PSI - Issue 71

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

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Fig. 2: (a) Machine used for the tests; (b) cylindrical indentation test setup; (c) three point bend test setup; (d) compression test setup (e) Specimen before and after tests under cylindrical indentation 3. Evaluation of scatter in failure load under different test configurations Different specimens of float glass were prepared for evaluation of its strength using different test setup. The load displacement behavior of the specimen was evaluated using the load-cell and displacement transducers fixed to the UTM machine. The details of the failure load obtained for different tests are discussed in subsequent sections. 3.1 Cylindrical indentation tests The cylindrical indenters were positioned perpendicular to the length of the specimen and pressed against it at a constant displacement rate of 0.5mm/min. As the indenter moves, more of the specimen's surface comes into contact with the roller. The load increases continuously as the indenter displacement into the specimen increases. A typical load-indentation curve for the cylindrical indenter is illustrated in Fig. 3(a). Indentation creates a tensile stress that acts perpendicular to the cross-section of the specimen. The specimen fails in two parts once the critical tensile stress threshold is exceeded beneath it. Since the stresses under this configuration can’t be obtained directly, finite element analysis has been carried out to determine the critical tensile stress developed on glass specimen. It is discussed in section 4. Fig 3(b) shows the variability in failure load, which ranges from 420 N to 1660 N, with an average failure load of 950 N. This variation is attributed to differences in flaw distribution under the indenter, as the critical stress is reached at these flaws, failure of the specimen occurs. 3.2 Three-point bend tests The specimen was placed in the machine attachment, which has a span of 14 mm. Proper alignment between the indenter and the specimen was ensured to maintain line contact. The indenter was pressed onto the specimen until failure occurred, at that point the failure load was recorded. The scatter in failure load is shown in Fig. 3(c) where the failure load varied from 300 N to 455 N, with an average failure load of 385 N. This failure load was then used to calculate the bending stresses using equations (1) to (3). = (1) where, = 1 4 (2) = 1 6 2 (3) where, ‘l’ is the span of the attachment, ‘P’ is the failure load, ‘b’ is the width of the specimen, ‘t’ is the thickness of the specimen. 3.3 Compression tests The specimen was positioned between compression platens made of precipitate hardened steel. A machine with a capacity of ±500 kN was employed for these compression tests, as a significant load is necessary to induce failure in the glass specimen under compression. The machine's crosshead was moved at a constant displacement rate of 0.5