Figure Rf-1 [1]. Tensile and Compressive Stress on Tempered Glass
Overview:
After or during the processing of any piece of material, stresses
may be applied to the material sample. These stresses are used
to help prevent failure of a material. Callister mentions two
examples of this type of fracture design, tempered glass and prestressed
concrete. Tempered glass is glass that has been heated up and
then quenched in an oil bath or cooled in a jet of air. The result
of the semi-rapid cooling process is that the interior of the
glass cools much slower than the outside; which places the exterior
in compression and the interior in tension. A graphical illustration
of the tensial and compressive forces on tempered glass is shown
in figure Rf-1.
Any tensile load must overcome the compressive stresses on the
exterior of the glass first, before the tension placed on the glass can cause it to fail.
The prestressed concrete that Callister mentions works in much
the same way. Concrete, before or after it hardens, has a compressive
load applied to it. Being a ceramic the concrete can easily withstand
the compressive loading without failing. The advantage is that
if a tensile load is ever applied to the prestressed concrete, like the tempered glass,
it would not fail as easily.
Submitted by Matt Gordon
Virginia Tech Materials Science and Engineering
http://www.eng.vt.edu/eng/materials/classes/MSE2094_NoteBook/97ClassProj/exper/gordon/www/gordon.html
Last updated: 4/25/97