Dynamic small strain measurements of Kevlar® 129 single fibers with a miniaturized tension Kolsky bar

We adopted a non-contact laser technique to measure axial small strain (<∼5%) of Kevlar® 129 fibers in a miniaturized tension Kolsky bar. Accurate small strain measurement is necessary to determine the elastic response of the fibers. In this optical arrangement, a laser beam passes through a line generator lens, which is known as a Powell glass, yielding a thin sheet of light with uniform intensity. This laser sheet passes through a gap formed by the fixture holding the fiber specimen. As the specimen is stretched, an increasing amount of light passes through the gap, which is measured by a high-speed, high resolution photo-detector mounted on the other side of the gap. Dynamic tensile experiments performed at a constant strain rate of ∼1500/s on Kevlar® 129 fibers demonstrate the capability of this non-contact laser technique in the determination of dynamic tensile strain histories with low amplitudes.