Fracture Mist Region in a Soda-Lime-Silica Float Glass

The mist region near the fracture origin was studied in a series of soda-limesilica float glass specimens ranging in strength from about 30 to 90 MPa. Both the mirror/mist and the mist/hackle radii were measured to ascertain the dependence of the width of the mist region on the strength level. The mirror/mist constant was found to be 1.80 ± 0.15 MN/m^3/2 and the mist/hackle constant to be 2.42 ± 0.16 MN/m^3/2. Both analytically and experimentally, the width of the mist region was found to be inversely related to the square of the fracture stress; that is, (W_mist) is proportional to (1/$σf2$⁠). This suggests a dependence of the mist region width on the elastic strain energy at fracture initiation.

The surface topography of the mist region was analyzed by a scanning electron microscopy computerized contour mapping technique to determine the surface roughness within the mist region. It was observed that the average root-mean-square roughness in the mist region was proportional to the fracture stress squared. This suggests that the fracture surface roughness of the mist region, or alternatively the true surface area of the mist region, is also determined by the stored elastic strain energy in the specimen before fracture.

It is concluded that the mist region width and the mist region roughness are both determined by a strain energy criterion. It is suggested that they may be related through a generalized mist region parameter.