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Question on fastener material

640 Views 23 Replies 7 Participants Last post by  hvymtlmcn
Hello all!
Being that it’s winter, I’ve had the free time to come up with a very specific question that’s probably more trouble than it’s worth. At the very least I might learn something in the process.

I am working on a non-functioning door hinge restraint, and found the culprit to be the two bolts (that hold the restraint assembly to the hinge) had snapped in half. I’ve been referring to these two threads for reference "Door Doesn't Stay Open" & "Problem: Door not staying open" but didn’t want to bump discussions that are over 7 & 12 years old, respectively.

Finally, on to my question: Has everyone replaced these bolts with new bolts of the same material? Or is there an improvement that can be made to prevent this issue from occurring again? I’ve played with the idea of Titanium bolts, which would carry the additional benefit of cutting weight. I just don’t have the mechanical background to figure out if a harder material will end up being more likely to snap in half.

Maybe the attached picture of the failure can be enough for someone more mechanically minded to bring up some ideas? I’d love to hear @[U]shinoo[/U] share some thoughts if possible. That's all the details I can think to share. I'd like to thank everyone in advance for any information that can be shared. This forum has been an incredibly welcoming and helpful place so far!
Cheers everyone!

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I had never heard of this issue until you posted and popped those two other threads in. I don't think it's very common. The stock bolts are probably A-2 or A-4. It should be stamped on the bolt head. I'd replace the the bolts with class 8.8 or 10.9. You could use grade 5 Titanium bolts, they are close to class 10.9 in shear and yield, but titanium has a much lower galvanic index than aluminum, not worth the corrosion risk.
 

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I wonder of there was a batch of bad fasteners since this is not more common
I would buy good quality bolts and use neverseeze.
I would not use titanium bolts but since I don't plan on leaving my car in salt water, it is not because of corrosion
 

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Discussion Starter · #4 ·
I had never heard of this issue until you posted and popped those two other threads in. I don't think it's very common. The stock bolts are probably A-2 or A-4. It should be stamped on the bolt head. I'd replace the the bolts with class 8.8 or 10.9. You could use grade 5 Titanium bolts, they are close to class 10.9 in shear and yield, but titanium has a much lower galvanic index than aluminum, not worth the corrosion risk.
The bolts that failed have "8.8" stamped on the head. I assume I would have to find something class 10.9 in order to have an improvement in strength over the hardware that failed.

You bring up a great point about corrosion. I would assume that the extra strength Titanium hardware can provide would be lost over time, leading to a similar failure down the road.
 

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The bolts that failed have "8.8" stamped on the head. I assume I would have to find something class 10.9 in order to have an improvement in strength over the hardware that failed.

You bring up a great point about corrosion. I would assume that the extra strength Titanium hardware can provide would be lost over time, leading to a similar failure down the road.
Or a class 12.9 but I'm kind of surprised an 8.8 broke like that. This is a tensile condition, the 10.9 is about 20% stronger and 12.9 is about 40% stronger than an 8.8.
 

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YOu mean a hot water tank that is full of water with electrolytes 24/7, the literal definition of a battery?
Yup, now put two metals that are far from each other on the potential scale and set them in an area that gets wet but not dried over several hundred cycles and a decade of time. You'll see pitting in the aluminum of the joint. It's not going to be structurally destructive but it will cosmetically effect parts that didn't need to happen. Salt water will accelerate it, of course, but it's not required.
 

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Yup, now put two metals that are far from each other on the potential scale and set them in an area that gets wet but not dried over several hundred cycles and a decade of time. You'll see pitting in the aluminum of the joint. It's not going to be structurally destructive but it will cosmetically effect parts that didn't need to happen. Salt water will accelerate it, of course, but it's not required.
Galvanic corrosion is simply not an issue in the vehicles we drive in the way we drive them. Yes water is necessary.
All of the examples used when anyone brings up galvanic corrosion involve long term total immersion in water, or deliberate misuse[IE run straight water in an engine with an aluminum head and cast iron block]

Good old fashioned corrosion is the enemy.
 

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Discussion Starter · #12 ·
Some of my research suggests that Titanium is actually more corrosion-resistant than steel for our typical use case. Source. Is this the case, or am I missing something? Thanks for all the input so far, looking forward to further discussion!
 

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Some of my research suggests that Titanium is actually more corrosion-resistant than steel for our typical use case. Source. Is this the case, or am I missing something? Thanks for all the input so far, looking forward to further discussion!
Titanium itself is very corrosion resistant, yes. It's coupling with aluminum is what exposes the aluminum to galvanic corrosion. It's just not worth the price of Titanium in this application.
 

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Hello all!
Being that it’s winter, I’ve had the free time to come up with a very specific question that’s probably more trouble than it’s worth. At the very least I might learn something in the process.

I am working on a non-functioning door hinge restraint, and found the culprit to be the two bolts (that hold the restraint assembly to the hinge) had snapped in half. I’ve been referring to these two threads for reference "Door Doesn't Stay Open" & "Problem: Door not staying open" but didn’t want to bump discussions that are over 7 & 12 years old, respectively.

