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

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.

Dom wrote:
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.

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.

David Billington wrote:

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.

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
--
The lowcost-DRO:
http://www.yadro.de

Nick Mueller wrote:
David Billington wrote:


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.


Grade 10.9 means:
tensile strength is 100 kp / mm^2 (there is no such thing as kgf)

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.

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

David Billington wrote:

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.

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
--
The lowcost-DRO:
http://www.yadro.de

"Dom" wrote in message
...
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.

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

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


"Dom" wrote in message
...
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.

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

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

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

On Tue, 15 Jan 2008 04:17:25 -0800, Larry Jaques
wrote:

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


"Dom" wrote in message
...
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.

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

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

Got em hanging from the mirror of her Volvo.

Gunner


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

On Tue, 15 Jan 2008 07:48:04 -0800, with neither quill nor qualm,
Gunner quickly quoth:

On Tue, 15 Jan 2008 04:17:25 -0800, Larry Jaques
wrote:

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


"Dom" wrote in message
...
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.

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

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

Got em hanging from the mirror of her Volvo.

Fuzzy, round not-dice? Got it.

---
Chaos, panic, and disorder--my work here is done.

On Tue, 15 Jan 2008 07:48:04 -0800, Gunner penned the following well
considered thoughts to the readers of rec.crafts.metalworking:


Got em hanging from the mirror of her Volvo.

Hmmmm...... wonder if that will be made illegal, too?
http://www.ananova.com/news/story/sm_2684454.html
--

Homepage
http://pamandgene.idleplay.net/MachineShop/index.htm
-----------------
www.Newsgroup-Binaries.com - *Completion*Retention*Speed*
Access your favorite newsgroups from home or on the road
-----------------

On Jan 14, 5:54 pm, "Jon Danniken"
wrote:
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


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


Dave

On Mon, 14 Jan 2008 14:54:01 -0800, Jon Danniken wrote:

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

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.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

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.



Jon Danniken wrote:
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

On Mon, 14 Jan 2008 21:55:07 -0600, RoyJ
wrote:

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.


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.)

wrote:

To me, killagram sounds like murder and is far
too violent for my tastes.

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
--
The lowcost-DRO:
http://www.yadro.de

Nick Mueller wrote:
wrote:


To me, killagram sounds like murder and is far
too violent for my tastes.


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

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

Lew Hartswick wrote:
Nick Mueller wrote:
wrote:


To me, killagram sounds like murder and is far
too violent for my tastes.


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

Evidently absolutely no sense of humor. :-)
...lew...
I expect a killergram is when the western union hitman shows up at your
door.

Lew Hartswick wrote:

Or is that too much culture for your taste?

Evidently absolutely no sense of humor. :-)

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


Nick
--
The lowcost-DRO:
http://www.yadro.de

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?

Unmarked bolts are usually grade 3, or worse.

"Stupendous Man" wrote:
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?

Unmarked bolts are usually grade 3, or worse.

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

On 2008-01-15, Jon Danniken wrote:
"Stupendous Man" wrote:
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?

Unmarked bolts are usually grade 3, or worse.

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.

i

On Tue, 15 Jan 2008 07:10:14 -0800, "Jon Danniken"
wrote:

"Stupendous Man" wrote:
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?

Unmarked bolts are usually grade 3, or worse.

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'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.

Stupendous Man wrote:
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?


Unmarked bolts are usually grade 3, or worse.


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

wrote in message
...


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?



No markings on the head are typically grade 2, crapy bolts, not good for
much!
http://www.americanfastener.com/tech...ings_steel.asp
Greg

"RoyJ" wrote:
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.

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

Jon

"Jon Danniken" wrote:

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).


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

Wes

Jon Danniken wrote:

While the factory doesn't specify the grade, the nuts they go into
have a six (or possibly a 60) on them.

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
--
The lowcost-DRO:
http://www.yadro.de

"Nick Mueller" wrote in message
...
Jon Danniken wrote:

While the factory doesn't specify the grade, the nuts they go into
have a six (or possibly a 60) on them.

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.

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

Jon

Nick Mueller wrote:

Jon Danniken wrote:


While the factory doesn't specify the grade, the nuts they go into
have a six (or possibly a 60) on them.


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


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

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


Richard

cavelamb himself wrote:

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

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

With screws!?


Nick
--
The lowcost-DRO:
http://www.yadro.de

Nick Mueller wrote:
cavelamb himself wrote:


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

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


With screws!?


Nick

Looks like he was talking about bolts - not screws.

???


Richard

cavelamb himself wrote:

Looks like he was talking about bolts - not screws.

Richard
Here we go again; Bolt vs Screw
I interpert as follows:
Bolt requires a nut
Screw goes into a threaded hole on something

Unless youre talking to a woodworker. :-)
...lew...

cavelamb himself wrote:
Nick Mueller wrote:

Jon Danniken wrote:


While the factory doesn't specify the grade, the nuts they go into
have a six (or possibly a 60) on them.



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



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

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

I'm guessing the difference between your opinions is the difference
between intentional plastic deformation as part of the design and
plastic deformation in an emergency.

Best wishes,

Chris

On Jan 14, 5:54 pm, "Jon Danniken"
wrote:
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


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)

http://www.rockcrawler.com/techrepor...ners/index.asp

Go with the grade 8.

Carl Boyd

"Carl" wrote:
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)

http://www.rockcrawler.com/techrepor...ners/index.asp

Go with the grade 8.

Great article, thanks Carl!

Jon

Jon Danniken wrote:
"Carl" wrote:

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)

http://www.rockcrawler.com/techrepor...ners/index.asp

Go with the grade 8.


Great article, thanks Carl!

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

Christopher Tidy wrote:
Jon Danniken wrote:
"Carl" wrote:

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)

http://www.rockcrawler.com/techrepor...ners/index.asp

Go with the grade 8.


Great article, thanks Carl!

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.

David Billington wrote:
Christopher Tidy wrote:

Jon Danniken wrote:

"Carl" wrote:

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)

http://www.rockcrawler.com/techrepor...ners/index.asp

Go with the grade 8.



Great article, thanks Carl!


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

A good article that EXPLAINS things well.



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)

http://www.rockcrawler.com/techrepor...ners/index.asp

Go with the grade 8.

Carl Boyd