Are higher grade bolts more brittle?

Howdy,

I recently purchased some (metric) bolts to attach a receiver hitch to my Jeep. While the factory doesn't specify the grade, the nuts they go into have a six (or possibly a 60) on them.

I didn't purchase the bolts from the stealership, because they want $11.00 (eleven dollars) *per* bolt, so I bought them from Fastenal instead.

When I bought the bolts, I got them in a grade 10.9 (metric).

Earlier today, I came across a discussion on a Jeep forum where someone alluded to their belief that higher grade bolts would be too "brittle" for this application.

Personally, I think I'm going to be just fine, but I know someone here will have something more substantial than my gut feeling.

So, do you think I should order some different bolts, or will I likely be just fine with the ones I already have?.

Thanks,

Jon

Reply to
Jon Danniken
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Grade 10.9

Ultimate Tensile Strength 10MPa Carbon Content 0.9%

This is a very strong bolt. If your application calls for a high tensile bolt then this is a good choice. You could go for a Grade 12, but this might be overkill. If the nuts are old, you should think about getting new ones.

HTH Dom.

Reply to
Dom

Of course, the bolts aren't supposed to be taking the shear load, but that's in a perfect world.

Dave

Reply to
spamTHISbrp

The 1st figure is 1/10 the tensile strength and 2nd figure is 1/10 the ratio between the minimum tensile strength and the minimum yield stress (or proof stress in the higher strength fasteners as this is), also IIRC the units are in kgf/mm2. So the yield stress is 90 kgf/mm2 and the tensile strength is 100kgf/mm2. Not sure what the US equivalent is but a standard socket cap in the UK is a 12.9, button head is 10.9. IIRC the socket cap screw in the US have equivalent characteristics to 12.9, and I think you have an equivalanet to 10.9 also.

Reply to
David Billington

Higher carbon steels that are hardened as much as they'll take are much more likely to break, rather than bend.

El cheapo "high strength" bolts that are _improperly_ hardened are much more likely to break than good ones that are tempered properly.

If a bend is a bad thing and a break is a disaster, a lower grade bolt may be indicated, or just sucking it up and buying from the dealership.

I'd try to find out the grade of bolt called out by Jeep, and buy that, from a reputable source.

Reply to
Tim Wescott

The usual argument among the off road groups is that the lower grade (US grade 5) bolts bend rather than break like the higher grade (US grade 8) bolts. That's true but the grade 8 bolts take more stress than the grade

5 bolts do before they break. The off roaders like the bolts that bend, it gives them a visual cue that they are about to do destructive things to their rigs. But that means that the bolts that hold (and bend) are the lower level items. And the argument goes on.

J> Howdy,

Reply to
RoyJ

I agree! My nuts are getting old and I'm thinking about getting new ones...

Reply to
Tom Gardner

I'd worry about other stuff in life. The important thing is that the clamping surfaces are parallel.

Wes

Reply to
Wes

That's grade 6. Standard is grade 8. The mating strength for a bolt would be grade 8.8. Grade 10.9 is just a waste of money. Sure, they are more brittle (they can't be *stretched* as much before they fail) but there is no construction that requires a *plastic* stretch.

So it is OK.

Nick

Reply to
Nick Mueller

Grade 10.9 means: tensile strength is 100 kp / mm^2 (there is no such thing as kgf) Multiplying the first number with the second (10 * 9 = 900) gives the yield strength times 10 (so 90 kp / mm ^2).

A 8.8 has 80 kp/mm^2 tensile and 64 kp/mm^2 yield strength. The numbers aren't very precise. That was the initial definition. Of course, the units now are in N and mm, or in Pa.

Nick

Reply to
Nick Mueller

I ran across kgf not being an official unit the other day but still widely used in some places. The tensile and compressive test stand software I work on sometimes supports kgf, gf, as well as N, kN, MPa, kPa, N/mm^2, lbf and a few others. The N/mm^2 was added recently to suit customer demand, although it is equivalent to kPa, some customers knew that but still asked for N/mm^2 as that was what they were used to. Likewise some parts of the world still use kgf.

What is the status of daN. I have run across it a few times before and finally looks it up, as I didn't know what it was, decanewton 1daN =

10N. Now the data sheets make sense.
Reply to
David Billington

This brings to mind a question I have had for a long time. Our local supply store (USA) carries Grade 8 (gold), Grade 5 (gray), and the common (standard-silver) bolts. My question is what grade are the common bolts? Or dont they grade them?

What is the difference in strength between Grade 8, Grade 5 and common bolts? Is there a website or file I can download with all the facts? (Please use american definations, (such as POUNDS) not metric. I dont understand metrics..... To me, killagram sounds like murder and is far too violent for my tastes.)

Reply to
3phase

That is legal. da (deca) is the multiplier (10) and N the unit (Newton). But at least here in Germany daN is very rare. Anyhow, the reason why it might be used is that the number is almost (0.981) the same as kp (no more legal, non-SI). The reason why people stick to N/mm^2 is, that the numbers are more handy compared to the Pa (N/m^2). Also, math in mechanical engineering often enough is done in mm and not in m, as dimensions are in mm. Anyhow, all can well be scaled and there is no conversion with weird factors. Just a thing of convenience, just depends on how you prefer to calculate.

Nick

Reply to
Nick Mueller

How about the right spelling? It is "kilogram"! Kilo means thousand and stems from khilioi in Greek, gram or gramme is from the Greek/Latin word gramma Or is that too much culture for your taste?

Nick

Reply to
Nick Mueller

On Tue, 15 Jan 2008 05:26:45 GMT, with neither quill nor qualm, "Tom Gardner" quickly quoth:

Um...what's a lesbian doing with nuts, pray tell?

----- = Dain Bramaged...but having lots of fun! =

Reply to
Larry Jaques

I was aware of the prefixes such as deca, deci etc but had not run across the abbreviation such as in daN. The only place I can recall seeing it in the UK was on the RS site

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when looking for vibration isolation mounts. I annoyed me enough the other day that I looked up what it was so the data sheet made sense, now I might consider using some if needed. Having done physics in high school in the US (all SI metric) and an engineering degree in the UK, I could not recall ever seeing daN before, always N, kg, mm, m etc. In the same way I had only recently run across kgf used so had to check what it was, always seen kg before. At least I have never had the pleasure of foot, poundals, and slugs, as one of the guys on my engineering course did. He got a year placement working at a US aerospace company that used foot, poundals, and slugs. He, having been educated entirely in the UK, had never heard of them before as they had gone out of use in the UK.

Reply to
David Billington

I google'd "grade 8 bolts brittle", and found this article that seems pretty informative. The author is a Senior Staff Mechanical Engineer for Lockheed Martin (DAMHIKT)

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Go with the grade 8.

Carl Boyd

Reply to
Carl

I think it is an invention of the US. A desperate abuse to adopt the logical SI units to the US-awkwardness like poundforce and such. ;-)

Nick

Reply to
Nick Mueller

Evidently absolutely no sense of humor. :-) ...lew...

Reply to
Lew Hartswick

I expect a killergram is when the western union hitman shows up at your door.

Reply to
David Billington

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