Stress Distribution And Spontaneous Breakage Control Of Tempered Glass

The stress in tempered glass follows a parabolic distribution along its thickness: maximum compressive stress occurs at the surface; maximum tensile stress occurs in the central region; and the zero-stress surface is located approximately one-third of the thickness from the surface. Typically, there is a fixed ratio between surface compressive stress (approximately 100 MPa) and internal tensile stress (32–46 MPa). When the additional stress generated by nickel sulfide expansion or surface damage reaches approximately 30 MPa, it can potentially trigger breakage. International standards such as ASTM C1048 and EN12150, and the Chinese standard GB 15763.2-2005, all set lower limits for the surface compressive stress of tempered glass to balance safety and the risk of spontaneous breakage.

 

Heat Soak Test (HST) is one of the most effective engineering methods for controlling the risk of spontaneous breakage.

 

The principle is to heat the tempered glass to 290 °C ± 10 °C and hold it for a period of time, causing potential nickel sulfide inclusions to undergo a phase transformation prematurely. This allows potentially spontaneously breakable glass to fracture at the factory stage, rather than posing a danger during engineering use.