Abstract
Most supercooled non-polymeric glass-forming melts exhibit a shear thinning phenomenon, i.e., viscosity decreases with increasing the strain rate. On compressing borosilicate glasses at high temperature, however, we discovered an interesting oscillatory viscous flow and identified it as a typical relaxation oscillation caused by the peculiar structure of borosilicate glass. Specifically, the micro-structure of borosilicate glass can be divided into borate network and silicate network. Under loading, deformation is mainly localized in the borate network via a transformation from the three coordinated planar boron to trigonal boron that could serve as a precursor for the subsequent formation of a BO4 tetrahedron, while the surrounding silicate network is acting as a stabilization/relaxation agent. The formation of stress oscillation was further described and explained by a new physics-based constitutive model.
Highlights
The nonlinear rheology of glassy materials is at the very centre of non-crystalline physics and mechanics[1,2,3,4], which represents the complex deformation mechanisms of a variety of advanced amorphous materials including soft-matter colloidal suspensions, polymer melts, gels, forms, structural glasses as well as metallic glasses[4,5]
According to the dependence of strain rate, the non-Newtonian liquid can be further divided into two groups: shear thickening flow if the viscosity increases with strain rate, and shear thinning flow if the viscosity decreases with strain rate[20]
This paper aims to investigate the nonlinear rheology of borosilicate glass in its supercooled liquid region
Summary
The nonlinear rheology of glassy materials is at the very centre of non-crystalline physics and mechanics[1,2,3,4], which represents the complex deformation mechanisms of a variety of advanced amorphous materials including soft-matter colloidal suspensions, polymer melts, gels, forms, structural glasses as well as metallic glasses[4,5]. Lubchenko stated that[22] all deeply super-cooled non-polymeric fluids, independent of their chemical details, should exhibit simple shear thinning. This statement was further supported by recent experimental results covering a wide range of inorganic glass-forming liquids including Na2Si2O5, Na2Si3O7, Na2Si4O9, K2Si3O7, K2Si4O9, Li2Si4O9, CaMgSi2O6 etc[21]. Rigid 4-fold coordinated boron transforms to softer 3-fold coordinated boron This transformation contributes to the viscous flow of borosilicate glass[31]. Most studies were only on the changes of viscosity influenced by compositions and thermal processing[27,28,29]
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