Delayed Cracking In Automotive Windshields

The laminated safety windshield has served the automotive industry and the consumer for well over 30 years. The invention of float process in the early 1960s provided high quality soda-lime-silica sheet glass which, due to its low cost, found ready acceptance in automotive and architectural glazing. In view of its excellent surface quality and thermal temperability, its initial strength is respectably high ranging from 13 Kpsi in the annealed state to 26 Kpsi following tempering. This paper describes the use of Friedel polarimeter for measuring membrane stresses in each of the glass plies as well as in laminated windshield as a function of manufacturing process, ply thickness and peripheral position.