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

Garth Scannell,Garth Scannell,Garth Scannell,Denis Laille,Tanguy Rouxel,Tanguy Rouxel,Fabrice Célarié,Liping Huang,Fabrice Célarié

doi:10.3389/fmats.2017.00006

Abstract

An observed minimum in the critical crack initiation load at Poisson's ratio (ν) of 0.21-0.22 in Na2O-TiO2-SiO2 glasses was investigated. Vickers indentation was used to examine hardness and average cracking length, fracture toughness was measured through the single-edge pre-cracked beam method (SEPB), and volumes of densification and shear flow around indents were measured using atomic force microscopy (AFM). Relations between the critical crack initiation load and hardness, average crack length, fracture toughness, and the volume fractions of densification and shear flow were studied. No correlations were observed between hardness, average crack length, or fracture toughness with the critical crack initiation load. A link between the minimum in crack initiation load and a change in deformation mechanisms (densification vs. shear flow) was observed.

Highlights

Understanding structure–property relationships in glasses remains a distinct challenge in designing new glasses for specific applications (Mauro et al, 2014)
It is likely that as the glass response changes from primarily deforming through densification to shear flow, an intermediate region could exist where the competing deformation mechanisms result in an increase in residual stresses around the indent, consistent with the bell-shaped curve for the residual stress intensity factor as a function of ν [ξ in Fig. 5 in Rouxel (2015)]
The hardness and average crack length were investigated through Vickers indentation, the fracture toughness was measured through the single-edge precracked beam method (SEPB), and the volume fractions of shear flow and densification around Vickers indents were measured using atomic force microscopy (AFM)

Summary

Introduction

Understanding structure–property relationships in glasses remains a distinct challenge in designing new glasses for specific applications (Mauro et al, 2014). In a recent study by the authors, an unexpected trend was observed, where the critical load (Pc) for initiating cracks at the corners of Vickers indentations went through a minimum as the Poisson’s ratio was increased from 0.18 to 0.24 in Na2O–TiO2–SiO2 glasses (Scannell et al, 2015), with the minimum occurring at ν = 0.21–0.22. This behavior is not anticipated by the driving forces maps developed by Rouxel et al (2014), which predict that the driving forces for radial cracking should increase with the Poisson’s ratio across the examined range (0.18–0.24). A structural model was proposed to explain the minimum in crack initiation load and a change in deformation mechanisms (densification versus shear flow) under indentation

Objectives

Results

Discussion

Conclusion