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

Christopher Tidy wrote:

If you can make a large bend in the bolt before it breaks the
brittleness probably isn't going to matter.

It's a requirement that you can hammer the bolt's head onto a surface tilted
15 (IIRC) degrees (bolt sticking in a hole) without fracture. They really
aren't brittle. Just more brittle than the soft iron grades with 6 or even
worse 4.


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

Nick Mueller wrote:
Christopher Tidy wrote:


If you can make a large bend in the bolt before it breaks the
brittleness probably isn't going to matter.


It's a requirement that you can hammer the bolt's head onto a surface tilted
15 (IIRC) degrees (bolt sticking in a hole) without fracture. They really
aren't brittle. Just more brittle than the soft iron grades with 6 or even
worse 4.

I haven't heard of that requirement, but it sounds sensible.
Nevertheless, I've seen wedge-shaped washers (5 degrees I think) which
are placed under bolts passing through the flanges of universal beams in
structural steelwork. Presumably to make a neater job of the work, and
perhaps because the bolts are too big to hammer.

Best wishes,

Chris

On 2008-01-15, Howard Eisenhauer wrote:
On Tue, 15 Jan 2008 12:37:12 -0600, wrote:

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.


I've cut, drilled & tapped grade 8s plenty of times, honestly I
haven't really noticed a differerence from anything else.

I drilled some and also did not see much difference. I would suppose
that using bolt cutters would be more difficult.

i

Christopher Tidy wrote:

Presumably to make a neater job of the work, and
perhaps because the bolts are too big to hammer.

Yes + LOL!

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

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

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.

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

On Tue, 15 Jan 2008 22:30:28 +0000, Christopher Tidy
wrote:

Jon Danniken wrote:

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?

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
As long as the bolts are properly torqued and everything fits snuggly
it will be no problem as they will be almost totally in tension. If
loose or ill-fitting parts, the bolt can be in shear, and they are
more likely to fail than a grade 5 or 8.8

Most trailer hitch attachment bolts are grade 5 (and a lot are either
grade 2 or ungraded

--
Posted via a free Usenet account from http://www.teranews.com

"Ignoramus25819" wrote:..

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


Thanks, Iggy, I'll keep that in mind the next time I put in an order.

Jon

On 2008-01-16, Jon Danniken wrote:
"Ignoramus25819" wrote:..

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


Thanks, Iggy, I'll keep that in mind the next time I put in an order.


They are about 20 miles away from me and I always get their stuff the
next day. I am usually pleasantly surprised by their stuff

i

You guys may find this interesting.

A number of years ago a friend of mine was the Service Manager for a large
Caterpillar dealer. They began having fracture problems with grade 8 bolts
(or maybe grade 8 studs) on the diesel engine oil pans. They replaced
numerous oil pan bolts and they still kept breaking.

Ken (my buddy) while not being trained as an engineer was a pretty sharp guy.
He noted that the shop had begun to use automotive silicon in place of the
composite oil pan gasket. He thought that the silicon was allowing the oil
pan to "float" slightly causing a high frequency vibration that was inducing
stress fractures in the grade 8 bolts. He ordered the shop to resume using
the original gaskets and the problem never recurred!

His theory made sense to me. What do you think?

--
Message posted via CraftKB.com
http://www.craftkb.com/Uwe/Forums.as...rking/200801/1

Ignoramus25819 writes:

On 2008-01-16, Jon Danniken wrote:
"Ignoramus25819" wrote:..

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

Thanks, Iggy, I'll keep that in mind the next time I put in an order.

They are about 20 miles away from me and I always get their stuff the
next day. I am usually pleasantly surprised by their stuff

Lucky you! For me, they're well worth the expense, but shipping tends
to cost as much as the product -- or more...

On Wed, 16 Jan 2008 04:36:18 GMT, with neither quill nor qualm,
"toolman946 via CraftKB.com" u40139@uwe quickly quoth:

You guys may find this interesting.

A number of years ago a friend of mine was the Service Manager for a large
Caterpillar dealer. They began having fracture problems with grade 8 bolts
(or maybe grade 8 studs) on the diesel engine oil pans. They replaced
numerous oil pan bolts and they still kept breaking.

