Polymer Communication Stressestrain behavior of a polyurea and a polyurethane from low to high strain rates Sai S. Sarva a , Stephanie Deschanel a , Mary C. Boyce a, * , Weinong Chen b,c a Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, United States b School of Aeronautics and Astronautics, Purdue University, West Lafayette, IN 47907, United States c School of Materials Engineering, Purdue University, West Lafayette, IN 47907, United States Received 17 January 2007; received in revised form 22 February 2007; accepted 23 February 2007 Available online 28 February 2007 Abstract The large deformation stressestrain behavior of thermoplasticeelastomeric polyurethanes and elastomeric-thermoset polyureas is strongly dependent on strain rate. Their mechanical behavior at very high strain rates is of particular interest due to their role as a protective coating on structures to enhance structural survivability during high rate loading events. Here we report on the uniaxial compression stressestrain behavior of a representative polyurea and a representative polyurethane over a wide range in strain rates, from 0.001 s 1 to 10,000 s 1 , successively marching through each order of magnitude in strain rate using equipment relevant for testing at each particular rate. These results are further analyzed in association with recently reported compressive data on the same materials by Yi et al. [Polymer 2006;47(1):319e29] and interme- diate rate tensile data on the same polyurea by Roland et al. [Polymer 2007;48(2):574e8]. The polyurea tested is seen to undergo transition from a rubbery-regime behavior at low rates to a leathery-regime behavior at the highest rates, consistent with the earlier compression study as well as the recent tension study; the polyurethane tested is observed to undergo transition from a rubbery-regime behavior at the low rates to a glassy behavior at the highest rates. The uniaxial compression data for the polyurea are found to be fully consistent with the recently reported uniaxial tension data over the range of rates studied, demonstrating the consistency and complementary aspects of testing at high rates in both compres- sion and tension. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Polyurea; Polyurethane; Stressestrain behavior 1. Introduction Elastomeric-like polyurea and polyurethanes offer a wide range in mechanical behavior due to the ability to tailor the un- derlying hard and soft domain structure through chemistry. Due to the versatility of these materials and their commercial viabil- ity in a myriad of applications, their large deformation behavior over a wide range in strain rates is of interest, particularly for those formulations where the polymer glass transition regime is near the temperature of use. Previous studies on a polyurea and three polyurethanes by Yi et al. [1] provided a first set of data quantifying the stressestrain behavior of these materials at low strain rates (<1s 1 ) in comparison to their behavior at very high rates (>10 3 s 1 ), showing different transitions in me- chanical behavior depending upon the particular chemistry and the location of the glass transition temperature. The polyurea displayed a transition from rubbery behavior at low rates to leathery behavior at the very high rates, whereas, one of the three polyurethanes displayed a transition from rubbery behavior at low rates to glassy-like behavior at the high rates. These transi- tions were observed to be consistent with the shift in mechanical glass transition (T g ) with strain rate, measured using dynamic mechanical analysis (DMA), as shown in the DMA data shown in Figs. 2e4 of [1]. However, the transition in the stressestrain behavior as strain rate increases has not been fully characterized due to experimental limitations in accessing the full range in * Corresponding author. Tel.: þ1 617 253 2294; fax: þ1 617 258 8742. E-mail address: mcboyce@mit.edu (M.C. Boyce). 0032-3861/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2007.02.058 Polymer 48 (2007) 2208e2213 www.elsevier.com/locate/polymer