Stainless steel bolt shear strength

[ARCHIVED THREAD] - Stainless steel bolt shear strength

Posted: 6/3/2008 5:12:57 PM EDT

I have will be screwing a 3/16" plate to a block using a 1/4-20 18-8 stainless steel cap screw. The screw isn't hardened ( if thats possible) or special in any way. Anyone have any idea how much weight can that bolt support before it shears off? Thanks zeekh

Posted: 6/3/2008 5:16:49 PM EDT

[#1]

Quoted:
I have will be screwing a 3/16" plate to a block using a 1/4-20 18-8 stainless steel cap screw. The screw isn't hardened ( if thats possible) or special in any way. Anyone have any idea how much weight can that bolt support before it shears off? Thanks zeekh

What application are you using it for?

Posted: 6/3/2008 5:18:07 PM EDT

[#2]

Does it have numbers or markings on the bolt head? You can usually just do a google search and find out what the markings mean for all kinds of bolts.

Posted: 6/3/2008 5:18:08 PM EDT

[#3]

How is weight being applied to the bolt? In a shearing direction across the centerline or a pulling along the centerline of the bolt?

Posted: 6/3/2008 5:25:56 PM EDT

[#4]

Single shear or double? What grade bolt?

A single 1/4x20 bolt ranges from about 160-370 pounds. But that applies to two smooth surfaces of similar material.

IT really depends on a whole bunch of factors.

Posted: 6/3/2008 5:30:07 PM EDT

[#5]

IIRC, all cap screws are grade 8. I don't have my Machinery's Handbook handy so I would suggest google.

Posted: 6/3/2008 5:36:16 PM EDT

[#6]

A grade 8 1/4-20 will support around 5400lbs in shear.

For an 18-8 bolt you need to multiply the shear area by the tensile strength and a constant to relate the shear to tensile strength. For steels this number is .5-.6 for a steady load and .3 for undulating loads.

You then decide your factor of safety and whether or not you want to add a stress riser correction for the root of the thread.

The root dia of a 1/4-20 bolt is .185 and the tensile strength of 18-8/A2 used in a SHCS is around 100ksi.

SO .185*100,000*.5 ~ 9250lbf. Using a factor of safety of 3 yields a shear loading of 3083lbf per fastener.

Posted: 6/3/2008 5:40:38 PM EDT

[#7]

Quoted:
A grade 8 1/4-20 will support around 5400lbs in shear.

For an 18-8 bolt you need to multiply the shear area by the tensile strength and a constant to relate the shear to tensile strength. For steels this number is .5-.6 for a steady load and .3 for undulating loads.

You then decide your factor of safety and whether or not you want to add a stress riser correction for the root of the thread.

The root dia of a 1/4-20 bolt is .185 and the tensile strength of 18-8/A2 used in a SHCS is around 100ksi.

SO .185*100,000*.5 ~ 9250lbf. Using a factor of safety of 3 yields a shear loading of 3083lbf per fastener.

I would recommend the part in red if it's going to have a significant load on it.

Posted: 6/3/2008 5:41:34 PM EDT

[#8]

ETA nope, nm

Posted: 6/3/2008 6:01:44 PM EDT

[#9]

Thanks for the replies. Basically it is a Stainless steel block with a stainless steel plate mounted to the side of it. The bolt in question will hold the plate to the side of the block. The plate will have a load of 50 lbs on it. The shear will be perpendicular to the center line of the bolt. Actuall there is a pltae on each side of the block. Both of the plates ( 3"long x 3/4" wide x 3/16" thick) will be bolted onto the ends of a 1" square piece of Stainless steel that is 4 1/2" long. They will form an upside down "U". The 2 legs of the U will be pinned ( 1/4" Stainless steel pins that are removable ) into a piece for steel to lift it. there will be a small gap betwwen the legs of the "U" and the piece being lifted ...maybe .040"total. It will only be lifted once a week or so. When not in use the "U" braket will not be mounted to the piece if steel being lifted. On paper the bolt looks a little small but it seems I have plenty of room to spare. Thanks zeekh

Posted: 6/3/2008 6:06:00 PM EDT

[#10]

Failure analysis? What will happen if it fails?

Is the only possible loading perpendicular to the axis?

Torque?

Posted: 6/3/2008 6:12:28 PM EDT

[#11]

Quoted:
Failure analysis? What will happen if it fails?

Is the only possible loading perpendicular to the axis?

Torque?

Big problems if it fails. No torque just verticle lift gently by hand.

