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From: Claes.Colmeus@farm.lu.se (Claes Colmeus)
Subject: Re: Holes in your bow
Date: Mon, 5 Feb 1996 10:43:08

In article <4eqimr$fd7@argentina.it.earthlink.net> Jim Buch
<jbuch@earthlink.net> writes:
>From: Jim Buch <jbuch@earthlink.net>
>Subject: Re: Holes in your bow
>Date: 1 Feb 1996 14:28:43 GMT


>I'm all ears and eyes.  I am ready,willing and able to be enlightened.

>dna1000@cus.cam.ac.uk (David Allsopp) wrote:
>>In article <Claes.Colmeus.11.000A17DB@farm.lu.se>,
>>Claes Colmeus <Claes.Colmeus@farm.lu.se> wrote:
>>

>>[Note for sci.materials readers - this thread concerns the milling/drilling
>>of holes in the alloy centre section (riser) of archery bows]
>>
>>>>> Oh -- holes also do a fourth thing: they make the riser weaker...
>>
>>>Not necessarily so. In fact, correctly shaped and placed holes can 
>>>actually improve strength by distributing stress concentrations. 
>>
>>Are you sure about this? Holes *create* stress concentrations. The only
>>case I can think of where a hole improves the stress distribution is if
>>it is drilled at the apex of a crack or notch, thereby blunting the notch.
>>(eg drilling holes at each end of a crack in a perspex sheet to stop the
>>crack growing)
>>
>>Have you ever 
>>>tried to tear perforated  paper? Does it ever part in the perforation? 
>>
>------
>>It can 
>>>be shown, even in theory, that a reasonable amount of perforation, especially
>>>with round holes, will improve the strength of any sheet material. 
>>------------
>>Do you have any references/calculations for this effect? 
>>David.

This thread is getting a bit complicated to follow with all the >>>>.  Maybe 
the reason for David's flames is that we don't mean the same thing with 
"weakening" and "strength". It is obvious that any hole will make the riser  
(or any metal contraption) less rigid. However, this can be the key to better 
resistance to failure. Too much rigidity in the wrong place will create stress 
concentrations and promote failure from inherent small material faults 
and/or fatigue. And David himself gives the other half of the key: he 
recognizes the method to stop cracks with a drilled hole at it's end, 
distributing the stress concentration created by the very shape of the 
crack.

That's the reason for a perforation often being the strongest place of a 
sheet (NOT the most rigid one): it can distribute stress by stopping cracks, 
and by being more flexible than the rest of the sheet.

I don't have any references or calculations. The matter came up during a 
lecture in materials engineering here at the univ. of technology ca 1965. My 
old notes are gone, but I remember that the discussion was about the 
all-welded supertankers that broke in two pieces and sank, even in rather fair 
weather. The reason was fatigue from stress concentrations in a too rigid 
design. This type of accident was almost unheard of in riveted ships, the 
reason being the riveted jointsare more flexible, thus stress-distributing. 
Also, a material failure in a riveted joint would only propagate to the next 
rivet and stop there. Riveted joints have a remarkable reliability. Even 
riveted boilers seldom failed in the joints. Also note that aircraft are 
riveted, not welded. I don't think perforation would be the optimum solution 
for supertankers though, as it might create other problems.

As for tearing paper, the main reason for a succesful result is that we have 
learnt to tear in such a way that the stress is concentrated in the 
perforation. I made a few practical tests with toilet paper. The one at home 
parted nicely in the perforation about 8 of 10 times, even though I tore 
rather carelessly. The failures usually started OK but the tear then left the 
perforation and continued in the "solid" material. The university toilet paper 
was a disaster, needing a sharp edge or the utmost care to tear in the 
perforation. Otherwise it would fail anywhere. The difference? The paper at 
home was perforated to 80% with sharp-edged slits. The perforation at my job 
was about 60%, also with sharp-edged slits. Thus the perforation was in some 
sense about twice as strong as the solid material.

