<VV> Re: VirtualVairs Digest, Vol 4, Issue 112

[JVHRoberts at aol.com]

Uh, dude, LOF stands for the manufacturer, Libby Owens Ford. 


In a message dated 5/17/2005 7:57:43 PM Eastern Standard Time, 
RoboMan91324 at aol.com writes:
Roger,

Great post.  The "compression trick" is used in many  applications.  
Pre-stressed concrete is a good example but the one we are  most familiar 
with is 
tempered glass.  In the manufacturing process, both  sides of the near molton 
glass plate/pane is cooled relatively quickly.   This shrinks the outside 
glass 
while the inside is still hot.  This is  usually done with oil.  You may have 
noticed "LOF" printed on a lot of  automotive glass.  This stands for "liquid 
Oil Float."  As the inside  cools relatively slowly, it also shrinks.  Since 
the 
outside has already  hardened and can't really shrink, it compresses.  As you 
point out, hard  and brittle substances will tend to crack and then propagate 
that crack if in  tension.  The compressed outside glass is very tough.  You 
may have  noticed the difference between regular plate glass and tempered 
glass if it is  struck.  If you want to break tempered glass relatively 
easily, 
tap it on  the edge with a hammer.  The inside layer is in tension and the 
crack 
will  propagate.  Wear safety glasses.

Just ask Mr. Wizard.

Doc