Rod Wuetherick on sat 23 apr 05
> always thought porcelain was inherently stronger than stoneware, but it
> seems I may be wrong about this. Maybe porcelain has the reputation for
> being stronger because people who make it are somehow more careful to
> formulate and fire it correctly.
I also thought this as well, actually I still mostly do. Though for
differing reasons from this current thread and I would appreciate other
opinions on this.
I was under the impression from literature I have read (Parmlee, Hamer, etc)
that one of the defining factors which separates stoneware/porcelains from
earthenware is "mullite spinel" formation which has been gathered from
recent scientific observation and cold hard data.
I thought it was fairly well proven that earthenware does not reach the
temperatures required to produce mullite spinels. It is my impression a
correctly fired porcelain would also then be somewhat stronger than a
stoneware and certainly stronger than earthenware because a) it produces
mullite spinels b) there is less free silica to produce crystobolite than
either stoneware or earthenware. Is this correct? True in theory but shown
to be false in testing?
So even with equally perfectly fitting glazes, slightly in compression
(among all the bodies), it would seem that at least theoretically, that
porcelain stands to have the greatest possible durability.
But theory aside, I thought Tony Hansen (and Ron Roy?) did extensive tests
on various clay bodies looking for this type of data? I would be interested
in seeing those results.
peace,
Rod
Ron Roy on mon 25 apr 05
Hi Rod,
I have never tested any clay bodies for relative strength - I know I should
have but never had the machines to do it.
I must admit that I do not see this as being the most important aspect - I
think properly fitting glazes is a much more important factor.
I would be interested in submitting samples of clays to be tested - all we
need is someone with the proper equipment and the mentality to do a proper
job.
Find me the right equipment and I will do it - RR
RR
>But theory aside, I thought Tony Hansen (and Ron Roy?) did extensive tests
>on various clay bodies looking for this type of data? I would be interested
>in seeing those results.
>
>peace,
>Rod
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Louis Katz on tue 26 apr 05
Do you want to test tensile or compressive strength?
We have a concrete testing machine at school. Compressive.
Louis
On Apr 25, 2005, at 1:45 PM, Ron Roy wrote:
> Hi Rod,
>
> I have never tested any clay bodies for relative strength - I know I
> should
> have but never had the machines to do it.
>
> I must admit that I do not see this as being the most important aspect
> - I
> think properly fitting glazes is a much more important factor.
>
> I would be interested in submitting samples of clays to be tested -
> all we
> need is someone with the proper equipment and the mentality to do a
> proper
> job.
>
> Find me the right equipment and I will do it - RR
>
> RR
>
>
>> But theory aside, I thought Tony Hansen (and Ron Roy?) did extensive
>> tests
>> on various clay bodies looking for this type of data? I would be
>> interested
>> in seeing those results.
>>
>> peace,
>> Rod
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
>
Louis Katz
http://www.tamucc.edu/~lkatz
Ron Roy on sat 30 apr 05
Hi Louis,
The type of testing I have heard of is a bar supported at each end and a
load is applied to the middle - there is a way of measuring the amount of
PSI or such at the point when the bar breaks.
Bars have to be identical I would guess?
Your machine do that?
RR
>Do you want to test tensile or compressive strength?
>We have a concrete testing machine at school. Compressive.
>Louis
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
pdp1@EARTHLINK.NET on sun 1 may 05
Hi Ron, all...
This is only one kind...
Others, are having a small cube or cylinder of some material which gets
crushed, usually in a hydraulic press of sorts which has a gauge that tells
the hydraulic pressure, which can readily be converted to other values for
the sample and it's square inch section.
A 'bar' suspended at the ends and having a load applied to the middle
implies some accomidation of resistance to compression, but involves other
complex force distributions as well, and likely is more revelent to bending
moments and elasticity or deflection...which are more nearly permutates of
tension.
Others are involved in twisting, or in pulling a sample held at the ends,
for pure torsion or tension tests...or, subjecting the cantelevered end of a
sample to forces near it's support for investigations of shear strengths.
I would think the forces usually effecting a (round) Pot, would be more
nearly compressive, and, usually of course, against relatively thin
sections.
