Non-Newtonian Flow to the Theoretical Strength of Glasses via Impact Nanoindentation at Room Temperature

Abstract

In many daily applications glasses are indispensable and novel applications demanding improved strength and crack resistance are appearing continuously. Up to now, the fundamental mechanical processes in glasses subjected to high strain rates at room temperature are largely unknown and thus guidelines for one of the major failure conditions of glass components are non-existent. Here, we elucidate this important regime for the first time using glasses ranging from a dense metallic glass to open fused silica by impact as well as quasi-static nanoindentation. We show that towards high strain rates, shear deformation becomes the dominant mechanism in all glasses accompanied by Non-Newtonian behaviour evident in a drop of viscosity with increasing rate covering eight orders of magnitude. All glasses converge to the same limit stress determined by the theoretical hardness, thus giving the first experimental and quantitative evidence that Non-Newtonian shear flow occurs at the theoretical strength at room temperature.

Lateral‐pushing induced surface lift‐up during nanoindentation of silicate glass

“…The parameters 𝑉 − a and 𝑉 + a stand for the volumes after annealing. Yoshida's method has been widely applied in indentation studies, [24][25][26][27][28][29][30][31][32][33] and numerous developments 12 have been achieved regarding the indentation-induced volume and structure evolution. Nevertheless, as stated by one recent study, 34 it remains challenging to accurately determine the amplitude of the blister field during the indentation process.…”

Anomalous Deformation Behavior in ULE Glass upon Microindentation: A Vibrational Spectroscopic Investigation in the Induced Structural Changes of a Ti-Silicate Glass

“…Indentation was found to induce structural changes in the investigated glasses as has previously been shown for Duran or silica. − ,, A comparison of indentation-induced structural changes in the three fully polymerized glasses v-SiO 2 , ULE, and Duran is given in Figures and , where Raman spectra before and after Vickers indentation are depicted. For all glasses, a shift to higher frequencies is observed for the maximum of the most intense band envelope below 500 cm –1 .…”

“…Earlier studies focused on pure vitreous silica , and soda-lime-silicate glasses, later to be augmented by other compositions and various studies on borosilicate glasses . We focused particularly on low-alkali borosilicate glasses, which, like “Pyrex”- or “Duran”-type glasses, are of high technical importance and which, like vitreous SiO 2 , exhibit a fully polymerized glass network and fall in the category of “anomalous” glasses when considering their response toward mechanical testing. ,,,− Another fully polymerized, technically important silicate-rich glass is the Ultra Low Expansion glass (ULE, Corning), a binary titano-silicate glass. With a TiO 2 fraction of 7.4 wt % (5.67 mol %), ULE exhibits an almost zero coefficient of thermal expansion (CTE) from 5 to 35 °C (CTE of 0 (±30) × 10 –9 /°C), and even between 100 and 300 °C the CTE is an order of magnitude smaller than for vitreous silica .…”

“…These laser-induced changes sparked our interest to look also into structural changes of a ULE glass under a purely mechanical impact, where a change in the oxidation state of titanium ions would not be likely. Attempting similar studies as performed earlier on low-alkali borosilicate or vitreous SiO 2 glasses, ,,,,, we aim at identifying any structural modifications in ULE occurring as a consequence of indentation. While we expect a similar “anomalous” densification-driven behavior as for the other named fully polymerized silica-rich glasses, we may also assume no reduction of titanium ions, contrary to the results of our laser modification studies.…”

Nanoindentation‐induced evolution of atomic‐level properties in silicate glass: Insights from molecular dynamics simulations

“…During indentation of glass, both elastic and inelastic deformations occur, and the latter is responsible for the indentation sink‐in (below the original contact surface) and pile‐up (above the original contact surface) 2 . Although not yet conclusive, previous experiments 5,14–23 and computer simulations 11,24–28 have suggested that shear flow and densification are the two main mechanisms responsible for the inelastic deformation of glass under indentation; the respective contribution of each mechanism may depend on the shape/sharpness of the indenter 5 . A recent experimental study 13 on a series of silicate glasses found that the region above the original contact surface can be further separated into pile‐up (close to the indent) and lift‐up (far away from the indent).…”