From these images, it can be seen that there are substantial differences in the magnitude and distribution of the stress birefringence due to indentation in these two glasses ( as expected, see Arora et al. JNCS 31 415-428, 1979). This is also to be expected based on the portions of flow due to shear and compaction in the two glasses (see Yoshida et al, J. Mater. Res, 20 (12) 3404-3412, 2005), as well as earlier work of Peters, Hagan and others. Detailed calculations of the 3D stresses are in progress and will be presented soon.
It is clear that an understanding of such indentation processes is critical to the development of more robust glasses as well to the development of appropriate scoring cracks for the 'thermal cutting' of substrate glasses used for liquid crystal displays. Such quantitative work has not been done to date. The availability of the CRI Abrio system as well as the analyses of Prof. H. Aben and A. Errapart at the Institute of Cybernetics at Tallinn University of Technology in Estonia (see 'links') have made this work possible.
SUMMARY AND NEW IMAGES(08 02 09), COURTESY OF
R. OLDENBOURG, WOODS HOLE MA.
Below are images (first perpendicular and then parallel to the indentation direction) of two glasses recently imaged. As with the above soda lime and silica glasses, 50 gram loads were applied to a cone indenter. It can be seen that substantial cracking occurred (compare with the 'uncracked' images above). Both of these glasses had been found to be 'less brittle' when indented with a Vickers diamond (see Ito et al., ito.pdf). This illustrates the complexity of the indentation problem, as well as the need to study it in great detail. This is necessary in order to understand it and to improve the 'robustness' of such oxide glasses (see also Yoshida, PACRIM8-24-yoshida.pdf)..

glass #1 perpendicular

glass#1 parallel

glass#2 perpendicular

glass#2 parallel