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Strength of M10 bolt ?


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#1 zim

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Posted 30 August 2011 - 08:44 PM

Evening,

Could someone roughly tell me (if it's possible), the strength of a 12.9 caphead 10mm bolt. I'm assuming it's measured in newtons ?

I am talking about if two plates are bolted together and you're trying to shift them sideways.

Am i correct in assuming, that if you have 2 bolts then the "strenght" is doubled ?

Is it as simple as that or not ?

Cheers

Gordon

#2 crclifford

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Posted 30 August 2011 - 09:06 PM

Evening,

Could someone roughly tell me (if it's possible), the strength of a 12.9 caphead 10mm bolt. I'm assuming it's measured in newtons ?

I am talking about if two plates are bolted together and you're trying to shift them sideways.

Am i correct in assuming, that if you have 2 bolts then the "strenght" is doubled ?

Is it as simple as that or not ?

Cheers

Gordon


Being a Civil Engineer i should know this of the top of my head..but i don't! However what i do know is that the first number is the Min Ultimate Tensile Strength and the second number is the Proof Load

Tensile Strength: The maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing.

Proof Load: An axial tensile load which the product must withstand without evidence of any permanent set.

1MPa = 1N/mm2

Therefore for a 12.9 the Tensile Ultimate Strength, is 1200MPa = 1.2kN/mm2 and the Proof Load is 970MPa = .97kN/mm2

HTH

P.S. Must get the books out again and reread on these stuff!!!
Chris
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#3 RedLineMike

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Posted 30 August 2011 - 09:25 PM

as a slight spin off from this, how much stronger is a M10 12.9 cap screw in comparison to an M8 12.9 cap screw?
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#4 Dave W

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Posted 30 August 2011 - 09:47 PM

In the case of 2 plates mounted in the manner described the bolt strength will probably exceed the bearing strength of the plate. How thick are the plates ?

Two bolts will double the strength though in either case.

A 10mm bolt shank through 3mm plate will take around 0.5 tons bearing force without distorting/tearing the plate whereas 6mm plate will take 1.03 tons. An 8.8 M10 bolt in shear will take over 3 tonnes in shear so the tensile strength of the bolt is less of a consideration than the bearing capability of the plates. An M12 shank will increase the bearing force to 0.62 and 1.64 tons for the same plates.

#5 zim

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Posted 30 August 2011 - 10:07 PM

Cheers for the replies.

For the example can we say the bolt is into the thread 12mm and the plate it's holding is also 12mm.

I've been searching google for calculations and i can see that it's
τ=F/A

Where τ = shear stress

F = Force applied in shear to the bolt

A = Area of the bolt

Most links say that shear force is .62 of the tensile force.

But what area ? in the 10mm bolt example, is it 8.5mm to use as the diameter?

G

#6 inaine

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Posted 30 August 2011 - 10:14 PM

Cheers for the replies.

For the example can we say the bolt is into the thread 12mm and the plate it's holding is also 12mm.

I've been searching google for calculations and i can see that it's
τ=F/A

Where τ = shear stress

F = Force applied in shear to the bolt

A = Area of the bolt

Most links say that shear force is .62 of the tensile force.

But what area ? in the 10mm bolt example, is it 8.5mm to use as the diameter?

G

yes

#7 Dave W

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Posted 30 August 2011 - 10:21 PM

For an M12 bolt on the thread I'd use 10mm as the bearing area to be safe.

Allowable bearing force on 12mm mild steel plate with a bolt diameter of 10mm would be 2.06 tons according to the table I have, 12mm shank/pin would be 2.47 tons. The shear strength of the bolt will far exceed the bearing capability as even an 8.8 rated M12 bolt would have a shear strength of 4323 kg.

The table I'm using has a safety factor of 5 which is the lifting industry standard rather than 3 which some non critical applications use.

#8 Team Idris

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Posted 31 August 2011 - 06:05 PM

Yeh, this thread isn't confusing enough yet :P

Because the bolt isn't actually taking the shear force. Its the friction between the two plates that keeps them static. If the shear force is only in one direction, then the plate could move until it contacts the side of the bolt, in which case it become simple shear. (According to mechanics lecturer). But if the load changes direction, it has to be a friction reliant joint.
i.e. we noticed lorry front wheels always finished up with the stud against the same part of the hole in the wheel, as the wheel creapt accross the face of the hub with braking.

I have absolutely no idea what the friction is between two sheets of steel :( What about dowling it?

But I reconed it was worth mentioning that things arn't as simple as they first appear :D

And I nearly forgot to mention, if it is shear rather than tensile on the 'bolt', it's better if the shank is a good fit in it's hole. Then you're back up to the full 12mm diameter.

#9 bishbosh

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Posted 31 August 2011 - 09:17 PM

Search for threads by me on bolts - there is an attachment from the steel designer's manual giving all the answers you need. I have also done worked examples several times and cannot be bothered to do another one. :rolleyes:

The one thing I will say is strength is not everything - connection design is extremely important and that includes selection of appropriate fasteners.

Be careful with "2 bolts are twice as strong as 1" too - depends a lot on how the load is applied to the assembly.

If you want advice on a specific detail then drop me a pm and I'll take a look.

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