Correlation between elongation at fracture and strain rate for dynamic loading

Strain rate sensitivity is known to act stabilising on a tensile deformatio n process. As soon as neck formation starts, the local strain rate in the n eck zone increases rapidly. the local flow stress increases as well, so tha t higher tensile forces are needed for the continuation of extension. Other specimen regions undergo additional de formation, so that the elongation a t fracture increases with increasing strain rate sensitivity and extension rate. The flow behaviour of iron, steel, copper, bronze, Tantalum, Al-Alloy and T ungsten is investigated in dynamic tensile and compression tests using a Sp lit-Hopkinson-bar. The elongation at fracture of the tensile specimens of a ll test materials is found to increase with increasing strain rate. Correla tions-are formulated of the dependency of elongation at fracture on strain rate as well as on the strain hardening exponent and the viscous damping pa rameter. A simple model is applied to determine these dependencies quantita tively.