Failure Analysis of Broken Tempered Glass Window

Failure analysis of tempered glass windows is normally impossible because the failed window falls apart into a large number of similar pieces, and locating the origin is impossible. However, there are cases when the window remains intact, and root cause failure analysis is possible. In this case the glass expert was able to preserve the origin and perform the failure analysis. Three failed windows were analyzed. In all cases the cause of failures were caused by a nickel sulfide contaminant particle (NiS). In one case, the NiS particle was visible in a macro-photograph. This is seen in the top left photograph. The other two images are photomicrographs of the NiS particle as it appears on the fracture surface at the origin. it is rare to be able to see the particle with the naked eye, but this is an exaple of such an event. The composition of the particle was determined to be Ni and S using energy dispersion spectroscopy. Failures of this nature are well understood and documented

California Glass Expert Discusses Nickel Sulfide in Tempered Glass

In glass failure analysis one uses evidence such as the the attached photograph to demonstrate that a nickel sulfide particle can initiate tempered glass failure. The NiS particle is at the center of expanding Wallner lines. The Wallner lines are used by the glass failure analysis expert to track the direction of the crack growth. In this case the Wallner lines are spreading from a single point; thus, this is the failure origin and the NiS particle is the cause of the tempered glass failure. The California glass expert has seen numerous examples of this type of glass failure.

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.

Glass Failure Analysis of Laminated and Tempered GLass

Glass failure analysis was performed by a failure analysis expert on a large laminated window of which one layer was tempered glass. The tempered half of the lamination failed. The other half of the window held the system together, and this allowed a failure analysis to be performed. The upper left photo is an over view of the window failure. The arrow indicates the general location of the failure origin of the tempered glass layer. The upper right photo is a closeup of the origin. The arrow indicates the location of a nickel sulfide particle (NiS) that caused the failure. It was reported that the tempered glass had been heat soaked. In this case the heat soak test (HST) did not eliminate on this window before it was sold.

Glass Failure Expert Looks at Tempered Glass Failure

Glass expert analyzed a broken tempered glass door. He was able to preserve the origin and perform a failure analysis. The spontaneous glass failure started in the center of the window and was caused by a nickel sulfide particle (NiS particle). This failure mechanism is well known and has been documented by others. In this case, the glass expert spent some time documenting the initial crack growth. The upper left photomicrograph shows two sets of Wallner lines spreading away from the general location of the 100 micron diameter spherical nickel sulfide particle. The photomicrograph on the upper right shows a circular crack arrest line surrounding the NiS particle. This circular artifact identifies the NiS particle (a manufacturing defect) as the cause of the failure. In addition, it also indicates that the crack stopped at least once before the glass went to failure. At first the crack started as a round crack due to the stresses from the nickel sulfide particle. Later the residual stresses in the glass took control. The circular crack opened up and turned into the classic sets of Wallner lines found in root cause failure analysis of tempered glass.