Interfibrillar behavior in ultra-high molecular weight polyethylene (UHMWPE) single fibers subjected to tension

In this effort, the interfibrillar behavior in UHMWPE fibers subjected to tension is investigated using a unique experimental setup that allows for the in-situ monitoring of the deformations of sub-fiber level components within the fiber. Digital image correlation (DIC) is used to measure fiber surface strains, quantify the stress-strain fiber response and interfibrillar sliding between adjacent macrofibrils within the fiber’s microstructure, and estimate the length of macrofibrils within the fiber. Finite element (FE) based models of the UHMWPE fibers are developed that account for the complex fibrillar microstructure and macrofibrillar interactions governing the macro-scale fiber response under uniaxial tension. The FE-based models are compared to both experimental results and previously developed analytical fiber models to study the effects of underlying model assumptions on the fiber’s stiffness and deformation response. The shortcomings of a continuum material model for the fiber are revealed. A unique beam connector model of the fiber is presented which mimics the inherent interfibrillar deformation mechanics observed in the experiments. A Design of Experiments (DoE) approach is used to facilitate development of the model. Predictions are shown to compare favorably with experimental results for both the fiber stress-strain response and the degree of interfibrillar sliding. The findings presented in this paper contribute towards the fundamental understanding of the complex microstructure-property relations in UHMWPE fibers and can ultimately be used to help guide the development of high performance fibers widely used in armor ballistic protection systems.