Re: Why does shattered toughened glass stick together?

From: Ian Stirling (root_at_mauve.demon.co.uk)
Date: 07/04/04 

Date: Sun, 04 Jul 2004 07:20:52 GMT

Edward Green <spamspamspam3@netzero.com> wrote:
> Ian Stirling <root@mauve.demon.co.uk> wrote in message news:<gSCFc.2691$Fc7.441121@stones.force9.net>...
>> OG <owen@gwynnefamily.org.uk> wrote:
>> >
>> > "tj Frazir" <GravityPhysics@webtv.net> wrote in message
>> > news:9650-40E4FA05-23@storefull-3214.bay.webtv.net...
>> >> I added the vaccume idia too.
>> >> without air between two sheets of glass , one bar is pushing them
>> >> together.
>> >>
>> >
>> > Possibly,
>> > The fact there are internal reflections at the cracks implies that there is
>> > a pretty large difference of refractive index across them (which means
>> > either air or vacuum between the fragments of glass).
>> > The fact that the internal reflections are white (all wavelengths from blue
>> > to red) tends to suggest that the separation is tending towards several
>> > huindreds of nanometres.
>
> Mygod, sir, that is a most excellent observation! I thought about

Indeed.
> something like that, and ignored it -- just what does it mean that we
> can see the cracks? OTOH, this does leave open the possibility of
> partial cold-welding, surface adhesion, whatever. That is, say 1% of
> the crack surfaces had essencially rewelded to become contiguous glass
> (low percentage attributable to mechanical mismatch following movement
> of fragments), the rest air or vacuum filled gap, as you say. This
> would account for both the significant yet greatly reduced residual
> strength, and the visibility of the cracks. Failing that we are left
> with the Frazir model: mechanical interlock.

I'm not happy with that model.
Examining the bits, very few of them have shapes that would seem to
allow any mechanical adhesion.

>
> Note to original observer of the Stirling phenomenon: do the sections
> networked with cracks, that you can yet easily pick up as a unit, show
> noticable flexure when you move them ... like, dare we say, a piece of
> complete jigsaw puzzle?

No, they are utterly inflexible, feeling just like an unshattered bit,
until they fracture (at vastly lower stresses than ordinary of course).
>
>> Hmm.
>> An interesting experiment would probably be to try a similar experiment,
>> but with the pane submerged in water.
>
> Or oil.
>
> I have a feeling that the oil would more readily penetrate the cracks.

Possiblt.
>
>> An interesting optical effect might be to put cling-film over one side,
>> to spread coloured epoxy over the other (and the edges), before leaving
>> for a couple of minutes, and wiping off the epoxy, then leaving to set
>> and removing the cling-film.
>> Unfortunately I have no spare toughened glass.
>
> Just what do you expect to achieve by this treatment?

Just a fine network of colour in the glass.