Transverse compression of high-performance ballistic fibers

High performance ballistic fibers have been in use for decades, specifically in protective applications against ballistic impact such as bulletproof vest layers and aircraft turbine engine fragmentation barriers. These high performance fibers have extremely high strength-to-weight ratios and high moduli of elasticity in the axial direction, making them extremely suitable for high impact situations. In particular, para-phenyleneterephthalamide (PPTA for short) fibers such as Kevlar® and ultra-high-molecular-weight polyethylene fibers such as Dyneema® are amongst the more popular high performance fibers in today\u27s world. While the longitudinal mechanical response of these fibers have been extensively researched, their transverse mechanical response is still not well-understood, even though most ballistic impact events occur in the radial direction of these fibers (especially in woven structures). The method of determining the transverse mechanical response of Kevlar ® KM2 and Dyneema® SK76 fibers was improved upon from previous versions of single fiber compression tests. Two fibers were laid parallel and compressed between two tool steel platens. The new experimental setup ensures that the individual fibers are being compressed evenly along the length and that the platens are parallel during compression. Nominal stress-strain curves were obtained for quasi-static loading of both types of fibers. Proper calibration was also performed to ensure the accuracy of the obtained nominal stress-strain results. Using finite element analysis with ABAQUS, the quasi-static compression behavior was simulated and compared with experimental results. Scanning electron microscopy was also performed to ensure uniform compression of the fibers. To evaluate the rate effects on the transverse behavior, high-rate transverse compression experiments were also performed using a 127 μm diameter miniature Kolsky bar loading on single-fiber specimens to obtain the corresponding stress-strain response of these high performance fibers at high rates of deformation