Three‐dimensional densification measurement of Vickers‐indented glass using digital holographic tomography

Abstract

We have used digital holographic tomography (DHT) to study the refractive index (density) changes occurring under Vickers indentations in silica, soda‐lime, and non‐alkaline aluminoborosilicate glasses. The measurements confirm that the maximum refractive index (density) is not constant but increases with load up to 300 gf. At higher loads (500 gf and 1 kgf), a subsurface (median) crack in soda‐lime glass is observed with no apparent surface trace. The appearance of this crack reduces the maximum refractive index (density) observed. In addition, the vertical cross section of the 3D refractive index (density) map has been successfully obtained using a square fiber sample and lateral observation. These results clearly demonstrate a promising potential of DHT to evaluate the shape and the density distribution of the structurally modified zone in a Vickers‐indented glass.

Radial cracking at Vickers indentations in pristine flat/square silica fibers

“…In order to do that, some experimental works such as the probe indentation, 44 the measurement of crack opening distance, 45 cathodoluminescence, 46 and micro-photoelasticity, 33 should be improved in terms of quantitative analysis. Not only direct measurement of the indentation-induced stresses but experimental evaluation of pressure-induced changes in structure and in properties 34,47 will help us to put reliable parameters in modeling calculation to obtain the precise indentation-induced stress field.…”

“…29 In addition, the absence of any residual stress of the square fiber before the indentation test was confirmed by using different types of polarization microscopes. 33,34 The use of these flat or square fibers enabled us to perform in-situ observation of the indentation process and measurement of the crack initiation load. Especially, the better surface parallelism and flatness for the square fiber permitted us to obtain a more symmetrical indentation imprint under a Vickers indenter.…”

Indentation and abrasion in glass products: Lessons learned and yet to be learned

“…Figure 9 shows the results for the densification due to Vickers indenter in a soda lime silicate glass using space‐resolved Brillouin spectroscopy 27 ; the densification region being similar to that shown in Figure 2B. Refractive index mapping along the central vertical plane after indenting with a 300 gf load in silica (Figure 10A), an aluminum borosilicate (Figure 10B), and a soda lime silicate (Figure 10C) are compared in Figure 10D 28 …”

“…Refractive index mapping along the central vertical plane after indenting with a 300 gf load in silica (Figure 10A), an aluminum borosilicate (Figure 10B), and a soda lime silicate (Figure 10C) are compared in Figure 10D. 28 Silica glasses show densification (or increase in refractive index) as much as 17% just below the Vickers indenter (red curve; Figure 10D). Densification decreases rapidly with distance from the indentation.…”

Compositional variation of indentation-induced deformation and cracking in glass

“…Since the crack initiation is accompanied with dynamic structural changes in an atomistic level, we should focus on dynamic changes in glass structure just before the crack initiation. Some experimental researches are now in progress using various techniques, such as Raman spectroscopy including low-energy spectrum or Boson peak, 53) Brillouin spectroscopy, 54) small angle X-ray scattering, 55) digital holographic tomography, 56) and X-ray tomography. 57) As for in-situ Raman spectroscopy of glass during the indentation, the present author and his colleagues fabricated a custom indenter for Raman measurements, and reported remarkable peak broadening of Raman spectrum of silica glass under a Vickers indenter.…”