Experimental Verification of Residual Compression in Tempered Automotive Glass with Holes

Tempered float glass is commonly used for both side windows and backlites in the automotive industry. The success of such products is primarily attributed to high level of residual compression, following tempering, which provides abrasion resistance as well as 3X higher functional strength to sustain mechanical, vibrational and thermal stresses during the vehicle's lifetime. Certain applications of tempered glass, however, require mounting holes whose surface-finish must be controlled carefully to withstand transient tensile stresses during tempering. Simultaneously, the nature and magnitude of residual compression at the hole must provide sufficient robustness to bear mounting, vibrational and thermal stresses throughout the life of the vehicle. This paper presents (i) analysis of residual compression at the hole, (ii) measurement of biaxial strength of annealed glass with hole at center, and (iii) measurement of biaxial strength of tempered glass with hole at center. Both fractographic analysis and the biaxial strength data of annealed and tempered glasses are used to deduce the magnitude of residual compression at the hole. These data show excellent agreement between analytical solution for residual compression and that inferred from biaxial strength.

The nature of residual stresses at the hole, which differs considerably from that of classical tempering, is highlighted.