Windshield Edge Stress
The band of edge compression around the perimeter of a windshield is very vital to the integrity of the unit. Insufficient edge compression can lead to cracking during installation or service. With this compression, comes a band of tension just inside the compressive edge. It is important that this tension not exceed limits or flow too far into the body of the window where a simple stone chip will turn into a run away crack.
The GFP line of products is ideally suited to measure edge stress of automotive products. GFP products do not require removing the black paint band from the edge of the window. The systems are so sensitive they can reflect off the black paint to make a valid measurement. A black backing is often used to fill in the clear gap near the edge.
This example shows the edge stress at three locations down the edge of a windshield. The edge compression was found to be very inconsistent and actually disappeared over a 10cm stretch. This glass was found to fail in cold climates.