The Strength of Glass Fibres. Part I. Elastic Properties

JSGT 1944 V28 T268-T387

The value of Young's modulus and of the modulus of rigidity of glass fibres of stated composition decreases as the fibre diameter is reduced; and the viscosity of the glass also falls in value with the decrease in elastic moduli. Heating the fibres to 400° causes an increase in the modulus of rigidity, but not in Young's modulus, and on heating to 520° or higher Young's modulus is increased as well as the modulus of rigidity. The viscosity of the glass is also increased by heat treatment. The author interprets the results as meaning that the process of drawing a glass fibre causes profound changes in the constitution of the glass. The suggested structure is such that long chains of molecules are formed lying parallel to the direction of drawing, and the lateral bonds between the chains are few. Heat treatment at low temperatures permits the formation of some lateral bonds, resulting in a stiffening of the structure. At the higher temperature levels the chain structure should break up, but is prevented from doing so to the fullest extent by the dimensions of the very fine fibres. It is suggested that heat treatment should also cause a reduction in strength due to the formation of strong lateral bonds and the consequent loss of "ductility."

J. B. Murgatroyd