Equibiaxial Flexure Strength of Glass: Influence of Glass Plate Size and Equibiaxial Ring Ratio

Abstract

Glass plays an important role in many engineering applications including transparent armor. Determining the actual strength of a glass is problematic because typical glass strength numbers are presented in the literature as ranges. Minor changes in surface finish, composition, test method employed, and processing all influence the mechanical strength of glass. A standardized method needs to be utilized to ensure that strength data can be compared universally. The use of a standard methodology is vital when comparing glass compositions or multiple sample lots of the same composition in order to attribute any real strength variations to the glass itself. While the procedures established in ASTM C1499 provide a good framework for glass strength measurement, flexibility in the experimental parameters of the standard allow for substantial strength variations when testing glass materials. The ratio between the load and support ring diameters, as well as the specimen dimensions, is shown to lead to variations in both the measured strength, as well as the number of valid/invalid tests based on where fracture initiates. The goal of this study is to quantify these effects in order to establish optimized testing conditions for determining the strength of float glass.

Borofloat and Starphire Float Glasses: A Comparison,

“…Knoop hardness for the two glasses was equivalent, so this characteristic does not appear to contribute to differences in triaxial or ballistic loading responses for these two glasses. Differences in flexure strength were observed, and these differences have been observed by the authors in a separate study and more recently by Swab et al . But the flexure strength of glass is limited by the surface flaw population size, and those flaws are not necessarily always the same for a given glass at all times in its history.…”

“…10,11 Knoop hardness for the two glasses was equivalent, so this characteristic does not appear to contribute to differences in triaxial or ballistic loading responses for these two glasses. Differences in flexure strength were observed, and these differences have been observed by the authors in a separate study 12 and more recently by Swab et al 13 But the flexure strength of glass is limited by the surface flaw population size, and those flaws are not necessarily always the same for a given glass at all times in its history. Similar to the discussion concerning differences of flaw populations on the tin and air sides, flexure strength may play a role during the onset of fracture initiation; however, once massive fragmentation or damage accumulates, those identified differences in flexure strength likely no longer have a contributing role.…”

On radial, circumferential, and spiral cracks in fractured glass plates

“…Vitman and Pugh 1 and Ritter et al 2 recommend large overhangs; in the latter paper as much as 1.75. Swab et al 11 showed how an overhang ratio approaching 2 significantly reduced the number of specimens that exhibited edge‐initiated (invalid) fracture. As will be shown later, the large overhang has an unexpected consequence.…”

High‐Strength Frosted Glass by Ion Exchange of Float Glass with a Potassium Water Glass Film

“…Furthermore, the values of strengths measured by a double ring test are somewhat larger at the atmosphere side than at the tin bath side. The values given in the literature for the atmosphere sides are in the range from 180 to 243 MPa, while they are 114 to 147 MPa for the tin bath side . It should be noted that also the ratio of the load to the support ring diameter affects the measured strength values.…”

“…By contrast, the strength measured after ion exchange in a salt bath is much higher than the strength reported in this study. For a temperature of 405°C and an ion exchange time of 20 h, the strength of 838 MPa can be interpolated from the data given in Refs . This is an increase in strength by 370%.…”