Tempered Glass Failure: Nickel Sulfide Particle

California failure analysis expert examines glass door failure to determine the root cause of the failure. The subject tempered glass door failed spontaneously, and because the glass was verticle, the broken pane remained intact. Read Consulting failure analysis laboratory was able to obtain the origin and perform a root cause failure analysis. The attached 25X Nomarski photomicrograph demonstrates that the glass failure originates at a nickel sulfide (NiS) particle. Once the glass failure has been initiated, the failure is driven by the residual stresses in the thermally tempered glass.  Glass fracture analysis shows the Wallner lines initiating at and expanding from a NiS particle. NiS particles are common in float glass, but they are only a problem in thermally tempered glass. Read Consulting Laboratory performs similar failure analyses on metals, plastics, ceramics and glass on a regular basis 

Glass Expert Examines a Tempered Glass Window Failure

California failure analysis expert uses glass fractography to perform a glass failure analysis on a tempered glass window failure. The glass fracture analysis showed that the window failure was a result of heating the glass in the center. Due to the heat, the center of the window expanded. This created additional tensile stress on the window edges. Although the window edge was ground and chamfered, there was enough residual damage at the edge that the thermal stresses were able to cause window failure. Upper left shows the failure initiation site on the edge of the window. Upper right is a 40X photo micrograph of the origin on one of the fracture surfaces. The glass fracture analysis showed that the glass failure initiated on the window's edge face and propogated inward until the tensile center of the tempered glass window was reached. At this point the residual tempering stresses caused the entire window to self destruct into small "cubic" pieces. This may be a manufacturing defect because of the severity of the edge damage.

Glass Fracture Due to Liquid Pressure

Glass failure analysis expert witness performs a failure analysis on a hollow glass tube that failed due to internal pressure. The glass fracture initiated at a small bruise on the outer surface of the glass tube. The upper left 25X photomicrograph gives an overview of the failure. One can see that the glass fracture analysis determined that the failure initiated at a small bruise. The upper right 100X photomicrograph gives more detail of the origin. This was a manufacturing defect because the bruise was created during manufacturing.

Shaping Flat Glass

Glass expert describes the condition of the edges of windows, mirrors and other flat glass pieces. Almost all flat glass pieces are shaped from larger pieces using glass scribe and break techniques. Thus the edge of the part has two distinct sides. The photograph above is a microscopic picture of a the edge of an automobile mirror that was shaped in automatic scribing machinery. The top of the photomicrograph is the surface where the scribing tool has created controlled glass damage (i.e. crush). In general the damage is uniform. This photo imcorporates the start of the glass scribing, and this point always has more significant damage. Glass failure analysis determined that glass cracking due to thermal stresses initiated at the start point. Glass fracture analysis indicates that glass cracking always starts at the weakest point under tensile stresses.