On 2008-01-18, clare at snyder.on.ca clare wrote:
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.

As was pointed out here, at the lad at which the low grade bolt would
completely fail, the high grade bolt would not even bend.

i

clare at snyder.on.ca wrote:
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.


Granted.

I guess I expressed it a little TOO simply (?)...

However, there are a lot of cases where the clamping force is minimal
and the bolt is simply a shear pin.

Ultralight wing tube style spars - for one.
Can't clamp much without crushing the tube.

Ignoramus29897 wrote:

On 2008-01-18, clare at snyder.on.ca clare wrote:

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.


As was pointed out here, at the lad at which the low grade bolt would
completely fail, the high grade bolt would not even bend.

i

Thus very likely transfering an excess load to even more critical
structure...

"cavelamb himself" wrote in message
...
Ignoramus29897 wrote:

On 2008-01-18, clare at snyder.on.ca clare wrote:

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.


As was pointed out here, at the lad at which the low grade bolt would
completely fail, the high grade bolt would not even bend.

i

Thus very likely transfering an excess load to even more critical
structure...


When you are cork screwed into the round, does it really make a difference
which part failed first??

I do understand the logic to a point over using Grade 5 versus Grade 8, but
are we forgetting that it makes a difference what the design of the whole
assembly is? I can see why a Grade 5 might be better than a Grade 8 in a
assembly that was designed for the lower strength bolt. Same with an
assembly designed for a Grade 8 over the Grade 5 bolt.
Back the the OP's question, as to mounting a trailer hitch. The Grade 5 will
more than likely do the job just fine, and the Grade 8 will give a larger
margin of safety, probably over kill, but I surely would not worry about a
Grade 8 bolt failing on a typical trailer hitch, something else will
probably fail first, like the frame member itself!
A few years back A friend of mine got rear ended, he was pulling a small
boat with a Chevy pickup, and a Class III hitch. He was hit so hard that
vehicle crushed his boat and rammed into the back of his pickup. Looking
over the wreck latter we noticed the six, 1/2 diameter, Grade 5 bolts
holding the hitch onto the frame were still tight, and appeared to be snug,
even though the hitch and rear portion of the frame was a tangled mess!
Greg

On Fri, 18 Jan 2008 13:42:31 -0600, Ignoramus29897
wrote:

On 2008-01-18, clare at snyder.on.ca clare wrote:
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.

As was pointed out here, at the lad at which the low grade bolt would
completely fail, the high grade bolt would not even bend.

i
Have you ever built a plane?
You need to take a REAL GOOD LOOK at the way they are designed, and
figure out why.
It just does not work the way you expect.
There are VERY GOOD reasons why AN hardware (aerospace standard) are
essentially grade 5 bolts with a pedigree.

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

On Fri, 18 Jan 2008 13:49:32 -0600, cavelamb himself
wrote:

clare at snyder.on.ca wrote:
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.


Granted.

I guess I expressed it a little TOO simply (?)...

However, there are a lot of cases where the clamping force is minimal
and the bolt is simply a shear pin.

Ultralight wing tube style spars - for one.
Can't clamp much without crushing the tube.



And VERY poor design when built that way. The proper way is to sleeve
the hole so the bolt is supported for it's full length instead of just
by the skin of the tube, and the bolt can be torqued to it's proper
torque to provide maximum strength.
Then they could likely even get away with lighter bolts.


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

On Fri, 18 Jan 2008 20:30:20 GMT, "Greg O"
wrote:


"cavelamb himself" wrote in message
...
Ignoramus29897 wrote:

On 2008-01-18, clare at snyder.on.ca clare wrote:

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.


As was pointed out here, at the lad at which the low grade bolt would
completely fail, the high grade bolt would not even bend.

i

Thus very likely transfering an excess load to even more critical
structure...


When you are cork screwed into the round, does it really make a difference
which part failed first??

I do understand the logic to a point over using Grade 5 versus Grade 8, but
are we forgetting that it makes a difference what the design of the whole
assembly is? I can see why a Grade 5 might be better than a Grade 8 in a
assembly that was designed for the lower strength bolt. Same with an
assembly designed for a Grade 8 over the Grade 5 bolt.
Back the the OP's question, as to mounting a trailer hitch. The Grade 5 will
more than likely do the job just fine, and the Grade 8 will give a larger
margin of safety, probably over kill, but I surely would not worry about a
Grade 8 bolt failing on a typical trailer hitch, something else will
probably fail first, like the frame member itself!

Grade 8 bolts have failed in trailer hitch mountings. - Where grade
5's would have held. (at least long enough to create a rattle to warn
of impending doom)
If a bolt is not providing almost exclusively clamping force, DO NOT
use a grade 8 - particularly if there is impact loading or reversal of
forces that will put impact shear loading on the bolt.

Looh at ANY light to medium duty hitch kit that fastens to either a
unibody or a typical automotive frame. The bolts are grade 5 AT BEST -
more often grade 2 or ungraded utility bolts.

A few years back A friend of mine got rear ended, he was pulling a small
boat with a Chevy pickup, and a Class III hitch. He was hit so hard that
vehicle crushed his boat and rammed into the back of his pickup. Looking
over the wreck latter we noticed the six, 1/2 diameter, Grade 5 bolts
holding the hitch onto the frame were still tight, and appeared to be snug,
even though the hitch and rear portion of the frame was a tangled mess!
Greg

Pickup frames and hitches are somewhat different in that the hitch
brackets are USUALLY a very good fit to the frame rails, so a properly
torqued bolt provides a LOT of friction between the frame and the
hitch brackets. Enough that the bolts are not taking any appreciable
shear loading.

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

clare at snyder.on.ca wrote:
On Fri, 18 Jan 2008 13:49:32 -0600, cavelamb himself
wrote:


clare at snyder.on.ca wrote:

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.


Granted.

I guess I expressed it a little TOO simply (?)...

However, there are a lot of cases where the clamping force is minimal
and the bolt is simply a shear pin.

Ultralight wing tube style spars - for one.
Can't clamp much without crushing the tube.




And VERY poor design when built that way. The proper way is to sleeve
the hole so the bolt is supported for it's full length instead of just
by the skin of the tube, and the bolt can be torqued to it's proper
torque to provide maximum strength.
Then they could likely even get away with lighter bolts.



Can you name one UL manufacturer who does that?

Ed Huntress wrote:

snip

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.

In the case of a seat belt anchor, the amount of energy it can absorb
before finally breaking is going to be important. It depends on what you
consider to be strength. I would consider strength to be a joint's
ability to resist the forces applied to it. And so a stronger joint
would be one which fails under a greater force. But you might also
consider strength to be a joint's ability to absorb energy before
breaking. Both are important, though sometimes one is more important
than the other.

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.

I disagree. Take a simple example: a single-shear joint made between two
mild steel flat bars. There's a hole in each bar, and a bolt connecting
the two holes.

Either the bars are weaker (the bolt will tear through one of the bars
when the joint fails), or the bolt is weaker (the bolt will fail in
shear). If a grade 5.6 bolt is weaker than the bars, then substituting a
grade 8.8 bolt can only make the joint stronger. If a grade 5.6 bolt is
stronger than the bars, subsituting a grade 8.8 bolt will make no
difference.

Now if the joint is part of a large and complex structure, it's possible
than using a weaker but more ductile bolt might, in some circumstances,
impose a safer distribution of forces within an overloaded structure,
making the whole structure stronger.

