Aluminum PHB vs. Steel PHB

[dirtyd88]

Search turned up no real discussion thread on this.

So....Aluminum panhard bar versus Steel panhard bar.

What are the pros and cons of each? (besides the obvious weight savings)

 

[04SNK390HP]

The adjustable jam nuts on the aluminum ones can seize together sometimes.

 

[CCS86]

Aluminum is fine in the ideal situation where the bar sees only tension and compression. If one of the bushings starts to bind, it will put a bending moment through the bar. This could weaken it quite a bit. Fatigue issues could come into play too.

I went steel.

 

[CCS86]

I just did a couple FEA simulations in Solidworks on tubular aluminum loaded in just compression, then in compression with a 30 lb-ft torque on one end...

The max stress was 8 times higher!

 

[dirtyd88]

I can see if they were aluminum on steel, because there would be corrosion between the 2 materials.

 

[dirtyd88]

Aluminum is fine in the ideal situation where the bar sees only tension and compression. If one of the bushings starts to bind, it will put a bending moment through the bar. This could weaken it quite a bit. Fatigue issues could come into play too.

I went steel.

That is what I was thinking.

But since you posted those findings from a FEM analysis, that is very sketchy if that we're to happen. Steel has a much higher E than aluminum, so fatigue stresses are definitely a factor.

I guess it comes down to what type and how much stress the PHB will see during its use. My car is a daily driver that sees spirited cornering MAYBE once a week, if that. It's not like I'm pushing it hard into corners every weekend, and expecting the PHB to take constant cyclic loads of tension, then compression, etc.

So is the weight saving really worth it?

 

[dirtyd88]

Also, I can see if being dependent on the type of steel being used, whether it is a high tempered steel or just mild steel, which I assume most of the suspension components are these days due to mass production. High temp steel would be hands down better choice than T6, but in terms of mild steel, kind of a toss up, and also what yield stress the two have in comparison to one another.

 

[me32]

well i can say on my GT500 ive never had a problem with my J&M aluminum PHB. as for the 2013 its still 100% stock

 

[CCS86]

That is what I was thinking.

But since you posted those findings from a FEM analysis, that is very sketchy if that we're to happen. Steel has a much higher E than aluminum, so fatigue stresses are definitely a factor.

I guess it comes down to what type and how much stress the PHB will see during its use. My car is a daily driver that sees spirited cornering MAYBE once a week, if that. It's not like I'm pushing it hard into corners every weekend, and expecting the PHB to take constant cyclic loads of tension, then compression, etc.

So is the weight saving really worth it?

Also, I can see if being dependent on the type of steel being used, whether it is a high tempered steel or just mild steel, which I assume most of the suspension components are these days due to mass production. High temp steel would be hands down better choice than T6, but in terms of mild steel, kind of a toss up, and also what yield stress the two have in comparison to one another.

The thing is, with the panhard mounted as it is, every bump and vibration in the road will excite the bar. Every cycle of those vibrations and every corner you take is contributing to the fatigue of the aluminum even though the associated stress is low from those inputs. Especially if a bushing is binding, because then every motion straight up and down bends the bar.

The elastic modulus isn't really a concern here, but yield strength and fatigue strength definitely are. Is it possible to design an aluminum panhard that has a high safety factor (even with a binding bushing), and will outlive the vehicle? Absolutely. But it is very possible that the company who manufactured it, haven't done a comprehensive engineering analysis of their design. Steel takes a lot of the worry out with much higher strength and infinite fatigue life.

If I ran an aluminum bar, I would never use one with double poly. One or both ends would be a del-sphere joint or spherical bearing.

 

[Tob]

Aluminum is fine in the ideal situation where the bar sees only tension and compression. If one of the bushings starts to bind, it will put a bending moment through the bar. This could weaken it quite a bit. Fatigue issues could come into play too.

I went steel.

If a bushing were to bind? The lever arm acting through an 'S197 chassis length' panhard bar wouldn't be stopped by a polyurethane or rubber bushing. It would instantaneously tear or shred it, were it unable to rotate about the sleeve. I've never heard of a heim jointed panhard bar binding either. Heims can go bad, but they don't jam solid.

Regarding fatigue 'issues', did you model them as well? A panhard rod is a simple axial loaded component. Considering I've never heard of one failing (the bar itself, in conditions other than an accident) I'd be interested in hearing theoretical commentary on the subject.

I like the way Jon Aadland put it (he's an engineer with Boeing) regarding the aluminum panhard bar he fabricated for his car...

In case you're wondering, yes, this PHB is strong enough. It's good to over 3g's in a right hand corner before it buckles. When I get done with my car it will handle well, but not quite that well. The PHB won't fail unless I crash. After a crash, whether or not $18 worth of aluminum survived will be the least of my worries.

From here.

As for steel being that much better...

Who'da thunk it?

