The Delayed Elastic Effect in Glass Fibres and the Constitution of Glass in Fibre Form

JSGT 1948 V32 T291-T300

The evidence produced by several investigators has shown that massive glass most probably has a constitution similar to that of a liquid. Such a system contains numerous weak bonds due to the distortion of the atomic structure, and some regions of weak bonds in glass are capable of viscous yield at room temperature. This explains the “delayed elastic effect” observed in glasses. Since glass fibres are drawn from glass at high temperature and are cooled very rapidly it is to be expected that they contain a greater proportion of weak bonds due to the greater fluidity of glass at high temperature. The system is frozen before it can reach its room-temperature equilibrium. Hence fibres should exhibit a greater delayed elastic effect than the massive glass from which they are drawn, and experiments are reported which prove this to be true. The delayed elastic effect increases as the fibre diameter is reduced, being five to six times that in the massive glass when the fibres have a diameter approximately 0·002 cm. The present work confirms earlier experiments, which showed that the elastic properties of glass fibres are smaller in value than those of massive glass. The increased strength of the fibres is due to the orientation of the weak bonds normal to their axis, it being shown that the method of drawing glass fibres must produce such an orientation. The conclusion is reached that the low strength of massive glass is due to the numerous weak bonds it contains, and there is therefore no necessity to suppose that glass contains “Griffith cracks.”

J. B. Murgatroyd