EXPERIMENTAL INVESTIGATION OF TRANSVERSE MECHANICAL PROPERTIES OF HIGH-PERFORMANCE KEVLAR KM2 SINGLE FIBER

摘要

Transverse nanoindentation modulus of high performance Kevlar KM2 single fibers are experimentally studied using a nanoindenter. Researchers have investigated the transverse compression behavior of these fibers using flat punch indentation heads, in which the curved circular transverse shape of the fiber is not included, and consecutively fit the data into the analytical models to calculate their mechanical properties. During this process, the force is normalized to a point on the transverse fiber surface and the analytical model assumes a flat semi-infinite plate for substrate. Other studies consider embedding the fibers on a substrate and indenting on the transverse surface. This method bounds the fibers resulting in inaccurate measurements of their mechanical responses. There has not been an appropriate study on the transverse material properties of the Kevlar fibers determined via nanoindentation without embedding them because it is challenging to rigidly secure the fibers. Here, we have developed a methodology to secure the Kevlar fiber on an SEM puck under pretension. The tension at the fiber is calculated and accounted for in the final determination of the mechanical properties. Fibers are glued at the ends and are not embedded. The employed Vantage nanoimpactor indents the fiber radially at three different loads, namely, 2, 3, and 5 mN and calculates the mechanical properties. A Berkovich indenter is used for indentation. The Kevlar fibers are assumed transversely isotropic and have 12µm diameter measured via the Vantage optical microscope. For Kevlar KM2 fiber the experimental transverse modulus using impact nanoindenter instrument is ~3.46 GPa. The presented experiments aim to improve our understanding of the mechanical properties of these high performance fibers on the transverse direction.