Stamps are notorious for stealing pieces of their neighbour, or leaving part 
of themselves, unless you really take care. They have the worst type of 
perforation, round holes in good quality paper. They act like riveted 
joints, stopping cracks and distributing stress.

This is getting a bit far from archery, and anyway, we usually want a rigid 
riser, not a flexible one. Neither do we usually stress our bows until they 
start to crack.

Let's shoot arrows instead

Claes

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

From: dna1000@cus.cam.ac.uk (David Allsopp)
Subject: Re: Holes in your bow
Date: 5 Feb 1996 15:01:02 GMT

In article <Claes.Colmeus.12.000AB85F@farm.lu.se>,
Claes Colmeus <Claes.Colmeus@farm.lu.se> wrote:

>That's the reason for a perforation often being the strongest place of a 
>sheet (NOT the most rigid one): it can distribute stress by stopping cracks, 
>and by being more flexible than the rest of the sheet.

However, this cannot make the sheet as a whole any stronger, since the sheet
will fail at the weakest point - if one small part of it becomes stronger
by perforations it will just fail elsewhere. So the holes can't add strength
to the sheet.

Drilling holes to stop an existing crack does not improve the strength of the
object but merely stops it getting worse. 

If you have a smooth riser with no steps in the profile, there are no special
points which can acts as stress concentrations. Driling holes is the riser
won't improve this, and will only add stress concentrations. Such holes
will just save weight. If the riser has steps or grooves machined into it,
the stress concentrations from these could be relieved (perhaps) by adding
holes.

>I don't have any references or calculations. The matter came up during a 
>lecture in materials engineering here at the univ. of technology ca 1965. My 
>old notes are gone, but I remember that the discussion was about the 
>all-welded supertankers that broke in two pieces and sank, even in rather fair 
>weather. The reason was fatigue from stress concentrations in a too rigid 
>design. 

It's not rigidity alone which causes problems, but changes in rigidity - if
you have a metal rod, half of which is 10mm diameter and half 5mm diameter
it will be less strong than an rod all of which is 5mm diameter, because
the step in thickness halfway along the rod concentrates the stress.

Welds can be a problem, as you say, because a crack can run all along the weld.
Welds may also become embrittled, and can introduce residual stresses even
before you've loaded the structure.

>I made a few practical tests with toilet paper. The one at home 
>parted nicely in the perforation about 8 of 10 times, even though I tore 
>rather carelessly. The failures usually started OK but the tear then left the 
>perforation and continued in the "solid" material. 

If it parted in the perforation then the perforation was weaker, not stronger,
and the paper as a whole must have been weaker.

I suspect the effects of perforations may also be different for brittle 
materials, ductile materials, and fibrous (paper) materials, and will depend
on what inherent flaws are present in the material.

David.

--
David Allsopp, Department of Materials Science and Metallurgy, 
Cambridge University, UK.            Email: dna1000@cam.ac.uk.

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

From: Claes.Colmeus@farm.lu.se (Claes Colmeus)
Subject: Re: Holes in your bow
Date: Tue, 6 Feb 1996 12:18:34

In article <4f563e$qjn@lyra.csx.cam.ac.uk> dna1000@cus.cam.ac.uk (David Allsopp)
writes:
>From: dna1000@cus.cam.ac.uk (David Allsopp)
>Subject: Re: Holes in your bow
>Date: 5 Feb 1996 15:01:02 GMT

>In article <Claes.Colmeus.12.000AB85F@farm.lu.se>,
>Claes Colmeus <Claes.Colmeus@farm.lu.se> wrote:

>>That's the reason for a perforation often being the strongest place of a 
>>sheet (NOT the most rigid one): it can distribute stress by stopping cracks, 
>>and by being more flexible than the rest of the sheet.

>However, this cannot make the sheet as a whole any stronger, since the sheet
>will fail at the weakest point - if one small part of it becomes stronger
>by perforations it will just fail elsewhere. So the holes can't add strength
>to the sheet.

No, but in a design with a known weak spot, caused by a stress concentration, 
it can be relieved by a well designed perforation.

