Performance enhancement of nylon/kevlar fiber composites through viscoelastically generated pre-stress

Kevlar-29 fibers have high strength and stiffness but nylon 6,6 fibers have greater ductility. Thus by commingling these fibers prior to molding in a resin, the resulting hybrid composite may be mechanically superior to the corresponding single fiber-type composites. The contribution made by viscoelastically generated pre-stress, via the commingled nylon fibers, should add further performance enhancement. This paper reports on an initial study into the Charpy impact toughness and flexural stiffness of hybrid (commingled) nylon/Kevlar fiber viscoelastically pre-stressed composites at low fiber volume fractions. The main findings show that (i) hybrid composites (with no pre-stress) absorb more impact energy than Kevlar fiber-only composites; (ii) pre-stress further increases impact energy absorption in the hybrid case by up to 33%; (iii) pre-stress increases flexural modulus by ∼40% in the hybrid composites. These findings are discussed in relation to practical composite applications.