Dynamic process of Vickers indentation made on glass surfaces

Dynamic processes of Vickers indentation on glass surfaces were observed with a newly developed apparatus. It enables us to take successive picture images of a growing indentation from behind a transparent specimen with a CCD camera through an optical microscope with a minimum time interval of 16.7 ms. Growing rates of indentations were measured under several conditions of loading weight and collision velocity of the indenter with the sample surface. An indentation rapidly grows at the initial stage, followed by decrease in growing rate, finally approaching a value specified with the loading weight and the hardness of glass. This behavior can be described by a Voigt model, indicating that ‘‘visco-elastic’’ nature in a microscopic sense is involved in the indentation process of glass. It is also found that the initial growing rate highly depends on the collision velocity; that is, the larger the collision velocity is, the higher the initial growing rate is. The result suggests that local temperature rise in the vicinity of the indentation due to friction or adiabatic compression reduces the viscosity of indented material.