Guide To Avoiding Glass Failure
Thermal Stress
Fracture
Thermal stress fractures are the result
of uneven temperature distributions across the surface of a
glass plate. The most common cause of uneven temperature
distribution is unequal heating of the glass as the result of
exposure to sunlight. Thermal stress fractures tend to
originate at the edges of glass plates as the result of the
interaction of thermally induced tensile stresses with edge
flaws or damage. In addition, severe surface damage or flaws
can also trigger thermal stress fractures. This problem can be
exacerbated by the type of glass, surface or edge damage, the
heat absorption characteristics of the glass, edge bite,
unfavorable interior shading devices, and exterior shading
conditions.
Provided that the fabrication and
installation of the glass is acceptable, thermal stress
fracture is usually not a problem with heat-treated glass
(heat-strengthened or tempered), and it usually does not
become a problem with properly fabricated and installed
annealed glass until the total solar absorption of the glazing
in-fill exceeds about 50% - 60 %. Clear safety film adds little
to the heat absorption characteristics of glass so its
application to annealed glass should have little effect.
However, the application of heat-absorbing film to annealed
glass can increase the total solar absorption of the glazing
in-fill to a level that may promote the occurrence of thermal
fracture. This can be a particular problem if the glass in
question is improperly fabricated or installed.
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