Glass transition dependence of ultrahigh strain rate response in amine cured epoxy resins

Abstract

Ultrahigh strain rate performance in a series of model amine cured epoxy resins was investigated as a function of the glass transition temperature (Tg) of the cured polymer network, where the network Tg was systematically varied through the monomer stiffness, structure, and size. The high rate response was characterized in terms of a projectile penetration velocity, V50BL(P) (ballistic limit, protection criteria), which describes the projectile velocity with a 50% probability of sample penetration. One factor that dictates the ballistic performance of the epoxy networks, at effective rates of 104–105 s−1, is the difference between the measurement temperature and the glass transition temperature of the network. Sub-Tg relaxations did not have a measurable effect on ballistic performance, and neither did the monomer structure and functionality outside of the influence of the resin Tg, while off-stoichiometric (excess amine) formulations improved V50BL(P) slightly with high Tg epoxies. The results have implications in protective materials for military, aerospace, transportation, and construction industries, where high strain rate insults from airborne debris, high rate collisions, and natural events are increasingly considered during product design.