Correlation between elongation at fracture and strain rate for dynamic loading

Abstract
Strain rate sensitivity is known to act stabilising on a tensile deformation process. As soon as neck formation starts, the local strain rate in the neck zone increases rapidly, the local flow stress increases as well, so that higher tensile forces are needed for the continuation of extension. Other specimen regions undergo additional deformation, so that the elongation at fracture increases with increasing strain rate sensitivity and extension rate. The flow behaviour of iron, steel, copper, bronze, Tantalum, Al-Alloy and Tungsten is investigated in dynamic tensile and compression tests using a Split-Hopkinson-bar. The elongation at fracture of the tensile specimens of all test materials is found to increase with increasing strain rate. Correlations are formulated of the dependency of elongation at fracture on strain rate as well as on the strain hardening exponent and the viscous damping parameter. A simple model is applied to determine these dependencies quantitatively.