• Christian Hermansen
4. term, Chemistry, Master (Scient) (Master Programme)
The Vickers hardness and the indentation induced densied and plastic flow volumes were determined in simple silicate glasses by atomic force microscopy by measuring before and after annealing at 0.9 x Tg for two hours.

It was found that the densified volume decreases linearly with the measured bulk modulus, and the plastic flow volume with the silica molar fraction (becoming zero close to 80%) of the glass. Hardness was related to the elastic properties, in particular the shear modulus, but it was not possible to develop an improved model for hardness prediction given the discovered relations to the deformation volumes.

The relative contribution of densification to plastic flow was attempted to be related to measures of the free volume, such as Poisson's ratio and the helium solubility. However there is no clear relationship with these properties, instead the results being described accurately by the ratio of the resistances described above.

For some glasses the loads for crack initiation were measured and the residual stresses at these loads estimated from the extrapolated plastic flow volumes. The estimated stresses range from 110 to 470MPa (with an error of 70MPa,) and thus it does not seem a single stress for crack initiation exists, even in simple silicates.
Publication date5 Jul 2011
Number of pages86
ID: 53339773