But even though the whole structure might be stronger, the individual
joint is still weaker. I can't see how the individual joint can possibly
be made stronger by substituting a weaker but more ductile bolt. If you
disagree, please explain why. Perhaps we agree and it's just a
misunderstanding?

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.

A weaker structure, possibly, but the individual joints are still stronger.

Best wishes,

Chris

clare wrote:

snip

If a bolt is not providing almost exclusively clamping force, DO NOT
use a grade 8 - particularly if there is impact loading or reversal of
forces that will put impact shear loading on the bolt.

I think you'll find that if the hitch bolts are tightened to the correct
torque, the load is carried by friction.

Chris

Nick Mueller wrote:

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.

I'm inclined to agree with Nick here. The few times I've made this
mistake myself in the past, the joint has come loose. Sure, there are a
few instances in which it can be okay to load a bolt in shear (a shackle
for example:
http://www.1st-chainsupply.com/image...shackleCM.jpg),
but they're cases in which loosening isn't an issue. Mostly it's a bad idea.

Best wishes,

Chris

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

snip


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.

I disagree. Take a simple example: a single-shear joint made between two
mild steel flat bars. There's a hole in each bar, and a bolt connecting
the two holes.

Either the bars are weaker (the bolt will tear through one of the bars
when the joint fails), or the bolt is weaker (the bolt will fail in
shear). If a grade 5.6 bolt is weaker than the bars, then substituting a
grade 8.8 bolt can only make the joint stronger. If a grade 5.6 bolt is
stronger than the bars, subsituting a grade 8.8 bolt will make no
difference.

Now if the joint is part of a large and complex structure, it's possible
than using a weaker but more ductile bolt might, in some circumstances,
impose a safer distribution of forces within an overloaded structure,
making the whole structure stronger.

I think you just disagreed, and then agreed. d8-) Yes, it applies mostly to
structures with multiple joints, or with multiple fasteners in one joint.


But even though the whole structure might be stronger, the individual
joint is still weaker. I can't see how the individual joint can possibly
be made stronger by substituting a weaker but more ductile bolt. If you
disagree, please explain why. Perhaps we agree and it's just a
misunderstanding?

It would have to be a very contrived case to make the point with a single
fastener, but the principle still applies. In a car or aircraft crash, for
example, you could have an extreme overload applied to a joint, bot only
through a distance of a fraction of an inch. If the bolt doesn't give,
something will break.


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.

I wouldn't get into energy because it complicates things, although it's an
issue with impact. We're just talking about distribution of forces, or, in
the case of a single fastener, an excessive force applied through a very
short distance.



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.

A weaker structure, possibly, but the individual joints are still
stronger.

A joint can have more than one fastener, as they often do in bridges and
vehicle structures.

--
Ed Huntress

Ed Huntress wrote:

snip

I disagree. Take a simple example: a single-shear joint made between two
mild steel flat bars. There's a hole in each bar, and a bolt connecting
the two holes.

Either the bars are weaker (the bolt will tear through one of the bars
when the joint fails), or the bolt is weaker (the bolt will fail in
shear). If a grade 5.6 bolt is weaker than the bars, then substituting a
grade 8.8 bolt can only make the joint stronger. If a grade 5.6 bolt is
stronger than the bars, subsituting a grade 8.8 bolt will make no
difference.

Now if the joint is part of a large and complex structure, it's possible
than using a weaker but more ductile bolt might, in some circumstances,
impose a safer distribution of forces within an overloaded structure,
making the whole structure stronger.


I think you just disagreed, and then agreed. d8-) Yes, it applies mostly to
structures with multiple joints, or with multiple fasteners in one joint.

I did. But I've thought this through very carefully, and I think I'm
prepared to mostly concede the argument. Suppose a joint has many bolts
arranged in a line parallel to the force on the joint, and that all the
bolt holes are equally spaced when the material is in the unstressed
condition. The joint is then overloaded to the point where the limiting
friction is exceeded. The first few bolts will carry most of the load,
because the material between the bolt holes stretches, causing the other
bolts to go slack. It's the same as the way in which the first five
turns of a long screw thread carry most of the load. So if relatively
brittle bolts are used, it's possible that the first bolts might break
before they transfer enough load to the bolts further down the line,
then the bolts further down the line will break, and so on until the
joint fails completely. The same would be true for rivets.

But I suspect this is only important for joints with many bolts or
rivets. Perhaps more than five in a line parallel to the force, at a
guess. Of course, if the load on the joint was constant and known (not
an overload) it might be possible to vary the spacing of the holes to
ensure that all the bolts carried an equal load. Now there's an
interesting idea.

But even though the whole structure might be stronger, the individual
joint is still weaker. I can't see how the individual joint can possibly
be made stronger by substituting a weaker but more ductile bolt. If you
disagree, please explain why. Perhaps we agree and it's just a
misunderstanding?


It would have to be a very contrived case to make the point with a single
fastener, but the principle still applies. In a car or aircraft crash, for
example, you could have an extreme overload applied to a joint, bot only
through a distance of a fraction of an inch. If the bolt doesn't give,
something will break.

Using a bolt in single-shear, perhaps. But a pin in double-shear or
multiple-shear is pretty common. Think of a tractor's three-point
linkage, a towing hitch or an eyebar suspension bridge.

I wouldn't get into energy because it complicates things, although it's an
issue with impact. We're just talking about distribution of forces, or, in
the case of a single fastener, an excessive force applied through a very
short distance.

The selt belt anchor is certainly a case in which energy is important. I
just raised it because I wasn't absolutely certain that you weren't
talking about energy at first.

A joint can have more than one fastener, as they often do in bridges and
vehicle structures.

I don't believe this argument applies to a joint consisting of a single
bolt, considered in isolation.

Thanks for an interesting discussion. This is what I come to RCM for!

Best wishes,

Chris

On Fri, 18 Jan 2008 17:37:45 -0600, cavelamb himself
wrote:

clare at snyder.on.ca wrote:
On Fri, 18 Jan 2008 13:49:32 -0600, cavelamb himself
wrote:


clare at snyder.on.ca wrote:

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.


Granted.

I guess I expressed it a little TOO simply (?)...

However, there are a lot of cases where the clamping force is minimal
and the bolt is simply a shear pin.

Ultralight wing tube style spars - for one.
Can't clamp much without crushing the tube.




And VERY poor design when built that way. The proper way is to sleeve
the hole so the bolt is supported for it's full length instead of just
by the skin of the tube, and the bolt can be torqued to it's proper
torque to provide maximum strength.
Then they could likely even get away with lighter bolts.



Can you name one UL manufacturer who does that?

Not off the top of my head, but I think the Kolb 500 trainer (2
seater) is sleeved.from the factory. A friend a few years ago had one
that was sleeved
Also I think the Beaver 2 seater does. I know a friend's Beaver does,
might not have been from the factory.
I know a lot of ultralights have SCARY engineering (or lack there-of)
and many owners modify them to make them significantly safer.

By "sleeved" I don't meed doubled tubes. I mean the hole is drilled
overside and a piece of tubing is welded or brazed into the hole, the
right size to fit the bolt snuggly.

Many ultralightes also have holes drilled through the tubes the wrong
way, seriously weakening the tube.

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

On Sat, 19 Jan 2008 00:21:47 +0000, Christopher Tidy
wrote:

Ed Huntress wrote:

snip

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.