>Drilling holes to stop an existing crack does not improve the strength of the
>object but merely stops it getting worse. 

Of course, but also a new crack from fatigue, manufacturing faults, design 
faults etc will be stopped. I don't mean that any material in any situation 
will be stronger, my point is that failure in a sheet with an uneven and/or 
varying load seldom takes place in the perforation, because of the flexibility 
and the tolerance to cracks.

>If you have a smooth riser with no steps in the profile, there are no special 
>points which can acts as stress concentrations. Driling holes is the riser 
>won't improve this, and will only add stress concentrations. Such holes 
>will just save weight. If the riser has steps or grooves machined into it, 
>the stress concentrations from these could be relieved (perhaps) by adding 
>holes.

We seem to agree.

>>I don't have any references or calculations. The matter came up during a 
>>lecture in materials engineering here at the univ. of technology ca 1965. My 
>>old notes are gone, but I remember that the discussion was about the 
>>all-welded supertankers that broke in two pieces and sank, even in rather fair
>>weather. The reason was fatigue from stress concentrations in a too rigid 
>>design. 

>It's not rigidity alone which causes problems, but changes in rigidity - if
>you have a metal rod, half of which is 10mm diameter and half 5mm diameter
>it will be less strong than an rod all of which is 5mm diameter, because
>the step in thickness halfway along the rod concentrates the stress.

And a change in rigidity could be made more gradual by drilling holes. 

>Welds can be a problem, as you say, because a crack can run all along the weld.
>Welds may also become embrittled, and can introduce residual stresses even
>before you've loaded the structure.

And these residual stresses could be relieved by a clever perforation. OK, 
there are better methods, especially for marine applications.  Welded 
construction is a field where rigidity is a problem, because residual stresses 
will remain and cause premature failures.


>>I made a few practical tests with toilet paper. The one at home 
>>parted nicely in the perforation about 8 of 10 times, even though I tore 
>>rather carelessly. The failures usually started OK but the tear then left the 
>>perforation and continued in the "solid" material. 

>If it parted in the perforation then the perforation was weaker, not stronger,
>and the paper as a whole must have been weaker.

My point here was that even an extensive perforation (80% of the material 
gone) does not guarantee that a failure will continue along the perforation, 
but will often propagate in the unperforated material instead. And the paper 
with a lesser degree of perforation failed just anywhere. 

>I suspect the effects of perforations may also be different for brittle 
>materials, ductile materials, and fibrous (paper) materials, and will depend
>on what inherent flaws are present in the material.

That's my point too, perforations will prevent the ill effects from inherent 
flaws to spread, thus making the material less prone to total failure.

Too much of our disagreement seems to be more semantic than real, let's go use 
our bows instead, with holes or without holes.


Claes
------------------------------------------------------------------------------
From: jdickson@festival.ed.ac.uk (John Dickson)
Subject: Re: Holes in your bow
Date: 6 Feb 1996 13:09:48 GMT

Hywel Owen <h.owen@dl.ac.uk> writes:

>Claes Colmeus wrote:
>> > 
>> This is getting a bit far from archery, and anyway, we usually want a rigid
>> riser, not a flexible one.

>Is this true? Do we want a completely rigid riser? Why was the 
>Avalon developed after the supposedly 'perfect' Radian riser?

I think we've come in full circle again! Unfortunately it doesn't matter
how *perfect* your riser is, if your archer and your limbs are not as
perfect. In theory the Radian is more accurate than the Avalon, in
practise it TENDS to be the reverse because the Avalon is easier on the
limbs and on the archer ie a little flexibility seems to be associated
with easier tuning.

The Radian and Avalon are both top of the range bows but it's up to the
archer to pick the one which suits him/her the best.

All my usual tosh of course,

                                
John Dickson,(aka Stretch) 
------------------------------------------------------------------------------

From: bo448@torfree.net (Rob Lee)
Subject: Re: Holes in your bow
Date: Tue, 6 Feb 1996 12:43:56 GMT

OK It's been quite some time (undergraduate engineering :-) ) since I did much
stress analysis, etc. but here are a few comments:

a beam loaded in bending (like a riser) has tensile stress along one side (the back
of the riser) and compressive stress along the other (the face), while along a line
in between you have zero stress -- the neutral axis.

