High-Rate Straining and Mechanical Properties of Materials

Abstract

In many conventional metal working or forming processes, such as machining, rolling or wire drawing, very large plastic strains may be applied to the workpiece in very short intervals of time, of the order of l0⁻⁴ s. Estimates of the resulting strain rate vary from 10² to l0⁴s⁻¹,¹ and may be as high as 10⁵ S⁻¹, ² i.e. some 6 to 9 orders of magnitude greater than the strain rates encountered in conventional tension, compression or torsion testing. The development of high energy rate fabrication methods, including the use of explosives, has meant that even such processes as sheet or plate forming can now be carried out at relatively high strain rates, in the range 10 to10³ S⁻¹,³ while in processes where the explosive is in direct contact with the workpiece the pressures generated may be so great that the metal behaves as if it were a fluid, i.e. its response is characterised by a viscosity rather than a flow stress.⁴