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Filament-Level Modeling of Aramid-Based High-Performance Structural Materials
CLEMSON UNIV SC DEPT OF MECHANICAL ENGINEERING
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Molecular statics and molecular dynamics are employed to study the effects of various microstructural and topological defects e.g., chain ends, axial chain misalignment, inorganic solvent impurities, and sheet stacking faults on the strength, ductility, and stiffness of p-phenylene terephthalamide PPTA fibers filaments. These fibers can be considered as prototypes for advanced high strengthhigh-stiffness fibers like KevlarRegistered, TwaronRegistered, New StarRegistered, etc. While modeling these fibers, it was taken into account that they are essentially crystalline materials consisting of stacks of sheets, with each sheet containing an array of nearly parallel hydrogen-bonded moleculeschains. The inter-sheet bonding, on the other hand, was considered as mainly being of van der Waals or p-electron character. The effects of various deviations of the PPTA fiber structure from that of the perfectly crystalline structure i.e., microstructuraltopological defects on the materials mechanical properties are then considered. The results obtained show that while the presence of these defects decreases all the mechanical properties of PPTA fibers, specific properties display an increased level of sensitivity to the presence of certain defects. For example, longitudinal tensile properties are found to be most sensitive to the presence of chain ends, in-sheet transverse properties to the presence of chain misalignments, while cross-sheet transverse properties are found to be most affected by the presence of sheet stacking faults.
APPROVED FOR PUBLIC RELEASE