Assessing Already Broken Tempered Glass

Glass Expert at Read Consulting is asked to assess whether a broken window or shower door was fully tempered. One method is to select the ten largest "crack free" pieces and determine if these can fit into a 10 square inch area. In the photo above, a 3" X 3" (approximately 10 square inches) "frame" is placed over the broken glass. In this example there are many more than 10 pieces in the opening. Before breaking this glass door, the temper stress was measured to be 16,000 psi using a Strainoptics grazing angle surface profilometer  (GASP). However, it is important to note that there are cases where the fully tempered glass will not fragment properly. The larger pieces result from the stresses applied to break the tempered glass door or tempered glass window.  

Manufacturing Defect on Tempered Glass Window

Glass failure analysis expert witness performed a root cause failure analysis on window defects found on a recently built custom home. The upper left photograph shows the defect from the building exterior. The window defect resembles a dust or dirt streak and was not detected until the post construction window cleannig. In all cases, the manufacturing defect is in the center of the window, is parallel to the long side and it looks like a streak or scuff. The upper right photograph is a 200X photomicrograph of a portion of the window defect. It is composed of an array of small glass particles strongly adhered to the glass surface. It is believed that these particles were generated during the window sizing process and were a contaminant on the horizontal rollers used in the glass temper process. During glass tempering they came into contact with the hot glass surface and welded to it. This is a manufacturing defect. It is not a construction defect. This defect is often blamed for window scratching from window cleaning operations. However, these particles were visibly obvious and could not be dislodged. Therefore, these particles don't fit the popular window damage model proposed by many window cleaning experts.

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.