Any stount mechanical clamping methods suited to testing Metal samples will
tend to be effecting a Ceramic Sample I would think with influential forces
from the clamps themselves...likely, the ends needing to be held would have
to be glued to something with an epoxy of some kind, otherwise, the forces
of clemping them will be unfairly subjecting them to unpredictable forces
themselves ready and willing to break them.
Or, quite uniform sqaure sections or rectangular sections could have their
ends wrapped in Leather maybe, to be clamped. Or slathered with epoxy and
then fitted into some holder to dry.
The apparatis itself need not be complicated or expensive to make, and could
rely on a guided application of simple weight. The weight could be lead
shot, or even Sand, added to continuously untill the sample fails, and then
the Lead shot or Sand could be weighed on a scale. A quite accurate set-up
could be made nicely and be quite low tech.
Phil
Las Vegas
----- Original Message -----
From: "Ron Roy"
> Hi Louis,
>
> The type of testing I have heard of is a bar supported at each end and a
> load is applied to the middle - there is a way of measuring the amount of
> PSI or such at the point when the bar breaks.
>
> Bars have to be identical I would guess?
>
> Your machine do that?
>
> RR
>
> >Do you want to test tensile or compressive strength?
> >We have a concrete testing machine at school. Compressive.
> >Louis
Ron Roy on wed 4 may 05
Hi Phil,
I think this is a standard kind of instrument used in the ceramics industry
- so results can be compared. All clay miners give MOR (modulus of rupture)
numbers with the specks sheets on there clays.
If a bar i broken by pressure mid point - down on the suspended sample bar
is it right to say compression on the top and tensile on the bottom?
Thanks - RR
>This is only one kind...
>
>Others, are having a small cube or cylinder of some material which gets
>crushed, usually in a hydraulic press of sorts which has a gauge that tells
>the hydraulic pressure, which can readily be converted to other values for
>the sample and it's square inch section.
>
>A 'bar' suspended at the ends and having a load applied to the middle
>implies some accomidation of resistance to compression, but involves other
>complex force distributions as well, and likely is more revelent to bending
>moments and elasticity or deflection...which are more nearly permutates of
>tension.
>
>Others are involved in twisting, or in pulling a sample held at the ends,
>for pure torsion or tension tests...or, subjecting the cantelevered end of a
>sample to forces near it's support for investigations of shear strengths.
>
>I would think the forces usually effecting a (round) Pot, would be more
>nearly compressive, and, usually of course, against relatively thin
>sections.
>
>Any stount mechanical clamping methods suited to testing Metal samples will
>tend to be effecting a Ceramic Sample I would think with influential forces
>from the clamps themselves...likely, the ends needing to be held would have
>to be glued to something with an epoxy of some kind, otherwise, the forces
>of clemping them will be unfairly subjecting them to unpredictable forces
>themselves ready and willing to break them.
>
>Or, quite uniform sqaure sections or rectangular sections could have their
>ends wrapped in Leather maybe, to be clamped. Or slathered with epoxy and
>then fitted into some holder to dry.
>
>The apparatis itself need not be complicated or expensive to make, and could
>rely on a guided application of simple weight. The weight could be lead
>shot, or even Sand, added to continuously untill the sample fails, and then
>the Lead shot or Sand could be weighed on a scale. A quite accurate set-up
>could be made nicely and be quite low tech.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
pdp1@EARTHLINK.NET on wed 4 may 05
Hi Ron,
Bearing in mind I am a layman occupied in only some impirical sundrys, who
might not ever have cracked a Book on some of this, and so I am not versed
very well in the larger nominclature...but who has heard some of the terms
and wondered about them and sometimes talked with structural engineers for
things I have designed...
Below, amid...
----- Original Message -----
From: "Ron Roy"
> Hi Phil,
>
> I think this is a standard kind of instrument used in the ceramics
industry
> - so results can be compared. All clay miners give MOR (modulus of
rupture)
> numbers with the specks sheets on there clays.
But the applications of, or probable eventual uses of their products, the
'Clays', are not anticipated to be 'Pottery' I do not think...but rather,
heavy Insulators, Sinks and Commodes, and (traditionally, ) heavy sectioned
or even some small somewhat complex electrical ancillaries or small fixtures
or components whose in-use imaginable loadings, mechanically, would be very
different than those to which a Pot or a Bowl or a Cup would be tried with,
or subjected to, in daily Life...