Ken (my buddy) while not being trained as an engineer was a pretty sharp guy.
He noted that the shop had begun to use automotive silicon in place of the
composite oil pan gasket. He thought that the silicon was allowing the oil
pan to "float" slightly causing a high frequency vibration that was inducing
stress fractures in the grade 8 bolts. He ordered the shop to resume using
the original gaskets and the problem never recurred!

His theory made sense to me. What do you think?

I think his other instruction (to torque the bolts instead of just
using the 1/2" impact driver until stalled) was the key. But that's
just me.

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

clare wrote:

snip

As long as the bolts are properly torqued and everything fits snuggly
it will be no problem as they will be almost totally in tension. If
loose or ill-fitting parts, the bolt can be in shear, and they are
more likely to fail than a grade 5 or 8.8

Indeed, the shear force is intended to be carried by friction, not the
bolt itself. But I'm not sure that high tensile bolts would be more
likely to fail in shear. Perhaps someone else knows for sure?

Best wishes,

Chris

toolman946 via CraftKB.com wrote:
You guys may find this interesting.

A number of years ago a friend of mine was the Service Manager for a large
Caterpillar dealer. They began having fracture problems with grade 8 bolts
(or maybe grade 8 studs) on the diesel engine oil pans. They replaced
numerous oil pan bolts and they still kept breaking.

Ken (my buddy) while not being trained as an engineer was a pretty sharp guy.
He noted that the shop had begun to use automotive silicon in place of the
composite oil pan gasket. He thought that the silicon was allowing the oil
pan to "float" slightly causing a high frequency vibration that was inducing
stress fractures in the grade 8 bolts. He ordered the shop to resume using
the original gaskets and the problem never recurred!

His theory made sense to me. What do you think?

It seems possible that the bolts were cracking as a result of fatigue
cracks growing slowly due to the vibration. But I suspect this could
only happen with a very rubbery gasket material.

Best wishes,

Chris

Larry Jaques wrote:

snip

I think his other instruction (to torque the bolts instead of just
using the 1/2" impact driver until stalled) was the key. But that's
just me.

That's possible, if he actually said that!

Chris

Christopher Tidy wrote:

But I'm not sure that high tensile bolts would be more
likely to fail in shear. Perhaps someone else knows for sure?

No, they aren't more likely to fail. If the softer one is bent, he already
failed.

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

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...

Christopher Tidy wrote:

I haven't heard of that requirement, but it sounds sensible.
Nevertheless, I've seen wedge-shaped washers (5 degrees I think) which
are placed under bolts passing through the flanges of universal beams in
structural steelwork. Presumably to make a neater job of the work, and
perhaps because the bolts are too big to hammer.

Chris

And it's difficult to swing a good sized hammer in the web area
of an I beam.
...lew...

On Wed, 16 Jan 2008 19:33:32 +0100, Nick Mueller
wrote:

Christopher Tidy wrote:

But I'm not sure that high tensile bolts would be more
likely to fail in shear. Perhaps someone else knows for sure?

No, they aren't more likely to fail. If the softer one is bent, he already
failed.

Nick
In double shear a loose grade 8 will snap uner impact. A grade 5 will
flex. It MAY permanently deform,
A loose grade 8 bolt in shear WILL brake on impact.

--
Posted via a free Usenet account from http://www.teranews.com

clare at snyder.on.ca wrote:

In double shear a loose grade 8 will snap uner impact. A grade 5 will
flex. It MAY permanently deform,
A loose grade 8 bolt in shear WILL brake on impact.

You forget to consider the forces.
A grade 5 bends under a certain load, where the grade 8 doesn't even bend
with the same load. Wen the grade 5 breaks, the grade 8 just bends.
Again, a bolt that is plastically deformed by design is simply an error.

Facts (metric grades):
grade 5.6 : 500N/mm^2 and 300N/mm^2
grade 8.8 : 800N/mm^2 and 640N/mm^2

A bit simplified:
The grade 5.6 bends at 300N/mm^2 and breaks at 500N/mm^2
The grade 8.8 bends at 640N/mm^2 and breaks at 800N/mm^2
So the grade 8.8 doesn't even bend when the grade 5.6 already failed
completely.


