The transverse compression of poly(para-phenyleneterephthalamide) and other, highly oriented fibers

The transverse compression of poly (para-phenyleneterephthalamide) (PPTA) and other, highly-oriented fibers is characterized by mechanical testing and microscopic observation.; A review of the literature on the transverse mechanical response of highly-oriented fibers is presented, with special attention to PPTA fibers. Experimental methods to directly measure transverse elastic and failure constants are reviewed. Analyses of these tests are rederived, and their predictions for PPTA compared. Other methods for characterizing the transverse mechanical response of highly-oriented fibers are discussed. Investigations of the structure of PPTA fibers are reviewed, with emphasis placed on what observations affect the transverse mechanical response. The literature supports two possible paradigms for the transverse compressive failure of PPTA fibers: microscopically homogeneous, plastic deformation, and fibrillation, a process of dense microcracking, with cracks predominantly parallel to the fiber axis.; Experimental characterization is presented from the single fiber transverse compression test, using a novel test device. The effects of fiber diameter, processing continuous filaments into staple yarns, testing fibers at various aspect ratios, heat treatment, skin thickness, and the orientation of hydrogen bonding are investigated. Test results are simulated by finite element modeling. Hypothesis about the failure process of PPTA fibers in transverse compression are supported by reflected light, confocal and interference microscopy.; This thesis concludes that PPTA fibers fail in transverse compression by fibrillation, in which the fiber cracks into several smaller fibrils, which move past each other to allow the fiber to comply with increasing transverse load. During fibrillation, a significant amount of work is I absorbed. The influence of several of the above parameters on the tendency to fibrillate is discussed.