Glass Expert Discusses Modern Auto Windshields

California glass expert has been involved with evaluation automobile windshields. One way car manufacturers can  increase automobile mileage is to decrease weight. A part of this effort has been to reduce the weight of automobile windshields. This is done by reducing the thickness of the windshield. Upper left is a representative cross section of a modern windshield. The glass is only 2mm thick, and the polyvinyl butyral (PVB) inter-layer is only 0.07 mm thick. On the positive side, this reduces weight and improves the mileage. On the negative side, this windshield is prone to cracking. Upper right is a photograph of a windshield failure. The crack that was started by an impact from a rock. This crack formed immediately and has grown continuously for several months. Older windshields were thicker and were less prone to this sort of cracking. 

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.