Pulley FEA
02-21-2003, 01:36 PM
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2002 C230 Coupe
Pulley FEA
The steel hub ASP Pulley has just arrived on my desk!! 
Since I have time now, I want to do a quick FEA on it before putting in on. Anyone interested on the results?
Since I have time now, I want to do a quick FEA on it before putting in on. Anyone interested on the results?
02-21-2003, 02:48 PM
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C230 Sports Coupe
Originally posted by avlis
And don't forget to post pictures of the result.
And don't forget to post pictures of the result.
02-21-2003, 02:55 PM
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2002 C230 Coupe
LOL! Graphical results are supposed to be proprietary, but I know you guys are starving for pics 
Originally I was gonna do a quick 2D axisymmetric model but then I decided to do a 3D slice because of the screws so it will take a while.
BTW, the software is ANSYS.
Originally I was gonna do a quick 2D axisymmetric model but then I decided to do a 3D slice because of the screws so it will take a while.
BTW, the software is ANSYS.
02-21-2003, 05:44 PM
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2002 C230 Coupe
I applied some arbitrary unit loads to get the stress. The loads do not represent the actual loads exerted on the pulley. This is okay since the main objective of the analysis is to determine the "weak spots" of the design, not the actually stress on the model.
Note: the clamping pressure is 10 times higher than the pulley belt pressure.
Note: the clamping pressure is 10 times higher than the pulley belt pressure.
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02-21-2003, 06:22 PM
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2002 C230 Coupe
FEA is Finite Element Analysis. A software simulation that numercially calculates the results intead of intense phsysical testing and experimentations.
On the stress plot, the more red the higher the stress intensity.
On the stress plot, the more red the higher the stress intensity.
02-21-2003, 06:38 PM
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2002 C230 Coupe
How do the stresses change if you move the set screws away from the center?
- BT
I expect them to be less localized, but need to verify.
Also the thickness of the steel hub is critical too, because if it is too thick then it will create another weak spot at the aluminum side.
In addition, although I used different material properties, the components are modeled as "glued" onto each other. But in reality, they are in contact only when in compression, if the stress is tensile they will separate and hence result in bending stress at the corners.
Maybe I'll use contact elements if I have time over the weekend.
- BT
I expect them to be less localized, but need to verify.
Also the thickness of the steel hub is critical too, because if it is too thick then it will create another weak spot at the aluminum side.
In addition, although I used different material properties, the components are modeled as "glued" onto each other. But in reality, they are in contact only when in compression, if the stress is tensile they will separate and hence result in bending stress at the corners.
Maybe I'll use contact elements if I have time over the weekend.
02-21-2003, 06:56 PM
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I'm stress testing it now and it's holding up.
Just because you find a weak spot it's all relative. Since you don't know what the forces are how do you know if this is critical. How does the alloy pulley/steel sleeve compare? Then how does the slightly thinner steel sleeve in other pulleys compare in your test? How does the factory pulley compare? My guess even the factory pulley will have a weak spot in the same place afterall it's where it makes a right angle, doesn't take a fancy program to see that.
Just because you find a weak spot it's all relative. Since you don't know what the forces are how do you know if this is critical. How does the alloy pulley/steel sleeve compare? Then how does the slightly thinner steel sleeve in other pulleys compare in your test? How does the factory pulley compare? My guess even the factory pulley will have a weak spot in the same place afterall it's where it makes a right angle, doesn't take a fancy program to see that.
02-21-2003, 07:21 PM
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2002 C230 Coupe
I'm not talking about general peak stress as the weak spot.
Weak spot for me means localized stress concentration. Localized stress concentration means high possibility for crack initiation. Under vibration, if the stress is tensile, you'll have crack growth.
I will shift the set crew away and tell you what the results are.
I will also make all materials to be all aluminum, which is equivalent to the all alloy pulley and tell you what the results are.
I will even make them all steel, which equivalent to the stock steel pulley without damper and tell u what the results are.
All analyses with the same magnitude of loads for comparison. I never say the ASP pulley is flawed. I present potential locations for inspection if you take it out.
And remember, aluminum has very low fatigue life than steel.
Weak spot for me means localized stress concentration. Localized stress concentration means high possibility for crack initiation. Under vibration, if the stress is tensile, you'll have crack growth.
I will shift the set crew away and tell you what the results are.
I will also make all materials to be all aluminum, which is equivalent to the all alloy pulley and tell you what the results are.
I will even make them all steel, which equivalent to the stock steel pulley without damper and tell u what the results are.
All analyses with the same magnitude of loads for comparison. I never say the ASP pulley is flawed. I present potential locations for inspection if you take it out.