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

Nick Mueller wrote:

clare at snyder.on.ca wrote:


In double shear a loose grade 8 will snap uner impact. A grade 5 will
flex. It MAY permanently deform,
A loose grade 8 bolt in shear WILL brake on impact.


You forget to consider the forces.
A grade 5 bends under a certain load, where the grade 8 doesn't even bend
with the same load. Wen the grade 5 breaks, the grade 8 just bends.
Again, a bolt that is plastically deformed by design is simply an error.

Facts (metric grades):
grade 5.6 : 500N/mm^2 and 300N/mm^2
grade 8.8 : 800N/mm^2 and 640N/mm^2

A bit simplified:
The grade 5.6 bends at 300N/mm^2 and breaks at 500N/mm^2
The grade 8.8 bends at 640N/mm^2 and breaks at 800N/mm^2
So the grade 8.8 doesn't even bend when the grade 5.6 already failed
completely.


Nick

That's the best argument I've ever seen to NOT use 8's in aircraft
structures.

cavelamb himself wrote:

That's the best argument I've ever seen to NOT use 8's in aircraft
structures.

Exactly. I know why they are using lead. It bends at once and fails soon
after.


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

cavelamb himself wrote:
Nick Mueller wrote:

clare at snyder.on.ca wrote:


In double shear a loose grade 8 will snap uner impact. A grade 5 will
flex. It MAY permanently deform,
A loose grade 8 bolt in shear WILL brake on impact.



You forget to consider the forces.
A grade 5 bends under a certain load, where the grade 8 doesn't even bend
with the same load. Wen the grade 5 breaks, the grade 8 just bends.
Again, a bolt that is plastically deformed by design is simply an error.

Facts (metric grades):
grade 5.6 : 500N/mm^2 and 300N/mm^2
grade 8.8 : 800N/mm^2 and 640N/mm^2

A bit simplified:
The grade 5.6 bends at 300N/mm^2 and breaks at 500N/mm^2
The grade 8.8 bends at 640N/mm^2 and breaks at 800N/mm^2
So the grade 8.8 doesn't even bend when the grade 5.6 already failed
completely.


Nick


That's the best argument I've ever seen to NOT use 8's in aircraft
structures.

Is it just me, or does that argument make no sense?

Chris

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
-----------------

"Christopher Tidy" wrote in message
...
cavelamb himself wrote:
Nick Mueller wrote:

clare at snyder.on.ca wrote:


In double shear a loose grade 8 will snap uner impact. A grade 5 will
flex. It MAY permanently deform,
A loose grade 8 bolt in shear WILL brake on impact.



You forget to consider the forces.
A grade 5 bends under a certain load, where the grade 8 doesn't even
bend
with the same load. Wen the grade 5 breaks, the grade 8 just bends.
Again, a bolt that is plastically deformed by design is simply an error.

Facts (metric grades):
grade 5.6 : 500N/mm^2 and 300N/mm^2
grade 8.8 : 800N/mm^2 and 640N/mm^2

A bit simplified:
The grade 5.6 bends at 300N/mm^2 and breaks at 500N/mm^2
The grade 8.8 bends at 640N/mm^2 and breaks at 800N/mm^2
So the grade 8.8 doesn't even bend when the grade 5.6 already failed
completely.


Nick


That's the best argument I've ever seen to NOT use 8's in aircraft
structures.

Is it just me, or does that argument make no sense?

Chris

In need of something to argue about, Huntress suggests, look at what Nick
has said. "Again, a bolt that is plastically deformed by design is simply an
error." The point is that the bolts Richard is referring to are not intended
to deform in normal use, but are designed to deform when design limits are
exceeded. Depending on the design of the joint, bending may prevent other
modes of failure, and a weaker bolt that will bend often has sufficient
strength to prevent failure of the joint even when its plastic limit *in
bending* has been exceeded. The *ultimate tensile strength* of the bolt will
be quit a bit greater than its yield strength in bending.

Complex structures, particularly those that have some bend and/or flex
intrinsic to their design, may not lend themselves to theoretically ideal
joint designs. A light aircraft frame may also incorporate a material
compromise, say in tube materials and their joints, that will yield and
break if a bolt doesn't yield first. The specific load imposed by a hard and
strong bolt may exceed the strength of the material being bolted together by
so much that the material being bolted fails, whereas it wouldn't fail if
the bolt deformed and thus redistributed the load on the joint itself.