In the case of a seat belt anchor, the amount of energy it can absorb
before finally breaking is going to be important. It depends on what you
consider to be strength. I would consider strength to be a joint's
ability to resist the forces applied to it. And so a stronger joint
would be one which fails under a greater force. But you might also
consider strength to be a joint's ability to absorb energy before
breaking. Both are important, though sometimes one is more important
than the other.

Automotive seal belt anchors are GENERALLY designed in such a way that
the floor pan will deform before the bolt or the belt breaks. The thin
floor is doubled with a heavier plate that retains the extra strength
bolts.

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.

I disagree. Take a simple example: a single-shear joint made between two
mild steel flat bars. There's a hole in each bar, and a bolt connecting
the two holes.

Either the bars are weaker (the bolt will tear through one of the bars
when the joint fails), or the bolt is weaker (the bolt will fail in
shear). If a grade 5.6 bolt is weaker than the bars, then substituting a
grade 8.8 bolt can only make the joint stronger. If a grade 5.6 bolt is
stronger than the bars, subsituting a grade 8.8 bolt will make no
difference.

If the two bars are properly joined with a properly engineered joint,
the bars themselves will almost stretch before either the bolt or hole
deform.
Now if the joint is part of a large and complex structure, it's possible
than using a weaker but more ductile bolt might, in some circumstances,
impose a safer distribution of forces within an overloaded structure,
making the whole structure stronger.

But even though the whole structure might be stronger, the individual
joint is still weaker. I can't see how the individual joint can possibly
be made stronger by substituting a weaker but more ductile bolt. If you
disagree, please explain why. Perhaps we agree and it's just a
misunderstanding?

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.

A weaker structure, possibly, but the individual joints are still stronger.

Best wishes,

Chris


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

On Sat, 19 Jan 2008 00:40:33 +0000, Christopher Tidy
wrote:

clare wrote:

snip

If a bolt is not providing almost exclusively clamping force, DO NOT
use a grade 8 - particularly if there is impact loading or reversal of
forces that will put impact shear loading on the bolt.

I think you'll find that if the hitch bolts are tightened to the correct
torque, the load is carried by friction.

Chris
In a well engineered and properly installed hitch, yes.. In this
case, the bolt is providing almost exclusively clamping force.

Believe me, there are LOTS of hitches out there where neither of these
conditions is true.

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

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

snip

I disagree. Take a simple example: a single-shear joint made between two
mild steel flat bars. There's a hole in each bar, and a bolt connecting
the two holes.

Either the bars are weaker (the bolt will tear through one of the bars
when the joint fails), or the bolt is weaker (the bolt will fail in
shear). If a grade 5.6 bolt is weaker than the bars, then substituting a
grade 8.8 bolt can only make the joint stronger. If a grade 5.6 bolt is
stronger than the bars, subsituting a grade 8.8 bolt will make no
difference.

Now if the joint is part of a large and complex structure, it's possible
than using a weaker but more ductile bolt might, in some circumstances,
impose a safer distribution of forces within an overloaded structure,
making the whole structure stronger.


I think you just disagreed, and then agreed. d8-) Yes, it applies mostly
to structures with multiple joints, or with multiple fasteners in one
joint.

I did. But I've thought this through very carefully, and I think I'm
prepared to mostly concede the argument. Suppose a joint has many bolts
arranged in a line parallel to the force on the joint, and that all the
bolt holes are equally spaced when the material is in the unstressed
condition. The joint is then overloaded to the point where the limiting
friction is exceeded. The first few bolts will carry most of the load,
because the material between the bolt holes stretches, causing the other
bolts to go slack. It's the same as the way in which the first five turns
of a long screw thread carry most of the load. So if relatively brittle
bolts are used, it's possible that the first bolts might break before they
transfer enough load to the bolts further down the line, then the bolts
further down the line will break, and so on until the joint fails
completely. The same would be true for rivets.

But I suspect this is only important for joints with many bolts or rivets.
Perhaps more than five in a line parallel to the force, at a guess. Of
course, if the load on the joint was constant and known (not an overload)
it might be possible to vary the spacing of the holes to ensure that all
the bolts carried an equal load. Now there's an interesting idea.

But even though the whole structure might be stronger, the individual
joint is still weaker. I can't see how the individual joint can possibly
be made stronger by substituting a weaker but more ductile bolt. If you
disagree, please explain why. Perhaps we agree and it's just a
misunderstanding?


It would have to be a very contrived case to make the point with a single
fastener, but the principle still applies. In a car or aircraft crash,
for example, you could have an extreme overload applied to a joint, bot
only through a distance of a fraction of an inch. If the bolt doesn't
give, something will break.

Using a bolt in single-shear, perhaps. But a pin in double-shear or
multiple-shear is pretty common. Think of a tractor's three-point linkage,
a towing hitch or an eyebar suspension bridge.

I wouldn't get into energy because it complicates things, although it's
an issue with impact. We're just talking about distribution of forces,
or, in the case of a single fastener, an excessive force applied through
a very short distance.

The selt belt anchor is certainly a case in which energy is important. I
just raised it because I wasn't absolutely certain that you weren't
talking about energy at first.

A joint can have more than one fastener, as they often do in bridges and
vehicle structures.

I don't believe this argument applies to a joint consisting of a single
bolt, considered in isolation.

Thanks for an interesting discussion. This is what I come to RCM for!

Best wishes,

Chris

Since you've put some thought into this, you may find that reading a more
sophisticated engineering treatment of it would be worth your while. It's
too far in the past for me to remember much of it but there is plenty of
material on ductility and brittle failure in the field of aerospace
engineering. It's a very big issue there.

You could try the SAE website, which has a bookstore and white papers in the
aerospace division.

--
Ed Huntress

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

Ed Huntress wrote:

snip

I don't believe this argument applies to a joint consisting of a single
bolt, considered in isolation.

Thanks for an interesting discussion. This is what I come to RCM for!

Best wishes,

Chris


Since you've put some thought into this, you may find that reading a more
sophisticated engineering treatment of it would be worth your while. It's
too far in the past for me to remember much of it but there is plenty of
material on ductility and brittle failure in the field of aerospace
engineering. It's a very big issue there.

You could try the SAE website, which has a bookstore and white papers in the
aerospace division.

--
Ed Huntress




Pardon the messy line wrapping - just wanted to show what's there...


http://euler9.tripod.com/analysis/asm.html



Astronautic Structures Manual (On-Line), NASA MSFC (Marshall Space
Flight Center), 1975.
Astronautic Structures Manual, Volume 1, NASA TM-X-73305, NASA MSFC,
August 1975, 839 pages.
Astronautic Structures Manual, Volume 2, NASA TM-X-73306, NASA MSFC,
August 1975, 974 pages.
Astronautic Structures Manual, Volume 3, NASA TM-X-73307, NASA MSFC,
August 1975, 673 pages.

