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 Post subject: Re: Stalker in accident
PostPosted: June 13, 2015, 7:30 am 
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It appears to be a typical HAZ " heat affected zone" failure. You notice the break(s) are right next to the weld edge. When welding the carbon propagates towards the edge, therfore that area has higher cabon content and less elastic proporites. DaveW


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 Post subject: Re: Stalker in accident
PostPosted: June 13, 2015, 10:05 am 
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davew wrote:
It appears to be a typical HAZ " heat affected zone" failure. You notice the break(s) are right next to the weld edge. When welding the carbon propagates towards the edge, therfore that area has higher cabon content and less elastic proporites. DaveW


So reinforcing such bits with gussets would simple add more HAZ issues?

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 Post subject: Re: Stalker in accident
PostPosted: June 13, 2015, 11:01 am 
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I'm still very interested in this bracket failure.

Quote:
Once metal begins to fatigue, it will exhibit signs of wear and corrosion in the affected area.


I would replace the word fatigue with something like fracture. The metal can and does fatigue without showing any signs. This is because the day before it starts a crack or a micro crack, it is fatigued and that is what is going to start the crack on the next day. Aluminum fatigues with every load cycle, which is why an aircraft designer de-rates the properties to account for that. An aluminum wheel for a truck is de-rated more than a car wheel for the street which is de-rated more than a car wheel for a track car. That's why my racing wheels are stamped "not for highway use", they mean that - it shouldn't rotate more than a certain number of times before exceeding the design engineer's limits.

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 Post subject: Re: Stalker in accident
PostPosted: June 13, 2015, 11:13 am 
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geek49203 wrote:
davew wrote:
It appears to be a typical HAZ " heat affected zone" failure. You notice the break(s) are right next to the weld edge. When welding the carbon propagates towards the edge, therfore that area has higher cabon content and less elastic proporites. DaveW


So reinforcing such bits with gussets would simple add more HAZ issues?


The HAZ is not an issue if there is no flexing. The failed bracket imho suffered from flex which was compounded with the HAZ and possible undercut around the weld. A gusset would take away the flex. I am going to set up the bracket as installed ,attach a dial gauge to the back side and measure the forces required to get deflection.

Bob

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 Post subject: Re: Stalker in accident
PostPosted: June 13, 2015, 10:33 pm 
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bob wrote:
This is where I beg to differ. That lug welded to the chassis is being hammered in just about every plane. Under braking with the torsional twisting and over bumps, it`s failure in my eyes is inevitable. Having the lug hanging off the side of the chassis like that is a failure waiting to happen and believe the outside portion of the lug should be braced back to the chassis. I think that the bracket has work hardened to the point of becoming brittle and sheared of when the car hit the pothole. Hence the clean break, its not torn off its a fracture.

Bob


The fracture happened at the event on the day of. In fact, there were two fractures to the LH mount that day; both the front and rear tabs of the mount fractured simultaneously. Post-accident analysis aside, I know this to be the case because my car receives (by me) a thorough inspection prior to the first HPDE for the year. The TWS event was the first such event for the year for me. Aside from fluid changes, checking and re-torqueing fasteners, etc., every component on my car received a visual and tactile inspection; this included all suspension components and mounts. In seven years, and almost 9,000 miles of driving, there has never been a single issue with the mounts. I reiterate, there was no damage to LH mount prior to impacting the pothole, and there was no damage to the RH mount prior to the car going airborne and impacting the ground. For the sake of discussion, it may well be better to refer to the fractures as tears, because the initial failure (tearing of the mount) was caused by excessive force being applied to the mount, not fatigue. Impacting the pothole exceeded the shock and spring compression travel limits which, in turn, exerted an outward and upward force against the mount; this force exceeded the structural integrity of the mount and was the cause of the tears. The pothole impact was very solid, and even hard enough to bend the lip (and the rim, slightly) on the inside rear wheel.

