On 10/25/2011 08:34 PM, Ron wrote:
jim beam wrote:
On 10/25/2011 07:32 PM, Ron wrote:
micky wrote:

First, they all flex some, amazingly since they are glass***. I
stsood the window in a garbage can and whacked it about 10 times, each
time harder, until finally I used a hammer iirc and wacked it really
hard and it finally borke. Like the other two, all the pieces
separated. I don't think they were even very sharp, some how.

It's tempered glass and it's 7 times stronger than non-tempered glass.

ever seen the little safety hammers by bus and train windows? they
weigh less than 1lb, but will smash tempered glass with ease because
they have a hardened point that will initiate cracking, and with
tempered glass, that crack instantly progresses into the thousands of
small pieces that the glass then becomes.

if you have to smash tempered glass, get a piece of broken spark plug
insulator, place that on the glass sharp side down, then strike that
with a hammer. works every time.



A piece of spark plug ceramic itself will break a piece of tempered
glass for some strange reason.

it's not strange, it's just outside most people's experience. it's all
perfectly normal if you're a fracture mechanics and stress
concentrations geek.


Tempered glass will break easily if you
tap it on the edge...especially the corner.

edge effects. glass surfaces are flawed. flaws can propagate into
cracks. tempered glass works by using tensile stress within the core to
compress surface flaws so they don't easily progress into cracks. but
you can't compress an edge because one of your three dimensions is
missing. on a corner, you're pretty much removing two of your three
dimensions. so, no compression means easy crack propagation.


And I believe those hammers
were phased out by spring loaded center punches.

often, yes. harder to get wrong if an operator is panicking.


--
nomina rutrum rutrum