 

[me32]

If a bushing were to bind? The lever arm acting through an 'S197 chassis length' panhard bar wouldn't be stopped by a polyurethane or rubber bushing. It would instantaneously tear or shred it, were it unable to rotate about the sleeve. I've never heard of a heim jointed panhard bar binding either. Heims can go bad, but they don't jam solid.

Regarding fatigue 'issues', did you model them as well? A panhard rod is a simple axial loaded component. Considering I've never heard of one failing (the bar itself, in conditions other than an accident) I'd be interested in hearing theoretical commentary on the subject.

I like the way Jon Aadland put it (he's an engineer with Boeing) regarding the aluminum panhard bar he fabricated for his car...



From here.

As for steel being that much better...

Who'da thunk it?

As usual interesting read from ya bud.

 

[dirtyd88]

I'm curious in contacting Freedom Racing, of whom I plan on buying my PHB from, and see what they can tell me as far as their bars are concerned. I'm pretty sure they design their owns bars, as I know they for sure manufacture them here in CONUS. They also offer heim joints for both chassis and axle ends. Might be interesting to see what they say. I doubt a reputable company would just stick an aluminum stick our their with their name and reputation on it without designing and testing to make sure it's up to par.

 

[Tob]

This one?

 

[dirtyd88]

This one?

Yup. I just emailed FRTD and have gotten an initial response. Just waiting on another. I'll post the emails in here when they conclude.

 

[CCS86]

If a bushing were to bind? The lever arm acting through an 'S197 chassis length' panhard bar wouldn't be stopped by a polyurethane or rubber bushing. It would instantaneously tear or shred it, were it unable to rotate about the sleeve. I've never heard of a heim jointed panhard bar binding either. Heims can go bad, but they don't jam solid.

Regarding fatigue 'issues', did you model them as well? A panhard rod is a simple axial loaded component. Considering I've never heard of one failing (the bar itself, in conditions other than an accident) I'd be interested in hearing theoretical commentary on the subject.

I like the way Jon Aadland put it (he's an engineer with Boeing) regarding the aluminum panhard bar he fabricated for his car...

From here.

As for steel being that much better...

Who'da thunk it?

I never said a binding bushing would stop the suspension from moving. I said that it could weaken the bar. I also never said anything about a heim joint binding, so you must have misread my post. I actually recommended them.

Think about it, under hard acceleration the axle 'wraps' backwards slightly due to deflection in the UCA and LCA bushings. This makes the axle side panhard mount rotate roughly about the bar's long axis, while the chassis mount does not. With double poly bushings reluctant to deflect, this puts the whole bar in torsion (not really a big deal). But it could also cause extra friction in the bushings as they try to move through their normal range of motion. Friction in the panhard bushings as the car squats will put a bending moment into the bar (about the mounting bolt axis), bending the whole bar into a (very slight) arc. If the bar is also put under very heavy compression, while slightly arced, the stress could increase quite a bit.

I did not do any fatigue analysis. It's just always worth mentioning with aluminum parts (especially when long, unsupported and subject to constant vibration).

I'm not sure what you're arguing with that picture. You can't argue material properties, and steel is significantly stronger than aluminum. What's the story behind that picture? It looks like the rod fractured, but without a better picture you can't know if it was a homemade panhard from junk material.

 

[Ry_Trapp0]

The adjustable jam nuts on the aluminum ones can seize together sometimes.

a little anti-seize should fix that

I never said a binding bushing would stop the suspension from moving. I said that it could weaken the bar. I also never said anything about a heim joint binding, so you must have misread my post. I actually recommended them.

Think about it, under hard acceleration the axle 'wraps' backwards slightly due to deflection in the UCA and LCA bushings. This makes the axle side panhard mount rotate roughly about the bar's long axis, while the chassis mount does not. With double poly bushings reluctant to deflect, this puts the whole bar in torsion (not really a big deal). But it could also cause extra friction in the bushings as they try to move through their normal range of motion. Friction in the panhard bushings as the car squats will put a bending moment into the bar (about the mounting bolt axis), bending the whole bar into a (very slight) arc. If the bar is also put under very heavy compression, while slightly arced, the stress could increase quite a bit.

I did not do any fatigue analysis. It's just always worth mentioning with aluminum parts (especially when long, unsupported and subject to constant vibration).

I'm not sure what you're arguing with that picture. You can't argue material properties, and steel is significantly stronger than aluminum. What's the story behind that picture? It looks like the rod fractured, but without a better picture you can't know if it was a homemade panhard from junk material.

what Tob is saying as that a rubber/poly bushing is made of material that is significantly weaker than aluminum. the effect of a seized bushing on the strength/durability of an aluminum panhard bar would be negligible at best.

 

[CCS86]

what Tob is saying as that a rubber/poly bushing is made of material that is significantly weaker than aluminum. the effect of a seized bushing on the strength/durability of an aluminum panhard bar would be negligible at best.

