Characterization of the Mirror Region With Atomic Force Microscopy
Sheldon M. Wiederhorn, Jose Lopez-Cepero, Jay S. Wallace, Jean-Pierre Guin, Theo Fett
In this paper we use atomic force microscopy to investigate the roughness of the mirror region in silica glass. We demonstrate a decrease in surface RMS Roughness from about 0.5 nm to about 0.4 nm with increasing stress intensity factor (0.5KIc to about 0.95KIc). We believe the roughness to be a consequence of elastic interactions of the crack tip with nano scale inhomogeneities in the glass. These results contrast with the usual observation that roughness increases with distance as the crack propagates from the mirror region and into the mist and hackle regions. At low values of KI crack surfaces are relatively smooth. It is only when cracks approach KIc that the roughness builds up in silica glass leading to the expected transition in surface topography as the crack gets longer.