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Deformation, Stress Relaxation, and Crystallization of Lithium Silicate Glass Fibers Below the Glass Transition TemperatureThe deformation and crystallization of Li(sub 2)O (center dot) 2SiO2 and Li(sub 2)O (center dot) 1.6SiO2 glass fibers subjected to a bending stress were measured as a function of time over the temperature range -50 to -150 C below the glass transition temperature (Tg). The glass fibers can be permanently deformed at temperatures about 100 C below T (sub)g, and they crystallize significantly at temperatures close to, but below T,, about 150 C lower than the onset temperature for crystallization for these glasses in the no-stress condition. The crystallization was found to occur only on the surface of the glass fibers with no detectable difference in the extent of crystallization in tensile and compressive stress regions. The relaxation mechanism for fiber deformation can be best described by a stretched exponential (Kohlrausch-Williams-Watt (KWW) approximation), rather than a single exponential model.The activation energy for stress relaxation, Es, for the glass fibers ranges between 175 and 195 kJ/mol, which is considerably smaller than the activation energy for viscous flow, E, (about 400 kJ/mol) near T, for these glasses at normal, stress-free condition. It is suspected that a viscosity relaxation mechanism could be responsible for permanent deformation and crystallization of the glass fibers below T,
Document ID
20040075691
Document Type
Preprint (Draft being sent to journal)
Authors
Ray, Chandra S. (NASA Marshall Space Flight Center Huntsville, AL, United States)
Brow, Richard K. (NASA Marshall Space Flight Center Huntsville, AL, United States)
Kim, Cheol W. (NASA Marshall Space Flight Center Huntsville, AL, United States)
Reis, Signo T. (Missouri Univ. Rolla, MO, United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 2004
Subject Category
Nonmetallic Materials
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.