Stress induced defects in vitreous calcium aluminates.
Induced flaws on vitreous calcium aluminates were investigated quantitatively by applying controlled loading forces to fresh breakage surfaces. Test surfaces were chemically treated to display surface flaws, dynamically created by an indenter. The mean value of flaw length was linearly related to the square root of the applied load on the indenter. A critical stress of flaw formation was calculated from the experimental data. Introduction of silica as a dopant and vacuum melting conditions were found to influence flaw length. Silica weakened the structure and produced a lower critical stress of flaw formation, whereas vacuum melting resulted in an increase in this value. An influence of internal defect concentration was also indicated by variations in the ir transmission characteristics of the glasses. The indicated OH(-) screening effects at 2.8 micro were in agreement with the findings from the flaw studies. A defect array on fresh breakage surfaces suggested the formation of vacancies, and within this pattern the indenter forces produced an interesting localized displacement effect. The magnitude of the displacement agreed with a proposed vacancy diffusion mechanism.
Levengood
W C
WC
University of Michigan, Institute ofScience and Technology, Ann Arbor, Michigan, USA.