Tensile Behavior of Single PPTA Fibers Measured by the Kolsky Bar Using the Direct Fiber Clamping Method

Abstract

The Kolsky bar test has been widely used in measuring material behavior under high strain rate conditions. In particular, this methodology has been used to characterize the high strain rate behavior of polymer and polymer composites during ballistic impact. Chen et al. measured the tensile properties of single poly(p-phenylene terephthalamide) (PPTA) fibers at high strain rates by gluing the fiber directly to the Kolsky bar. However, the application of this technique is somewhat limited because of the time-consuming nature of the gluing procedure [1]. Due to the highly stochastic nature of fiber tensile strength, large test-sample sizes are required to analyze distributions of fiber properties such as tensile strength, modulus, and strain-to-failure. The authors have investigated the direct gripping method to facilitate high throughput single fiber tensile testing at high strain rates. As an extension of these efforts, the polymethyl methacrylate (PMMA) platens used for directly gripping the fibers are replaced here by rubber platens to assess the impact of the platen material properties on the stress transfer from the Kolsky bar to the fiber at high strain rates. In this study, the system compliance for the PMMA grips is measured under the quasi-static condition to assess the stress transfer from the grip and to correct the modulus and failure strain of the fiber. In preliminary tests using a PMMA grip, the system compliance was obtained by the 5, 10 and 60 mm gauge lengths. These data will be compared with similar data using the rubber grips to investigate the influence of the gripping material properties.