Statistical Mechanics of Kevlar® KM2® Plus Nanostructure: Deformations and High-Rate Impact

A detailed understanding of all phenomena that determine high-rate impact response of woven polyaramid systems is needed to design more effective materials and save lives. This study investigates the detailed nanostructures of Kevlar® KM2® Plus fibers from woven systems subjected to controlled rheometric deformations and high-rate impact. The rheometric tension, axial compression following tensile failure, and transverse compression are basic deformations not previously studied by our methods and hypothesized in high-rate impact. The impact of a high-rate object causes significant, layer-dependent nanostructural changes to woven systems. Multichannel AM-FM atomic force microscopy characterizes interior fiber nanostructure with spatially-resolved topological and viscoelastic property measurements of pleat lengths, crystal misorientation angles, fibril widths, and void widths. Statistical analyses were developed to assess convergence of nanostructure feature measurement distributions and compare the correlated nanostructure feature distributions between samples. The data and analyses indicate that tension is not the only mechanism of energy transfer from the impact of a high-rate object and that compressions, both in the axial and transverse directions, are also significant. The varying localized responses to high-rate impact and the presence of both tension and compression imply better systems can be created by improving tensile and compressive properties, tailoring fabric layers to perform to specific types of mechanical deformations.