Effect of moisture and orientation on the fracture of nylon 6,6 fibers

The effect of relative humidity on the fracture of single nylon 6,6 fibers is determined using fracture mechanics. The fracture energy release rate, G_Ic, of these fibers is shown to be 8× that for injection-molded nylon 6,6 at 0% RH. G_Ic varies from 31.3 kJ/m² at 0% RH to 15.6 kJ/m² at 100% RH. The dependence of G_Ic on RH is in agreement with previous studies indicating two types of water in nylon: a tightly bound and a loosely bound type. In addition, G_Ic is shown to be 10× greater for transverse fiber breaks than for axial splitting of the fiber due to the high degree of orientation in these fibers. These studies are the first of their kind for organic fibers. © 1994 John Wiley & Sons, Inc.