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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