Glass - Back to the Future!

Presenting Author:
Chuck.R. Kurkjian

article posted 7 April 2016

Dr Chuck.R. Kurkjian specializes in the study of the mechanical properties of inorganic glasses. This involves the measurement of fundamental properties of simple and commercial glasses and the mechanical properties and reliability of lightguide fibers. In brief: BS Rutgers University (1952), ScD: MIT (1955): Post-doc Fellow, University of Sheffield (1957-1959): AT&T Bell Labs (1959-1994): Bellcore (1994-1999): Princeton University (1999-2001): Rutgers University (1999-present, retired).

Crack Initiation and Plasticity in Silicate Glasses

E. Barthel1, S. Yoshida2, Y. Sung3 & C.R. Kurkjian4*

When a hard, pointed object is moved along or impressed onto a glass surface, a plastic zone is created under the point. This plastic zone is formed by a combination of shear flow and densification. Cracks are then nucleated and grown as a result of the stresses generated by this flow. For many years, attempts have been made to understand these processes by MD and FEA modelling, by measuring changes in cracking probabilities and by correlating these changes with changes in physical properties as the glass composition is changed. Recent models have made strong correlations, especially with Poissonís ratio. While these efforts have advanced our understanding to some extent, it seems that a more specific/direct approach is needed. We have recently assembled an international team to directly measure the events, the physical processes and the stresses involved in flow during scratching and indentation. A tomographic technique is used to directly measure the index change, and thus the density change in the plastic zone under the indent. In parallel, we monitor the birefringence around aggressive contacts such as by a cone or Vickers indenter. Using finite element modelling, we combine the results of these experiments to provide a description of the plastic stress fields under sharp indents in glasses with unprecedented accuracy, and by comparison with crack initiation conditions, we hope to propose criteria for crack formation.

1 ESPCI, Paris, France
2 The University of Shiga Prefecture, Japan
3 University of Wisconsin- Milwaukee
4 Rutgers University (retired)