Test methodology for strength testing of soda-lime-silica float glass before and after enameling

Different biaxial flexure test geometries were investigated to determine the most reliable test for evaluating the strength of float glass specimens before and after enameling. The enameled and unenameled samples were tested using the ring-on-ring (ROR) and ball-on-ring (BOR) strength tests. The strengths of each sample set were analyzed using a conventional two-parameter Weibull analysis. For direct comparison of the data, combined Weibull moduli were calculated for the unenameled tin side, unenameled air side, and enameled tin side data sets. The principle of independent action (PIA) was assumed to be the appropriate fracture criterion and the data were scaled to determine if discrepancies existed between the different testing methodologies. The scale parameters (σ_O) were also calculated for the different test geometries. The results showed that there were no statistical differences between the scaled data. Based on the results it was concluded that the ROR test geometry was the better choice compared to the BOR test geometry because of the larger stressed area. The use of a concentric support ring was also found to be more desirable than a ring on equally spaced balls because of the stress concentrations at the support balls, which can lead to problems.