Compressive Properties of Soybean Oil-Based Polymers at Quasi-Static and Dynamic Strain Rates Bo Song, 1 Weinong Chen, 1 Zengshe Liu, 2 Sevim Z. Erhan 2 1 Department of Aerospace and Mechanical Engineering, The University of Arizona, Tucson, Arizona 85721 2 NCAUR, ARS, USDA, Peoria, Illinois 61604 Received 13 August 2004; accepted 7 April 2005 DOI 10.1002/app.22627 Published online 19 December 2005 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Quasi-static and dynamic compressive prop- erties of three soybean oil-based polymeric materials, which were made through the reaction of epoxidized soybean oil with diamine compounds, have been determined. Quasi- static properties were determined with an MTS 810 hydrau- lically driven testing machine, whereas dynamic experi- ments were conducted with a split Hopkinson pressure bar (SHPB) modified for low-impedance material testing. All three materials were capable of deforming to very large strains, with significant nonlinear stress–strain response. Their compressive behaviors were strain-rate sensitive with distinctive rate sensitivities. On the basis of the experimental results at various strain rates, a compressive one-dimen- sional stress–strain material model with strain-rate effects was developed to describe the experimental results for all three materials under both quasi-static and dynamic loading conditions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2759 –2770, 2006 Key words: soybean oil-based polymers; split Hopkinson pressure bar (SHPB); stress–strain curve; strain rate; com- pressive properties INTRODUCTION Recently, there has been a growing interest in the development of polymers obtained from biodegrad- able and environmentally friendly resources. One of these resources is soybean oil. Besides the major use in food products, soybean oil has been used in nonfood applications, including lubricants, plastics, coatings, fuel, inks, and chemical intermediates. 1–5 It was used as a plasticizer for polyvinyl chloride (PVC) com- pounds, chlorinated rubber, and polyvinyl alcohol (PVA) emulsions, in the past. Recently, epoxidized soybean oil (ESO) has been reacted with diamine com- pounds to produce three new soybean oil-based ma- terials, which are studied in this paper. The expected applications of these materials are in the automotive industry, civil engineering, construc- tion industry, and sports equipment industry. How- ever, as a class of new materials, knowledge about their mechanical properties at quasi-static and dy- namic strain rates is scarce, and thus, it is desirable to understand the mechanical properties before the pro- jected strain-rate-dependent load-bearing applica- tions. Systematic research is needed to experimentally determine their mechanical properties and to analyti- cally develop realistic material models for numerical simulations and design optimizations. Since material models need reliable experimental data to determine the material constants and to check the accuracy of the models over the ranges of their applications, detailed stress–strain curves for such materials at various strain rates must be accurately determined under valid experimental conditions. Under quasi-static loading conditions, standard ex- perimental techniques can be directly employed to determine the mechanical properties of those materi- als. 6,7 However, it is much more challenging to deter- mine the mechanical properties under dynamic load- ings because most dynamic experimental techniques are not adequate to load the soft materials at both large strains and high strain rates. For example, dy- namic viscoelastic properties of the materials prepared by curing ESO with various cyclic acid anhydrides in the presence of tertiary amines by Gerbase et al., 8 and of soybean oil-based composites with and without fibrous filler prepared by Xu et al. 9 have been inves- tigated. This type of experimentation determines the storage modulus and loss modulus of polymers at very small strains instead of large strains. For the purpose of dynamic material model development, de- tailed stress–strain curves over wide ranges of strains and strain rates are necessary. The split Hopkinson pressure bar (SHPB), originally developed by Kol- sky, 10 has been widely used and modified to deter- mine families of stress–strain curves as a function of strain rates for a variety of engineering materials, in- cluding metals, 11,12 composites, 13–15 and soft materi- als. 16 It is noted that, when the specimen in a SHPB is Correspondence to: W. Chen (wchen@purdue.edu). Journal of Applied Polymer Science, Vol. 99, 2759 –2770 (2006) © 2005 Wiley Periodicals, Inc.