Finally, on to my question: Has everyone replaced these bolts with new bolts of the same material? Or is there an improvement that can be made to prevent this issue from occurring again? I’ve played with the idea of Titanium bolts, which would carry the additional benefit of cutting weight. I just don’t have the mechanical background to figure out if a harder material will end up being more likely to snap in half.

Maybe the attached picture of the failure can be enough for someone more mechanically minded to bring up some ideas? I’d love to hear @[U]shinoo[/U] share some thoughts if possible. That's all the details I can think to share. I'd like to thank everyone in advance for any information that can be shared. This forum has been an incredibly welcoming and helpful place so far!
Cheers everyone!
I don’t understand why those bolts would ever break.I’m going to guess the wind or someone opened the with a lot of force. The door has a lot of leverage over this stop mechanism.Don’t waste your time with Titanium it’s only a little stronger than grade 8.8 Use a grade 10.9 use a little lock tight and don’t tighten the crap out of it.When you tighten a bolt you use up some of it’s tensile strength.A 6mm bolt isn’t very strong so go easy.
All this talk of corrosion and Titanium and is silly.
Those who can afford it know you always use anti seize which negates these effects.It’s also used on stainless hardware. The big issue is galling and seizing when you go to take it apart. I have never had any corrosion issues and I have been using Titanium for longer than most of you have been alive.Then again I try not to put my cars in the ocean so maybe that’s why I haven’t had problems.
 
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All this talk of corrosion and Titanium and is silly.
Those who can afford it know you always use anti seize which negates these effects.It’s also used on stainless hardware. The big issue is galling and seizing when you go to take it apart. I have never had any corrosion issues and I have been using Titanium for longer than most of you have been alive.Then again I try not to put my cars in the ocean so maybe that’s why I haven’t had problems.
25 years of mechanical engineering, designing systems for high humidity and real world contamination environments. What I do isn't "silly"
 

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If the assembled bolt is not torqued/tensioned (stretch) sufficiently (usually about 20%) above the expected cyclic loads, it will fail from fatigue. If you install a bolt with a higher tensile/yield rating, you must torque/tension higher to its required stretch, otherwise it will fail prematurely from fatigue. If the material between the bolt and nut is soft, the cyclic loads may allow the bolt tension to be lost and the bolt will fail from cyclic fatigue.

Link to example chart below. Note there are torque values for both dry and wet threads. If wet values are used, the underside of the head and the nut must be lubricated as well.

 

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25 years of mechanical engineering, designing systems for high humidity and real world contamination environments. What I do isn't "silly"
No what you do is not silly, but in nearly 40 years of working on building restoring driving Lotus cars in the rain[and in some cases year round in snow and salt] I have never seen an example of galvanic corrosion.
And I have made a habit of replacing virtually all small hardware with stainless. 39 years ago I replaced most of the small screws in the tailights and marker lights [you know the pot metal ones] in my +2 with stainless and there is no corrosion.
There are things that are possible, but they remain unlikely.
 

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If the assembled bolt is not torqued/tensioned (stretch) sufficiently (usually about 20%) above the expected cyclic loads, it will fail from fatigue. If you install a bolt with a higher tensile/yield rating, you must torque/tension higher to its required stretch, otherwise it will fail prematurely from fatigue. If the material between the bolt and nut is soft, the cyclic loads may allow the bolt tension to be lost and the bolt will fail from cyclic fatigue.

Link to example chart below. Note there are torque values for both dry and wet threads. If wet values are used, the underside of the head and the nut must be lubricated as well.

You guys with your big fancy edemecations drive me crazy sometimes. I didn’t set out to piss anyone off but sometimes you guys way overthink things.
I think it’s helpful to post those charts so thank you for that.So now the OP knows a 6mm bolt only needs about 7 ft# Not very much so he should go easy.There is no way to get a torque wrench in there so he just needs to go easy.
As to bolt stretch and cyclical loads neither applies in this case.The length of bolt under tension is not sufficient for bolt stretch to be a factor here.You know about length to diameter ratios and there relationship to stretch.There are no cyclical loads here relative to the amount that could cause a failure.You know how many cycles are involved in fatigue testing.This is a car door that only loads the bolt when fully opened and gets pushed hard against the stop. I don’t think he will do this a 100,000 times or more.
This is just a car door let’s not get carried away and confuse the op.
 

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25 years of mechanical engineering, designing systems for high humidity and real world contamination environments. What I do isn't "silly"
Yes talking about corrosion in this case is silly.
There isn’t enough moisture here for it to be a factor.
If you were so concerned about moisture why didn’t you tell the op about different the different coatings
available?Titanium is available with special coatings for applications where it’s not desirable to use anti seize.It’s right on Pro Bolts website.
I don’t think you guys with your big fancy education’s respect my educational background so my feelings get hurt.The school of hard knocks is not as easy to grageate from as you may think.
 

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In my mind, I’d replace with the same grad and material type as factory.
I’d hate to transfer the failure to somewhere else that costs more to fix later. A bolt is cheap insurance to prevent needing a new hinge or door/a panel/clam repair.
That bolt is meant to break at a given load.
 
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