Direct comparison of the loss of load transfer to ?E? and ?S? glass fibres manufactured by drawing into different environments

Abstract

Accelerated water uptake tests have been used to compare the onsets of destruction of the ability to transfer shear stress at fibre/matrix interfaces in epoxy matrix glass reinforced plastic (GRP) manufactured with each of four different fibres. The ability to transfer shear stress has been monitored directly by measurement of stress birefringence through and adjacent to individual fibres. Full theoretical and practical details of the experimental method are given. “S” glass fibres, drawn into an atmosphere of ammonia in an attempt to promote the deposition of primary amines and/or secondary amines, rapidly lose their ability to receive shear stress from the matrix. This is attributed to neutralization of CO2 by NH3 within interfacial pockets of dissolved water, and the associated generation of osmotic pressure. Commercial samples of “S” and “E” glass fibres and “E” glass fibres drawn into an atmosphere of ammonia, all survive much larger water uptakes although, in the case of both kinds of “E” glass fibre, immersion in boiling water eventually gives rise to interfacial pressure pockets. These pressure pockets are also attributed to osmosis, with the role of dissolved solutes tentatively ascribed to the modifying agents present in “E” glass formulations.