Bolt question for an engineer.

[Gribble]

What is the shear strength of an 8.8 grade m12 bolt?

[Gribble]

Is it 5.7t? or close?

[dumbdunce]

ISO metric fastener material strength property classes (grades) is specified in ISO Standard 898-1. The 8 in 8.8 means nominal (minimum) tensile ultimate strength is 8 * 100 = 800 MPa (Megapascal); the 8 means the yield strength is 0.8 times tensile ultimate strength or 0.8 * 800 = 640 MPa.

for alloy steels, ultimate shear stress is approx .75 times the ultimate tensile stress and yield shear stress is approx .6 times the tensile yield stress.

so for ultimate shear strength of an 8.8 bolt you have 800MPa * 0.75 = 600MPa (this is the load that will break the bolt)

for yield shear strength of an 8.8 bolt you have 640MPa * .6 = 384MPa (this is the load that will start to deform the bolt.

NOTE you need to DOUBLE these for double shear.

If you know which part of the bolt (thread or shank) is loaded, and the pitch of the thread, you can work out the cross sectional area of the loaded portion, and work out the actual load in Newtons for a given bolt, with the stress = load/area formula.

(can I have a job at EA now?)

[dumbdunce]

Is it 5.7t? or close?

for a nominal 11mm diameter the cross sectional area is:

a=pi*d^2/4
a = 95mm^2

stress = load/area so load (yield) = stress (yield) * area

load (yield) = 384MPa * 95mm^2 (exponents cancel neatly)

load (yield) = 36.5kN

using our old friend force = mass * acceleration and using 9.8m/s/s for acceleration;

force = 36,500/9.8 = 3725kg

note this is for 11mm nominal diamter in single shear. a 12mm bolt has a 12.4mm or greater shank so the yield stress will be higher by proportion of the cross sectional area. note also that this is the yield stress so this load will probably not break the bolt but will start to deform it; as the bolt deforms the cross sectional area decreases so under this load the bolt may wall continue to deform to the point where it fails completely.

[Gribble]

(can I have a job at EA now?)

No, your too smart to work for the Government.

Thanks dude!

[dumbdunce]

(can I have a job at EA now?)

No, your too smart to work for the Government.

Thanks dude!

doh :(((

looks like they're not offering any mechanics's apprenticeships this time around anyway :(

[YankeeDave]

there you go, and i went to uni for 4 years to learn the same thing

[mickyd555]

i cant believ a man that drew that picture on a napkin, can also say all that...........there were some big words in there. awesome stuff dumdunce, what do you do for a living...........

[CJ Burns Esq]

Whilst we have all the right people looking,
Which is stronger fine thread or coarse thread for the opposite of shear eg pull, is that yeild?

[Mytqik]

i cant believ a man that drew that picture on a napkin, can also say all that...........there were some big words in there. awesome stuff dumdunce, what do you do for a living...........

He's an engineer.

He opens car bonnets and says "there's an engine in 'ere"

Mechanic in other words (I think)

[CJ Burns Esq]

Whilst we have all the right people looking,
Which is stronger fine thread or coarse thread for the opposite of shear eg pull, is that yeild?

[Mytqik]

Whilst we have all the right people looking,
Which is stronger fine thread or coarse thread for the opposite of shear eg pull, is that yeild?

Yeild is the point when a material will no longer spring back to its original shape when the load is removed. In other words, the load required to bend it. Normally around 0.7 as Dumbdunce mentioned.

Ultimate is the point where it will fail.

shear is where the load is applied at right angles to the shank of the bolt

tensile/compressive is when the load is applied along the axis

torsional is when the load is applied around the axis (IE twisting)

Because a course thread is deeper than a fine thread, it is marginally weaker than a fine thread.

The main difference between the 2 is their ability to tighten, maintain that load & its resistance to vibration.

[ISUZUROVER]

Here is another thread with good bolt info.

http://www.outerlimits4x4.com/PHP_Modul ... hp?t=44573

[Bush65]

Dumbdance looses marks for incorrect use of terminology, but is good enough for this forum.

Engineers don't work it out like that though - they look in the capacity tables.

Shear capacity depends whether the shear plane is located at the shank or the thread of the bolt.

Also there is an interaction between shear and tension - they have to be reduced if both loads are present. Look at the interaction diagrams for these cases.

Anyway, minumum breaking load for class 8.8 M12 bolt in single shear, taken from the tables is - 57kN for shank and 38kN for thread.

Coarse thread bolts are generally stronger than fine thread bolts when loaded in tension, in fatigue situations - which is the common way that bolts in tension fail.

