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Thermomechanical Modeling of Laser‐Induced Structural Relaxation and Deformation of Glass: Volume Changes in Fused Silica at High Temperatures
Author(s) -
Vignes Ryan M.,
Soules Thomas F.,
Stolken James S.,
Settgast Randolph R.,
Elhadj Selim,
Matthews Manyalibo J.
Publication year - 2013
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.12110
Subject(s) - materials science , thermal expansion , relaxation (psychology) , deformation (meteorology) , laser , amorphous solid , thermal , glass transition , composite material , thermodynamics , optics , chemistry , crystallography , polymer , psychology , social psychology , physics
A fully coupled thermomechanical model of the nanoscale deformation in amorphous SiO 2 due to laser heating is presented. Direct measurement of the transient, nonuniform temperature profiles was used to first validate a nonlinear thermal transport model. Densification due to structural relaxation above the glass transition point was modeled using the Tool‐Narayanaswamy ( TN ) formulation for the evolution of structural relaxation times and fictive temperature. TN relaxation parameters were derived from spatially resolved confocal Raman scattering measurements of Si – O – Si stretching mode frequencies. Together, these thermal and microstructural data were used to simulate fictive temperatures which are shown to scale nearly linearly with density, consistent with previous measurements from Shelby et al . Volumetric relaxation coupled with thermal expansion occurring in the liquid‐like and solid‐like glassy states lead to residual stresses and permanent deformation which could be quantified. However, experimental surface deformation profiles between 1700 and 2000 K could only be reconciled with our simulation by assuming a roughly 2 × larger liquid thermal expansion for a‐ SiO 2 with a temperature of maximum density ~150 K higher than previously estimated by Bruckner et al . Calculated stress fields agreed well with recent laser‐induced critical fracture measurements, demonstrating accurate material response prediction under processing conditions of practical interest.