Abstract: This document (Volume 1, 2, and 3) presents a compilation of
industry-wide methods in aerospace strength analysis that can be carried
out by hand, that are general enough in scope to cover most structures
encountered, and that are sophisticated enough to give accurate
estimates of the actual strength expected. It provides analysis
techniques for the elastic and inelastic stress ranges. It serves not
only as a catalog of methods not usually available, but also as a
reference source for the background of the methods themselves.
Volume 1 (37.1 MB)
Section A: Introduction, stress and strain, loads, combined stress,
and interaction curves.
A0.0.0 Downloadable hyperlink TOC, asm-A000.htm, 0.02 MB.
A1.0.0 Stress and strain, asm-A100.pdf, 1.31 MB.
A2.0.0 Loads, asm-A200.pdf, 0.35 MB.
A3.0.0 Combined stresses, asm-A300.pdf, 0.98 MB.
A4.0.0 Metric system, asm-A400.pdf, 1.03 MB.
Section B: Methods of strength analysis.
B1.0.0 Joints and fasteners, asm-B100.pdf, 2.14 MB.
B2.0.0 Lugs and shear pins, asm-B200.pdf, 0.60 MB.
B3.0.0 Springs, asm-B300.pdf, 1.08 MB.
B4.0.0 Beams, beam tables, asm-B400.pdf, 1.32 MB.
B4.5.0 Plastic bending, asm-B450.pdf, 1.27 MB.
B4.5.5 Plastic bending curves: stainless steel, asm-B455.pdf, 6.03 MB.
B4.5.6 Plastic bending curves: alloy steel, asm-B456.pdf, 2.82 MB.
B4.5.7 Plastic bending curves: titanium, asm-B457.pdf, 0.96 MB.
B4.5.8 Plastic bending curves: aluminum, asm-B458.pdf, 5.06 MB.
B4.5.9 Plastic bending curves: magnesium, asm-B459.pdf, 1.31 MB.
B4.6.0 Beams under axial load, asm-B460.pdf, 1.38 MB.
B4.7.0 Lateral buckling of beams, asm-B470.pdf, 0.50 MB.
B4.8.0 Shear beams, asm-B480.pdf, 1.76 MB.
B5.0.0 Frames, frame tables, asm-B500.pdf, 2.47 MB.
B6.0.0 Rings, asm-B600.pdf, 4.68 MB.
Volume 2 (28.7 MB)
Section B: Methods of strength analysis (cont.).
B7.0.0 Thin shells, asm-B700.pdf, 0.74 MB. -- Slightly faded copy.
B7.1.0 Membrane analysis of thin shells of revolution,
asm-B710.pdf, 0.74 MB.
B7.1.2 Dome membrane analysis, asm-B712.pdf, 1.18 MB.
B7.2.0 Local loads on thin spherical shells, asm-B720.pdf, 1.70 MB.
B7.2.2 Local loads on thin cylindrical shells, asm-B722.pdf, 0.86 MB.
B7.3.0 Bending analysis of thin shells, asm-B730.pdf, 2.43 MB.
-- Some tables faded!
B7.3.4 Bending analysis of thin shells (cont.), asm-B734.pdf, 0.91 MB.
B8.0.0 Torsion of solid sections, asm-B800.pdf, 0.85 MB.
B8.3.0 Torsion of thin-walled closed sections, asm-B830.pdf, 0.73 MB.
B8.4.0 Torsion of thin-walled open sections, asm-B840.pdf, 0.97 MB.
B9.0.0 Plates, asm-B900.pdf, 1.72 MB.
B9.4.0 Plates (cont.), asm-B940.pdf, 1.76 MB.
B10.0 Holes and cutouts in plates, asm-B970.pdf, 0.73 MB.
B10.2 Large holes and cutouts in plates, asm-B972.pdf, 0.96 MB.
Section C: Structural stability analysis.
C1.0.0 Long columns, short columns, crippling, asm-C100.pdf, 1.06 MB.
C1.5.0 Torsional instability of columns, asm-C150.pdf, 1.18 MB.
C2.0.0 Stability of flat plates, asm-C200.pdf, 1.20 MB.
C2.2.0 Stability of curved plates, asm-C220.pdf, 2.59 MB.
C3.0.0 Stability of shells, asm-C300.pdf, 0.52 MB.
C3.1.0 Stability of cylinders, asm-C310.pdf, 1.96 MB.
C3.2.0 Stability of conical shells, asm-C320.pdf, 0.80 MB.
C3.3.0 Stability of doubly curved shells, asm-C330.pdf, 0.96 MB.
C3.4.0 Computer programs in shell stability analysis,
asm-C340.pdf, 0.87 MB.
C4.0.0 Local instability of flat panels, asm-C400.pdf, 1.31 MB.
Volume 3 (21.4 MB)
Section D: Thermal stresses.
D1.0.0 Thermal stresses, asm-D100.pdf, 0.54 MB. -- Some
characters faded.
D3.0.0 Thermal stresses in beams, asm-D300.pdf, 0.99 MB. --
Some characters slightly faded.
D3.2.3 Thermal stresses in beams (cont.), asm-D323.pdf, 1.07 MB.
D3.7.0 Thermal stresses in plates, asm-D370.pdf, 1.39 MB.
D3.8.0 Thermal stresses in shells, asm-D380.pdf, 1.88 MB.
D4.0.0 Thermoelastic stability, asm-D400.pdf, 1.20 MB.
D5.0.0 Inelastic thermal effects, asm-D500.pdf, 0.55 MB.
D6.0.0 Thermal shock, asm-D600.pdf, 2.21 MB.
Section E: Fatigue and fracture mechanics.
E1.0.0 Fatigue, asm-E100.pdf, 1.06 MB.
E1.3.0 Fatigue (cont.), asm-E130.pdf, 2.43 MB.
E1.5.0 Fatigue (cont.), asm-E150.pdf, 0.76? MB.
E2.0.0 Fracture mechanics, asm-E200.pdf, 1.49 MB.
E2.4.0 Fracture mechanics (cont.), asm-E240.pdf, 2.21 MB.
Section F: Composites.
F1.0.0 Composites, basic concepts, asm-F100.pdf, 0.77 MB.
F1.2.0 Mechanics of laminated composites, asm-F120.pdf, 0.74 MB.
F2.0.0 Strength of laminated composites, asm-F200.pdf, 0.24 MB.
Section G: Rotating machinery.
G1.0.0 Rotating disks, asm-G100.pdf, 0.55 MB.
Section H: Statistics.
H1.0.0 Statistical methods, introduction, asm-H100.pdf, 0.56 MB.
H1.2.0 Statistical methods, measuring
performance of a material, asm-H120.pdf, 0.66 MB.

Ed Huntress wrote:

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.

OK. Now I got you. The image were several rows of bolts (classical sheet
overlapping joint) that are calculated more like rows of rivets. Not yet
fully convinced that a stronger bolt has an disadvantage (except the
price). *)
But anyhow, the point is more the hole in the sheet and its projected
surface area that has to accept a certain pressure (when shearing) and you
can't make the bolt smaller because of the pressure. The clamping force is
(almost) ignored in that setup. But maybe that was an old approach in
design. I know, that joints like these are now glued (to take the shear)
and screwed/riveted) to take the peeling forces.

*)
But I also got your point about distributing load and what happens if one
joint fails and you get an avalanche failure of the neighboring joints.


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

Christopher Tidy wrote:

I'm inclined to agree with Nick here. The few times I've made this
mistake myself in the past, the joint has come loose. Sure, there are a
few instances in which it can be okay to load a bolt in shear (a shackle
for example:

Sure I'm right! ;-)
No, I got the point now. We had different pictures in our minds.
The grade-5 fraction had this in mind:
Overlapping sheet that is held together with rows of bolts. You have that
picture of several rows of rivets?
OK, here it really pays to have soft bolts. Because what happens when you do
have overload is, that the bolt most stressed and being at his second
failure (plastic deformation) still takes some load but also is partially
giving in and thus handing the overload to his neighboring bolts/rivets. If
that bolt would be too strong, the sheet would start to tear and this is
certainly more catastrophic than a bent bolt with an oval hole in the
sheet.