The stresses vary from tensile through zero to compressive from the back to the face.
You don't *need* any material along the neutral axis, except to keep the back and the
face apart, which is why 'I' beams have the shape they do -- the wide flanges take the
stresses while the thin web keeps them separated using the minimum material.

So, you can thin or even put holes in a riser near the neutral axis to make it lighter without
_significantly_ affecting the strength, providing you do it _correctly_.

Of course, the foregoing ignores the fact that the riser has to curve to give you a sight
window and must withstand some lateral bending and torsional stresses as well... so 'doing
it correctly' is non-trivial, as the neutral axis will meander through three dimensions
-- and then there's the matter of the *dynamic* stress levels... which gets into
the area of fatigue... ack!

Rob Lee

------------------------------------------------------------------------------
From: tim@housenet.demon.co.uk (Tim Mundon)
Subject: Re: Holes in your bow - Riser Strength
Date: Wed, 07 Feb 1996 00:25:12 GMT


I am afraid that in my opinion weight is important, in fact it is
critical, not nececerrly just the physical weight in your hand but the
distribution of weight throughout the bow, 
        you cannot compare the differences in weights of stabilisers
against weights of risers as they are intended for specifically
different jobs. 
        The feel of the bow and the way it reacts are all linked to
the weight of the riser
        Besides, if you had a CNC'd riser without holes and the same
shape...i.e. the radian  then it would be very!  heavy
         
Tim Mundon

tim@housenet.demon.co.uk
spe4trm@cf.ac.uk

From: Hywel Owen <h.owen@dl.ac.uk>
Subject: Re: Holes in your bow
Date: Tue, 06 Feb 1996 12:08:56 +0000

Claes Colmeus wrote:
> > 
> This is getting a bit far from archery, and anyway, we usually want a rigid
> riser, not a flexible one.

Is this true? Do we want a completely rigid riser? Why was the 
Avalon developed after the supposedly 'perfect' Radian riser?

Hywel
'Questions, questions, too many questions.....'
----------------------------------------------------------------------
Subject: Re: Holes in your bow
Date: Wed, 7 Feb 1996 14:50:24
In article <311744D8.4D93@dl.ac.uk> Hywel Owen <h.owen@dl.ac.uk> writes:
>Claes Colmeus wrote:
>> > 
>> This is getting a bit far from archery, and anyway, we usually want a rigid
>> riser, not a flexible one.
>Is this true? Do we want a completely rigid riser?
Well, I do anyway, and flexible limbs.
>Why was the Avalon developed after the supposedly 'perfect' Radian riser?
Don't ask ME that, I plead 'not guilty' of both Radian and Avalon. I haven't 
even tried them, just seen the price tag here (about $1700!) and quickly 
looked the other way to avoid starvation the next three months. 
>'Questions, questions, too many questions.....'
Answers, answers, too few answers.....   BTW, What's life?...
Claes
------------------------------------------------------------------------------
From: jdickson@festival.ed.ac.uk (John Dickson)
Subject: Re: Holes in your bow
Date: 8 Feb 1996 11:11:40 GMT

ldiehr@eth233.eld.ford.com (L S Diehr (Lawrence)) writes:

>The holes serve the same purpose as the holes in Swiss Cheese.  They 
>provide a place for archers to store small amounts of stale air that 
>can be reclaimed in times of great angst and released on the unsuspecting
>shooting line along with appropriate sound effects.  

Oh god we've come full circle, similar thread about 18 months ago!

include>
--------------------------------------------------------------------

In article sb3@lyra.csx.cam.ac.uk, R Ascham writes:
> Yeah seems like ages, but I'm working on a new book about bows thru'
> the ages. These new fangled ones with bits cut out look very
> interesting. Anyone know why the holes are the same shape as those
> little cheeses that come in round boxes??

