Dynamic mechanical properties of polyurethane elastomers using a nonmetallic Hopkinson bar

A modified split Hopkinson-bar apparatus, in which the striker and input/output bars are made of polycarbonate instead of metal, was used to study three typical examples of a high-density flexible polyurethane elastomer (PORON) in sheet form. This variation of the device reduces a mismatch in impedance between the input/output bars and the specimen, thus allowing the stress in the specimen to reach a uniform state before significant engineering strain is induced. Dynamic compressive stress-strain curves were obtained from the measured incident, transmitted, and reflected waves. This article presents the behavior of these foams as a function of strain rate; for PORON 4701-05-20125-1637 under strain rates of 2.67 × 10−3 s−1 to 4500 s−1, the stress-strain response can be described by a function comprising a rate-dependent modulus and a strain-dependent factor, while for PORON 4701-01-30125-1604 and 4701-12-30062-1604, only loading at high strain rates yields similar characteristics. Empirical equations were derived to characterize these mechanical properties; in addition, characteristics relating to energy-absorption capability as well as deformation under approximately constant stress were also studied.