Tempered Glass Expert Performs Failure Analysis

California Failure Analysis Lab routinely performs tempered glass failure analysis. In this case the glass expert determined that the tempered glass failed as a result of a pointed object that created crush damage that penetrated the compressive layer of the tempered glass. The glass was a large piece  10 mm thick. Thus, the compressive layer is approximately 2 mm thick on each face. It is interesting to see how the failure initiates on the surface and progresses inward. Later the residual tensile stress causes the entire glass panel to break into small "cubes". On the face of the panel there is a glass crush point.

Glass Expert Discusses Termpered Glass Cookware

Modern Pyrex glass cookware is now made from tempered soda lime glass. As a result there is a potential that the tempered glass failure will create dangerous projectiles. In one case it was found that if the temper glass stresses are not symetrical, flying glass pieces will occur. In the present case, tempered glass cookware lids were caused to fail; the resulting failure was completely contained by the stainless rim. The rim performs two functions. It protects the vulnerable edges of the tempered glass lids from glass damage. In addition, it appears that it contains any glass particles that could become projectiles.

Glass Expert Discusses Visibility of NiS Particles

Tempered glass failure analysis is mainly difficult because the panel disintegrates into a very large number of semi identical particles; therefore, the failure origin is impossible to locate. In several cases Read Consulting has had the opportunity to examine several failed (caused by Nickel Sulfide, NiS, particles) tempered glass panels that have remained intact. In some cases the windows were laminated; in the others, the windows remained verticle and stayed interlocked. Once the origin is located and preserved, an eyeloop or low power microscope is all that is required to see the NiS particle. The upper left photograph is a macrophotograph of an inplace failed laminated window. In this case the NiS particle is visible to the naked eye. It is a sphericle particle on the fracture surface. Upper right is an 8X photo-micrograph of the particle after the window has been taken apart. This root cause failure analysis does not require scanning electron microscope. This type of tempered glass fracture analysis merely needs an intact failed window.