When you pay a thousand pounds for your bow Hoyt throw in a free
lunchbox???

I believe that extensive research by Hoyt has found that when you make a
bow very light there is nothing to absorb vibration. Further to this they
found that Dairylea Cheese had excellent vibration damping properties. By
cutting the wholes in the radian this shape (they were of course
originaly heart shaped), Hoyt found that they could use Dairylea to dampen
the vibrations in the Radian.

Please note that the Dairylea Damping system is an optional extra with
the Radian. It is available at most good stores from around a pound for 8
segments. Hoyt recommend that segements are replaced frequently, especially
on hot days.

WARNING!!: If your segements begin to drip or smell dispose of them
immediately or four legged animals will begin to take interest in your
equipment. Often resulting in a squatting action or a lifting of the rear
leg.

end include
---------------------------------------------------------------------

Hey did that Cheese and Wine party ever happen in Cambridge? Or does
nobody know what the hell I'm on about?

                               
John Dickson,(aka Stretch)     
------------------------------------------------------------------------------

From: jdickson@festival.ed.ac.uk (John Dickson)
Subject: Re: Holes in your bow - Riser Strength
Date: 8 Feb 1996 11:00:22 GMT

tim@housenet.demon.co.uk (Tim Mundon) writes:
 
>I am afraid that in my opinion weight is important, in fact it is
>critical, not nececerrly just the physical weight in your hand but the
>distribution of weight throughout the bow
 
This is nothing to do with physical mass, it's mass distribution ie
balance. A badly balance bow will feel like a lead weight a better
balanced bow *feels* lighter. eg the Spigarelli 1300 feels lighter than
the Hoyt TD4+ although the mass is very similar. I believe that the
Avalon and Radian are similar. (Although the Radian is still well
balanced)
 
Within reason, mass of the handle is not important. Balance is.
 
>       you cannot compare the differences in weights of stabilisers
>against weights of risers as they are intended for specifically
>different jobs.

Mmmm, there are arguments for heavy/light stabilisers which are not the
issue here. I do agree with Hewyl that the overall mass of your setup
can be important. I also wouldn't say that stabilisers and risers are
intended for specifically different jobs. Both of their jobs being to
asisst in the clean, accurate launch of an arrow with as little wasted
energy as possible and as much comfort as possible to the archer.
 
>       The feel of the bow and the way it reacts are all linked to
>the weight of the riser
 
I feel that the bow reaction is dependent on the total weight and
balance of the shooting system including length of riser, limb, draw
weight, draw length, grip shape, stabilisers, sight and anything else
that the bow has on it.
 
>       Besides, if you had a CNC'd riser without holes and the same
>shape...i.e. the radian  then it would be very!  heavy

I think if you CNC'd a bow the same shape as the Radian without holes
you'd be retarded ( sorry ;-) )The whole shape of the bow is developed
around the holes. If you CNC'd a bow like the original Stylist, it
wouldn't have holes and it would be a reasonable weight, in fact you'd
have a Stylist (Insert: Monarch, Advantage, OK, Atletic or any other non
holey machined riser that takes you're fancy)
 
Holes are not essential to a good riser (eg Atletic and Stylist). In
fact if you put the holes in the wrong place you're riser will be a lot
worse than if it where solid. Look at the Advantage and the Monarch,
only one of them can have got the shape right (I won't say which) but
both handles shoot very well.

Fortunately most of the holey bows so far have been designed properly!
 
However, if I was going to choose a handle I'd go for the Supreme or the
Avalon for completely different reasons, not because they have holes but
because of their shooting characteristics.
 
