PSI - Issue 71

A.B. Penurkar et al. / Procedia Structural Integrity 71 (2025) 150–157

152

(2013). The presence of internal defects varies significantly among manufacturers. Based on the author’s experience in testing float glass, these defects are infrequent unless stress has been introduced through edge processing. Pisano and Carfagni (2015) demonstrated that strength differs between the Sn and air sides. Most studies on glass indentation have focused on spherical indentation. The load bearing capacity of the cylindrical indenter can be increased by increasing the height of the cylinder. Also, spherical indentation develops a complex multi-axial state of stress which complicates the analysis as compared to cylindrical indentation. Therefore, this work aims to assess glass strength using cylindrical roller indentation. The load necessary to fracture the glass specimen was recorded. Finite element analysis was conducted to evaluate the tensile stresses beneath the indenter at the fracture load. The distribution of tensile stress at various fracture loads was assessed and compared with standard TPB tests. Additionally, a comparison was made between the tensile and compressive strength of the glass specimen. 2. Experimental details The roller indentation, TPB tests and compression tests were carried out on annealed float glass specimen. The schematic of different test fixtures is shown in Fig. 1. The load at fracture of the glass specimen is noted and their scatter is evaluated. The details of the experiment are discussed in subsequent sections. 2.1 Design and fabrication of test specimen and machine fixtures The tests were conducted on 4 mm thick float glass. All specimens were cut from a single large sheet using a scratch tool to achieve the desired dimensions. The sizes used for testing were 10 x 27 mm for cylindrical indentation, 10 x 22 mm for the three-point bend setup, and 10 x 10 mm for compression tests. The roller length was 30 mm, ensuring complete contact with the specimen to confirm Hertzian contact between the roller and the glass. The span for the TPB test was taken as 14 mm. The material was sourced from commercially available float glass sheets, with the typical composition in weight percentage detailed in Table 1. Table 1: Typical chemical composition of float glass used for evaluation of its strength. Material Silica Sodium Carbonate Calcium Carbonate Boron Iron Zinc Titanium Float glass 72-74 14-16 10.5-11.5 0.1-0.2 0.19 0.029 0.068 2.2 Test matrix for evaluation of strength of glass sheet Tests were conducted on 4 mm thickness of float glass specimen using different test setup as discussed in previous sections. Minimum 22 tests were carried out in all the test set up to determine the statistical scatter in the fracture load of the glass specimen. Exact details of the test matrix used are specified in Table 2. The tests were carried out using cylindrical indenter, TPB tests and compression test with different specimen design and test fixtures. While making the specimens it made sure to use a single side of plate, in this work the differentiation between tin-side and air-side had not been considered. 2.3 Experimental procedure The tests were carried out on float glass specimen using different test fixtures (Fig. 2(a)). For conducting the indentation tests, a special universal type fixture is prepared that makes proper alignment of specimen with roller ensuring line contact between them. Proper lubrication is applied between the roller and glass specimen to reduce the amount of friction between these surfaces. The setup was fixed on the servo-controlled universal testing machine (Fig. 2(b)) having a load capacity of ±50 kN. The roller was indented onto the float glass at a displacement rate of 0.5 mm/min. The load continuously increases with increase in displacement of the roller. The fracture of the specimen in two parts occurs (Fig. 2(e)) due to the tensile stress generated perpendicular to the cross-section of the specimen during indentation. The failure load is noted for each tested specimen. Similarly, the specimens were tested under compression (Fig. 2(d)) and TPB setup (Fig. 2(c)). The specimen were loaded ensuring proper contact between the moving attachment and glass surface. The specimen fails in two parts for TPB setup while it gets broken into powder after failure under compression loading. The failure load is obtained for all the tests and comparison between different setup has been made. Table 2: Test matrix used for evaluation of strength of float glass. S. No. Type of test No. of tests Specimen size (mm x mm) 1 Cylindrical indentation 32 10 x 27 2 Three point bend test 26 10 x 22 3 Compression test 22 10 x 10