> If a bar i broken by pressure mid point - down on the suspended sample bar
> is it right to say compression on the top and tensile on the bottom?
I do not believe so.
Or, not unless we knew more about the actual sitution -
I think this is either under the heading of modulus of elasticity, or of
bending moment, or some order of distortion or deformation or deflection,
whether or not unto whatever constitutes failure.
The forces and their internal negotiations or distributions 'in' something
like a rectangular 'Bar', when suspended at each end, and having a force
appllied to it's middle top...are immediately very complex and to my
recollection, pretty well defy all aspires to represent concisely with
arithmetic models. Or, the arithmetic models serve no better than one's
looking at the situation carefully, anyway, and, or, often, appearently,
have served much worse ( see Kansas City Hyatt House Regency or whatever it
was when them 'bolts' in sheer let go the 2nd story 'dance Floor'. )
Or...
The forces ( 'in' such a 'Bar', being held and subjected to force as you
describe, ) are confluent and in-flux, and co-existantly of many named or
distinct kinds of idealized or formalized conceptions, of various force's
effects or natures....coexisting in the same 'area' or section, with
eachother internally.
In practice, I would expect the compression of the central area, to be
roughly of a 45 degree 'wedge' whose apex is from the point at which the
pressure is being applied. And, depending then on the height of the section,
and the length of the Bar, that 45 degree area may or may not find footing
in or near the ends being supported.
This 'wedge' would be interfaceing with or describeing or induceing what
properly are tension forces, at it's boundaries.
If the 45 degree area find footing in or on the end's supports, then one may
suppose the sample to be enjoying or suffering an application of what, in
practice, under that condition's attributes, is a qualified kind of
Compression proper, with respect also to the size of the area of it's
origin.
If the origin is a point, or if it is more widely distributed. If from a
'point', then other complicating tension forces are being generated which
seek to add new compression forces and secondary tension forces radially,
wishing to, and resisting, the influences trying to divide the test sample
from the point of pressure, 'outward'...also at roughly 45 degrees, so...it
gets complicated in it's way, immediatly.
If not, if the height section and or length do not allow the roughly 45
degree area to find footing in or on the end supports, then, it is not
Compression which is afoot in the experiment, but, ( so far as I recall, or
concueve, ) a function or activity of the modulus of elasticity, or in
effect, of bending moment or deflection, (which of course involve complex
tension and compression force's co-existance ) whether or not unto failure.
In the latter scenario, at least to my reconning, the top chord ( as such, )
is under no particular force at all, unless the material is, or only to the
degree to which the material is able to bend within certain kinds of
elasticity, in which case, the top chord may be under something of a
longitudinal compression, and, the bottom chord is in fact under a
longitudinal tension, since, for the item or test sample section or 'Bar',
to deflect or bend downward from pressure at it's top in the center, the
bottom chord must become longer, while, to a lesser degree, the top chord
must resist forces asking it to become shorter, or at least to resist
possibly some forces asking it to do so. In something like Lead, I doubt
there are any compressive forces at play for the top chord in such a testing
scenario. And in a very hard, brittle Ceramic 'Bar', likewise, I doubt there
are much for forces practically, allowed by the nature of the material, to
be acting longitudinally in the top chord. But in some materials, such as
Steel or other metals, or in Wood, there might be, and it can pucker a
little to show it, too.
Pure compression, to my mind anyway, is where the sample ( the uniformly
sized sample I would think, ) of some material, is subjected to a loading
which presses down on it uniformly across it's section, and slowly
increasing the force of pressure unto failure.
And, that the sample is set on some surface calculated to resist entirely
the force being transmitted through the sample...the deformation or swelling
or rupture or puckering or shattering or failure in some way at any rate,
one way or another, is the measure ultimately then, of it's resistance to
Compression.
A 'crushing' scenario in effect...made to be 'even' and not from some point
or abbreviated section of it's top area.
As far as I know...anyway...
> Thanks - RR
Yours,
Phil
el ve
| |
|