All my opinion, you're welcome to yours but I'll probably disagree just
for the hell of it ;-)
 
                                Stretch

PS Tim you have you're follow-ups set to your E-mail address, screws my
newsreader for sure!
--
John Dickson,(aka Stretch)  
------------------------------------------------------------------------------------
From: Brian LaBorde 
Subject: Re: Holes in your bow - The Truth
Date: Thu, 15 Feb 1996 18:37:02 -0500

Hi...
I am Bear/Jennings design engineer and I design the handles you are
 referring to. I have been doing this for 7 years. I have a masters
 in mechanical engineering with a specialty in composites and finite
 element stress analysis. This compels me to respond to all of the
 mis-information that has been posted.
Let me start off by responding to some of the things that have been
 said and then address the bow handle issue. 
------------------------------------------------------
> >>>>> Oh -- holes also do a fourth thing: they make the riser weaker...

Yes... they do...

> >>>Not necessarily so. In fact, correctly shaped and placed holes can
> >>>actually improve strength by distributing stress concentrations.

No... (more later as to why)

> >>Are you sure about this? Holes *create* stress concentrations. The only
> >>case I can think of where a hole improves the stress distribution is if
> >>it is drilled at the apex of a crack or notch, thereby blunting the notch.
> >>(eg drilling holes at each end of a crack in a perspex sheet to stop the
> >>crack growing)

Yes Exactly. A stress concentration is caused by a disruption in the flow of
 stress. It actually can be visualized to flow like water. If it has to flow
 around a crack, the stress flow "concentrates" around the crack tip. The
 magnitude of the stress concentration is governed by the radius, or effective
 radius for non-round holes, of the corner it has to go around. A crack has a
 zero (approximately, or better yet theoretically) radius, whereas a hole
 replacing the crack tip has a much more finite, larger radius. It is this
 fact and no other that reduces the stress concentration. Let me back up my
 argument with a quote from my fracture mechanics text, Deformation And
 Fracture Mechanics Of Engineering Materials, Richard W. Hertzberg,
 third edition - page 243:
"Many textbooks and standard handbooks describe stress concentrations in
 components with a wide range of crack configurations. Although the exact
 formulations vary from one case to another, they all reflect the fact
 that kt (the stress concentration factor) increases with increasing crack
 length and decreasing radius. ...... once a crack has developed, the
 relative severity of the stress concentration can be reduced by drilling
 a hole through the crack tip. In this way p (the crack effective radius
 or curvature) is increased from a curvature associated with a natural,
 sharp crack to that of the hole radius."

> >>Have you ever tried to tear perforated  paper? Does it ever part in the
    perforation?
> >>It can be shown, even in theory, that a reasonable amount of perforation,
    especially
> >>with round holes, will improve the strength of any sheet material.

This is absurd. In no case can removing material increase the strength of a
 member. As stated above it can help crack propagation, but never does a
 perforation or any holes increase the strength of a material section. Can you
 show me this theory?

>  Maybe the reason for David's flames is that we don't mean the same thing with
> "weakening" and "strength". It is obvious that any hole will make the riser
> (or any metal contraption) less rigid.

Yes... 

> However, this can be the key to better
> resistance to failure. Too much rigidity in the wrong place will create stress
> concentrations and promote failure from inherent small material faults
> and/or fatigue. And David himself gives the other half of the key: he
> recognizes the method to stop cracks with a drilled hole at it's end,
> distributing the stress concentration created by the very shape of the
> crack.

No. There is no such thing as too much rigidity in a member, assuming you are
 speaking of a homogenous, isotropic material (a single material that has all
 of the same properties in all different directions). Any additional material
 will decrease the stress, by some amount. Granted if the material is in an area
 that already has nearly zero stress, the material is not carrying any appreciable
 load and it's removal will not significantly increase the stresses in proximity,
 but again never does removing material increase strength. (Note: this is assuming
 that the material's weight is not a factor.) For example, look at an I-Beam.

The material on the top and bottom is stressed the most but the material in the
 center is close to, or on the neutral axis (the axis where there are little to
 no tensile or compressive loads). So designers took the material away from that
 area and just left the material "flanges" on the ends of the beams. Thereby allowing
 the "flanges" to carry the tensile loads and the "web" to transfer the shear
 stresses between the "flanges".

> That's the reason for a perforation often being the strongest place of a
> sheet (NOT the most rigid one): it can distribute stress by stopping cracks,
> and by being more flexible than the rest of the sheet.

