Fatigue Mechanism Analysed Based on the Changes in Microstructure and Axial Compression Strength of a Poly(p-phenylene-2,6-benzobisoxazole) Fiber

Abstract

The fatigue mechanism of high-strength fibers from liquid crystalline polymers such as poly(p-phenylene-2,6-benzobisoxazole) (PBO) and poly(p-phenylene terephthalamide) is considered to be completely different from that of general-purpose plastics because of the microfibrillar fiber structure of the former. The present paper investigates the progress of fatigue damages for the PBO fiber based on a structure analysis using the synchrotron radiation small-angle X-ray scattering and the measurement of the axial compression strength. The result indicated that tensile fatigue continues because of the gradual splitting of the microfibrils. Hence, the axial microvoid length increases, and theaxialcompressionstrength decreases.Moreover, an equationhas been proposedforthesingle-fiber axial compression strength of this fiber type, which fails along with the formation of kink band.