The photos below reveal clean (fresh) breaks running the full length of the section of mount still welded to the frame as well as fresh breaks running the full length of the tabs. The edges of the breaks are jagged and the tabs deformed (bent) indicating the tabs were forcefully torn away in a pulling, twisting motion (such as that which occurs during braking) following the initial damage. Once the primary damage was done, the integrity of the mount was compromised to the point that it was only a matter of time before complete failure would occur; this happened 5 minutes and 32 seconds after impacting the pothole.

Bob, to echo your concern, tabs that extend beyond the edge of the frame rail absolutely do need to be braced back to the frame. My new chassis (currently being built) will have additional bracing in this area. I dare say that had my chassis had such bracing, the pothole may have very well ended up being nothing more than a very hard hit that left me with a bent wheel.

Again, what I shared initially in my USA7’s post was for the sake of safety with the truest of hopes that some may learn from my tragedy and avoid serious injury or death to themselves or someone else. Perhaps it will prevent some one’s wife from getting a phone call from a stranger telling her that her husband has been involved in an accident, and she’s a minimum six-hour drive away. As for those of you who want to go on debating whether or not my mounts were damaged prior to the accident, that’s your prerogative on this forum. For me, it’s a moot point; sixteen weeks in a back brace has left me with a slightly different perspective and more pressing concerns, some of which may have long-term effects on my profession and my family’s livelihood. Bottom line is this; the accident happened and I can’t change that. But hopefully, there’s something positive to be learned here. And just maybe, what I’ve shared, will prove useful to someone else. For me, it’s not about any one person being right or wrong about metal fatigue, or about proving someone else’s viewpoint wrong or mine right. It’s about what can be learned here and moving forward with it; it’s about preventing another accident such as mine from happening in the future.


Attachments:
forward_ lower a-arm and bracket.JPG
forward_ lower a-arm and bracket.JPG [ 99.49 KiB | Viewed 3161 times ]
forward_ lower a-arm and bracket_a_.JPG
forward_ lower a-arm and bracket_a_.JPG [ 84.97 KiB | Viewed 3161 times ]
forward_ lower a-arm bracket fracture _2_.JPG
forward_ lower a-arm bracket fracture _2_.JPG [ 103.67 KiB | Viewed 3161 times ]
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 Post subject: Re: Stalker in accident
PostPosted: June 14, 2015, 1:06 pm 
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Quote:
truest of hopes that some may learn from my tragedy and avoid serious injury or death to themselves or someone else.


I applaud your efforts for this. And I think you got a truly raw deal for making such a small mistake, it is very unfortunate.

The thing is, if you want your next bracket or someone else's bracket to be more robust - the cause of the failure of this bracket should be understood. I am not being argumentative when I say the bracket may have been subject to fatigue due to how it is welded to the frame.

It's not clear if we can get a definitive answer on that type of thing. The pictures of other cars posted in the thread sort of point that direction (fatigue), there have also been pictures of failures like this on the UK site, but my recollection on that is hazy.

Improving the susceptibility to fatigue of the the shapes involved would be a good thing. I think it would make just as much sense to increase the size of the bracket - make it taller at the base in the vertical direction by about 2x. Then the bracket can be tapered towards the mounting hole to the same width as before. This would make it more resistant to being teared by improving the leverage involved.

Drilling thru the frame and welding a sleeve, then mounting the arm in single shear is also a better situation, I think. This would avoid a weld at a place where the metal is potentially flexed.

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 Post subject: Re: Stalker in accident
PostPosted: June 14, 2015, 2:50 pm 
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horizenjob wrote:
I applaud your efforts for this. And I think you got a truly raw deal for making such a small mistake, it is very unfortunate.



You just can't make a comment without taking a stab.....amazing.


