The strength of glass, hidden damage

Abstract

The strength of float glass is a necessary engineering parameter. Determining this strength is a complex problem. Earlier results have shown that statistically bending test results are not a homogeneous group. To explain this, a theoiy of hidden is proposed. The essence of this theory is that the different sides of float glass are unequal, not only because of the differences between the Tin and nitrogen sides, but because of the difference between the side scored under the sheet glass cutting and the side which has the crack propagation ftom the scored side in breaking. Extensive tests on rolled glass suggest that the rolling process damages the glass in a special way, causing invisible damage - statistically not a homogeneous distribution of micro-cracks on the edge surface of glass element. These micro-cracks are different on the scored and broken sides of glass. They are the fracture source under the loading and influence negatively on glass element strength and statistics of strength data.This invisible damage explains most if not all of the non-homogenous distribution of the test results. It is shown that removal of this damage on the edges of glass elements increases the engineering strength of float glass significantly.