Modeling failure mechanisms of poly(p-phenylene terephthalamide) fiber using reactive potentials

Failure mechanisms of poly(p-phenylene terephthalamide (PPTA) under extreme tensile deformation has been studied using reactive potentials with molecular dynamics simulations. Amorphous PPTA systems with different molecular weights generated using an in-house developed amorphous builder. Tensile modulus of amorphous PPTA has been calculated as up to 6.7 GPa. Nitrogen and carbon vacancy defects were introduced to both crystalline and amorphous systems. The tensile modulus of defects-free crystalline PPTA calculated as 350 GPa. Introduction of 5% nitrogen vacancy defects reduced the tensile modulus to 197 GPa. To estimate fiber modulus, PPTA fiber considered to be composed of amorphous and crystalline phases. Rule of mixtures formula modified to incorporate influence of defects on tensile modulus. Histograms of various quantities such as bond lengths, bond angles and phenyl ring diameters were calculated at different strain levels. Tensile load was mostly accommodated through stretching of bonds between amide group and phenyl groups. Under extreme tensile deformation PPTA chains failed at these C-N bonds.