As soon as you are going away from sheet metal and do have more solid
constructions with longer bolts things are getting different and the grade
5 fraction is getting wrong.

Is that acceptable? :-)

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

How do you drill through a tube the wrong way?

Many ultralightes also have holes drilled through the tubes the wrong
way, seriously weakening the tube.

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

Ed Huntress wrote:

snip

I don't believe this argument applies to a joint consisting of a single
bolt, considered in isolation.

Thanks for an interesting discussion. This is what I come to RCM for!

Best wishes,

Chris


Since you've put some thought into this, you may find that reading a more
sophisticated engineering treatment of it would be worth your while. It's
too far in the past for me to remember much of it but there is plenty of
material on ductility and brittle failure in the field of aerospace
engineering. It's a very big issue there.

You could try the SAE website, which has a bookstore and white papers in
the aerospace division.

--
Ed Huntress


Pardon the messy line wrapping - just wanted to show what's there...


http://euler9.tripod.com/analysis/asm.html



Astronautic Structures Manual (On-Line), NASA MSFC (Marshall Space
Flight Center), 1975...

snip

Cripes, there goes the next three years of spare time. g

Thank God for FEA, eh? I used to try to optimize spaceframe structures by
hand. I spent most of a year, when I was 18, trying to optimize a little
Lotus-type frame that I designed, using a slide rule and paper. Now I can
change an element or two and run the whole stress/strain analysis in less
than 30 seconds. And if I spent serious money on the software I could even
let the program do the optimizing for me.

However, you still have to know what it is you're analyzing. You have to be
able to look at a design and smell where there could be trouble.

--
Ed Huntress

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

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.

OK. Now I got you. The image were several rows of bolts (classical sheet
overlapping joint) that are calculated more like rows of rivets. Not yet
fully convinced that a stronger bolt has an disadvantage (except the
price). *)
But anyhow, the point is more the hole in the sheet and its projected
surface area that has to accept a certain pressure (when shearing) and you
can't make the bolt smaller because of the pressure. The clamping force is
(almost) ignored in that setup. But maybe that was an old approach in
design. I know, that joints like these are now glued (to take the shear)
and screwed/riveted) to take the peeling forces.

Yes! And you've identified an issue here that most people miss: Those
rivet-bonded wing skins and so on are *not* designed to share the load
between the glue and the rivets. The rivets are just there to prevent peel
and cleavage, failure modes in which high-strength epoxy is very weak. But
the glue is much stronger at resisting shear than an all-riveted joint would
be, even one that's optimized for resolving the shear loads in the rivets.


*)
But I also got your point about distributing load and what happens if one
joint fails and you get an avalanche failure of the neighboring joints.

Yes, but that's only one of the issues with ductility in fastening. As I
mentioned, I'm too rusty to get into the whole schtick, but there are other
reasons you need ductile fasteners, as well. Sometimes.



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

--
Ed Huntress

On Sat, 19 Jan 2008 02:56:38 -0500, "Ed Huntress"
wrote:

Either the bars are weaker (the bolt will tear through one of the bars
when the joint fails), or the bolt is weaker (the bolt will fail in
shear).
=============
And herein lies the rub.

Proper lap joints *NEVER* rely of fastener shear strength. The
proper function of the fastener is to clamp the surfaces together
such that friction between the two is what resists the load. For
location in such a situation you would use dowel pins, but still
rely *ONLY* on the friction the fasteners generate by clamping
the surfaces together for strength.

In correctly designed and assembled lap joints, any axial failure
should be in the base/joint material. If this is not the case
(i.e. fastener shear failure), using more but smaller fasteners
to more evenly distribute the clamping (and friction) across the
joint, or "washers" to distribute the clamping force is
indicated, not harder bolts.

While stronger bolts may allow increased assembly torque and
therefore higher clamping force/pressure on the joint members at
assembly and thus "solve" the problem, it is due to the higher
clamping force and not the "harder" bolt.

Fine v course threads, assembly techniques [thread
lube/antiseize] and applied torque are also factors. Harder
bolts are also less prone to cold flow/creep under stress, and
thus may maintain joint clamping pressure better than lower grade
fasteners. Joint member material can also be a problem in this
regard if enough cold flow occurs to reduce the clamping pressure
and thus the friction, and periodic re-torquing may be required
to maintain joint strength.

"F. George McDuffee" wrote in message
...
On Sat, 19 Jan 2008 02:56:38 -0500, "Ed Huntress"
wrote:

Either the bars are weaker (the bolt will tear through one of the bars
when the joint fails), or the bolt is weaker (the bolt will fail in
shear).
=============
And herein lies the rub.

Proper lap joints *NEVER* rely of fastener shear strength. The
proper function of the fastener is to clamp the surfaces together
such that friction between the two is what resists the load.

You're thinking of thick materials, George. There are lots of structural
designs in which the shear strength of the fastener is the issue, such as
riveted aircraft skins.

For
location in such a situation you would use dowel pins, but still
rely *ONLY* on the friction the fasteners generate by clamping
the surfaces together for strength.

In correctly designed and assembled lap joints, any axial failure
should be in the base/joint material. If this is not the case
(i.e. fastener shear failure), using more but smaller fasteners
to more evenly distribute the clamping (and friction) across the
joint, or "washers" to distribute the clamping force is
indicated, not harder bolts.

While stronger bolts may allow increased assembly torque and
therefore higher clamping force/pressure on the joint members at
assembly and thus "solve" the problem, it is due to the higher
clamping force and not the "harder" bolt.

Fine v course threads, assembly techniques [thread
lube/antiseize] and applied torque are also factors. Harder
bolts are also less prone to cold flow/creep under stress, and
thus may maintain joint clamping pressure better than lower grade
fasteners. Joint member material can also be a problem in this
regard if enough cold flow occurs to reduce the clamping pressure
and thus the friction, and periodic re-torquing may be required
to maintain joint strength.

On Wed, 23 Jan 2008 06:16:27 GMT, Winston
wrote:

Howard Eisenhauer wrote:
On Tue, 22 Jan 2008 01:15:05 GMT, Winston
wrote:


Howard Eisenhauer wrote:
(...)

http://tantel.ca/Waste%20Oil%20Furnace.html


Had me busting up..the ol lady was looking at me like I had gone nuts.

Great job!

Gunner



"Pax Americana is a philosophy. Hardly an empire.
Making sure other people play nice and dont kill each other (and us)
off in job lots is hardly empire building, particularly when you give
them self determination under "play nice" rules.

Think of it as having your older brother knock the **** out of you
for torturing the cat." Gunner

Dan wrote:
How do you drill through a tube the wrong way?

Many ultralightes also have holes drilled through the tubes the wrong
way, seriously weakening the tube.



He doesn't like to see holes drilled vertically in a spar tube.

Actually, he's right in that removing material from the top and bottom
do reduce the amount of bending load the tube can ultimately take before
bending permanently.

The reason is that the top and bottom are the highest stressed areas.
The top skin is normally in compression and the bottom in tension.

Drilling here reduces the amount of material to carry the load.

But, like the sleeved bolt holes he mentioned, it is unnecessary -
if the stresses at that point are below what the structure will stand.

Now, the two seaters that Clare mentioned (there is no such thing as a
two seat ultralight in the US) are considerably heavier airplanes.

At that point they probably do need the sleeves (bushings?) in the tube
to take the compression load that the wing imposes on the root connection.