Yes and No. The perforation is not the strongest place, or the most rigid one.

Now what you are confusing is strength, rigidity and flexibility. An area with
 perforations increases the stresses in that area to a point where the stresses
 in that area will yield before the rest of the material, and possibly fail before
 anywhere else in the material. This is why the perforations are put there. Now,
 being more flexible, the material will yield to the loads and hold less of the load.
 This yielding can allow the load to shift to another part of the material thereby
 increasing the stresses at another point and possibly causing failure, because of
 a change in loading geometry, not re-distribution of the stresses. Understand, it
 is not that the perforations are stronger, but they allow the loads to be carried
 by another part of the member, causing it to fail. What I am describing is not a
 change in the stresses or failure location because the holes are put there, but due
 to the flexibility of the material with the perforations , the GEOMETRY of the part
 changes, causing changes in the way the loading is handled, thereby causing failure
 at a point other than the predicted perforated location.

> I don't have any references or calculations. The matter came up during a
> lecture in materials engineering here at the univ. of technology ca 1965. My
> old notes are gone, but I remember that the discussion was about the
> all-welded supertankers that broke in two pieces and sank, even in rather fair
> weather. The reason was fatigue from stress concentrations in a too rigid
> design. This type of accident was almost unheard of in riveted ships, the
> reason being the riveted joints are more flexible, thus stress-distributing.
> Also, a material failure in a riveted joint would only propagate to the next
> rivet and stop there. Riveted joints have a remarkable reliability. Even
> riveted boilers seldom failed in the joints. Also note that aircraft are
> riveted, not welded. I don't think perforation would be the optimum solution
> for supertankers though, as it might create other problems.

The ships you are probably referring to are the Liberty ships, that were one of,
 if not the first all welded design ship. You can look back at case studies on
 this for more detailed information. The Liberty ships failed for a couple of
 reasons. Constructing the ship in an all welded design had a few consequences,
 not fully understood or accounted for at that time.
 
First, you are correct in that the welded design was more rigid, and in higher
 seas the ship had to accept the stresses induced by the seas versus flexing with
 the seas. This was a factor, but the ship, in a riveted design, wouldn't have
 flexed enough to fully compensate for the seas. The ship would have to move tens
 of feet to compensate for the seas, not an option. 
 Second, as you mentioned, the riveted design did serve as a crack arrester.
 Cracks  propagating across a panel would not initiate in the next because of the
 riveted joint. This is to say the cracks may have existed in a riveted design, but not
 resulted in a catastrophic failure. The holes in the panels are not responsible
 for this, but the fact that the panels were independent of each other.
The other consideration not known at the time is the effects of welding steel.
 Welds cause a number of problems. They can have voids in them causing a stress
 concentration factor and an initiation site for crack propagation. And, as the
 weld is applied, with the temperatures associated with welding, the crystalline
 structure of the surrounding metal is affected on the atomic level as well as
 leaving micro-cracks around the weld. These factors alone may not have caused
 catastrophic failure but combined with the lack of knowledge, at the time, of
 the transition temperature phenomenon, they did result in the failures. Let me
 again quote the same book as above, Page 325:
"Of considerable importance in pressure vessel and bridge and ship structure
 applications was the fact that in body-centered-cubic metals, such as ferritic
 alloys, the yield strength is far more sensitive to temperature and strain rate
 changes than it is in face-centered-cubic metals, such as aluminum, nickel,
 copper, and austenitic steel alloys."
In conclusion the combination of all these factors attributed to the Liberty ship
 failures. Cracks that either initiated in welds or near welds due to existing
 inclusions in welds, or from stress concentrations near the weld site, propagated
 across panels that were more sensitive to strain rate and or operating
 temperatures, and were not arrested by joints that were previously riveted,
 caused catastrophic failure.
I am quoting all of this from memory, for a more detailed account of this
 failure and more failures, read a book named "To Engineer Is Human". I do not remember
 the author, but is an excellent book.
Getting back to the topic, what does this have to do with bows, except to show
 that it was not the holes that made the riveted ships survive, but other factors
 have to be accounted for.

