Sharp indentation of silicate glasses: investigating mechanical response through stress-strain fields and their dependencies

Abstract

The solid mechanics of silicate glasses have recently drawn increased attention in both commercial and academic settings, due to the market expansion of consumer flat-panel displays and other applications that demand continuously improving mechanical properties. Susceptibility to sharp contact damage is of the utmost concern, as this damage event introduces flaws which are larger than the native population, resulting in a significant reduction in bulk material strength. The present studies herein investigate the mechanical properties of silicate glasses and their effects on the continuum mechanics response to sharp indentation. Finite element analysis (FEA) is the primary method used for solving non-linear solid mechanics boundary value problems which include both contact and plastic deformation. Experimental indentation is employed in a supportive capacity, generating veritable responses which are used in the validation of FEA models. Overall, the purpose of these studies is to advance the understanding of silicate glass contact mechanics and contribute to the zeitgeist toolset available to commercial and academic researchers alike.

The work herein is presented in sequential studies. First, an existing analytic stress solution was evaluated, revealing limitations in cracking predictions. A sharp indentation FEA model was developed, and simulations correlated to experimental results in all cases. A Python-coded Abaqus ``Plug-In'' was also developed, to provide semi-automation of FEA. Exploratory studies were performed with further simulations, to evaluate the correlation structure of 13 input factors and 6 outcomes. From this work, unique correlations highlighted the most important factors, while also revealing limitations in using stress field magnitudes for direct-correlation to cracking. In pursuit of improved predictive capabilities, a fracture mechanics model was evaluated as a potential method for developing future post-processing techniques which can link FEA stress field results to a single-value predictor of indentation cracking response. Although qualitative indicators show promise in results which indicate both a size-effect and acuity-effect, a complete quantitatively predictive model has yet to be realized. Finally, FEA simulations were performed in support of experimental micropillar crush tests which demonstrate a stress-dependent elastic modulus for fused silica. The resulting elastic modulus was also demonstrated to have a significant effect on sharp indentation stress field results. Altogether, these studies advance the state-of-the-art in the subject of silicate glass sharp indentation, and the publicly-available Abaqus ``Plug-In'' contributes to the overall toolset available to researchers.