A Comparative Study of Nylon Fiber Fracture

Abstract

This investigation deals with the comparative study of the fracture morphology of 15-denier nylon 66 filament subjected to various modes of deformation. The modes of deformation included in the study are simple tensile (low and high rate of extension, low temperature, and room temperature), tensile fatigue, simple torsion, cyclic torsion, flex fatigue, and various combinations of these simple modes. The tensile breaks (dry and in liquid nitrogen) were obtained by extending the fiber to break on an Instron tensile tester. Tensile breaks at extremely high rates of extension were accomplished by the use of a device based on the principle of the “relaxation catapult,” Fiber-fracture experiments in tensile fatigue, simple torsion, and bending fatigue were carried out by the techniques developed at UMIST. In order to obtain fiber breaks in cyclic torsional fatigue, a special apparatus was constructed which was capable of imposing repeated torsion with a high degree of twist at a rate of approximately 5Hz. The biaxial rotation apparatus could not be used with fine filaments; consequently, a new test was developed which simulated filament deformation due to bending fatigue. This test involves the rotation of a fiber around a pin. It is found that a variety of failure mechanisms are operative in nylon. Ductile crack growth dominates in simple tensile and torsion failures. The tensile failure at low temperature and in fatigue studies shows axial splitting of the fiber. The nylon 66 filaments ruptured in the flex-fatigue mode show the formation of kink bands on the underside of the bent filament. However, the failure along these kink bands does not dominate the rupture behavior of nylon.