ガラスのK_Icとビッカース押込みにおける垂直割れ目の発生について

抄録

Crack formation around Vickers indentation has been studied on PbO-ZnO-B₂O₃ glasses with a wide range of K_Ic and commercial silicate glasses; fused silica, Pyrex, and float glasses.
Observations of crack initiation indicated that the Palmqvist type radial cracks generated in the lower loading range, and median cracks were formed in the higher loading range. Fused silica and Pyrex glasses showed cone cracks in addition to the radial and median cracks in all over the loading range.
The relationship between the initiation load for the median crack and the material parameters (K_Ic and H_V) obtained in this study supported the Lawn-Evans model. The magnitude of the initiation load was, however, considerably higher than that calculated by their theory, suggesting a necessity of some corrections for the parameters related to the deformed zone beneath the indenter. The initiation load increased with an increase in plastic zone size estimated from the Dugdale model, indicating that less plastically deformable glasses require lower load to form the median crack because of greater mismatch at the elastic/plastic boundary beneath the indenter. In spite of little plastic deformation, fused silica showed slightly higher initiation load than the other glasses probably due to densification.
Resistance to the crack formation in the indentation was discussed in terms of fracture toughness and elastic/plastic properties of glasses.