Load dependence of densification in glass during Vickers indentation test

Abstract

The load dependence of densification during a Vickers indentation test was investigated for three commercial glass compositions, soda-lime silicate glass, aluminoborosilicate glass, and lead borosilicate glass, each of which exhibits markedly different susceptibility to crack initiation. The contribution of densification to the total deformation due to indentation was evaluated as the ratio of the depths of indentation before and after heat treatment measured with an atomic force microscope (AFM). For the soda-lime silicate and aluminoborosilicate glasses, the contribution of densification decreases with increasing applied load, but the rate of the decrease is less for the alumonoborosilicate glass than for the soda-lime silicate glass. For the lead borosilicate glass, the contribution of densification is low throughout the range of loads investigated. The residual stress can be estimated from the contribution of densification, and the variation of load dependence of the residual stress is considered to result in a large difference in the crack initiation load among the glasses.

Interaction between Deformation and Crack Initiation under Vickers Indentation in Na2O–TiO2–SiO2 Glasses

“…This would be expected to promote an easier path to fracture, so a slight decrease in the fracture toughness would be expected. These values approximately match literature values of glasses with similar compositions Ito, 1998, 1999;Kato et al, 2011). The fracture toughness does not appear to have any correlation with the minimum observed in the critical crack initiation load.…”

“…An important distinction between the shear volume calculated here and that calculated by Sellappan et al is that the shear volume here includes all volume deformed through shear, both upward resulting in pileup and downward resulting in residual stresses, while Sellappan et al only included the shear flow upward that contributed toward pileup. The Na2O-TiO2-SiO2 system appears particularly susceptible to shear flow downward with negligible amounts of pileup around indents prior to annealing, similar to some of the indent profiles observed by Kato et al (2011). Thus, only a portion of the shear volume reported here contributes toward relaxing the deformed volume, while the remainder contributes toward residual stresses.…”

Measurements of density distribution around Vickers indentation on commercial aluminoborosilicate and soda-lime silicate glasses by using micro Raman spectroscopy

“…Moreover, Glass C contains much 3-coordinated boron with oxygen [22], which possibly increases both shear flow and flexibility of the network. According to the previous study [23], however, the calculated packing densities of Glass C (0.542) and Glass D (0.544) are very close to each other, indicating that there is little difference in the amount of the free volume between these glasses. Shear stress should enhance densification according to Mackenzie [25], but since the Glass C shows less shear lines under the indentation (Fig.…”

Mixed alkali effect on Vickers hardness and cracking

“…Densification of a given glass system is primarily affected by the magnitude of indentation load [12] and atomic packing density [13]. Atomic packing density here refers to the ratio between the measured density and the density computed from estimates of atomic radii.…”

“…Accordingly, the coefficient ξ should be scaled by D P /D. The fraction of indent depth due to densification is typically 10-40%, and depends on glass structure and atomic packing density [12,13,[19][20][21]. We thus estimate the indent depth due to plastic flow as just the fraction of indent depth attributed to densification.…”