Nucleation and crystallization as induced by bending stress in lithium silicate glass fibers

Glass fibers of Li2O · 2SiO2 (LS2) and Li2 O · 1.6SiO2 (LS1.6) compositions were heated near, but below, the glass transition temperature for different times while subjected to a constant bending stress of about 1.2 GPa. The nucleation density and the crystallization tendency, estimated by differential thermal analysis, of a glass sample in the vicinity of the maximum in bending stress increased relative to that of ‘stress-free’ glass fibers. LS2 glass fibers were found more resistant to nucleation and crystallization than the LS1.6 glass fibers. The scanning electron microscopy results for lithium silicate glass fibers clearly demonstrate that the crystallization temperature decreased by more than 150 °C when the glass fibers were subjected to a bending stress confirming that a bending stress on a glass fiber enhances its overall tendency for crystallization.