[DR Frankenstine]

Would someone speak english
he asked how many tonnes is the shear strength

[mickyd555]

Would someone speak english
he asked how many tonnes is the shear strength

i think it translates to "she'll be roight maaate"

[Mytqik]

1kN = 981kgs

[dumbdunce]

Dumbdance looses marks for incorrect use of terminology, but is good enough for this forum.

doh :( where specifically?

Engineers don't work it out like that though - they look in the capacity tables.

agreed - but a good engineer knows how to arrive at a similar conclusion to the table - every table has those scary letters at the bottom: 'E&OE' - so a first principles approximation is always a good idea.

Anyway, minumum breaking load for class 8.8 M12 bolt in single shear, taken from the tables is - 57kN for shank and 38kN for thread.

so at least my maths is good

Coarse thread bolts are generally stronger than fine thread bolts when loaded in tension, in fatigue situations - which is the common way that bolts in tension fail.

interesting. why?

[Gribble]

Dumbdance looses marks for incorrect use of terminology, but is good enough for this forum.

Are you calling us forumites retards?

Oh, and the weight is going to be on the bolts shank, not the threads, so i was right? 5.7t?

To ask another quick one, what is the allowable "tolerance" there?
For instance, a riggers D shackle is rated at 3.5t but in reality doesn't shit itself until 14t (this is for arguments sake, ok?) so it has a saftey factor of 4.

When ISO set this standard out, what factor(s) are set into it? Or does the bolt just need to pass the standard by 1 gram?

[dumbdunce]

i cant believ a man that drew that picture on a napkin, can also say all that...........there were some big words in there. awesome stuff dumdunce, what do you do for a living...........

He's an engineer.

He opens car bonnets and says "there's an engine in 'ere"

Mechanic in other words (I think)

I am basically a bum... I used to work in IT but I hated it so I quit. Now I do dodgy backyard mechanical repairs (anyone got an apprenticeship needs filling?)

[ISUZUROVER]

Dumbdance looses marks for incorrect use of terminology, but is good enough for this forum.

Are you calling us forumites retards?

Oh, and the weight is going to be on the bolts shank, not the threads, so i was right? 5.7t?

To ask another quick one, what is the allowable "tolerance" there?
For instance, a riggers D shackle is rated at 3.5t but in reality doesn't shit itself until 14t (this is for arguments sake, ok?) so it has a saftey factor of 4.

When ISO set this standard out, what factor(s) are set into it? Or does the bolt just need to pass the standard by 1 gram?

If the shank of the bolt is in shear then you were almost right, it is 5.8 tonne.

AFAIK the values given above by Bush65 give the load at which the bold will begin to yield (plastically (permanently) deform). The value you are talking about for the shackle is the SWL - safe working load - which is a long way below the yield point.

[Gribble]

Dumbdance looses marks for incorrect use of terminology, but is good enough for this forum.

Are you calling us forumites retards?

Oh, and the weight is going to be on the bolts shank, not the threads, so i was right? 5.7t?

To ask another quick one, what is the allowable "tolerance" there?
For instance, a riggers D shackle is rated at 3.5t but in reality doesn't shit itself until 14t (this is for arguments sake, ok?) so it has a saftey factor of 4.

When ISO set this standard out, what factor(s) are set into it? Or does the bolt just need to pass the standard by 1 gram?

If the shank of the bolt is in shear then you were almost right, it is 5.8 tonne.

AFAIK the values given above by Bush65 give the load at which the bold will begin to yield (plastically (permanently) deform). The value you are talking about for the shackle is the SWL - safe working load - which is a long way below the yield point.

Yeh yeh, i get that, but not every single brand of bolt manufactured would break at exactly the same force. So that rating would be like a minimum.

The bolt might take twice as much before it deforms, but for saftey they say dont put anymore that 5.8 tonnes on an m12 8.8 bolt, when in their quality testing the bolt might take 7 or more, so it passes that standard easily.

Its irrelavent to my problem anyway, coz 5.7 is way more than i need. Im just curious to know if there is a saftey factor or not.

[dumbdunce]

Dumbdance looses marks for incorrect use of terminology, but is good enough for this forum.

Are you calling us forumites retards?

Oh, and the weight is going to be on the bolts shank, not the threads, so i was right? 5.7t?

To ask another quick one, what is the allowable "tolerance" there?
For instance, a riggers D shackle is rated at 3.5t but in reality doesn't shit itself until 14t (this is for arguments sake, ok?) so it has a saftey factor of 4.