Posted: 6/3/2008 6:53:57 PM EDT

[#12]

50 pound load? I'd say you don't have anything to worry about.

Posted: 6/3/2008 7:08:01 PM EDT

[#13]

man, I get enough of this stuff at work

what material is the plate so we can do a bearing check. always want fasteners to be bearing critical

Posted: 6/4/2008 3:31:53 AM EDT

[#14]

Quoted:
A grade 8 1/4-20 will support around 5400lbs in shear.

For an 18-8 bolt you need to multiply the shear area by the tensile strength and a constant to relate the shear to tensile strength. For steels this number is .5-.6 for a steady load and .3 for undulating loads.

You then decide your factor of safety and whether or not you want to add a stress riser correction for the root of the thread.

The root dia of a 1/4-20 bolt is .185 and the tensile strength of 18-8/A2 used in a SHCS is around 100ksi.

SO .185*100,000*.5 ~ 9250lbf. Using a factor of safety of 3 yields a shear loading of 3083lbf per fastener.

I'm not familiar with "18-8/A2" SS bolts. According to McMaster-Carr (page 3094), SS 18-8 bolts only have 70ksi tensile strength (which is Grade 2 territory), vs. 150ksi for a standard Grade 8 bolt.

McMaster has 17-4 High Strength SS bolts, at 140kSI TS, a 1/4-20x2" costs about $6 each (page 3096).

McMaster (enter the page # in the search bar)

Good luck.

Merlin

Posted: 6/4/2008 3:44:23 AM EDT

[#15]

Quoted:
A grade 8 1/4-20 will support around 5400lbs in shear.

For an 18-8 bolt you need to multiply the shear area by the tensile strength and a constant to relate the shear to tensile strength. For steels this number is .5-.6 for a steady load and .3 for undulating loads.

You then decide your factor of safety and whether or not you want to add a stress riser correction for the root of the thread.

The root dia of a 1/4-20 bolt is .185 and the tensile strength of 18-8/A2 used in a SHCS is around 100ksi.

SO .185*100,000*.5 ~ 9250lbf. Using a factor of safety of 3 yields a shear loading of 3083lbf per fastener.

I have no idea what the fuck you just said, but it sure sounds cool!

Posted: 6/4/2008 3:49:33 AM EDT

[#16]

Garden variety stainless fasteners are NOT grade 8.

I looked into this once, and I believe they are only grade 5 at best,
unless you specifically buy better bolts.

I think you will find that most are only grade 2.

Posted: 6/4/2008 4:03:55 AM EDT

[#17]

Quoted:
I have will be screwing a 3/16" plate to a block using a 1/4-20 18-8 stainless steel cap screw. The screw isn't hardened ( if thats possible) or special in any way. Anyone have any idea how much weight can that bolt support before it shears off? Thanks zeekh

I can get you a detailed answer later this morning, but the joint strength is also dependent on the depth the screw engages the block.

This is a socket problem, and bending in the screw is not negligible.

Annealed 18-8 steel is extremely low strength and you may want to find another material if you are fabricating the screw yourself.

How much load do you want the joint to carry?
Is the load introduced as a shearing load in the 3/16 inch plate?
Is there any load eccentricity, i.e., out of plane load on the 3/16 inch plate?
Can you send me a sketch of the joint and loading details?

Joint design is one of my principle specialties if you want help.

Never mind, the original description of the problem is insufficient.

Posted: 6/4/2008 4:05:49 AM EDT

[#18]

double tap

Posted: 6/4/2008 4:06:58 AM EDT

[#19]

Never mind, I should have read the date the thread was posted and the rest of the thread.

But here's a piece of information for some of the posters here that might be interested - 18-8 is the generic family of 300 series stainless steels. The A-Basis ultimate tensile strength is about 72 ksi, the yield strength is in the mid 30's.

Also a piece of advice for zeekh;

When designing for overhead hoisting around personell, I recommend you use a factor of safety of 5.0 against ultimate loads, and I also recommend you use a load factor of 2.0 to 3.0 to account for jerking the load when it's being picked up.

That changes your 50 pound static load to a ultimate design load of 50(2.0)5.0= 500 pounds.

That's not so bad, until fastener bending is superimposed, and with the gaps and clearances in your joint, bending is not negligible. In a hurry, I would put all the gap at one side of the joint and conservatively calculate the fastener bending moment as the product of the shear on that leg of the joint and [plate thickness]/2 + Gap + [block thickness]/4.

I don't have a figure for the allowable bending moment in the bolt handy, but it's not very large, probably in the 200 in-lbf range.

