Driving force for indentation cracking in glass: composition, pressure and temperature dependence

Abstract

The occurrence of damage at the surface of glass parts caused by sharp contact loading is a major issue for glass makers, suppliers and end-users. Yet, it is still a poorly understood problem from the viewpoints both of glass science and solid mechanics. Different microcracking patterns are observed at indentation sites depending on the glass composition and indentation cracks may form during both the loading and the unloading stages. Besides, we do not know much about the fracture toughness of glass and its composition dependence, so that setting a criterion for crack initiation and predicting the extent of the damage yet remain out of reach. In this study, by comparison of the behaviour of glasses from very different chemical systems and by identifying experimentally the individual contributions of the different rheological processes leading to the formation of the imprint-namely elasticity, densification and shear flow-we obtain a fairly straightforward prediction of the type and extent of the microcracks which will most likely form, depending on the physical properties of the glass. Finally, some guidelines to reduce the driving force for microcracking are proposed in the light of the effects of composition, temperature and pressure, and the areas for further research are briefly discussed.

Evaluation of Sinking-In and Cracking Behavior of Soda-Lime Glass under Varying Angle of Trigonal Pyramid Indenter

“…However, indentation cracking methods for evaluating fracture toughness (Kc) are open to question due to, for example, a lack of a definite solution for the stress intensity factor at the crack tip (Quinn and Bradt, 2007). In addition, glassy materials exhibit permanent densification, which sometimes reduces the residual stress for cracking and results in the value much different from the fracture toughness (KIc) measured by a self-consistent method (Rouxel, 2015). These are the reasons much care should be taken if the indentation fracture toughness are used as a measure of resistance to extension of a crack.…”

“…Thus, resultant cracks after complete unload sometimes accompany with plastic deformation. Consequently, elastic and plastic deformation behaviors of glass under the sharp indenter should be closely connected with cracking behaviors or brittleness of glass (Cook and Pharr, 1990;Rouxel, 2015). However, a conventional hardness tester cannot enable us to visualize the mechanical response of glass during indentation cycle.…”

Vickers Indentation Cracking of Ion-Exchanged Glasses: Quasi-Static vs. Dynamic Contact

“…This mechanism has been described as a preferential deformation along pathways through ionically bonded modifier-rich interfaces between anions, or along modifiers associated with NBOs (Peter, 1970;Ernsberger, 1977). Glasses with high NBO content also tend to have higher packing densities which favor shear deformation by reducing the free volume that can accommodate the competing densification mechanism (Mackenzie, 1963;Ernsberger, 1968;Neely and Mackenzie, 1968;Yoshida et al, 2005;Greaves et al, 2011;Rouxel, 2014). Shear deformation during indentation leads to high residual stresses (Yoffe, 1982) and extensive subsurface damage (Hagan and Swain, 1978;Arora et al, 1979;Hagan, 1980;Hagan and Van Der Zwaag, 1984;Gross, 2012), thus the load required to form strength limiting median/radial cracks is relatively low.…”

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

“…To the authors' knowledge, specific structural mechanisms have only been attributed in the silica glass system. Rouxel (2015) discusses the relationship between shear flow, pressure, and densification, mainly focusing on silica, but also extending his discussion to silicate glasses in general.…”

“…Rouxel et al (2014) developed indentation cracking maps to predict driving forces for cracking in glasses. They found a critical value at ν ≈ 0.21-0.23 where the indentation stress field was greatly reduced during indentation, as well as a transition from easily damaged to highly resilient glasses at ν = 0.33 (Rouxel, 2015).…”