Evaluation of Strength of Float Glass Using Indentation Technique and its Comparison with Results from Conventional Tests

Indentation tests are, generally, used for evaluating material properties of brittle as well as ductile material due to its ability to induce deformation in a controlled manner. Evaluation of properties of float glass from direct tensile test is a challenge due to difficulty in fabrication of accurate specimens and holding of specimen with the attachment connected to the load string of the machine. However, indentation tests can be easily carried out and this does not require fabrication of standard specimen from glass. In this work, indentation tests have been carried out on 4 mm thickness float glass sheet to understand the nature of fracture during the indentation process and to evaluate the strength of the glass sheet. Indentation tests have also been carried out using cylindrical type indenter. From the test data, the failure load of the glass sheet has been evaluated. The tests have been repeated multiple times in order to study the statistical scatter in failure load of glass. Finite element analysis has been carried out to determine the tensile stresses acting beneath the indentation during indentation. The stresses were obtained corresponding to all the failure load data. For modelling statistical scatter in failure strength, Weibull statistics has been used. The results obtained from cylindrical indentation tests have been compared with results of conventional three-point bend tests and compression type tests carried out using specimens of standard geometry. It was observed that the median stress values are 42.5 MPa for the indentation test, 50.5 MPa for the three-point bend test, and 740 MPa for the compression test. The methodology developed in this work can be used for large scale evaluation of statistical scatter in strength of glass without using standard specimens.