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| Effect of edge defects on sheet glass bending strength | | Published by: cfz 2010-03-17 |
| | Glossary of Terms::
Glint: A visual defect in a fiber glass reinforced cured organic (usually This usually does not effect the strength of a laminate, but could be an
http://kreysler.com/glossary/glossary.htmHOME |
I am involved in a research project in which we use slumped sheet
glass (alkaline free borosilicate glass .3 mm thick) in telescopes.
The glass is cut using a scriber, leaving microcracks in each cut
edge. I am looking for a quantitative answer (whether in the form of
an equation or a graph) that directly relates the number of
microcracks to the decrease in overall bending strength of the glass.
I have searched the web, as well as various school libraries, for a
scientific paper that addresses this issue. I have found many, but
none of them are quantitative. They all come to the same
conclusion--that edge defects do in fact have significant effects on
bending strength. However, I need an exact scientific method in order
to convince a committee to invest money in a wire cutter which would
greatly improve the edge condition.
I have already searched the Corning glassware site, the Schott glass
site (where we order the glass from), Columbia University Libraries
(which has a pretty comprehensive website), and various scientfic
journal databases online. I have also read through mechanical
engineering and material science texts discussing fracture toughness,
but was unable to come up with a congruent method.
I am a student, so I cannot afford to offer a high price, however,
receiving this information (the sooner, the better) would greatly
contribute to the efforts of our research team. The ToneQuest Report::
and it provided a huge amount of strength right where you wanted it – on the outside of the neck. way – to resist the bending forces imposed on it in
http://www.tonequest.com/articles/article23.htmHOME |
The growth of a crack has been studied and a
complex equation describing it does exist. However,
that does not translate into what you asking
for: Number of cracks is nor sufficient to
dtermine the strength. One would need a statistical
measure of the crack size distribution. Would
you consider either of the above as an answer?
To convince a comittee a more practical, engineering
approach, may be more effective,than "exact scientific method"
such as comparing cost of polishing to the cost of a
different cutter. Performance Motor for Impreza WRX::
electrode on a V-Power spark plug forces the spark to the outer edge of the The effect is similar to fitting a lightened flywheel and is particularly
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Exploring complementary cutting methods: Comparing capabilities of ::
product in the direction of the lens or produces defects on the cut surface. On single layers of thin sheet metal, lasers cut at fast speeds with tolerances
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Hedgie,
Rather than comparing the "cost of polishing to the cost of a
different cutter," we are trying to prove whether or not we need to
change anything at all. We have a hot wire-cutter which produces a
very smooth edge with almost no microcracks. However, much money
would be needed to make the machine more effecient and user friendly.
What the committe would like to see is proof that the microcracks in
our existing glass (cut with the scriber) decreases bending strength
significantly enough to invest money in the wire-cutter (or even
polishing, if that turns out to be a more efficient means).
The only reason I asked for a "quantitative answer that directly
relates the number of microcracks to the decrease in overall bending
strength of the glass" is because our research director mentioned once
seeing such an existing method (but I have not been able to find it).
Saying that such a method does not exist is definitely helpful, but I
still need a quantitative way of measuring the bending strength of our
glass with microcracks vs. that of the same piece with a smooth edge.
Can you elaborate on "a statistical measure of the crack size
distribution"? This sounds like it might be very helpful.
Please let me know if any further clarification is necessary. And
thank you for your time and effort. Crowns and extra-coronal restorations: Materials selection : Article ::
Strength is conferred by painting a slurry of lanthanum containing glass onto effect of sandblasting and silica coating on shear bond strength of luting cements.
http://www.nature.com/bdj/journal/v192/n4/full/4801334a.htmlHOME |
hello again, sblowen
Thanks forthe clarification, it helps.
The literature on 'cracks and material strength'
is extensive and the challenge is to find the needle
which will serve your purpose, in the haystack of
specialized studies which are available on the web,
which is a small fraction of the total.
Since no one picked up the challenge so far,
I will go ahead and list few links which appear to be relevant.
Here is a bit of overview and history:
" As early as the 1920s, the strength of glass and other
brittle materials was understood to be limited by the
presence of small cracks. Under stress, the small cracks
would grow into larger cracks until reaching a critical
size, at which point the material would fracture
catastrophically. It also was well known that humid
environments reduced the strength more severely than
did dry environments... .."
http://nvl.nist.gov/pub/nistpubs/sp958-lide/181-183.pdf.
Simple Model of the crack propagation
www.poco.phy.cam.ac.uk/~rbb11/EIS.pdf
Griffith's contribution : (energy balance)
Griffith's criterion was based on the observation that glass is not
internally
homogeneous but rather contain pores ...
http://www.geosc.psu.edu/~engelder/geosc465/lect14.rtf
A bit of theory and some basic equations (Griffith-Irwin)
www.utm.edu/departments/engin/lemaster/
Machine%20Design/Lecture%2012.pdf
Limitations of the Griffith approach
http://www.mpg.de/english/illustrationsDocumentation/documentation/pressReleases/2000/news15_00.htm
Empirical study of slow crack propagation in glass
http://www.physics.usyd.edu.au/apphys/crack.html
Lot of the material can be found in subscription journals
such as:
J . Appl. Physics (subscription required)
J E Flitcroft and R D Adams
Dept. of Mech. Engng., Univ. of Bristol, Bristol, UK
".. Shear crack propagation has been studied in unidirectional glass
and carbon
fiber reinforced plastics.."
or monographs
http://www.solid.ikp.liu.se/solidbook/lawn.htm
Since growth of cracks depends on local stress, solution of the
Navier-Stokes eq.
for the structure is often necessary in engineering design studies.
That probably is
more then you want to do in your case, but as an illustration, this
link may be of interest:
simu.ulb.ac.be/newsletters/N3VI.pdf
Search Terms
Crack Propagation
Griffith Theory
crack propagation, Navier Stokes
hedgie
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