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I'm no expert in math but wouldn't this require an exact pressure on the whole rotation? Assuming the suspension will keep the tire planted and there's is no slip of the tire. Also, how many times during the track day he went over the curb or curbs, how radius or type of the curve(s) taken so we get an idea of how far in the curb(s) he went and for how long?
I'm no expert in math but wouldn't this require an exact pressure on the whole rotation? Assuming the suspension will keep the tire planted and there's is no slip of the tire. Also, how many times during the track day he went over the curb or curbs, how radius or type of the curve(s) taken so we get an idea of how far in the curb(s) he went and for how long?
I agree, even if the distance between dimples matched the distance on the ground between tops of individual curbs, seems non-intuitive it could happen. But, often times our intuition is not right when it involves high energy and high speed events that we don't encounter on a day-to-day basis.
I am leaning on the theory there was some initial defect, like OP says, which then caused the cylinder shape to be more vulnerable to mechanical buckling. Google "buckling modes of cylinder" and choose images and check those out. Here is an example:
Last edited by aryork; 03-22-2017 at 10:07 AM.
Reason: typo
...and that initial defect would be in the metallurgy.
I'm still putting my bet on too thin rather than inconsistent metallurgy because of the smoothness of the warping. A set of calipers on an unshod wheel set will quickly tell.
Originally Posted by aryork
I agree, even if the distance between dimples matched the distance on the ground between tops of individual curbs, seems non-intuitive it could happen. But, often times our intuition is not right when it involves high energy and high speed events that we don't encounter on a day-to-day basis.
I am leaning on the theory there was some initial defect, like OP says, which then caused the cylinder shape to be more vulnerable to mechanical buckling. Google "buckling modes of cylinder" and choose images and check those out. Here is an example:
Originally Posted by Perimeter
Thank you, I didn't see past the spoke until you mentioned it.
I would get a pair of calipers and start measuring material thicknesses at different points at equal radii. Could provide the proof the material was too thin in some spots and deformed hence a manufacturing defect.
Originally Posted by aryork
Let's do some math. Let’s find the linear distance between dimples and compare to the track to test the theory that curbing might have caused it. There are 8 dimples. 360/8 = 45 degrees between each dimple. We need to know the approximate diameter of the tape. I know this is a 20” wheel, but not sure if inside or outside is 20”. Anyway, let’s assume diameter D = 20”. The circumference of the taped line is pi*D = 3.14*20 = 62.8 inches = 159.5 cm. Now divide the circumference by the number of dimples which gives 7.85 in = 20 cm.
The $64,000 question is…is the curbing spaced at about 8 inches or 20 cm?
ASM_GT4: if you can measure the inside diameter of the wheel we can get a better estimate (I assumed 20 inches).
Someone check my numbers.
Went and looked for curb dimensions...here's a version of FIA curbing...don't think it will match. Distance between curb peaks looks fairly large.
That does not explain the undamaged rim. Curbing on low tires yielding central damage would also leave marks on the rim
The spokes provide rigidity and each deformation is between those rigid points.
Another plus for possible explanation being metallurgy failure or too thin manufacturing failure
Originally Posted by aryork
I agree, even if the distance between dimples matched the distance on the ground between tops of individual curbs, seems non-intuitive it could happen. But, often times our intuition is not right when it involves high energy and high speed events that we don't encounter on a day-to-day basis.
I am leaning on the theory there was some initial defect, like OP says, which then caused the cylinder shape to be more vulnerable to mechanical buckling. Google "buckling modes of cylinder" and choose images and check those out. Here is an example:
...and that initial defect would be in the metallurgy.
That does not explain the undamaged rim.
OP says "there was a single bend, recorded in PORSCHE center of Bahrain. that bend is the key element of the next point." This single initial bend can cause the cylinder to buckle under far less loading. The single bend could have been caused by hitting a curb too early where the dirt has been eroded. Seen it quite a few times.
Once you have the geometric defect, the resistance to buckling is less. If you look at google images of buckling you'll see various "modes" where there are 2, 3, 4, 5, etc. lobes (aka dimples). The total deformation we see now would have happened incrementally by repeated pounding of the car on the curb. The number of lobes could have been influenced by spokes, but not necessarily.
I'm really just thinking out loud. Not promoting this as "the" answer.
Agree the undamaged rim of the wheel makes it more mysterious.
It's hard to imagine how the thickness of material there is off. Two ideas though: 1) a problem casting, and 2) problem in machining.
I would guess they cast and then machine these parts. I would also think the cylindrical part that is deformed got a final machining inside and outside. For there to be missing material in the wheel center section from casting, you would think it (i.e., air "bubbles") would have extended into the material that was machined off and would leave obvious surface defects.
Given that these parts are run one after the other on the same machine using the same program and undergo inspection afterwards, the probability that the part came off the machine with some type of variability in its thickness due to machining, IMO, is very low. They are probably turning these on a lathe so it's next to impossible to get some type of significantly varying thickness profile around the part like we see with the 8 dimples.
Also agree, however, if there were some internal defect due to casting or a machining defect, it could lead to the overall deformation that we see now.
