The brittle to ductile transition in a soda-lime-silica glass

The brittle to ductile transition (EDT) occurring in a standard window glas s around T-g has been studied both theoretically and experimentally by intr oducing artificial cracks in glass specimens tested in bending at different temperatures with different displacement rates. The transition results fro m the competition between the loading and the relaxation kinetics in the vi cinity of the most critical flaws. The results show that the higher the loa ding rate the higher the transition temperature range where the behavior tu rns from elastic (brittle) to viscoelastic. This study therefore examines t he BDT, which corresponds to a change in the mechanical behavior from elast ic to viscoelastic and is relevant to the general problem of the crack tip singularity in viscoelastic solids. In order to pet insight into this compl icated problem, the temperature dependence of Young's modulus, shear viscos ity, and relaxation kinetics were first characterized A simple model was fu rther developed to address the BDT more quantitatively, using both crack ti p stress, and stress intensity factor as key parameters. Depending on the i mposed strain-rate between 10(-5) and 10(-3) s(-1), the BDT ranges from 490 degrees C to 560 degrees C. The model allows for a good description of the behavior, accounting either for the strain-rate dependence or the temperat ure sensitivity. Furthermore, the increase in the apparent fracture toughne ss usually reported in most glasses or glass-containing ceramics near the g lass transition temperature is also predicted by the model. (C) 2000 Elsevi er Science B.V. All rights reserved.