Fatigue behaviour of composite bars subjected to bending and torsion

In this study, an experimental device was designed to apply both bending an d torsion loads to unidirectional glass-fibre/epoxy composite bars in a sim ple tensile machine. Tests were performed to characterise the quasi-static failure criterion and the fatigue behaviour under varied stress conditions. Because the material was transparent, a CCD camera was used to follow dama ge progression. Fibre failure, delamination and cracking were studied and i mage-processing software was developed to gather reliable data automaticall y. Tests showed that composite bars exhibited complex damaging processes wh ich varied depending on the stress ratio between bending and torsion and on the ratio between minimum and maximum stresses. (C) 1999 Published by Else vier Science Ltd. All rights reserved.