Vol.:(0123456789) 1 3 Journal of Dynamic Behavior of Materials https://doi.org/10.1007/s40870-018-0144-8 Experimental Investigation of Strain Rate and Temperature Dependent Response of an Epoxy Resin Undergoing Large Deformation Sandeep Tamrakar 1,3  · Raja Ganesh 1,4  · Subramani Sockalingam 1,4,5  · Bazle Z. Haque 1,4  · John W. Gillespie Jr. 1,2,3,4 Received: 28 November 2017 / Accepted: 15 January 2018 © Society for Experimental Mechanics, Inc 2018 Abstract Experimental investigation of the efect of strain rate and temperature on large inelastic deformation of an epoxy resin is presented. Uniaxial compression tests were conducted on DER 353 epoxy resin at strain rates ranging from 0.001 to 12,000/s. Experimental results showed signifcant rate sensitivity in yield stress, which increased from 85 MPa at 0.001/s to 220 MPa at 12,000/s strain rate. Thermal softening became more prominent as the strain rate was increased, resulting in complete absence of strain hardening at high strain rates. Rise in temperature under high strain rate, due to adiabatic heating, was esti- mated to increase above glass transition temperature (T g ). A series of compression tests carried out at temperatures ranging from ambient to T g  + 80 °C showed yield stress vanishing at T g . Above T g , the epoxy became completely rubbery elastic at quasi-static loading rate. Epoxy became less sensitive to strain rate as the temperature was increased further above T g . The strain rate and temperature dependent yield behavior of the epoxy resin is predicted using Ree–Eyring model. Keywords Epoxy resin · High strain rate · Large strain · Temperature · Eyring model Introduction Polymers and polymer composites are used extensively in military applications. The response of a composite material subjected to impact loading is dependent on the time and temperature dependent properties of its constituents [1–4]. Dynamic loading of polymer composites is complex and modeling and simulation tools such as explicit fnite ele- ment (FE) models [5, 6] are used at various length scales ranging from microscale to mesoscale to the continuum. At all length scales, accurate strain rate dependent mechanical properties of the materials are needed. Glass fber reinforced epoxy composites are commonly used for ballistic protection because of their high specifc strength, stifness and energy dissipation capability [7]. Epoxy resin is one of the most common thermosets used as the matrix in polymer compos- ites because it ofers a balance of properties (mechanical properties, resistance to environmental degradation, thermal stability, etc.), and processablity (low viscosity, low pres- sure and low cure temperatures). A wide range of glass fber sizings for epoxy exists to promote wetting and adhesion that allows interphase properties to be designed for ballistic applications [7, 8]. During ballistic impact and penetration, a composite plate is subjected to large through thickness compression strain and high strain rate on the strike face and in-plane tensile strain and intermediate tensile strain rates on the back surface [9]. The ballistic limit velocity (V 50 ) of S-2 glass/epoxy composite panels impacted by a steel projectile [9] with a panel thick- ness in the range of 10–20 mm is about 360–540 m/s. Due to the huge impedance mismatch between the composite plate and a steel projectile, the particle velocity of the composite underneath the impact is essentially the same as the striking velocity of the projectile [10]. Based on the composite panel thickness and the particle velocity, the average strain rate for * Sandeep Tamrakar tamrakar@udel.edu 1 Center for Composite Materials (UD-CCM), University of Delaware, Newark, DE 19716, USA 2 Department of Materials Science & Engineering, University of Delaware, Newark, DE 19716, USA 3 Department of Civil & Environmental Engineering, University of Delaware, Newark, DE 19716, USA 4 Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA 5 Present Address: Smart State Center for Multifunctional Materials and Structures, Department of Mechanical Engineering, University of South Carolina, Columbia, SC 29201, USA