COMPRESSION TESTS OF POLYCRYSTALLINE ALPHA-IRON UP TO HIGH STRAINS OVER A LARGE RANGE OF STRAIN RATES

Compression tests have been performed on polycrystalline b.c.c. iron i n order to study dynamic plasticity and evolution of microstructure. T he paper describes the experimental setups and the results obtained at 295 K for strain rates 10(-3)s(-1)less than or equal to <(epsilon)ove r bar> less than or equal to 10(4)s(-1) and plastic strains up to larg e values epsilon-0.8. Stress-strain diagrams have been found for all c onditions mentioned. The rate dependence of stress indicates two regio ns of the rate sensitivity. The low strain rate range shows only sligh t rate sensitivity, but it increases rapidly at strain rates above 10( 3)s(-1). This effect is accompanied by formation of twins. Optical and TEM micrographs confirm these observations. Dislocation density and m icrohardness have been also measured.