Disclosing the fatigue deformation mechanisms of different types of poly (ethylene terephthalate) industrial fibers on the base of the multiscale structural evolutions

Abstract

The fatigue behavior of poly (ethylene terephthalate) industrial fibers is a key issue in their long‐term service for engineering applications. To have a comprehensive understanding of the fatigue behavior, the high‐tenacity (HT) and low‐shrinkage (LS) PET fibers were selected to analyze the room temperature dynamic fatigue properties with different stress. Various techniques such as WAXD/SAXS and FTIR were employed to study the multiscale structure changes to disclose the fatigue mechanisms. Although the crystalline structure including orientation and crystallinity did not change, the amorphous structures varied with fatigue stress. The HT fiber exhibited a higher fatigue recovery ratio. The slight increase in amorphous orientation, and amorphous thickness was attributed to the oriented coiled molecular chains during tensile fatigue stress. In contrast, the LS fiber experienced plastic fatigue deformation with a lower recovery ratio. The molecular chains in the large amorphous domain are easily extended and oriented under tensile loading, increasing amorphous orientation and lamellar thickness. The fatigue mechanism for the LS fiber involved the conformation transition from gauche to trans conformers and a higher proportion of irreversible amorphous regions were formed. It is indicated that developing industrial filaments with small amorphous orientation and content is crucial to improving their fatigue resistance.