Tesla Upper Control Arm CRACKED

[wycolo]

Looking at the image 3 posts prior we can conclude that this vehicle sustained a massive blow on the inside bottom of the wheel towards the outside, thus (sacrificially) folding and partially cracking the aluminum piece during compression. Likely the wheel or wheels that were discovered bent were also damaged during this event but they might be holdover issues from prior events. So conclude: the suspension skidded into a pothole or curb at a significant rate of speed. [armchair forensics]

This obvious sacrificial failure prevents the bending of other frame/suspension parts that could easily go undetected had the sacrificial part been made stronger. It is a passenger car and not an off-road racer, rock climber etc.
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[McRat]

I agree with this, with the caveat that it is not evidence of a defect.

It could certainly be accounted for in the design. We have no way of knowing what materials properties and max loads were used in the design process.

And, we don’t know if this part was designed to fail first as an energy absorbing mechanism.

Correct it's not a defect, it's a design decision, and even grain direction issues are not a defect unless the blueprint specifies it.

Yeah, I should have realized the inside radii were too small to be efficiently cut with an endmill and wire EDM is silly expensive for something like that. In a way, extrusions are much like billets, except certain alloys do not like to be extruded, 7075 comes to mind. Most likely, these parts are just 6061.

But if I wanted the part to collapse at a certain loading, I'd still have went to a I-beam forging using a malleable alloy, and just machine a narrow section where I wanted it to fold. This would insure it always bends where you want it, at the pressure you want it, and remains in a single piece, while absorbing the most energy. Once something snaps, it can't absorb energy.

This is how make shear members for rockets and such. We tightly control the area we want it to fail. ±0.001" 32 finish or better. It doesn't break early, it doesn't break late.

 

[JohnSnowNW]

Appreciate the last couple pages in this thread. It would be nice if cooler heads prevailed early on in these threads, instead of the FUD that consistently follows the initial posting.

 

[SMAlset]

Looking at the image 3 posts prior we can conclude that this vehicle sustained a massive blow on the inside bottom of the wheel towards the outside, thus (sacrificially) folding and partially cracking the aluminum piece during compression. Likely the wheel or wheels that were discovered bent were also damaged during this event but they might be holdover issues from prior events. So conclude: the suspension skidded into a pothole or curb at a significant rate of speed. [armchair forensics]

This obvious sacrificial failure prevents the bending of other frame/suspension parts that could easily go undetected had the sacrificial part been made stronger. It is a passenger car and not an off-road racer, rock climber etc.
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Based on the photo of the part, do people feel certain this was some latent issue caused by a prior pothole or such incident? At first I wondered if one of those broken humongus DOTs pictured could have become a flying projectile if hit just a certain way and damaged the part causing the failure. Seeing some of the articles with photos however, I can see where logistically that would be hard to do and there doesn't seem to be any white "chalk mark" on the part in question indicating it was struck (unlike other underside car photos with the chalk marks).

BTW once a photo of the actual broken arm was posted (thanks so much OP, have been wondering how this car repair was resolved at your end), I've enjoyed the metallurgy discussions.

Appreciate the last couple pages in this thread. It would be nice if cooler heads prevailed early on in these threads, instead of the FUD that consistently precedes the initial posting.

Assume you meant "after" there. With little to go on however (ie no actual photo of the part that failed), I think it is understandable that there was a lot of speculation.

 

[JohnSnowNW]

Assume you meant "after" there.

Correct, and edited for clarity.

 

[bhzmark]

do people feel certain this was some latent issue caused by a prior pothole or such incident?

perhaps not certain, but likely, yes

 

[AWDtsla]

I agree with this, with the caveat that it is not evidence of a defect.

It could certainly be accounted for in the design. We have no way of knowing what materials properties and max loads were used in the design process.

And, we don’t know if this part was designed to fail first as an energy absorbing mechanism.

This part doesn't look like the primary failure to me regardless. If this was the source of the problem, you would only be driving around with massive camber angle, but otherwise intact.

 

[mongo]

...snip...
And, we don’t know if this part was designed to fail first as an energy absorbing mechanism.

I think this may be the case based on the concave section intersecting the center to center line of the mounting bolts. (Based on cell phone graphical analysis).
Having tweaked my frame by sliding on ice into a curb (non-Tesla), I can appreciate a feature like that.

 

[David.85D]

This features gives me pause. Could easily be a odd shadow, but it also could be the remnants of a crack that had been growing.

 

[mongo]

This features gives me pause. Could easily be a odd shadow, but it also could be the remnants of a crack that had been growing.

Could be a couple things (said the armchair qb). The metal may have different properties where it was forced against the extrusion die.
Break may have been in shear, or the main break was tensile, but the last part separated due to the bending moment.
This piece should be in compression normally, unless cornering....
??

 

[AWDtsla]

Could be a couple things (said the armchair qb). The metal may have different properties where it was forced against the extrusion die.
Break may have been in shear, or the main break was tensile, but the last part separated due to the bending moment.
This piece should be in compression normally, unless cornering....
??

No, it's in tension. When cornering weight and force concentrates on the outside wheel, which is in tension. Compression loads will be less for the inside wheel.

 

[mongo]

No, it's in tension. When cornering weight and force concentrates on the outside wheel, which is in tension. Compression loads will be less for the inside wheel.

