rod statics analysis, and is a descretized FE type of analysis for our rotating thin walled tube.
I don't like the plastic idea either, but I have to at least give it it's due since I HAVE
come off the track with tweaked soft axles (CRG S20) with absolutely no collision
induced impulse. I got plastic deformation in normal operation...by definition. Normal
operation: no collision, no curbs, fresh tires, grippy track. Plastic deformation:
permanent deflection. So no matter what statics analysis someone did on this forum,
I have experimental evidence that we ARE close to the limit, at least with an S20 axle.
Again, I do not like the plastic idea either, and basicly I hope it is not the case that
we have localized (and by localized, I mean possibly just little patches that could be
restraightened via neighoring still-elastic wall) plastic deformation regions on our
axles. I am game to find some other property that has significant variance in steel
types and has some dynamic consequence for a kart axle. Just explain to me how
'hardness', the advertised variable, can be valid without localized plastic deformation.
CRG's axle chart even has what looks like valid Brinell hardness numbers on it.
BTW, for those 'just shut and and drive' types shaking their heads about now, I will
just shut up and drive when I am free to do so. But this kind of stuff helps make
the waiting between track days go quicker. |
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William Sandoval
Joined: 03 Jun 2005
Posts: 885
Location: United States, Puerto Rico, Guaynabo
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| Posted: Wed Oct 26, 2005 10:23 am Post subject: |
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| Quote: |
That "transition zone" ... where the Stress / strain curve starts to become non-linea, is the plastic deformation zone.
It would be a very brave designer to contemplate using a structural material in this area of its abilities, and a very clever one to sucessfully make it work.
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Is it possible that these guys aren't really designing as engineers do? Maybe they are just building something then taking it to the track with no regard to safety factors, plastic deformation or the like then building whatever works. |
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Mike Goebel
Joined: 28 Jul 2001
Posts: 5766
Location: United States, California, Winnetka
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| Posted: Wed Oct 26, 2005 11:18 am Post subject: |
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| Andrew (AJ) Weber wrote: | I got plastic deformation in normal operation...by definition. Normal
operation: no collision, no curbs, fresh tires, grippy track. Plastic deformation:
permanent deflection. So no matter what statics analysis someone did on this forum,
I have experimental evidence that we ARE close to the limit, at least with an S20 axle. |
Mount your Mychron such that the G sensor reads vertical G's intead of lateral and then you will have some idea of the dynamic vertical loads from normal operation. Turn one at Moran has got to be a few G's with the dip.
Mike G. |
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Chad Stapleton
Joined: 19 Jul 2001
Posts: 4403
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| Posted: Wed Oct 26, 2005 1:51 pm Post subject: |
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| Andrew (AJ) Weber wrote: |
Yes, yes, I understand all of that, and I am not trying to ignore facts. I am trying to figure
out where we are mismodeling the system such that the facts don't fit the model.
. |
I personally believe the answer may be related to Vibration frequency, which is very varyiable with "hardness" and other material properties...
Consider that the "deflection" is in effect constantly reversing as the axle rotates , then this is very akin to an osillation or vibration characteristic....
....but its an area i have insufficient knowledge of to investigate in depth.
..Any experts ??
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Chad
"Those of you who think you know everything are annoying to those of us who do !!" |
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Chris Livengood
Joined: 24 Jul 2001
Posts: 2432
Location: United States, Pennsylvania, Da Burgh
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Chad Stapleton
Joined: 19 Jul 2001
Posts: 4403
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| Posted: Wed Oct 26, 2005 9:26 pm Post subject: |
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| Chris Livengood wrote: | | I noticed that on track the karts seems to brake better with the 50 v.s. the 40. Where there seemed to be a moment of torsioning before the rear wheels reacted to the braking action, that fealt less with the 50. |
I suspect this illustrates much of the problem we see with the whole of the "axle dynamics" discussion. Too many people "feel " or believe a certain thing is happening rather than reporting real data.
If you can detect the difference in torsional deflection between a 40mm and a 50mm axle....then you have a very special career ahead of you........in the field of ESP !!!
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Chad
"Those of you who think you know everything are annoying to those of us who do !!" |
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