This is one key reason why the elongation properties of materials often are
critical to the safety of a design. Any joint that is likely to be loaded to
a high percentage of its ultimate strength has to be engineered as a whole.
Stronger bolts may, in some circumstances, result in a weaker joint.

I anticipate argument on this point from Nick, but that's no problem,
because he's wrong. g

--
Ed Huntress

Ed Huntress wrote:

snip

In need of something to argue about, Huntress suggests, look at what Nick
has said. "Again, a bolt that is plastically deformed by design is simply an
error." The point is that the bolts Richard is referring to are not intended
to deform in normal use, but are designed to deform when design limits are
exceeded. Depending on the design of the joint, bending may prevent other
modes of failure, and a weaker bolt that will bend often has sufficient
strength to prevent failure of the joint even when its plastic limit *in
bending* has been exceeded. The *ultimate tensile strength* of the bolt will
be quit a bit greater than its yield strength in bending.

I agree. Some designs need to consider what might happen under abnormal
circumstances. Are you talking about bolts loaded in bending, or being
elongated? Loading bolts in bending is often a bad idea because of the
high stresses it creates. But I guess you can see a double-shear joint
as bending on a small scale, if it isn't a joint in which the shear
force is carried by friction, or if the limiting friction is exceeded.

Complex structures, particularly those that have some bend and/or flex
intrinsic to their design, may not lend themselves to theoretically ideal
joint designs. A light aircraft frame may also incorporate a material
compromise, say in tube materials and their joints, that will yield and
break if a bolt doesn't yield first. The specific load imposed by a hard and
strong bolt may exceed the strength of the material being bolted together by
so much that the material being bolted fails, whereas it wouldn't fail if
the bolt deformed and thus redistributed the load on the joint itself.

I can see what you're saying here, Ed. I'm not sure how many structures
it would apply to, though. It would need to be a (probably statically
indeterminate) structure in which the elongation of some bolts imposes a
safer distribution of stresses within the structure.

This is one key reason why the elongation properties of materials often are
critical to the safety of a design. Any joint that is likely to be loaded to
a high percentage of its ultimate strength has to be engineered as a whole.
Stronger bolts may, in some circumstances, result in a weaker joint.

Do you mean a weaker structure as a whole? If you're talking about
strength in terms of forces, then according to Nick's figures a joint
made with grade 8.8 bolts would either have the same strength (if the
other parts of the structure were the limiting factor), or a greater
strength (if the bolts were the limiting factor), than a joint made with
grade 5.6 bolts. But things might be different if you're talking about
strength in terms of the energy a joint can absorb before it fails,
because we don't know the elongation at which the two types of bolt break.

Best wishes,

Chris

"Christopher Tidy" wrote in message
...
Ed Huntress wrote:

snip

In need of something to argue about, Huntress suggests, look at what Nick
has said. "Again, a bolt that is plastically deformed by design is simply
an error." The point is that the bolts Richard is referring to are not
intended to deform in normal use, but are designed to deform when design
limits are exceeded. Depending on the design of the joint, bending may
prevent other modes of failure, and a weaker bolt that will bend often
has sufficient strength to prevent failure of the joint even when its
plastic limit *in bending* has been exceeded. The *ultimate tensile
strength* of the bolt will be quit a bit greater than its yield strength
in bending.

I agree. Some designs need to consider what might happen under abnormal
circumstances. Are you talking about bolts loaded in bending, or being
elongated? Loading bolts in bending is often a bad idea because of the
high stresses it creates. But I guess you can see a double-shear joint as
bending on a small scale, if it isn't a joint in which the shear force is
carried by friction, or if the limiting friction is exceeded.

That's the idea. You'll see joints of flattened tube, or shear plates, in
old race car designs, and similar things in some home-built aircraft. It can
be single-shear as well as double-shear. And it can be rivets or bolts.

As for loading in bending versus elongation, keep in mind that bending is
the result of tension on the outside of the bend, and compression on the
inside (and shear in between). Steel and most structural metals have similar
values for yield in tension and compression, so bending results in
elongation of the outside.


