Higher Grade Bolts vs. Lower Grade Bolts Benefits

[struclearner]

One of the advantage of using higher grade bolt is to get higher clamping force and higher compression between the joint members giving a higher factor of safety against joint separation.
Does the higher grade bolts with higher torques also helps in vibration loading only, in the absence of other loads (tensile or shear) on the joint as compared to using low grade bolts.
What other potential benefits of using higher grade bolts are, and not using the lower grade bolts.

Thank you very much for your response and valuable comments.

 

[mfgenggear]

Higher tensile and shear strength.
Low alloy steel, tougher and stronger
USA grade 5 and 8

 

[desertfox]

Hi

What is often overlooked when using higher garage bolts is the effect of the higher preload on the jointEd materials Yield strength. Or put another way I regularly see people select higher grade bolts to increase the preload on a joint to such an extent that the jointed material yields meaning the advantage of the higher preload is lost.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[drawoh]

struclearner,

If you are selecting bolts for a structure that can fail catastrophically, you can make things idiot proof by analysing for low strength bolts. Make your design work with low strength bolts. Specify low strength bolts. Sleep nights knowing the assemblers cannot switch your bolts for something weaker.

--
JHG

 

[BrianE22]

If your vibration amplitude is high enough to tend to separate the members then, yes, higher strength allows more preload and would help keep the parts from separating.

 

[hydtools]

May be able to use fewer high grade bolts.

Ted

 

[dvd]

Higher grade more subject to hydrogen embrittlement. Higher grade may only allow one tensioning, depending on specifics - can't be reused.

 

[kingnero]

I link hydrogen embrittlement to welding. There should be no welding allowed on bolts or nuts!
On a similar note, high strength bolts should not be hot dip galvanized, for reasons of LME.

 

[drawoh]

If your vibration amplitude is high enough to tend to separate the members then, yes, higher strength allows more preload and would help keep the parts from separating.

You can increase pre-load by enlarging your crappy bolts. It all depends on your attitude towards your assembly people.

--
JHG

 

[moltenmetal]

High strength materials can embrittle due to corrosion mechanisms, not just from welding. Lower strength steel fasteners are tougher.

 

Toughness is not a criterion for most bolts. Do you mean ductile?

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[hydtools]

I experienced hydrogen embrittlement with a post-heattreatment coating treatment that did not received the required baking following the surface treatment.

Ted

 

[mfgenggear]

I hear this a lot about embrittlement
I done thousands of parts for temper etch,
And plating. The specifications are very clear stress relief prior to and post embrittlement bake required .
And never had an issue
Just make sure to call out the correct specification.
I know from experience if doesn't.
I do it any way, because the cost
Is cheap.

 

[dvd]

One can dip a toe in the embrittlement waters with this article - Fastenal Embrittlement Article

 

[mfgenggear]

Toughness is not a criterion for most bolts. Do you mean ductile?

so what's the point of grade 5 and 8 bolts,
made from low alloy steels, and arp bolts,
High strength lock bolts for aircraft. surely don't want cheap junk stuff
I don't under stand why anyone would want to design with sub par hardware.
the way I see if you design with high grade any thing hardware you have done your job.
it's up manufacturing to follow the engineering requirement and they better have, or go to jail

 

[mfgenggear]

DVD
"One can dip a toe in the embrittlement waters with this article - Fastenal Embrittlement Article"

that's because these bolts are made by the millions, and most likely the lowest bidders, and very poor manufacturing
Every carburized gear has to be temper etch , and has to be post embrittlement bake and there is very close
Q.C. control, never had a problem. fasteners on the other hand if manufacture correctly should not have an issue.

with manufacturing being out sourced to other countries I will not say who, but they lack Q.C controls.
I mean even India is complaining about out sourcing their work. India of all countries.
you get what you pay for.

 

Then there was this in 1988

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[mfgenggear]

Exactly , poor Q.C controls, make sure the requirements are stated right on the drawing and don't leave any loop holes.
per ISO 9001 requirements manufactures have to follow to the letter. or get their certification yanked.
EG that goes for heat treat, plating, coating and NDT an on
there is a loop hole in ISO, calibration , but that can be an other day.

 

[Tmoose]

The attached page is HoloKrome's view on this. US Bucks per ksi holding power. That's one way.

In my experience there are a dozen or so devil-ish design details to be carefully attended to before placing an order for SHCS from McM*st*r C*rr. Or even for a some whopping Grade 2 fasteners.

 

Tmoose,
I looked at the link. Interesting analysis, but I struggle to get my head around the equivalence of

"(15) 3/8 diameter Grade 2 hex heads or (4) 3/8 diameter socket screws."

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."