> As for tearing paper, the main reason for a successful result is that we have
> learnt to tear in such a way that the stress is concentrated in the
> perforation. I made a few practical tests with toilet paper. The one at home
> parted nicely in the perforation about 8 of 10 times, even though I tore
> rather carelessly. The failures usually started OK but the tear then left the
> perforation and continued in the "solid" material. The university toilet paper
> was a disaster, needing a sharp edge or the utmost care to tear in the
> perforation. Otherwise it would fail anywhere. The difference? The paper at
> home was perforated to 80% with sharp-edged slits. The perforation at my job
> was about 60%, also with sharp-edged slits. Thus the perforation was in some
> sense about twice as strong as the solid material.
> 
> Stamps are notorious for stealing pieces of their neighbour, or leaving part
> of themselves, unless you really take care. They have the worst type of
> perforation, round holes in good quality paper. They act like riveted
> joints, stopping cracks and distributing stress.

One very important aspect you are not taking into consideration is the material
 itself and not just the perforations. Paper is not a homogenous material, It is
 made from wood and is fibrous. Any material will fail at the weakest point. The
 old adage about the chain breaking at the weakest link is still true. What happens
 with paper, especially cheap paper, is the fibers tends to be fairly large.
When you are tearing the paper along the perforations, the tear may hit a fiber/fibers
 broad side. The weakest point is not across the fiber but along the fiber, so the
 tear will skew off the perforation. Perforations in higher quality paper is easier
 to tear because the more refined paper tends to have a finer fiber.

As far as why there are holes in risers, no it is not for wind resistance. If you
 are shooting in a cross wind of the magnitude to make the bow move, having a
 cross section of only a couple of inches wide, then you should be more concerned
 about the wind's effect on the arrow instead. Holes were originally put in
 machined risers to make them lighter. (See above section concerning I beams).
It is possible to remove material near the neutral axis and not dramatically
affect the strength of the handle. In no case does adding holes strengthen the handle,
 only make it lighter. The irony is if the public did not have the mis-conception
 that a light handle must have holes in it, manufacturers could make even lighter
 handles. Just like an I beam, the web material does transfer the shear stresses
 and allow a smaller cross section, translating into a lighter handle. A lot of
 theory has been developed on this concept in I beam design as well as aircraft
 structures (the monocoque design), where the ribs/flanges handle the tensile
 loads and the skin/web transfers the shear loads, but this is another topic
 altogether. For further reading on this, see Introduction to Aerospace
Structural Analysis, David Allen & Walter Haisler, pp 205 - 221, 
(chapter covering shear in advanced beams).


-- 
Brian LaBorde

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

From: jdickson@festival.ed.ac.uk (John Dickson)
Subject: Re: Holes in your bow - The Truth
Date: 16 Feb 1996 10:42:45 GMT

Brian LaBorde  writes:

< Snip, A very proffesional an knowledgeable reply>

I tried to keep out of this thread once we elevated past "increases
strength to weight ratio". It's great that you took the time to write
such a detailed post. Thanks.

                                Stretch

PS If I'd only drilled a hole in my KG1 it might still be going (as
opposed to sitting around at home in 2 bits) ;-)
--
John Dickson,(aka Stretch)

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

From: ldiehr@eth233.eld.ford.com (L S Diehr (Lawrence))
Subject: Re: Holes in your bow - The Truth
Date: 16 Feb 1996 15:53:28 GMT

Brian LaBorde (laborde@atlantic.net) wrote:
: Hi...
: I am Bear/Jennings design engineer and I design the handles you are



Thankyou Brian for your engineering analysis.  This all goes to prove my point 
that those holes are there to hold the hot air that archers all tend to give off
on a regular basis. :-).

: -- 
: Brian LaBorde
: mailto://laborde@atlantic.net
: http://rio.atlantic.net/~laborde/
: Design Engineer - Bear / Jennings Archery

--
Larry Diehr



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