Complex structures, particularly those that have some bend and/or flex
intrinsic to their design, may not lend themselves to theoretically ideal
joint designs. A light aircraft frame may also incorporate a material
compromise, say in tube materials and their joints, that will yield and
break if a bolt doesn't yield first. The specific load imposed by a hard
and strong bolt may exceed the strength of the material being bolted
together by so much that the material being bolted fails, whereas it
wouldn't fail if the bolt deformed and thus redistributed the load on the
joint itself.

I can see what you're saying here, Ed. I'm not sure how many structures it
would apply to, though. It would need to be a (probably statically
indeterminate) structure in which the elongation of some bolts imposes a
safer distribution of stresses within the structure.

I think it shows up in a lot of places in high-performance structures. I
recall seeing it in the design of seat-belt anchors in race cars; fastener
ductility also factors into the safety margins in bridge and building
design. Note that a lack of ductility in a bolt can increase stress
concentrations and thus can precipitate a failure in the material being
bolted, even when the loads don't even approach the strength of the bolt.


This is one key reason why the elongation properties of materials often
are critical to the safety of a design. Any joint that is likely to be
loaded to a high percentage of its ultimate strength has to be engineered
as a whole. Stronger bolts may, in some circumstances, result in a weaker
joint.

Do you mean a weaker structure as a whole? If you're talking about
strength in terms of forces, then according to Nick's figures a joint made
with grade 8.8 bolts would either have the same strength (if the other
parts of the structure were the limiting factor), or a greater strength
(if the bolts were the limiting factor), than a joint made with grade 5.6
bolts.

That's incorrect, because it's unknown. All you can say for sure there is
that the BOLT will be stronger, not that the joint will be stronger. The
joint may, as we've been discussing, turn out to be weaker with the stronger
bolt because it may increase stress concentrations.

But things might be different if you're talking about strength in terms of
the energy a joint can absorb before it fails, because we don't know the
elongation at which the two types of bolt break.

It's not only the bolts themselves. It's the entire design of the joint that
determines joint strength. Stronger bolts can, and sometimes do, result in a
weaker joint.

The whole subject is treated in structural engineering texts, but I haven't
read one for years, so I can't give any references. Richard has experience
with airframe design so he can probably point to references better than I
can.

Keep in mind also that for complex structures, especially things like
airframes and other tetrahedral or geodesic structures, ductility of
individual joints is important for preventing failure of the overall
structure, because it allows a local overload to be distributed to other
joints in the structure without breaking the individual joint. A ductile,
but weaker joining element will "give," to put it in ordinary terms, without
breaking; before the ultimate strength of that individual joint is reached,
the load in a geodesic or tetrahedral structure will then be distributed to
other joints in the structure. Thus, weaker but more ductile joints can
result in greater overall strength and integrity of the structure.

--
Ed Huntress

On Fri, 18 Jan 2008 00:23:57 +0000, Christopher Tidy
wrote:

cavelamb himself wrote:
Nick Mueller wrote:

clare at snyder.on.ca wrote:


In double shear a loose grade 8 will snap uner impact. A grade 5 will
flex. It MAY permanently deform,
A loose grade 8 bolt in shear WILL brake on impact.



You forget to consider the forces.
A grade 5 bends under a certain load, where the grade 8 doesn't even bend
with the same load. Wen the grade 5 breaks, the grade 8 just bends.
Again, a bolt that is plastically deformed by design is simply an error.

Facts (metric grades):
grade 5.6 : 500N/mm^2 and 300N/mm^2
grade 8.8 : 800N/mm^2 and 640N/mm^2

A bit simplified:
The grade 5.6 bends at 300N/mm^2 and breaks at 500N/mm^2
The grade 8.8 bends at 640N/mm^2 and breaks at 800N/mm^2
So the grade 8.8 doesn't even bend when the grade 5.6 already failed
completely.


Nick


That's the best argument I've ever seen to NOT use 8's in aircraft
structures.

Is it just me, or does that argument make no sense?

Chris

Well, grade 8 bolts are NOT used in aircraft, for what it's worth. AN
bolts are closer to grade 5.
They DO bend. They don't(theoretically, and hopefully) snap.

