Experimental evaluation of static fatigue of window glass under rapid loading rates

Window glass strength is a time-dependent quantity. One parameter which has been found to serve as measure of the time-dependent nature of window glass strength is the static fatigue constant which is denoted by n. The static fatigue constant is a material property of window glass. Several researchers have investigated static fatigue by testing destructively, glass rods and charpy specimens which were mechanically or chemically treated. Their results were conflicting. Results based on failure tests of large window glass lites under uniform lateral load were inconclusive.

The research reported herein provides an estimate of the static fatigue constant, n, based upon data obtained from testing 353 specimens of window glass to failure at eight different load rates. The test method used the concentric rings tester to apply loads. Stress rates ranged from 26 psi/s to 2600 psi/s. Several models which describe the behavior of n as stress rates vary were investigated. A value of n = 14.5 for all the stress rates was found to best fit the glass lite failure data.