Multi-length scale computational derivation of Kevlar^® yarn-level material model

The results of an extensive set of molecular-level computational analyses regarding the role of various microstructural/morphological defects on the Kevlar^® fiber mechanical properties are used to upgrade the associated yarn-level model of the same material. While carrying out this analysis, the hierarchical multi-scale (atoms/ions—molecular chains—fibrils—fibers—yarn) of the problem was taken into account. To construct various defects, the appropriate open-literature experimental and computational results were used while the concentration of defects was set to the values comparable with their counterparts observed under “prototypical” polymers synthesis and fiber fabrication conditions. Due to the stochastic nature of the defect distributions, their effect on the yarn-level strength and ductility are included in the form of the corresponding two-level Weibull distribution. As far as the material stiffness is concerned, it was assumed that the first-order effect of the defects is to change the mean value of the stiffness parameters and that this effect is of a deterministic character. While upgrading the yarn-level material model for Kevlar^® it was recognized that a yarn is an assembly of nearly parallel fibers (often lightly twisted, or tied with wrap-around filaments) with relatively weak lateral coupling.