--
Posted via a free Usenet account from http://www.teranews.com

Christopher Tidy wrote:


Do you mean a weaker structure as a whole? If you're talking about
strength in terms of forces, then according to Nick's figures a joint
made with grade 8.8 bolts would either have the same strength (if the
other parts of the structure were the limiting factor), or a greater
strength (if the bolts were the limiting factor), than a joint made with
grade 5.6 bolts. But things might be different if you're talking about
strength in terms of the energy a joint can absorb before it fails,
because we don't know the elongation at which the two types of bolt break.

Best wishes,

Chris



In a way, yes.

We design to a give load limit.
Anything beyond that is excess weight.
So we don't ever expect an unbreakable structure.

It will survive up to the yield point - beyond which the structure
is damaged - but not broken.

At teh ultimate load point the structure breaks.

And yes, we know the elongation of both the joint material and the bolts
(AN bolts are typically grade 5).

But the real deal is simply this...

WHEN the structure is over stressed - i.e.: it has been loaded beyond
the yield point - how do you know? And - what gets damaged?

Do you want the bolt to bend visibly?

Or a few hundred rivets (or welds?) to be invisibly damaged?

?

Richard

Ed Huntress wrote:

The specific load imposed by a hard and
strong bolt may exceed the strength of the material being bolted together
by so much that the material being bolted fails, whereas it wouldn't fail
if the bolt deformed and thus redistributed the load on the joint itself.

I kind of see your argument. The grade 8.8 bolt has a stretch of 12% before
he breaks (no numbers for the 5.8, should be something around 17%).
But lets get back to the "I'll never use a grade 8 bolt":
If the joint is *designed* the bolts are calculated to take the load. If
that structure is overloaded, the two parts that are held together will
lose contact and now we do have to distinguish two cases:
* The bolt was stretched, and the joint will rattle and no longer work
(you'll see that later).
* The bolt was elastically stressed and the joint is back in contact after
the overload and is still working (albeit maybe in a bit different
position).
Now we have a closer look at the second case:
All joints with bolts relay on the elasticity modulus of the bolt. The
modulus is the same for any grade. The bolt keeps two parts together with
the preload given by the bolt (by the torque it was tightened with) and
they will lift/move/shift as soon as the outer force is bigger than the
inner force.
Now there are two cases:
A joint that is stressed with shearing forces:
Design flaw: The *bolt* is designed to take the shearing force. You are
fired! That is wrong by design! It always are the two parts and the
friction between the two and the preload given by the bolt. There is no
difference between different grades of bolts (- modulus). OK, there are
*rare* exceptions where a shearing pin (which needs to have tolerances in
the diameter together with the hole it goes into) and a bolt are merged
into one piece. But that is *not* a normal bolt.
A joint that is stressed by pull:
Lets take two hypothetical bolts. One with 500 N/mm^2 and one with 1000
N/mm^2. I call them grade 5 and grade 10 for now.
For a given designed load, the grade 10 bolt can have half the cross-section
of the grade 5. Now if we overload the joint, the grade 10 acts *softer*
than the grade 5 (half the cross-section, same modulus. acts like a spring,
half the spring rate) that looks to be an advantage, because parts can move
easier with the grade 10, before we do have a plastic deformation.
Now if we come into the pastic region of stress, the grade 5 bolt was
elongated *half* the distance of the grade 10. The fact that it has about
30% (17% vs. 12%) more plastic elongation than the grade 10 bolt doesn't
help, because it has double the spring rate of the grade 10.
So by design -assuming propper design- a grade 10 is more forgiving than a
grade 5.
And now finally to the case a grade 5 is replaced by a grade 10 without
changing the diameter:
Well, something will bend/stretch. It makes a difference what will bend. But
it is already a failure. We will find enough examples where the slight
bending of the structure is better (and keeps the whole structure in a
still perfect working condition) contrary to where a rattling joint will
have its advantages. Uh? Read above, a joint that is loaded by shearing
forces no longer works *at* *all*. A joint that is stressed by pulling
forces is just rattling and not keeping things together.


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

Nick Mueller wrote:
Ed Huntress wrote:


The specific load imposed by a hard and
strong bolt may exceed the strength of the material being bolted together
by so much that the material being bolted fails, whereas it wouldn't fail
if the bolt deformed and thus redistributed the load on the joint itself.



