Experimental study of glass plate strength at rapid loading rates
Pal, Himansu Sekhar
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The time dependent nature of the strength of glass plates, commonly referred to as "static fatigue," is modeled by an equation involving an exponent "n" which is a material property relating to the rate of loading. Except for field explosion and shock tube tests, which were not instrumented for detailed response, glass plate tests to date have been essentially static. The highest loading rate achieved so far in a laboratory has been 3.6 psi/sec. The main objective of this study is to investigate the value of "n" at rapid loading rates. Secondary objectives are experimental verification of a nonlinear analytical model for dynamic plate response and of a dynamic failure prediction model for window glass. This dissertation presents and evaluates results of six series of tests to failure on 27" x 32" x 0.088" glass plates for loading rates ranging between 0.01 and 240 psi/sec. Each test series consisted of at least twenty specimens. The series with the slowest loading rate was tested in a conventional static test set-up. For the other five series, each plate was loaded in uniform air suction by rapidly pulling a plunger away from the plate which was mounted on a chamber. In the two series with slower loading rates, the plunger movement was controlled by a universal testing machine. For the three series with faster loading rates, the plunger was activated by a dropping weight. For the oscillating stress-time histories found at the most rapid loading rates, direct determination of "n" is not judged to be appropriate, and an indirect method is employed. The value of "n" is found to increase as the loading rate increases. The nonlinear dynamic finite difference model is shown to agree well with the experimental plate response, and the dynamic failure prediction model for glass plates is validated by the breakage results. The results of these experiments should aid in the prediction of the strength of window glass plates under rapid loading.