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Abstract
Changes occurring during tensile deformation in highly oriented poly(amidobenzimidasole) (PABI) fibers have been investigated in time (creep) at room temperature. Macrodeformation was experimentally determined with stresses varying from 1.2 to 3.0 GPa. Microdcformation (tensile relative deformation of the PABI crystal lattice) was defined from the angular shift of meridional X-ray reflexes. It was shown that the creep of PABI fibers on both macro- and microlevels changed nonlinearly with stress. The measurements of the dynamic elastic modulus of PABI fibers allowed to establish that chain molecules in the PABI crystal lattice become more extended, i.e. cis-trans transitions occur. The transition kinetics determines the intensity of the lattice creep, or the creep of the whole fiber. The formula for the quantitative description of macro- and microcreep in PABI fibers is presented, which takes into account the nonlinearity of viscoelastic properties of PABI fibers and has a small number of parameters.
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