Design flaw: The *bolt* is designed to take the shearing force. You are
fired! That is wrong by design! It always are the two parts and the
friction between the two and the preload given by the bolt. There is no
difference between different grades of bolts (- modulus). OK, there are


Actually, in aircraft work it's the exact opposite.
Bolts are never (?) loaded in tension.
Shear only.

For what it's worth...

cavelamb himself wrote:

Bolts are never (?) loaded in tension.
Shear only.

So you are suggesting that the bolts aren't tightened? Maybe you have to
re-read what I wrote. Friction & clamping forces are the keywords to look
for.
If it is shear only, you are at the *second* failure of the joint.


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

Christopher Tidy wrote:

Is it just me, or does that argument make no sense?

Chris

This whole discussion makes no sense to me. Stronger is stronger.
Would you rather have a joint fail (by bending) at some stress
or have it fail at a LOT higher stress by breaking. It's a no-
brainer to me.
...lew...

"Lew Hartswick" wrote in message
...
Christopher Tidy wrote:

Is it just me, or does that argument make no sense?

Chris

This whole discussion makes no sense to me. Stronger is stronger.
Would you rather have a joint fail (by bending) at some stress
or have it fail at a LOT higher stress by breaking. It's a no-
brainer to me.
...lew...

If you ever design an airplane, I want to make sure I'm never in it. d8-)

--
Ed Huntress

"Nick Mueller" wrote in message
...
Ed Huntress wrote:

The specific load imposed by a hard and
strong bolt may exceed the strength of the material being bolted together
by so much that the material being bolted fails, whereas it wouldn't fail
if the bolt deformed and thus redistributed the load on the joint itself.

I kind of see your argument. The grade 8.8 bolt has a stretch of 12%
before
he breaks (no numbers for the 5.8, should be something around 17%).
But lets get back to the "I'll never use a grade 8 bolt":
If the joint is *designed* the bolts are calculated to take the load. If
that structure is overloaded, the two parts that are held together will
lose contact and now we do have to distinguish two cases:
* The bolt was stretched, and the joint will rattle and no longer work
(you'll see that later).
* The bolt was elastically stressed and the joint is back in contact after
the overload and is still working (albeit maybe in a bit different
position).
Now we have a closer look at the second case:
All joints with bolts relay on the elasticity modulus of the bolt. The
modulus is the same for any grade. The bolt keeps two parts together with
the preload given by the bolt (by the torque it was tightened with) and
they will lift/move/shift as soon as the outer force is bigger than the
inner force.
Now there are two cases:
A joint that is stressed with shearing forces:
Design flaw: The *bolt* is designed to take the shearing force. You are
fired! That is wrong by design! It always are the two parts and the
friction between the two and the preload given by the bolt. There is no
difference between different grades of bolts (- modulus). OK, there are
*rare* exceptions where a shearing pin (which needs to have tolerances in
the diameter together with the hole it goes into) and a bolt are merged
into one piece. But that is *not* a normal bolt.
A joint that is stressed by pull:
Lets take two hypothetical bolts. One with 500 N/mm^2 and one with 1000
N/mm^2. I call them grade 5 and grade 10 for now.
For a given designed load, the grade 10 bolt can have half the
cross-section
of the grade 5. Now if we overload the joint, the grade 10 acts *softer*
than the grade 5 (half the cross-section, same modulus. acts like a
spring,
half the spring rate) that looks to be an advantage, because parts can
move
easier with the grade 10, before we do have a plastic deformation.
Now if we come into the pastic region of stress, the grade 5 bolt was
elongated *half* the distance of the grade 10. The fact that it has about
30% (17% vs. 12%) more plastic elongation than the grade 10 bolt doesn't
help, because it has double the spring rate of the grade 10.
So by design -assuming propper design- a grade 10 is more forgiving than a
grade 5.
And now finally to the case a grade 5 is replaced by a grade 10 without
changing the diameter:
Well, something will bend/stretch. It makes a difference what will bend.
But
it is already a failure. We will find enough examples where the slight
bending of the structure is better (and keeps the whole structure in a
still perfect working condition) contrary to where a rattling joint will
have its advantages. Uh? Read above, a joint that is loaded by shearing
forces no longer works *at* *all*. A joint that is stressed by pulling
forces is just rattling and not keeping things together.

