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.