MORPHOLOGICAL-STUDY OF FATIGUE-INDUCED DAMAGE IN ISOTACTIC POLYPROPYLENE

This article reports initial results of an investigation whose aim is to characterize fatigue damage induced in semicrystalline polymers sub jected to uniaxial high cycle fatigue. Herein we report results obtain ed from fatiguing tensile bars of high molecular weight compression-mo lded alpha-phase iPP. Samples were fatigued for up to one million cycl es at a frequency of 2 Hz. During fatigue, in situ measurements of dyn amic mechanical response and energy densities were recorded. Postmorte m morphological studies were also conducted using SEM of etched surfac es and TOM. The results show that damage formation occurs in a regular ly spaced array of crazes. This damage, its evolution, and energetics are discussed as they relate to the overall fatigue life of the materi al. A methodology to isolate the energy consumption for the formation of a single craze is given. (C) 1998 John Wiley & Sons, Inc.