Bolts

[Ted in NE-OH]

Does a grade 5 or 8 bolt have increased shear strength over a grade 2 bolt? I know the 3 and 8 bolts have increased tensile strength but did not know about shear strength.

 

[Stephen Newell]

Yes, the higher the number the harder the steel is in the bolt.

 

[Steve@Advance]

Well, yes...

And no.

Under ideal, or acceptable conditions, the higher grade bolt will have more shear strength. The condition I'm referring to is both surfaces machined, and the thread and clearance hole are straight, true, and in tolerance.

But add real world application, like the original bolt has been broken before, one or both surfaces are not machined flat, or the surfaces have been moving on each other and are no longer flat. Or the bolt is used as a safety shear, and the recommended grade bolt has sheared repeatedly and the edges of the hole are rounded out.

In the later case, a harder bolt may be more prone to break instead of shear. Of course there are many more variables, results could vary...

Here is some engineering info. Check out the chart at the end of the page.
Fastner Info

 

[kcm.MN]

There's a nice chart here:
https://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

In far right column, under [b:4516b45c03]Mechanical Properties[/b:4516b45c03], you'll see [i:4516b45c03]Proof Load[/i:4516b45c03], [i:4516b45c03]Yield Strength[/i:4516b45c03] and [i:4516b45c03]Tensile Strength[/i:4516b45c03].

[i:4516b45c03]Proof Load[/i:4516b45c03]: An axial tensile load which the product must withstand without evidence of any permanent set.

[i:4516b45c03]Yield Strength[/i:4516b45c03]: The maximum load at which a material exhibits a specific permanent deformation

[i:4516b45c03]Tensile Strength[/i:4516b45c03]: The maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing.

 

[cwtech]

Take a 1/4" x 3" long grade 2 bolt and clamp 1" of it into a vise. ....Whack the side of the bolt head with a large hammer to apply a shear force.

Take a 1/4" x 3" long grade 8 bolt and clamp 1" of it into a vise. ....Whack the side of the bolt head with a large hammer to apply a shear force.

You will find the grade 2 bolt will bend before it will shear.

You will find the grade 8 bolt will shear before it will bend.

 

[unc]

There is a handy rule-of-thumb to determine shear strength in steel: multiply the Tensile Strength by 0.7
Example- If the Tensile Strength is 140,000 PSI,
140,000 X 0.7= 98,000 PSI
This formula isn't perfect, but it's pretty close. unc

 

[Texasmark1]

......and this is why the Grade 2 is preferred over the 8 in most (my JD 375 round baler excepted) of my experiences with shear bolt specs on equipment. The 2 will take several whacks and be deformed in it's slot doing it's job where you may have replaced the 8 several times.

Other thing I have noticed in settling on 2 vs 8 is that when a 2 does shear, I can find it to punch the remains out of the gearbox input shaft. With the 5 or 8 I had a hard time finding it to punch it out.

 

[sotxbill]

Texas Farm Bureau had an article on hitch pins a couple of months back. Lots of pins break and the heavy produce trailers then run wild and kills someone. They recommended a grade 5 as being the best of all worlds... hardened enough but not too hard to shear faster. The Grade 5 was recommend over all others.... iirc...

 

[dr sportster]

The grade 5 will fail in every test before the grade 8 fails. There is no spec for bolts called brittleness.

 

[Texasmark1]

..............shear strength, because (opinion) the shearing stresses have to be defined.....tensile is easy, you just pull on it till it separates.