At the other end of the spectrum, the mast on my sailboat (and on the
bigger boats too) have only a simile bolt pinned through an unsleeved
aluminum tube to secure the base of the mast. AND - the compression
loads on it are right near the same as the wing root compression loads
on the airplane's wing root! Interesting.

To bring it back to the thread topic...

I used grade 8's on my airplane - for the landing gear axles.

5/8" diameter by 5 to 6 inches - to fit the wheels you want ti use.
The heads are cross-drilled for a 3/16 (AN-3!) bolt that attaches to the
shock absorber tubes (telescoping tubes with bungees).

After drilling a 3/16 hole through the heads, there is not a lot of
metal left - but we've never had a failure there.

So we can conclude that the stresses imposed here (gear loads are the
highest on the whole airplane) are lower than what the bolt head can
safely stand.

And - that - is all that matters.

Richard

Nick Mueller wrote:

Christopher Tidy wrote:


I'm inclined to agree with Nick here. The few times I've made this
mistake myself in the past, the joint has come loose. Sure, there are a
few instances in which it can be okay to load a bolt in shear (a shackle
for example:


Sure I'm right! ;-)
No, I got the point now. We had different pictures in our minds.
The grade-5 fraction had this in mind:
Overlapping sheet that is held together with rows of bolts. You have that
picture of several rows of rivets?
OK, here it really pays to have soft bolts. Because what happens when you do
have overload is, that the bolt most stressed and being at his second
failure (plastic deformation) still takes some load but also is partially
giving in and thus handing the overload to his neighboring bolts/rivets. If
that bolt would be too strong, the sheet would start to tear and this is
certainly more catastrophic than a bent bolt with an oval hole in the
sheet.


Excellent, Nick!


As soon as you are going away from sheet metal and do have more solid
constructions with longer bolts things are getting different and the grade
5 fraction is getting wrong.

Is that acceptable? :-)

Nick

Well, better anyway,
We can't judge this part right or wrong without putting numbers on it.

Like the example one fellow mentioned - hard bolts on an oil pan that
started breaking when they replaced the old hard gaskets with silicone.


But this outta be a good place to start for general sizing to loads...
http://trs.nis.nasa.gov/archive/0000...1/asm-B200.pdf


Richard

Ed Huntress wrote:
"F. George McDuffee" wrote in message
...

On Sat, 19 Jan 2008 02:56:38 -0500, "Ed Huntress"
wrote:


Either the bars are weaker (the bolt will tear through one of the bars
when the joint fails), or the bolt is weaker (the bolt will fail in
shear).

=============
And herein lies the rub.

Proper lap joints *NEVER* rely of fastener shear strength. The
proper function of the fastener is to clamp the surfaces together
such that friction between the two is what resists the load.


You're thinking of thick materials, George. There are lots of structural
designs in which the shear strength of the fastener is the issue, such as
riveted aircraft skins.

This is interesting. I know that in bolted steel-framed buildings, the
shear force is intended to be carried entirely by friction. But these
structures use relatively thick steel (probably 1/4" minimum) and have
high factors of safety. I'm also under the impression that it's more
acceptable for rivets to carry a shear force than bolts, because the
shank of the rivet expands to completely fill the hole when the rivet is
set.

In airframe construction, do the rivets carry a shear force in normal
operation, or only when the structure is overloaded?

Best wishes,

Chris

Ed Huntress wrote:
"cavelamb himself" wrote in message
...

Ed Huntress wrote:

"Christopher Tidy" wrote in message
...


Ed Huntress wrote:

snip

I don't believe this argument applies to a joint consisting of a single
bolt, considered in isolation.

Thanks for an interesting discussion. This is what I come to RCM for!

Best wishes,

Chris


Since you've put some thought into this, you may find that reading a more
sophisticated engineering treatment of it would be worth your while. It's
too far in the past for me to remember much of it but there is plenty of
material on ductility and brittle failure in the field of aerospace
engineering. It's a very big issue there.

I'm definitely interested in doing some reading. I'm building a small
library of engineering books at the moment.

You could try the SAE website, which has a bookstore and white papers in
the aerospace division.

--
Ed Huntress


Pardon the messy line wrapping - just wanted to show what's there...


http://euler9.tripod.com/analysis/asm.html



Astronautic Structures Manual (On-Line), NASA MSFC (Marshall Space
Flight Center), 1975...

That looks like a really useful set of books. I'd like to get a copy of
those. Anyone got a set they'd like to sell?

Cripes, there goes the next three years of spare time. g

Thank God for FEA, eh? I used to try to optimize spaceframe structures by
hand. I spent most of a year, when I was 18, trying to optimize a little
Lotus-type frame that I designed, using a slide rule and paper. Now I can
change an element or two and run the whole stress/strain analysis in less
than 30 seconds. And if I spent serious money on the software I could even
let the program do the optimizing for me.

However, you still have to know what it is you're analyzing. You have to be
able to look at a design and smell where there could be trouble.

Indeed. That's where I'm building my knowledge at the moment.

Thanks for an interesting discussion!

Best wishes,

Chris

On Sun, 20 Jan 2008 00:45:54 +0000, Christopher Tidy
wrote:

Ed Huntress wrote:

"F. George McDuffee" wrote in message
...



Proper lap joints *NEVER* rely of fastener shear strength. The
proper function of the fastener is to clamp the surfaces together
such that friction between the two is what resists the load.


You're thinking of thick materials, George. There are lots of structural
designs in which the shear strength of the fastener is the issue, such as
riveted aircraft skins.

This is interesting. I know that in bolted steel-framed buildings, the
shear force is intended to be carried entirely by friction. But these
structures use relatively thick steel (probably 1/4" minimum) and have
high factors of safety. I'm also under the impression that it's more
acceptable for rivets to carry a shear force than bolts, because the
shank of the rivet expands to completely fill the hole when the rivet is
set.


It's just not true that the joints in structural steel must always be
designed such that the joint will never slip. It may have been true,
due to conservatism, early in the transition (in the 1950s & 1960s)
from rivets to bolts in steel erection. But even when I took my
structural courses in the early 70s there was a design procedure for
joints where the bolts bear on the periphery of their holes.

It appears the use of bearing connections has become much more common,
and accepted in more situations, in the last 35 years. This is the
AISC spec for bolted joints. Section 4 includes comments on the
history and suitability of bearing connections.
http://www.boltcouncil.org/files/200...cification.pdf

(I don't mean to single you out, Chris. This has come up several times
before and is another candidate for the RCM dogma file. g)

--
Ned Simmons

Ned Simmons wrote:
On Sun, 20 Jan 2008 00:45:54 +0000, Christopher Tidy
wrote:


Ed Huntress wrote:


"F. George McDuffee" wrote in message
...




Proper lap joints *NEVER* rely of fastener shear strength. The
proper function of the fastener is to clamp the surfaces together
such that friction between the two is what resists the load.


You're thinking of thick materials, George. There are lots of structural
designs in which the shear strength of the fastener is the issue, such as
riveted aircraft skins.

This is interesting. I know that in bolted steel-framed buildings, the
shear force is intended to be carried entirely by friction. But these
structures use relatively thick steel (probably 1/4" minimum) and have
high factors of safety. I'm also under the impression that it's more
acceptable for rivets to carry a shear force than bolts, because the
shank of the rivet expands to completely fill the hole when the rivet is
set.



It's just not true that the joints in structural steel must always be
designed such that the joint will never slip. It may have been true,
due to conservatism, early in the transition (in the 1950s & 1960s)
from rivets to bolts in steel erection. But even when I took my
structural courses in the early 70s there was a design procedure for
joints where the bolts bear on the periphery of their holes.

