Abstract

An impact experiment is designed to obtain the deformation and fracture characteristics of SBR specimens under tensile impact loading. The experimental apparatus is capable of achieving very large strains (about 300%) and high strain rates (between 10 and 1000 s−1) in the specimen. Dynamic stress‐strain curves reveal that SBR goes through several phases of deformation and fracture as the strain rate increases in the specimen. In the first phase, the initial modulus, yield stress, tensile strength, and fracture strain increase, while the final modulus remains fairly constant with increasing strain rate. Increases in the initial modulus, tensile strength, and strain at fracture with increasing strain rate are due to a lack of stress relaxation in constituents that have longer relaxation times than the load duration. Local scale relaxation times are shorter than the load duration in this phase so that the final modulus is almost insensitive to strain rate. In the second phase, the initial modulus and the yield stress remain roughly constant while the final modulus increases with increasing strain rate. The tensile strength also increases, but the fracture strain decreases as the strain rate increases. Increases in the final modulus and tensile strength are due to a lack of relaxation on a local scale. The tensile fracture strain decreases because convolutions do not have sufficient time to slip completely. In the third phase, all stress‐strain curves follow a master curve, but both the tensile strength and fracture strain decrease with increasing strain rate. The decrease in tensile strength as the strain rate increases could be due to stress concentration at the tip of microcracks within the SBR.

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