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 Post subject: Re: Stalker in accident
PostPosted: June 14, 2015, 10:58 pm 
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xcarguy wrote:
For me, it’s not about any one person being right or wrong about metal fatigue...
xcarguy, I too appreciate you "going public" with the details of this accident (and its results). And as the man on the scene, with the strongest interest in finding out what happened (and with the credentials to do so) I give your opinion the highest rating of the opinions/hypotheses on this topic.
xcarguy wrote:
...it’s about preventing another accident such as mine from happening in the future.
There's a lot I don't get about this structural failure. If the tabs failed simultaneously, why did they fail 5 minutes and 32 seconds after the impact? Where did the "twisting motion" come from? And though I understand how braking puts a pull on the front chassis attachment, it doesn't seem like it would be within an order of magnitude as great as the "pull" caused by hitting the pothole. I'm still flummoxed.

Can you summarize the lesson we should take home from this? What can we do to avoid reliving your experience in our own cars?

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xcarguy wrote:
horizenjob wrote:
I applaud your efforts for this. And I think you got a truly raw deal for making such a small mistake, it is very unfortunate.
You just can't make a comment without taking a stab.....amazing.
I don't see the stab in horizonjob's comment...unless you think he was being sarcastic.
PPS-As a fellow small-mistake-leads-to-spinal-injury guy (I did mine as a pilot, and it was 90 days before I could lift my head off the pillow and drink out of a water glass), I feel your pain. I wish you a prompt and full recovery.

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 Post subject: Re: Stalker in accident
PostPosted: June 15, 2015, 12:52 pm 
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xcarguy wrote:
And just maybe, what I’ve shared, will prove useful to someone else.


Right now there are 91 views on the accompanying picture. I'm sure this thread will prompt some to think carefully about suspension mounts. Thanks for posting it.

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 Post subject: Re: Stalker in accident
PostPosted: June 16, 2015, 10:12 am 
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Ok.
What I have learned from reading all the above is this.
1. Close attention should be paid to the design and strength of the front end suspension attach points of my car.
2. Hitting a pothole, railroad track crossing, or anything hard enough to bend a wheel will necessitate a pit stop to check my suspension, just as I do on a 4 off.
Thanks for the knowledge but sorry for your pain and the dammage to your beautiful car. I am sure your rebuild will be even better. Best wishes.
Gale

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 Post subject: Re: Stalker in accident
PostPosted: June 16, 2015, 10:36 am 
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Just thinking out loud.

Since cars have been made in some variation of this way just about forever and the vast majority have no real issues, we would think some level of care and attention would suffice in most cases.

I know the red heat affects us all and we've spent a lot of time and money preparing for a track day or autocross and so when we're out there we don't want to stop which is where things like this happen. We've all said "I don't feel any thing wrong" or "I don't hear anything wrong" and kept on when prudence would have dictated us to stop and check things out.

I've stopped and checked and I've also NOT stopped and checked. I've never had a serious issue, which probably leads to some level of complacence on my part which hopefully has been replaced with more caution after seeing this.

BUT it appears to me, and I'm not an engineer nor an airline inspector or whatever xcarguy is, that the weld is what created the weak spot in the first place.

SO... I've seen people making the br@ckets (sorry JD) by cutting off one side of a square tubing. What if you did that and then bolted the br@cket on? Yes that would require a redesign of the front of the frame, but it also eliminates any weld induced weakness, although it does give you the issues of bolt tightness or bolt failure. But a regular program of replacing the bolts should eliminate most of those fears plus be cheap, fast & easy.

It also doesn't guarantee you won't deform that bracket from a hard hit which could cause it to fail and you'd have to inspect the bolts periodically, but I'd think a loose bolt or a bolt replacement periodically would be much easier than spotting a hairline crack. And you could fairly easily replace a suspect bracket at the track.

That's not to say you wouldn't have to keep checking the brackets for fatigue.

What got me thinking about the relative merits of a bolt or a weld was this picture of what I think is a Speedway Motors Circle track set up. I didn't look it up, but that's where I think I've seen it before.

Attachment:
1.jpg
1.jpg [ 104.53 KiB | Viewed 3031 times ]


I asked the question of whether the bolt through the tube was any stronger than a bracket. And while no one had a real answer it made me begin to wonder.

