The mechanical response to contact of Soda Lime Silica float glass and the effects of hydration and high temperature

The response of the surface of the Soda Lime Silica float glass to contact was studied by means of instrumented indentation. The research was focused on two specific conditions to which the glass can be exposed during manufacturing and use, first, the change in the hardness and elastic modulus of the near surface of glass exposed to different periods of accelerated weathering at 40°C and 95% relative humidity, and second, changes in the mechanical properties at 520, 540 and 560°C, the latter being the glass transition temperature of this type of glass. There is an extensive literature about the effects that weathering has on the chemical composition of the air and tin sides surfaces of float glass. Nevertheless, research into the mechanical properties of weathered glass is rather limited. In this study it was found that the air side of the float glass showed an evolution of the nanoindentation hardness and elastic modulus with the exposure time, while in the tin side, the change was almost negligible under the same experimental conditions. Regarding the contact at elevated temperature on glass, it is possible to find several studies in which hardness is reported over a wide range of temperatures from below 0 up to 700°C. There are discrepancies in the reported results at high temperatures due to the different experimental conditions used by the researchers. This study investigated the effect of the testing parameters such as loading and unloading rate, dwell time, and temperature. The creep behaviour was also studied using mechanical models with Maxwell and Kelvin elements. Such models were fitted to the creep curves and explained well the viscoelastic behaviour near the glass transition temperature. The experiments were carried out on a specially developed apparatus, which has the ability to perform micro and macro-indentations with Vickers and Hertzian indenters from room temperature up to 560°C.