Abstract
Improving the fracture resistance of oxide glasses through adjustment of the chemical composition remains a challenging task, although composition-mechanical property relations have been established for simple model systems. The glass mechanical properties are, among other methods, conventionally tested using instrumented indentation, which is a fast and convenient technique that mimics the real-life damage for certain applications, although interpretation can be challenging due to the complex stress fields that develop under the indenter. Early indentation experiments have shown that oxide glasses exhibit pronounced tendency to densify under compressive load compared to metals and ceramics. After decades of investigations, it is now known that the extent of densification is strongly dependent on the glass' chemical composition and in turn its atomic packing density and Poisson's ratio. Spectroscopic techniques have shed light on the mechanism of densification, which include changes in the bond angle distributions as well as an increase in the coordination number of the network-forming cations. Knowledge of such details is crucial for understanding the link between chemical composition and resistance to cracking in oxide glasses, since densification is an efficient way to dissipate the elastic energy applied to the material during indentation. Here, we review the experimental work on identification and quantification of indentation deformation in glasses, as well as on probing the accompanying structural changes in the glassy network. We also include the conclusions drawn from computer simulation studies, which can provide atomistic details of the indentation deformation mechanisms. Finally, we discuss the link between the mechanism of deformation and the crack resistance.
Highlights
Oxide glasses are textbook examples of brittle materials
On the other hand, when Al2O3 or B2O3 are added to the silicate framework rather than the depolymerizing alkali or alkaline earth oxides, the structural response to indentation resembles that of amorphous silica, i.e., the Raman bands corresponding to three- and four-membered rings appear at higher wavenumbers following the indentation-induced increase in density [113,114,115]
We have reviewed the open literature on the deformation mechanisms associated with indentation in oxide glasses
Summary
Oxide glasses are textbook examples of brittle materials. When subjected to loading, amplification of stresses occurs around surface flaws, leading to catastrophic fracture [1]. Various studies suggest that the resistance to initiate cracking upon indentation is associated with the ability of a glass to dissipate the supplied mechanical energy through densification facilitated by structural rearrangements [31,32,33,34,35]. The data is evaluated with respect to indentation cracking throughout the paper, as the ultimate aim is to improve the current understanding of deformation mechanisms, which can in turn facilitate design of novel glasses, which are less damaged by sharp contact loading.
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