And remember, aluminum has very low fatigue life than steel.
02-21-2003, 08:30 PM
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2002 C230 Coupe
Case 3:
Simulation of an all-aluminum pulley.
Results:
Stresses concentrate around the hub-to-pulley connection, but with less localized disctibution and have lower magnitude (67996 units max) than Case 1.
Simulation of an all-aluminum pulley.
Results:
Stresses concentrate around the hub-to-pulley connection, but with less localized disctibution and have lower magnitude (67996 units max) than Case 1.
02-21-2003, 08:36 PM
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2002 C230 Coupe
Case 4:
Simulation of an all-steel pulley.
Results:
Same stress distribution as Case 3 and same stress intensity magnitude (67995 units max) as Case 3 as well. This shows that the stress is dominated by axial stress, which is produced by the bolt force and less dependent on elastic modulus.
But the strength of aluminum is about 1/3 of that for steel, so under the same stresses aluminum is more likely to fail.
Simulation of an all-steel pulley.
Results:
Same stress distribution as Case 3 and same stress intensity magnitude (67995 units max) as Case 3 as well. This shows that the stress is dominated by axial stress, which is produced by the bolt force and less dependent on elastic modulus.
But the strength of aluminum is about 1/3 of that for steel, so under the same stresses aluminum is more likely to fail.
02-21-2003, 08:36 PM
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2002 E55K RENNtech HP
Why don't you add a stress relief radius groove at the max stess point and rerun the results? Also, what grade of aluminum are you using?
02-21-2003, 08:43 PM
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2002 C230 Coupe
CONCLUSION
All loads are unit loads for purpose of comparison. Thus, the results do NOT represent the actually stresses on the real pulley. And this analysis is not intended to show any design flaws and failures.
One pulley sheared off at the high stress location, although it does not need a fancy program to figure this out, but it proves that the program is giving correct results. On the other hand, there are many other installed pullies have no problems at all.
It is like the harmonic damper, I and some people think it is not significant, while other people strongly oppose. And in the mean time some people have solid pullies with no dampers on their cars for many years without any problems.
Reality is: it is your pulley; it is your car. I cannot tell you what is right what is wrong. You are the one who decide what to do to your car.
If you decide to do it, you need to take the consequence. Don't blame manufacturer because nothing in the world is perfect - even the car makers rolling out cars for decades still facing problematic models.
One pulley sheared off at the high stress location, although it does not need a fancy program to figure this out, but it proves that the program is giving correct results. On the other hand, there are many other installed pullies have no problems at all.
It is like the harmonic damper, I and some people think it is not significant, while other people strongly oppose. And in the mean time some people have solid pullies with no dampers on their cars for many years without any problems.
Reality is: it is your pulley; it is your car. I cannot tell you what is right what is wrong. You are the one who decide what to do to your car.
If you decide to do it, you need to take the consequence. Don't blame manufacturer because nothing in the world is perfect - even the car makers rolling out cars for decades still facing problematic models.
Last edited by 20FHK02; 02-21-2003 at 08:46 PM.
02-21-2003, 08:47 PM
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2002 C230 Coupe
Originally posted by James F. Cannon
Why don't you add a stress relief radius groove at the max stess point and rerun the results? Also, what grade of aluminum are you using?
Why don't you add a stress relief radius groove at the max stess point and rerun the results? Also, what grade of aluminum are you using?
02-21-2003, 10:10 PM
#21
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In the all alloy pulley you left out one huge detail, the thickness of the hub is considerably smaller because of the steel sleeve which is not supporting any weight so you have to take that into consideration. For example if the hub walls are .20" thick on the factory pulley then the alloy pulley may only be .12" thick.
02-21-2003, 10:12 PM
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2002 C230 Coupe(M111)
Recreate the stock pulley as a model. Where's the stress now? Same area I would imagine.
I'm so sick of hearing the bs about the dampner. Some say the dampner is there to prevent damage to the engine...some say its for the accessories, some say its for NVH reasons, and even more surprising, some say the lack of one is the reason the ASP pulley failed. Ha! That's a good one!!!
I'm so sick of hearing the bs about the dampner. Some say the dampner is there to prevent damage to the engine...some say its for the accessories, some say its for NVH reasons, and even more surprising, some say the lack of one is the reason the ASP pulley failed. Ha! That's a good one!!!
02-21-2003, 10:22 PM
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Just remember, ASP does make a Renntech style pulley using the factory damper and it's the least expensive solution. Not a solution I chose so if someone is considering this let me know, I may lend my factory pulley out to have converted and then get your old one back from you. The condition is that you pay a deposit equal to the cost of a factory pulley that I'll refund you in the end minus any shipping costs.
