Nanometric AFM Observation of Fiber Surface Damage and Influence of Vacuum and Water on Tensile Fracture Behavior of Aramid Fibers

Abstract

We describe the influence of a vacuum and water absorption on the tensile fracture behavior of four different types of aramid fibers : Kevlar 29, Kevlar 49, and Kevlar 149, manufactured by DuPont, and Technora from Teijinn Co. Ltd. Single fiber tensile tests were conducted in air and in vacuum (4-5×10^-3Pa) for fibers preconditioned in air, in water at 80°C for two months, and in vacuum for about four hours. The mechanical properties of aramid fibers, longitudinal elastic modulus and fracture strength decreased as a result of water absorption. Fiber fracture was associated more with fiber splitting when preconditioned in water. When tested in a vacuum, the air-preconditioned fiber strength decreased from that in air. Moreover, the strength of the fibers preconditioned in vacuum decreased more when tested in air compared with that of the air-preconditioned fibers tested in a vacuum. The fiber surfaces were closely examined using an atomic force microscope (AFM). The AFM's nanometric resolution showed fiber surface damage caused by water absorption, high temperature, and preconditioning in a vacuum. The degradation and fracture mechanisms of the fibers were discussed.