Posted: 6/4/2008 5:20:52 AM EDT

[#20]

It is also good design practice to use a shoulder bolt in a situation like this. Drill and ream the hole ~3 times as deep as the fastener diameter, this will let the larger shoulder portion deal with the bending moment on the bolt. You also have a larger shear area with no stress riser so it is much better with an adulating load.

Or use a shoulder bolt thru with a nut on the backside.

Posted: 6/4/2008 6:35:56 AM EDT

[#21]

Quoted:
Garden variety stainless fasteners are NOT grade 8.

I looked into this once, and I believe they are only grade 5 at best,
unless you specifically buy better bolts.

I think you will find that most are only grade 2.

18-8 fasteners should not be categorized as "Grade 2", "Grade 5", and so on, lumping them with carbond steel fasteners. 18-8 steel is strengthened by work hardening as it does not respond to heat treatment for strengthening.

The stock will either be labeled 1/4 Hard, 1/2 Hard, or some other desination up to Full Hard. Equivalent letters (A, B, C, etc.) may also be used, a step backwards in communication in my opinion.

Posted: 6/4/2008 6:38:16 AM EDT

[#22]

Quoted:
IIRC, all cap screws are grade 8. I don't have my Machinery's Handbook handy so I would suggest google.

Soft stainless is far from grade 8.

Posted: 6/4/2008 6:50:49 AM EDT

[#23]

Quoted:

Quoted:
Garden variety stainless fasteners are NOT grade 8.

I looked into this once, and I believe they are only grade 5 at best,
unless you specifically buy better bolts.

I think you will find that most are only grade 2.

18-8 fasteners should not be categorized as "Grade 2", "Grade 5", and so on, lumping them with carbond steel fasteners. 18-8 steel is strengthened by work hardening as it does not respond to heat treatment for strengthening.

The stock will either be labeled 1/4 Hard, 1/2 Hard, or some other desination up to Full Hard. Equivalent letters (A, B, C, etc.) may also be used, a step backwards in communication in my opinion.

I think that 18-8 which is falls into the specs for 304 stainless is work hardened while being formed, and then annealed down to the desired hardness and strength charteristics.

As a general guidline, for connecting 3/16 plate, I would reccommend you drill and tap for 3/8 fasteners.

At this point I would also like to see a ms paint just for the heck of it.

Posted: 6/4/2008 6:56:12 AM EDT

[#24]

Quoted:
It is also good design practice to use a shoulder bolt in a situation like this. Drill and ream the hole ~3 times as deep as the fastener diameter, this will let the larger shoulder portion deal with the bending moment on the bolt. You also have a larger shear area with no stress riser so it is much better with an adulating load.

Or use a shoulder bolt thru with a nut on the backside.

Agreed with the shoulder bolt. Other pluses include them being hard as fuck, and ground round for nice even stress distribution.

Posted: 6/4/2008 7:26:26 AM EDT

[#25]

Quoted:

Quoted:
Garden variety stainless fasteners are NOT grade 8.

I looked into this once, and I believe they are only grade 5 at best,
unless you specifically buy better bolts.

I think you will find that most are only grade 2.

18-8 fasteners should not be categorized as "Grade 2", "Grade 5", and so on, lumping them with carbond steel fasteners. 18-8 steel is strengthened by work hardening as it does not respond to heat treatment for strengthening.

The stock will either be labeled 1/4 Hard, 1/2 Hard, or some other desination up to Full Hard. Equivalent letters (A, B, C, etc.) may also be used, a step backwards in communication in my opinion.

I think that 18-8 which is falls into the specs for 304 stainless is work hardened while being formed, and then annealed down to the desired hardness and strength charteristics.

As a general guidline, for connecting 3/16 plate, I would reccommend you drill and tap for 3/8 fasteners.

At this point I would also like to see a ms paint just for the heck of it.

Nope. Annealing is just that, there are no intermediate stages, or at least not in use by any reputable maker.

I sure as heck wouldn't trust a "partially" annealed fastener as it's metallurgy would be non-uniform.

Any of the 300 series alloys could be formed into a forged bolt blank, or machined from bar stock. That's not to say all of them would be the best choice for one or the other process, just that it's possible.

Posted: 6/4/2008 7:32:26 AM EDT

[#26]

Quoted:
A grade 8 1/4-20 will support around 5400lbs in shear.

For an 18-8 bolt you need to multiply the shear area by the tensile strength and a constant to relate the shear to tensile strength. For steels this number is .5-.6 for a steady load and .3 for undulating loads.