Most joints work as you have described. Most structures are designed for
ridigity, not for strength, and the stronger the fasteners, the more rigid
is the structure. But ductility/elongation come into play in structures that
require high ratios of strength to weight, as is the case with some bridges
and many aircraft, as well as some other things.

Where that's the case, designing for ductility can be an important issue for
the overall strength of the structure in at least a couple of different ways
(not counting the visible near-failure that Richard is talking about, which
also is of practical importance). The primary way relates to distribution of
loads by avoiding point loads that will cause progressive failure. Some
riveted sheet structures and shear panels are examples. It can also be an
issue where there are multiple bolts in a heavier plate structure, with
holes that have some reasonable production tolerance and where the bolts are
going to be loaded in shear as the limits of strength are approached. This
is what I had in mind with the trailer-hitch example. As with the sheet
structures, the value of some ductility here can be distribution of the load
among multiple fasteners, where harder/stronger ones would localize the load
until the first hole tore out, and then then second, and so on.

As I said, I was just looking for an argument. g Most of the time, what
you're talking about is the important design parameter. But not always. And
aircraft designers, as well as designers of many other types of highly
loaded structures, must design around ductility to avoid excessive point
loads. One well-known example is in the welding of tubular space frames. A
pure space frame does not load joints in bending but a *real* space frame
always does. If the weld is too strong it will not allow plastic deformation
of the joint. That will cause a failure where the tube joins the weld,
because of the high point loads. The situation with bolts and rivets is
similar.

Sometimes, weaker is stronger. That's why we have structural engineers.

--
Ed Huntress

Lew Hartswick wrote:
Christopher Tidy wrote:


Is it just me, or does that argument make no sense?

Chris

This whole discussion makes no sense to me. Stronger is stronger.
Would you rather have a joint fail (by bending) at some stress
or have it fail at a LOT higher stress by breaking. It's a no-
brainer to me.
...lew...

Can't be done that way, Lew.

A solid steel wing would be a WHOLE lot stronger - but won't get off the
ground...

We design to load limits.
Say (typical light plane) 4 Gs + 50% safety margin.

The structure should take the load up to 4 G's, flex under load, and
return to it's original shape (exactly) when the load is removed.

Then we enter the plastic region.

Above the yield limit (4 Gs in this case) the structure does not return
to original shape when the load is removed. It has deformed - and is
now "damaged" by over stress. But it should not break (catastrophic
failure) below the 6 G ultimate limit.

Then comes the scary part...

Above the ultimate limit, you WANT the structure to break.
If it doesn't, it simply weighs too much.

Weight verses strength.

Not absolute strength.

Try not to think about it next time you board an airliner...


Richard

On Fri, 18 Jan 2008 05:00:26 -0600, cavelamb himself
wrote:

Nick Mueller wrote:
Ed Huntress wrote:


The specific load imposed by a hard and
strong bolt may exceed the strength of the material being bolted together
by so much that the material being bolted fails, whereas it wouldn't fail
if the bolt deformed and thus redistributed the load on the joint itself.



Design flaw: The *bolt* is designed to take the shearing force. You are
fired! That is wrong by design! It always are the two parts and the
friction between the two and the preload given by the bolt. There is no
difference between different grades of bolts (- modulus). OK, there are


Actually, in aircraft work it's the exact opposite.
Bolts are never (?) loaded in tension.
Shear only.

For what it's worth...

Not quite true. The bolt is in tension to hold parts together so the
friction takes the shear. Clamping load is still tension.

--
Posted via a free Usenet account from http://www.teranews.com

On Fri, 18 Jan 2008 07:44:02 -0700, Lew Hartswick
wrote:

Christopher Tidy wrote:

Is it just me, or does that argument make no sense?

Chris

This whole discussion makes no sense to me. Stronger is stronger.
Would you rather have a joint fail (by bending) at some stress
or have it fail at a LOT higher stress by breaking. It's a no-
brainer to me.
...lew...
Unless you are 15000 feet in the air when something goes wrong. Rather
bend and hold than snap. You can't afford the extra weight to make
something that will neither bend nor snap.


--
Posted via a free Usenet account from http://www.teranews.com