Abstract
Polyamide and polyester fibres have been subjected to flex fatigue by pulling to and fro over a pin, in order to investigate the alternative damage modes, namely cracks along kink-bands due to compression, and axial splitting due to shear stresses. Initial studies determined the conditions that were sufficiently severe to give a short enough test time but not so severe that abrasion on the pin was dominant. Fibres were then cycled for varying periods, the damage viewed in a scanning electron microscope, and the change in tensile properties, including residual strength, determined.