Structure sensitive measurements on e-glass fibers

Abstract

The following properties of continuously drawn fibers from a nozzle have been measured over a broad range of drawing parameters (temperature, pressure on the nozzle, drawing speed): density, thermal expansion, contraction, and birefringence. These properties show characteristic changes of the fiber structure as compared with the structure of the bulk glass. The structure of the fibers is influenced mainly by the following parameters: the cooling rate and the drawing stress. The cooling rate, which rises up to 10 5 K/s causes an isotropic effect on the glass network of the fiber: an open structure which corresponds to a fictive temperature of up to more than 100 K above the usual glass transition temperature of the bulk glass. The drawing stress acting on the jet during the fiber drawing process causes an anisotropic, frozen-in network deformation which approaches the order of the thermal isotropic deformation. Glass fibers which have been produced at different temperatures but with the same drawing stress show an increasing optical anisotropy with increasing temperature. This effect and similar effects for the density and shrinkage may be a direct indication of a structural orientation in the fiber direction. Although this orientation (anisometry) is negligibly small for a three-dimensional network structure of oxide glass fibers, the anisotropic effect for the frozen-in structural strain-stress is considerable, because these values are as much as 1 10 or more of those for the strength of the originating glass fibers.