When ISO set this standard out, what factor(s) are set into it? Or does the bolt just need to pass the standard by 1 gram?

If the shank of the bolt is in shear then you were almost right, it is 5.8 tonne.

AFAIK the values given above by Bush65 give the load at which the bold will begin to yield (plastically (permanently) deform). The value you are talking about for the shackle is the SWL - safe working load - which is a long way below the yield point.

Yeh yeh, i get that, but not every single brand of bolt manufactured would break at exactly the same force. So that rating would be like a minimum.

The bolt might take twice as much before it deforms, but for saftey they say dont put anymore that 5.8 tonnes on an m12 8.8 bolt, when in their quality testing the bolt might take 7 or more, so it passes that standard easily.

Its irrelavent to my problem anyway, coz 5.7 is way more than i need. Im just curious to know if there is a saftey factor or not.

the numbers quoted for shear yield stress is nomial (ie minimum) shear yield stress for a bolt to 'make the grade' - and since adding strength adds expense, you find that bolts are pretty damn close in strength to their actual grading. in other words, there is is no safety factor involved in those figures.

it might also be worth investigating how you intend to use the bolt - it might look like it's in shear when it is acutally loaded in bending and/or tension, which obviously changes the allowable stresses in the bolt.

[Bush65]

Dumbdance looses marks for incorrect use of terminology, but is good enough for this forum.

doh :( where specifically?

I hope no offence was taken, That comment wasn't meant to be taken seriously. I have read many of your posts and it is obvious that you know what you are talking about.

You did mess up in the part about shear strength, which you correctly stated in MPa, but then incorrectly said that this was a load. In fact it is stress, but this leads to more confusion for the lay person.

Engineers don't work it out like that though - they look in the capacity tables.

agreed - but a good engineer knows how to arrive at a similar conclusion to the table - every table has those scary letters at the bottom: 'E&OE' - so a first principles approximation is always a good idea.

Actually most design is carried out in complience with codes, which stipulate how these things are calculated.

For example, the various clauses in section 9 of AS4100 (steel structures code) for bolts and bolted connections are more involved than discussed here. But it is much simpler to use the safe load tables from the Australian Institute of Steel Construction, where most of the work has been done for you.

By the way, I did not refer to the safe load tables when I gave the minimum breaking strength for an M12 bolt - M16 is the smallest bolt permitted in a steel structure and minimum breaking strength is not a design capacity.

Anyway, minumum breaking load for class 8.8 M12 bolt in single shear, taken from the tables is - 57kN for shank and 38kN for thread.

so at least my maths is good

Coarse thread bolts are generally stronger than fine thread bolts when loaded in tension, in fatigue situations - which is the common way that bolts in tension fail.

interesting. why?

The thread form for external metric threads has a significant radius in the root. When fatigue is considered, the lower stress raising cooefficient at the root of coarse threads more than offsets the reduction in the cross sectional area. Published results from testing support this.

[V8Patrol]

What is the shear strength of an 8.8 grade m12 bolt?

Has any body answered this yet







Kingy

[ISUZUROVER]

What is the shear strength of an 8.8 grade m12 bolt?

Has any body answered this yet

YES - can't you read ?

minumum breaking load for class 8.8 M12 bolt in single shear, taken from the tables is - 57kN for shank and 38kN for thread.

[Gribble]

What is the shear strength of an 8.8 grade m12 bolt?

Has any body answered this yet







Kingy

Yep, all there.

Now how do I fit 35's under my hilux?

[dumbdunce]

Dumbdance looses marks for incorrect use of terminology, but is good enough for this forum.

doh :( where specifically?

I hope no offence was taken, That comment wasn't meant to be taken seriously. I have read many of your posts and it is obvious that you know what you are talking about.


You did mess up in the part about shear strength, which you correctly stated in MPa, but then incorrectly said that this was a load. In fact it is stress, but this leads to more confusion for the lay person.

no, no offence taken at all - you're absolutely correct on that one. It's the sort of mistake I used to yell at other engineers for - obviously I'm getting slack in my old age

Coarse thread bolts are generally stronger than fine thread bolts when loaded in tension, in fatigue situations - which is the common way that bolts in tension fail.

interesting. why?

The thread form for external metric threads has a significant radius in the root. When fatigue is considered, the lower stress raising cooefficient at the root of coarse threads more than offsets the reduction in the cross sectional area. Published results from testing support this.

that makes sense. I doubt it will ever matter to me, but it gives me a nice warm feeling just knowing