| Abstract: | Highly oriented filaments of nylon 6 and polypropylene (PP) are shown to craze when deformed slowly at room temperature. A marked yield point occurs at 20-40 percent elongation. After this point extensive voiding occurs until at fracture the overall density is reduced by ∽25 percent for PP and ∽15 percent for nylon 6. SAXS analysis indicates that for PP the voids are elongated in the fiber axis while for nylon 6 voiding occurs both parallel and perpendicular to the fiber axis. Optical and electron microscopy show typical craze structures. The use of etching demonstrates that crazing occurs across the whole filament cross section. This yielding behavior is shown to be associated with the use of a low temperature of drawing during fiber production and becomes less important when a higher temperature of drawing or a separate annealing step are used. The crazing mechanism is thought to involve progressive separation of interfibril boundaries with the production of elongated voids. |
