Glass Failure AnalysisExpert Examines Cracked Automobile Windshield

Glass expert performs a glass failure analysis on a cracked automobile windshield. Records show that the windshields on this particular make and model of automobile are cracking at a very high rate. The windshield shown here is the third replacement in two years. In this case, glass failure analysis shows that the crack started at an impact point two inches below the top of the windshield. Initially the windshield crack was driven by bending stresses. Later it was driven by thermally generated stresses (caused the crack to curve). Factors that are of concern are the glass thickness, mounting (i.e. bending) stresses in the windshield, perpendicularity of the windshield and glass lamination stresses. Eventhough the failure was caused by an impact point; this damage should not have caused a large crack to form. The upper left photo is an overview of the crack. In the center is a close up of the impact point. Upper right is a 40X photomicrograph of the crack origon.

Tempered Glass Expert Describes Failure Origin for Tempered Glass

Glass failure analysis expert demonstrates how to locate the origin of a tempered glass failure. Glass failure analysis of a tempered glass piece is difficult (if not impossible) because tempered glass fracture results in many small pieces. In many cases the glass failure falls apart and there is no pattern left to trace to the origin. Thephotograph above provides a pattern that can be a useful tool for locating the general location of the failure origion of a partial crack pattern. In the above example a glass expert taped a tempered glass pickup truck rear window with transparent tape and impacted it with a simulated human head. The resulting crack pattern is preserved. The impact point is the center of a "web" of cracks. The predominant pattern is a series of "spokes" eminating from the impact point which is also the failure origin.