Probing the internal structures of Kevlar® fibers and their impacts on mechanical performance

Advancements in processing techniques have facilitated the development of a series of unique high-performance DuPont (TM) Kevlar (R) fibers. Directly characterizing interior structures of these fibers is vital for connecting processing variations with resulting mechanical properties. Here we report detailed investigations of processing-internal structure-property relationships among four distinct classes of Kevlar (R) fibers (K119, K29, KM2+, and K49). We employ a novel focused ion beam (FIB) notch technique to obtain pristine interior fiber planes and measure morphology and transverse stiffness across these surfaces via multifrequency atomic force microscopy (AFM) maps. Combining these observations with tensile tests of single fibers drawn from the same tows, we acquire remarkable insights into structural motifs that strongly correlate with measured mechanical properties. Most notably, we uncover alternating stiffness bands that are especially apparent in low-modulus, non-heat-treated fibers, revealing a unique manifestation of internal structural variations that helps explain the observed trends in material response. Published by Elsevier Ltd.