BS 7034-3:1988

Provides a method of determining the dynamic viscosity of glass by measuring the elongation of a glass fibre under a defined uniaxial stress. In addition, the viscosity-temperature relationship and the dependence of the viscosity on the thermal history can be determined. Covers field of application, reference, definitions, principle, apparatus, sample and test specimen, procedure, expression of results and test report.

This part of ISO 7884 specifies a method of determining the dynamic viscosity of glass by measuring the elongation of a glass fibre under a defined uniaxial stress. In addition, the viscosity-temperature relationship and the dependence of the viscosity on the thermal history can be determined.

NOTE Using this method, all parts of the tested material are subject to the same mechanical stress when the shape of the fibre is correct, the glass is homogeneous and isotropic, and the influence of gravity on the fibre itself can be neglected. The deformation is a pure elongation instead of a simple shear. Without major uncertainty, the determination of the shear viscosity by an elongation experiment is possible only when the material behaves like a Newtonian fluid.

The knowledge of equilibrium viscosities in the low-temperature range is useful for fitting suitable viscosity-temperature formulae over the whole range of glass viscosities and for a more detailed survey on thermal history influences than can be derived from fixed-point methods alone.