It appears the use of bearing connections has become much more common,
and accepted in more situations, in the last 35 years. This is the
AISC spec for bolted joints. Section 4 includes comments on the
history and suitability of bearing connections.
http://www.boltcouncil.org/files/200...cification.pdf

(I don't mean to single you out, Chris. This has come up several times
before and is another candidate for the RCM dogma file. g)

That's an interesting document, Ned. Am I still right in thinking that
the bearing type of joint is less common that the friction grip type of
joint in structural engineering today? I'm a mechanical engineer rather
than a structural engineer, so I don't deal with architectural
structures on a day-to-day basis.

Best wishes,

Chris

On Sun, 20 Jan 2008 02:08:40 +0000, Christopher Tidy
wrote:

Ned Simmons wrote:
On Sun, 20 Jan 2008 00:45:54 +0000, Christopher Tidy
wrote:


That's an interesting document, Ned. Am I still right in thinking that
the bearing type of joint is less common that the friction grip type of
joint in structural engineering today? I'm a mechanical engineer rather
than a structural engineer, so I don't deal with architectural
structures on a day-to-day basis.


I'm an ME as well and haven't had any contact with actual structural
practice since I graduated in 1974. Certainly at that time friction
type connections were more common, but after looking around the web a
bit, I'm not sure that's true anymore. If I remember, I'll ask my
daughter to ask one of the structural engineers she deals with.

--
Ned Simmons

Ned Simmons wrote:


It's just not true that the joints in structural steel must always be
designed such that the joint will never slip. It may have been true,
due to conservatism, early in the transition (in the 1950s & 1960s)
from rivets to bolts in steel erection. But even when I took my
structural courses in the early 70s there was a design procedure for
joints where the bolts bear on the periphery of their holes.

It appears the use of bearing connections has become much more common,
and accepted in more situations, in the last 35 years. This is the
AISC spec for bolted joints. Section 4 includes comments on the
history and suitability of bearing connections.
http://www.boltcouncil.org/files/200...cification.pdf

(I don't mean to single you out, Chris. This has come up several times
before and is another candidate for the RCM dogma file. g)



Thank you, Ned.
Fascinating...


I wonder if the whole argument is not explained on page 9 of that doc?

Hydrogen embattlement of hot dipped galvanized bolds???

The "brittle" hard bolt legend (not myth?)...


Richard

"Christopher Tidy" wrote in message
...

snip

In airframe construction, do the rivets carry a shear force in normal
operation, or only when the structure is overloaded?

I can't answer that with authority, but the literature on joint strength in
aircraft design and testing is loaded with references to rivet shear
strength. When they talk about bearing in this context it's almost always
about the bearing of the rivet on the hole. And the references to bearing of
the faying surfaces of skin are mostly about fretting and corrosion. Also,
thermal cycling is an issue with jet airliners, and maintaining sufficient
rivet clamping tension, just to prevent the rivets becoming loaded in
tension in service, is a big problem. Certainly a rivet loaded in tension by
displacement of the skins is not contributing to friction between the skins
by its clamping force.

So it looks to me like they are designed to be loaded in shear. Maybe you
can find an aircraft engineer who can confirm it. If I had to research it
for an article I'd be calling the engineers at the rivet manufacturers.

--
Ed Huntress

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

snip

In airframe construction, do the rivets carry a shear force in normal
operation, or only when the structure is overloaded?


I can't answer that with authority, but the literature on joint strength in
aircraft design and testing is loaded with references to rivet shear
strength. When they talk about bearing in this context it's almost always
about the bearing of the rivet on the hole. And the references to bearing of
the faying surfaces of skin are mostly about fretting and corrosion. Also,
thermal cycling is an issue with jet airliners, and maintaining sufficient
rivet clamping tension, just to prevent the rivets becoming loaded in
tension in service, is a big problem. Certainly a rivet loaded in tension by
displacement of the skins is not contributing to friction between the skins
by its clamping force.

So it looks to me like they are designed to be loaded in shear. Maybe you
can find an aircraft engineer who can confirm it. If I had to research it
for an article I'd be calling the engineers at the rivet manufacturers.

--
Ed Huntress



That's pretty much my understanding of it too, Ed.


Also note that the rivets work harden from the first stroke of the gun.

But the skins don't really until the rivet is way overdriven.

Don't have a clue how to over analyze that...


Richard

Christopher Tidy wrote:

In airframe construction, do the rivets carry a shear force in normal
operation, or only when the structure is overloaded?

Can't tell for airframe, but rivet constructions are designed for shear. Or
maybe we should say the *were* constructed for shear. Don't forget, that
the holes have to be drilled (or even reamed) in place, so the two bores
align perfect.


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

Ned Simmons wrote:

Certainly at that time friction
type connections were more common, but after looking around the web a
bit, I'm not sure that's true anymore.

There do exist bolts for both. Those for shearing do have a tighter
tolerance on their shaft and the two mating bores have to be drilled in
place while erecting the building (- architectural).

Here's a link (in German), but you also get the pictu
http://www.wuerth.de/de/service/dino/07schrauben-stahlbau.html

Interesting enough, shearing (called SL) is not allowed with dynamically
loaded constructions (cranes, bridges etc). They work with friction (called
HV) and have to be precisely torqued (including rules how to regularly
check the torque and the number of samples measured).


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

On Sat, 19 Jan 2008 22:26:32 -0500, with neither quill nor qualm, Ned
Simmons quickly quoth:

On Sun, 20 Jan 2008 02:08:40 +0000, Christopher Tidy
wrote:

Ned Simmons wrote:
On Sun, 20 Jan 2008 00:45:54 +0000, Christopher Tidy
wrote:


That's an interesting document, Ned. Am I still right in thinking that
the bearing type of joint is less common that the friction grip type of
joint in structural engineering today? I'm a mechanical engineer rather
than a structural engineer, so I don't deal with architectural
structures on a day-to-day basis.


I'm an ME as well and haven't had any contact with actual structural
practice since I graduated in 1974. Certainly at that time friction
type connections were more common, but after looking around the web a
bit, I'm not sure that's true anymore. If I remember, I'll ask my
daughter to ask one of the structural engineers she deals with.

Your post reminded me of Take 6, but here are all the fun eng. jokes:
Enjoy!

--snip--

Comprehending Engineers-Take One
----------------------------------------------------
A pastor, a doctor and an engineer are waiting one morning
behind a particularly slow group of golfers. They see the
course marshal and ask why he isn't doing something to
expedite play.
"They're blind firefighters," says the marshal, "They lost
their sight saving our clubhouse from a fire last year, so we let
them have free access to the course anytime they want."
After a moment's reflection, the group responds:
Pastor: "That's so sad. I think I will say a special prayer
for them tonight."
Doctor: "I'm going to contact an ophthalmologist friend, and
see if there's anything he can do for them."
Engineer: "Why can't these guys play at night?"

------------------------------------------------------------------
Comprehending Engineers-Take Two
-----------------------------------------------------
In a high school gym class, all the girls are lined up
against one wall, and all the boys against the opposite
wall. Every ten seconds, they walk toward each other
exactly half the remaining distance between them. A
mathematician, a physicist, and an engineer are asked,
"When will the girls and boys meet?"
Mathematician: "Never."
Physicist: "In an infinite amount of time."
Engineer: "Well... in about two minutes, they'll be close
enough for all practical purposes."

