Fatigue behaviour of composite bars subjected to bending and torsion

In this study, an experimental device was designed to apply both bending and torsion loads to unidirectional glass-fibre/epoxy composite bars in a simple 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 damage progression. Fibre failure, delamination and cracking were studied and image-processing software was developed to gather reliable data automatically. Tests showed that composite bars exhibited complex damaging processes which varied depending on the stress ratio between bending and torsion and on the ratio between minimum and maximum stresses. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.