Microstructural mechanisms governing the fatigue failure of polyamide 66 fibres

The tensile and fatigue behaviours of two types of high performance polyamide 66 fibres have been studied. Marked differences have been found in their fatigue behaviours although their simple tensile behaviours were almost identical. The fibres have been analysed by DSC, X-ray diffraction and by Raman spectroscopy. The fibres have been seen to possess different microstructures with different percentages of ordered regions. In addition the compressive stresses in the regions near the surfaces of the fibres have been found to differ markedly, which may explain the existence of a minimum cyclic load threshold for fatigue failure and suggest a method for improving fatigue resistance