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The impact of densification on indentation fracture toughness measurements
Author(s) -
Gross Timothy M.,
Liu Hongshen,
Zhai Yue,
Huang Liping,
Wu Jingshi
Publication year - 2020
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.16793
Subject(s) - indentation , materials science , composite material , fracture toughness , chevron (anatomy) , vickers hardness test , residual stress , toughness , diamond , microstructure , paleontology , biology
The fracture toughness was measured by the Vickers indentation method and by chevron notch for a series of x CaO‐ x Al 2 O 3 ‐(100 − 2 x )SiO 2 glasses. As the silica content was increased, the fixed ξ value Vickers indentation fracture toughness (IFT) values increased, while the chevron notch values decreased. Glasses with higher silica contents deform with more densification and less shear when indented with a Vickers tip, thus resulting in reduced residual stress in the region surrounding the indent. The reduction in residual stress for high silica glasses results in less median/radial crack extension and unreasonably high Vickers IFT values. This indicates that a fixed ξ value of 0.016 is not appropriate for the glasses in this series. By repeating the IFT method with a sharper 110° four‐sided pyramidal diamond indenter, it is demonstrated that indentation toughness and chevron notch toughness values now trend in the same direction and are in good agreement with a fixed ξ value of 0.0297. With the sharper indenter tip, the densification component to the deformation is substantially reduced for all glass types such that it no longer has such a prominent influence on the residual stress field. This result suggests that a fixed ξ value IFT method may be appropriate for all glass types if a sharper indenter tip is substituted in the place of the Vickers tip.