You're thinking about it too simplistically. It's not the magnitude of the frictional force from the bushing, but the application of that force changes the loading configuration drastically. I only applied a 30 lb-ft moment, with the same compressive load and saw 800% higher stress.

Picture a thin drinking straw. You put one end against your thumb, the other end against a wall and push. When the force you exert passes straight through the straw, it is strong, maybe even digs into your skin. Now push only half that hard, but use the other hand to put a very small force downwards in the middle. It fails.

If the bind deforms the panhard enough, further straight compressive force will continue to bend the rod.

 

[dirtyd88]

You're thinking about it too simplistically. It's not the magnitude of the frictional force from the bushing, but the application of that force changes the loading configuration drastically. I only applied a 30 lb-ft moment, with the same compressive load and saw 800% higher stress.

Picture a thin drinking straw. You put one end against your thumb, the other end against a wall and push. When the force you exert passes straight through the straw, it is strong, maybe even digs into your skin. Now push only half that hard, but use the other hand to put a very small force downwards in the middle. It fails.

If the bind deforms the panhard enough, further straight compressive force will continue to bend the rod.

P-delta effect is a pain in the ass.

 

[Tob]

I never said a binding bushing would stop the suspension from moving. I said that it could weaken the bar.

And you implied that the bar would weaken from trying to rotate about a 'bound' bushing. And you again implied as such in the example you made in a following post...

Now push only half that hard, but use the other hand to put a very small force downwards in the middle. It fails.

If the bind deforms the panhard enough, further straight compressive force will continue to bend the rod.

I also never said anything about a heim joint binding, so you must have misread my post. I actually recommended them.

You had only mentioned 'bushings' and specified neither polyurethane nor a heim. That's why I mentioned both in response to your statements.

Think about it, under hard acceleration the axle 'wraps' backwards slightly due to deflection in the UCA and LCA bushings. This makes the axle side panhard mount rotate roughly about the bar's long axis, while the chassis mount does not. With double poly bushings reluctant to deflect, this puts the whole bar in torsion (not really a big deal). But it could also cause extra friction in the bushings as they try to move through their normal range of motion.

Yet double poly bushings do deflect. Their higher (typically than stock) durometer has a theoretical potential to induce torsional stress about the panhard bar, just the same as the natural arc the axle swings when traveling from full droop to full compression can. The effect on our beloved S197 chassis cars is minimal. With a heim it is non-existant. And yes, I mentioned a heim as plenty aftermarket panhard bars have these ends as an option.

Poly bushings have their own issues with friction, cold flowing, etc. They aren't optimal in an aftermarket control arm or panhard bar, let alone stock.

Friction in the panhard bushings as the car squats will put a bending moment into the bar (about the mounting bolt axis), bending the whole bar into a (very slight) arc. If the bar is also put under very heavy compression, while slightly arced, the stress could increase quite a bit.

The issue is that 'increased quite a bit' doesn't actually translate into failure with the use of aluminum in a typical aftermarket panhard bar whether it is utilizing a stock rubber or aftermarket bushing.

I'm not sure what you're arguing with that picture. You can't argue material properties, and steel is significantly stronger than aluminum. What's the story behind that picture? It looks like the rod fractured, but without a better picture you can't know if it was a homemade panhard from junk material.

The photo is of a stock S197 panhard bar that failed. Some would argue that it belongs in the 'junk material' class as it were. My point was directed at your initial post that in its summation was to use steel over aluminum.

 

[CCS86]

And you implied that the bar would weaken from trying to rotate about a 'bound' bushing. And you again implied as such in the example you made in a following post...

It will.

You had only mentioned 'bushings' and specified neither polyurethane nor a heim. That's why I mentioned both in response to your statements.

Yet double poly bushings do deflect. Their higher (typically than stock) durometer has a theoretical potential to induce torsional stress about the panhard bar, just the same as the natural arc the axle swings when traveling from full droop to full compression can. The effect on our beloved S197 chassis cars is minimal. With a heim it is non-existant. And yes, I mentioned a heim as plenty aftermarket panhard bars have these ends as an option.

Poly bushings have their own issues with friction, cold flowing, etc. They aren't optimal in an aftermarket control arm or panhard bar, let alone stock.

Spherical bearing and heim joint are the same thing Tob.

Is it possible to design an aluminum panhard that has a high safety factor (even with a binding bushing), and will outlive the vehicle? Absolutely...

If I ran an aluminum bar, I would never use one with double poly. One or both ends would be a del-sphere joint or spherical bearing.

The issue is that 'increased quite a bit' doesn't actually translate into failure with the use of aluminum in a typical aftermarket panhard bar whether it is utilizing a stock rubber or aftermarket bushing.

Yet again...

Is it possible to design an aluminum panhard that has a high safety factor (even with a binding bushing), and will outlive the vehicle? Absolutely...