You then decide your factor of safety and whether or not you want to add a stress riser correction for the root of the thread.

The root dia of a 1/4-20 bolt is .185 and the tensile strength of 18-8/A2 used in a SHCS is around 100ksi.

SO .185*100,000*.5 ~ 9250lbf. Using a factor of safety of 3 yields a shear loading of 3083lbf per fastener.

Hubba hubba......

Props...

Posted: 6/4/2008 12:55:50 PM EDT

[#27]

Some room temp allowables for 300 series steels, for those that care.

Annealed, S basis
All allowables are "L" direction unless shown otherwise
Ftu: 73 ksi
Fty: 26 ksi
Fcy: 23 ksi
Fsu: 50 ksi
E: 29.0 msi
Ec: 28.0 msi
e: 40%, LT direction

1/4 hard, B basis
Ftu: 129 ksi
Fty: 83 ksi
Fcy: 54 ksi
Fsu: 69 ksi
E: 27.0 msi
Ec: 26.0 msi
e: ~25%, LT direction

1/2 hard, B basis
Ftu: 151 ksi
Fty: 110 ksi
Fcy: 69 ksi
Fsu: 82 ksi
E: 26.0 msi
Ec: 26.0 msi
e: ~18%, LT direction, stock thickness > 0.016 in

3/4 hard, B basis
Ftu: 168 ksi
Fty: 135 ksi
Fcy: 88 ksi
Fsu: 95 ksi
E: 26.0 msi
Ec: 26.0 msi
e: ~12%, LT direction, stock thickness > 0.031 in

Full hard, B basis
Ftu: 185 ksi
Fty: 153 ksi
Fcy: 94 ksi
Fsu: 100 ksi
E: 26.0 msi
Ec: 26.0 msi
e: ~9%, LT direction, stock thickness > 0.016 in

Thermal stress relief between 500F and 800F can be used to increase yield strength and modulus of elasticity.

Room temp strength of some variants is reduced if heated to temps above 900F.

and so on.

Posted: 6/4/2008 3:41:14 PM EDT

[#28]

Quoted:

Quoted:
Garden variety stainless fasteners are NOT grade 8.

I looked into this once, and I believe they are only grade 5 at best,
unless you specifically buy better bolts.

I think you will find that most are only grade 2.

18-8 fasteners should not be categorized as "Grade 2", "Grade 5", and so on, lumping them with carbond steel fasteners. 18-8 steel is strengthened by work hardening as it does not respond to heat treatment for strengthening.

The stock will either be labeled 1/4 Hard, 1/2 Hard, or some other desination up to Full Hard. Equivalent letters (A, B, C, etc.) may also be used, a step backwards in communication in my opinion.

I think that 18-8 which is falls into the specs for 304 stainless is work hardened while being formed, and then annealed down to the desired hardness and strength charteristics.

As a general guidline, for connecting 3/16 plate, I would reccommend you drill and tap for 3/8 fasteners.

At this point I would also like to see a ms paint just for the heck of it.

Nope. Annealing is just that, there are no intermediate stages, or at least not in use by any reputable maker.

I sure as heck wouldn't trust a "partially" annealed fastener as it's metallurgy would be non-uniform.

Any of the 300 series alloys could be formed into a forged bolt blank, or machined from bar stock. That's not to say all of them would be the best choice for one or the other process, just that it's possible.

I do like a good fastener discussion.

I found one quick reference to a partial annealing process here:

http://www.specialbolts.net/fastenerterms.htm

Anneal also refers to the heat treatment given 400 series stainless fasteners after their manufacture (also called hardening and tempering) to lower hardness and increase toughness. For example, fasteners of 410 stainless may score over 200,000 psi after manufacture and be too brittle. By annealing at 1000 degrees F., tensile strength would reduce to 125,000-150,000 psi, while annealing the same material to 500 degrees F. would bring tensile to 160,000-190,000 psi.

Of course that is not an 18-8 stainless.

Here is a pretty pic of some hi-tech fastneres to keep everyone entertained.

Posted: 6/4/2008 4:25:42 PM EDT

[#29]

Thanks for all the repiles. Some of them are a bit too technical for my feeble mind

. I decided to use the shoulder bolt and counter bore the threaded side a bit so the shoulder will be at the shear point. As mentioned before, the load is hand lifted with no jerking or sudden take up of slack.

[ARCHIVED THREAD] - Stainless steel bolt shear strength

General » General Discussion

Warning

Confirm Action

About AR15.COM

Stay Connected

Newsletter

Contact Us