SiC- and carbon-fibre-reinforced glass under alternating bending stress loadings

Abstract

Alternating bending stress experiments are described which were performed with various fibre/DURAN-glass composites reinforced by Nicalon NL 202 SiC fibres and by two different types of carbon fibres, a high-tensile strength (ht) and a high-modulus (hm) fibre. Also the influence of unidirectionally homogeneous and inhomogeneous fibre distribution as well as the bidirectional 0°/90° ply distribution are studied. In contrast to previously investigated strain-controlled experiments the present stress-controlled experiments show after the pretreatment of 1000 alternating tensile-compressive stress cycles fatigue (beginning damage) already at amplitudes below the limit of pure elasticity (below bendover stress) of a simple bending-load experiment. Despite of this difference the "training effect" of the previous investigation, the increase of the bendover stress with increasing stress amphtude after 1000 alternating-load cycles, is found to be similar and can be established also for the present experiments. The carbon-fibre-reinforced composites show a better tolerance of damage due to their smaller fibre diameters than the SiC-fibre-reinforced composites.