Indirect Tensile Characterization of Graphite Platelet Reinforced Vinyl Ester Nanocomposites at High-Strain Rate

Abstract

An indirect tensile testing method is proposed for characterizing low strength graphite platelet reinforced vinyl ester nanocomposites at high-strain rate. In this technique, the traditional Bra-zilian disk (diametrical compression) test method for brittle materials is utilized along with con-ventional split-Hopkinson pressure bars (SHPB) for evaluating cylindrical disk specimens. The cy-lindrical disk specimen is held snugly in between two concave end fixtures attached to the inci-dent and transmission bars. To eliminate the complexities of conventional strain gage application, a non-contact Laser Occluding Expansion Gage (LOEG) has been adapted for measuring the diame-trical transverse expansion of the specimen under high-strain rate diametrical compressive load-ing. Failure diagnosis using high-speed digital photography validates the viability of utilizing this indirect test method for characterizing the tensile properties of xGnP (exfoliated graphite nanop-latelets) reinforced and additional CTBN (Carboxyl Terminated Butadiene Nitrile) toughened vinyl ester based nanocomposites. Also, quasi-static indirect tensile response agrees with previous in-vestigations conducted using the traditional dog-bone specimen in direct tensile tests. Investiga-tion of both quasi-static and dynamic indirect tensile test responses shows the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. The contribution of reinforcement to the tensile properties of the candidate materials is presented.