Are higher grade bolts more brittle?

Oh, I forgot to put a ;-) behind my last sentence. ;-)

Nick

Thanks, Roy, that puts it into a good perspective.

Jon

Thanks, Nick, I was a bit confused on the nomenclature of the metric fastners. Much appreciated!

Jon

Great article, thanks Carl!

Jon

I made the mistake of buying a bunch of the 1/4" bolts out of the bulk bin at Home Despot a few years ago. They came apart tightening them with a 1/4" ratchet drive, and looked like pot metal on the inside.

I don't look to HD for fastners anymore.

Jon

I buy bolts at McMaster, they are slightly cheaper than Home Depot and I never had quality problems with them.

Got em hanging from the mirror of her Volvo.

Gunner

"Candygram for Mr. Mongo...Candygram for Mr. Mongo...."

Gunner

Gunner wrote in news: snipped-for-privacy@4ax.com:

I just hope he got credit for that.....

Bill

I'm a farmer and my tractor loader was always breaking bolts. THey are constatly lifting one ton hay bales, pushing heavy snow and dirt, and all sorts of hard work. Last summer I got fed up with breaking down in the middle of jobs, often out in the field. I removed every bolt from the loader and one by one replaced them with grade 8 bolts and nuts. I wanted to put locking insert nuts on bolts that tend to loosen, but could not find them in grade 8, so I used common grade 8 nuts, and put the standard locking nuts on top. I have not had one single breakdown since. It may have cost twice as much as regular bolts, but it sure beats the hassles I was having and likely paid for itself the first time I used the loader because I didn't damage anything. For example I was lifting a large hay bale onto my pickup a couple years ago, when the bucket snapped a few bolts and the bale fell and busted off my tailgate. I dont even bother to buy regular bolts anymore for machinery. I only use them for decorative steel items and bolting stuff to wood.

My only concern about the grade 8 bolts are how hard they will be to grind off if I ever have to remove one that rusted. I have never done it, but it's easy to use a grinder on a common bolt, but wonder how well those grade 8s grind off???? I dont have a cutting torch.

Grade-8s are hard... but grinding wheels are a *lot* harder. You won't have much trouble. Obviously not as easy as grinding mild steel, but easy enough. Don't worry about it.

I disagree with the "no construction that requires a *plastic* stretch" part.

That's a common requirement in almost all aircraft construction.

Richard

With screws!?

Nick

Yes. In general, as you increase the yield stress of steel by alloying there is a reduction in its ductility. This causes a reduction in the fracture toughness (the amount of energy required to turn a small crack into a large one), which manifests itself as increased brittleness.

However, it's much harder to say how much the brittleness will increase. It may or may not be significant in your case.

You could try bending one of the bolts if they are of a fairly small diameter. If you can make a large bend in the bolt before it breaks the brittleness probably isn't going to matter.

Best wishes,

Chris

That article is quite right that brittleness is relative, and that materials are only usually thought of as brittle when they fracture before reaching their elastic limit. Even the most brittle steel isn't as brittle as glass.

Best wishes,

Chris

Then I seem to remember that for glass the brittleness only comes into effect when the thickness of the piece exceeds the critical crack length of the material, hence the reason that glass fibre exhibits the properties it does, its diameter is less than the critical crack length.

Not sure about this. Won't the critical crack length depend on the stress the material is under?

The fibres in glass fibre are very flexible because they're very thin, but I've never actually tried to break a single fibre. I'll have to try it sometime.

Also, when a crack begins to grow in a composite made of glass fibre and resin, it will turn and travel sideways along the boundary between the resin and the fibre. This increases the fracture toughness.

Best wishes,

Chris

I'd guess they flunked Kindergarden. (for Nick: "Thats a joke son") ...lew...

Looks like he was talking about bolts - not screws.

???

Richard