It's interesting that there was a first bend, and then others that followed, which I agree rules out the gator theory. It does look like a buckling mode. Wow, that would seriously put into question quality of OEM wheels. The safety factor alone I'd assume would keep you very far away from yield strength of aluminum, making it next to impossible for that particular buckling mode to happen. Amazing. There must be a defect in the "matrix" around where you track you car.
Spacing wise, (from the gator theory that is now dismissed) the distance between bumps changes with the diameter of the corner the curbing is following, so I think it would be possible - I'm just using my experience with tracks in the US for that hypothesis.
...Wow, that would seriously put into question quality of OEM wheels. The safety factor alone I'd assume would keep you very far away from yield strength of aluminum, making it next to impossible for that particular buckling mode to happen. Amazing.
I was thinking along the same lines, but if you look at the number of these OEM wheels out there compared to the variety of other brands, there is a lot more community experience with OEMs than others. Although maybe that is an incorrect statement if we talk about track cars.
I was looking at some wheel failure images and those are nightmarish to say the least! I am thinking my desire to shave off a few pounds per wheel is not very important compared with keeping the wheel together.
Originally Posted by ShakeNBake
Spacing wise, (from the gator theory that is now dismissed) the distance between bumps changes with the diameter of the corner the curbing is following, so I think it would be possible - I'm just using my experience with tracks in the US for that hypothesis.
And, yes, the FIA curbing geometry is quite complicated. Germans must have been on the committee!
I was looking at some wheel failure images and those are nightmarish to say the least! I am thinking my desire to shave off a few pounds per wheel is not very important compared with keeping the wheel together.
I've seen a lot of cases where the spokes shear off crappy OEM look-a-like wheels. You're driving a 150K car, and you buy 700 dollar/set knock off wheels for the track....don't understand it.
I agree, even if the distance between dimples matched the distance on the ground between tops of individual curbs, seems non-intuitive it could happen. But, often times our intuition is not right when it involves high energy and high speed events that we don't encounter on a day-to-day basis.
I am leaning on the theory there was some initial defect, like OP says, which then caused the cylinder shape to be more vulnerable to mechanical buckling. Google "buckling modes of cylinder" and choose images and check those out. Here is an example:
Man I like the analysis you've done in the previous post .. the yellow marks made it very clear that the bends are identical. great stuff.
btw, I have purchased a measuring tape so I can provide you all possible data. I will measure it very soon.
The buckling theory IMHO is a fact now. but what caused it ? .. I am leaning to the manufacturing defect more and more.
Regarding the First single bend mentioned in the OP. you have assumed that Buckling could be a result of this initial trigger. But let me highlight that all bends are identical, where the initial "hit" should be different in somehow. right ? I think it was the the beginning of a major collapse of material specs .. and buckling could be caused by heat expansion. im just thinking out loud.
I really appreciate your scientific brainstorming .. keep it up guys and I will provide more info so we can have a very interesting investigation/R&D post !!
The spokes provide rigidity and each deformation is between those rigid points.
Another plus for possible explanation being metallurgy failure or too thin manufacturing failure
We are in the same page .. I am now 100% sure that "PORSCHE MOTORSPORT" reply lack of logic and professionalism. too quick and out of any physical/lab investigation #unfortunately .
Man I like the analysis you've done in the previous post .. the yellow marks made it very clear that the bends are identical. great stuff.
btw, I have purchased a measuring tape so I can provide you all possible data. I will measure it very soon.
The buckling theory IMHO is a fact now. but what caused it ? .. I am leaning to the manufacturing defect more and more.
Regarding the First single bend mentioned in the OP. you have assumed that Buckling could be a result of this initial trigger. But let me highlight that all bends are identical, where the initial "hit" should be different in somehow. right ? I think it was the the beginning of a major collapse of material specs .. and buckling could be caused by heat expansion. im just thinking out loud.
I really appreciate your scientific brainstorming .. keep it up guys and I will provide more info so we can have a very interesting investigation/R&D post !!
While I agree the buckling theory is very strong based on the failure mode, it would require a significant and fairly uniform compression load of the wheel. A wheel is subjected to a lot of forces especially under track conditions but I have a hard time envisioning a situation that exerts significant compression as if it was a column under load. I would think if the wheel was that weak from some defect, that it would fail from forces from other directions and in other ways first... ?
I suspect the wheel casting was improperly heat treated. As such, it's likely the barrel is "softer" than it should be.
This is my opinion as well .. because it sounds totally different when knocking both barrels .. the damaged one sounds thinner .. dont ask me how .. it reminds me when knocking a thin metal sheet. but ... that could be the effect of the expansion ... a result of the damage.
I suspect the wheel casting was improperly heat treated. As such, it's likely the barrel is "softer" than it should be.
Not that it's worth much but this is where I would be which then resulted in the buckling. It's also why I really don't understand why Porsche don't want the rim back. It's a very important safety component on one of their halo cars which is produced by and external supplier and at the very least has a pretty descent chance of being a manufacturing defect and could (would) have led to a catastrophic failure causing a serious accident. Someone had a serious brain fade back at Porsche HQ.
03-22-2017, 09:58 AM
.. it reminds me when knocking a thin metal sheet. but ... that could be the effect of the expansion ... a result of the damage.