Agreed for the cornering case. For the straight/ static situation, is the wheel wanting to tip in or out at the top? (depends on instant center vs tire position and I don't know either but was guessing that the wheel would be outboard. A hit on the outside rim would cause compression, yah?)

 

[AWDtsla]

For the straight/ static situation, is the wheel wanting to tip in or out at the top? (depends on instant center vs tire position and I don't know either but was guessing that the wheel would be outboard. A hit on the outside rim would cause compression, yah?)

Hit on the bottom outside would still be in tension. Without pictures of all the damage it's hard to say what happened, but again this does not look like a fatigue failure or start of the failure, but a result.

 

[mongo]

Hit on the bottom outside would still be in tension. Without pictures of all the damage it's hard to say what happened, but again this does not look like a fatigue failure or start of the failure, but a result.

Just trying to clear things up, I'm thinking of running over something with the outer edge, were you referring to hitting something with the outer edge (slide into curb for instance)? Also, are you referring to the link as a whole, or the top web of the link?

Pic of rear suspension from Comments on Tesla Model S public engineering presentation

The shock/ spring looks to be connected inboard of the bottom A-arm. The top camber link then counters the resultant torque from the static load.
When the wheel runs over anything, the damping of the shock causes additional torque around it's attachment point which translates to compression of the camber link.
Too strong an impulse could overload the link and result in the type of damage seen.

 

[AWDtsla]

Just trying to clear things up, I'm thinking of running over something with the outer edge, were you referring to hitting something with the outer edge (slide into curb for instance)? Also, are you referring to the link as a whole, or the top web of the link?

If you slide into a low curb, it would be tension. If you slide into a wall, it would be compression.

The shock/ spring looks to be connected inboard of the bottom A-arm. The top camber link then counters the resultant torque from the static load.
When the wheel runs over anything, the damping of the shock causes additional torque around it's attachment point which translates to compression of the camber link.
Too strong an impulse could overload the link and result in the type of damage seen.

True. After reviewing all the images again it does look like vertical impact alone could have caused it, but really one hell of an impact which likely bottomed out the damper. Otherwise, force would be limited to a fraction of damping force, not impact force.

Regardless, I think it's still clear that this arm was not the cause of the failure, but a result. The arm failing and bending like that would not cause the car to "slam into the ground", but you'd have a camber problem.

edit - Also reminds me I did almost exactly the same damage to car had I had a little too much fun with in a snowy parking lot. Drove on it like that for about 300 miles before swapping out the arm.

 

[mongo]

If you slide into a low curb, it would be tension. If you slide into a wall, it would be compression.



True. After reviewing all the images again it does look like vertical impact alone could have caused it, but really one hell of an impact which likely bottomed out the damper. Otherwise, force would be limited to a fraction of damping force, not impact force.

Regardless, I think it's still clear that this arm was not the cause of the failure, but a result. The arm failing and bending like that would not cause the car to "slam into the ground", but you'd have a camber problem.

edit - Also reminds me I did almost exactly the same damage to car had I had a little too much fun with in a snowy parking lot. Drove on it like that for about 300 miles before swapping out the arm.

Yah, not the arm's fault. For the amount it bent, the tire may have been tipped enough to lower the car. Displacement of the top of the knuckle could then be enough to rip the brake line (other result of incident)

 

[GeorgeCM]

My wife was driving us home this Saturday, as we were coming back from a wedding party. There was nobody on the other side of the road. She hit a small, really small pothole when the car became hard to control. For a short time we went on the other side of the road, then she managed to get back on our side while reducing speed to a complete stop. I first believed that we got a tire explosion, but it was not the case. The tire was fine, but the wheel was in an incorrect position. We managed to slowly drive the car in a position safe for other drivers, in a parking place nearby. The upper control arm was broken. I also observed interior side tires abnormal wear on both rear wheels. The car was driving with these tires less than 3000 miles!


This looks to me like a catastrophic failure of that control arm, does anybody has knowledge if Tesla has a newer, reinforced version of this part ? I am looking to replace them on both sides. Anybody who has a reliable source for new parts, preferably in Europe please send me a message. The nearest Tesla service from me is 2000 km away.

 

[jelloslug]

My wife was driving us home this Saturday, as we were coming back from a wedding party. There was nobody on the other side of the road. She hit a small, really small pothole when the car became hard to control. For a short time we went on the other side of the road, then she managed to get back on our side while reducing speed to a complete stop. I first believed that we got a tire explosion, but it was not the case. The tire was fine, but the wheel was in an incorrect position. We managed to slowly drive the car in a position safe for other drivers, in a parking place nearby. The upper control arm was broken. I also observed interior side tires abnormal wear on both rear wheels. The car was driving with these tires less than 3000 miles!
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This looks to me like a catastrophic failure of that control arm, does anybody has knowledge if Tesla has a newer, reinforced version of this part ? I am looking to replace them on both sides. Anybody who has a reliable source for new parts, preferably in Europe please send me a message. The nearest Tesla service from me is 2000 km away.

That control arm looks like it had been cracked for a while.

 

[K-MTG]

Super glue?

 

[jaguar36]

The stair stepped crack looks like you had a two stage failure. Its hard to tell from the pictures, but both crack surfaces look like they were brittle overload failures. That indicates that it cracked once from a major overload (pothole or curb) and was hanging on for a little while which cause the extreme tire wear. Then you hit another pothole and that finished it off.