Yes, you'd have to change the design of the front of your frame, but depending upon your design, you might be able to design it so that the whole vertical tube was replacable as well. I guess you could figure out a way to even replace it at the track in a reasonable amount of time.

Anyway just babbling today.

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 Post subject: Re: Stalker in accident
PostPosted: June 16, 2015, 12:36 pm 
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First... Xcarguy, sorry to hear about everything! wish you a speedy and thorough recovery!

Second, this post is absolutely fascinating mainly because so many people have put a lot of thought into the analysis of the failure. I am game! Considering my setup is vastly (orientation, etc) different than what is done on these cars, I would love to have you guys rip it apart for the better of the community!

I will start a new thread to do so...

Lastly, has anyone considered taking the book and updating it with cliff notes or something that covers things like these?? "The book shows it like this but the community has shown that this new approach might possibly work better... " The knowledge on this forum is so great and complete but too widely spread though many post.

FYI, (for a bit of humor) too me I think you guys all load your bearings wrong anyway, from an engineering stand point, but it works! Also does every one on here either own a plane, have flown them, or worked on them??

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 Post subject: Re: Stalker in accident
PostPosted: June 16, 2015, 1:24 pm 
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I'm still wondering how this all happened. Looking at the parts of the bracket connected to the control arm you can see only the top part of the ears are bent backwards. So there was backwards movement when the top part gave away but not the bottom part.

How did a big vertical load get to that bracket? The control arm has a bearing ( bushing ), so the vertical load should just be a percentage of the load at the coilover. Did it get an outwards load from the front wheel getting pushed backwards hitting the pothole?

So that seems most likely to me, a large amount of the bracket failed in tension from rearward force, that would show up as outward force on this bracket (tension ). At some point there must have been rearward movement of the control arm to cause the rearward bending of the remainder of the tabs still on the control arm.

I'm surprised there isn't more damage to the frame. Wouldn't that front corner drag on the pavement/ground when the front suspension gave away?

I think the sloped front bulkhead contributes to the difficulty of making good brackets. When mjalaly starts his thread I'll show what I did for Car9 and ask for input and we can discuss these traditional front bulkheads also...

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 Post subject: Re: Stalker in accident
PostPosted: June 16, 2015, 1:25 pm 
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carguy123 wrote:
SO... I've seen people making the br@ckets (sorry JD) by cutting off one side of a square tubing. What if you did that and then bolted the br@cket on?
You seem to be implying the same basic bracket design, which would not inspire me with great confidence. Either method of attachment would benefit from a rethink of the bracket design itself, or at least a thicker material.

carguy123 wrote:
I asked the question of whether the bolt through the tube was any stronger than a bracket. And while no one had a real answer it made me begin to wonder.
Yeah, the circle track stuff isn't exactly an 'ideally' loaded design either, but it has been battle tested. I would trust a purchased shaft type UCA to have sufficient strength and durability...I would expect that the specific manner in which it's mounted to the chassis would be the critical factor in determining just how safe/strong/durable the overall implementation is.


mjalaly wrote:
Also does every one on here either own a plane, have flown them, or worked on them??
Didn't you get the NOTAM?

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 Post subject: Re: Stalker in accident
PostPosted: June 16, 2015, 1:37 pm 
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Driven5 wrote:
carguy123 wrote:
SO... I've seen people making the br@ckets (sorry JD) by cutting off one side of a square tubing. What if you did that and then bolted the br@cket on?
You seem to be implying the same basic bracket design, which would not inspire me with great confidence. Either method of attachment would benefit from a rethink of the bracket design itself, or at least a thicker material.


Well yes, sort of. Using the square tubing you don't introduce any weakness from bending flat stock plus, while the bracket would look the same, the attachment would eliminate the welding and the subsequent weakness along the edges of the weld.

And it would be more easily replaceable as a precaution or upon inspections if/when you found a hairline crack developing.

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