------------------------------------------------------------------
Comprehending Engineers-Take Three
------------------------------------------------------
There was an engineer who had an exceptional gift for fixing
all things mechanical. After serving his company loyally for
over 30 years, he happily retired. Several years later his
company contacted him regarding a seemingly impossible
problem they were having. One of their multi-million dollar
machines wasn't working and no one knew how to fix it. The
engineer reluctantly took the challenge. He spent a day
studying the huge machine. At the end of the day he marked
a small "x" in chalk on a particular component of the
machine and proudly stated, "Replace this part and the machine
will work." The part was replaced and the machine worked
perfectly once again.
The company received a bill for $50,000 from the engineer.
They demanded an itemized accounting of his charges.
The engineer responded:
One chalk mark ........ ..... ..... $1
Knowing where to put it ... $49,999

------------------------------------------------------------------
Comprehending Engineers-Take Four
-----------------------------------------------------
Three engineers and three mathematicians are traveling by
train to a conference. At the station, the three
mathematicians each buy tickets and watch as the three
engineers buy only a single ticket.
"How are three people going to travel on only one ticket?"
asks a mathematician.
"Watch and see," replies an engineer. They all board the
train. The mathematicians take their respective seats, but
all three engineers cram into a restroom and close the door.
Shortly after the train departs, the conductor comes around
collecting tickets. He knocks on the restroom door and says,
"Ticket, please."
The door opens just a crack and a single arm emerges with a
ticket in hand. The conductor takes it and moves on. The
mathematicians see this and agree it is quite a clever idea.
After the conference, the mathematicians decide to copy the
engineers on the return trip and save some money. They buy
a single ticket for the return trip, but are astonished to
see that the engineers don't buy any ticket at all.
"How are you going to travel without a ticket?" asks one
perplexed mathematician. "Watch and see" is the answer.
They board the train, the three mathematicians cram into one
restroom and the three engineers cram into another one
nearby. Shortly after the train departs, one of the
engineers leaves his restroom and walks over to the restroom
where the mathematicians are hiding. He knocks on the door
and says, "Ticket, please."

------------------------------------------------------------------
Comprehending Engineers-Take Five
-----------------------------------------------------
The Top 10 Things Engineering School didn't teach
10. There are at least 10 types of capacitors.
9. Theory tells you how a circuit works, not why it does not
work.
8. Not everything works according to the specs in the
databook.
7. Anything practical you learn will be obsolete before you
use it, except the complex math, which you will never use.
6. Always try to fix the hardware with software.
5. Engineering is like having an 8 a.m. class and a late
afternoon lab every day for the rest of your life.
4. Overtime pay? What overtime pay?
3. Managers, not engineers, rule the world.
2. If you like junk food, caffeine and all-nighters, go into
software.
1. Dilbert is a documentary.

------------------------------------------------------------------
Comprehending Engineers-Take Six
---------------------------------------------------
Q: What is the difference between Mechanical Engineers and
Civil Engineers?
A: Mechanical Engineers build weapons, Civil Engineers build
targets.

------------------------------------------------------------------
Comprehending Engineers-Take Seven
---------------------------------------------------
Two engineering students were walking across campus when one
said,"Where
did you get such a great bike?"

The second engineer replied, "Well, I was walking along yesterday
minding
my own business when a beautiful woman rode up on this bike. She
threw
the bike to the ground, took off all her clothes and said, 'Take what
you
want.'"

"The second engineer nodded approvingly, "Good choice; the clothes
probably wouldn't have fit."

------------------------------------------------------------------
Comprehending Engineers-Take Eight
---------------------------------------------------
To the optimist, the glass is half full. To the pessimist, the glass
is
half empty. To the engineer, the glass is twice as big as it needs
to
be.

------------------------------------------------------------------
Comprehending Engineers-Take Nine
---------------------------------------------------
Normal people ... believe that if it ain't broke, don't fix it.
Engineers believe that if it ain't broke, it doesn't have enough
features yet."

------------------------------------------------------------------
Comprehending Engineers-Take Ten
---------------------------------------------------
An architect, an artist and an engineer were discussing whether it
was
better to spend time with the wife or a mistress.

The architect said he enjoyed time with his wife, building a solid
foundation for an enduring relationship.

The artist said he enjoyed time with his mistress, because of the
passion and mystery he found there.

The engineer said, "I like both."

"Both?"

Engineer: "Yeah. If you have a wife and a mistress, they will each
assume you are spending time with the other woman, and you can go to
the lab and get some work done."


------------------------------------------------------------------
Comprehending Engineers-Take Eleven
---------------------------------------------------
An engineer was crossing a road one day when a frog called out to him
and
said, "If you kiss me, I'll turn into a beautiful princess".

He bent over, picked up the frog and put it in his pocket.

The frog spoke up again and said, "If you kiss me and turn me back
into a
beautiful princess, I will stay with you for one week."

The engineer took the frog out of his pocket, smiled at it and
returned it
to the pocket.

The frog then cried out, "If you kiss me and turn me back into a
princess,
I'll stay with you and do ANYTHING you want."

Again the engineer took the frog out, smiled at it and put it back
into
his pocket.

Finally, the frog asked, "What is the matter? I've told you I'm a
beautiful princess, that I'll stay with you for a week and do anything
you
want. Why won't you kiss me?"

The engineer said, "Look I'm an engineer. I don't have time for a
girlfriend, but a TALKING frog, now that's cool."

------------------------------------------------------------------
Comprehending Engineers-Take Twelve
---------------------------------------------------
Several engineers are standing around one day trying
to decide what type of engineer must have designed
the human body. (All right, for the purpose of the joke
there is an assumption of some sort of higher being that
actually designed the human body.....work with me people.)

The chemical engineer says "the human body was designed
by a chemical engineer. Look how the body takes in
nutrients and then turns them into energy and body
parts just by re-organizing a few chemical bonds."

The electrical enginner says "the human body was
clearly designed by an electrical engineer. Just observe
how tiny electrical impulses cause the muscles to move,
cause the person to feel, see and listen to all that is
happening around them. And finally look how a few
very tiny tiny electrical impulses can store a memory
for a lifetime, and yet bring that information back at a moments
notice. Clearly the work of a brillaint electrical engineer."

The mechanical engineer says "bahh! The human body was
designed by a mechanical engineer. Notice how the muscles and the
bones work to make the body move.
Notice how the organs work to move the food and other
nutrients around to the places where they are needed."

Finally the Civil engineer pipes up and says "you're all
wrong. The human body was designed by a civil engineer.
Who else would put a waste treatment plant right next
to a recreational facility?"
--snip--

--
You cannot depend on your eyes when your imagination is out of focus.
-- Mark Twain

Nick Mueller wrote:
Ned Simmons wrote:


Certainly at that time friction
type connections were more common, but after looking around the web a
bit, I'm not sure that's true anymore.


There do exist bolts for both. Those for shearing do have a tighter
tolerance on their shaft and the two mating bores have to be drilled in
place while erecting the building (- architectural).

Here's a link (in German), but you also get the pictu
http://www.wuerth.de/de/service/dino/07schrauben-stahlbau.html

Interesting enough, shearing (called SL) is not allowed with dynamically
loaded constructions (cranes, bridges etc). They work with friction (called
HV) and have to be precisely torqued (including rules how to regularly
check the torque and the number of samples measured).

That makes sense. If bolts are loaded in shear and the load reverses,
the bolts will pretty quickly come loose.

Best wishes,

Chris